Martin Brown wrote:
> On 23/10/2022 09:38, Jan Panteltje wrote:
>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin Brown
>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1@gioia.aioe.org>:
>>
>>> On 23/10/2022 06:39, Jan Panteltje wrote:
>>>> on chip spectrometer?
>>>>    https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>
>>> Possibly. I'd like to see a bit more of the specifications and light
>>> intensity it requires before I take that press release at face value.
>>>
>>> There is a bit more here but the main article is behind a paywall :(
>>>
>>> https://www.science.org/doi/10.1126/science.add8544
>>
>> I see.
>> Well, CCD sensor with prism in front of it should work too?
>
> The best super high resolution systems use an echelle method modest
> dispersion prism one way and a very high dispersion grating at almost 90
> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
>
> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
>
> That example was actually observed with a Fourier transform method and
> then displayed in the fashion of a traditional echelle spectrum. It is a
> very impressive piece of kit even it it only works on bright stars:
>
> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
>
> This is a real physical highres echelle spectroscope
>
> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
>
>
> They are seriously nice pieces of kit. PE did an atomic
> absorption/emission spectroscope using a similar configuration and early
> CCDs back in the 1990's. Must have been ~95 because I saw it in Japan at
> one of the big analytical trade fairs where we were also exhibiting.
>
>
Yeah, a cross-dispersed echelle system can get resolving powers
(lambda/FWHM) up near 1E6, which is pretty impressive.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Mon, 24 Oct 2022 10:36:41 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:

>On 23/10/2022 16:15, John Larkin wrote:
>> On Sun, 23 Oct 2022 14:27:56 +0100, Martin Brown
>> <'''newspam'''@nonad.co.uk> wrote:
>>
>>> They are seriously nice pieces of kit. PE did an atomic
>>> absorption/emission spectroscope using a similar configuration and early
>>> CCDs back in the 1990's. Must have been ~95 because I saw it in Japan at
>>> one of the big analytical trade fairs where we were also exhibiting.
>>
>> The spectrometer business seems to be a race for resolution in narrow
>> bands. There's no wide-range low-resolution stuff that we can find.
>
>What are you roughly trying to do? You can't go too far either side of
>the visible band without running into problems with glass transparency.

Test various lasers to see if they are the right wavelength, as in
1550 vs 1310 vs 850 vs 800.

We can gross separation with a fiber WDM splitter and several
detectors, but that's klunky.

On Mon, 24 Oct 2022 10:24:58 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>Martin Brown wrote:
>> On 23/10/2022 09:38, Jan Panteltje wrote:
>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin Brown
>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1@gioia.aioe.org>:
>>>
>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
>>>>> on chip spectrometer?
>>>>>    https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>
>>>> Possibly. I'd like to see a bit more of the specifications and light
>>>> intensity it requires before I take that press release at face value.
>>>>
>>>> There is a bit more here but the main article is behind a paywall :(
>>>>
>>>> https://www.science.org/doi/10.1126/science.add8544
>>>
>>> I see.
>>> Well, CCD sensor with prism in front of it should work too?
>>
>> The best super high resolution systems use an echelle method modest
>> dispersion prism one way and a very high dispersion grating at almost 90
>> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
>>
>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
>>
>> That example was actually observed with a Fourier transform method and
>> then displayed in the fashion of a traditional echelle spectrum. It is a
>> very impressive piece of kit even it it only works on bright stars:
>>
>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
>>
>> This is a real physical highres echelle spectroscope
>>
>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
>>
>>
>> They are seriously nice pieces of kit. PE did an atomic
>> absorption/emission spectroscope using a similar configuration and early
>> CCDs back in the 1990's. Must have been ~95 because I saw it in Japan at
>> one of the big analytical trade fairs where we were also exhibiting.
>>
>>
>Yeah, a cross-dispersed echelle system can get resolving powers
>(lambda/FWHM) up near 1E6, which is pretty impressive.
>
>Cheers
>
>Phil Hobbs

How would you do a small spectrometer that works from 750 to, say,
1900 nm? Better yet 350 to 1900.

(Mo just gave me a bybye hug. She says hi.)

On Mon, 24 Oct 2022 10:37:39 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:

>On 23/10/2022 22:15, John Larkin wrote:
>> On Sun, 23 Oct 2022 12:34:11 -0700 (PDT), Rich S
>> <richsulinengineer@gmail.com> wrote:
>>
>>> On Sunday, October 23, 2022 at 7:04:21 PM UTC, whit3rd wrote:
>>>> On Sunday, October 23, 2022 at 10:49:29 AM UTC-7, John Larkin wrote:
>>>>
>>>>> We buy all sorts of lasers and LEDs and we can't be sure they are the
>>>>> right wavelength. Even 1% wavelength resolution would be plenty.
>>>>>
>>>>> Nobody makes it.
>>> [snip}
>>>
>>> would this work? Handheld, ca. $1500,
>>> https://www.intl-lighttech.com/products/ilt350-chroma-meter
>>
>> That covers the visible, which would check the colors of LEDs, which
>> is not really much of a problem.
>>
>> The more serious problem is that we buy a bunch of lasers in the 800
>> to 1550 sort of range and we'd like to make sure they are right.
>
>I'm assuming for the moment that you are serious.

Would anyone joke about that? We buy thousands of pcb mount fiber
lasers per year, most of them at four wavelengths and the occasional
oddball, and they all look alike. I'd like to final test our products
and be sure we are shipping the correct wavelength.

>
>Semiconductor laser lines tend to be on *very( specific wavelengths.
>(as do all the common laser and excimer gas mixes)
>
>We tended to be on 1066, 533, 266 ie NdYAG + doublers.
>
>I always found the amount of visible green in the beam a bit worrying
>and the promise that the perspex enclosure was entirely opaque to 266nm.
>I never spent much time in close proximity to the systems when running.
>
>Low pass filters plus a few detectors should be good enough to
>discriminate between most of them.

Yes, a WDM splitter or two and several detectors and a bunch of
opamps. We might build that in a box, with an LED to indicate each
band.

Recently a customer asked for a some units with 800 nm lasers, which
we hadn't done before. We offer 850 as one of our standards. At least
you can see the 800, to make sure it's not one of the IRs.

>I'd have thought that for a known
>part number whether or not it emits laser light or not would be good
>enough.

Our policy is to test everything that has a spec. Mixups are possible.

I vaguely recall an amateur astronomers tunable visible
>wavelength dichroic filter (I know someone who bought a prototype) but
>it seems to have sunk without trace. I'll ask next time I see him.
>
>Otherwise try Young's slits to figure out the wavelength.

I want something that looks like a DVM... not an optical bench.

Maybe there is a linear or circular graduated bandpass filter. Rotate
a marked knob for max output. Or a metal disc with multiple,
selectable bandpass windows. I'd rather buy something.

We could build N boxes, each a bandpass o/e converter. Run a
production source into the right one and it should light up.

On Monday, October 24, 2022 at 8:37:46 AM UTC-7, John Larkin wrote:

> How would you do a small spectrometer that works from 750 to, say,
> 1900 nm? Better yet 350 to 1900.

Just as your eyes don't cover that whole range, so most detectors don't.
This one <https://www.thorlabs.com/thorproduct.cfm?partnumber=DSD2>
is actually a pair, and only covers 400 to 1700 nm, and not terribly sensitive
at the endpoints, nor inexpensive.

If you can modulate the light source, you can use a bolometer or photoacoustic sensor
with wide range. The scheme will be, effectively, a lock-in amplifier.

On Mon, 24 Oct 2022 10:39:25 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:

>On 23/10/2022 22:10, John Larkin wrote:
>> On Sun, 23 Oct 2022 12:04:17 -0700 (PDT), whit3rd <whit3rd@gmail.com>
>> wrote:
>>
>>> On Sunday, October 23, 2022 at 10:49:29 AM UTC-7, John Larkin wrote:
>>>
>>>> We buy all sorts of lasers and LEDs and we can't be sure they are the
>>>> right wavelength. Even 1% wavelength resolution would be plenty.
>>>>
>>>> Nobody makes it.
>>>
>>> I don't know what 'all sorts' means, but for red visible and most IR, a silicon
>>> photodiode is a good detector. A grating (those start at a dollar or so)
>>> and a protractor will complete the ensemble. You already have a milliammeter, I trust.
>>
>> "Don't be a jerk. Nobody likes jerks."
>
>He isn't that far off the mark though.
>
>Your choices for discriminating between various LED laser emitters might
>be met by using one of each device in a 5x5 grid and illuminating them
>with the DUT. Sum the current that they produce with a opamp and with a
>bit of cunning you should be able to approximately get the wavelength
>from the actual current it produces. That's one device per 50nm.
>
>Only the diodes emitting the same or lower energy photons will generate
>photo electrons when so illuminated.
>
>You might get away with just one example of each of the common laser
>diodes. I assume the problem is to check that anonymous black plastic
>blobs are in fact the emitting the right wavelength ones.
>
>The other option would be one or more photo detectors and various Schott
>of Hoya low pass filter glasses available from various dealers.
>
>I recall a tunable visual band dichroic interference filter intended for
>amateur astronomers from a few years back that was quite impressive but
>I think only covered 400-700nm. I know someone who has one next time I
>see him I'll ask for the spec. I don't think they ever took off.
>
>Not sure you really need to do the visible ones since there are not all
>that many semiconductor laser lines possible in practice.

We really need to check IR fiber lasers. LEDs are pretty obvious.

I'd need a dispersal mechanism and a bunch of detectors. If there is
any wavelength ambiguity, a bunch of software might look at all the
detectors and untangle things and report a single wavelength in plain
sight; this would be a production test, not a research project.

Software might work from an imager, in the case of 2d dispersion, but
it might be tough to find a wideband imager chip. Lotta work.

On Mon, 24 Oct 2022 08:59:04 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Monday, October 24, 2022 at 8:37:46 AM UTC-7, John Larkin wrote:
>
>> How would you do a small spectrometer that works from 750 to, say,
>> 1900 nm? Better yet 350 to 1900.
>
>Just as your eyes don't cover that whole range, so most detectors don't.
>This one <https://www.thorlabs.com/thorproduct.cfm?partnumber=DSD2>
> is actually a pair, and only covers 400 to 1700 nm, and not terribly sensitive
>at the endpoints, nor inexpensive.

And doesn't report wavelength.

>
>If you can modulate the light source, you can use a bolometer or photoacoustic sensor
>with wide range. The scheme will be, effectively, a lock-in amplifier.

Our sources are always pulsed, so we could use an ac-coupled detector,
like a few wavelength-specific SFP modules maybe.

No, bad idea, they have wide range AGC.

On 24/10/2022 16:52, John Larkin wrote:
> On Mon, 24 Oct 2022 10:37:39 +0100, Martin Brown
> <'''newspam'''@nonad.co.uk> wrote:
>
>> On 23/10/2022 22:15, John Larkin wrote:

>>> That covers the visible, which would check the colors of LEDs, which
>>> is not really much of a problem.
>>>
>>> The more serious problem is that we buy a bunch of lasers in the 800
>>> to 1550 sort of range and we'd like to make sure they are right.
>>
>> I'm assuming for the moment that you are serious.
>
> Would anyone joke about that? We buy thousands of pcb mount fiber
> lasers per year, most of them at four wavelengths and the occasional
> oddball, and they all look alike. I'd like to final test our products
> and be sure we are shipping the correct wavelength.

Fair enough.

>> Low pass filters plus a few detectors should be good enough to
>> discriminate between most of them.
>
> Yes, a WDM splitter or two and several detectors and a bunch of
> opamps. We might build that in a box, with an LED to indicate each
> band.

That might be the simplest solution.

> Recently a customer asked for a some units with 800 nm lasers, which
> we hadn't done before. We offer 850 as one of our standards. At least
> you can see the 800, to make sure it's not one of the IRs.

I found 800nm dim red and 400nm disappointing dim in the purple.

>> I'd have thought that for a known
>> part number whether or not it emits laser light or not would be good
>> enough.
>
> Our policy is to test everything that has a spec. Mixups are possible.

Indeed.

> I vaguely recall an amateur astronomers tunable visible
>> wavelength dichroic filter (I know someone who bought a prototype) but
>> it seems to have sunk without trace. I'll ask next time I see him.
>>
>> Otherwise try Young's slits to figure out the wavelength.
>
> I want something that looks like a DVM... not an optical bench.
>
> Maybe there is a linear or circular graduated bandpass filter. Rotate
> a marked knob for max output. Or a metal disc with multiple,
> selectable bandpass windows. I'd rather buy something.

Yes that was basically it a rotating disk with a graduated shift in
bandpass as you moved it. This isn't like the one I remember but a
related idea based on crossed polars and an electrical tuneable cavity.

https://www.nature.com/articles/s41598-018-29544-x

Selectivity isn't great but it might be good enough for your application.

and references therein especially (1)

Xiang, J. et al. Electrically Tunable Selective Reflection of Light from
Ultraviolet to Visible and Infrared by Heliconical Cholesterics. Adv.
Mat. 27, 3014–3018 (2015).

If they have any working prototypes they might be worth talking to...

> We could build N boxes, each a bandpass o/e converter. Run a
> production source into the right one and it should light up.

I was thinking more in terms of a splitter and a grid of sensors each
one covered with a different bandpass (or cheaper low pass filter). You
can get annealed selelenium glass low pass filters over quite a wide
range of wavelengths from any of the glass companies.

--
Regards,
Martin Brown

John Larkin wrote:
> On Mon, 24 Oct 2022 10:24:58 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> Martin Brown wrote:
>>> On 23/10/2022 09:38, Jan Panteltje wrote:
>>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin Brown
>>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1@gioia.aioe.org>:
>>>>
>>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
>>>>>> on chip spectrometer?
>>>>>>    https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>>
>>>>> Possibly. I'd like to see a bit more of the specifications and light
>>>>> intensity it requires before I take that press release at face value.
>>>>>
>>>>> There is a bit more here but the main article is behind a paywall :(
>>>>>
>>>>> https://www.science.org/doi/10.1126/science.add8544
>>>>
>>>> I see.
>>>> Well, CCD sensor with prism in front of it should work too?
>>>
>>> The best super high resolution systems use an echelle method modest
>>> dispersion prism one way and a very high dispersion grating at almost 90
>>> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
>>>
>>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
>>>
>>> That example was actually observed with a Fourier transform method and
>>> then displayed in the fashion of a traditional echelle spectrum. It is a
>>> very impressive piece of kit even it it only works on bright stars:
>>>
>>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
>>>
>>> This is a real physical highres echelle spectroscope
>>>
>>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
>>>
>>>
>>> They are seriously nice pieces of kit. PE did an atomic
>>> absorption/emission spectroscope using a similar configuration and early
>>> CCDs back in the 1990's. Must have been ~95 because I saw it in Japan at
>>> one of the big analytical trade fairs where we were also exhibiting.
>>>
>>>
>> Yeah, a cross-dispersed echelle system can get resolving powers
>> (lambda/FWHM) up near 1E6, which is pretty impressive.

>
> How would you do a small spectrometer that works from 750 to, say,
> 1900 nm? Better yet 350 to 1900.
>

For lab use with collimated beams, probably an 800 l/mm grating, a white
card with a scale, and a lead salt vidicon camera. (I have a couple
that I need to repair one of these times--both tubes work but there's
something wrong in the black level circuitry that makes the picture
disappear after a few tenths of a second.)

For barefoot diode lasers, maybe a shear plate instead of the
grating--you know the radius of curvature of the wavefront, because it's
just the perpendicular distance between the plate and the laser, so the
fringe spacing gives you the wavelength. I have a couple of nice shear
plate devices that would probably work at some level, although the
coatings would be badly mistuned.

> (Mo just gave me a bybye hug. She says hi.)

Say hi back. She's a jewel.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

John Larkin wrote:
> On Sun, 23 Oct 2022 15:44:10 -0700 (PDT), whit3rd <whit3rd@gmail.com>
> wrote:
>
>> On Sunday, October 23, 2022 at 2:19:55 PM UTC-7, John Larkin wrote:
>>> On Sun, 23 Oct 2022 15:42:32 -0400, Joe Gwinn <joeg...@comcast.net>
>>> wrote:
>>
>>>> One can cobble something together with a replica grating and a silicon
>>>> photo detector array of some kind.
>>>>
>>>> .<https://www.sargentwelch.com/store/product/8885837/replica-diffraction-gratings>
>>
>>> How wide a spectral range can a grating cover before things get
>>> ambiguous?
>>
>> Huh? If you just want to distinguish 850 from 1350 nm, that's no problem.
>> The $1 replica that looks like a 35mm slide will do it fine. You can worry about
>> blaze angles and UV transmission (the slide is a transparency, but not to UV) and
>> line spacing fineries, but why?
>>>
>>> I was thinking that a grating could fire into several detectors, each
>>> with a different spectral range, and ...
>>
>> Or, you could swing a detector over a range of angles and register a 'hit'.
>> It'll take only seconds, why bother with a computer analysis?
>
> I don't think a grating will cast a wavelenght-linear unambiguous
> image over a wide spectral range, like 5:1 or so.
>
> I think the 700 nm lines will wind up on top of the 1400's. And
> probably much worse.
>
> https://tinyurl.com/ext8r82d
>
> "The diffracted beams of different colors and corresponding to
> consecutive orders can overlap, this phenomenon becomes more likely to
> grow in the order of diffraction."
>

If you use a low-res grating, you'll get multiple orders from everybody.
Since you know a priori that it's only one wavelength, there's no
ambiguity.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On 24/10/2022 17:00, John Larkin wrote:

> I'd need a dispersal mechanism and a bunch of detectors. If there is
> any wavelength ambiguity, a bunch of software might look at all the
> detectors and untangle things and report a single wavelength in plain
> sight; this would be a production test, not a research project.
>
> Software might work from an imager, in the case of 2d dispersion, but
> it might be tough to find a wideband imager chip. Lotta work.

I think your problem will be with the longer wavelengths even thinned
back illuminated CCDs fall off in sensitivity steeply at around 1000nm.

--
Regards,
Martin Brown

On Sun, 23 Oct 2022 14:19:47 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

>On Sun, 23 Oct 2022 15:42:32 -0400, Joe Gwinn <joegwinn@comcast.net>
>wrote:
>
>>On Sun, 23 Oct 2022 10:49:22 -0700, John Larkin
>><jlarkin@highlandSNIPMEtechnology.com> wrote:
>>
>>>On Sun, 23 Oct 2022 17:23:12 GMT, Jan Panteltje
>>><pNaonStpealmtje@yahoo.com> wrote:
>>>
>>>>On a sunny day (Sun, 23 Oct 2022 09:58:18 -0700) it happened John Larkin
>>>><jlarkin@highlandSNIPMEtechnology.com> wrote in
>>>><m0salh9pp7c3gqortagaj6ualh9g23ar4n@4ax.com>:
>>>>
>>>>>On Sun, 23 Oct 2022 15:26:39 GMT, Jan Panteltje
>>>>><pNaonStpealmtje@yahoo.com> wrote:
>>>>>
>>>>>>On a sunny day (Sun, 23 Oct 2022 08:10:42 -0700) it happened John Larkin
>>>>>><jlarkin@highlandSNIPMEtechnology.com> wrote in
>>>>>><96malhldkco3pnjog22sqb7dq8jm4c7hdb@4ax.com>:
>>>>>>
>>>>>>>On Sun, 23 Oct 2022 05:39:23 GMT, Jan Panteltje
>>>>>>><pNaOnStPeAlMtje@yahoo.com> wrote:
>>>>>>>
>>>>>>>>on chip spectrometer?
>>>>>>>> https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>>>>
>>>>>>>I've always wanted a handheld DVM-like spectrometer that covers a wide
>>>>>>>range, specifically 1600 to 300 nm to verify LED and laser
>>>>>>>wavelengths.
>>>>>>
>>>>>>That should not be difficult to make
>>>>>>
>>>>>>In the UNI we had small spectrometers that consisted of a rotating prism
>>>>>>and a photocell looking at it through a slot (to look at a spectral line)
>>>>>>A 'white' light source and a tube with the stuff that had to
>>>>>>be investigated in the light beam.
>>>>>>Big knob on top to rotate the prism, the knob had a scale with numbers on it,
>>>>>>the wavelength.
>>>>>>Small box, 3x3 inch or so I think.
>>>>>>Had to repair one once.
>>>>>>You could perhaps use a rotating prism, a slot and a photocell, tune for maximum and
>>>>>>read the rotation from the knob?
>>>>>
>>>>>The challenge is to make a spectrometer with a wide wavelength range.
>>>>>It would at least need several detectors, and a prism or grating that
>>>>>would work over about a 5:1 wavelength range.
>>>>>
>>>>>Nobody seems to make one.
>>>>>
>>>>>We're lucky in electronics. We can easily measure resistance and
>>>>>capacitance and frequency over million or billion or sometimes
>>>>>trillion-to-one spans.
>>>>>
>>>>>Our Keysight counter can measure picoseconds to kiloseconds, microHz
>>>>>to gigahertz.
>>>>>
>>>>>A Fluke DVM can measure microvolts and kilovolts.
>>>>>
>>>>>I can measure femtofarads to kilofarads with the gear on my little
>>>>>workbench.
>>>>
>>>>If you a need wide range IR detector:
>>>> https://www.irlabs.com/products/bolometers/bolometer-systems/#:~:text=Bolometers%20are%20detectors%20used%20to,5000%C2%B5m%20(30THz%20to%2060GHz).
>>>> 20 THz to 150 GHz 15 to 2000 um
>>>>I have a cryocooler also workbench size.
>>>>You have a very strong signal using laser output,
>>>>should make things easier.
>>>
>>>I want a spectrometer. We don't need quantified power measurement but
>>>it would be nice.
>>>
>>>We buy all sorts of lasers and LEDs and we can't be sure they are the
>>>right wavelength. Even 1% wavelength resolution would be plenty.
>>>
>>>Nobody makes it.
>>
>>One can cobble something together with a replica grating and a silicon
>>photo detector array of some kind.
>>
>>.<https://www.sargentwelch.com/store/product/8885837/replica-diffraction-gratings>
>>
>>This is one example. There are many others.
>>
>>You will need a calibration source of some kind. A neon tube or the
>>like, to provide some known lines for reference.
>>
>>Joe Gwinn
>
>How wide a spectral range can a grating cover before things get
>ambiguous?

If it's one source with a dominant wavelength, one can disentangle the
overlapping diffraction orders with software. If the source contains
a frequency doubler, there will also be some of the original un-
doubled drive also present, but this approach may still work.

>I was thinking that a grating could fire into several detectors, each
>with a different spectral range, and the resulting confusion might be
>sorted out in software.

I would use a linear photodetector array, but silicon won't work for
1550 nm at all. There may be a detector material that will span 800
nm to 2000 nm, but it may not be suitable for a camera.

More generally, if the task is simply to detect mixups in production,
and we are testing a bright laser source, I'd go for simple and
rugged. This approach others have mostly suggested:

Acquire a four-way passive optical power divider made of Ge-doped
fused silica optical fiber. Step index is OK. This divider will
provide four outputs of roughly equal power (if so designed). Attach
each output to a detector for one of the possible (nominal)
wavelengths, using optical filters as needed. Estimate the dominant
wavelength from the combined output currents in such a way that the
source brightness mostly cancels out.

If the response patterns are complex, four dedicated
pattern-recognizers in parallel may be used between outputs and the
decision process.

Model the decision algorithm on Receptive Fields in Biology:

..<https://en.wikipedia.org/wiki/Receptive_field>

This will give an unambiguous answer representing the best guess of
the mixup-detecting box.

One can also use the four outputs to drive four green LED lights is a
square, and let the human to the receptive-field processing visually.

Or both, at least initially.

This can be done in analog hardware, or in code.

Joe Gwinn

On 24/10/2022 21:30, Joe Gwinn wrote:
> On Sun, 23 Oct 2022 14:19:47 -0700, John Larkin
> <jlarkin@highlandSNIPMEtechnology.com> wrote:
>
>> On Sun, 23 Oct 2022 15:42:32 -0400, Joe Gwinn <joegwinn@comcast.net>
>> wrote:
>>
>>> On Sun, 23 Oct 2022 10:49:22 -0700, John Larkin
>>> <jlarkin@highlandSNIPMEtechnology.com> wrote:
>>>
>>>> On Sun, 23 Oct 2022 17:23:12 GMT, Jan Panteltje
>>>> <pNaonStpealmtje@yahoo.com> wrote:
>>>>
>>>>> On a sunny day (Sun, 23 Oct 2022 09:58:18 -0700) it happened John Larkin
>>>>> <jlarkin@highlandSNIPMEtechnology.com> wrote in
>>>>> <m0salh9pp7c3gqortagaj6ualh9g23ar4n@4ax.com>:
>>>>>
>>>>>> On Sun, 23 Oct 2022 15:26:39 GMT, Jan Panteltje
>>>>>> <pNaonStpealmtje@yahoo.com> wrote:
>>>>>>
>>>>>>> On a sunny day (Sun, 23 Oct 2022 08:10:42 -0700) it happened John Larkin
>>>>>>> <jlarkin@highlandSNIPMEtechnology.com> wrote in
>>>>>>> <96malhldkco3pnjog22sqb7dq8jm4c7hdb@4ax.com>:
>>>>>>>
>>>>>>>> On Sun, 23 Oct 2022 05:39:23 GMT, Jan Panteltje
>>>>>>>> <pNaOnStPeAlMtje@yahoo.com> wrote:
>>>>>>>>
>>>>>>>>> on chip spectrometer?
>>>>>>>>> https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>>>>>
>>>>>>>> I've always wanted a handheld DVM-like spectrometer that covers a wide
>>>>>>>> range, specifically 1600 to 300 nm to verify LED and laser
>>>>>>>> wavelengths.
>>>>>>>
>>>>>>> That should not be difficult to make
>>>>>>>
>>>>>>> In the UNI we had small spectrometers that consisted of a rotating prism
>>>>>>> and a photocell looking at it through a slot (to look at a spectral line)
>>>>>>> A 'white' light source and a tube with the stuff that had to
>>>>>>> be investigated in the light beam.
>>>>>>> Big knob on top to rotate the prism, the knob had a scale with numbers on it,
>>>>>>> the wavelength.
>>>>>>> Small box, 3x3 inch or so I think.
>>>>>>> Had to repair one once.
>>>>>>> You could perhaps use a rotating prism, a slot and a photocell, tune for maximum and
>>>>>>> read the rotation from the knob?
>>>>>>
>>>>>> The challenge is to make a spectrometer with a wide wavelength range.
>>>>>> It would at least need several detectors, and a prism or grating that
>>>>>> would work over about a 5:1 wavelength range.
>>>>>>
>>>>>> Nobody seems to make one.
>>>>>>
>>>>>> We're lucky in electronics. We can easily measure resistance and
>>>>>> capacitance and frequency over million or billion or sometimes
>>>>>> trillion-to-one spans.
>>>>>>
>>>>>> Our Keysight counter can measure picoseconds to kiloseconds, microHz
>>>>>> to gigahertz.
>>>>>>
>>>>>> A Fluke DVM can measure microvolts and kilovolts.
>>>>>>
>>>>>> I can measure femtofarads to kilofarads with the gear on my little
>>>>>> workbench.
>>>>>
>>>>> If you a need wide range IR detector:
>>>>> https://www.irlabs.com/products/bolometers/bolometer-systems/#:~:text=Bolometers%20are%20detectors%20used%20to,5000%C2%B5m%20(30THz%20to%2060GHz).
>>>>> 20 THz to 150 GHz 15 to 2000 um
>>>>> I have a cryocooler also workbench size.
>>>>> You have a very strong signal using laser output,
>>>>> should make things easier.
>>>>
>>>> I want a spectrometer. We don't need quantified power measurement but
>>>> it would be nice.
>>>>
>>>> We buy all sorts of lasers and LEDs and we can't be sure they are the
>>>> right wavelength. Even 1% wavelength resolution would be plenty.
>>>>
>>>> Nobody makes it.
>>>
>>> One can cobble something together with a replica grating and a silicon
>>> photo detector array of some kind.
>>>
>>> .<https://www.sargentwelch.com/store/product/8885837/replica-diffraction-gratings>
>>>
>>> This is one example. There are many others.
>>>
>>> You will need a calibration source of some kind. A neon tube or the
>>> like, to provide some known lines for reference.
>>>
>>> Joe Gwinn
>>
>> How wide a spectral range can a grating cover before things get
>> ambiguous?
>
> If it's one source with a dominant wavelength, one can disentangle the
> overlapping diffraction orders with software. If the source contains
> a frequency doubler, there will also be some of the original un-
> doubled drive also present, but this approach may still work.
>
>
>> I was thinking that a grating could fire into several detectors, each
>> with a different spectral range, and the resulting confusion might be
>> sorted out in software.
>
> I would use a linear photodetector array, but silicon won't work for
> 1550 nm at all. There may be a detector material that will span 800
> nm to 2000 nm, but it may not be suitable for a camera.

Detectors are available typically InGaAs for the NIR as are whole module
solutions but I don't think he is going to like the price! eg.

https://www.stellarnet.us/spectrometers/portable-nir-spectrometer-line-up/

or from Edmund

https://www.edmundoptics.com/p/900---1700nm-bw-tek-ingaas-nir-spectrometer/43100/

--
Regards,
Martin Brown

On 23/10/2022 16:15, John Larkin wrote:
> On Sun, 23 Oct 2022 14:27:56 +0100, Martin Brown
> <'''newspam'''@nonad.co.uk> wrote:
>
>> On 23/10/2022 09:38, Jan Panteltje wrote:
>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin Brown
>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1@gioia.aioe.org>:
>>>
>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
>>>>> on chip spectrometer?
>>>>> https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>
>>>> Possibly. I'd like to see a bit more of the specifications and light
>>>> intensity it requires before I take that press release at face value.
>>>>
>>>> There is a bit more here but the main article is behind a paywall :(
>>>>
>>>> https://www.science.org/doi/10.1126/science.add8544
>>>
>>> I see.
>>> Well, CCD sensor with prism in front of it should work too?
>>
>> The best super high resolution systems use an echelle method modest
>> dispersion prism one way and a very high dispersion grating at almost 90
>> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
>>
>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
>>
>> That example was actually observed with a Fourier transform method and
>> then displayed in the fashion of a traditional echelle spectrum. It is a
>> very impressive piece of kit even it it only works on bright stars:
>>
>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
>>
>> This is a real physical highres echelle spectroscope
>>
>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
>>
>> They are seriously nice pieces of kit. PE did an atomic
>> absorption/emission spectroscope using a similar configuration and early
>> CCDs back in the 1990's. Must have been ~95 because I saw it in Japan at
>> one of the big analytical trade fairs where we were also exhibiting.
>
> The spectrometer business seems to be a race for resolution in narrow
> bands. There's no wide-range low-resolution stuff that we can find.
>
> Something like a grating and a bunch of detectors could work. It would
> have a lot of wavelength overlap confusion which could be mostly
> computed out.
>

Regular silicon detectors cover 900-300nm (or thereabouts) at low cost
so I wonder if a non-linear crystal can be switched in ahead of the
grating to double or triple 1600nm into the Si-detectable range. JL
wants to verify single bright monochromatic sources so losses needn't be
a worry?

piglet

On Tue, 25 Oct 2022 16:03:40 +0100, piglet <erichpwagner@hotmail.com>
wrote:

>On 23/10/2022 16:15, John Larkin wrote:
>> On Sun, 23 Oct 2022 14:27:56 +0100, Martin Brown
>> <'''newspam'''@nonad.co.uk> wrote:
>>
>>> On 23/10/2022 09:38, Jan Panteltje wrote:
>>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin Brown
>>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1@gioia.aioe.org>:
>>>>
>>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
>>>>>> on chip spectrometer?
>>>>>> https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>>
>>>>> Possibly. I'd like to see a bit more of the specifications and light
>>>>> intensity it requires before I take that press release at face value.
>>>>>
>>>>> There is a bit more here but the main article is behind a paywall :(
>>>>>
>>>>> https://www.science.org/doi/10.1126/science.add8544
>>>>
>>>> I see.
>>>> Well, CCD sensor with prism in front of it should work too?
>>>
>>> The best super high resolution systems use an echelle method modest
>>> dispersion prism one way and a very high dispersion grating at almost 90
>>> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
>>>
>>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
>>>
>>> That example was actually observed with a Fourier transform method and
>>> then displayed in the fashion of a traditional echelle spectrum. It is a
>>> very impressive piece of kit even it it only works on bright stars:
>>>
>>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
>>>
>>> This is a real physical highres echelle spectroscope
>>>
>>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
>>>
>>> They are seriously nice pieces of kit. PE did an atomic
>>> absorption/emission spectroscope using a similar configuration and early
>>> CCDs back in the 1990's. Must have been ~95 because I saw it in Japan at
>>> one of the big analytical trade fairs where we were also exhibiting.
>>
>> The spectrometer business seems to be a race for resolution in narrow
>> bands. There's no wide-range low-resolution stuff that we can find.
>>
>> Something like a grating and a bunch of detectors could work. It would
>> have a lot of wavelength overlap confusion which could be mostly
>> computed out.
>>
>
>Regular silicon detectors cover 900-300nm (or thereabouts) at low cost
>so I wonder if a non-linear crystal can be switched in ahead of the
>grating to double or triple 1600nm into the Si-detectable range. JL
>wants to verify single bright monochromatic sources so losses needn't be
>a worry?
>
>piglet
>
>
>

A typical source is a connectorized fiber-coupled laser of a couple of
milliwatts. Multiplication usually requires very high powers.

The longest wavelength lasers that we now use are 1550, and we have
corresponding photodiodes. The shortest are 800, ditto.

A wavelength splitter and three photodiodes would at least identify
the band of a laser: 1500ish, 1300ish, and 850ish.

On Tuesday, October 25, 2022 at 8:52:40 AM UTC-7, John Larkin wrote:
> On Tue, 25 Oct 2022 16:03:40 +0100, piglet <erichp...@hotmail.com>
> wrote:

> >Regular silicon detectors cover 900-300nm (or thereabouts) at low cost
> >so I wonder if a non-linear crystal can be switched in ahead of the
> >grating to double or triple 1600nm into the Si-detectable range. JL
> >wants to verify single bright monochromatic sources so losses needn't be
> >a worry?

> A typical source is a connectorized fiber-coupled laser of a couple of
> milliwatts. Multiplication usually requires very high powers.
>
> The longest wavelength lasers that we now use are 1550, and we have
> corresponding photodiodes. The shortest are 800, ditto.
>
> A wavelength splitter and three photodiodes would at least identify
> the band of a laser: 1500ish, 1300ish, and 850ish.

If there's enough energy to unbalance a thermistor bridge, a single detector
would handle the whole range. Just put one thermistor in shade, and expose
the other to the 'beam'. That does require a mirror for beam forming from a
small-spot source, but no wavelengths omitted if you spend the money for a reflective
grating do do the wavelength selection. The replica gratings, at $1 each, don't
come with a lot of detailed specs for 1500 nm.

You'd not want the operator to breathe on the detector, of course.

piglet wrote:
> On 23/10/2022 16:15, John Larkin wrote:
>> On Sun, 23 Oct 2022 14:27:56 +0100, Martin Brown
>> <'''newspam'''@nonad.co.uk> wrote:
>>
>>> On 23/10/2022 09:38, Jan Panteltje wrote:
>>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin
>>>> Brown
>>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1@gioia.aioe.org>:
>>>>
>>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
>>>>>> on chip spectrometer?
>>>>>>     https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>>
>>>>> Possibly. I'd like to see a bit more of the specifications and light
>>>>> intensity it requires before I take that press release at face value.
>>>>>
>>>>> There is a bit more here but the main article is behind a paywall :(
>>>>>
>>>>> https://www.science.org/doi/10.1126/science.add8544
>>>>
>>>> I see.
>>>> Well, CCD sensor with prism in front of it should work too?
>>>
>>> The best super high resolution systems use an echelle method modest
>>> dispersion prism one way and a very high dispersion grating at almost 90
>>> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
>>>
>>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
>>>
>>> That example was actually observed with a Fourier transform method and
>>> then displayed in the fashion of a traditional echelle spectrum. It is a
>>> very impressive piece of kit even it it only works on bright stars:
>>>
>>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
>>>
>>> This is a real physical highres echelle spectroscope
>>>
>>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
>>>
>>>
>>> They are seriously nice pieces of kit. PE did an atomic
>>> absorption/emission spectroscope using a similar configuration and early
>>> CCDs back in the 1990's. Must have been ~95 because I saw it in Japan at
>>> one of the big analytical trade fairs where we were also exhibiting.
>>
>> The spectrometer business seems to be a race for resolution in narrow
>> bands. There's no wide-range low-resolution stuff that we can find.
>>
>> Something like a grating and a bunch of detectors could work. It would
>> have a lot of wavelength overlap confusion which could be mostly
>> computed out.
>>
>
> Regular silicon detectors cover 900-300nm (or thereabouts) at low cost
> so I wonder if a non-linear crystal can be switched in ahead of the
> grating to double or triple 1600nm into the Si-detectable range. JL
> wants to verify single bright monochromatic sources so losses needn't be
> a worry?
>
> piglet

Even if they were 400 dB? ;)

Seriously, optical materials are so linear that you really have to stand
on one leg to get any SH signal to speak of.

If you have a gigawatt of peak power, you can do a lot of things, e.g.
use topical disinfectant for SHG. Nitrofurazone (5-nitro 2-furaldehyde
semicarbazone, Aldrich Catalog #73340) does a good job of making a
little bit of visible from a whole lot of IR.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On 25/10/2022 23:06, Phil Hobbs wrote:
> piglet wrote:
>> On 23/10/2022 16:15, John Larkin wrote:
>>> On Sun, 23 Oct 2022 14:27:56 +0100, Martin Brown
>>> <'''newspam'''@nonad.co.uk> wrote:
>>>
>>>> On 23/10/2022 09:38, Jan Panteltje wrote:
>>>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin
>>>>> Brown
>>>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1@gioia.aioe.org>:
>>>>>
>>>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
>>>>>>> on chip spectrometer?
>>>>>>>     https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>>>
>>>>>> Possibly. I'd like to see a bit more of the specifications and light
>>>>>> intensity it requires before I take that press release at face value.
>>>>>>
>>>>>> There is a bit more here but the main article is behind a paywall :(
>>>>>>
>>>>>> https://www.science.org/doi/10.1126/science.add8544
>>>>>
>>>>> I see.
>>>>> Well, CCD sensor with prism in front of it should work too?
>>>>
>>>> The best super high resolution systems use an echelle method modest
>>>> dispersion prism one way and a very high dispersion grating at
>>>> almost 90
>>>> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
>>>>
>>>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
>>>>
>>>> That example was actually observed with a Fourier transform method and
>>>> then displayed in the fashion of a traditional echelle spectrum. It
>>>> is a
>>>> very impressive piece of kit even it it only works on bright stars:
>>>>
>>>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
>>>>
>>>> This is a real physical highres echelle spectroscope
>>>>
>>>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
>>>>
>>>> They are seriously nice pieces of kit. PE did an atomic
>>>> absorption/emission spectroscope using a similar configuration and
>>>> early
>>>> CCDs back in the 1990's. Must have been ~95 because I saw it in
>>>> Japan at
>>>> one of the big analytical trade fairs where we were also exhibiting.
>>>
>>> The spectrometer business seems to be a race for resolution in narrow
>>> bands. There's no wide-range low-resolution stuff that we can find.
>>>
>>> Something like a grating and a bunch of detectors could work. It would
>>> have a lot of wavelength overlap confusion which could be mostly
>>> computed out.
>>>
>>
>> Regular silicon detectors cover 900-300nm (or thereabouts) at low cost
>> so I wonder if a non-linear crystal can be switched in ahead of the
>> grating to double or triple 1600nm into the Si-detectable range. JL
>> wants to verify single bright monochromatic sources so losses needn't
>> be a worry?
>>
>> piglet
>
> Even if they were 400 dB? ;)
>
> Seriously, optical materials are so linear that you really have to stand
> on one leg to get any SH signal to speak of.
>
> If you have a gigawatt of peak power, you can do a lot of things, e.g.
> use topical disinfectant for SHG. Nitrofurazone (5-nitro 2-furaldehyde
> semicarbazone, Aldrich Catalog #73340) does a good job of making a
> little bit of visible from a whole lot of IR.
>
> Cheers
>
> Phil Hobbs
>
>

I bow to your superior knowledge, my only experience was years ago my
kids had a tiny green laser pointer that ran off some button cells - the
green was doubled IR. The DC input power cannot possibly have been more
than 100-200 milliwatts. Whole thing was incredibly cheap and tiny.

piglet

onsdag den 26. oktober 2022 kl. 13.45.34 UTC+2 skrev erichp...@hotmail.com:
> On 25/10/2022 23:06, Phil Hobbs wrote:
> > piglet wrote:
> >> On 23/10/2022 16:15, John Larkin wrote:
> >>> On Sun, 23 Oct 2022 14:27:56 +0100, Martin Brown
> >>> <'''newspam'''@nonad.co.uk> wrote:
> >>>
> >>>> On 23/10/2022 09:38, Jan Panteltje wrote:
> >>>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin
> >>>>> Brown
> >>>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1...@gioia.aioe.org>:
> >>>>>
> >>>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
> >>>>>>> on chip spectrometer?
> >>>>>>> https://www.sciencedaily.com/releases/2022/10/221020140615.htm
> >>>>>>
> >>>>>> Possibly. I'd like to see a bit more of the specifications and light
> >>>>>> intensity it requires before I take that press release at face value.
> >>>>>>
> >>>>>> There is a bit more here but the main article is behind a paywall :(
> >>>>>>
> >>>>>> https://www.science.org/doi/10.1126/science.add8544
> >>>>>
> >>>>> I see.
> >>>>> Well, CCD sensor with prism in front of it should work too?
> >>>>
> >>>> The best super high resolution systems use an echelle method modest
> >>>> dispersion prism one way and a very high dispersion grating at
> >>>> almost 90
> >>>> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
> >>>>
> >>>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
> >>>>
> >>>> That example was actually observed with a Fourier transform method and
> >>>> then displayed in the fashion of a traditional echelle spectrum. It
> >>>> is a
> >>>> very impressive piece of kit even it it only works on bright stars:
> >>>>
> >>>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
> >>>>
> >>>> This is a real physical highres echelle spectroscope
> >>>>
> >>>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
> >>>>
> >>>> They are seriously nice pieces of kit. PE did an atomic
> >>>> absorption/emission spectroscope using a similar configuration and
> >>>> early
> >>>> CCDs back in the 1990's. Must have been ~95 because I saw it in
> >>>> Japan at
> >>>> one of the big analytical trade fairs where we were also exhibiting.
> >>>
> >>> The spectrometer business seems to be a race for resolution in narrow
> >>> bands. There's no wide-range low-resolution stuff that we can find.
> >>>
> >>> Something like a grating and a bunch of detectors could work. It would
> >>> have a lot of wavelength overlap confusion which could be mostly
> >>> computed out.
> >>>
> >>
> >> Regular silicon detectors cover 900-300nm (or thereabouts) at low cost
> >> so I wonder if a non-linear crystal can be switched in ahead of the
> >> grating to double or triple 1600nm into the Si-detectable range. JL
> >> wants to verify single bright monochromatic sources so losses needn't
> >> be a worry?
> >>
> >> piglet
> >
> > Even if they were 400 dB? ;)
> >
> > Seriously, optical materials are so linear that you really have to stand
> > on one leg to get any SH signal to speak of.
> >
> > If you have a gigawatt of peak power, you can do a lot of things, e.g.
> > use topical disinfectant for SHG. Nitrofurazone (5-nitro 2-furaldehyde
> > semicarbazone, Aldrich Catalog #73340) does a good job of making a
> > little bit of visible from a whole lot of IR.
> >
> > Cheers
> >
> > Phil Hobbs
> >
> >
> I bow to your superior knowledge, my only experience was years ago my
> kids had a tiny green laser pointer that ran off some button cells - the
> green was doubled IR. The DC input power cannot possibly have been more
> than 100-200 milliwatts. Whole thing was incredibly cheap and tiny.

maximum for a legal laser pointer is 5mW

On 26/10/2022 13:19, Lasse Langwadt Christensen wrote:
> onsdag den 26. oktober 2022 kl. 13.45.34 UTC+2 skrev erichp...@hotmail.com:
>> On 25/10/2022 23:06, Phil Hobbs wrote:
>>> piglet wrote:
>>>> On 23/10/2022 16:15, John Larkin wrote:
>>>>> On Sun, 23 Oct 2022 14:27:56 +0100, Martin Brown
>>>>> <'''newspam'''@nonad.co.uk> wrote:
>>>>>
>>>>>> On 23/10/2022 09:38, Jan Panteltje wrote:
>>>>>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin
>>>>>>> Brown
>>>>>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1...@gioia.aioe.org>:
>>>>>>>
>>>>>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
>>>>>>>>> on chip spectrometer?
>>>>>>>>> https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>>>>>
>>>>>>>> Possibly. I'd like to see a bit more of the specifications and light
>>>>>>>> intensity it requires before I take that press release at face value.
>>>>>>>>
>>>>>>>> There is a bit more here but the main article is behind a paywall :(
>>>>>>>>
>>>>>>>> https://www.science.org/doi/10.1126/science.add8544
>>>>>>>
>>>>>>> I see.
>>>>>>> Well, CCD sensor with prism in front of it should work too?
>>>>>>
>>>>>> The best super high resolution systems use an echelle method modest
>>>>>> dispersion prism one way and a very high dispersion grating at
>>>>>> almost 90
>>>>>> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
>>>>>>
>>>>>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
>>>>>>
>>>>>> That example was actually observed with a Fourier transform method and
>>>>>> then displayed in the fashion of a traditional echelle spectrum. It
>>>>>> is a
>>>>>> very impressive piece of kit even it it only works on bright stars:
>>>>>>
>>>>>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
>>>>>>
>>>>>> This is a real physical highres echelle spectroscope
>>>>>>
>>>>>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
>>>>>>
>>>>>> They are seriously nice pieces of kit. PE did an atomic
>>>>>> absorption/emission spectroscope using a similar configuration and
>>>>>> early
>>>>>> CCDs back in the 1990's. Must have been ~95 because I saw it in
>>>>>> Japan at
>>>>>> one of the big analytical trade fairs where we were also exhibiting.
>>>>>
>>>>> The spectrometer business seems to be a race for resolution in narrow
>>>>> bands. There's no wide-range low-resolution stuff that we can find.
>>>>>
>>>>> Something like a grating and a bunch of detectors could work. It would
>>>>> have a lot of wavelength overlap confusion which could be mostly
>>>>> computed out.
>>>>>
>>>>
>>>> Regular silicon detectors cover 900-300nm (or thereabouts) at low cost
>>>> so I wonder if a non-linear crystal can be switched in ahead of the
>>>> grating to double or triple 1600nm into the Si-detectable range. JL
>>>> wants to verify single bright monochromatic sources so losses needn't
>>>> be a worry?
>>>>
>>>> piglet
>>>
>>> Even if they were 400 dB? ;)
>>>
>>> Seriously, optical materials are so linear that you really have to stand
>>> on one leg to get any SH signal to speak of.
>>>
>>> If you have a gigawatt of peak power, you can do a lot of things, e.g.
>>> use topical disinfectant for SHG. Nitrofurazone (5-nitro 2-furaldehyde
>>> semicarbazone, Aldrich Catalog #73340) does a good job of making a
>>> little bit of visible from a whole lot of IR.
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>>
>>>
>> I bow to your superior knowledge, my only experience was years ago my
>> kids had a tiny green laser pointer that ran off some button cells - the
>> green was doubled IR. The DC input power cannot possibly have been more
>> than 100-200 milliwatts. Whole thing was incredibly cheap and tiny.
>
> maximum for a legal laser pointer is 5mW
>

Exactly! But PH was saying doubling required huge power, I doubt the
kids toy lipstick sized pointer optical output was even a milli-watt but
it showed optical doubling happens at sub-watt levels?

piglet

onsdag den 26. oktober 2022 kl. 17.15.35 UTC+2 skrev erichp...@hotmail.com:
> On 26/10/2022 13:19, Lasse Langwadt Christensen wrote:
> > onsdag den 26. oktober 2022 kl. 13.45.34 UTC+2 skrev erichp...@hotmail.com:
> >> On 25/10/2022 23:06, Phil Hobbs wrote:
> >>> piglet wrote:
> >>>> On 23/10/2022 16:15, John Larkin wrote:
> >>>>> On Sun, 23 Oct 2022 14:27:56 +0100, Martin Brown
> >>>>> <'''newspam'''@nonad.co.uk> wrote:
> >>>>>
> >>>>>> On 23/10/2022 09:38, Jan Panteltje wrote:
> >>>>>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened Martin
> >>>>>>> Brown
> >>>>>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1...@gioia.aioe.org>:
> >>>>>>>
> >>>>>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
> >>>>>>>>> on chip spectrometer?
> >>>>>>>>> https://www.sciencedaily.com/releases/2022/10/221020140615.htm
> >>>>>>>>
> >>>>>>>> Possibly. I'd like to see a bit more of the specifications and light
> >>>>>>>> intensity it requires before I take that press release at face value.
> >>>>>>>>
> >>>>>>>> There is a bit more here but the main article is behind a paywall :(
> >>>>>>>>
> >>>>>>>> https://www.science.org/doi/10.1126/science.add8544
> >>>>>>>
> >>>>>>> I see.
> >>>>>>> Well, CCD sensor with prism in front of it should work too?
> >>>>>>
> >>>>>> The best super high resolution systems use an echelle method modest
> >>>>>> dispersion prism one way and a very high dispersion grating at
> >>>>>> almost 90
> >>>>>> degrees to it so as to map a linear spectrum onto a 2D rectangular CCD.
> >>>>>>
> >>>>>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
> >>>>>>
> >>>>>> That example was actually observed with a Fourier transform method and
> >>>>>> then displayed in the fashion of a traditional echelle spectrum. It
> >>>>>> is a
> >>>>>> very impressive piece of kit even it it only works on bright stars:
> >>>>>>
> >>>>>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
> >>>>>>
> >>>>>> This is a real physical highres echelle spectroscope
> >>>>>>
> >>>>>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
> >>>>>>
> >>>>>> They are seriously nice pieces of kit. PE did an atomic
> >>>>>> absorption/emission spectroscope using a similar configuration and
> >>>>>> early
> >>>>>> CCDs back in the 1990's. Must have been ~95 because I saw it in
> >>>>>> Japan at
> >>>>>> one of the big analytical trade fairs where we were also exhibiting.
> >>>>>
> >>>>> The spectrometer business seems to be a race for resolution in narrow
> >>>>> bands. There's no wide-range low-resolution stuff that we can find.
> >>>>>
> >>>>> Something like a grating and a bunch of detectors could work. It would
> >>>>> have a lot of wavelength overlap confusion which could be mostly
> >>>>> computed out.
> >>>>>
> >>>>
> >>>> Regular silicon detectors cover 900-300nm (or thereabouts) at low cost
> >>>> so I wonder if a non-linear crystal can be switched in ahead of the
> >>>> grating to double or triple 1600nm into the Si-detectable range. JL
> >>>> wants to verify single bright monochromatic sources so losses needn't
> >>>> be a worry?
> >>>>
> >>>> piglet
> >>>
> >>> Even if they were 400 dB? ;)
> >>>
> >>> Seriously, optical materials are so linear that you really have to stand
> >>> on one leg to get any SH signal to speak of.
> >>>
> >>> If you have a gigawatt of peak power, you can do a lot of things, e.g.
> >>> use topical disinfectant for SHG. Nitrofurazone (5-nitro 2-furaldehyde
> >>> semicarbazone, Aldrich Catalog #73340) does a good job of making a
> >>> little bit of visible from a whole lot of IR.
> >>>
> >>> Cheers
> >>>
> >>> Phil Hobbs
> >>>
> >>>
> >> I bow to your superior knowledge, my only experience was years ago my
> >> kids had a tiny green laser pointer that ran off some button cells - the
> >> green was doubled IR. The DC input power cannot possibly have been more
> >> than 100-200 milliwatts. Whole thing was incredibly cheap and tiny.
> >
> > maximum for a legal laser pointer is 5mW
> >
> Exactly! But PH was saying doubling required huge power, I doubt the
> kids toy lipstick sized pointer optical output was even a milli-watt but
> it showed optical doubling happens at sub-watt levels?

doesn't take much to make it not work, https://youtu.be/9tOcUyakk0Q

On a sunny day (Wed, 26 Oct 2022 16:15:28 +0100) it happened piglet
<erichpwagner@hotmail.com> wrote in <tjbiug$2g6r6$1@dont-email.me>:

>Exactly! But PH was saying doubling required huge power, I doubt the
>kids toy lipstick sized pointer optical output was even a milli-watt but
>it showed optical doubling happens at sub-watt levels?
>
>piglet

Most of your questions are answered here:
https://www.rp-photonics.com/frequency_doubling.html#:~:text=Frequency%20doubling%20is%20a%20frequently,usually%20based%20on%20this%20approach.

https://www.quora.com/Semiconductors-How-does-a-frequency-doubler-work-in-a-green-laser-pointer

OTOH there are now green laser diodes (not doubling).
I have an iconnect picop laser projector,
it is said it uses a true red, green and blue laser (green not doubling)

Nice thing to play with.
https://www.sapiensbryan.com/review-i-connect-view-x-laser-pico-projector-ipod-iphone-ipad-compatible/
that was already 10 years or longer ago, I did read it uses a true green laser (else scan artifacts I'd think)
Its all low power.

You cn test if your green laser is doubling (and uses high energy pulses) by swinging it
against some wall and see it it produces a line of dots (swicthing frequency)
But if it is younger than 10 years maybe it is just a green laser diode?

https://arstechnica.com/gadgets/2009/07/green-diode-lasers-a-big-breakthrough-for-laser-display-tech/

piglet wrote:
> On 25/10/2022 23:06, Phil Hobbs wrote:
>> piglet wrote:
>>> On 23/10/2022 16:15, John Larkin wrote:
>>>> On Sun, 23 Oct 2022 14:27:56 +0100, Martin Brown
>>>> <'''newspam'''@nonad.co.uk> wrote:
>>>>
>>>>> On 23/10/2022 09:38, Jan Panteltje wrote:
>>>>>> On a sunny day (Sun, 23 Oct 2022 09:13:53 +0100) it happened
>>>>>> Martin Brown
>>>>>> <'''newspam'''@nonad.co.uk> wrote in <tj2t42$1jlg$1@gioia.aioe.org>:
>>>>>>
>>>>>>> On 23/10/2022 06:39, Jan Panteltje wrote:
>>>>>>>> on chip spectrometer?
>>>>>>>>     https://www.sciencedaily.com/releases/2022/10/221020140615.htm
>>>>>>>
>>>>>>> Possibly. I'd like to see a bit more of the specifications and light
>>>>>>> intensity it requires before I take that press release at face
>>>>>>> value.
>>>>>>>
>>>>>>> There is a bit more here but the main article is behind a paywall :(
>>>>>>>
>>>>>>> https://www.science.org/doi/10.1126/science.add8544
>>>>>>
>>>>>> I see.
>>>>>> Well, CCD sensor with prism in front of it should work too?
>>>>>
>>>>> The best super high resolution systems use an echelle method modest
>>>>> dispersion prism one way and a very high dispersion grating at
>>>>> almost 90
>>>>> degrees to it so as to map a linear spectrum onto a 2D rectangular
>>>>> CCD.
>>>>>
>>>>> https://solarsystem.nasa.gov/resources/390/the-solar-spectrum/
>>>>>
>>>>> That example was actually observed with a Fourier transform method and
>>>>> then displayed in the fashion of a traditional echelle spectrum. It
>>>>> is a
>>>>> very impressive piece of kit even it it only works on bright stars:
>>>>>
>>>>> https://www.jstor.org/stable/26660057#metadata_info_tab_contents
>>>>>
>>>>> This is a real physical highres echelle spectroscope
>>>>>
>>>>> https://www.shelyak.com/le-woppshel-un-spectro-echelle-a-grande-resolution/?lang=en
>>>>>
>>>>>
>>>>> They are seriously nice pieces of kit. PE did an atomic
>>>>> absorption/emission spectroscope using a similar configuration and
>>>>> early
>>>>> CCDs back in the 1990's. Must have been ~95 because I saw it in
>>>>> Japan at
>>>>> one of the big analytical trade fairs where we were also exhibiting.
>>>>
>>>> The spectrometer business seems to be a race for resolution in narrow
>>>> bands. There's no wide-range low-resolution stuff that we can find.
>>>>
>>>> Something like a grating and a bunch of detectors could work. It would
>>>> have a lot of wavelength overlap confusion which could be mostly
>>>> computed out.
>>>>
>>>
>>> Regular silicon detectors cover 900-300nm (or thereabouts) at low
>>> cost so I wonder if a non-linear crystal can be switched in ahead of
>>> the grating to double or triple 1600nm into the Si-detectable range.
>>> JL wants to verify single bright monochromatic sources so losses
>>> needn't be a worry?
>>>
>>> piglet
>>
>> Even if they were 400 dB? ;)
>>
>> Seriously, optical materials are so linear that you really have to
>> stand on one leg to get any SH signal to speak of.
>>
>> If you have a gigawatt of peak power, you can do a lot of things, e.g.
>> use topical disinfectant for SHG. Nitrofurazone (5-nitro 2-furaldehyde
>> semicarbazone, Aldrich Catalog #73340) does a good job of making a
>> little bit of visible from a whole lot of IR.
>>
>> Cheers
>>
>> Phil Hobbs
>>
>>
>
> I bow to your superior knowledge, my only experience was years ago my
> kids had a tiny green laser pointer that ran off some button cells - the
> green was doubled IR. The DC input power cannot possibly have been more
> than 100-200 milliwatts. Whole thing was incredibly cheap and tiny.
>
> piglet
>
>
Yes, you can do that at surprisingly low power, but it takes focusing
the beam down in just the right material, cut with the crystal axes just
so.

The issues are:
(1) the size of the elements in the nonlinear susceptibility tensor
chi'' (normally very small except in special materials), and
(b) getting the nonlinear electric polarization (*) to phase-match with
a propagating wave at the second harmonic, which it normally doesn't.

A good material has large coefficients of chi-double-prime, which helps
with the first, and enough birefringence, which makes the second possible.

The reason phase matching matters is that the growth of the
second-harmonic wave is a coupled-modes problem--the fundamental beam
causes a component of polarization at the second harmonic, and the SH
beam grows from that, just like a microwave directional coupler.

The k vector of the SH _polarization_ is obviously exactly twice that of
the fundamental beam, whereas the SH _beam's_ k vector is defined by the
frequency and refractive index. (Normally the refractive index increases
considerably towards short wavelengths, so this does not happen by
accident.)

Cheers

Phil Hobbs

(*) This is dielectric polarization, the material response to the
applied field, not polarization as in linear or circular or elliptical
polarization of a propagating wave.

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com