nir light sources?

posted in optics also.

You can get CCDs with some residual sensitivity out to about 1.2um and colloidal long pass filters to match (cheap alternative unexposed slide film). It is usually a nuisance factor that requires a IR cold mirror filter in front of the sensor for normal use, but some cameras and aftermarket people will remove them for a price or DIY. eg.

You can buy highly selective bandpass filters from the likes of Edmund or have them custom made for a price. Anything unusual costs a *lot*. You can tune them a bit by tilting.

Diffraction gratings form a spectrum.

The remainder is such garbled gibberish as to be incomprehensible.

--
Regards, 
Martin Brown

Sure.. once you get past 1.5 um they are rarer. Thor labs lists some, (Though you can probably find them cheaper if you are looking for more than a few.)

and then different thermal sources.

George H.

Is that low res as in low resolution, or is there something known as lores images.

If you are going to use filters, can't you just use a broadband light source like a quartz lightbulb? LEDs are a line spectra source, at least for NIR, so I don't see what you would filter.

If you are going to go the broadband source plus filter route, check out Andover.

Yes, garbled. Have you done any FT spectroscopic imaging or pattern recognition?

What I am looking for is an "image cube" a stacked image consisting of many images next to each other. So if the camera is taking 30 fps, then each frame has a different narrow-band wavelength. (the $25 RPi cam is sensitive to NIR.)

One way is to illuminate the subject with a series of wavelengths - generated from a grating or individual led's. Or else sequentially (time) filter the light input to the camera.

A flashed led would do the trick, but how many are in the NIR?

Specifically of FT-IR no, of image and spectral reconstruction from coherence functions very often and on major scientific experiments.

You should understand that FT-IR is a non imaging technique. Intro here:

--
Regards, 
Martin Brown

A nice source of infra-red is used SFP optical transceivers. These are readily available on eBay with wavelengths of

850nm, 1310nm and (more expensively) 1550nm. There are also some other wavelengths but they are much harder to find. Lots of 1Gbit/s ethernet and 4Gbit/s fibre channel SFPs are being pulled out of data centres and replaced with 10Gbit/s devices, so prices are very low. The SFP module can be plugged into an inexpensive "media converter" giving a total cost for the complete light source of around GBP25.

The VCSEL lasers used in these devices have a beam spread of about 30 degrees and a source diameter of a few tens of um for multimode lasers and a few um for single mode lasers.

Polarisation is random.

Most digital cameras will easily see the 850nm lasers.

With a little adaptation is should be possible to use the built-in modulators for arbitrary duty cycles. (There are dc blocking capacitors which may need to be increased in value in order to operate at low frequencies.)

John

Yep - Read many books on FTIR, esp. FTNIR. There has been some work on adapting it to imaging. With attern reco, you need maybe 6-10 bands in the NIR, so individual sources attractive. Idea is to do reflectometry on illuminated subjects... Thanks.

Thanks. How bright are they? Could they illuminate a subject for reflectometry?

They typically have an output power of 0.25 to 0.5mW, although some of the long range ones deliver several mW. You really need to look at the data sheet for the particular part number you are interested in. Many of the brands are actually made by Finisar and Avago so it is worth looking at their websites for application notes.

I found that pointing an 850nm SFP at a white wall about 1m away a standard digital camera had no trouble in seeing the bright patch which was fairly uniform in brightness. The camera almost certainly had an infra-red filter, so for the SFP to be clearly visible suggests that it was really very bright.

If you want to create a multi-wavelength light source with almost the same location for each wavelength you could easily plug optical fibres into each SFP module and co-locate their ends (or even use a fibre combiner for true co-location).

The extra wavelengths I mentioned are used for optical wavelength multiplexing and are all in the long-wave end of the band.

SFP connectors are readily available if you want to power your modules directly rather than with a media converter or network switch.

John

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They are plentiful at 850, 1300, and 1550 nm wavelengths but low power (10 mW max). Other wavelengths are all specialty products. $$$$

?-)