how can people post things this stupid?

rather

chip.

The laser does not have to be at 2 microns, 700 nm should go through the grating as well and the camera chip can be monochrome (grayscale).

?-)

Thanks; i was pretty sure you didn't miss that, but i regularly work with engineers who can't fathom such a simple technique.

?-)

rather

chip.

the

The 700 nm laser is NOT to make the transcutaneous measurement, it is to measure the angle of the grating internal to the device only. Closed loop servo. Now i get why you didn't hear what i was trying to say.

?-)

An optical encoder would be a possibility, true. The difficulty with cottage-industry methods like that is that they take a surprising amount of (expensive) development to make them into a product. Things like assembly tolerances, imager location uncertainty, and the motion of fringes and speckle are easy to deal with in a proto but harder in a real device.

One potentially interesting method would be to use an auxiliary single-mode fibre to look at the specular reflection. That would eliminate pointing instability, but it would have to fit inside the aperture of the spectrometer. There might be a second-order diffracted peak we could sense, but all of that is way beyond the capabilities of these folks.

Cheers

Phil Hobbs