How to monitor wavelength shift without expensive equipment?

[kecked]

here is an idea I had about 20 years ago but never developed. Take a hene laser and put it down a piece of fiber optic that you made leaky by opening a section of the fiber along one side. Take a second and put it next to the same fiber again leaking. Put the signal down this fiber and measure the beats between the hene reference and the signal with a linear ccd array that is long but one or a few pixels wide.

I was able to use the to measure concentrations of gasses in air in the infrared by measuring absorption in a large coil with measurement on the end that measured the interaction of the ref with the air. should work in water too. Anyway you should be able to extract a signal from the heterdyne you can watch and measure. The hene gives a stable ref but this can be anything. For example an uncooled diode and a cooled diode.

PS: I had this as a patent which expired so have fun.

[mixedgas]

The "Toy Train" wavemeter is a similar scheme to Kecked's, only it uses moving parts. You have a set of retro-reflectors on a toy train car. They are part of a interferometer, one side has a HENE as the reference, the other side has the diode. As you move the toy train, the ratio of the count of the two photodetectors on the interferometer is the diode wavelength. Can get down into the picometers if done right.

Steve

[Eidetic]

Here's a cheap and accurate spectrometer with resolution to 1nm. Might at least provide the grating you could use to build an instrument. http://www.amazon.com/Carolina-Proje.../dp/B0062AVWPY

[Bbe]

http://myspectral.com

Very strange project. 2048 pixels sensor and 9nm resolution.. Arduino kills

[kecked]

the idea of the leaky fiber is two fold. first a large absorption area for measurement and a calibrated reference for distance. The two allow very precise controlled spectroscopy by measuring wave interference. The fiber can expand and contract with temperature. The reference recalibrates the fiber length. I was also looking to use an infrared source but that required a diode that also needed calibration or a temp controlled oven. hene gives a physical first place calibration rather than a second or third. This was originally a hand held infrared gas spectrometer back when the smallest one barely fit on a desk. It's common place now.

[planters]

I have one of these and it works quite well. The company will customize it for a desired wavelength range within the sensitivity of the CCD and can provide a cooled and a high resolution version. Not cheap, but not bad compared to Ocean Optics and others.

http://www.ebay.com/sch/alex_priv/m....p2047675.l2562

[RedlumX]

Those are cheap and after some alignment, they go down to approx 1nm, they were available on ebay too:

http://www.science-surplus.com/products/spectrometers

Here about my experience with one of those:

http://redlum.xohp.pagesperso-orange...ctrometer.html