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I am keen to perform some experiments cooling the Oclaro 642nm diodes that Dave was kind enough to send me recently, before I complete the red modules for my SATs.
I plan to record both power and wavelength vs temperature, yet don't have access to a spectrograph. Is there a simple way to cobble a simple sensor together that can detect wavelength?
You could use a diffraction grating and a camera (or any imaging-type sensor). This will translate your wavelength shift into a [more easily] quantifiable 1-dimensional pixel/position shift.
An EVEN LOWER-TECH approach would be to use a diffraction grating, a really big room, and a ruler *retardo
Thanks for the ideas, I was hoping for an electronic solution so I can log the sweep.
I think I have found my next project.
http://myspectral.com
Not enough resolution at 9 nm steps!!!!!Quote:
Originally Posted by dnar
Let the professional teach you. Or just send him the diode :-) He hangs here sometimes.
You need to read ALL his pages to grok it.
http://redlum.xohp.pagesperso-orange...eanalysis.html
http://redlum.xohp.pagesperso-orange...r/spectra.html
http://redlum.xohp.pagesperso-orange...ratingOSA.html
Some astronomy and chemistry folks have had really good luck with high end, off the shelf, multi-megapixel personal cameras with big lenses and a cheap thin film grating.
If you have a frequency counter with AB ratio inputs it can be done even more precisely using a "toy train wavemeter".
Decent grating spectrometers go for around 200$ on Ebay, and self clocking linear CCDs are even cheaper.
Steve
Thanks Steve, much reading to do.
You'd have a sellable product at 1 to 1.5 nm resolution and a cost 1/3rd that of Ocean Optics. USB spectrometers are hugely overinflated in price.
Steve
/puts on Chinese factory voice
What is your target price?
Quote:
Originally Posted by dnar
Less then 500$.
In my case 300$ instead of 2700$
Steve
How about prisms? They "bend" light at different angles according to wavelength.
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.
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
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
Very strange project. 2048 pixels sensor and 9nm resolution.. Arduino kills :(Quote:
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.
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
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