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04-27-2010, 11:24 AM #1
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Xplorer877
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Home Spectroscopy - Any Ides?

It used to be that Laser Power Meters were very expensive for the laser hobbyist but nowadays, thanks to many of you guys, they are available for pretty cheap. But what about that OTHER aspect of lasers we are so keen on... wavelength!

How can the average hobbyist measure the wavelength precisely? Or at least have a means on comparing wavelength shifts from diode to diode?

For example if you've got a few 405nm diodes that appear to be different wavelengths because the "apparent" intensities are different between them even though they are all the same power, how could you verify this without expensive equipment?

What if you were to use two parallel lasers, that you want to compare the wavelengths, and use a prism to turn any difference in wavelength into a difference in the angles of the resultant beams. The beam that measure a larger angle than the other will be of a longer wavelength. You could then use Snell's law to figure out the difference in wavelength.

You might say that the angles would be to difficult to measure accurately. But you can measure the distance between the beams, then let them diverge a bit and measure again. Using simply geometry you should be able to figure it out.

Anyways I just figured it would be a fun experiment to set up and try. It'll be interesting to see the results.

-Tony

04-27-2010, 11:38 AM #2
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lasersbee
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Re: Home Spectroscopy - Any Ides?

Use a Single Axis Diffraction Grating at a fixed distance from a wall and
Then measure the distance between 2 dots.. That is your reference....
Different Wavelengths will exhibit different distances...
Red Lasers will have a larger distance between dots than Blu-Ray..

Or you can get one of these.....

Project Star Spectrometer | Science Kit

Jerry
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04-27-2010, 01:04 PM #3
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Re: Home Spectroscopy - Any Ides?

You can use a diffraction grating (linear, not cross), or a diffraction mirror too (i have something similar planned, but lack of time for realize it, so it ended in the "to do (maybe)" box ) ..... or also a sequence of 2 or 3 prisms, instead a single one, for get a better diffraction .....
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04-28-2010, 07:51 AM #4
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Xplorer877
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Re: Home Spectroscopy - Any Ides?

Good idea. Where is the best place to get prisms and diffraction gratings?

-Tony
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04-28-2010, 08:16 PM #5
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Re: Home Spectroscopy - Any Ides?

I actually have a home made spectroscope that clearly illustrates how you can use a diffraction grating from many places to determine the wavelength of a laser.

I'll find a good source for gratings for this and post it here.

these are what I have yet you have to get 50 of them
http://www.rainbowsymphonystore.com/difgratslidl.html

http://cgi.ebay.com/Diffraction-Grat...item2eac9c490a

Last edited by Kenom; 04-28-2010 at 08:20 PM.

04-28-2010, 08:28 PM #6
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Re: Home Spectroscopy - Any Ides?

Lasersbee and Kenom.... get the whole measure distance thing. but how would i come up with base numbers to start with? Like for example only... 3.5" is 632nm and 3.55 is 635nm? or is this not really something that can be used for exact calculations? or am i missing something?
i go to rainbow symphony when ever im in the area. i just bought a 10 sheet pack of double axis diff grating to make some glasses for a rave. LoL.

michael

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04-28-2010, 08:33 PM #7
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Re: Home Spectroscopy - Any Ides?

You will first need to build it... (there are always variations in builds)
Then using known laser Wavelenghts you will need to mark your scale yourself.

There may be a trigonometry formula but I don't know of one..

BTW... Double Axis Gratings won't work...

Jerry
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04-28-2010, 08:38 PM #8
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Re: Home Spectroscopy - Any Ides?

doubles axis is no good for this... this makes michael a sad panda.
my wording is poor sometimes... is this project, if done correctly able give specifice numbers or is it a fun project that will confirm a hunch that a 405nm diode is running at a longer wavelength?

michael.
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Last edited by chipdouglas; 04-28-2010 at 08:41 PM.

04-28-2010, 08:43 PM #9
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Re: Home Spectroscopy - Any Ides?

Diffraction Grating

there is the math.

04-28-2010, 08:56 PM #10
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Re: Home Spectroscopy - Any Ides?

Some of these techniques have been used for a long time, and require a bit of math. I don't have a problem with that, but I would be interested to see if there are any digital setups that we could look at. How about like a concave lens mounted in front of a CCD sensor? This setup coupled with the right software would be useful for measuring wavelength and looking at beam profiles. Useful for some of us with multi-mode diodes and exotic DPSS handhelds...
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04-28-2010, 09:03 PM #11
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Re: Home Spectroscopy - Any Ides?

The one that Lasersbee posted is available in plastic or cardboard for \$10 less.
See what it will produce here. Including result from a red laser pointer. Tho I would recommend using a camera instead of your eye.
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Last edited by HaloBlu; 04-28-2010 at 09:21 PM.

04-28-2010, 09:12 PM #12
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Re: Home Spectroscopy - Any Ides?

If anyone is interested, I have an extra Spectrometer for sale for \$20.00 + S&H. It operates just like the "Project Star Spectrometer" only it's a bit smaller. A plastic housing holds a diffraction grating at the correct angle to the incoming light, where the nm's are read on a plastic film scale. I should have posted this in the BS & T Section, sorry. rob
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04-29-2010, 12:15 AM #13
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Re: Home Spectroscopy - Any Ides?

Quote:
 Originally Posted by HaloBlu The one that Lasersbee posted is available in plastic or cardboard for \$10 less. See what it will produce here. Including result from a red laser pointer. Tho I would recommend using a camera instead of your eye.
I have one of those spectrometers that I linked to...
You DO NOT shine the Laser into the unit...
You shine the Laser onto a white surface (a wall) and look at
the Laser beam's wavelength reflecting off the wall...

Jerry
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04-29-2010, 12:30 AM #14
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Re: Home Spectroscopy - Any Ides?

Spectroscopes are available on ebay. They often need calibration and you observe the reflected beam. Often this style of scope isn't good enough to see 405 vs 410. You would need a good eye to see that in this style meter.

HMike

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04-29-2010, 12:44 AM #15
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Re: Home Spectroscopy - Any Ides?

As far as calibration goes: you can use a 532 green laser for that, those are accurate to the nanometer regardless of conditions or quality.

Observing the reflected dot can be a problem with blurays in particular, you need to find a totally non-fluorescent surface to do that properly.

04-29-2010, 12:58 AM #16
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Re: Home Spectroscopy - Any Ides?

Benm -- That's why I use hardwood charcoal for a target. Really flat black surface.
I also cook steaks with that stuff !!!! It's also called Cowboy Charcoal.

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Last edited by Hemlock_Mike; 04-29-2010 at 01:05 AM.

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