homemade laser spectrometer.

[Kenom]

I've been fiddling with the idea of making a spectrometer so I can determine the wavelength of each of my laser pointers and for unknown laser diodes.  If I have a laser diode that I don't know if it's a 650 or 660nm I can use this to test and try to get a rough idea.

Essentially it's a difraction grating and a black balloon over with only a pin prick to allow only just a small amount of light.  This light is then spread specifically a certain distance apart for each wavelength. All I have to do is put the primary dot on one place, then measure the distance to the second dot, and I've got the website to input the information and it will tell me the wavelength. Even if I didn't use the website, I can still guage just by eye.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/gratcal.html

 

[Kenom]

Obviously all I have to do now is make a measuring stick along the large black end to give me my reading just by shining my laser into it.  The pictures are kind of hard to see but the green is closer to the initial dot unlike the red which is further out.  You can see it best by guaging the distance to the base board.

I've got the balloon over the grating right now but I'm going to use two peices of black plastic, and cut a slit all the way from the bottom to the top so I don't have to raise the beam to the hole.

 

[drlava]

Yep should work relatively well. But how far apart are the dots of the different red wavelengths?

 

[Kenom]

I honestly havn't had a chance to test anything but the open can diode and my BFG.  I have a bunch of 9mm diodes here that need to be tested and determine the wavelength.  Specifically 635nm.  Apparently there are a few in this bunch.  So, I want to be able to determine easily.  So, I built this.

First I need to put a ruler or some kind of marks on the measurement area. Then I'll fire up a couple of these other diodes and we'll see.

 

[Hemlock_Mike]

Ken -- You going to test every diode?  How many different #'s?
Edmunds has some cheap hand held spectros.

Mike

 

[Kenom]

they do?  Nah, I wasn't going to test each one, I've only got 4 different diodes to test.  The QY###, the OA###, the SP###, and the SI###.  Each diode is a specific wavelegth then the remaining numbers stand for a number in a batch or something along those lines as each is different yet each type of OA appears to be 635nm at about 30-50mw.  We'll soon see.

*edit* ahh I see what your lookin at. There is no way, I am putting my eye onto something that my laser is shining into. Laser light is entirely too bright to be shining into one of those pocket spectroscopes.

 

[Kenom]

here is an example I made of some basic measurements of 3 different wavelengths.  I've yet to determine if I can see the difference between 635nm and 660nm.  I'm waiting for the money for a meridith module.  Anyone want to donate to the needs of science?  *I'll refund money when I get it.* I don't have a 9mm diode housing.

 

[Cyparagon]

Where did you get a 725nm open can? :

 

[Hemlock_Mike]

Ken --

I shine the laser at white paper and look at the dot through the spectro.
The paper disperses the beam a little and I stay back several inches.

Mike

 

[Kenom]

Where did you get a 725nm open can?   :

they aren't open cans. The other diode I tested in the 700nm range was a 9mm diode.

 

[Cyparagon]

But your open can reads 725nm :-? :

 

[Kenom]

Oh hahahaha. That doesn't line up perfectly. Not to mention, there is no way that 700nm is that red. The color bar I put underneath is just a rough approximation. I actually have some pictures of the 9mm diode I've been testing and kind of killed. Decided to pull it apart and do a diodeacansectomy.

 

[Montana64]

Nice surgical skills there Kenom! ;D

Ted :

 

[Kenom]

Hahahah if you saw the rest of the diode you wouldn't think so. We sacrified the face in order to open up the top of his head. hehehe.

 

[Kage]

OMG Kenom, this is a real classic experiment!

I would love to try making one, and the photos make it look easy enough...

Is the diffraction grating anything special? Where would one obtain this for a reasonable fee?

Anyway, thanks for posting this. If it can be made sensitive enough, I would like to try and observe the change in wavelength of some LDs as current is increased.

 

[Kenom]

The only thing you need to do is make sure your diffraction grating has got a small enough number of lines. I went with 500 lines per mm.
http://cgi.ebay.com/Laser-Diffracti...1QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247

The smaller the number the more spacing there will be between the lines or spectrum. So obviously, if you want to determine the small shift in wavelength in a bluray for example, you want to move it further away from the grating than I have, and a small number of lines per mm on the grating. I think 500 is the smallest you can go.