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# [PIC HEAVY] Got a Monochromator!

#### Cyparagon

##### Well-known member
^Say, why haven't we seen yours? Pictures/thread hereby requested

#### The Lightning Stalker

##### Well-known member
"Mine" or bloom's?

#### Cyparagon

##### Well-known member
You've got one too?

#### The Lightning Stalker

##### Well-known member
Lol, well it's a bit more humble than the others. A general outline of the setup can be found in
this post:

http://laserpointerforums.com/f42/what-do-your-diffraction-glasses-i-wavelength-determination-42599.html#post1230142

I'm working on getting a glass grating for more accurate results. There will eventually be a
custom stand for the grating and DUT as well. I got a few Al bars and misc. pieces to put
something together with the other day.

The grating is positioned a set distance from a white ruler. (Usually 100mm) The pattern
is then photographed.

Here is the pattern from a 940nm diode:

660nm:

Then the distance from the center to the first order line is plugged into this:

The results are accurate within ±5nm or so. No lens or slit is needed for a collimated laser
beam source since it is already narrow and has its own lens. I'm still trying to figure out
how to get a good spectrum through a pair of LSGs. bloompyle's PCM would work great
for that.

#### Cyparagon

##### Well-known member
That's a grating and a formula - not a monochrometer. I did a write-up on that method a couple years back. That's quite a complex formula as well. You can simplify it to:

λ = dsin(arctan(S/L))

Where d is the distance between the slits (10^-6 meters for that grating), S is the distance between the diffraction orders (in meters), L is the length to the screen (in meters), and λ is the wavelength (in meters)

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#### Atomicrox

##### Well-known member
I'm not 100% sure this is safe (please confirm before trying), but have you tried shining the laser at a white paper in front of the entrance slit and looking directly into the exit slit?

Should work with low power lasers, right?

#### Wolfman29

##### Well-known member
Probably not a good idea. Anyway, I got a PCM from Sam so I don't need to do that! In fact, I set up a little circuit that'll detect it for me