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# NEW TOOL: Determine Wavelength Using a Diffraction Grating

#### rhd

##### New member
Hey all,

This is a follow-up to my Wavelength to RGB / HEX and my Relative Laser Beam Brightness web tools.

A few months ago, Cyparagon pointed me in the direction of his thread on calculating the wavelength of a laser by using a diffraction grating (this thread), and suggested that it would make a good candidate for one of my web-based tools. I agreed! While it took me a few months, I finally got to it this weekend

Using a diffraction grating, and a ruler, you can calculate the wavelength of your laser. This tool helps bypass any math on your end. Math is hard. Have a look
Calculate Wavelength (nm) Using Diffraction Grating

#### lasersbee

##### Well-known member
Nicely done....
I'll check this out tomorrow...

Jerry

#### laser_freak

##### New member
This is a great tool. Well done. My only suggestion is to be able to calculate the lines per mm of a diffraction grating using a known wavelength. This would be helpful for people who have diffraction gratings with unknown line densities.

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#### rhd

##### New member
This is a great tool. Well done. My only suggestion is to be able to calculate the lines per mm of a diffraction grating using a known wavelength. This would be helpful for people who have diffraction gratings with unknown line densities.
Interesting - ok

In order to keep this tool as simple as possible for those who do know their density, I think I'll make that a separate tool.

EDIT: You'd probably only want to do that with a DPSS right ?

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#### laser_freak

##### New member
Also does this use the small angle approximation using tan(x) ~ x, so that x ~ (m lambda L) / d ?
I would suggest not using it just in case.

Yes, you would only want to calculate the line density using a known wavelength laser, such as a DPSS or gas laser.

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#### rhd

##### New member
Also does this use the small angle approximation using tan(x) ~ x, so that x ~ (m lambda L) / d ?
I would suggest not using it just in case.

Yes, you would only want to calculate the line density using a known wavelength laser, such as a DPSS or gas laser.
It uses:
λ = diffraction-grating * sin(arctan(distance-between-dots/distance-from-screen))

Cool

#### LarryDFW

##### Well-known member
Now . . .

who did I buy those diffraction gratings from: :undecided:

LarryDFW

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#### jcranmer

##### Well-known member
Using a diffraction grating, and a ruler, you can calculate the wavelength of your laser. This tool helps bypass any math on your end. Math is hard. Have a look
:beer: Here's to no more math!

#### jakeGT

##### New member
I. HATE. MATH

So, this is cool!

#### Cyparagon

##### Well-known member
I use this type of grating. For better accuracy, take the average of the distance to the dot directly to the left and the dot directly to the right.

And yes: small angle approximation is a no-no because many gratings will... not have a small angle.

You'd probably only want to do that with a DPSS right ?
Yes. Only DPSS or gas lasers have precise known wavelengths for all operating conditions.

Thanks, rhd!

#### Johnyz

##### New member
I vote for a sticky! Very cool tool!