Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



Laser Pointer Store

How to Determine the Wavelength of your Laser with a CD!!


Alex2893

Active member
Joined
Jun 6, 2014
Messages
402
Points
43
that light blue pen laser is like my dream laser. Its so pretty !!! I also just realized i need to go back to college. Thats probably easy math more most on here but its over my head. :cryyy:

Pretty amazing video none the less:D
 

BowtieGuy

Well-known member
LPF Site Supporter
Joined
Oct 14, 2012
Messages
5,504
Points
113
This is probably a dumb question, but is the distance between slits on the particular CD that you are using a "standard" width?
In other words, would a different CD have the same distance between slits?
 

styropyro

New member
Joined
Jun 13, 2007
Messages
5,385
Points
0
that light blue pen laser is like my dream laser. Its so pretty !!! I also just realized i need to go back to college. Thats probably easy math more most on here but its over my head. :cryyy:

Pretty amazing video none the less:D
That blue laser is definitely my all time favorite laser that I've owned...the actual wavelength is probably near 480nm considering the spectrometer tests that were done on this type of laser diode.

If you are ever wanting to brush up or learn more math, the internet is full of great resources! I have learned a lot from places like "Paul's Online Notes". Spending a couple hours here and there with a pencil, paper, and a good math resource can be very enlightening. :beer:

This is probably a dumb question, but is the distance between slits on the particular CD that you are using a "standard" width?
In other words, would a different CD have the same distance between slits?
I would assume this would be a standard thing, and according to some websites is 1.6 microns. If that's true, my measurement (~1.5 micron) was close, but definitely not perfect. :D Oh well, this experiment isn't meant to be perfect, just to show that cool science can be done with household items.
 

Mattronium

Active member
Joined
Dec 12, 2012
Messages
728
Points
43
Good video!

I doubt you can ever do a DIY wavelength measurement with with greater certainty than +/- 1nm, even that would be very difficult.

Once I tried to measure the WL of all my lasers using a diffraction grating I measured to be 261.5 lines/mm. I had 4.159m from the grating to the wall.
Unfortunately, a shift of one mm for the measurement of the dot locations on the wall equaled a shift of ~0.9nm of the wavelength calculated and one mm shift in the distance from the grating to the wall equaled a shift of ~0.2nm. Since I doubt I could measure any better than +/- 2mm the MOST accurate I could say the wavelength for my 515nm laser that I tested would be, is 513.8nm +/- 2nm. And that's not considering that if the laser passes through a transmission diffraction grating at an angle the effective line spacing would change too.
 
Last edited:

SteveT

Member
Joined
Jan 20, 2015
Messages
252
Points
18
Another great vid; might have to give this a go later. Need to dust off my Pythagorus and trig skills before I do though, haven't used them since 1998 :)
 

paul1598419

Well-known member
Joined
Sep 20, 2013
Messages
14,361
Points
113
I've done it with a known diffraction grating, but never with a CD. That is a very interesting way to use common items to measure something that one would not normally think of. At least I haven't. Nice presentation of the set up and math. Kudos!


Styro, I went back and checked your math and found you have some typos in your notes. Just thought I'd mention it since it is on YouTube and people pick up on stuff like that. Still, very nice!
 
Last edited:

styropyro

New member
Joined
Jun 13, 2007
Messages
5,385
Points
0
Are you referring to the absence of the factorial sign for the mclauren series expansion of the sine function? If so, I saw that mistake while uploading it and I added an annotation to fix it. :p
 

paul1598419

Well-known member
Joined
Sep 20, 2013
Messages
14,361
Points
113
Yeah. But, also, ( 1.4964 X 10^-6M ) Sin ( 18.5576 degrees ) = 4.76 X 10^-7 = 476nm.
No big deal. :D

I'm sorry. I made a mistake here, not you.:p
 
Last edited:

CelticLaser1

New member
Joined
Mar 1, 2013
Messages
63
Points
0
Does the distance from the cd to the wall change anything? Obviously if it was closer to the wall the dots would be closer together. Keep the videos coming. They're very informative.
 

styropyro

New member
Joined
Jun 13, 2007
Messages
5,385
Points
0
This is where the trig comes in. Yes the dots would be closer together if the cd was closer to the wall, but the angle between the beams will be the same no matter the distance. You only need that angle to plug into the formula, so theoretically you could just use a protractor if you could somehow be precise enough.

And that's awesome it made it to Hackaday!
 

Gadget

Active member
Joined
Dec 28, 2013
Messages
326
Points
43
OMG....look at all the burn marks on the wall behind you Styro!!! heheheh

Naawww...that's not a laser lab!

-G
 




Top