If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Print this picture, cut a piece out of an old CD (DVD will not work), apply tape, done!
This is how the positions of the markings are calculated: angle = Asin(wavelength / lineSpacing) scalePosition = baseline * Tan(angle)
If you know the angle of deflection and want to find the wavelength you use: wavelength = lineSpacing * sin(angle)
The line spacing of a CD is 1.6 um and DVD is 0.74 um. It is possible to find discs with non standard line spacing but they are not very common. DVDs can be double layer and cause problems.
It is possible to use this method to determine the wavelength and spectrum of other light sources than lasers but because of the low efficiency it is difficult unless you use a camera and a fairly long exposure. Make a narrow vertical slit in the middle of the laser window using black tape. Adjust the distance between the light source and the slit to find a compromise between resolution of the spectrum and brightness.
The example shows a mystery "UV" LED that seems to be about 410 nm.
Registered Member #1806
Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136
That's awesome! Thanks for the info.
It reminds me of the time my chemistry professor in college handed out diffraction grating slides, then used an HV supply to excite various gasses and we could use the slides to directly view the spectra lines.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Will this function with CD-R's, or does it have to be injection molded? I suspect it has to be injection molded due to the lines being physically part of the plastic acting like a diffraction grating vs the amorphous phase change material in a blank CD-R.
Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
The coating comes off a CD-R quite easily (or used to a few years ago) with a bit of bending and leaves the clear plastic disk as a good transmission grating due to some sort of guide track impressed on the plastic during manufacture. Some sellers used to use a pair of uncoated discs (with the diffraction pattern) as protection at each end of a cheap shrink wrapped stack of 100 discs. Don't touch the patterned surface as finger marks are enough to ruin the effect and diffraction gratings are too fragile to easily clean.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Yes, CD-Rs have a guide line for the laser to follow while writing to the disc. It is also much easier to get the reflective coating off CD-Rs, the last time I removed the coating from a moulded CD I had to boil it.
Here is the spectrum I got from a white LED, it is overexposed but it is easy to see that the LED under the phosphor is about 450 nm.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
After testing most of the different CDs I got I found out that modern CDs are not very reliable when it comes to track pitch. Most of my CD-Rs have tracks closer than 1.6 um. On some it makes a difference between reflection and transmission, others change depending on what side is used.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Make your own laser spectrometer in 3 minutes
