Cheap way to measure laser wavelength

[paul1598419]

Sure. I have done it for members here before. I still have a large sheet.

 

[JimK]

Where does one obtain those tripod clamps if I may ask.

Can they hold big lasers too?

 

[Skittles]

Where does one obtain those tripod clamps if I may ask.

Can they hold big lasers too?

Someone from these forums found them and made a post was it Paul? I don't remember.

Here is the link for them: https://www.ebay.com/itm/Adjustable-Desktop-Desk-Table-Top-Tripod-Microphone-Mic-Stand-Holder-With-Clip/272564869129?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

Pretty good deal, and yeah they do hold my PL-E Mini but because the tripod is so short and the laser is long I can't point it straight up unless I put it on a ledge or something.

 

[JimK]

Bought 3. Should be good for my emisar flashlights too.

Thanks again.

 

[Atomicrox]

Keep in mind the grating has to be parallel with the wall and the laser beam has to hit it as close as possible to 90º, otherwise it will skew results. If the grating is flexible care must be taken that it is well stretched.

 

[paul1598419]

There are many ways the accuracy of this setup can fail. The best you can do to get the highest accuracy is to make the distance from the grating to the wall as far as possible. Those cheap $1.00 gratings on eBay are made primarily for entertainment, not scientific measurements. The grating inside the cardboard it very thin and flexible, so that alone, can produce errors.

 

[steve001]

Wavelength determinations can be accomplised also using a cd or dvd.

 

[paul1598419]

Wavelength determinations can be accomplised also using a cd or dvd.

Yes, you can. But, it requires you have a known wavelength laser to figure out the pitch of the tracks on the CD. It gets easier if you have a known scientific grating to work with. Then you don't need the extra steps to get there.

 

[steve001]

Yes, you can. But, it requires you have a known wavelength laser to figure out the pitch of the tracks on the CD. It gets easier if you have a known scientific grating to work with. Then you don't need the extra steps to get there.

In case someone has a CD here is a video by Braniac.

https://youtu.be/ZUszmEDm3FU

 

[paul1598419]

I noticed this guy insists you measure your angles in radians, but this is certainly not necessary. It certainly works just fine if you use degrees too. Using a DPSS laser like the 532nm is the best choice, but a higher quality 532nm laser would be likely closer to 532nm instead of these cheap eBay ones. I have two of these that give multiple lines. One gives four lines and the other, six.

 

[Benm]

Radians or degrees both work as long as you are consistent, and you'll probably get idiotically far off figures if you mix them up in your calculations at some point.

As mentioned you can use a CD as a grating, but you need to know how many slots/mm it actually has, as this can vary a bit between discs where they deviate from the ideal spec to fit a bit more data onto it and such.

One way to go about is is using a 532 green dpss (or HeNe) laser to determine the slots/mm value of the CD first, and use the result found to evaluate other lasers.

Since HeNe lasers are not that commonly available it'd probably go for the 532 nm green. The wavelength of those things is -really- well defined since it's a solid state Nd:YAG to begin with, which is then frequency doubled, a process that only works with photons of very similar wavelength.

All in all you can calibrate and measure things down to 1 nanometer or perhaps even a bit better by just using these simple tools. If you need higher accuracy than that the whole setup becomes problematic since you'd have to know all distances within 0.1% as well, and measuring the position of a grating from a wall 2 meters away withing a millimeter is practically quite hard to do.

Using actual gratings becomes problematic too at this accuracy level: Let's say i'ts defined for 1000 lines/mm, but to what tolerance? If it's 999 or 1001 due to thermal expansion or whatever the error from that already results in an error in the order of half a nanometer if you get everything else perfect.

 

[paul1598419]

This is not the way to get an accuracy of a fraction on a nm. It is for getting an accuracy of 1 to 2 nm if you set it up carefully and can repeat your results several times.

 

[steve001]

Types of diffraction gratings.

https://www.edmundoptics.com/search/?#stq=diffraction grating

https://www.thorlabs.com/navigation.cfm?guide_id=9

 

[paul1598419]

The Edmund's and Thorlab's gratings are made for Scientific research. You will also pay more for these.

 

[Radim]

Not long ago I came across an interesting youtube video about measuring wavelengths of lasers, its fairly recent and I haven't seen a post about it here, so I'm guessing most people don't know about the video or the method the youtuber proposes in it.

Here it is: https://www.youtube.com/watch?v=i9WS7Jo2TAY

I thought it was very cool so I decided to buy a diffraction grating and try it my self, I don't have a big ruler so I used measuring tape its harder with it but that's all I had.

So far I tried this with just two lasers and with at least 10 attempts.
First my LaserBTB pen, it has an amazing perfect symmetrical round dot which made it easier for measuring, multiple attempts had me at 528nm - 530nm until I got the setup as perfectly aligned as possible and here are the final results:

Pretty close to the advertised wavelength, I am happy with that number.
Next I tried Sanwu pocket 505nm:

Also very close.

Pics of my setup:

Conclusion: My final results were pretty close to the advertised wavelengths, but I do not wish to state that that's what the actual wavelengths of these lasers are, my setup was not perfect, and I used a closet door instead of a solid wall. (I had my reasons ) Maybe if you get a laser and you have no idea what wavelength it is, this is one way to measure it. Nevertheless it was fun and I thought it was important enough to share. :beer:

It also depends on actual laser, temperature, batts etc. As far as I know, this method is pretty accurate.

R.

 

[Skittles]

It also depends on actual laser, temperature, batts etc. As far as I know, this method is pretty accurate.

R.

Yeah I forgot to mention that the batts in 532nm were not fresh but on the 505nm they were. that 532nm eats AAAs in minutes, got to get some rechargeable ones. :thanks: