Measure beam profiles?

[daedal]

I'm just wondering... is it possible to calculate divergence with only a beam profile, or as I think it is needed to move the laser or the camera for that?

in the same approach, I have some linear CCD arrays I would like to use as sensors for some basic grating wavemeters like monochromators and the like... does anybody know if some easy ways of interfacing them already exist?

I have a box of those for a project that never took off. I was going to sample the data and dump it to serial/USB and read it into an app that measures and allows calibration (thusly replacing the need for a $2000 spectrometer).

Perhaps we can open up the cork on this in a new thread if a patent is not protecting that methodology?

--DDL

[Roy G. Biv]

Steve,

Do you think it is possible to use a camera with PAL resolution together with the VBeam demo though the program only uses 640x480?

It says:
"Full calculations are performed on all images. Maximum resolution is limited to 640x480 and the report generators are disabled."

I hope this means it is possible to see all the results and calculations made, though you can´t get a report of them.

Shrad,

I asume it would be possible to calculate the divergence by measuring the beam diameter at one point and then move the camera a distance and make a new measurement.

[Roy G. Biv]

DDL,

A ccd spectrum analyzer, this is something I would like to build also, but it is unfortunately a bit too complicated for me. W has an interesting description on his pages:
http://pagesperso-orange.fr/redlum.x...ratingOSA.html

[shrad]

yes indeed, but the movement needs to be well known to get reliable measurements, so if it is a professional software, I guess the solution is elsewhere... but I may be wrong

if I happen to make something out of python and a webcam, no doubt I'll share my results

I'll move to my new house the 27 of september, and as soon as I have unpacked everything, I start working on lasers related stuff again

[mixedgas]

1, you dont have to move the camera that accurately, +/- 1 mm in length is easy enough with a piece of plumbing pipe etc and the software handles centration.

My bet is the software will truncate PAL, as will most cheap frame grabbers to make windows happy. I dont have my frame grabber set up here to try it.

Spectrum is easy with a good digital camera, many people have done it with just a slit, a grating and a good camera lens.

I've posted links before.

Steve

[weartronics]

A practical technique I have used in the past, which only requires a power meter is:

Set up a horizontal bench some distance away from the source, so that the power meter is vertically centered on the beam. Slide the power meter along the bench in 1cm increments, taking a measurement each time to form a 1D profile. If you want to calculate the divergence, you have to repeat this at a second distance from the source.

If your beam has modest divergence, you can get a good result with one profile 10m from the source and another profile 20m from the source. If your beam has lower divergence or you don't have that much space available, you can use a telescope.

Of course a true 2D beam profiler will give you more information about the beam, but what are you going to do with this information? Probably assume a symmetrical gaussian profile to perform conventional fitting and modeling steps anyway. I used this technique on horrible multi-mode beams without any problem. Here is my result:

[mixedgas]

http://www.sbf1.sbfisica.org.br/proc...endido/c60.pdf

http://www.bme.vanderbilt.edu/bme286.../knifeEdge.PDF


http://www.uslasercorp.com/envoy/diverge.html

now just decide if you want to use 10-90 or 80-20 or 19-82 as your cutoffs

http://en.wikipedia.org/wiki/Beam_diameter

or the good old Divergence = 2arctan(Df-Di/2l)

there are other ways with pinholes, slits, lenses.....

remember, you should measure at the beam waist and at a point on the far field side.

Steve

[mixedgas]

Other then a bit of math, why is this such rocket science???

http://www.sbf1.sbfisica.org.br/proc...endido/c60.pdf

http://www.bme.vanderbilt.edu/bme286.../knifeEdge.PDF


http://www.uslasercorp.com/envoy/diverge.html

now just decide if you want to use 10-90 or 80-20 or 19-82 as your cutoffs

http://en.wikipedia.org/wiki/Beam_diameter

or the good old Divergence = 2arctan(Df-Di/2l)

there are other ways with pinholes, slits, lenses.....

remember, you should measure at the beam waist and at a point on the far field side.

In two weeks I'll have access to my library and can scan in:

2. Simple Beam Propagation Measurements on Ion Lasers, SPIE Vol. 1414 Laser Beam Diagnostics, 1991. Its Spectra Physics way of doing it.

Steve[/QUOTE]

[Laser Ben]

Try contacting LaserBen on this forum, he has beam profiler he may be willing to let go for not way more than a decent CCD camera.

I do have a pretty high res (2048 pixel) beam profiler setup with ND filter holder and breadboard mount for $300 shipped. It hooks right up to an oscilloscope and gives a clean reading of the beam profile with actual measurable results.

[Daedronus]

I use this for my IR beams:
http://www.youtube.com/watch?v=KIizzSHFHEQ

On a unaligned YAG (but still aligned enough to get a small output) it allows me to see exactly which way I need to turn the mirrors.

Works really nice, but it's not exactly cheap.