User:Pranav Rathi/Notebook/OT/2010/03/08

E-mail talk
Steve Koch 22:37, 5 March 2010 (EST): Hey Pranav -- thank you for starting to use the wiki! I, or hopefully Anthony, can show you a bit about how to more easily use it for taking notes (where to put things, etc.). For now, I'll comment here: 10^-7 ... is tough! Hopefully Mr. Gunn's contacts have a good idea. We do have a beam choppper. Maybe that could help, sweep a pinhole or strip through the beam and use the QPD w/ KG filters to profile the beam? I'm not sure where the beam chopper is, but sounds promising (because then you wouldn't worry about the KG distorting the beam. Maybe some google searching and / or talking to experts to see if beam chopper + photodiode is good method for high power beam profiling?

Our e-mail conversation over beam-profiling (03/09/2010-03/03/2010)

I talked to Kevin at Ophir-Spiricon, LLC. Ophir-Spiricon, LLC Mr. Daniel L. Ford Southwest Southern CA, AZ, NM, and Las Vegas

dan.ford@ophir-spiricon.com www.ophir-spiricon.com

Toll Free: +866-755 5499 Cell: +480-650 1103 Fax: +480-718 7721

He gave me the price for Beam Tap I-$575 and II-YAG-$995 with 5% university discount. I asked him to send me a final quote.

For AR coated blanks: 45 degree cold mirror-Cold Mirror

■ Angle of Incidence: 45°

■ Transmission: >85% Average

from 750-1200 nm

■ Reflection: >90% Average

from 420-630 nm

FM03 $ 32.20 45° 1.0 mm 25.4 mm (1") Cold Mirror

FM203 $ 71.90 45° 1.0 mm 50.8 mm (2") Cold Mirror PR

Hi Pranav,

AR coated blanks should have almost no beam distortion -- just make sure they have a decent flatness specification, which I imagine almost all of them will.

That link took me to a beam tap, which would probably work on a collimated portion of your optical path -- it's up to you to figure out if the power numbers make sense for you. The benefit of that device is that you could set up a beam profiler on the tapped light, and use the main beam for the optical tweezer. If you want to measure the optical profile directly at the trapping location, then you have another problem, since you would need to insert this device in your setup in such a manner that the low power tap proceeds to your focusing lenses. Another way would be to place a beam pick, or AR reflector after the focusing lens of the tweezer, and use a relay system to project that mode onto a beam profiler, but this might be a little more advanced of an approach than you need.

It will be more expensive to do it this way, but probably faster than putting it together yourself with the blanks.

Best of luck,

Cary

On Sun, Mar 7, 2010 at 10:44 PM, PRANAV RATHI  wrote:

Dear Mr. Gunny, Thanks for helping us with this, our lab sincerely appreciate your effort. Mr. William told me that it is OK if i contact you directly. I have a question in the same line: Would AR coated blanks accurately represent the beam, because it looks like that we most probably have to use 2 of them? And also do you think this kind of a system: http://www.ophiropt.com/laser-measurement-instruments/beam-profilers/products/industrial-applications/the-accessories---beam-profiling/beam-tap-i--ii-ya can be a good match in solving our problem? Thanks once again for your time Mr. Gunn. Best, Pranav CHTM-UNM

Thanks for looking into this, Pranav! The antireflection coated blank is a possibility, but I worry about whether that would accurately represent the beam. Did you find any blogs or other “how to” sites out there that may talk about beam profiling with AR blanks? We’d only need two of those (10^-3)^2 probably.

I couldn’t see the prices for how expensive the spiricon complete systems are. Imagine they’re pretty pricey and a significant part of the cost is the software. We don’t need the software (or the CCD), so maybe we can get part of the system from them for “affordable” price. This system from them supposedly gives 2.5*10^-5 attenuation:

http://www.ophiropt.com/laser-measurement-instruments/beam-profilers/products/industrial-applications/the-accessories---beam-profiling/beam-tap-i--ii-ya

On Monday, can you find out:

· Pricing on above system (and the others)

· Pricing on very flat AR coated blanks

· A little blog searching (blogsearch.google.com) to see if you can find any very good “how to” articles on our issue.

Here’s another idea: We can use AOM to attenuate the beam quite a bit. We know in the near field it distorts the beam (cross-hatched)…but in the farfield, I think it looks OK. This may be our best bet for seeing _change_ in beam as we go from low laser power to high power.

I can see you going down the same long road I did: trying to beam profile without enough money. It may be worth doing the AOM idea, and then putting the heat sink on to see if it substantially improves the profile. If so, we may have our answer without too much headache.

Can talk in person if this doesn’t make too much sense!

--Steve

From: Pranav Rathi Sent: Saturday, March 06, 2010 4:55 PM To: dna Subject: YAHOO: Beam profiling at higher powers

I received reply from Mr Gunn: He is some what suggesting the same thing as we were trying to do with simple glass strips and NDs. He is suggesting to use Plellicle beamsplitters + Antireflectivity mirrors +NDs to cut down the intensity. Please take a look very below. I also like Dr. Kock's idea, so i think we should try both of them I also did some research over high power beam profilers; below are some links please take a look. They look very promising but expensive-

-( http://news.thomasnet.com/fullstory/558749 http://www.youtube.com/watch?v=xGtuNCMghNM (i just love this one) http://www.ophiropt.com/laser-measurement-instruments/beam-profilers (expensive one) http://www.newport.com/Laser-Beam-Profiler/318103/1033/catalog.aspx this all info will be on wiki also soon |:-(|) PR

You're welcome to, but you could also get in touch with Cary directly.

On Sat, Mar 6, 2010 at 3:58 PM, PRANAV RATHI  wrote:

Thanks in millions Mr. Gunn. The information is really help-full, I am working on it right now. Can i get back to you if i have some questions. Thank you, Pranav CHTM - UNM

--- On Fri, 3/5/10, William Gunn  wrote:

From: William Gunn  Subject: Re: Beam profiling at higher powers To: "Cary Gunn"  Cc: "Bradley Spaugh" , muzammil@genalyte.com, pranav_rathi@yahoo.com Date: Friday, March 5, 2010, 3:44 PM

Thanks, I've forwarded this to him. Is it OK if he gets back in touch directly if he has further questions?

Your help is sincerely appreciated.

On Fri, Mar 5, 2010 at 1:49 PM, Cary Gunn  wrote:

I'd bounce the beam off of a few pellicles,

http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=898&pn=BP108

That way you don't pick up distortions related to transmission through a thick ND filter. If the attenuation is not enough, you can use lower reflectivity mirrors, like a simple quartz blank (R<4%), an anti-reflective coated blank at that wavelength (R<0.1%), like this:

http://www.thorlabs.com/catalogPages/v20/689.pdf

Cary

On Fri, Mar 5, 2010 at 11:05 AM, William Gunn  wrote:

A graduate student working for a friend of mine at UNM had some simple questions about beam profiling, and I thought you'd probably know the answer off the top of your head, so I thought I'd put you in touch.

Don't spend too much time on it, but can you help him?

Best,

Grady

Forwarded message -- From: PRANAV RATHI  Date: Thu, Mar 4, 2010 at 7:54 PM Subject: Beam profiling at higher powers To: william.gunn@gmail.com

Hello Mr. Gunn, My name is Pranav; I am working with Dr. Koch on the optical tweezer. We have 4 watt 1064 nm laser with approx 1mm beam waist. We are trying to view the beam profile on ccd camera ( cheap one). At lower powers (approx .04W), with 2OD, +1OD ND-filters we can view without saturating our ccd and distorting the beam profile. But we do not know how we can view the beam profile at higher powers (1 to 4 watts) without distorting it. Because if we use too many ND filters, they will distort the beam profile completely. Can you please help us with some technique; the power can be cut down far enough (roughly 1e-5W) without distorting the profile and saturating the ccd? Our Lab appreciate you helping hand thank you in advance for your time, Pranav CHTM-UNM