Laserscope collimation (or lack thereof)

Hi PL,

I removed the fiber coupler from a Laserscope and measured the collimation of the beam coming off the optical table. Interestingly, the beam without the q-switch is well approximated with a gaussian distribution.

I fitted the gaussians to the beam profiles to calculate the 1/e^2 radii, then I calculated the divergence is 8.50 mrad full angle. In simple terms, this means ~100mm diameter beam with ~10m throw distance, ~200mm diameter beam with ~20m throw distance.

I assume that Laserscope already did the best job they could of collimating the horrible multimode beam coming out of the OC, but this is much higher divergence than I expected. Are your results similar, or do I have a problem?

Best regards,

weartronics

http://external.weartronics.com/lase...am_profile.png

I assume that Laserscope already did the best job they could of collimating the horrible multimode beam coming out of the OC, but this is much higher divergence than I expected. Are your results similar, or do I have a problem?

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Your actually doing better then most examples I have seen.

No problem, quite normal!

It gets worse with thermal lensing/mode hopping/beam wander when misadjusted and with the Q switch.

I've never found a good solution, as I only get to work on them for a few hours at a time, but I bet laserman532 can sell you something or point you in the right direction.

Steve

yep, thats pretty much it. A small trick is to move the provided collimating lens down the path about 6 inches if you locate big mirror scanners there you will have a better shot of not over filling them. The only other thing you can do is up collimate the beam, your divergence numbers will be better but your beam diameter will increase.:(

Hey Nic -

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Originally Posted by weartronics

Hi PL,

...the fiber coupler...

I assume that Laserscope already did the best job they could of collimating the horrible multimode beam coming out of the OC, but this is much higher divergence than I expected. Are your results similar, or do I have a problem?

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No, no 'problem', buddy - and you answered your own question! :D Remember that Laserscope only had to worry about 'collimating' the beam to get down the length of the deck, into the endoscope fiber-launcher - with UNcollimated bare-fiber output as the desired-result for this surgical-purpose laser - you kinda don't want a nicely-collimated beam inside a gut! :D

I think (...yeah, you did get all that info I sent ya, right?) you'll find much better results with the 400mm, for on-deck galvos, or, for launch-into a topside / external beam-table, etc, a 750mm, than that 'stock' 200mm... yes, that is the best you will get out of that lens... :cool:

KIT... ciao
j

Hi Steve and Pat and Jon,

Thanks for all your comments! I understand that moving the stock lens or replacing it with a longer FL could decrease the diameter, but this must be at the expense of divergence, right? If anything, I want to go the other way (increase diameter to reduce divergence). At this stage, I will keep the current ~7mm diameter and 8.50mrad divergence, though I might up-collimate later. Originally I thought I would have to buy a telescope, but maybe I can just move or replace the stock lens in the unconventional direction (good idea thanks Pat)!

The reason I measured the divergence is because I wanted to see how much worse it would get if I fiber coupled the laser source to the projector. According to my calculations, if I used an 800um core, 0.37 NA fiber, divergence would be approximately 10 times larger for the same beam diameter :mad:. However, if I could use a 100um core, 0.22 NA fiber, divergence would actually be smaller for the same beam diameter :eek:. Unfortunately this idea is not feasible because the power capacity of such a small fiber is insufficient, but is it really possible to improve the beam characteristic just by putting it through a fiber? Are there current applications for this?

Best regards,

weartronics

http://external.weartronics.com/lase...r_coupling.png

Hey Nic -

Quote:

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Originally Posted by weartronics

Hi Steve and Pat and Jon,

Thanks for all your comments! I understand that moving the stock lens or replacing it with a longer FL could decrease the diameter, but this must be at the expense of divergence, right? ... but maybe I can just move or replace the stock lens in the unconventional direction

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:confused: Umm, well, no not quite - the whole point of changing the 'stock' 200mm to a 400mm (or whatever you determine works-best for your desired 'end-result'...) FL, IS to 'wrangle' the divergence - yes, it will 'change' beam-diameter a bit, but only to it's focal-point and then back-out - the 'divergence-management' COMES-from the focal-length you choose, and like Pat said, finding the 'sweet-spot' along the beam-path, to optimize between fitting on your galvos, / gaining the 'longer-range' results you desire... really, the only reason to 'up-collimate' is to get 'better divergence' over a very, very, very long distance - or - if you just like / want a big-fat (but well-collimated) beam...

Quote:

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Originally Posted by weartronics

The reason I measured the divergence is because I wanted to see how much worse it would get if I fiber coupled the laser source to the projector. ...but is it really possible to improve the beam characteristic just by putting it through a fiber? Are there current applications for this?

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No. It WILL 'get worse'. BUT that doesn't mean that you can't end-up with a 'reasonably well-collimated' result, out of a fiber-fed projector. ie: What we have found works best, is 200µm fiber, 20W MAX, going in, and keeping your 'run' to less-than 150', and - actually - using a OEM Laserscope INput-coupler lens (see below) AS the OUTput coupler lens.. :cool: I've experimented extensively, with all-kinds of lenses / FL's / combos / off-the-shelf telescope / colli-combos, etc - and I have never seen better 'overall' results, than the 400mm, in that on-deck 'sweet-spot' I sent you...

I'd suggest, before 'pulling your hair out' too much-more :D get a simple 400mm and 750mm plano-convex from Edmunds Optics (400mm, AR-coated: part# NT47-724; 750mm, AR-coated: part# NT47-388) and, well... experiment! :cool: But be careful!!! (sorry, I know that was rather 'grandmotherlike' :D

Yeah, sure, you can also try the 500mm, but I never found it was needed... like I said, we found 400mm was perfect for 7-8mm-aperture on-deck galvos, and the 750mm was better for a 'beam-only' unit, that, say, had a removable / umbilicalized deck to sit on a giant, external beam-table (or, for one where you built an 'upper-deck' version...)

Hope this helps, Nic... maybe re-read that PDF (??) :D

ciao
j

Jon,

Your recent pictures .... I thought You were on holiday .... or ... did You get Your toys to San Sal with You ?? :eek:
Piotr.K

Hi Jon,

Thanks for more tips and photos of your fiber coupling. I really appreciate you sharing so much knowledge about this machine, it saves me a lot of time and experimenting. I did read all the good stuff you sent me, and if I go ahead with putting a projector on the optical table I would use your advice re: collimator positioning and focal length.

However, I'm still thinking fiber coupling would be preferable... :D

Could you tell me a bit more about your fiber coupling? I have only used pre-assembled cables in the past, I never terminated a fiber before. Wouldn't you have to AR coat the end faces? I am not equipped for coating :mad:. Could you give me any more details about the type of fiber and connectors you're using (can I buy them from Edmund)?

Another crazy idea, I wonder if the beam from the resonator is sufficiently randomly polarised that I could use a PBS as a 50/50 splitter to get two fibers out of one machine, or is there a better way to accomplish this?

Best regards,

weartronics

Hey Piotr -

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Originally Posted by LesioQ

Jon,

Your recent pictures .... I thought You were on holiday .... or ... did You get Your toys to San Sal with You ?? :eek:

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Hah, no these are just pix I have with me on my laptop, from the 'Bat-archives' :cool:... but, um... "holiday"... what's that? :D

ciao...
j

Hey Nic -

Quote:

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Originally Posted by weartronics

Thanks for more tips and photos of your fiber coupling. I really appreciate you sharing so much knowledge about this machine,...I go ahead with putting a projector on the optical table I would use your advice re: collimator positioning and focal length.

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Well, my only point is - experiment! :cool: There is not really an 'absolute', 'end-all / be-all' answer for collimating these things - best approach is to try a few things to see what works for your-particular systems' beam-characteristics / goals for your system is...Even though Laserscopes are very-well engineered laser-systems, you will see differences in beam chars from system to system - again, all LS had to worry about was getting each one 'in-tolerance' for THEIR specs / purposes, that is, down a fiber, with 'raw' output...pretty 'mushy' by our 'standards' / expectations... And proof-that there IS intrinsic fluctuations in beam chars, is WHY they have such an extensive beam shaping / attenuation / control-stage, post-collimator (you know, all that 'medicaly-stuff' :D on-deck...)

Which, btw, is a 'treasure-trove' of optics and solenoids - you can even 'R-E' the 'photocels' they use for beam-power sampling, to make your 'own' on-deck power-meter :cool: and those lucas-ledex solenoids make (in addition-to great beam-shutters) for very-stable fx-position actuators, and even fiber-launcher actuators...:cool:

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Originally Posted by weartronics

However, I'm still thinking fiber coupling would be preferable... :D

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Well, again - depends on what your 'goals' are... fiber CAN work, but it WILL give you an inherently larger, and more-divergent beam to 'work with'... if you're expecting 'crisp graphics' out of it, prolly forget it - fiber-remotes are usually best for fx / aerial / atmos projectors only...not to say, it cannot work for 'graphics', but they'll just be 'mushy', at best...:rolleyes:

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Originally Posted by weartronics

Could you tell me a bit more about your fiber coupling? I have only used pre-assembled cables in the past, I never terminated a fiber before.

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Well, unless you really wanna do it for the 'mountain-climb' of-it :D I'd suggest just buying a 'show-ready' fiber, from someone who knows how to build fibers for KTP - ie: Precision Projection Systems, out in CA, or, PL-Members 'One Stop Laser Shop' in FL - they have actually done quite a bit with KTPs / conversions, and can def. hook you up with a good KTP fiber, with the SMA connectors, etc - even a 'polishing' kit, for when you 'burn' an end... to get into cleaving and terminating your own fibers is quite a 'juggernaut' (..not trying to discourage you, but just being honest - it's a bit of a 'learning-curve'..:cool:)

Quote:

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Originally Posted by weartronics

Another crazy idea, I wonder if the beam from the resonator is sufficiently randomly polarised that I could use a PBS as a 50/50 splitter to get two fibers out of one machine, or is there a better way to accomplish this?

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Yeah, a simple 532-coated 50/50 dichro will be just fine - there is usually at least one in all the 'attentuators' on a 'raw-medical' deck (some are 60/40, 70/30, etc - you have-to just test to see what 'came' with yours...) and the twin-ports of the LS-deck make for PERFECT twin-launcher-ports... :cool:

Anyhoo, gotta run... can type more later..

ciao for now...
j

Hi Jon,

That's an unconventional prism arrangement... what's it do? :D

I would really like to learn how to terminate the fibers, I have read a lot about it before and I would like to have a go. Previously I thought the reflection would be too high without AR coated ends, but I am prepared to try it.

Could you give me any clues about the 200um fiber and SMA connectors you use? I can't seem to find 200um fiber at Edmund. :confused:

Cheers,

weartronics

http://www.ppsfx.com/html/fiber.html

Hey Nic -

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Originally Posted by weartronics

Hi Jon,

That's an unconventional prism arrangement... what's it do? :D

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...'UP-PERISCOPE!!!' :D Bascially, it is a 'home-brew' periscope to deal with the beam-height disparity between the on-deck fx / galvo-level MM1s, and the fiber input-coupler we used on this particular-build - it is a 'retroreflecting' prism, used by LS to steer the 1064nm on the OEM medical-deck, but 2x, butted-together (and one flips-around) you get a very nice, nearly-lossless periscope...(don't let that 'huge glow' in that one pic 'fool-you', there is zero 532-leak thru the 'top-face'...)

..Like I said, the 'raw-medical-deck' of these things is like a 'free trip to the candy-shop'... :D (not to mention, at-least ~$50. or-so worth of quality cap-, pan-, and countersink-head screws...:cool:)

This can also be used 'sideways' for beam-steering, but works 'better' vertically, cause they can just 'sit' on top of one-another (albeit, epoxied on the sides, for 'security'...) - sideways, you'd have to rig-up more to keep the faces perfectly 'mated'...

Here's another 'trick' (see pix-below) using the 'real' periscope that LS uses down-the-line, (to 'engage' the beam into the final fiber-delivery IC)... it makes for a nearly ideal 'beam-shifter', up-deck for on-deck galvos... :cool: Used in-conjunction with the 'OEM' stepper-controlled polarizing-stage, you can actually use this to both 'control' power-output (via pass-thru / reflection by polarization-rotation, just like they do it...) and be the 'metering' point for a 'real-time' power-meter... :cool:

So, when can you schedule-me-in to come 'down-under' and help you convert this thing? :D

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Originally Posted by weartronics

I would really like to learn how to terminate the fibers, I have read a lot about it before and I would like to have a go. Previously I thought the reflection would be too high without AR coated ends, but I am prepared to try it.

Could you give me any clues about the 200um fiber and SMA connectors you use? I can't seem to find 200um fiber at Edmund. :confused:

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Well, #1, scratch Edmunds ...IMO, they are only 'good' for a few lenses / acromats and the 'CDAR' super-high-AR glass windows, (which - btw, is THE BEST, IMHO, for making aperture / projector-windows for these things - when you are dealing with 40+ WATTS, <0.5% back-reflection vs ~10% for 'standard' glass, becomes REAL IMPORTANT!!! :D - everything-else Edmunds sells is pretty-rediculously over-priced / marked-up...:rolleyes:

...So, yeah, (Thanks, Ben! :)) PPS sells component-level kits, and so-does 'OSLS' - and they will prolly be a bit-more 'wallet-friendly'.. we use PPS fibers for WL / non-Q-Sw'd 532 apps, and OSLS' fibers for KTP- always had good results.... :cool: And, while I 'pat you on the back' :D for wanting-to learn how to cleave / polish / make your own fibers, http://www.photonlexicon.com/forums/...ons/icon14.gif:cool:, I do feel obligated to '411-you' to be-prepared to drop a good $2K + on all the 'stuff' :eek: - fiber-cleavers / finishing kits are not 'cheap'... 'Word to the wise'...

A small side-note (from PPS' site / fiber-specs) about '30W down-a-fiber', that is for CW-ONLY (ie, a giant Argon, etc) it is NOT recommended to pump more-than 20W MAX down a 200µm fiber, Q-Sw'd, because of the MUCH-higher 'peaks' of 532 in those pulses... best to do like, 20W, 50/50'd into 2- 10W launchers, and then *try* for 8-9W for SL/SR remote heads... PLENTY of power...(see shot below w/ 4x ~8W heads and 2- 4W beam-table units, SL/SR...:cool:) If you want to truly-use +20W, you will need to go bigger (400µm - 600µm) - then, of course, up-goes the beam-diam. / divergence...

Pat / Steve - (couple of my favorite-mentors... :D) feel-free to jump-in anytime, and augment / correct my 'advice', here... :cool:

ciao for now... :)
j

Quote:

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Originally Posted by dsli_jon

A small side-note (from PPS' site / fiber-specs) about '30W down-a-fiber', that is for CW-ONLY (ie, a giant Argon, etc) it is NOT recommended to pump more-than 20W MAX down a 200µm fiber, Q-Sw'd, because of the MUCH-higher 'peaks' of 532 in those pulses... best to do like, 20W, 50/50'd into 2- 10W launchers, and then *try* for 8-9W for SL/SR remote heads...

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Very good point about the q-switching. I didn't even think about that! Do you guys have any use for the medical fibers that are used with the laserscope system? I know a guy around here who has nearly a thousand of them. :)

And how's the Laserscope 600 dye att. pumped by q-sw 532nm via fiber ? Is it some large core / huge face spot attitude ? I thought these were designed for up to full 40W 532nm pumping, right ? :confused:
Piotr.K

Still as I mentioned earlier I think (claim ?) that if z-fold's 20cm r.o.c. mirror was allowed to pass green, we would be able to get far better beam specs for lasershow use.

532nm beam spot on this mirror is about twice smaller than on OC (50cm r.o.c.), so with additional optics right here the final spot could be smaller.

I'm considering trying to replace this 20cm r.o.c. HR@1.06/HR@532nm mirror with 15cm r.o.c.HR@1.06/AR@532nm to check this thesis, but this change may require shortening the relay optics distance. This would also change the relay factor from 2.5 up to 3.3

Anyone ?

Piotr.K

run the cavity model in PSST! ?

http://www.st-andrews.ac.uk/~psst/

note lens duct in psst = rod. :-)


Steve

Hey Ben -

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Originally Posted by Laser Ben

Do you guys have any use for the medical fibers that are used with the laserscope system?

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Nah, thanks... got a few for 'experimentation's-sake' and no real need for show-use... thanks anyway...:cool:

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Originally Posted by Laser Ben

I know a guy around here who has nearly a thousand of them.

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Wow - he could make QUITE a cool lit-up 'Millennium Falcon' model with that!! :D (I tried that as a teen, after seeing a 'special' on 'the making of Star Wars, and man, it reeeeally 'works' for making little 'window lights' in a model... very-cool...:cool:)

Hey Piotr-

Quote:

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Originally Posted by LesioQ

And how's the Laserscope 600 dye att. pumped by q-sw 532nm via fiber ? Is it some large core / huge face spot attitude ? I thought these were designed for up to full 40W 532nm pumping, right ?

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Well, if I understand what you are asking, correctly, the 600 Series Dye was designed (according to 'specs') to-be pumped with exactly (probably +/- a percent or two..) 16W of 532, to-give the 'spec' 3W of 630nm (for its 'particular treatment-purposes) - which can 'shift' power-output depending on what wavelength the grating is 'tuned for'. While the fiber that comes 'standard' with the unit, I believe is a 400µm, I am sure you *could* pump MORE into it, with a 6 or 800µm fiber. ie: I pumped ~20W into ours, and saw ~5W peak... it was niiiiice...:D

The point I was making to Nic was that you don't wanna pump a 200µm fiber with more-than 20W, cause with such a 'relatively tiny' fiber-end vs such high-peaks as-are found in any Q-Sw'd beam, you stand a greater chance of 'burning' the end - not so-much of the FIBER, but of the TIP - focused-down to that tiny spot, even 20W's (+ 'spikes') IS DEFINITELY ENOUGH to 'burn' a fiber-tip - the 'power density' is MONSTER at that point...:eek: So, yes, you CAN pump more into fiber - it just has to be correspondingly-bigger fiber...

Take THIS beast, for example - boasts - no, MEASURES 80 Watts - OUT of the fiber!!! :eek: Read the listing: "... On Laserscope's test sheet (prior to shipping the system), the technician measured 110 Watts of 532 nm at 53 Amps..." Holy schnikey, that's a lotta green!!!:D Not exactly-sure, but I am pretty-sure that uses at-LEAST 800µm fiber, with that much power...

As-to how this relates to the Dye sys - well, yeah, with bigger fiber, you *can* pump more into the dye-cell, and because the dye-beam is a separate 'lasing-process', the dye-beam-quality is the result-of the dye-cavity optics, NOT the 532 pump-beam... In fact, I'd bet you could just rig one of these dye heads up-to a 532-deck (maybe an over-under config) and DIRECT-pump it (lose the fiber, and you'd also have-to do a little minor optics-rework in the dye head...) with 30+ Watts, and see 8-10W of Red!!...Imagine that...10W of 629nm!!! :eek::D

The only 'limiting-factor' then-becomes dye-cooling / power-handling / efficiency, and keeping the dye-cel window 'clean' (cause any dust or 'funk' that floated into the beam would 'burn' on the window very quickly, and thus, take power down drastically...) Worse, if some 'funk' got inside, and the burn happened inside the dye-cel, than you'd have to take it apart (read: drain it..ugh) and clean.. of course you 'could' also 'shift' the dye-cel 'up' to a 'new', clean part of the dye-cel window.... But I am getting off-track, here... :D

Nic - again, if you get a 'kit' from either 'PPS' OR 'OSLS', you mostly need to make-sure you tell-them it is 'destined for-use with Q-Sw'd KTP' - there are different-spec fibers (even at same diameters) for-use with Ions vs KTP... (really, it is non-pulsed vs pulsed...) They do things like cleave the fibers at a 'slight angle' (vs 90˚) to minimize back-reflection, down the optical-train (PS - Thanks to Steve Roberts for that little gem of info... :cool:

Anyhoo, ciao for now...
j

Yeah, there are a lot of Laserscope parts around here. Unfortunately, most of them end up in the hands of people who think selling a used part at 90% of the new cost is a great deal. :(

Just for interests sake, has anyone done a conversion to a greenlight?

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Originally Posted by dsli_jon

Take THIS beast, for example - boasts - no, MEASURES 80 Watts - OUT of the fiber!!! :eek: Read the listing: "... On Laserscope's test sheet (prior to shipping the system), the technician measured 110 Watts of 532 nm at 53 Amps..." Holy schnikey, that's a lotta green!!!:D Not exactly-sure, but I am pretty-sure that uses at-LEAST 800µm fiber, with that much power...

j

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I think it is a relativly new system so I doubt anyone had done something to the model. 80W CW is quite impressive! I love the look of that fiber.

Thanks to everybody (especially Jon) for the tips and photos throughout this thread!

For reasons of cost, complexity and divergence, I have decided to build the aerial beam projectors on to the Laserscope optical tables, with some very sturdy trusses to lift them! >:) I will probably use Jon or Pat's idea to move or replace the collimating lens to up-collimate a little for 10mm beam with lower divergence. 10mm aperture Eye-Magic galvos arrived just as I was typing this post!

I'm still interested to fiber couple some other projectors, and I would like to be able to repair them, so I have decided to have a go at terminating fibers myself. I see your point about buying kits because the process looks very involved, but I have a steady hand and the tools are not very expensive to try. If it turns out to be too tricky then I will buy kits from PPFX or OSLS.

FYI, I found Thorlabs seems to have an OK price and a good range of suitable fibers.

Best regards,

weartronics

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Originally Posted by weartronics

Thanks to everybody (especially Jon) for the tips and photos throughout this thread!

For reasons of cost, complexity and divergence, I have decided to build the aerial beam projectors on to the Laserscope optical tables, with some very sturdy trusses to lift them! >:)

I'm still interested to fiber couple some other projectors, and I would like to be able to repair them myself, so I have decided to have a go at terminating fibers myself, it's not very expensive to try. If it turns out to be too tricky then I will buy kits from PPFX or OSLS.

FYI, I found Thorlabs seems to have an OK price and a good range of suitable fibers.

Best regards,

weartronics

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I am not a huge fan of connectorized fibers with the yag. With every other laser i am, but not the yag. I prefer to divide the beam in at least 2 parts but 4 is better and go with 10x microscope objectives and a standard Newport fiber launcher. It is easy to strip and cleave a 100 micron glass fiber and chuck it up in 5 minutes. Polishing and so forth should be reserved for lower power lasers where time is allowed to get it dialed in.

if you dammage a connectorized fiber it is a PITA to get it going in a hurry (if necessary) It really sucks to burn your fiber 30 minutes to show go, connectorized fibers cant be repaired in 10 minutes...well that would be rushing it.;)

Hey Pat, that's another good idea I hadn't considered. The 10X objectives I have seen are NA 0.25, but that's too big for NA 0.22 fiber, right? Or is there a trick I missed... :D

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Originally Posted by weartronics

Hey Pat, that's another good idea I hadn't considered. The 10X objectives I have seen are NA 0.25, but that's too big for NA 0.22 fiber, right? Or is there a trick I missed... :D

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hhhhhmmm it might have been a 20 x but I dont think so:confused: depends on what fiber you are using of course. Pick a fiber, match the NA;)

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Originally Posted by dsli_jon

... In fact, I'd bet you could just rig one of these dye heads up-to a 532-deck (maybe an over-under config) and DIRECT-pump it (lose the fiber, and you'd also have-to do a little minor optics-rework in the dye head...) with 30+ Watts, and see 8-10W of Red!!...Imagine that...10W of 629nm!!! :eek::D

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Here I have installed the dye laser cavity onto a KTP yag and have achieved 14.6W of red with excellent beam quality and dye life. The dye circulator is behind the front door of the yag. I can split off green to mix with red creating yellow, orange, etc.

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Originally Posted by Photonbeam

Here I have installed the dye laser cavity onto a KTP yag and have achieved 14.6W of red with excellent beam quality and dye life. The dye circulator is behind the front door of the yag. I can split off green to mix with red creating yellow, orange, etc.

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nice job! Looks Great!:)

That looks interesting ! What's the origin of Your dye cell ?
Running just plain Rhodamine 6G in water/alcohol mixture ? Any boosters ?
Piotr.K

16.4watts of red.... wow

Where do I have to go to see a show with this red?
Steve

Quote:

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Originally Posted by Photonbeam

Here I have installed the dye laser cavity onto a KTP yag and have achieved 14.6W of red with excellent beam quality and dye life. The dye circulator is behind the front door of the yag. I can split off green to mix with red creating yellow, orange, etc.

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Please post pics of that baby kicking ass !!

wow...