Frequency doubling the SSY-1

[LORDJET]

Greetings all! I remember reading in the Laser Faq a number of years ago, about a theory of frequency doubling the SSY-1. And in another thread, goninanbl00d and rhd were discussing this as well. And as a result it has me thinking about this again. So I submit this idea to my piers, and ask those here far more learned than I, can it be done? :thinking: I really REALLY like idea of trying to accomplish this.

But I also recall reading that the passive q-switch may or may not make this more difficult. It's been years since I have toyed with my SSY-1s ( yes plural, I have two of them. ) And instead of sitting around collecting dust, I was thinking about pulling them out and making something out of them again.

So much so, that I would be willing to donate one of these to a fellow forum member that feels that they might be up to this challenge! I have thought long and hard about doing this myself, but I feel I just don't have the knowledge, time, and resources to attempt this myself. I am totally open to any offers or advice that anyone here may have. Again I would be willing to ship one of my beloved SSY-1s for dissection, and modification. to any forum member with the clout! :bowdown:

If this could be accomplished, this visible green blaster, at this power level would be the ultimate in pew pew!!

:lasergun:

Peace, James

 

[Prototype]

If they have the Q-switch, it would be somewhat easier as less power would be lost due to inefficiency (relatively less power, as without the Q-switch the pulsed power is much higher, resulting in more power after doubling.) It's entirely possible to do this, yes, it just requires a KTP capable of handling the power (the coating moreso than the crystal itself, flux grown KTP when heated properly can handle a large amount of power) and a TEC heating rig that keeps it within <.1*C of the appropriate temperature. Then there's phase matching for optimal power out, aligning the beam waist within the KTP, etc. I probably could do this, but I'd need to order a TEC and controller along with a KTP and some 1064nm goggles. Another thing to keep in mind is that while the green peak pulse power will be very large, the average power will likely be <10mW.

 

[LORDJET]

If they have the Q-switch, it would be somewhat easier as less power would be lost due to inefficiency (relatively less power, as without the Q-switch the pulsed power is much higher, resulting in more power after doubling.) It's entirely possible to do this, yes, it just requires a KTP capable of handling the power (the coating moreso than the crystal itself, flux grown KTP when heated properly can handle a large amount of power) and a TEC heating rig that keeps it within <.1*C of the appropriate temperature. Then there's phase matching for optimal power out, aligning the beam waist within the KTP, etc. I probably could do this, but I'd need to order a TEC and controller along with a KTP and some 1064nm goggles. Another thing to keep in mind is that while the green peak pulse power will be very large, the average power will likely be <10mW.

Thanks Proto for the imput! I was unaware of the temperature requirement for this. I just had in my head that one could "scale up" the same thing that is based in a typical green pointer. But at that power level, I believe I can understand it! :thanks: I just didn't know that the whole process would be so lossy! Thanks again for your reply.:beer:

 

[HIMNL9]

Aren't some medical pulsed units already working in this way ?

I know here in Italy is impossible to find them, but perhaps in the USA they can be found (ebay and similars, second-hand, etc ..... first brand that come me in mind is laserscope, but there are others).

 

[Prototype]

There are some 'cheap' Nd:YAG frequency doubled units for skin care on eBay, all from China, they're 1064/532, pulsed. Average price is about $1800 or so I believe. Laserscopes are another option, but are usually $10k+ and incredibly dangerous pieces of equipment for a multitude of reasons, one of the main ones being the lethal voltages present and the fact that you're dealing with many thousands of watts of laser energy.

 

[LORDJET]

Oh well this dream is quickly being woke up to reality. Sounds like there is allot more to it than finding an appropriate KTP, and just start firing away. To make an SSY-1 lase in the first place wasn't that hard at all. I built my own PSU from photo flash caps and boards from three hacked Kodak max disposable cameras wired in parallel. Certainly not optimal, but it worked well enough!

 

[Bluefan]

If they have the Q-switch, it would be somewhat easier as less power would be lost due to inefficiency (relatively less power, as without the Q-switch the pulsed power is much higher, resulting in more power after doubling.) It's entirely possible to do this, yes, it just requires a KTP capable of handling the power (the coating moreso than the crystal itself, flux grown KTP when heated properly can handle a large amount of power) and a TEC heating rig that keeps it within <.1*C of the appropriate temperature. Then there's phase matching for optimal power out, aligning the beam waist within the KTP, etc. I probably could do this, but I'd need to order a TEC and controller along with a KTP and some 1064nm goggles. Another thing to keep in mind is that while the green peak pulse power will be very large, the average power will likely be <10mW.

A Q-switch makes it many many times more easy. Actually as easy as aligning the nonlinear crystal.
A Q-switch doesn't lower the pulse energy much actually, but that depends on how soon the Q-switch opens. I'd expect 10-20% loss, but a 1000x higher peak power.
The laser is pulsed, so heat won't be much of a problem. The KTP or KDP needs to be heated anyway. There is no fancy TEC rig needed, just some resistor based heater which keeps it warm. Only because the nonlinear crystal is more efficient when it's warm and it keeps the moisture out. LBO is the crystal that needs that kind of stability.
The last thing you want to do is make a beam waist in the crystal, that will definately damage it. With the megawatts of peak power you don't need to focus, just add the crystal in the beam. Aligning it won't be that difficult, just 2 axis of rotation that are important.
I could make something like this, I have some experience in replacing a KD*P crystal in a Spectra Physics Quanta-Ray laser. I have the needed safety goggles, I just lack some time for a few weeks to come.
The conversion efficiency is a few 10s of percent, not that bad. It's a pulsed laser, if you fire it once a minute it won't have an impressive average power. But it will definately have a nice peak power.

 

[HIMNL9]

..... if you fire it once a minute it won't have an impressive average power. But it will definately have a nice peak power.

Firing it at, say, 100Hz, for the other hand ..... :eg: :eg: :eg:

 

[LORDJET]

A Q-switch makes it many many times more easy. Actually as easy as aligning the nonlinear crystal.
A Q-switch doesn't lower the pulse energy much actually, but that depends on how soon the Q-switch opens. I'd expect 10-20% loss, but a 1000x higher peak power.
The laser is pulsed, so heat won't be much of a problem. The KTP or KDP needs to be heated anyway. There is no fancy TEC rig needed, just some resistor based heater which keeps it warm. Only because the nonlinear crystal is more efficient when it's warm and it keeps the moisture out. LBO is the crystal that needs that kind of stability.
The last thing you want to do is make a beam waist in the crystal, that will definately damage it. With the megawatts of peak power you don't need to focus, just add the crystal in the beam. Aligning it won't be that difficult, just 2 axis of rotation that are important.
I could make something like this, I have some experience in replacing a KD*P crystal in a Spectra Physics Quanta-Ray laser. I have the needed safety goggles, I just lack some time for a few weeks to come.
The conversion efficiency is a few 10s of percent, not that bad. It's a pulsed laser, if you fire it once a minute it won't have an impressive average power. But it will definately have a nice peak power.

Hmmm, thanks Bluefan for the imput! This is why I love this forum. It's good that you have practical experience working on these, so it seems that it may be doable after all? I know that there are different types and sizes of SHG crystals. And of course the placement ( inside the cavity, or outside of it ) Almost sounds like I could do it myself, if I had the proper materials, and heating element in hand! :thinking:

 

[goninanbl00d]

The SSY-1 can't possibly be fired at 100Hz. You'll actually melt the lamp (or make it explode in a dramatic fashion).

Besides, the recommeded duty cycle for the Q-switched SSY-1 is 120 seconds or so between shots. Any more and you risk damaging cavity optics including the Q-switch, as well as causing the lamp to overheat.

There isn't an easy way to cool the cavity to prolong duty cycle either- the ceramic shroud makes it hard to direct flow of any cooling medium (air or oil) through. The SSY-1 was never designed for frequent operation anyway, so it didn't matter.

As has been said before, the Q-switch makes doubling much easier. Even without a heater and phase-matching, you should be able to get some green out just by firing at a KTP of the suitable size.

Remember, doubling is non-linear. The higher the peak power (and power density), the better it works. Too high, though, and the KTP blows up (no, literally, KTP does crack and deform if hit with too much power in one shot). Just find a KTP large enough (or use a set of lenses to alter the beam profile before it enters the KTP), and you should be fine.

Of course, just firing at a piece of KTP will get you green, but it won't be very efficient. The green output will definitely be noticable, but nowhere as powerful as it could be. That's where all the fancy-schmancy pieces of equipment come in.

First off, with KTP, phase matching simply involves orienting the KTP correctly in the beampath. Unlike LBO, BBO or other SHG crystals, there isn't much more to it.

However, for optimal efficiency (as others have said), the KTP will need to be heated. KTPs all have different operating temperatures (from 50C up to 120C). They don't need to be at an exact temperature, however, being closer to their operating temperature reduces the likelihood of damaging the crystal.

It's LBO that needs to be kept within 0.1C of it's operating temperature when being non-critically phase matched. KTP should have no need for that.

In any case, it really isn't hard to do. If you can find a decent KTP that can handle the power, you're pretty much set. Once you can get green output then you can start tuning the optics for better power output.

Now, if you were going to have it intracavity, then it certainly complicates things, depending on whether you want to use the Q-switch or not.

Firstly, if I remember correctly, the Q-switch isn't permeable to visible light(whether it's open or closed), meaning a significant portion of the intracavity green will be absorbed by the Q-switch, resulting in little output and damage to the Q-switch. I could be wrong on this one; I can't remember the details on this. You could always try shooting a pen greenie down the cavity, and firing it to find out.

Secondly, you're going to need new cavity optics. For starters, Brewster plates (to give a polarised beam) would aid in doubling, but are not necessary (strictly speaking). Secondly, your cavity mirrors won't do. They are completely transmissive at 532nm, which won't do. For optimal efficiency you want the output coupler to reflect 1064 and pass 532, while the high reflector reflects both 532 and 1064. You'll also need mirrors with the right curvature to match the length of the cavity.

Of course, you could probably get away with reusing the optics, but there's a chance that you'll lose a significant portion of your power. Then again, in the grand scale of things, it is just one big experiment anyway.

 

[HIMNL9]

LOL, i know ..... i destroyed one, too ..... it was a joke, sorry :beer:

 

[Bluefan]

A polarising element in the cavity would also help with extracavity doubling, only one polarisation is doubled. A polarizing element can be as simple as a window with sufficient flatness at the brewster angle.

 

[LORDJET]

First off A big thanks to you guys! I knew the answer could be found here, you all are winners in my book!:wave: goninanbl00d, you have given me a good direction on how to go. External cavity doubling would be easier. I had totally forgotten about how the optics are matched to the wavelength, ( 1064 not 532, duh! ). And while I was at it I also want to do something about the horrible divergence. In my crude burn testing I noted that any distance beyond 6 to 8 inches, the beam lost it's tight circular profile. I was thinking of mounting a plate in front of the OC, and in it have the beam pass through an expander, and then pass through something like an Axiz 3 element lense. This would hopefully give me some much needed range, that the raw beam output lacked!

 

[LSRFAQ]

Rangefinder doubler.

Qswitched single shot yags use type I shg, no temperature control, and large diameter crystals. Unless you want a perfect beam, you dont even place it on a precision x-y mount, you can just HOLD the doubler in the beam and get green.
No difference between EO-AO-DYE qswitches in this regard.

A brewster plate intracavity is optional.

People do holography this way, just adding a spatial filter.

BTDTGTS.

Steve

 

[LORDJET]

Thanks Steve for the input, that should make things easy. My mission now is to find a suitable KTP for the task!

 

[Bluefan]

I can remember a few spectra physics pulsed YAG lasers with type II SHG (and THG). What would be the advantage of type I or II?