Determining Q-switch operating frequency

With the two other lightwave lasers I have I also acquired a Spectra-Physics YHP70-106QM head unit that is an engineering sample. I plan on running it off a couple Coherent FAP modules I have. Real basic head. End pumped Vandanate q-switched head. Nothing special here. The problem is the Q-switch. I have no idea what frequency it ran at. I know SP used 41Mhz and possibly 80 Mhz drivers. I have no idea which though for this one. The q-switch in the head is different than the ones I have seen in similar heads.

Any ideas on how to figure out what this thing ran at? Try a driver and watch for reflected energy on the rf?

Dont know for sure...but 41 mhz sounds high to me...41 mhz was the frequency that we mode locked the ion lasers for sync pumped dye laser applications. For q switching (at least for green yags) we used about 10 k to 25 k hz. Steve will probably know more but i think for q switching applications you will need to give the cavity more time to build up...you need to balance the cavity gain, recovery time with q switching speed. Sorry im not more help but the 41mhz thing jogged my memory (which rarely happens)

The 41Mhz may be OK as this is for the RF signal which is modulated at the 10's of Khz range. The big 'ol LS rods 10-25kHz, the several W ( average ) Coherent markers up to about 100Khz. The crystal will have to be driven at a RF that it was designed for and I'm not knowledgeable enough to know how out of spec is OK. I am curious though, the Q-switch module might have a performance plate that identifies the required input power/frequency/wavelength etc?

Laserman, the q-switch has a carrier frequency that activates it. Most modern ones are between 27MHz and 80MHz. Apparently the higher carrier frequencies are better for shorter beam paths. The head I have is actually pretty long, over 2 feet. This RF signal is modulated and thats what turns the q-switch on and off. No RF and the beam passes though, RF and it is deflected.

The Q-switch is inside the head which is pretty much sealed. I did peek and there is nothing marked on it, nor on the one that I took apart after they started scrapping. I have a NEOS Q-swiitch driver that came out of a SP power supply that was similar to the ones that pumped these heads. Just don't know for sure.

Oh yes, I should have considered that you might be talking about the carrier frequency, which for the devices i use is 27.12mhz. I had the PRF in my mind, sorry. We did however did use 41mhz to create a standing wave in a 171 ion laser for modelocking. We would adjust the frequency while watching output power (dip) to match the resonance of the prism assembly (highest depth of modulation) then adjust the cavity length to create a train of short pulses (increasing power) (approx 200 picoseconds) at approx 41 mhz...(some cobwebs are clearing)

Laserman532,

You are the LS guru right? What about simply replacing the entire Q-switch assembly in the lightwave with a LS Q-switch/driver assembly as this would also include the LF standoff function (prevents cavity dumping). How much would this cost, hundreds?

Here is the rub, you need to know the carrier frequency or the crystal blows its piezo transducer to smithereens.
If you have a modern driver, the driver might live, dispite the bad HIGH VSWR reflection. Being 5 Mhz off in some cases is enough to cause problems.

Common license free freqs used are 27.125 (Aka cb channel 14, the Cbers love this, I'm sure! :p)

Qswitch frequencies I've seen:

27.125
40.66 ( some pump lasers for dye and modelocking ion/yag for used for a cavity resonance reason)
48.1
50.00
68.xx
76.0 (pump lasers for dye and picosecond systems, used for a cavity resonance reason)
80.0
110.00
200.00



13.553 MHz to 13.567 MHz , 26.957 MHz to 27.283 MHz, and 40.660 MHz to 40.700 MHz are popular because they are "ISM" frequencies dedicated to be designated electronic wasteland for industrial use. You wont see a 13 Mhz AO though, too slow, so the crystal would have to be huge.
Not all AOs are ISM, some piggyback on frequencies used for other services. Xerox AOs from printers are right in the heart of the Air Navigation bands.
So I go out of my way never to run a xerox driver without a load to adsorb the RF.

80.0 is popular because it used to be ISM, makes for a good small spot size out of the AO cell, and the use carried over to modern use.

I have the frequency sweeper and calibrated wideband bridge needed to test the AO cell. I can test it with a few milliwatts, which will not blow the cell. Takes 10 minutes on the bench. I can sweep 0-250 Mhz in a few minutes. I can also sweep 2 Ghz to 22 Ghz, but that is outside the scope of this descussion.

These cells need anywhere from 0.25 watts to 50 watts drive, depending on the Q-switch.

Otherwise you have to send it to Neos-Gooch and Housego, or ISOMET for a sweep. And that is not going to be cheap.

Does the Q-Switch have water cooling? If water cooled, it is usually 27 to 68 Mhz, because RF power amplifier transistors for this band are cheap.

If you shutter the intracavity light at a N/2 frequency of the cavity longitudinal mode spacing in Megahertz, you can modelock and make short pulses with some lasers. That is what Laserman532 is talking about. It is becoming the bain of my existance in this lab, so much so that my output coupler is on a micrometer "Z" stage to adjust the mode length of the laser to the AO.

76 Mhz is popular with Coherent, because of their larger ring dye lasers, the Antares-76 Doubled YLF laser, and some of their ti-saphs are all length adjusted for 76 Mhz for picosecond or femtosecond pulses.

TOO LOW A PRF and YOU GIANT PULSE, which may damage the laser. You may also need "first pulse supression" to avoid the stored energy in the laser crystal to not be released in one Q-Switched BIG first pulse. FPS ramps the RF power up or down depending on the model, bleeds the stored energy, then goes pulsed. Every time you blank/unblank, you may need FPS. This is why laser show AO blanking some Laserscopes(or Industrial yags) using the wrong AO driver can result in expensive damage to the KTP or Optics. This is not just a YAG thing, on Ruby can blow off parts of the rod.

Steve

Thanks for the info.

Spectra Physics just sent me the manual for it and it specs it at 40MHZ at 10 watts. So it looks like I have the right driver after all. It does have the first pulse suppression feature.

-Jerry

I cant really add anything to what Steve said except...yeah what he said...

isnt it cool steve when you are watching the scope and tuning the cavity length then all of a sudden...BAM...a nice short pulse (200ps)

THEN...you are watching the autocorrelator scope signal and adjusting the length of a dye laser and then all of a sudden....BAM....2 pico seconds

THEN....if you are totally OLD SCHOOL and you are matching the length with a fiber grating pulse compressor then BAM....50 fempto seconds

THEN...if you want to get totally retarded....you can pulse pick and amplify!!!! MUAHAAAAAAAAAA

all of that train of pulses at 41 mhz....good times

Well that is some really old school stuff right there...it is probably all done in a laser pointer now.

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It does have the first pulse suppression feature.

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That was my biggest fear with alt. sourcing a driver. Good.

Now, you have these neat lightwave lasers and you don't have a plan for them. OK, but what do you think is interesting? Machining? Pumping? Display? (I know maybe not with the 355)

sure, micro machining if you are bored. I personally would slap that bitch on ebay and buy something fun with the money from the sale. :)

Marking and cutting thin metallic materials. I have been building a CO2 laser cutter for quite a while, one of those work on it as I feel like it things. Building out of a lab robot that FEI was experimenting with for loading wafers in their electron microscopes. A build log here: http://www.buildlog.net/forum/viewtopic.php?f=16&t=264 I have done more work on it since. I am messing with optics now trying to get mirrors where I want them.

The thing is if I sell it who know when or if I will run across another. And since I am not really putting out money for these I can justify keeping them around. They are not like a gas laser that can go bad just sitting.

Ya, don't sell it ( unless you want to sell it to me). The beam quality sounds really good for the 532. Is it as good for the 355? The 355 should be a lot better re metallic absorption.

Regarding marking/cutting, do you fiber feed? Do you move the head itself or do you move mirrors similar to the X/Y scanners used for entertainment? Have you worked with Z axis focus control?

Alternatively, do you move the sample on an X/Y table

Looks like the 355 is just as good. It does look like it starts out a little larger than the 532. I have not done any tests of any great length for the 355 but at 10' it is still pretty small. The 532 was intended to be frequency doubled to 266nm and both were for trimming and wafer marking. They both seems to have real good absorption properties. The 532 is supposed to real good at marking gold.

I did magage to increase the output of the 355. I noticed at startup the output was higher than after the diode temp stabilized. After 30000 hours the frequency of the diodes had shifted. I reset the temp set point of the diode and am now getting about 4.24 watts out of it.

On the co2 I am just going to do flying optics. I have seen ZnSe fiber, no thanks. Possibilities are launching the 532 or 355 into a fiber and delivering it to an auxiliary lens on the gantry. The issue with this is making the machine light tight. CO2 is nice. Just about anything we sw as transparent is opaque to 10.6u. 532 and 355 seem to pass through most things. 355 is still cose enough to visible where glass does not absorb a lot.

My friend who I got these from has some Cambridge galvos and even a theta lens. Those the controller are proprietary.

I'm looking for one, because my boss wants me to make him a few milliwatts of 266 to 279 for spectroscopy. If I own the laser, that is job security.

Steve

There may be a rail available for 266nm. It has all the optics and fhg crystal for 266 with a collimator on the output. It's totally out of alignment as it sits so that will have to be adjusted. I am going to check out the laser a but more as all I have done is a quick power on test.

Though this will probably put out more like a couple watts, a few orders higher than you wanted.

Glad to see that the head is running, its always fun playing around with 'modern' laser technology! 4.2w of 355nm is quite impressive, what is the input power?

Steve - I have a 2mw 193nm laser (fourth harmonic generation), its all solid state but it takes up a whole optical table. I will give you a hint, 10w of 532nm goes in but 193nm is not an integer harmonic of that *warn

It may be higher output than what the front panel is saying. I took four different power heads and they are all telling me it is putting out at least 6 watts 10khz. So maybe the photodiode has aged after all this time as well. From what I have been told by a company that works on these lasers the Nd crystal is pumped by three coherent 40w bars. They are $4000 each to replace. The problem is they need to be matched and coherent is the only ones that will do that. One plus for Spectra Physics design with the remote pump diodes.

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Originally Posted by krazer

Glad to see that the head is running, its always fun playing around with 'modern' laser technology! 4.2w of 355nm is quite impressive, what is the input power?

Steve - I have a 2mw 193nm laser (fourth harmonic generation), its all solid state but it takes up a whole optical table. I will give you a hint, 10w of 532nm goes in but 193nm is not an integer harmonic of that *warn

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Bad enough I have a Verdi, Mira, Spitfire and " SPECIAL MAGIC" just on ONE table.
I dont even want to think about 193.

At least your not thwacking flying liquid Xenon drops like some folks are.

Steve

Macona, if there is a 266 rail available I'm (meaning me or MY BOSS) is VERY interested.
Drop me a PM.

Steve

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Originally Posted by mixedgas

Not all AOs are ISM, some piggyback on frequencies used for other services. Xerox AOs from printers are right in the heart of the Air Navigation bands.
So I go out of my way never to run a xerox driver without a load to adsorb the RF.

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That's the 110.000 MHz frequency, used for VOR navigation and ILS localizers.

Fortunately, it's not going to harm any aircraft unless you squeeze it into a directional antenna. Aircraft receivers aren't going to pick it up unless you transmit the 30Hz subcarrier used to determine the bearing to the station.

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Originally Posted by Stoney3K

That's the 110.000 MHz frequency, used for VOR navigation and ILS localizers.

Fortunately, it's not going to harm any aircraft unless you squeeze it into a directional antenna. Aircraft receivers aren't going to pick it up unless you transmit the 30Hz subcarrier used to determine the bearing to the station.

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--------- Yeah, I know, not much harm, but I still warn folks not to leak em-----------

Depends on which Xerox AO, I have the older ones and the newer ones.
The newer ones stay on ~110 with say 250 mW. No issue.
The older ones tune 110 to 128 with a "TRIM" input used to vary the deflection angle by changing frequency. They have a prism milled into the AO crystal, and if you can get six feet of bounce into your projector with mirrors, by turning the trim 10 turn, you can pick out argon lines one at a time. Those go well into the Aviation voice range and have 1 watt of RF, which is significant if they ever were coupled to a good antenna.

In the intended use, they are remarkably close to VHF Guard when running!

Steve