Laserscope KTP oven temperature

[dsli_jon]

Hey Simon -

Well, I'm late to the party, but looks-like you've been well taken-care-of ...

...Only a couple small-morsels I can add to the salad:

The KTP should be around 82C which is about 750 ohms on the thermistor in the heater. The crystal is phase matched with both the physical orientation (i.e. the 5 axis mount) and the temperature....

Yes, and ie: I often find that they 'like to be run a bit-hotter' ie: for CW-mode operation, yes, keep the range @ ~750Ω, but for heavy-duty Q-Sw-mode-use, the output always seemed more 'stable' with the controller keeping it @ ~780Ω - the 'OEM LS' specs say '750Ω +/- 50', but it seems they like to be 'kept warm'... who doesn't, right?

It also depends, too, on your-particular crystals 'voodoo' some like it hotter, some like it 750Ω, on-the-button... point-is, play-n-watch... Oh, and 's m a l l m o v e s' - take your time, put your laser-output on on a nice analog power-meter, and observe...

I've been told that model 5C7-350 is a good replacement...

Yes, the part you want (according to OI) IS the 5C7-350, it-being the 'closest-equivalent' to the 'old' / discontinued OEM-box - the 5C5-263 (little gold-box, shown-below....) - We used-to build these 'stages' for the 5C5, (when they were still available) to-replace the original OI 5C5-262, which-was a similar-layout 'stage' for the 263... has a nice terminal-bus for easy wiring, and a nnniiiccee, real-time range-feedback LED, and test-points for Ω and V... Have not had the time to 'design' a new one to interface with the 5C7, but will-post when we do...

The man you wanna chat-with is Richard Goodheart, at OI, (in the US, of course..) 717-766-0721 - he told me, that in-fact, if you 'let them know ahead-of-time, that you are using this to-replace a 5C5-263 (which, essentially, you are...) they can pre-wire it for you, so it will 'match-up' to the correct-I/O of the ceramic-heater in the oven, up-top... you'll have to retro-fit the OEM LS-plug, but I'm sure you can handle that...

And PS - he might need a bit of a 'memory-jog' about 'what this is for' since the 5C5-263 has not been-around for quite awhile, and it takes them a bit, just to 'remember' what it was 'for'... But a nice chap...

Anyhoo, hope this is-of help, too...

cheers...
j

[Xytrell]

My understanding is you want the temperature higher than ambient.

It would be strange to come across an oven that didn't make the temperature higher than ambient

[Simon]

An update....

I have installed this heating controller and it works a treat !

Many thanks all for the help and information.
I am so in love with my laserscope at the moment I cant leave it alone !

And for my next trick..... I want more watts and better columation ! LOL

I have been following the advice on Sams repair FAQ site and have had some good results although I think my Q switch needs a bit more RF power as it is struggling and just have to figure which of the 3 pots to adjust !

[mixedgas]

watts and better columation ! LOL

I have been following the advice on Sams repair FAQ site and have had some good results although I think my Q switch needs a bit more RF power as it is struggling and just have to figure which of the 3 pots to adjust ![/quote]
'
Unless you have Rf wattmeter and SWR meter, DONT ADJUST!

you can change the frequency the of the pulses to the q switch and peak that way, but DONT adjust the RF blind.

Steve

[Simon]

Unless you have Rf wattmeter and SWR meter, DONT ADJUST!

you can change the frequency the of the pulses to the q switch and peak that way, but DONT adjust the RF blind.

Steve, thanks for that.

By coincidence, I used to be an RF engineer so have a selection of SWR and RF power meters. I intend to scope and measure everything first !
I have learned from bitter experience not to do things blind...LOL

So far I have upped the lamp current to around 32 amps along with uprating the cooling and it runs fine.
Anymore current and the lasing becomes eratic but the lamp is stable.
The optics are all aligned ok so I have assumed the Q switch isnt driving enough.
If I turn the Q switch off, the CW beam is perfectly stable at the higher lamp currents.

I appreciate that pushing the limits reduces components life but I am having so much fun doing this !

As for columation, I think that may be a lost cause... !

[mixedgas]

Steve, thanks for that.

By coincidence, I used to be an RF engineer so have a selection of SWR and RF power meters. I intend to scope and measure everything first !
I have learned from bitter experience not to do things blind...LOL

So far I have upped the lamp current to around 32 amps along with uprating the cooling and it runs fine.
Anymore current and the lasing becomes eratic but the lamp is stable.
The optics are all aligned ok so I have assumed the Q switch isnt driving enough.
If I turn the Q switch off, the CW beam is perfectly stable at the higher lamp currents.

I appreciate that pushing the limits reduces components life but I am having so much fun doing this !

As for columation, I think that may be a lost cause... !

You may find you need to align the qswitch to a internal physical sweet spot, where you get the best compression waves in the crystal. then adjust its angle. Sweet spot is usually a MM or so off the transducer side of the crystal. The whole mess interacts,

Usually one of the ISM bands, about 50-70 watts worth of drive, 27.125 or 68 mhz, in rare cases the matching network inside the crystal housing needs a peak for best forward power to the network of piezos that hammers the side of the crystal. If you open uo the crystal head, watch out for the tiny gold bond wires.

Overdrive gets you echos inside the crystal, which results in multiple diffracted orders and sometimes the cavity doesnt get cleanly blocked.

Laserscope usually has two settings high RF, and low RF, are you sure your not in low RF? Or is your CPU bypassed? There is a sweet spot for the PRF too, the buildup time in the yag likes to be dumped anywhere from say 5 khz to 15 khz or more. I think laserscope likes 7 khz or so. Upper storage time in ND:YAG is 800 uSec, so it can hold on to a lot of energy.

Laserman 532 can probably give you a solid procedure for positioning the Qswitch if you dont have the manual.

Is it a intra-action or neos/gooch housgo in yours ?? If neos-gooch, they will gladly send you a PDF with the details and a ATR sheet for your particular crystal from final test.

watch out that you do not accidently disable a function on the driver that slowly ramps the RF when you unblank for the first time, or a giant pulse of energy rips through the cavity and usually does damage to the doubling crystal.

If you need to check the qswitch, you can set up a table lamp about 20 feet away, look through it , and look for the diffracted orders as images of the lamp when the RF is on. increasing power =more diffraction, FM changes the angle of diffraction.

The fact that you are a RF engineer means you know dips and peaks, and poles and zeros, and means I am no longer alone here. yeah!

I'm a laid off lab guy, DC to 640 Thz. I Like to do 10 ghz ham.

PS, by uprating the cooling, does that mean you bypassed the constant temperature thermostat in the cooling loop?


Steve N8VKD

[dsli_jon]

Hey Simon -

Anymore current and the lasing becomes eratic but the lamp is stable.
The optics are all aligned ok so I have assumed the Q switch isnt driving enough. If I turn the Q switch off, the CW beam is perfectly stable at the higher lamp currents.

That (MAY-be, since I am not in front of your unit, but is most-likely...) simply your 'KTP-performance-curve' you're seeing - every crystal is a bit 'unique' in-terms-of it's 'performance' - like a 'bell curve', each will exhibit different output-levels at different lamp-currents - some are 'hot' at lower lamp-levels, some like it 'hotter' - some will even 'dip-down' in power, say, from 36-38A, then 'magically' put-out WOW-power right-at 39 or even 40A - (not that it is 'recommended' to run that high, full-time... )...

Closely monitor your 'oven temp' as you slowly ramp-up / down in current... if it dips, when you hit higher currents (as-you see the KTP 'struggling') try upping the temp to ~780-800Ω...

If it maintains 750Ω, even-at higher currents, (or whatever you set it at), you might try 'finding' a different 'sweet-spot' on the KTP crystal (ONLY IN CW-mode - NEVER DO ALIGNMENTS IN Q-SW MODE - or you can kiss your KTP-goodbye!! also, NO-MORE than 26A, when aligning...) - you might find that it 'likes it's back scratched' at a slightly different angle...

I appreciate that pushing the limits reduces components life but I am having so much fun doing this !

yeah, I can relate...

As for columation, I think that may be a lost cause... !

PM-me your email, I'll send you the 'magic 411' (as-least as far-as I have found... on collimation...

cheers
j

[LesioQ]

I Like to do 10 ghz ham.

I prefer 2.5GHz chicken
Sorry, I couldn't resist

Piotr.K

[Laserman532]

simon...define eratic, I know what eratic means but what is your laser doing? At what current does it act up, if you increase current does it become less eratic?