Arc Lamp driven green laser question

[badger16485]

Hello all,

I have a Laserscope Aura that I currently have in bits - I appreciate the rules on big greens and happy to speak to someone privately. If this post is too detailed, I can remove it.

The LCB is dead and I have no way of replacing / calibrating / setting up, so i'm attempting to put together a PCB to replace this and trying to figure some things out:

Arc Lamp driver / Starter - I have a basic datasheet (Analog Modules 590-5 & 592-T)

- There is two 4 Ohm 50Watt resistors in series with the Neutral to the Arc lamp driver, I originally assumed this was some form of soft start resistor, but the Power distribution board doesn't appear to short out these resistors. At full power these must be dissipating a lot more than the rated 50watts (assuming 10A @ 230Vac in), is this right?
- The majority of the signals to the driver are isolated apart from the Lamp current, presumably this is why there is a CT on the Power distribution board to measure the supply current?
- There is two wires connected to the relay coil on the starter PCB, which are cabled to the LCB. Presumably, this is to allow the LCB to trigger the starter (rather than the Arc driver board)?
- Does anyone have experience with these ARC Lamp drivers, are they reliable ?

The KTP Crystal:
- Two wires for the heater, approx 30Ohms.
- Two wires for the temp sensor, 7kOhms @ 18C (ish), guessing a 5K NTC?
- No idea on operating temperature, seen information suggesting temperatures anywhere between 50 - 80C?

PTEK Q-Switch driver, 27Mhz, 30Watts.
- 24V input, with a aux 5V output (Derrived from an internal 5V Regulator)
- Has a SMA RF output cabled to the Q-Switch
- Has a BNC connector marked Blank.

Shutter & Power measurement
- Shutter appears to be 12VDC driven
- Photodiode behind and in front (presumably as a safety measure) of the shutter.

Can't find any information about PTEK or their drivers. The driver looks very basic - 27Mhz Osc and Power amplifier. I'm guessing (will have to experiment with a 50Ohm load, scope and signal generator) there's no initial pulse suppression and all management of that is done by the LCB? - i.e. RF is ramped off first to prevent a large pulse and then driven with a TTL square wave?

The laser is specified to do 15W CW @ 532nm and 160Watt pulsed (1ms), it's not clear to me how the 160Watt pulses are achieved.

Ultimately, I would like to use this for marking / engraving, which would involve me controlling power / modulating the beam somehow.

- Can ARC Lamps be modulated in this manner without damaging them?
- Presumably, at laser on, the ARC Lamp is started an held at a current below lasing threshold (simmering?) and ramped.
- The current duty cycle is 50% with a max on time of 3 Minutes. The manufacturer clearly put safe guards in to measure water temperature and also included an over pressure switch. Is the duty limitation related to the capacity of the water cooling system - i.e. if upgraded with a larger cooling system, could the system be run for much longer periods, or is there other limitations to consider?

Any comments / suggestions / help is greatly appreciated.

[mixedgas]

Arc lamps generally do not like wide range modulation, usually just flipping between idling and some modest current level is ok. If modulated, it is a ramped step up in current, but not at "fast blanking:
150W pulses use q-switch gated storage in the rod coupled with up-driving the lamp briefly . (Forget it until you are so NOT attached to the laser as to be willing to risk parts learning.)

A quick google suggests Aura and her 1064 Nm sister Lyra are long pulse lasers, and run in short bursts of 500 milliseconds or less at low rep rates.. (Starpulse) Plus have a CW option.

https://www.accessdata.fda.gov/cdrh_...df/K990903.pdf

Analog Modules parts are the professional cat's meow. They will support you.

Leave the Q-switch in system, it should weakly lase CW green at a fraction of a Watt or more with the q-switch driver disconnected. Watch the coolant temperature....

EDIT UPDATE Just found this.....

https://www.youtube.com/watch?v=yQI3mb5_A5A Update, Video says Briggs... So. Whoya gonna call.. He hasn't posted on PL in a long, long time, but is a good guy. I saw Badger and assumed your our UK member Badger.. If elsewhere let me know. Find Daniel Briggs in the laser universe.

ASK Analog Modules why the resistors exist.

Find a ham radio operator with a 50 ohm dummy load and power meter for VHF low to help you characterize the Q switch driver. A more modern strategy is aim a HENE down it with a mirror and watch what happens as you trigger the blanking gate. HiENE because you need some semblance of polarization. AO devices are pretty position sensitive, so this may require "fiddling".

If possible don't remove anything from the resonator and make sure you have ultrapure water around the lamp so the water doesn't conduct, if required. I'm assuming you have all the water goodies in the unit. It may take a day or two to get the resistivity down if needed. A conductive coolant and submerged lamp electrodes will generally pop the lamp, or the arc power supply, or the reflector, or all three.


Not familiar with AURA, just its bigger KTP cousins. Aura may be limited duty cycle, needing a cool down based on how hard you drive the lamp etc.

This thread is worthless without pictures. ALSO my suggestions MBG = my best guess.... My med friend doesn't have an Aura manual on his bookshelf that I have seen, but I will call him and ask tomorrow.

Aura needs some sort of security key to run, the medical laser forums have techs asking for service keys.

OD 6 at 1064 / 532 Goggles please.

[badger16485]

Hi Steve,

Cheers for the message. I am from the UK and I did have a PL login a few years back. I briefly spoke with Daniel Briggs over a HPS system. I gave up on that owing to the cost of replacement diode stacks ! I'll see if I can get ahold of him for a chat!

I've attached some images of the laser and safety googles !

I have a 50Ohm paint can load, good scope and waveform gen at work, so can feed some trigger pulses in to the Q-Switch driver and get some screen caps. My understanding is that it'll ether have some first pulse supression or it will accept a 0-5v (or similar range) analog level in and output 0-100% RF?

Presumably, without any form of first pulse supression, you would need to run the Q-Switch BEFORE bringing up the lamp current?

I'll contact Analog modules and see if they have anything further than the datasheet:
https://www.analogmodules.com/adminc...heets/592t.pdf
https://www.analogmodules.com/adminc...heets/591a.pdf

I've found a source for a new Lamp, should I get this running. Guessing lamp life of around 400hrs for a Krypton ARC Lamp from what i've read? I see that their failure mode can be catastrophic, so a new lamp and hour counter is probably the way to go after testing...

The cooling system is intact and works, has a DI cartridge. Replacement cartridges appear to be expensive, so i was planning on installing a standard filter chamber and filling with DI-Resin, refilling with store bought DI water and running the cooling system for a while, then measure the resistance.

Ref the security key / service key - the LCB is totally dead - First power on a few Tantalum caps failed and magic smoke escaped. Everything else appears to be intact. If I get this to run, it will be by putting together a controller myself.

Best

Steve

[mixedgas]

iIs there a module marked "oven industries " to control the KTP temp? That crystal gets ran/run hot to prevent greytracking. It's also a doped KTP, to prevent Greytracking.

First pulse, Giant Pulse can also be suppressed by starting Q Switch at low lamp current and ramping up current , or by lasing CW first. Rod storage time is considered 256 microseconds in ND:YAg. Which is close to what I've measured in the past. Start lamp at low currentvwith beam diverted by Qswitch, leave gated on for say 500 uSec or more,
switch qswitch to internal clock if so equipped.

It may self clock, the q-switch that is. Laserscope used to use q-switch drivers with a bunch of internal optoisolators for programming, I have no idea what that driver is.

There is an optimal frequency for the PRF for stable green. It's like Goldielocks chair, too high is bad, too low is bad,bad, and then there is just right.

Welcome back to PL!

Steve

[badger16485]

Hi Steve,

The KTP crystal heater is part of the LCB. There's a section of the PCB with a power transistor and a PWM IC with KTP "Drive" and "Temp" test points. I was going to either build or buy a KTP heater.

The Q-Switch driver appears to want a 5V logic level input only and appears to be Active Low.

I've attached the waveforms. Doesn't look like it has any functionality other than RF on / off.

[mixedgas]

I love modern digital storage scopes when dealing with controls issues. Thank you for the graphics. On a 1-10 the modulation on that is a 7 or so. Lots of ringing and decay on the RF.

OK, you have an on/off q-switch driver, but you knew that. So your going to need to figure out how many Kilohertz rep rate to modulate the Q-switch gets you best average power, and modulate the lamp current at startup to avoid any giant pulsing. Thus keep the shutter. If there is a mechanical intracavity shutter, that can help too. But unless your controlling the q-switch and lamp before you open that intracavity shutter, you could giant pulse.

The heater is in the crystal mount, as is the temperature sensor, probably a platinum resistance sensor or a thermistor for sensing.



Steve

[badger16485]

Hi Steve,

Thanks for the reply. The screen grab is very useful on the newer scopes, great for documenting things.

I do have a Landwher Q-Switch driver out of a HPS. This might be a better option. It's 27Mhz (matching the existing driver) but much higher output. According to the datasheet it supports analog and ttl modulation and the power is adjustable right the way down to a few watts, so it should be a drop in replacement if i reduce its power down to 30 Watts.

Analog Modules were very helpful and have given me some application notes to be getting on with. It has been factory modified to support up to 55A Pulsed. Presumably that is to support pulsed operation (1ms 160Watt pulses). Driving it seems straight forward - Feed it line current, provide a enable signal, pulse the Arc start relay to trigger a lamp start. The current control is done via a IL300 linear opto, with 2ma = 3A current to 11ma = 30A current.

I think over the next few weeks i'll put together a heater controller for the KTP and see if I can get the ARC Lamp driver to work and see if I can make it lase.

Any tips for first power up? I was going to run the cooler and measure the DI water conductivity, when low enough start the ARC lamp at low current and see about getting an old camera to spot any 1064?

[mixedgas]

Its a V-fold.

The trick is measuring the water conductivity. I have personal experience of cracking a cavity reflector and lamp when the handheld indicator says good to go but the water wasn't.

Let the water system run for a few days, grocery store or drugstore DI isn't that good. You need something greater then 8 MEG.

Might be two gold plated probes in your coolant some where. They are excited with kilohertz or more AC so you don't get electrolysis.

You have a "V" fold from looking above, I cant find a it looks like, so....

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.allen.dj/laserscope/Laserscope_800_Service.pdf

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.allen.dj/laserscope/Laserscope_Patent.pdf

What it says about tuning IR with two power meters, using leakage through the mirrors, it means. Peaking green is the last step.,

I'm looking for a 700 series manual on line, but no luck so far.

Steve



Steve