figuring out the pulse forming network of a YAG laser

[Bluefan]

I have a yag laser from a range finder, but the electronics are quite a mystery. It was way to complicated to work out completely, so I tried to figure out the pfn, pretty all I need for a start. The active q-switch circuit is glued in a case, so I won't be getting that one out soon, but first I want to have a flash. I included the circuit diagram as far as I could figure it out.

There are 4 wires sticking out, I can trace them futher into another pcb, but I think that would be the control, not the pfn. All I've drawn here is from a single pcb and the storage cap.

On the left top part of the circuit I've drawn the two coils (L1 and L2) close to eachother, these are stacked op top of eachother and probably interacting. The thing I've drawn as a fuse is a small glass component I couldn't easily measure what it was.

The inductor L3 is a coil sitting below a similar round shaped part of the first large unknown component drawn by the box.

There are 2 boxes drawn. The big one on the top connects the high voltage of the storage cap directly to the flashlamp with some fat wires and with an internal resistor to another part. The box is a single large part of the pfn which I only can measure the resistance. I can't measure inductance with my meter, so the direct connection may have a inductance.

The second one is a small part, a small metal can connected to the circuit and on the other end two connections. I have no idea what it, but I measures a practically direct connection between two pins and nothing to the other pin. I included a photo of the object.

The transformer is actually a very small black box on the pcb, I think to seperate the circuit from the control logic. I think it is used to trigger the circuit somehow, but the circuit doesn't make sense to me.

Anyone any idea how it should work? I've drawn thing with an upside, but I don't even know the polarity of the circuit, so crude testing may be dangerous.

The attachments:
- circuit diagram
- foto from side of electronics
- closeup of second "box" component with in front the small transformer
- the big "box" component with L1 and L2 visible

I you want a high-res picture of the circuit diagram, look at images.bluefan.nl/circuit_yag.png

 

[Bluefan]

I hope I understand the electonics just a bit futher.
My guess it that the big box is the secondary of the pulse transformer AND the inductor of the network. L3 is, as you can see in the photo's, directly underneath the secondary. So neat that I think it's the primary. This way C4 and C5 can discharge through L3 and produce the trigger pulse needed.
The measured short in the big box is the inductor, like it should be but not what I initially expected. I think the small box is some sort of switch to initiate the discharge of C4 and C5. D1 is some sort of protection diode, I think the indicated that I've drawn the polarity of the circuit correct, the top wire is positive.

Anyone has any comment on these thoughts? Am I completely wrong or could this be how it works?

 

[seoguy]

Sam's has a LOT of information on these things -

Sam's Laser FAQ - Preface, Introduction, What is a Laser?, Safety

including -

Sam's Laser FAQ - Complete SS Laser Power Supply Schematics

Sam's Laser FAQ - Solid State Laser Power Supplies

Sam's Laser FAQ - Commercial Solid State Lasers

They even have information on using the flash units from disposable cameras to pump a YAG rod!

I would caution, however, that all of this stuff is high-voltage and HIGHLY dangerous (i.e. - deadly ), so be sure to exercise appropriate safety precautions!

 

[Bluefan]

I regularly read sam's laser faq, a LOT of knowledge I have is from there. I know that high voltage is dangerous. I even plan on making a N2 laser, so I'll even be working with 20kV in the future. I'm very carefull with high voltage, even just line voltage. I only got zapped once by line voltage, my isolation was not as good as I tought. I learned from it, I'm now more carefull at isolating high voltage and very carefull with measuring on a live circuit. And I'll never measure around in a dangerous live circuit. I'll just connect anything I want to measure before I apply power, and watch from a distance. And turn everything of and discharge caps before doing anything on the circuit after.

I measured a bit more, and removed some errors from the design.
And, I've finally found the datasheet of the (what I now know is a) thyristor! I've attached the new circuit layout. The unknown component probably is the trigger transformer, I'm quite sure about how the circuit works now. I'll probably start testing the circuit at low voltages to see if it works.

And for the fun I attached a picture of the inside of the cavity, displaying the 6.5x80mm YAG rod and the flash lamp. Anyone knows why on the right side of the flash lamp there's a slight white color? I think it's normal, but I'm curious what it is.

Anyone else here got a pulsed YAG laser?

 

[Hemlock_Mike]

Bluefan --

Is this an SSY-1 laser you are asking about? You ramble too much.

Mike

 

[Bluefan]

This is definately NOT a SSY-1. The SSY-1 has a passive q-switch, much smaller YAG rod and a way smaller package. If it was an SSY-1, I'd already have all the info I need.
This YAG laser is from a german Siemens range finder, I bought the whole range finder assembly just to take it appart for the laser. the complete rangefinder was WAY too complicated to figure out.

Anyway I'll be making charging circuit next, I'm thinking of wiring a 9v transformer backwards and adding a voltage tripler to the output to get to nearly 1000V. The q-switch electronics are still a mystery, but I think I'll be able to fire the laser without it.

 

[Bluefan]

To dig up my old thread: I figured out the electronics of the flashlamp. But I think the q-switch is a Pockels cell, and is in the blocking state when at 0v. Does anyone here have experience with driving Pockels cells? My first approach would be finding the voltage that opens the Pockels cell, just by applying a DC voltage and see if I get any light out. It would make long pulses, but that's a start. What voltage for the Pockels cell range can I expect?