Coherent Sapphire power output problems...

[alesniak]

I recently got a couple used Coherent Sapphire 488-20 lasers, one works great, the 2nd unit has some really strange behavior, initially it will power up and output
full 20mw of power, but after about 30sec to a minute it will just shut down, and restart but will only output about 3mw of power. I pretty much assume the pump diode
is on it's last legs but was wondering how much more juice I could squeeze out of this unit, it appears still capable of 20mw output verified with a lasercheck question
is how to disable or override whatever safety mechanism is causing the laser to shut down, wondering if anyone has any experience hacking these lasers and controllers?

I did do some research and the closest thing I found that was helpful is this page. (http://redlum.xohp.pagesperso-orange.../Sapphire.html)
I attempted to increase the headroom for the diode current hoping it would help, I tried 0.2ohm and 0.5ohm resistor in parallel with the sense resistor, but it didn't
appear to change anything, same problems.

I also have serial control over the laser, here is a log of basic startup and operation behavior.

Sapphire:0-> ?lt
Sapphire 20mW
Sapphire:0-> ?wave
488
Sapphire:0-> ?sv
6.710
Sapphire:0-> ?hh
  3591:52
Sapphire:0-> ?maxlp
22.000
Sapphire:0-> ?minlp
0.500
Sapphire:0-> ?nomp
20

Sapphire:0-> L=1
Sapphire:0-> ?p
19.990
Sapphire:0-> ?c
1.748

<-----------     laser shuts off (about 30sec of full power output)

Sapphire:0-> ?ff
0
Sapphire:0-> ?FL
Fault(s):
        None

<----------- turn main power off/on
		
Sapphire:*-> ?p
0.814
Sapphire:*-> ?sp
20.000
Sapphire:*-> ?c
0.008
Sapphire:*-> ?c
1.703
Sapphire:0-> ?p
20.000
Sapphire:0-> ?c
1.710
Sapphire:0-> ?c
1.709
Sapphire:0-> ?c
1.710
Sapphire:0-> l=0
Sapphire:0-> ?dt
19.997
Sapphire:0-> ?bt
22.041
Sapphire:0-> ?c
0.009
Sapphire:0-> ?bt
23.185
Sapphire:0-> l=1
Sapphire:0-> ?c
1.738

<--------------- 5sec full output then shuts off

Sapphire:0-> ?c
0.008
Sapphire:0-> l=1
Sapphire:0-> ?p
20.000

<--------------- 3sec full output then shuts off

Sapphire:0-> l=1
Sapphire:0-> ?c
1.800
Sapphire:0-> ?p
1.990
Sapphire:0-> ?p
2.157
Sapphire:0-> ?p
2.324
Sapphire:0-> ?ff
0
Sapphire:0-> ?FL
Fault(s):
        None

<-------------- laser stays on now, but with only 2.3mw output power

I will continue to probably mess with the system untill I kill it, might learn a thing or 2 about these lasers in the process, I'll post my findings along the way if I make
any progress... any input or suggestions is appreciated! thanks in advance...

[Jem]

PM Phil Bergeron, aka 142Laser. He may be able to help you

[alesniak]

Thanks Jem for the info, I will send him a PM.....

[alesniak]

here are some more results for those interested, I did make progress by modifying the current sense resistor.

default resistor is 0.015 ohm, I added 1x 0.05ohm as well as 2x 0.05 ohm and 3x 0.05 ohm in parallel to offset the sensed current.

0.015 ohm = 2.7mw max output
0.015 ohm + 1x 0.05 ohm = 0.0115 ohm = 6mw max output <--- now we're getting somewhere
0.015 ohm + 2x 0.05 ohm = 0.0093 ohm = 15mw max output <--- that's more like it, that's pushing it a bit about 20-25% more current?
0.015 ohm + 3x 0.05 ohm = 0.0078 ohm = eratic behavior >15mw turns beam off but controller thinks it's still on, (thought it killed it... luckily powcycled and all still works)

right now I'm pretty happy going from 2.7mw to 15mw, but since this is a experimental throw away unit, still curious on other options since I have seen it output >20mw for
about 30-40 sec before.. so must still be some other things to explore..

the power up sequence is a bit strange with the modified current resistor, system powers up to set power, but displays really low current draw, after about a minute it
shuts down, takes about 3 restarts of the beam each time will turn off after a few sec but each time it seems to try adjusting itself until after the 3rd or 4th start it
reaches set power then shows a much higher current draw but now is completely stable.

here's another log with the 2x0.05ohm resistors in place.

Sapphire:*-> ?sp
10.000
Sapphire:*-> ?c
0.009
Sapphire:*-> ?f
0
Sapphire:*-> ?fl
Fault(s):
        None
Sapphire:*-> ?p
10.000
Sapphire:0-> ?c
0.975
Sapphire:0-> ?c
0.977
Sapphire:0-> ?p
10.000

<------ 45sec laser shuts off

Sapphire:0-> ?c
0.984
Sapphire:0-> ?c
0.009
Sapphire:0-> l=1

<------ 5 sec laser shuts off

Sapphire:0-> ?c
0.985
Sapphire:0-> l=1    
Sapphire:0-> l=1
Sapphire:0-> l=1

^^^^^ --- laser shuts off instantly but does a strange power ramp during power up
          finally after 3rd try it stabilizes and now shows larger current draw.
		  from here on laser power is stable.. 
		  
Sapphire:0-> ?c
1.627
Sapphire:0-> ?p
10.010
Sapphire:0-> ?p
10.010
Sapphire:0-> ?c
1.565
Sapphire:0-> p=13
Sapphire:0-> ?bt
23.757
Sapphire:0-> ?p
13.127
Sapphire:0-> ?c
1.731
Sapphire:0-> ?p
13.000
Sapphire:0-> ?c
1.723
Sapphire:0-> ?c
1.723
Sapphire:0-> ?c
1.604
Sapphire:0-> ?p
13.000
Sapphire:0-> p=14
Sapphire:0-> ?c
1.661
Sapphire:0-> ?p
14.000
Sapphire:0-> p=15
Sapphire:0-> ?c
1.739
Sapphire:0-> ?p
15.000
Sapphire:0-> ?p
15.000
Sapphire:0-> ?p
15.000
Sapphire:0-> ?p
15.000
Sapphire:0-> l=0

[mixedgas]

things to explore..

the power up sequence is a bit strange with the modified current resistor, system powers up to set power, but displays really low current draw, after about a minute it
shuts down, takes about 3 restarts of the beam each time will turn off after a few sec but each time it seems to try adjusting itself until after the 3rd or 4th start it
reaches set power then shows a much higher current draw but now is completely stable.

Sounds like a temperature issue, diode cooler or crystal heater.

Steve