Greetings! I have an old Verdi V8 (2007 vintage with 2 FAPs) with power locking issues that I'm hoping someone on here might help diagnose. In light control mode it gets up to 4-5W when set to 8W, but is not stable (varying up to 20% on the scale of minutes) and always displays "Laser Seeking" at all power settings I've tried, despite all the servos being locked and no faults. Also, the displayed current (~20.3A) does not change more than a few tens of mA as the power setting is adjusted through its entire range. The LBO (151.7), diode(25.4/25.5), vanadate(30.0), and etalon(29.2) temperatures are stable and seem nominal.

However, when in the jumper-activated service/current-control mode, I can get it to stably output up to ~10W at diode currents of 21.09 and 21.56. I observed that as the current is manually ramped up in 10mA increments, the power jumps suddenly from ~0.5W to ~8W at ~21.7A, and when the current is manually ramped down, it drops equally suddenly from ~7W to ~0.2W at ~21.2A, so there is ~0.5A of hysteresis. Also, there is a discrepancy of 6-8% between the current setting on the panel and the diode current readings (e.g. diode current readings of 21.09/21.56 at 10W correspond to a setting of 23.00A).

Since the laser produces up to 10W in current mode, it seems there's nothing wrong with the FAPs, LBO or etalon settings. Instead, it seems to me like there might be some current offset/gain errors that drifted out of range of the output power control electronics.

I hope I can get it to work in light control mode again since I'd like to use it not just for pumping, but for experiments requiring coherence, stability, and low noise.

Thanks for any ideas!