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Reconfigurable Laser Servo
Product Manuals - https://www.vescent.com/manuals/
Ramp IN / OUT
The Laser Servo is shipped with the Ramp in MASTER MODE. In this configuration, the RAMP IN / OUT
is an output of the maximum ramp signal, generated internally. Removing the side-panel RAMP
MASTER / SLAVE jumper will put the Laser Servo in slave mode. In this configuration, RAMP IN / OUT is
an input of an external ramp signal. When the LASER STATE is in RAMP MODE, the SERVO OUTPUT is
an attenuated version of the input to RAMP IN / OUT. The attenuation is controlled by the RAMP AMP
knob. If controlling multiple lasers with multiple D2-125's to sync the ramps, one D2-125 must be in
master mode and the rest in slave mode with all the RAMP IN / OUT signals connected. In this way
each laser will sweep off a synced signal and only one oscilloscope trigger is needed for all the lasers.
The Ramp I/O has a bandwidth of roughly 50 kHz.
DC Offset Input
This signal is attenuated by a factor of 10 and summed into the DC ERROR. Inputting a square wave
into the DC OFFSET INPUT jumps the laser lock point and can be used to measure the closed-loop
transfer function of the laser system. It has a bandwidth of about 300 kHz (-3 dB point). The maximum
voltage at this input should be no more than ±10 V (±1 V of DC offset).
Laser Jump Amp (BNC)
The LASER JUMP AMPLITUDE is an analog signal that is used to jump the frequency of the diode laser.
See preceding sections on RELATIVE JUMP and ABSOLUTE JUMP for a full explanation.
Laser Lock Troubleshooting
Most laser locking problems can be attributed to the following:
Gain set too high (or too low). Reduce the coarse and fine gain all the way and try locking.
Increase the coarse gain by one click at a time.
Gain sign wrong (trying to lock to the wrong slope).
Make sure the oscilloscope is triggering to positive slope
.
Make sure oscilloscope is not in inverting mode.
Make sure your desired lock-point has a positive slope.
If all else fails, flip the gain sign and try again.
Note: sometimes the laser will lock even if the slope is wrong because there are legitimate lock-points
nearby. This can fool you into thinking you are locking to the proper spot.
DC OFFSET not adjusted properly.
When monitoring DC ERROR make sure you are not AC coupled on the oscilloscope!
When locking to spectroscopy, ramping fast through the transition can change the DC
value on the scope (due to atom transit time through laser beam coupling to optical
pumping rates). Reduce RAMP AMP towards zero on the desired transition until the DC
value is not affected. Adjust DC OFFSET if necessary.
Loop Filter Too Fast. Try turning off the differential feedback and only use one integrator.
Then try slowing down your integrator. If you get a lock, you can then put back double
integration and the differential feedback.
The ramp center is not located at the center of the oscilloscope. When adjusting the
