285 nm-Laser (S-MOT)

The 285 nm Laser consists of a two-stage frequency doubled, raman-fiber-amplifier MOPA. The raman-fiber-amplifier is seeded by a diode laser.

• Laser-Diode current: 280 mA @which settings?
• Seed power (is displayed in the FLPM RMU CCT 1.1.0.0 program): ~ 20 mW

• Enable main-switch. Now set the key to standby.
• Wait for the LED to change the color from orange to green to orange (~15 seconds after turning on). Turn the key now.
• Start the program FLPM RMU CCT 1.1.0.0 and select the checkbox of Laser Enable.
• The Power Setpoint must stay at 0.500 W
  • Optimize fiber coupling to Iodine Spectroscopy. Transfer-efficiency > 70%
• Change Power Setpoint for 285nm SHG operation
  • 2 - 2.500 W for 100-150 mW directly after 285 nm SHG.
  • Do not exceed much more than 3.5 W
• Flush the SHG with oxygen, by opening the bypass for roughly 10 seconds.
• Scan the SHG and optimize the incoupling and crystal position
• Lock the SHG, the voltmeter should display a value around 115 mV (@ 2 W Power Setpoint)
• Activate the powerstabilization

• Unlock the laser in DigiLock
• Now just turn off the main-power on the laser
• Disable oxygen to 285nm SHG.

• Start DigiLock-Module Server and connect to S-MOT-Laser
  • Push Scan on and AutoLock
  • Change the Offset Value to 0 V
  • Change the frequency with the piezo on the toptica rack electronics to be close to the iodine resonance (check with wavemeter)
  • Change the Setpoint (under AutoLock) to be in the middle of the error signal. Check, if the crosshair snaps to the slope.
  • Move the crosshair to the second slope, rightclick on press PID: Lock to Slop.

• Troubleshooting
  • If signal in DigiLock-Software does not update/ signal is frozen → click the sampling checkbar to activate
  • If signal in DigiLock-Software does not show the usual error-signal at correct frequency, but is saturated at left and right edge of the frame (see picture) → Check the ref input for the lock-in-amplifier (near the iodine spectroscopy). Probably the input signal is too low. It should be slightly higher than 2 V (~2.2V works fine).

The 285nm SHG was build by Jan Friebe and is described in his diplomathesis.

• Outputpower after cube to 285 nm-SHG: ~ 1.2 W @ 2.5 W 1140nm pump
• Operationpower: < @ 3 W
• Max outpupower: ??? W @ ??? W

• Infront fiber: ~ 38 mW
• After fiber: ~ 29 mW @ 0.500 W (= 400 mV @ 0.500 W) [efficiency ~ 70 %]

• After fiber: ~ 100 mW
• At iodine cell: 20-40 mW

• Outputpower: ~ 100+ mW @ 2.000 W
• Stabilized power (infront AOM): 80-90 mW
• Power behind the AOM: 43 mW @ 2.000 W (efficiency ~ 50 %)

• Power for the Zeaman-slower: 10 mW

• Power behind the mystical mirrow: 30 mW