3. Wavelength532 nm Power1500 Watts Gain15,000 Q-factor1.8 x 10 11 Length0.85 m ModeCW, TEM 00 Free Spectral Range176 MHz Cavity Band Width3.12 kHz Mirror Reflectivity99.996266 % CIP spot size ( )87 m 1) Low power Green Laser -> High Finesse cavity -> Feedback to laser PZT to lock 2) High power IR Laser + single pass PPLN SHG -> Low Finesse Cavity, Feedback to laser PZT to lock Solutions :

4. Medium and high gain cavity locking was never achieved due to inadequate locking electronics. Low gain cavity locking was robust, but the power level was much lower than what we expected. Room environment was dirty and not suitable for handling cavity mirrors. Cavity mirror storing and cleaning method wasnt correct.

5. AD5664 The first PCB version of CavLock box has been assembled (Dan Sexton) 16-bit buffered voltage-out DAC module AD5664 successfully integrated to Olimex ADuC7026 micro controller (summer student: Larry Lee) ADuC7020 miniboard has been tested and chosen as a candidate for the next upgrade of CavLock ADuC7020

6. Air flow readjusted so that the room is under positive pressure, 2 HEPA fan filters directly connected to circulated air pipe. The ceiling is covered with tiles to block the dust. A softwall frame with the total volume of 600 cf has been assembled around optics table. 3 HEPA fan filters provide laminar flux to keep the dust particles away from softwall frame.

7. #1#2#3 Transmission (ppm)2429548 Loss (ppm)10 Max Gain3811861714270 Bandwidth (kHz)14.165.903.26 ROC=0.5m, Φ=10mm, Thickness=5mm Substrate: fused silica 0.5 Å Surface RMS roughness < 0.5 Å

8. Spots are abundant on the mirror surface possibly due to bad packaging.

9. PDR PDH FFBK PDT Smooth lock didnt last very long. Oscillatory lock sustains for a long time. Noise in the locking electronics is the possible culprit. Should be able to smooth out the oscillation.

10. GoalMeasurement (Scan)Measurement (Lock) Power Injected Pi (mW)9088.2 Cavity Decay Time T_d (us)11.24N/A10.8 Cavity Finesse F=*T_d/L_c124661208311975 Cavity Bandwidth (kHz)14.114.614.74 Transmission T (ppm)242231.4226.1 Loss L (ppm)1028.636.2 Mode Match Coupling0.90.570.53 Intra Cavity Power (W)308.7173.2153.5 150 Watts For the first time we measured more than 150 Watts of intra cavity power !

11. GSI-240 is the highest finesse (~12500) cavity we have locked so far ! Achieved the highest intra cavity power (~150 W) so far ! Still need to get the peak power by improving the injection optics. Need to develop good mirror cleaning technique (it is crucial to maximize the power). Improve electronics and resolve the oscillation in the lock. Move on to next higher finesse mirrors.

13. 2 W 0.3 W BPPLN 3.5 kW 2.1 kW 900 W #1 #2 #3 Lock=, Solution= Lock= ?, Solution= Prometheus 0.1 W A #1 #2 #3 1.1 kW 700 W 300 W Lock=, Solution= Lock= ?, Solution= Prometheus