Wavelength 532 nm

Power 1500 Watts

Gain 15,000

Q-factor 1.8 x 1011

Length 0.85 m

Mode CW, TEM00

Free Spectral Range 176 MHz

Cavity Band Width 3.12 kHz

Mirror Reflectivity 99.996266 %

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 :

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 wasn’t correct.

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

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.

#1 #2 #3

Transmission (ppm) 242 95 48

Loss (ppm) 10 10 10

Max Gain 3811 8617 14270

Bandwidth (kHz) 14.16 5.90 3.26

ROC=0.5m, Φ=10mm, Thickness=5mmSubstrate: fused silica Surface RMS roughness < 0.5 Å

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

PDR

PDHFFBK

PDT

Smooth lock didn’t 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.

Goal Measurement (Scan) Measurement (Lock)Power Injected Pi (mW) 90 88.2 88.2Cavity Decay Time T_d (us) 11.24 N/A 10.8Cavity Finesse F=∏*T_d/L_c 12466 12083 11975Cavity Bandwidth (kHz) 14.1 14.6 14.74Transmission T (ppm) 242 231.4 226.1Loss L (ppm) 10 28.6 36.2Mode Match Coupling 0.9 0.57 0.53Intra Cavity Power (W) 308.7 173.2 153.5

For the first time we measured more than 150 Watts of intra cavity power !

• 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.

2 W 0.3 WB PPLN

3.5 kW

2.1 kW

900 W #1

#2

#3

Lock=✔, Solution=✘

Lock=?, Solution=✔

Lock=?, Solution=✔

Prometheus

0.1 WA

#1

#2

#31.1 kW

700 W

300 WLock=✔, Solution=✘

Lock=?, Solution=✘

Lock=?, Solution=✘

Prometheus