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The High-finesse Fabry-Perot Cavity Abdurahim Rakhman Advisors: Prof. Paul Souder, Dr. Sirish Nanda PREx Collaboration Meeting 12/07/2007.

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Presentation on theme: "The High-finesse Fabry-Perot Cavity Abdurahim Rakhman Advisors: Prof. Paul Souder, Dr. Sirish Nanda PREx Collaboration Meeting 12/07/2007."— Presentation transcript:

1 The High-finesse Fabry-Perot Cavity Abdurahim Rakhman Advisors: Prof. Paul Souder, Dr. Sirish Nanda PREx Collaboration Meeting 12/07/2007

2 Outline Compton Upgrade at Jefferson Lab Principles of the Fabry-Perot Cavity Cavity Parameters & Prometheus Laser Mode Matching Cavity Locking Conclusions and Future Plans

3 Compton Polarimeter: Z e- e-

4 Compton Upgrade: Gain: GeV 4GeV 1GeV λ=1064nm 8GeV 4GeV 1GeV λ=532nm 0.85

5 Fabry-Perot Cavity: Incident Reflected Circulation Transmission r1r1 r2r2 L Previously locking was successful with a G~2,000 Current Cavity Mirror: Los Gatos Research, Inc. (LGR) Type: Plano-Concave Radius of Curvature: 1 m Reflectivity: ±0.001% G=6,000 F=18,000

6 Prometheus Laser: 2 W 0.1W Innolight GmbH, Germany 809 nm Pump Diodes 1064 nm Nd:YAG 532 nm SHG via PPKTP

7 Prometheus Laser Profile: Beam is highly elliptic, circularization is needed Before After

8 Mode-Matching: incident reflected mode matched laser mode (beam) should match the cavity resonator mode beam waist at the center should match the natural waist of the cavity TEM00 mode cavity waist L1 L2 L3

9 OptoCad: FORTRAN90 program for tracing Gaussian beams computes the parameters of the optical system Green cavity optical layout by OptoCad

10 Complete ray tracing by OptoCad (in development):

11 Pound-Drever-Hall (PDH) Locking Scheme: Photo detector Beam Splitter Cavity Oscillator Phase Shifter Mixer Low Pass Filter 0 Tunable Laser PID- Regulator Error signal Detect phase of the resonance from reflected light Feedback to tunable element to stay locked to resonance

12 Digital CavLock Electronics (Homemade): 4 current previous

13 Search / scan / lock logic: Successful locking with low gain cavity Transmission Reflection Fast Scan Slow Search Signals of LGR cavity Reflection Error Signal Transmission

14 Cavity Locking: 2 sec level lock, only with fast PZT feedback, but unacceptable due to large fluctuations reworked electronics, 40 msec level short lock with fast PZT feedback only Feedback loop tuning in progress Reflection Error Signal Transmission Reflection Transmission

15 Conclusions: Prometheus Laser has been reprofiled Mode matching of LGR mirror has been accomplished Complete ray tracing of the system by OptoCad is in development Cavity feedback loop tuning in progress Short duration lock has been achieved Thank you !

16 Cavity Parameters: Free Spectral Range : Gain: Finesse: Band Width:


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