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The High-finesse Fabry-Perot Cavity

The High-finesse Fabry-Perot Cavity. Abdurahim Rakhman Advisors: Prof. Paul Souder, Dr. Sirish Nanda PREx Collaboration Meeting 12/07/2007. Outline. Compton Upgrade at Jefferson Lab Principles of the Fabry-Perot Cavity Cavity Parameters & Prometheus Laser Mode Matching Cavity Locking

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The High-finesse Fabry-Perot Cavity

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  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:   e- e- Z

  4. λ=1064nm λ=532nm 8GeV 8GeV 4GeV 4GeV 1GeV 1GeV Compton Upgrade: 0.85 Gain: 700015000

  5. Fabry-Perot Cavity: Circulation Incident Transmission L Reflected r1 r2 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: 99.987±0.001% G=6,000 F=18,000

  6. Prometheus Laser: Innolight GmbH, Germany ▪809 nm Pump Diodes ▪1064 nm Nd:YAG ▪532 nm SHG via PPKTP 2 W0.1W

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

  8. Mode-Matching: • laser mode (beam) should match • the cavity resonator mode • beam waist at the center should • match the natural waist of the cavity L3 L2 cavity waist L1 0.5787 TEM00 mode incident reflected mode matched

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

  12. Digital CavLock Electronics (Homemade): 4” previous current

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

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

  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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