1. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 1 The Hall A Compton Polarimeter Upgrade Sirish Nanda Jefferson Laboratory Parity Collaboration Meeting July 22, 2008

2. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 2 The Hall A Compton Polarimeter Upgrade Goal: High Power Green Fabry-Perot Cavity Twice the Analyzing power of present IR cavity  Increased in Figure-of-Merit Provide 1% beam polarimetry from 1 to 11 GeV. High precision Parity violating experiments are feasible with this upgrade New Electron Detector - High resolution silicon microstrips to improve systematic errors - Movable in dispersive plane for wide energy coverage New Photon Detector - Large single crystal GSO calorimeter - Integrating FADC for improved accuracy - Preserve counting abilities Participating Institutions: Jefferson Lab, Saclay, Syracuse, Clermont-Ferrand, Uva, Duke, Carnegie-Mellon, William & Mary Scope:

3. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 3 Electron Detector LPC Clermont-Ferrand Scope 768 ch 240  m pitch silicon  strips 4 Planes, 192 strips/plane, 1 cm spacing between planes 120 mm Vertical motion to allow coverage of Compton edge from 0.8-11 GeV New custom front-end, FPGA trigger module (ETROC) New DAQ and Analysis Software Installation in Aug-Sep 08. Commissioning during the Transversity expt Oct 08-Jan 09

4. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 4 Electron Detector Plans Installation Installation of e-detector in Aug/Sep 08 Mechanical design complete (Miller/Gavalya). Fabrication of parts in progress. Neil Wilson (Jlab) and Francois Daudon (Clermont) heading installation activities Survey and Alignment plans (Curtis) in place Checkout Control system interface (Segal/Witherspoon) in progress DAQ (Camsonne/Brossard) developed Commissioning First beam during Transversity Expt in Oct 08. Pressing need: New Electron Event Analyzer!! Requires collaboration help

5. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 5 Photon Detector Carnegie-Mellon University Calorimeter Single crystal GSO, 6  x15 cm cylinder, Single PMT High light output, fast decay time (less than 60 ns) Can do triggered counting as well as integration. GSO Crystal procured from Hitachi, under test at CMU Mechanical support/electronics in design Integrating DAQ Required for 1% polarimetry @1Gev New Flash ADC’s beam tested in Feb 08 Further tests planned this fall/winter Installation Installation planned for Spring 09

6. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 6 Green Fabry-Perot Cavity Jefferson Lab, Syracuse U Specification Intra-cavity power 1.5 kW Wavelength 532 nm Mode CW, TEM 00 CIP Spot size (  ) 65  m Locking PDH Solutions Primary: Prometheus Laser + PPLN Doubler -> High Finesse cavity »PDH Feedback to laser for TEM 00 mode lock Alternate: Lightwave IR laser + IPG fiber Amplifier + PPLN doubler -> Medium Finesse Cavity »PDH Feedback to laser

7. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 7 Optical Setup

8. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 8 Cavity in the Compton Lab Photograh: Alan Gavalya

9. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 9 Cavity Progress Power So far we are doing <100 Watts in intra-cavity power. Need more that an order of magnitude improvement! Progress Laser, Optics, Mechanics well understood Home made Cavlock feedback solution is successful in locking On demand stable locking demonstrated at low power (Abdurahim) High power locking in development Cavlock production version in implementation (Dan Sexton) Electronic noise issues being chased (Lawrence Lee) Problems Our cavity mirrors are too lossy, limiting power gain Need new mirrors with < 10 ppm scatter and absorption loss. Need clean-room to maintain low loss in mirrors

10. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 10 Cavity Plans New Mirrors We need new low loss mirrors! Mirror substrates with <0.5 Angstrom surface finish ordered from General Optics Corp. Delivery in Oct/Nov In talks with General Optics, Advanced Thin Flims (ATF), Research Electro Optics (REO), and Layertec for low loss mirror coatings Hope to finalize mirror coating contract soon Mirror Characterization MOU in development with ODU to surface map high finesse mirrors to provide SEM, AFM, and Diffusion Scatter studies of mirrors. Will give us quantitative measure of losses in cavity mirrors Existing IR Cavity Losing Power, presently at ~450 Watts Plan to replace 230 mW laser with 700 mW Boost power to ~1.3kW

11. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 11 PPLN Frequency Doubler Passive SHG with periodically poled (PP) Lithium Niobate (LN) Use IR Nd:YAG laser as 1064 nm pump Double frequency with Quasi-phase matching (QPM) of non-linear crystals e.g KTP or LN LN is more efficient that KTP Our accomplishments with PPLN Doubling QPM is sensitive to temperature We have achieved temp stabilization ~ 10 mK with home made TEC temp control Better than 20 mK temp uniformity along a 50 mm crystal Better optical mode matching of pump IR beam >> We have achieved >12%/W SHG conversion efficiency. >> Demonstrated 1 watt green power with 2.9 watt IR pump Plans Go to higher power Demonstrate locking capabilities of the PPLN Laser Progress recently stalled due do lack of man power Brian Han (W&M) is now ramping up the effort

12. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 12 Schedule Aug-Sept 08 Aug-Sep 08 March 09 Jan-Feb 10 200820092010 June-Aug 09

13. Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 13 Summary Electron detector ready for Installation in Aug 08 Photon detector development proceeding well, installation in March 09 Progress with Green FP cavity Robust cavity lock at low power has been achieved High power lock-in in development New low loss mirrors on order Cleanroom infrastructure under implementation PPLN laser @1 watt demonstrated. Further development necessary Aiming for installation of green cavity in Winter 09