The Hall A Compton Polarimeter Upgrade

1. The Hall A Compton Polarimeter Upgrade Sirish Nanda Jefferson Laboratory Parity Collaboration Meeting July 22, 2008

2. The Hall A Compton Polarimeter Upgrade Goal: Provide 1% beam polarimetry from 1 to 11 GeV. High precision Parity violating experiments are feasible with this upgrade Scope: • 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 High Power Green Fabry-Perot Cavity Twice the Analyzing power of present IR cavity Increased in Figure-of-Merit Participating Institutions:Jefferson Lab, Saclay, Syracuse, Clermont-Ferrand, Uva, Duke, Carnegie-Mellon, William & Mary

3. Electron Detector LPC Clermont-Ferrand • Scope • 768 ch 240 mm pitch silicon mstrips • 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. 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. Photon DetectorCarnegie-Mellon University • Calorimeter • Single crystal GSO, 6fx15 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. Green Fabry-Perot CavityJefferson Lab, Syracuse U • Specification • Intra-cavity power 1.5 kW • Wavelength 532 nm • Mode CW, TEM00 • CIP Spot size () 65 m • Locking PDH • Solutions • Primary: Prometheus Laser + PPLN Doubler -> High Finesse cavity • PDH Feedback to laser for TEM00 mode lock • Alternate: Lightwave IR laser + IPG fiber Amplifier + PPLN doubler -> Medium Finesse Cavity • PDH Feedback to laser

7. Optical Setup

8. Cavity in the Compton Lab Photograh: Alan Gavalya

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. 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. 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. Schedule 2008 2009 2010 Aug-Sept 08 Aug-Sep 08 March 09 June-Aug 09 Jan-Feb 10

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