Optical Cavity construction at LAL 2000 : polarimeter at HERA 2-mirror cavity cw ND:YAG laser, F=30000 ( ~ ) 2005 : Ti:sapph pulsed laser locking to a F=30000 cavity ( ~ ) 2010 : 4-mirror non planar cavity installed at KEK, pulsed laser (Yb fiber) F=3000 2010 : 4 mirror planar cavity foir ThomX (design construction end 2012) ( ~ )
2-mirror cavity at HERA (polarimetry) Finesse =30000, cw ND:YAG laser Tube protons In 2000
HERMES à 100m ZEUS 1km
From 2006 Still used From 2006 Still used At LAL we have a Ti:sapph oscillator / 2 mirror cavity Finesse = (MIRA : 800nm, pumped with a green laser beam)
5 ATF e - beam Injection laser 2 flat mirrors 2 spherical mirrors laser/beam Interaction point Angle laser / e - beam= 8° Non planar 4-mirror at ATF (circularely polarised eigen modes) Non planar 4-mirror at ATF (circularely polarised eigen modes) ATF beam pipe: 5mm slit…
6 2 flat mirrors 2 spherical mirrors e-e- laser Mirror positioning system Invar base to ensure length stability Mounting in class 10 room 12 encapsulated Motors R. Cizeron
Gimbal θx θy Actuator Piezo Mounting Z Translation on 3 balls θx θy Ring Piezo Spring ring Mirror
8 Vacuum inside ~3x10 -8 mbar without baking (in situ) Vacuum inside ~3x10 -8 mbar without baking (in situ) Vacuum vessel for ATF
9 Implementation at ATF Pulse Motor Port for Up-Down Move Pulse Motor Port for Horizontal Move From Hirotaka-san Assumed ATF Beam Line ATF table mount system (~1µm precision) used for spatial laser and e - beam matching Electron beam pipe Class 100 air flow KEK 2-mirror cavity Cavity Finesse=3000
10 Numerical Pound-Drever-Hall feedback Rétroaction on laser frequency 10 Clk = 100 MHz 8x ADC 14 bits 8x DAC 14 bits => Filtering => 18 bits / 400 kHz FPGA Virtex II Clk = 100 MHz 8x ADC 14 bits 8x DAC 14 bits => Filtering => 18 bits / 400 kHz FPGA Virtex II We are developing our own card for ThomX optimised for ‘fast’ feedback
36mm 24mm Prototype of nonlanar 4 mirrors resonator (low finesse) Check the general astigmatism mode shape/propagation ( Arnaud, Bell Syst. Tech. ( 1970)2311 ) Ok but strong abherations:non-parxiale corrections In the strong divergent regime 50cm