1. High finesse cavity for Polarised Positron Source on ILC.
LAL – ORSAY
PLIC
Pulse Laser Injected Cavity
Brisson V., Chiche R., Cizeron R., Jacquet-Lemire M.,
Jehanno D., Soskov V., Variola A., Zomer F.,
Content of the talk
Goal of the R&D
Introduction to cavity locking with pulsed laser
Setup for a high finesse cavity at Orsay & status of the R&D
Setup of the 4 mirror scheme

2. Present R&D at Orsay (funded by EUROTEV & IN2P3:CNRS)
2 Goals:
1 operate a very high finesse Fabry-Perot cavity in pulsed regime
2 mirrors cavities Gain:
Started in sept 2005
2 reduction of the laser beam size (waist)
4 mirrors non-planar cavity
Setup started in sept. 2006

3. Optical pulse train description
Time Domain
Frequency Domain

4. Build-up process in Cavity
∆Vgr
∆φCE

5. Physical Review A, vol.69, 051803(R), (2004)
Locking of Fce and Frep PD PD PD
Physical Review A, vol.69, (R), (2004)
Cavity modes
Laser comb
spectrum

6. Pound-Drever-Hall technique

7. Optical Scheme MIRA 900P Feedback System Generator Demodulator AOM EOM
Shifter
EOM
Generator
Demodulator
Feedback System fc
fcwedge
fr mirror
fc GTI fr
Pump laser
Verdi 6W
MIRA 900P
FREP
Coarse tuning:
1. Mirror motor
Fine tuning”
1. Mirror PZT
2. AOM FC
Coarse tuning:
1.Wedge
2. GTI
Fine tuning:
1. AOM-shifter

8. Digital Feedback Scheme
8 ADC:
14 bits 105Msps
8 DAC :
14bits 125 Msps
fpga latency=60ns

9. Optical Setup at Orsay

10. Experiment setup. Laser & Cavity installed

11. Present status sept.-2006 Cavity aligned
Error signals have been measured with a small finesse cavity ( )
Error signal
Signal transmited by the cavity
Present activity: reduction of the noise of the error signal and implementation of a feedback control of the small finesse cavity
Manpower: 1 physicist, 2 ingeneers, 1 tech Full time

12. Error signal now (oct-2006)

14. 4 mirrors non-plannar cavity
Cavity vessel under construction in the LAL workshop
Cw laser diode in extended cavity config
(optical feedback forseen)
In test at Orsay since 2 weeks
Manpower: 1PhD. & 1 technician full time

15. Build (finished last week)

17. 2 mirror pulsed laser cavity
Near future
2 mirror pulsed laser cavity
Operate the feedback with finesse cavity
Then Switch to finesse (in a month)
4 mirror scheme
Start now the mode study with a laser diode