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K.Somiya

Japan 4m RSE Experiment. LSC Meeting @ Hannover Aug. 2003 Kentaro Somiya, Osamu Miyakawa, and Seiji Kawamura LIGO-G030447-00-Z. K.Somiya. Japan 4m RSE. Detuned RSE Prototype Interferometer Built in NAO Japan (just near TAMA300) 500mW LASER, 40g test masses. Vacuum chamber :

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K.Somiya

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  1. Japan 4m RSE Experiment LSC Meeting @ Hannover Aug. 2003 Kentaro Somiya, Osamu Miyakawa, and Seiji Kawamura LIGO-G030447-00-Z K.Somiya

  2. Japan 4m RSE Detuned RSE Prototype Interferometer Built in NAO Japan (just near TAMA300) 500mW LASER, 40g test masses Vacuum chamber : 3.4e-7 torr (w/o optics) 1.0e-6 torr (with optics) • Osamu came and helped us in May 2003. • Seiji moved to Caltech for 14 months from July 2003.

  3. FPMI BSR BRSE DSR DRSE SQL Specialties of Japan RSE • Low-frequency control ~ THD (3rd Harmonics Demod.) • Small test masses ~ only 40g! • Simple & Easy • With DC readout, high-freq control seems better for Ad-LIGO • Radiation pressure effect can be • observed with 40g mirrors Verification of Optical Spring

  4. Japan 4m M=40g, I=200mW, F=2000, f=0.4, r=0.89 1023 1021 1019 PRG=5 M=40kg, I=200W BRSE FPMI 100 1k 10k 100k (Hz) Transfer Function including RP Effect Using small mirrors is a big advantage to observe the optical spring.

  5. Control System L1 No PRC 17MHz L2 ls l- No L+/L- Control

  6. Double Demodulation 51MHz l- 51MHz offset 34MHz l- 51MHz BPF 17MHz L- 17MHz l- 51MHz l- 51MHz offset l- Signal Q-Phase 17MHz • Polarity doesn’t change after arms locked • Offset can be removed with appropriate demo. phase We have installed this DDM.

  7. Double Demodulation • FPMI lock with DDM • Not robust • Lock keeps less than 1 min. • Somehow polarity changes • with arm cavities Finally we decided not to use double demodulation for now.

  8. Control System (4) L1 (3) L2 (2) ls 1st demod. (1) l- Lock (1) (2) (3) (4) ( Change the polarity of l-)

  9. Lock Acquisition l- vs. BP DC Power SRMI (w/o arm cavities) ls vs. DP DC Power

  10. RSE Lock (with arms, without PR) It takes some time to lock the whole interferometer, but once locked it keeps locking as long as I want.

  11. G H VO GH VI H G Transfer Function Measurement IFO Feedback Signal Error Signal L1 (Inline) Open-Loop Transfer Function Servo VS VO L- = L1-L2 L2 (Perpend.) (We do not have L- port yet..) VI

  12. Experimental Results OLTF of detuned RSE measured in low frequency (10-10kHz) and high frequency (100-100kHz), compared with FPMI (20-20kHz). It shows differences! Let’s take the ratio of these two.

  13. Relative Frequency Response (Signal Gain) Optical Spring Detuned Peak Two peaks!!

  14. Conclusion • We confirmed the control method of DRSE with THD. • We tried Double Demodulation and gave up for the present. • We succeeded to lock detuned RSE with suspended masses. • We measured the transfer function of L-. • We can hopefully say we’ve observed something like an • optical spring effect. • There are many things to do for a better measurement.

  15. -2nd 0th +1st -1st +2nd To Be Improved • FPMI contrast should be increased. • 2nd harmonics should be resonant in SRC for DRSE. • Additional LASER injected from the end mirrors • will provide more broadband TF measurement. • L- detection at dark port is necessary. (detuned RSE w/o arms) (locked state with arms) END

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