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K.Somiya

Interferometer Configurations. Fujihara Seminar May 2009 Kentaro Somiya Caltech. K.Somiya. Gravitational-wave detector. GW. Base line (arm) = 3~4km. LASER. Photo-detector. Proper location of mirrors to detect GWs. Interferometer Configuration. =. Detector sensitivity. total.

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K.Somiya

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  1. Interferometer Configurations Fujihara Seminar May 2009 Kentaro Somiya Caltech K.Somiya

  2. Gravitational-wave detector GW Base line (arm) = 3~4km LASER Photo-detector Proper location of mirrors to detect GWs Interferometer Configuration =

  3. Detector sensitivity total Standard Quantum Limit • Various kinds of noise • Shot noise is one of the limiting noise sources

  4. Reduction of shot noise Shot noise Phase fluctuation of photons [Quantum noise] LASER • Increase the power • Increase the signal • Inject squeezing keys of good configurations

  5. 1st generation detectors; type-I Power-recycled Fabry-Perot Michelson interferometer (LIGO, Virgo, TAMA) GW Fabry-Perot cavity (power + signal ) power signal GW power recycling (power ) Both power and signal are enhanced.

  6. 1st generation detectors; type II Dual-recycled Michelson interferometer (GEO) GW power signal GW power recycling (power ) signal recycling (signal ) Both power and signal are enhanced.

  7. Power/Signal recycling Power recycling improve the floor level Power Recycling Signal recycling Signal Recycling improve the floor level and narrower the bandwidth Frequency response of an interferometer is determined by the floor level and the bandwidth.

  8. 2nd generation detectors Nevertheless…. 2G detectors will accommodate all threes. resonant resonant resonant anti-resonant Why do we need three kinds of cavity?

  9. Resonant Sideband Extraction (RSE) [Mizuno 93] High finesse cavity (power ) (signal ) power signal decent power recycling (power ) signal extraction (signal ) This system changes the power balance

  10. Power balance heat transfer 400kW 20K 20K 400W coating substrate ~300ppm heat absorption (=0.125W) ~1W cooling capability [safety factor of 8] High finesse + low power-recycling (RSE) is suitable for LCGT

  11. Detuning RSE SR: resonant RSE: anti-resonant detune: intermediate SR Mirror detune SR Signal at a certain frequency resonates Narrow-band signal enhancement

  12. Radiation-pressure noise 1st generation detector (50W at BS, FPMI) RP noise 2nd generation detector (1kW at BS, RSE) Shot noise Standard Quantum Limit (SQL) Heisenberg’s principle High precision Back action Radiation pressure noise Reduction of shot noise (high power) Sensitivity of a broadband detector is limited by the SQL

  13. Radiation pressure in a detuned detector signal (phase) signal (phase) signal (phase+amp) laser + signal (amp) [radiation pressure] rotation due to the detuning This loop makes an optical spring and allows us to overcome the SQL

  14. Detuning in LCGT detuned (opt. for BNS) broadband SQL thermal noise Observable range for Binary Neutron Stars Broadband RSE : SN=10 at 185Mpc Detuned RSE : SN=10 at 242Mpc Better sensitivity by detuning!

  15. Broadband NSNS BHBH High Freq Variation of the signal response w/ detuning [Ballmer 07] total noise level of AdLIGO • Reflectivity of the mirrors is fixed • Changing the SRM location and the input power • Tunable for each GW source

  16. 3rd generation detector [Chen 03] Detuned Sagnac interferometer with Fabry-Perot arm cavities Baseline 5~10km ring cavity speed-meter measure x back action of p measure p no back action PRM SRM Overcoming the SQL in a broad frequency band

  17. Sensitivity curve of detuned Sagnac [Mueller-Ebhardt 09] 300ppm loss/arm 20ppm loss/arm • Overcoming the SQL in a broad frequency band • Better than other methodsin the optical-loss issue

  18. End-mirror cavity [Khalili 2005] Replacing a mirror to a cavity… anti-reso cavity less coatings more coatings total thermal-noise level decreases Configuration to reduce thermal noise

  19. Xylophone with SPI (suspension-point interferometer) • Top stage: MF 10-100Hz • Mid stage: HF 100-10kHz • Bottom stage: LF 1-10Hz Low mirror thermal noise High power Extremely high power Low optical loss + squeezing 10m Low power + very low temperature Low suspension thermal noise 10km

  20. Summary 1st generation detector 2nd generation detector 3rd generation detector • Power-recycled FP Michelson configuration • Reduction of shot noise • Broadband/detuned RSE configuration • Reaching/overcoming the SQL • Overcoming the SQL in a broad frequency band • Any ideas being welcome

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