Cryogenic Xylophone Kyoto May Kentaro Somiya Waseda Inst. for Adv. Study Collaboration work with S.Hild, K.Kokeyama, H.Mueller-Ebhardt, R.Nawrodt, P.Puppo, etc.

Xylophone Single Low-T High-power IFO Problem in cooling Xylophone Cryogenic Low power + Room-T High power ET-LF: 10K, 20kW, Silicon, DRSE + 10dB SQ ET-HF: 290K, 3MW, Silica, BRSE + 10dB SQ Heat absorption via suspension fiber

An issue in ET-HF Thermal lensing TCS noise Parametric instability heat problem 1 st generation detector: ~30kW in arm 2 nd generation detector: ~800kW in arm ET-HF: 3MW in arm Can we really realize such high power? RSE Squeezing

Contents of talk Proposal of cryogenic ET-HF Suspension-TN issue Substrate-TE issue Suspension-TE issue Optimization of ET-LF

Cryogenics to avoid the heat problems 1.Almost no thermal lensing 2.Room to reduce beam radius calculation by M.A.Arain ~0.03% deviation of T ~50km ROC of lensing Same TN with small beam Less overlap of opt modes PI is eased calculation by K.Yamamoto

Can we cool down the 3MW IFO? 5K 10K 1ppm absorption per mirror -> 3W  3cm Silicon fiber absorbs only 200mW Susp TN limits the sensitivity Solutions 1.Ribbon suspension 2.Increase test-mass temperature ~ thin in longitudinal direction ~ heat flow increases increase But thermoelastic noise becomes high.

Substrate TE noise ET-HF sensitivity at 100Hz Thermal expansion is zero at T=18K,121K. TE noise Big susp TNBig TE noise Free from both problems at around 121K

Thermoelastic noise of suspension 5K 121K Silicon ribbon w=1cm, l=60cm  =2.4e-6 Suspension TE noise could limit the sensitivity

290K vs. 121K ET-HF sensitivity (290K) ET-HF sensitivity (121K) l=60cm,  0.6mm silica fiber LG33 beam T=290K l=60cm, 1cm x 1mm silicon ribbon (bad) 3cm x 0.4mm ribbon (good) TEM00 beam, w=10cm T=121K Mirror TN levels are almost equal Suspension TN is low enough with the 3cm ribbon QN susp mirror gravity QN susp mirror gravity

Summary of Low-T ET-HF Thermal lensing and PI problems will be eased With T=20K, suspension is too thick With higher T, suspension can be thin, but TE is high With T=121K, suspension is thin and TE is zero Suspension TE is large, but a thin ribbon will help.

Before ET-LF optimization gravity gradient ET-HF quantum ET-LF quantum (dashed: freq-dependent squeezing, solid: fixed squeezing) susp TN mirror TN We could omit filter cavities to realize FD squeezing Especially if we can make ET-LF a little wider opt losses are included

RSE vs. Speed-meter RSE + filter cavityResonant Sagnac (Speedmeter) Less power required Narrow-band Broadband with more power Less sensitive to mass

ET-LF optimization 10kW100kW in arm 2MW in arm 20MW in arm 18kW DRSE gravity gradient The more power, the better SM sensitivity The more power, the more thermal noise Homodyne phase can be tuned opt losses are included

ET-LF optimization gravity gradient 10kW 100kW in arm 2MW in arm 20MW in arm 18kW DRSE ET-HF (w/o filter) Thermal noise is included Homo-phase and mass temperature are optimized DRSE (not yet optimized) seems better than SM? opt losses are included

Summary and discussions I would recommend… 20K ET-LF + 121K ET-HF ET-HF as an SPI for ET-LF No filter cavity for ET-HF Probably DRSE w/filter for ET-LF TBD: Payload thermal noise (Puppo. et al) High power 1550nm LASER DRSE optimization Other options