Measurement of Geophysical Effects with large scale gravitational interferometers V.N.Rudenko Sternberg Astronomical Institute, MSU GGD Workshop April 2012, IPGP, Paris (France) Part I : Physical mechanisms for geodynamical signals in Virgo.

Introduction

at quasi static frequencies VIRGO interferometer can be considered as a conventional two coordinate strain meter, four points tilt meter and as a new type of gravity field gradiometer

Sensing of pure gravity field variations

Geo-application of GW-interferometers Estimates of Virgo intrinsic noises

Virgo control circuit signals

Signal Recycling Beam Splitter Power Recycling The vacuum chambers of Virgo Central Area West input Nord input

Principle scheme of the VIRGO angular control system

recycling mirror angular noise ( around the beam direction ) in  rad/Hz -1/2 ; LC (red) – local control regime ; GC (black) – global control regime..

Geo signals at the main output

(LIGO) data vs. prediction for 5 days, December 7, 2006 (Neither the phase or amplitude have been normalized) It is assumed: h t = g || L/c 2 LIGO tidal signal at FSR-frequency ~ 37 kHz Meliessinos A., MG-12 Paris, July 12–18, 2009; v.2.pdf. Forrest C.V., Tidal Effects on Laser Gravitational Wave Detectors, Thesis Univ. of Rorester, LIGO Document P v1 (2009).

. ISSN 0021_3640, JETP Letters, 2010, Vol. 91, No. 10, pp. 495–499. © Pleiades Publishing, Inc., Original Russian Text © A.V. Gusev, V.N. Rudenko, 2010, published in Pis’ma v Zhurnal Йksperimental’noі i Teoreticheskoі Fiziki, 2010, Vol. 91, No. 10, pp. 543–547. Gravitational Modulation of the Optical Length of Long Baseline Laser Interferometers A. V. Gusev* and V. N. Rudenko** Sternberg Astronomical Institute, Moscow State University, Universitetskii pr. 13, Moscow, Russia * e_mail: ** e_mail: Received February 15, 2010 The effect of quasi static variations of the Earth’s gravitational field on the output signal of long baseline gravitational-wave interferometers has been considered. The relativistic representation of the gravitational field in the form of a varying refractive index is used. An analytical calculation with numerical estimates of the tidal effect has been performed to explain the recent results observed on the LIGO interferometers

Pump with a finite width of line pump frequency pedestal width FSR interval neighbors mode

PD in the “dark spot” Mechanism FSR-harmonic at the main output relativistic gravity effect !

phase difference at the PD n – tidal variation modulation index ~ 0.02 % observable value ~ 1 % observable effect was too big in respect of RG estimate

A.Melissinos GR «red shift model»

If it is not GR effect, … then what ? the only hypothesis  it is a residual arm shift… L  const. behind the control accuracy ~  L= cm tidal  L T ~ L residual t-deformation ~ /3·10 5 = GR effect  (10 -7 g 0 L/c 2 )  F ~ 5·10 -18

(Frasca effect: Sidereal periodicity in Virgo noise data) t he mean pseudo spectrum of the noise in the region 22 Hz

Interferometer Optical Scheme (without recycling mirror)

analysis logic → OS – optical system configuration optical pump: E(t)=Re{ E 1 *(t) exp jω 0 t}, ω 0 - carrier E 1 *(t) = [A* + a*(t)] exp{ j  sin  m t }, L ~ L 1  L 2 →  L ;  (0) = ω 0 ( 1 +  ), - geo length variations  =  l/L, = c/2L  =  1 -  2 =  st +  gw (quasi static variations + gw-signal frequencies)

OS output → E 2 (t) =  E 1 *(t)  g*(t) ,    →  E 1 *(  ) g*(t-  )d  ; g(t) – OS impulse characteristic frequencies :  (0) = ω 0 (1 +  ) – central mode G(0), G(  1)  (0) = ω 0 (1 +  )  2  FSR – side modes transf. functions G(  m )  (0) = ω 0 (1 +  )   m - sidebands  G  (  m ) = G(  m ) + G(  m )  G  (  m ) = G(  m )  G(   m ) symmetric TF PD output → quadratures : V S, V C output signals V S  Re [ A G(0) + < a(t)  g(t)  ] jG + (  m ) V C  Re [ A G(0) + < a(t)  g(t)  ] jG  (  m )

OS Transfer Function ( k = 0 center, k =  1 side modes ) G(  (k))  1-exp j[  0 (2  l/c)+  ]  exp j[k (  /(1-r))(  L/L)]  l ~   ~   =  1 (  ) -  2 (  ) ={2  /(1-r)} (L/ ) ,  l = +  l “dark spot”→ 4(  l/ ) +  st /  =0, →  l opt  (L/2(1  r))  st main point: G(  )  f (  st,  l ) → coupled values!    st   gw  (  st +  gw )

E 1 (t) ~ [A + a(t)] → a(t) = 0 central mode regime: E 1 ~ A V S (t)  0, V C (t)  A Re [ G*(0) j G + (  m )] V C (t)  A [4(  l/ ) + (  st +  gw )/  ]  m (  l/c),  l = +  l   st  l =  l opt =  [L/2(1-r)]  st V C (t)  A  gw  m ( +  l)/c  (Frasca effect ?) h gw ~ (1+  cos  st) sin (  t +  )

neighbour mode regime : a*(t) ≠ 0 V S  Re[ j G  (  m )] ; V C  {G  (  m )] V(t) = V C + j V S ; → { FSR filter } → V (t) →  2 Melissinos regime FSR amplitude modulation  2  [|G(1)| 2 +|G(  1)| 2 ]  [|G + (  m )| 2 +|G  (  m )| 2 ]  l opt  dark spot [4(  l/λ) + ((  st +  gw )/  ] 2 +[ΔL/L(1  r)] 2 → no linear effect! But if  l ≠  l opt →  l =  l opt +  l er ← a small detuning  2  4(  l/λ) (  st +  gw )/  ; [ m = L/(1  r)  l er ] Melissinos effect reconstruction ; change  l er – satisfies exp. data

Interferometer with power recycling mirror. Transfer Function G I (  ) = G R (  ) G(  ) . recycling cavity TF model: FP composed by M R - (Michelson – FP arms cavity) tuning parameters:  l = l 1 – l 2,   l R = l RB + l i «geo amplitude modulation» of ITF output spectral components is kept but more powerful and with a new tuning

Conclusions Geophysical information from GW interferometers can be readout using compensation signal of circuits controlling the device operation regime. - besides due to parametric variations of FP resonance frequencies - Geo - information might be received through the amplitude modulation of the free spectral range frequency filtered at the main interferometer output. Noise spectral density at the main output also is modulated by very slow (quasi static) variations of the interferometer base, produced by geophysics. It was demonstrated that VIRGO can be used as a two coordinate very long base strain meter. However the quality of the data strongly depends on a number of operational regime brakes during the observational time. Idea of measuring relative angular variations of mirror’s “plumb lines” for a sensing pure “gravity perturbations” up to now was not realized and requires a more detailed study..

Radical method for the linear parametric response reconstruction would be a using the two mode pump at neighbor frequencies ω 0 and  1 =  0 +ω fsr 11 “dark spot” condition is kept for the mode ω 0 ; A residual part of the mode  1 iteracting at photo diode with radio sideband ω 1 +  r will produce directly at the Pound-Drever mixer output a low frequency signal I(t) proportional to the optical length variations . A possibility of application this method for a registering weak global geodynamical effects as well as detection of very low frequency GW is under the process in SAI MSU

Thanks for attention !