STREG WP1M1 mirror substrates LIGOStrega wp1m1镜基板 LIGO

1、temperature dependence of the mechanical dissipation in single layer tantalum pentoxide coatings on thin single-crystal silicon substrates.geoi. martin, s. reid, d. crooks, j. hough, s. rowanuniv. of glasgowm.m. fejer, r. routestanford universitya. remillieux, j.m. mackowski, c. comtet, n. morgadol.

2、 pinard, ch. michel lma, lyong. harryligo mith. armandula, ligo caltech s. penn, hobart and william smith collegesscientific motivationgeosilicon is of interest as a mirror substrate material for future detectors its mechanical loss is predicted to decrease at low temperaturesmechanical dissipation

3、from dielectric mirror coatings is predicted to be a significant source of thermal noise for advanced detectors. (coatings must also be of low optical loss.)experiments suggestta2o5 is the dominant source of dissipation in current ion-beam-sputtered sio2/ta2o5 coatingsdoping the ta2o5 with tio2 can

4、reduce the mechanical dissipationmechanism responsible for the observed mechanical loss in ta2o5 as yet not clearly identifiedexperimental setupschematic of cryostatuncoated cantilever in situcoated cantilever in situsamplestantala coatingelectrostaticdrivesilicon cantilever with coatingthe silicon

5、samples have been fabricated by wet etching from silicon wafers at stanford (stefan zappe)the coatings were deposited by lma. silicon substrate properties: 92 m mm thick, p-type boron doped, resistivity = 10-20 w w-cmtantala coating applied to bottom surface tantala coating properties: 0.5 m mm sing

6、le layer tantala, doped with 14.5 1 % titania (formula 5)coatingclamping block34mm500m mm92m mmamplitude ring-down of uncoated silicon cantilever forthe third bending mode at f1.9 khz at 120kexperimental procedureresonant modes of samples excited using an electrostatic drivesample displacement monit

7、ored using shadow sensormeasure rate of decay of the mode amplitudes, from which mechanical dissipation, f(wf(w0 0) ), can be determined.0200400600800-0.04-0.020.000.020.04cantilever displacement angle (rads)time (s) cantilever displacement angle exponential fitcoated silicon cantileverresults third

8、 bending mode at 1.9khz1x101x101x10-750100150200250300mechanical lossf(w)temperature (k) measured loss, coated, 27 april 06 measured loss, coated, 4 may 06 measured loss, coated, 15 may 06 measured loss, coated, 16 may 06 measured loss, coated, 19 may 06 measured loss, uncoated (control) calculated

9、thermoelastic loss-5-6(b)(a)(c)temperature dependence of (a) measured uncoated loss, (b) measured coated loss and (c) calculated thermoelastic loss for the third bending mode at 1.9khz.coated silicon cantileverresults fifth bending mode at 3.8khz1x10-51x10-61x1050100150200250300mechanical lossf(w)te

10、mperature (k) measured loss, coated, 7 may 06 measured loss, coated, 15 may 06 measured loss, coated, 16 may 06 measured loss, coated, 19 may 06 measured loss, uncoated (control) calculated thermoelastic loss-7(b)(a)(c)temperature dependence of (a) measured uncoated loss, (b) measured coated loss an

11、d (c) calculated thermoelastic loss for the fifth bending mode at 3.8khz.likely to be energy coupling to the clamping structurethe energy stored in the surface layer as it stretches may be described as:where the increase in length, dl may be written as:the energy stored in the half of the beam under

12、 compression may be written as:where dl=(r-r)q and integrating over half the beam thickness gives:interpretation: calculating the energy stored in the coating layerdeflected beam with a lossy surface layer (heptonstall et al pla 2006)a = thickness of substrateh = thickness of coatingb = width, l = i

13、nitial lengthl+dl = increased (stretched) lengthesurface = energy stored in the surfaceebeam = energy stored in the beamysurface = youngs modulus of the surfaceybeam = youngs modulus of the beamcoated silicon cantilever energy distributionwe can approximate the energy stored in the compressed half o

14、f the beam to be equal to the energy stored in the stretched half. scaling by a factor of two therefore gives the ratio of energies stored in the surface layer (coating) and the bulk to be:the mechanical loss of the coating layer can now be calculated from the measured loss of the coated sample by s

15、caling by this energy ratio, such that:coated silicon cantilever energy distributioninterpretation: calculating the energy stored in the coating layer ctda = thickness of substrateh = thickness of coatingb = width, l = initial lengthl+dl = increased (stretched) lengthesurface = energy stored in the

16、surfaceebeam = energy stored in the beamysurface = youngs modulus of the surfaceybeam = youngs modulus of the beamdeflected beam with a lossy surface layer (heptonstall et al pla 2006)interpretation: calculating the energy stored in the coating layer ctddeflected beam with a lossy surface layer (hep

17、tonstall et al pla 2006)we have also evaluated the energy ratios by finite element analysis and they agree within a few %.the energy ratio used: esurface/ebeam= 0.014youngs modulus of silicon substrate: 162.4 gpareid et al, pla 2005youngs modulus of tantala coating: 140.0 gpak. srinivasan et al, lig

18、o-t970176-00-d 2001,“coating strain induced distortion in ligo optics”/docs/t/t970176-00.pdf coated silicon cantilever energy distributioncoating loss - resultsresults third bending mode coating loss501001502002503002x10-44x10-46x10-48x10-41x10-3 27 april 2006 4 may 2006 15

19、 may 2006 16 may 2006 19 may 2006coating mechanical lossf(w)coatingtemperature (k)temperature dependence of the measured loss in a single layer doped tantala coating applied to a 92mm silicon substrate at 1.9khzcoating loss - resultsresults fifth bending mode coating loss50100150200250300-2x10-402x1

20、0-44x10-46x10-48x10-41x10-3 7 may 2006 15 may 2006 16 may 2006 19 may 2006coating mechanical lossf(w)coatingtemperature (k)temperature dependence of the measured loss in a single layer doped tantala coating applied to a 92mm silicon substrate at 3.8khzinvestigation to study energy coupling to the cl

21、amping structure.both sets of results show similar features, with the loss of the tantala coating typically decreasing with temperature from 290200k then increasing from 20080k.need to investigate whether energy coupling to clamping structure is responsible for any of these features.this can be carr

22、ied out using a piezo-sensor mounted to the clamping structure.setup for monitoring energy residing in the clamping structureresults energy residing in clamping structureinvestigation to study energy coupling to clamping structure (third mode)501001502002503002x10-44x10-46x10-48x10-41x10-3 1.9khz be

23、nding mode - 19 may 2006 piezo responsetemperature (k)measured coating lossf(w)coating0.02.0 x10-44.0 x10-46.0 x10-48.0 x10-41.0 x10-31.2x10-31.4x10-3normalised piezo response (arb. units)plot of the measured loss of the third bending mode at f1.9khz compared with the normalised magnitude of the sig

24、nal from the piezo-sensorinvestigation to study energy coupling to clamping structure (fifth mode)50100150200250300-2x10-402x10-44x10-46x10-48x10-41x10-3 3.8khz bending mode - 19 may 2006 piezo responsetemperature (k)measured coating lossf(w)coating0.02.0 x10-44.0 x10-46.0 x10-48.0 x10-41.0 x10-31.2

25、x10-31.4x10-3normalised piezo response (arb. units)plot of the measured loss of the fifth bending mode at f3.8khz compared with the normalised magnitude of the signal from the piezo-sensorresults energy residing in clamping structureconclusionsevidence for coupling of energy to clamp affecting loss at room temperature for 3rd bendi