DAVID H. SHOEMAKER - LIGO - Caltech

{ I
3) l'luctuatlo!3 of regidual ga! ple3sure
Fonctionnement de I'ensemblc L2L
Thc cotire iaterferoo.etcr is cottai8ed in a r.cuuE systrE to leduce ihe rfect
of rc&acliv. ild€x EuctuatioE aad ambieoa a.ouitic dois. ol thc apparcat path
leagth. The va€uuE sysretE has threr vertical tads, l.O m i! diaEete!, l.l ro
ir hciglt. The'certral ta*', which houses the bea.Erplitter, thc acar dclaf line
o.irron, ald. tbc ilpur optics, ir coo,aected to thc two ,crrd ta!-kj, fwhich coataia
the far de.lay lloe mirron) by horizontal tubes 0.4 D i! diaEct*. ibc md t."t.
a,rc oo a.systcE of raib,. aod it i! polsibl€ to add .xtelEion tub.3 (oaxjnuq
Iength 3 !B) to sdjEt tLe rcparation betwc?s th€ ta*!. O[ly thc centEl ta.s!
ir ia thc laboratoryi thc eod taDI! arc i[ lcparate eld-houscs. T!. holirolEal
tube. arc lupportcd by stccl guider o! a conclrrc bed, which ia tura ir covcred
by a rcoj.circalar cotclete cove. aad about ooe.belf ncter of cartL Rotary aad
tubouolccul..s puqps allow thc syrtcro to bc puaped froo atuosphcric pres:ure
(f0! Pa) to I0-. Pa i! 6 houn; wit! thc ps4p! tumed of, thc sysao presrure
!is.! to !, Pr i.!,2,1 hourr. Thc E !!sr.qtedt! prcsro,tcd hcrc wcrc icrforacd with
Dte!!ur€. b.tw.ca 10-r and I Pa.
A lroi!..oruc. to bc colridrccd, althoud not s siBii6caat oo. at pr!srB!,
!t.E! froE' thc rcridual 8.,r i! th. v..uqE !y!teE. The nu.ab.r of oohculca ia
the light path 8uctuater, lcadiag co sEell cba.agr! ia thc appar.tt optical iod,er,
tEd hcqcc ia path l.nsrh. Aa cltidrte {2ll of thc roagaitudc of tbir eEect givc:
4[ cquivaleat Eilror Eotion with r lidear lp.ctral d.olify
t =
t
,/G r't? I no- . N. rt.(L\ .(
co .,/i
T))
To\3/2lL/2
\Po,/ \
wbcrc lo i! Avog.d!o'! oumbcr (6.02.1023 aolruler/nolc), I/o ir rhc volu.ac of
ore aolc of gar ar STP 22.,1.10-3 n3/mole), no ir thc iad& oi rcfractioa qf rhc
ga!, so i! thc oort probablc thcranl oolecular !pc.d i-o rbc gls (for aibog.r !t
looE' t€Ep.rriur. I, - 300.K, no :r I + 2,?. I0-{ e.trd .o .: IOO afs ), atd p6 a''d
ro :llc llc t!.. lt.a.dard pr!+lu.rc a,ad tcEp.t|tru.. For tl.!c yaluet |Ed b"picd
Ecalu!€rocnt prcsuret p ouc 6ads i * 2 . 10-19 a/VE (currc b in figurc 2).
{) MotioE! of th€ optical cottlpoleltt
. A! EcatioEld, to ilol.t tha optical coEpod..!,t! froEo EovcEeat of thc ru:pc.ulioo
poirt, tLcy arc Luag as pcaduluan of leugtl l, aad thus of resoaa.at eagular
frequcacy rns = r/o/1. T:be (r,r9/r,r)2 bolatioa that onc would cxpcct froo' aa ideEl
plrdulu.a. i! coEproEilcd by lhc 0!itc qualitt factos e of thc peadulun, ard by
t.hc sugp.$ioa wbc rcronr.uccs ('violil string, modcs); a oodcl whic! prcdict well
the Ecrsured trasf€r function .fl(or) (ratio of mirror lsotio! to lulpcElioa poi!.t
EotioE) of the ruspcariou syrtea ir dcrivcd ia Appcadix B, a[d th. E..surcd
ald predictcd tlr.o.sfer fulction arc plotted ia 6gurc 6. For thc pcadulur: in u:c
lt Garclirg, ote 6a& a trarufcr futctioa whic! ca.o bc rouglly charactctizcd as
(uglulz to thc 6rst $iqli!. srringt wirc lesonance of Zir2 Ez, ih* "rhibitirrg a,
qoEplerc lesoEaD.! structule with aa isolation typically bette! than 10-{.