033109-10 Dooley et al. Rev.Sci.Instrum.83,033109(2012) 1000 1.6 0.2 W data no EOM,x 。=105umat5.811m,2=1.02 1.4 :no EOM,y B00 口26.3 W data… ● with EOM.x w。=103umat5.811m,2=0.96 1.2 ◆ with EOM,y 0.8 E 0.8 0.4 200 0.2 6 5.65 5.7 5.75 5.8 5.85 5.9 5.95 6 6.05 0.1 02 03 0.40.5 06 0.8 09 distance from MC waist(m) 0.7 distance from RTP [m] FIG.9.Profile at high and low powers of a pick-off of the beam transmitted through the MC.The precision of the beam profiler is +5%.Within the error FIG.11.EOM thermal lensing data.The x-and y-direction beam profiles with 160 W through the EOM(closed circles and squares)place a lower of the measurement,there are no obvious degradations. limit of 4 m on the induced thermal lens when compared to the beam profiles without the EOM (open circles and squares). to increased higher-order-mode content.The percentage of E.Mode-matching power in higher-order modes depends strongly on the mode We measured the total interferometer visibility (refer to order and relative phases of the modes,and thus cannot be Eg.(1))as an indirect way of determining the carrier mode- determined from this measurement.34 matching to the interferometer.In this case,Pin is the power The results for the MC are consistent with no thermal in the refected beam when the interferometer cavities are un- lensing.The high and low power beam profiles are within locked and Prea is the power in the reflected beam when all of each other's error bars and well below our requirements. the interferometer cavities are on resonance. We also measured the thermal lensing of the EOM prior The primary mechanisms that serve to reduce the inter- to its installation in Enhanced LIGO by comparing beam pro- ferometer visibility from unity are:carrier mode-matching, files of a 160 W beam with and without the EOM in its path carrier impedance matching,and sideband light.We measured The data for both cross sections of the beam is presented the impedance matching at LLO to be >99.5%;impedance in Fig.11.We observe no significant thermal lensing in the matching therefore makes a negligible contribution to the y-direction and a small effect in the x-direction.An upper power in the reflected beam.We also measured that due to the limit for the thermal lens in the x-direction can be calcu- sidebands,the carrier makes up 86%of the power in the re- lated to be greater than 4 m,which is 10 times larger than flected beam with the interferometer unlocked and 78%with the Rayleigh range of the spatial mode.The mode matching the interferometer locked;to compensate,we reduce the total degradation is therefore less than 1%.Although a direct test Prea/Pin ratio by 10%.With the interferometer unlocked,there for Advanced LIGO because of the power used,this measure is also a 2.7%correction for the transmission of the RM. ment also serves to demonstrate the effectiveness of the EOM Initially,anywhere between 10%and 17%of the light design for Enhanced LIGO powers. was rejected by the interferometer due to poor,power- dependent mode matching.After translating the mode- matching telescope mirrors during a vacuum chamber incur- sion and upgrading the other IO components,the mode mis- 800 match we measured was 8%and independent of input power. O 1W data 700 -w。=139umat95.029m.M2=1.04 The MMT thus succeeds in coupling 92%of the light into the 口25 W data interferometer at all times,marking both an improvement in 600 w。=137umat95.027m,M=1.1g MMT mirror placement and success in eliminating measur- 500 able thermal issues. 400 300 VI.IMPLICATIONS FOR ADVANCED LIGO 200 As with other Advanced LIGO interferometer compo- nents,Enhanced LIGO served as a technology demonstrator 100 for the Advanced LIGO Input Optics,albeit at lower laser 94.9 94.95 95 95.0595.195.15 powers than will be used there.The performance of the En- 952 95.25 95.3 distance from MC waist(m) hanced LIGO IO components at 30 W of input power allows us to infer their performance in Advanced LIGO.The require- FIG.10.Faraday isolator thermal lensing data.With 25 W into the Faraday isolator(corresponding to 50 W in double pass),the beam has a steeper di- ments for the Advanced LIGO IO demand are for similar per- vergence than a pure TEMoo beam,indicating the presence of higher order formance to Enhanced LIGO,but with almost 8 times the modes.Errors are +5.0%for each data point. laser power Reuse of AlP Publishing content is subject to the terms at:https://publishing.aip.org/authors/rights-and-permi sions. Downlo8dolP:183.195251.60:Fi.22Apr2016 00:5410033109-10 Dooley et al. Rev. Sci. Instrum. 83, 033109 (2012) 5.6 5.65 5.7 5.75 5.8 5.85 5.9 5.95 6 6.05 0 200 400 600 800 1000 beam radius (um) distance from MC waist (m) 0.2 W data w0 = 105 um at 5.811 m, M2 = 1.02 26.3 W data w0 = 103 um at 5.811 m, M2 = 0.96 FIG. 9. Profile at high and low powers of a pick-off of the beam transmitted through the MC. The precision of the beam profiler is ±5%. Within the error of the measurement, there are no obvious degradations. to increased higher-order-mode content. The percentage of power in higher-order modes depends strongly on the mode order and relative phases of the modes, and thus cannot be determined from this measurement.34 The results for the MC are consistent with no thermal lensing. The high and low power beam profiles are within each other’s error bars and well below our requirements. We also measured the thermal lensing of the EOM prior to its installation in Enhanced LIGO by comparing beam pro- files of a 160 W beam with and without the EOM in its path. The data for both cross sections of the beam is presented in Fig. 11. We observe no significant thermal lensing in the y-direction and a small effect in the x-direction. An upper limit for the thermal lens in the x-direction can be calcu￾lated to be greater than 4 m, which is 10 times larger than the Rayleigh range of the spatial mode. The mode matching degradation is therefore less than 1%. Although a direct test for Advanced LIGO because of the power used, this measure￾ment also serves to demonstrate the effectiveness of the EOM design for Enhanced LIGO powers. 94.9 94.95 95 95.05 95.1 95.15 95.2 95.25 95.3 0 100 200 300 400 500 600 700 800 beam radius (um) distance from MC waist (m) 1W data w0 = 139 um at 95.029 m, M2 = 1.04 25W data w0 = 137 um at 95.027 m, M2 = 1.19 FIG. 10. Faraday isolator thermal lensing data. With 25 W into the Faraday isolator (corresponding to 50 W in double pass), the beam has a steeper di￾vergence than a pure TEM00 beam, indicating the presence of higher order modes. Errors are ±5.0% for each data point. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 beam radius [mm] distance from RTP [m] no EOM, x no EOM, y with EOM, x with EOM, y FIG. 11. EOM thermal lensing data. The x- and y-direction beam profiles with 160 W through the EOM (closed circles and squares) place a lower limit of 4 m on the induced thermal lens when compared to the beam profiles without the EOM (open circles and squares). E. Mode-matching We measured the total interferometer visibility (refer to Eq. (1)) as an indirect way of determining the carrier mode￾matching to the interferometer. In this case, Pin is the power in the reflected beam when the interferometer cavities are un￾locked and Prefl is the power in the reflected beam when all of the interferometer cavities are on resonance. The primary mechanisms that serve to reduce the inter￾ferometer visibility from unity are: carrier mode-matching, carrier impedance matching, and sideband light. We measured the impedance matching at LLO to be > 99.5%; impedance matching therefore makes a negligible contribution to the power in the reflected beam. We also measured that due to the sidebands, the carrier makes up 86% of the power in the re- flected beam with the interferometer unlocked and 78% with the interferometer locked; to compensate, we reduce the total Prefl/Pin ratio by 10%. With the interferometer unlocked, there is also a 2.7% correction for the transmission of the RM. Initially, anywhere between 10% and 17% of the light was rejected by the interferometer due to poor, power￾dependent mode matching. After translating the mode￾matching telescope mirrors during a vacuum chamber incur￾sion and upgrading the other IO components, the mode mis￾match we measured was 8% and independent of input power. The MMT thus succeeds in coupling 92% of the light into the interferometer at all times, marking both an improvement in MMT mirror placement and success in eliminating measur￾able thermal issues. VI. IMPLICATIONS FOR ADVANCED LIGO As with other Advanced LIGO interferometer compo￾nents, Enhanced LIGO served as a technology demonstrator for the Advanced LIGO Input Optics, albeit at lower laser powers than will be used there. The performance of the En￾hanced LIGO IO components at 30 W of input power allows us to infer their performance in Advanced LIGO. The require￾ments for the Advanced LIGO IO demand are for similar per￾formance to Enhanced LIGO, but with almost 8 times the laser power. Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 183.195.251.6 On: Fri, 22 Apr 2016 00:54:10