Method for compensation of thermally induced modal distortions in the input optical components of gravitational wave interferometers

Abstract

The next generation of interferometric gravitational wave detectors will employ laser powers approaching 200 W to increase shot-noise limited sensitivity. Optical components that transmit the laser light will exhibit increased thermal lensing induced by bulk absorption and concomitant changes in the material refractive index, resulting in significant changes in the modal characteristics of the beam. Key interferometer components such as electro-optic modulators and Faraday isolators are particularly at risk, since they possess relatively large absorption coefficients. We present a method for passive correction of thermally induced optical path length () changes induced by absorption in transmissive optical components. Our method relies on introducing material in the optical path that possesses a negative index temperature derivative, thereby inducing a compensating opposite. We experimentally demonstrate a factor of 10 reduction in higher order spatial mode generation for terbium gallium garnet, a Faraday isolator material.

Faraday Isolators for High Average Power Lasers

“…Hereinafter we shall call this method "telescopic compensation" and indicate corresponding losses by subscript "TC". In (Mansell et al, 2001;Mueller et al, 2002) an adaptive method (subscript "AC") for compensating the thermal lens was suggested and experimentally studied. A compensating glass was placed before polarizer 1 (dotted line in Fig.…”

“…Parameters of the compensating glass were chosen so that the thermal lens had the same focus as in FI but opposite (typically negative) sign. In (Mueller et al, 2002) it was shown numerically that the influence of diffraction can be insignificant. In this case the isotropic losses were totally compensated: γ iAC =0.…”

“…As a result, heat release power is at least tenths of percent of transmitted laser power P 0 . (Zarubina & Petrovsky, 1992), 2 (Zarubina et al, 1997), 3 (Chen et al, 1998), 4 (Jiang et al, 1992), 5 (Kaminskii et al, 2005), 6 (Yasuhara et al, 2007), 7 (Raja et al, 1995), 8 (Barnes & Petway, 1992), 9 (Ivanov et al, 2009), 10 (Slack & Oliver, 1971), 11 (Chen et al, 1999), 12 (Wynands et al, 1992), 13 , 14 (Mueller et al, 2002), 15 (Mansell et al, 2001), 16 (Khazanov et al, 2002a), 17 (Mukhin et al, 2009), 18 (VIRGO-Collaboration, 2008), 19 (Malshakov et al, 1997), 20 (Andreev et al, 2000a), 21 (Zarubina, 2000), 22 (Davis & Bunch, 1984).…”

Fabrication and performance optimization of the magneto-optical (Tb1−xRx)3Al5O12 (R = Y, Ce) transparent ceramics

“…1,2 A high Verdet constant, size scalability, a high laserinduced-damage threshold, and a high thermal conductivity are required for such material for high power laser applications. Terbium aluminum garnet (Tb 3 Al 5 O 12 (TAG)) single crystal is an excellent magneto-optical material with good transmittance in the 500-1500-nm region, 3,4 high thermal conductivity, and higher Verdet constant than the most commonly used terbium gallium garnet (Tb 3 Ga 5 O 12 (TGG)) single crystal.…”

“…Two-step sintering has been commonly used to obtain transparent ceramics with small grain sizes. [16][17][18] Typically, the above sintering process involves (1) first, heating the ceramic green body to a higher temperature in a short time, (2) then cooling it down to a lower temperature rapidly, (3) and then holding at the second temperature stage for a long time to achieve densification and meantime to keep the grains within relatively small size. In this paper, Y 3þ doped TAG transparent ceramic was also fabricated by using this method.…”