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Case Study: Faraday Rotators in LIGO

Physics 208, Electro-opticsPeter Beyersdorf

1

Input Optics Overview

Requirements for LIGO faraday isolator

LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY

LIGO Laboratory / LIGO Scientific Collaboration

LIGO-T050226-00-D ADVANCED LIGO 10/06/05

Faraday Isolator Specifications for Advanced LIGO

UF Group

Distribution of this document: LIGO Science Collaboration

This is an internal working note

of the LIGO Project.

California Institute of Technology LIGO Project – MS 18-34 1200 E. California Blvd.

Pasadena, CA 91125 Phone (626) 395-2129 Fax (626) 304-9834

E-mail: info@ligo.caltech.edu

Massachusetts Institute of Technology LIGO Project – NW17-161

175 Albany St Cambridge, MA 02139 Phone (617) 253-4824 Fax (617) 253-7014

E-mail: info@ligo.mit.edu

LIGO Hanford Observatory P.O. Box 1970

Mail Stop S9-02 Richland WA 99352 Phone 509-372-8106 Fax 509-372-8137

LIGO Livingston Observatory

P.O. Box 940 Livingston, LA 70754

Phone 225-686-3100 Fax 225-686-7189

http://www.ligo.caltech.edu/

Optical Requirements

0-180 W CW power

Tforward>96%

Tbackwards>80%

“p” Input polarization

“p” output polarization

>38 dB power isolation

<5% coupling out of TEM00 mode

<100 μrad thermal beamsteering

Verdet Constant of Common Materials

Motivation for Terbium

Substances with paramagnetic ions (such as Terbium) have the largest Verdet constants. Maximum paramagnetism comes from lanthanide and actinide ions with maximum number of singly filled f shells

Mateial Properties of TGG

1.2 x 10-4

4.6 x 10-4

deg x gauss-1 x mm^-1

Terbium Gallium Garnet - TGG (Tb3Ga5O12)

Thermal conductivity is an order of magnitude

higher than for terbium doped glasses

Verdet constant is twice that of terbium

doped glasses

Typical Faraday Isolator Design

Large permanent magnet surrounds magneto-optic glass or crystal.

Amount of insertion of magneto-optic material in magnet can be adjusted to compensate change in birefringence asa function of wavelength.

Quartz rotator restores polarization of forward beam to match the input polarization.

Polarizers redirect retro-reflected beams

Quartz Rotator

PolarizerPolarizer

Magneto-optic

Permanent Magnet

Thermal Lensing

Parabolic radial temperature profile in optic leads to non-uniform thermal expansion producing “thermal lens”

Temp dependence of Verdet Constant

Temperature gradient in crystal due to beam profile results in a non-uniform polarization rotation

TEM00 mode power distribution and thermally induced strain field

parabolic distribution of depolarization

Stress Induced Birefringence

Like high power rod lasers, stress induced birefringence causes depolarization

TEM00 mode power distribution and thermally induced strain field

Spatial map of polarization conversion by stress induced birefringence

LIGO Faraday Isolator Design

Material with negative thermal lens compensates for thermal lensing in the magneto-optic crystal (TGG)

Quartz rotator (λ/2 plate at 22.5°) is placed between the two halves of the TGG crystal, allowing one crystal to compensate for the depolarization in the other one.

Thin Film Polarizers replace cube polarizers to reduce thermal drift of beam steering

Thin FilmPolarizer

TGG

Permanent Magnet

TGG

Quartz Rotator

-dn/dt material

Thin FilmPolarizer

LIGO Faraday Isolator Design LIGO faraday Isolator Design

LIGO Faraday Isolator Picture

LIGO faraday Isolator Design

Faraday Isolator Performance

Faraday Isolator Performance

Faraday Isolator Performance

Faraday Isolator Performance

Depolarization ratio (γ) measued versus input power for traditional configuration (a) and LIGO configuration (c)

Faraday isolators at high average power is determined bythe photoelastic effect rather than by the temperature de-pendence of the Verdet constant. In addition, the depo-larization ratio in the dual-glass-based isolation methodsdemonstrated here is significantly lower than in the tra-ditional method. The geometry shown in Fig. 1(c) is mostoptimal, reducing the depolarization ratio by two ordersof magnitude with respect to the single-isolator method.These experimental results confirm the possibility of de-signing a Faraday isolator based on glass magneto-optical

elements with isolation of 30 dB at an average laserpower of hundreds of watts. Such isolators will be usefulin applications such as gravitational-wave inter-ferometry11–14 that require both high-power lasers andhigh isolation ratios.

ACKNOWLEDGMENTSD. H. Reitze gratefully acknowledges the support of theNational Science Foundation (PHY 97-22114) in supportof this research.

REFERENCES1. R. J. Shine, A. J. Alfrey, and R. L. Byer, ‘‘40-W cw,

TEM00-mode, diode-laser-pumped, Nd-YAG miniature-slablaser,’’ Opt. Lett. 20, 459–461 (1995).

2. S. A. Payne, R. J. Beach, C. Bibeau, C. A. Ebbers, M. A.Emanuel, E. C. Honea, C. D. Marshall, R. H. Page, K. I.Schaffers, J. A. Skidmore, S. B. Sutton, and W. F. Krupke,‘‘Diode arrays, crystals, and thermal management for solid-state lasers,’’ IEEE J. Sel. Top. Quantum Electron. 3, 71–81(1997).

3. A. N. Malshakov, G. A. Pasmanik, and A. K. Potemkin,‘‘Comparative characteristics of magneto-optical materi-als,’’ Appl. Opt. 36, 6403–6410 (1997).

4. N. P. Barnes and L. P. Petway, ‘‘Variation of the Verdetconstant with temperature of terbium gallium garnet,’’ J.Opt. Soc. Am. B 9, 1912–1915 (1992).

5. J. D. Foster and L. M. Osterink, ‘‘Thermal effects in aNd:YAG laser,’’ J. Appl. Phys. 41, 3656–3663 (1970).

6. E. Khazanov, O. Kulagin, S. Yoshida, D. Tanner, and D. Re-itze, ‘‘Investigation of self-induced depolarization of laserradiation in terbium gallium garnet,’’ IEEE J. QuantumElectron. 35, 1116–1122 (1999).

7. E. A. Khazanov, ‘‘Compensation of thermally induced polar-ization distortions in Faraday isolators,’’ Quantum Elec-tron. 29, 59–64 (1999) [Kvant. Elektron. (Moscow) 26,59–64 (1999)].

8. K. Shiraishi, F. Tajima, and S. Kawakami, ‘‘Compact Fara-day rotator for an optical isolator using magnets arrangedwith alternating polarities,’’ Opt. Lett. 11, 82–84 (1986).

9. W. A. Clarkson, N. S. Felgate, and D. C. Hanna, ‘‘Simplemethod for reducing depolarization loss resulting fromthermally induced birefringence in solid-state lasers,’’ Opt.Lett. 24, 820–822 (1999).

10. A. V. Mezenov, L. N. Soms, and A. I. Stepanov, Thermo-optics of Solid-State Lasers (Mashinostroenie, Leningrad,1986), p. 44.

11. A. Abramovici, W. E. Althouse, R. W. P. Drever, Y. Gursel,S. Kawamura, F. J. Raab, D. Shoemaker, L. Sievers, R. E.Spero, K. S. Thorne, R. E. Vogt, R. Weiss, S. E. Whitcomb,and M. E. Zucker, ‘‘LIGO—the laser interferometer gravi-tational wave observatory,’’ Science 256, 325–333 (1992).

12. A. Giazotto, ‘‘Wide-band measurement of gravitationalwaves—the Virgo Project,’’ Nuovo Cimento C 15, 955–971(1992).

13. M. V. Plissi, K. A. Strain, C. I. Torrie, N. A. Robertson, S.Killbourn, S. Rowan, S. M. Twyford, H. Ward, K. D. Skel-don, and J. Hough, ‘‘Aspects of the suspension system forGEO 600,’’ Rev. Sci. Instrum. 69, 3055–3061 (1998).

14. K. Kawabe, ‘‘Status of TAMA project,’’ Class. QuantumGrav. 14, 1477–1480 (1997).

Fig. 3. Images of the spatial profiles of the depolarized beamsafter transmission through the isolators for each geometryshown in (a) Figs 1(a), (b) Fig. 1(b), and (c) Fig. 1(c).

102 J. Opt. Soc. Am. B /Vol. 17, No. 1 /January 2000 Khazanov et al.

Faraday isolators at high average power is determined bythe photoelastic effect rather than by the temperature de-pendence of the Verdet constant. In addition, the depo-larization ratio in the dual-glass-based isolation methodsdemonstrated here is significantly lower than in the tra-ditional method. The geometry shown in Fig. 1(c) is mostoptimal, reducing the depolarization ratio by two ordersof magnitude with respect to the single-isolator method.These experimental results confirm the possibility of de-signing a Faraday isolator based on glass magneto-optical

elements with isolation of 30 dB at an average laserpower of hundreds of watts. Such isolators will be usefulin applications such as gravitational-wave inter-ferometry11–14 that require both high-power lasers andhigh isolation ratios.

ACKNOWLEDGMENTSD. H. Reitze gratefully acknowledges the support of theNational Science Foundation (PHY 97-22114) in supportof this research.

REFERENCES1. R. J. Shine, A. J. Alfrey, and R. L. Byer, ‘‘40-W cw,

TEM00-mode, diode-laser-pumped, Nd-YAG miniature-slablaser,’’ Opt. Lett. 20, 459–461 (1995).

2. S. A. Payne, R. J. Beach, C. Bibeau, C. A. Ebbers, M. A.Emanuel, E. C. Honea, C. D. Marshall, R. H. Page, K. I.Schaffers, J. A. Skidmore, S. B. Sutton, and W. F. Krupke,‘‘Diode arrays, crystals, and thermal management for solid-state lasers,’’ IEEE J. Sel. Top. Quantum Electron. 3, 71–81(1997).

3. A. N. Malshakov, G. A. Pasmanik, and A. K. Potemkin,‘‘Comparative characteristics of magneto-optical materi-als,’’ Appl. Opt. 36, 6403–6410 (1997).

4. N. P. Barnes and L. P. Petway, ‘‘Variation of the Verdetconstant with temperature of terbium gallium garnet,’’ J.Opt. Soc. Am. B 9, 1912–1915 (1992).

5. J. D. Foster and L. M. Osterink, ‘‘Thermal effects in aNd:YAG laser,’’ J. Appl. Phys. 41, 3656–3663 (1970).

6. E. Khazanov, O. Kulagin, S. Yoshida, D. Tanner, and D. Re-itze, ‘‘Investigation of self-induced depolarization of laserradiation in terbium gallium garnet,’’ IEEE J. QuantumElectron. 35, 1116–1122 (1999).

7. E. A. Khazanov, ‘‘Compensation of thermally induced polar-ization distortions in Faraday isolators,’’ Quantum Elec-tron. 29, 59–64 (1999) [Kvant. Elektron. (Moscow) 26,59–64 (1999)].

8. K. Shiraishi, F. Tajima, and S. Kawakami, ‘‘Compact Fara-day rotator for an optical isolator using magnets arrangedwith alternating polarities,’’ Opt. Lett. 11, 82–84 (1986).

9. W. A. Clarkson, N. S. Felgate, and D. C. Hanna, ‘‘Simplemethod for reducing depolarization loss resulting fromthermally induced birefringence in solid-state lasers,’’ Opt.Lett. 24, 820–822 (1999).

10. A. V. Mezenov, L. N. Soms, and A. I. Stepanov, Thermo-optics of Solid-State Lasers (Mashinostroenie, Leningrad,1986), p. 44.

11. A. Abramovici, W. E. Althouse, R. W. P. Drever, Y. Gursel,S. Kawamura, F. J. Raab, D. Shoemaker, L. Sievers, R. E.Spero, K. S. Thorne, R. E. Vogt, R. Weiss, S. E. Whitcomb,and M. E. Zucker, ‘‘LIGO—the laser interferometer gravi-tational wave observatory,’’ Science 256, 325–333 (1992).

12. A. Giazotto, ‘‘Wide-band measurement of gravitationalwaves—the Virgo Project,’’ Nuovo Cimento C 15, 955–971(1992).

13. M. V. Plissi, K. A. Strain, C. I. Torrie, N. A. Robertson, S.Killbourn, S. Rowan, S. M. Twyford, H. Ward, K. D. Skel-don, and J. Hough, ‘‘Aspects of the suspension system forGEO 600,’’ Rev. Sci. Instrum. 69, 3055–3061 (1998).

14. K. Kawabe, ‘‘Status of TAMA project,’’ Class. QuantumGrav. 14, 1477–1480 (1997).

Fig. 3. Images of the spatial profiles of the depolarized beamsafter transmission through the isolators for each geometryshown in (a) Figs 1(a), (b) Fig. 1(b), and (c) Fig. 1(c).

102 J. Opt. Soc. Am. B /Vol. 17, No. 1 /January 2000 Khazanov et al.

References

Güido Mueller, “Faraday Isolator Specifications for Advanced LIGO”, LIGO document number LIGO-T050226-00-D

Efim Khazanov, Nikolay Andreev, Alexey Babin, Alexander Kiselev, and Oleg Palashov, “Suppression of self-induced depolarization of high-power laser radiation in glass-based Faraday isolators”, JOSA B, Vol. 17, 2000

Yariv & Yeh “Optical Waves in Crystals” chapter 4