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Glenn de Vine, Matthieu Vangeleyn, Alain Brillet, C. Nary Man David McClelland, Malcolm Gray

A Sagnac interferometer with frequency modulation for sensitive saturated absorption (and applications for LISA!). Glenn de Vine, Matthieu Vangeleyn, Alain Brillet, C. Nary Man David McClelland, Malcolm Gray. Observatoire de la Côte d'Azur Département ARTEMIS NICE glenn.devine@obs-nice.fr.

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Glenn de Vine, Matthieu Vangeleyn, Alain Brillet, C. Nary Man David McClelland, Malcolm Gray

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  1. A Sagnac interferometer with frequency modulation for sensitive saturated absorption(and applications for LISA!) Glenn de Vine, Matthieu Vangeleyn, Alain Brillet, C. Nary Man David McClelland, Malcolm Gray Observatoire de la Côte d'Azur Département ARTEMIS NICE glenn.devine@obs-nice.fr Observatoire de la Cote d'Azur

  2. Talk Outline: LISA - lasers and frequency noise Sagnac interferometer basics Saturation spectroscopy basics Sagnac interferometer for noise-rejection Details of the technique Theoretical modeling Experimental results The Future… Observatoire de la Cote d'Azur

  3. The LISA Interferometer • Arm lengths = 5 million km • Arm length difference ≈ 50,000 km (1%) • Frequency noise now couples in due to unequal arm length • Equal arm length Michelson • freq noise is common and not a concern • white light interferometer Observatoire de la Cote d'Azur

  4. Frequency Noise Coupling Observatoire de la Cote d'Azur

  5. Measurement Sensitivity • In order to measure a relative arm length difference, dx= 2pm/Hz, using: we require a detector (laser) frequency sensitivity (stability), d, of 6x10-6Hz/Hz Observatoire de la Cote d'Azur

  6. LISA Lasers • LISA will employ the most stable CW lasers currently available: • Nd:YAG lasers at 1064nm • Intensity noise requirements should be met with noise-eaters • Laser frequency noise needs to be overcome: Typical free running laser frequency noise: 104/f Hz/Hz LISA detection band is 100Hz to 1Hz At 100Hz we require a stability improvement of over 13 orders of magnitude Observatoire de la Cote d'Azur

  7. Frequency Stabilisation Methods • Arm locking - stable reference, well established in ground-based GWD’s • Time-delay interferometry - new technique, currently being tested • Mechanical reference (cavity) - ULE, ZeroDur, etc • Atomic or molecular reference • No method alone will achieve the 13 orders of magnitude improvement required • Solution will be a combination Observatoire de la Cote d'Azur

  8. Atomic vs Mechanical (Cavity) • Atomic - for: • absolute reference, best long term stability against: • not space-rated, absorptions typically very weak at 1064nm • Cavity - for: • simple, space-rated, best short term stability against: • not absolute, aging, long term stability is susceptible to thermal variations Observatoire de la Cote d'Azur

  9. Iodine Spectroscopy for LISA Laser Frequency Stabilisation • develop high performance frequency stability by locking a laser using Doppler-free saturated absorption spectroscopy of iodine at 532nm for 1064nm absolute stability • achieve LISA laser frequency stability requirement of < 1Hz/√Hz from 100Hz to 1Hz Observatoire de la Cote d'Azur

  10. Iodine • Sufficient absorption from hyperfine resonances at 532nm (the harmonic of 1064nm - weak absorptions:Cs2,CO2,C2H2) • Commercially available lasers with doubled (532nm) and fundamental (1064nm) outputs • The spectroscopy (and thus, frequency stability) can benefit from improved techniques to enhance the signal and/or reduce the noise Observatoire de la Cote d'Azur

  11. Sagnac Interferometry Observatoire de la Cote d'Azur

  12. Saturation Spectroscopy • Energy levels of I2 : 1. electronic 2. vibrational 3. rotational Observatoire de la Cote d'Azur

  13. Observatoire de la Cote d'Azur

  14. Saturation Spectroscopy • Energy levels of I2 : 1. electronic 2. vibrational (1GHz) 3. rotational (1MHz) Observatoire de la Cote d'Azur

  15. Saturation Spectroscopy • Energy levels of I2 : 1. electronic 2. vibrational (1GHz) 3. rotational (1MHz) • Boltzmann thermal distribution - Doppler shifts transition frequencies relative to laser frequency • Doppler shifting is greater than hyperfine linewidth • Counter-propagating pump and probe fields - both interact only with molecules of zero longitudinal velocity (to first order) Observatoire de la Cote d'Azur

  16. Saturation Spectroscopy • Pump saturates vibrational transition, allows probe to interact with hyperfine (rotational) transitions • When pump and probe frequency are coincident with hyperfine transition, the transparency from the hole burnt by the pump produces the inverted Lamb dip Observatoire de la Cote d'Azur

  17. A new spectroscopy technique Observatoire de la Cote d'Azur

  18. Observatoire de la Cote d'Azur

  19. Observatoire de la Cote d'Azur

  20. 3rd Harmonic Sagnac Spectroscopy Observatoire de la Cote d'Azur

  21. Observatoire de la Cote d'Azur

  22. Experimental Results Observatoire de la Cote d'Azur

  23. Observatoire de la Cote d'Azur

  24. Applications for LISA Laser frequency stabilisation Initial phase-locking of LISA lasers Could use Cs2 at 1064nm Observatoire de la Cote d'Azur

  25. Further Work • Optimise error signal: fringe visibility, show 1st harmonic. Then stabilise laser • Complete 2nd identical system • Independent long-term laser frequency stability measurement against LISA requirements • Compare with modulation transfer results • Simple, yet powerful (potentially shot-noise-limited) technique can be used for any spectroscopic application Observatoire de la Cote d'Azur

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