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Applications of intense coherent optical laser beams

Applications of intense coherent optical laser beams. Axions. Holographic information bound. New forces. Aaron S. Chou Wilson Fellow, FNAL Detector R&D Retreat May 5, 2011. Use large, coherent photon fluxes for. Searches for exotic, rare scattering processes

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Applications of intense coherent optical laser beams

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  1. Applications of intense coherent optical laser beams Axions Holographic information bound New forces Aaron S. Chou Wilson Fellow, FNAL Detector R&D Retreat May 5, 2011

  2. Use large, coherent photon fluxes for Searches for exotic, rare scattering processes Precision position measurements Precision angle measurements A. S. Chou, Detector R&D Retreat, 5/5/11

  3. The Actors A. S. Chou, Detector R&D Retreat, 5/5/11 Fermilab: • Aaron S. Chou, Hank Glass, Gaston Guitierrez, Craig Hogan, Jason Steffen, Chris Stoughton, Ray Tomlin, Jim Volk, William Wester. • Al Baumbaugh, Peter Mazur MIT LIGO: • Sam Waldman, Rai Weiss U.Chicago • Steve Meyer, Bobby Lanza, Lee McCuller U. Michigan LIGO • Dick Gustafson U. Florida LIGO • Guido Mueller, Pierre Sikivie, David Tanner Naval Postgraduate School • Karl van Bibber

  4. Credits AD • Alex Chen, Bill Dymond, Dan Lambert, Scott McCormick, Bob Steinberg, James Williams PPD • John Korienek, Carl Lindenmeyer, Todd Nebel, Jerry Taccki • Herman Cease • Sten Hansen, Mark Kozlovsky ES&H • John Anderson, Raymond Lewis, Gary Ross, Rich White, Bill Wickenberg, Randy Zifko • Rob Bushek, Eric McHugh, Tim Miller, Angela Sands FESS • Steve Dixon, Carl Holmgren … A. S. Chou, Detector R&D Retreat, 5/5/11

  5. Application 1: Use lots of photons to search for rare photon-photon scattering processes mediated by axion-like or Higgs-like particles Tevatron Increase photon flux from 1019 to 1024γ/s, increase L from 6 to 40m, resonantly detect improve axion sensitivity by 4 orders of magnitude. A. S. Chou, Detector R&D Retreat, 5/5/11

  6. Application 2: Use lots of photons to make precise position measurements, search for holographic jitter in beamsplitter position in a Michelson interferometer Each Nd:YAG photon has position resolution 1064 nm. Measuring with N photons gives resolution: Measure intrinsic blurriness of beamsplitter position due to Planck-scale quantization of space-time Use cross-correlation technique and extended integration time to reach the predicted signal at a tiny distance scale 10-20 m/rtHz

  7. Power Recycling using optical cavities Highly reflective, curved end mirror Partially transmissive input coupling mirror Laser beam Resonance occurs when the wavelength λ and/or the cavity length L are tuned such that integer number of wavelengths fits inside the cavity. Then a standing wave builds up as the beam is recycled. The power recycling factor is 1/η where η=total power lost per pass. • This determines the resonance bandwidth and the cavity lifetime. A. S. Chou, Detector R&D Retreat, 5/5/11

  8. Optical cavities are narrow-band filters Highly reflective, curved end mirror Partially transmissive input coupling mirror Laser beam Heisenberg Uncertainty Principle gives Laser frequencies outside of the resonance band(s) simply reflect from the input mirror, since they do not satisfy the cavity boundary conditions. This makes a narrow band optical filter. The bandwidth depends only on cavity parameters and is independent of the optical frequency. A. S. Chou, Detector R&D Retreat, 5/5/11

  9. Light on resonance builds up! Power build-up Laser beam If the dominant cavity loss mechanism is back out through the input coupling mirror: • All incident power at the resonant frequency enters the cavity, spends some time circulating, and then exits back through the way it came. Example: Holometer L=40 m cavity, η=10-3 • Circulating power = 1000 × input power  1022γ/s • Cavity harmonic resonances separated by c/2L = 3.75 MHz • Δf=3.75 kHz (compare to Nd:YAG laser frequency = 280 THz) A. S. Chou, Detector R&D Retreat, 5/5/11

  10. 4/18/11: Completed installation of 40m long vacuum system at MP8. Thanks to AD Tevatron vacuum group! (Scott McCormick, Bill Dymond, Dan Lambert, Bob Steinberg, James Williams) North end, looking south South end, looking north

  11. End station vacuum vessels hold custom optical cavity mirrors and eventually beamsplitters A. S. Chou, Detector R&D Retreat, 5/5/11

  12. Beamspot on injection mirror. Due to seismic motion of cavity and laser frequency noise, different modes (with different transverse momentum) drift in and out of resonance. A. S. Chou, Detector R&D Retreat, 5/5/11

  13. Pound Drever Hall Locking Laser beam Measure the length of the cavity by looking at the coherent interference between: A) Light that reflects directly from the (partially transmissive) injection mirror and B) Light near resonance that makes a roundtrip in the cavity and leaks back out Lock condition: Zero phase difference when cavity length = integer number of ½ wavelengths. A. S. Chou, Detector R&D Retreat, 5/5/11

  14. Sinusoidal sweep of laser frequency by piezo-electric pressure on laser crystal. Separation of cavity harmonics indicates the laser PZT frequency response is 1.5 MHz/Volt. 3.75 MHz A. S. Chou, Detector R&D Retreat, 5/5/11

  15. Pound-Drever-Hall technique gives a signed error signal for detecting instantaneous mismatches between the laser frequency and the cavity resonance. Width of resonance indicates a power-recycling factor of around 20. (1W builds up to 20 W). Just for fun: Q=280 THz/150 kHz = 2×109 A. S. Chou, Detector R&D Retreat, 5/5/11

  16. Cavity lock achieved in 3 ways Analog loop using benchtop amplifiers, filters Analog loop using custom servo box. Feed back to the laser PZT to force the laser frequency to follow the instantaneous resonant frequency of the cavity. Digital loop using Labview, digital data acquisition, FPGAs A. S. Chou, Detector R&D Retreat, 5/5/11

  17. Cavity locked on Gaussian fundamental mode. A 40m long standing wave with 8×107 nodes! A. S. Chou, Detector R&D Retreat, 5/5/11

  18. Working on stability of lock, via negative feedback loop. Feedback signal adjusts the laser wavelength to match small changes in the instantaneous length of the cavity. A. S. Chou, Detector R&D Retreat, 5/5/11

  19. Application 3: Precise angle measurement via Wavefront Sensing Interference of plane waves traversing two different paths, one of which samples an optic cocked from its ideal alignment. A. S. Chou, Detector R&D Retreat, 5/5/11

  20. Measure brightening and dimming of fringe using a quadrant photodiode Fringe brightness gives phase difference along the wavefront, and hence the longitudinal lead/lag distance Shot-noise-limited resolution. Lots of photons help! A. S. Chou, Detector R&D Retreat, 5/5/11

  21. Gaussian spot size w provides the lever arm Resulting angular resolution: w (angular divergence) × (phase resolution) A. S. Chou, Detector R&D Retreat, 5/5/11

  22. 10 mW laser power, L~ 1 meter A. S. Chou, Detector R&D Retreat, 5/5/11

  23. Uses for intense coherent optical beams Searches for exotic, rare scattering processes • 1024 photons/s Precision position measurements • 10-18m/rtHz resolution Precision angle measurements • 10-12 radians/rtHz resolution A. S. Chou, Detector R&D Retreat, 5/5/11

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