applications of intense coherent optical laser beams

Applications of intense coherent optical laser beams

Aaron S. ChouWilson Fellow, FNAL

Detector R&D RetreatMay 5, 2011

Axions Holographic information bound New forces

A. S. Chou, Detector R&D Retreat, 5/5/112

Use large, coherent photon fluxes for

1) Searches for exotic, rare scattering processes

2) Precision position measurements

3) Precision angle measurements

• 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


The Actors


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

…


Application 1: Use lots of photons to search for rare photon-photon scattering processes mediated by axion-like or Higgs-like particles

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Tevatron

Increase photon flux from 1019 to 1024 γ/s, increase L from 6 to 40m,resonantly detect improve axion sensitivity by 4 orders of magnitude.

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:

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1064 nmN

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


Power Recycling using optical cavities

• 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.

Laser beam

Partially transmissive input coupling mirror

Highly reflective, curved end mirror


• 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.

Laser beam

Partially transmissive input coupling mirror

Highly reflective, curved end mirror

Optical cavities are narrow-band filters

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Δf =c2πL

×ηHeisenberg Uncertainty Principle gives


• 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 1022 γ/s Cavity harmonic resonances separated by c/2L = 3.75 MHz Δf=3.75 kHz (compare to Nd:YAG laser frequency = 280 THz)

Laser beam

Light on resonance builds up!

Power build-up

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)

South end, looking north North end, looking south


End station vacuum vessels hold custom optical cavity mirrors and eventually beamsplitters


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.


Pound Drever Hall Locking

Measure the length of the cavity by looking at the coherent interference between:

A) Light that reflects directly from the (partially transmissive) injection mirror andB) 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.

Laser beam


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


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


Cavity lock achieved in 3 ways Analog loop using

custom servo box.Analog loop using benchtop amplifiers, filters

Digital loop using Labview, digital data acquisition, FPGAs

Feed back to the laser PZT to force the laser frequency to follow the instantaneous resonant frequency of the cavity.


Cavity locked on Gaussian fundamental mode.

A 40m long standing wave with 8×107 nodes!


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.


Application 3: Precise angle measurement via Wavefront Sensing

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Interference of plane waves traversing two different paths, one of which samples an optic cocked from its ideal alignment.


Measure brightening and dimming of fringe using a quadrant photodiode

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Fringe brightness gives phase difference along the wavefront, and hence the longitudinal lead/lag distance

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σL =σφ2π× λ

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σφ ≡2

dNγ /dtShot-noise-limited resolution.Lots of photons help!


Gaussian spot size w provides the lever arm

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€

σL

w

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σθ =σLw

≈λ2πL

×2

dNγ /dt

Resulting angular resolution:

(angular divergence) × (phase resolution)


10 mW laser power, L~ 1 meter


Uses for intense coherent optical beams

Searches for exotic, rare scattering processes 1024 photons/s

Precision position measurements 10-18 m/rtHz resolution

Precision angle measurements 10-12 radians/rtHz resolution

applications of intense coherent optical laser beams

Documents

rare photonphoton

fnal detector rd retreatmay

cavity length

cavity parameters

cavity lifetime

position resolution

input mirror

yag photon