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Photo-thermal Deflection Spectroscopy

Photo-thermal Deflection Spectroscopy. George Noid LIGO SURF Student. Summary. Introduction Theory Experiment Results. Fused Silica Currently uses Thermal Conductivity is 1.38 W/mK. Synthetic Sapphire Proposed for LIGO II Crystal Systems

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Photo-thermal Deflection Spectroscopy

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  1. Photo-thermal DeflectionSpectroscopy George Noid LIGO SURF Student

  2. Summary • Introduction • Theory • Experiment • Results

  3. Fused Silica Currently uses Thermal Conductivity is 1.38 W/mK Synthetic Sapphire Proposed for LIGO II Crystal Systems Thermal Conductivity is 23.1 parallel to optical axis LIGOTESTMASSES

  4. Photothermal Deflection Spectroscopy (PDS) • PDS First used: 1979 • Two Lasers: • Pump • Probe • Temperature Gradient => Gradient in the index of refraction • Useful as a non-destructive spectroscopic method • Can observe microscopic impurities in a crystal • Ex: trace metals in a sapphire crystal

  5. PDS • Probe • Does not disturb sample • Detected • Pump • More powerful • Modulated • Not detected

  6. Deflection

  7. Deflection (cont.) • Snells law: a sin A = b sin B • (..) = arcsin { (n0)/(n(..)) * sin (pi/2 - )} •  = laser angles • = angle of deflection • n0 = index of refraction of sapphire (1.862) • n = index of refraction function caused by PDS

  8. Pump table 700 mW Nd YAG laser Chopper Fiber coupler Fiber Probe table 5 mW He Ne Fiber Telescope 1064 mirror Biconvex lens Sapphire crystal Quad cell Detetector The Experiment: two laser tables

  9. Pump Table 5- axis fiber aligner Polarization Selecting filter chopper Nd YAG

  10. Injecting and Maximizing

  11. Probe table HeNelaser 1064 mirror Fiber conduit XYZ stage Fiber chuck sample beamtube Aspheric lens holder telescope Photo detector XY stage

  12. Probe Table: laser alignment • Small angle theta in the y direction • Increases interaction length • Beam waists: 80 microns • Nd Yag • Magnified, collimated in telescope • Reflected off mirror • Focused in biconvex lens into sapphire • He - ne • Passes through 1064 mirror • Focused in biconvex lens into sapphire

  13. Data • Initial results were inconclusive with lock- in amplification. • Observed PDS with signal analyzer • Pump power incident: 300 mw • Chopping frequency: 500 Hz • Maximum signal to noise ratio: 27 to 3 • Crystal mapping ongoing

  14. Representative Peak

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