Chapter 4 Other Techniques: Microscopy, Spectroscopy, Thermal Analysis
Photo-thermal Deflection Spectroscopy
description
Transcript of Photo-thermal Deflection Spectroscopy
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Photo-thermal DeflectionPhoto-thermal DeflectionSpectroscopySpectroscopy
George Noid
LIGO SURF Student
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SummarySummary
Introduction Theory Experiment Results
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LIGOLIGO TESTTEST MASSESMASSES
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
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Photothermal Deflection Spectroscopy (PDS)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
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PDSPDS
Probe– Does not disturb sample– Detected
Pump- More powerful- Modulated- Not detected
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DeflectionDeflection
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Deflection (cont.)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
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The Experiment: two laser The Experiment: two laser tablestables
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
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Pump TablePump Table
Nd YAG
chopper
5- axis fiberaligner
PolarizationSelecting filter
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Injecting and MaximizingInjecting and Maximizing
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Probe tableProbe table
Photo detector
sample
He Ne laser
Fiber conduit
telescope
Fiber chuck
Aspheric lensholder
1064 mirror
beam tube
XY stage
XYZstage
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Probe Table: laser alignmentProbe 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
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DataData
• 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
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Representative PeakRepresentative Peakfourier transform of photothermal deflection
0.00E+005.00E-061.00E-051.50E-052.00E-052.50E-053.00E-053.50E-054.
50E+
02
4.58
E+02
4.67
E+02
4.75
E+02
4.83
E+02
4.91
E+02
5.00
E+02
5.08
E+02
5.16
E+02
5.24
E+02
5.33
E+02
5.41
E+02
5.49
E+02
frequency(Hz)
sign
al(m
Vrm
s)
Series2