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PHYS231 presentation @ POSTECH
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PHOTON COUNTING AND STATISTICS OF LIGHTDongwook Goh
LIGHT AS A PRTICLE
Figure : hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
Single Photon Counting Module (SPCM)
Figure : http://www.perkinelmer.com/
SPCM-AQRH-10FC
Single Photon Timing Resolution : ~1 ps
Dark Counting : ~1500 /s
One can vary the “cut-off time”
LIGHT SOURCES : THERMAL AND COHERENT LIGHT
Figure : Wikipedia
Thermal Light Coherent Light
§ Various Frequencies§ Out of Phase§ Bose-Einstein Distribution§ Blackbody
§ Single Frequency§ In Phase§ Poisson Distribution§ Laser
LIGHT SOURCES : THERMAL AND COHERENT LIGHT
Thermal Light : Bose Einstein Distribution
Coherent Light : Poisson Distribution
LIGHT SOURCES : THERMAL AND COHERENT LIGHT
Thermal Light : Bose Einstein Distribution
Coherent Light : Poisson DistributionStatistics of photon
depends on the nature of the source.
THE PRINCIPLE OF LASER
LASERLight Amplification by Stimulated Emission of Radiation
Watch the Video !Figure : Wikipedia
PSEUDO-THERMAL LIGHT
Figure : D. Meschede – Optics, Light, and Lasers
Original paper :F. T. Arecchi, Phys. Rev. Lett. 15, 912, Measurement of the Statistical Distribution of Gaussian and Laser Sources
PSEUDO-THERMAL LIGHT
Figure : Kang-Hee Hong, Young-Sun Song, Yoon-Ho Kim,Student Manual : Electronics & Instrumentation Lab, POSTECH, 2009.
Velocity of the Rotating Disk : Average Irregularities Size :
Coherence Time~~10m/s, ~10mAssume~ = à
PSEUDO-THERMAL LIGHT
Figure : Kang-Hee Hong, Young-Sun Song, Yoon-Ho Kim,Student Manual : Electronics & Instrumentation Lab, POSTECH, 2009.
Velocity of the Rotating Disk : Average Irregularities Size :
Coherence Time~~10m/s, ~10mAssume~ = à
Cut-off time of the SPCM should be
smaller than .
Experiment Setup
He-Ne Laser
Single Mode Fiber
SPCM
Mirror
NI ELVIS
ND filter
Experiment Setup
He-Ne Laser
Single Mode Fiber
SPCM
Mirror
NI ELVIS
Lens
Rotating Disk
Result : Coherent Light
Cut-off Time
Photon Flux = ~30,000 counts/s
Poisson Distribution Curve Fitting
Result : Pseudo-Thermal LightBose-Einstein Distribution Curve Fitting
Cut-off Time = Photon Flux = 46,084 counts/s
Result : Pseudo-Thermal Light
Cut-off Time =
Photon Flux
Photon Flux = ~500,000 counts/s
Cut-off Time
Coherence time : ~
Conclusion§ Laser follows a Poisson statistics, so laser is a coherent light.
§ Rotating glass plate generates a pseudo-thermal light.
§ Pseudo-thermal light follows Bose-Einstein statistics when the cut-off time is smaller than 20 .
§ The coherence time of the pseudo-thermal light is about 10~20 in this experiment.
§ As the cut-off time increases, statistics of pseudo-thermal light approaches Poisson distribution
§ One can say that pseudo-thermal light is approximately a thermal light when time resolution is larger than the coherence time.
