PHYS231 presentation @ POSTECH

1. PHOTON COUNTING AND
STATISTICS OF LIGHT
Dongwook Goh

2. LIGHT AS A PRTICLE
Figure : hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

3. Single Photon Counting Module
(SPCM)
SPCM-AQRH-10FC
Single Photon Timing
Resolution : ~1 ps
Dark Counting : ~1500 /s
One can vary the “cut-off time”
Figure : http://www.perkinelmer.com/

4. LIGHT SOURCES :
THERMAL AND COHERENT LIGHT
Thermal Light
§
§
§
§
Coherent Light
Various Frequencies
Out of Phase
Bose-Einstein Distribution
Blackbody
§
§
§
§
Figure : Wikipedia
Single Frequency
In Phase
Poisson Distribution
Laser

5. LIGHT SOURCES :
THERMAL AND COHERENT LIGHT
Thermal Light :
Coherent Light :
Bose Einstein Distribution
Poisson Distribution

6. LIGHT SOURCES :
THERMAL AND COHERENT LIGHT
Thermal Light :
Coherent Light :
Bose Einstein Distribution
Poisson Distribution
Statistics of photon
depends on the nature
of the source.

7. THE PRINCIPLE OF LASER
LASER
Light Amplification by Stimulated Emission of Radiation
Figure : Wikipedia
Watch the Video !

8. 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

9. PSEUDO-THERMAL LIGHT
Velocity of the Rotating Disk :
Average Irregularities Size :


Coherence Time

 ~

Figure : Kang-Hee Hong, YoungSun Song, Yoon-Ho Kim,
Student Manual : Electronics &
Instrumentation Lab, POSTECH,
2009.
Assume
~10 m/s, ~10 m
 ~   =  
à

10. PSEUDO-THERMAL LIGHT
Velocity of the Rotating Disk :
Average Irregularities Size :


Coherence Time
Cut-off time of

 ~
the SPCM should be

smaller than  .
Figure : Kang-Hee Hong, YoungSun Song, Yoon-Ho Kim,
Student Manual : Electronics &
Instrumentation Lab, POSTECH,
2009.
Assume
~10 m/s, ~10 m
 ~   =  
à

11. Experiment Setup
Mirror
NI ELVIS
ND filter
SPCM
Single Mode Fiber
He-Ne Laser

12. Experiment Setup
Mirror
NI ELVIS
Rotating Disk
SPCM
Lens
He-Ne Laser
Single Mode Fiber

13. Result : Coherent Light
Poisson Distribution Curve Fitting
Cut-off Time
Photon Flux = ~30,000 counts/s

14. Result : Pseudo-Thermal Light
Bose-Einstein Distribution Curve Fitting
Cut-off Time =  
Photon Flux = 46,084 counts/s

15. Result : Pseudo-Thermal Light
Photon Flux
Cut-off Time =  
Cut-off Time
Photon Flux = ~500,000 counts/s
Coherence time : ~ 

16. 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.