Investigations of self-pumped phase conjugate laser beams and coherence length.

62 Pages·0.64 MB·en_US

by  Sutton, George M.;Biblarz, Oscar.

MOHTETCY CA 93943-5101

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sI.TTVITELSET(IInGclAudTeISeOcuNriStyCOlaFssifiScaEtioLn)F-PUMPED PHASE CONJUGATE LASER BEAMS AND COHERENCE LENGTH (Unclassified)
PERSONAL AUTHOR(S)
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jtton, George M.
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Master's Thesis FROM TO March, 1993 54
SUPPLEMENTARY NOTATION: The views expressed in this thesis are those of the author and do not reflect the official policy or
I
3sition of the Department of Defense or the U.S. Government.
COSATI CODES 18. SUBJECT TERMS (Continueonreverseitnecessaryandidentifybyblocknumber)
Coherence Length, Photorefractive Effect, Barium Titanate. Self-Pumped Phase
FIELD GROUP SUB-GROUP
Conjugation
J. ABSTRACT (Continueonreverseifnecessaryandidentifybyblocknumber)
The phase conjugation process by a nonlinear, photorefractive crystal is not completely ideal and losses should be expected
i occur after a beam is conjugated. This thesis research investigates possible changes in coherence length as a result of internal
»sses in barium titanate (BaTi03). Additionally, laser reflections from a comer cube reflector is also examined for changes in
jherence length. Experimental findings are inconclusive because the conventional spectrometer used to measure coherence length
id not possess the required resolution. It is recommended that an interferometer which can resolve the laser line width be utilized
>r future coherence length measurements, together with a means of blocking the conjugated beam from entering the laser cavity
nd destabilizing the oscillations within.
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2a. NAME OF RESPONSIBLE INDIVIDUAL 22D. TELEPHONE (IncludeAreaCooe, 22c. OFFICE SYMBOL
Oscar Biblarz 408-656-3096 AA/Bi
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INVESTIGATIONS OF SELF-PUMPED PHASE
CONJUGATE LASER BEAMS AND COHERENCE LENGTH
by
George M. Sutton
Lieutenant, United States Navy
B.S., Southern University, 1986
Submitted in partial fulfillment of the
requirements for the degree of
MASTER OF SCIENCE IN PHYSICS
from the
NAVAL POSTGRADUATE SCHOOL
March, 1993
ABSTRACT
The phase conjugation process by a nonlinear, photorefractive crystal is not
completely ideal and losses should be expected to occur after a beam is
conjugated. This thesis research investigates possible changes in coherence length
as a result of internal losses in barium titanate (BaTi0 Additionally, laser
3).
reflections from a corner cube reflector is also examined for changes in coherence
length. Experimental findings are inconclusive because the conventional
spectrometer used to measure coherence length did not possess the required
resolution. It is recommended that an interferometer which can resolve the laser
line width be utilized for future coherence length measurements, together with
a means of blocking the conjugated beam from entering the laser cavity and
destabilizing the oscillations within.
111
ACKNOWLEDGEMENTS
I would like to thank Professor Biblarz for his support and guidance
throughout my research. I am also appreciative to Dr. Hossin Abeledeyem of
Marshall Space Flight Center for his assistance in performing the phase
conjugation experiments for this thesis. Finally, I am especially grateful to my
wife, DeAnne, for her unfailing support during my tenure here at the Naval
Postgraduate School.
IV
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TABLE OF CONTENTS
INTRODUCTION
I. 1
THEORY AND BACKGROUND
n. 3
PHASE CONJUGATION
A. 3
WAVE EQUATION IN NONLINEAR MEDIUM
B. 5
C
THE PHOTOREFRACTIVE EFFECT
9
D. WAVE MIXING IN PHOTOREFRACTIVE MEDIA 12
1. Two-Wave Mixing 13
2. Four Wave Mixing 15
E. SELF PUMPED PHASE CONJUGATION 17
THE BARIUM TITANATE CRYSTAL
F. 21
1. Domains and Poling of BaTi0 21
3
2. Electro-optic Properties of BaTiO, 24
LASER COHERENCE
G. 25
m. EXPERIMENTAL INVESTIGATION 26
OVERVIEW
A. 26
PHASE CONJUGATE COHERENCE LENGTH
B.
MEASUREMENTS
26
1. Setup 27
2. Procedure 29
CORNER CUBE REFLECTOR MEASUREMENTS
C. 33
1. Setup 33
2. Procedure 34
DISCUSSION OF RESULTS
IV. 38
CONCLUSIONS AND RECOMMENDATIONS
V. 40
LIST OF REFERENCES 42
APPENDIX. POSSIBLE MECHANISIMS OF BROADENING IN BaTi0 ... 44
3
INITIAL DISTRIBUTION LIST 46
VI