vii
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
DECLARATION
ii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
LIST OF CONTENTS
vii
LIST OF TABLES
x
LIST OF FIGURES
xii
LIST OF SYMBOLS
xvi
INTRODUCTION
1.1 Literature Review
1
1.2 Q-Switching Laser
2
1.3 Passive Q-Switching
5
1.4 Research Objective
6
1.5 Research Scope
6
1.6 Thesis Outline
7
THEORY
2.1 Introduction
9
2.2 Pulsed Dye Laser
9
2.2.1
Active Medium
10
2.2.2
Wavelength Selection in Pulsed Dye Lasers
10
2.2.3
Excitation Method
11
viii
2.3
2.4
2.5
3
2.3.1
15
Pumping Mechanism of Q-Switching
Q-Switching Methods
16
2.4.1
Mechanical Q-Switches
17
2.4.2
Electro-Optic Q-Switches
17
2.4.3
Acousto-Optic Q-Switches
18
Passive Q-Switches
19
2.5.1
20
Mechanism Of Bleaching
3.1
Introduction
24
3.2
Sample Preparation
25
3.2.1
Organic Dyes
25
3.2.2
Cr4+: YAG Crystal
26
3.4
Dye Laser
26
3.3.1
Pulse Detection
28
3.3.2
Mode of Triggering
29
Image Processing System
31
3.4.1
31
Processing Software
3.5
Calibration of Optimum Laser Performance
33
3.6
Experimental Setup
34
DYE LASER
4.1
Introduction
36
4.2
Externally Triggrering Dye Laser
37
4.3
Diagnose The High Performances of Dye Laser
40
4.3.1
Wavelength
40
4.3.2
Cavity Length
44
4.4
5
14
METHODOLOGY AND MATERIAL
3.3
4
Q-Switching
Summary
50
PASSIVELY Q-SWITCHED DYE LASER
5.1
Introduction
51
5.2
Passive Q-Switch With Different Saturable Absorber
52
ix
5.2.1
Organic Dyes Saturable Absorber
52
5.2.1.1
DODCI
53
5.2.1.2
DQOCI
60
5.2.1.3
Cryptocyannine
65
5.2.1.4
Comparison of Organic Dyes
70
Saturable Absorber
5.2.2
5.3
6
Summary
75
76
DIAGNOSE OF PASSIVE Q-SWITCH LASER BEAMS
6.1
Introduction
78
6.2
Analyzing The Beam
79
6.2.1
Gaussian Fit Analysis
79
6.2.2
Beam Spot
86
6.3
7
Cr4+: YAG Crystal Saturable Absorber
Summary
89
CONCLUSIONS AND SUGGESTION
7.1
Conclusions
90
7.2
Problems And Suggestion
93
REFERENCES
95
APPENDIX 1
100
x
LIST OF TABLES
TABLE NO.
4.1
TITLE
Power depending on wavelength of dye laser with
PAGE
41
Coumarin 500 as a lasing medium
4.2
Power depending on wavelength of dye laser with
Rhodamine 590 as a lasing medium
41
4.3
Pulse duration of dye laser with Coumarin 500 as lasing
medium produced at different cavity length
45
4.4
Pulse duration of dye laser with Rhodamine as lasing
medium produced at different cavity length
45
4.5
Pulse Energy of dye laser with Coumarin 500 as lasing
47
medium produced at different cavity length
4.6
Pulse Energy of dye laser with Rhodamine 590 as lasing
medium produced at different cavity length
47
5.1
Pulse duration of passive Q-switch laser upon concentration
of DODCI
53
5.2
Pulse energy of passive Q-switch laser upon concentration
of DODCI
55
5.3
Peak Power of passive Q-switch laser upon concentration of
58
DODCI.
xi
5.4
Pulse duration of passive Q-switch laser upon concentration
of DQOCI.
61
5.5
Pulse energy of passive Q-switch laser upon concentration
of DQOCI
63
5.6
Peak power of passive Q-switch laser upon concentration of
DQOCI
64
5.7
Pulse duration of passive Q-switch laser upon concentration
66
of Cryptocyannine.
5.8
Pulse energy of passive Q-switch laser upon concentration
of Cryptocyannine
67
5.9
Peak power of passive Q-switch laser upon concentration of
DQOCI
69
5.10
Pulse duration, pulse energy and peak power for different
position of saturable absorber
75
6.1
Gaussian width in horizontal and vertical profiles for
83
DQOCI saturable absorber due to working distance.
6.2
Gaussian width in horizontal and vertical profiles for Cr4+:
YAG saturable absorber due to working distance.
83
6.3
Beam spot perimeter and area due to working distance for
passively Q-switched dye laser with Coumarin 500 as a
lasing medium
87
6.4
Beam spot perimeter and area due to working distance for
passively Q-switched dye laser with Rhodamine 590 as a
lasing medium
88
xii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
2.1
Energy level diagram of a dye laser
2.2
Absorption and fluorescence emission spectrum of a typical
organic molecule
13
2.3
Mechanism for dye laser action
2.4
Development of a Q-switched laser pulse. (a). The pumping
source output, (b). Cavity loss, (c).Population inversion,
and (d). Q-switch output.
2.5
Mechanical Q-switch (rotating chopper).
2.6
Electro-optic Q-switch
2.7
Acousto-optic Q-switch.
2.8
Saturable absorber Q-Switch
2.9
Absorption as a function of incident light intensities for a
saturable absorber
12
14
16
17
18
19
20
21
xiii
2.10
Energy-level diagram for most saturable absorber dye
molecules in solution
21
2.11
Schematic illustration of the three processes, absorption,
spontaneous emission and stimulated emission.
22
3.1
Schematic dimension of Cr4+: YAG crystal
26
3.2
LN120C top view
27
Dye module Optical Layout
27
3.4
BPX 65 Photo detector Circuit
29
3.5
Block diagram of trigger unit
30
3.6
Experimental set-up for measuring the delay time of the dye 30
laser
3.7
CCD Profiler Window
31
3.8
Calibration screen option for Video Test 5.0 Software
32
3.9
Dye laser alignment set-up for calibration
34
3.10
Laser cavity of passively Q-switched dye laser
34
3.11
Schematic diagram of experimental set up for passively QSwitched dye laser
35
4.1
Pulse of input voltage from trigger unit
37
4.2
(a). Channel 1: Pulse from trigger unit.
38
3.3
(b). Channel 2: Pulse from BPX 65 photo detector
4.3(a)
Pulse shape of the dye laser with Coumarin 500 as a lasing
medium.
39
4.3(b)
Pulse shape of the dye laser with Rhodamine 590 as a
lasing medium
39
xiv
4.4
Accumulated power of dye laser with Coumarin 500 upon
on wavelengths
42
4.5
Accumulated power of dye laser with Rhodamine 590 upon
on wavelength
43
4.6
The pulse duration and output power versus cavity length of 46
passively Q-switched Rhodamine 590 dye laser.
4.7
The output energy of dye laser upon cavity length with
different lasing medium
4.8
The pulse duration and output power versus cavity length of 49
passively Q-switched Rhodamine 590 dye laser.
5.1
Pulse Duration versus concentration of DODCI on different
lasing medium
54
5.2
Pulse Energy versus concentration of DODCI on different
lasing medium
55
5.3
Graph natural logarithm of pulse energy versus
concentration
57
5.4
Peak Power versus concentration of DODCI on different
lasing medium
59
5.5
Graph natural logarithm of peak power versus concentration 60
5.6
Pulse Duration versus concentration of DQOCI on different
lasing medium
61
5.7
Graph natural logarithm of pulse duration versus
concentration
62
5.8
Pulse Energy versus concentration of DQOCI on different
lasing medium
63
5.9
Peak Power versus concentration of DQOCI on different
lasing medium
65
5.10
Pulse Duration versus concentration of Cryptocyannine on
different lasing medium
66
48
xv
5.11
Pulse Energy versus concentration of Cryptocyannine on
different lasing medium
68
5.12
Peak Power versus concentration of Cryptocyannine on
different lasing medium
69
5.13(a)
Figure 5.13(a): Pulse duration versus concentration of
different saturable absorber materials
70
5.13(b)
Pulse duration versus concentration of different saturable
absorber materials
71
5.14(a)
Pulse energy versus concentration of different saturable
absorber materials
72
5.14(b)
Pulse energy versus concentration of different saturable
absorber materials
73
5.15(a)
Peak power versus concentration of different saturable
absorber materials
74
5.15(b)
Peak power versus concentration of different saturable
absorber materials
74
6.1
Gaussian profile of passive Q-switch laser beam. (a)
Vertical profile, (b). Horizontal profile
80
6.2
Beam Profile of Q-switching laser; (a). Three-dimensional
image shows the distribution of Gaussian beam profile (b).
Two-dimensional image.
81
6.3
Correlation upon working distances for DQOCI saturable
absorber.
85
6.4
Correlation upon working distances for Cr4+: YAG
saturable absorber.
85
6.5
Two-dimensional image of passively Q-switched dye laser
using DQOCI upon different working distance
86
6.6
Two-dimensional image of passively Q-switched dye laser
using Cr4+: YAG crystal upon different working distance
87
6.7
Beam spot area against working distance
88
xvi
LIST OF SYMBOLS
Q
-
Quality factor
F
-
Photon flux of the incident light
σ12
-
Absorption cross section
W12
-
Absorption probability
σ 21
-
Stimulated emission cross section
m
-
Grating order
λ
-
Wavelength
d
-
Grating constant
θ
-
Angle between the grating and the laser gain axis
I
-
The intensity of a pixel at location x
i(h, v)
-
The intensity at location (h, v)
V
-
The maximum intensity of the fitted Gaussian curve (Peak
Intensity)
C
-
The centre of the Gaussian fit peak (Centroid)
σ
-
The radius of the Gaussian fit curve at the 1/e2 intensity
level (diameter)