Laser với buồng cộng sản gần ppsx

Acknowledgments

The writing of this graduate research paper would not have been

possible without the help and encouragement of many people.

I first acknowledge the support of my family. Without their encour￾agement and patience, I would never have completed this topic.

I wish to warmly acknowledge my teachers and friends, whose helps,

suggestions and encouragements have certainly contributed to improv￾ing the page.

Specially, I would like to offer my sincerely thanks to my research

advisor Dr.Hoàng Hữu Hòa, belong to Department Of Educational

Testing - Quality Assurance of Hue University, who have taught, al￾tered, encouraged with all one’s heart to complete graduate research

paper.

Student

Nguyễn Văn Khuyên

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Contents

Acknowledgments i

List of figures vi

INTRODUCTION vii

Chapter 1 - STRUCTURES AND CHARACTERISTICS

OF LASERS 1

1.1 Laser structure . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 Active medium . . . . . . . . . . . . . . . . . . 1

1.1.2 Resonant cavity . . . . . . . . . . . . . . . . . . 3

1.1.3 Pumping mechanism . . . . . . . . . . . . . . . 4

1.2 Absorption, spontaneous and stimulated emission pros￾esses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.2.1 Absorption processes . . . . . . . . . . . . . . . 5

1.2.2 Spontaneous emission processes . . . . . . . . . 7

1.2.3 Stimulated emission processes . . . . . . . . . . 7

1.3 Laser characteristics . . . . . . . . . . . . . . . . . . . 10

1.3.1 Coherence . . . . . . . . . . . . . . . . . . . . . 10

1.3.2 Monochromaticity . . . . . . . . . . . . . . . . . 11

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1.3.3 Directionality . . . . . . . . . . . . . . . . . . . 11

Chapter 2 - REQUIREMENTS FOR OBTAINING POP￾ULATION INVERSIONS 12

2.1 Population inversion (necessary condition for a laser) . 12

2.2 Population inversion in two-level system . . . . . . . . 13

2.3 Population inversion in three-level system . . . . . . . 16

2.3.1 Three-Level Laser with the Intermediate Level as

the Upper Laser Level . . . . . . . . . . . . . . 16

2.3.2 Three-Level Laser with the Upper Laser Level as

the Highest Level . . . . . . . . . . . . . . . . . 18

2.4 Population inversion in four-level system . . . . . . . . 20

Chapter 3 - GENERAL OF LASER DYES AND DYE

LASERS 22

3.1 Introduction to laser dyes . . . . . . . . . . . . . . . . 22

3.2 Structure and spectrum of laser dyes . . . . . . . . . . 23

3.3 Spectral energy levels transitions . . . . . . . . . . . . 25

3.4 Characteristics of integrated dye lasers spectra . . . . . 28

Chapter 4 - INFLUENCE OF CAVITY LENGTH ON

INTEGRATED SPECTRAL OF BROADBAND DYE

LASER FROM LOW-Q AND SHORT CAVITY 33

4.1 Rate equation system analysis of spectral . . . . . . . . 33

4.2 Influence of the cavity length on integrated spectral of

broadband dye laser from low-Q and short cavity . . . 35

CONCLUSION 39

Graduate Research Paper Nguyễn Văn Khuyên

Contents iv

REFERENCES 40

APPENDIX 42

A - The absorption and stimulated emission cross sections of

NB/ethanol . . . . . . . . . . . . . . . . . . . . . . . . 42

B - The absorption and stimulated emission cross sections of

Rh6G/ethanol . . . . . . . . . . . . . . . . . . . . . . . 44

C - The absorption and stimulated emission cross sections of

C30/ethanol . . . . . . . . . . . . . . . . . . . . . . . . 47

Graduate Research Paper Nguyễn Văn Khuyên

List of figures

1.1 The structure of Lasers . . . . . . . . . . . . . . . . . . 1

1.2 The processes: (a) absorption, (b) spontaneous emis￾sions, (c) stimulated emission . . . . . . . . . . . . . . 5

1.3 Properties of laser light . . . . . . . . . . . . . . . . . . 10

2.1 Inversion in two-level system . . . . . . . . . . . . . . . 14

2.2 The relationship between N0/N with Ω . . . . . . . . . 15

2.3 Energy levels and relevant excitation and decay pro￾cesses for the traditional three-level laser. . . . . . . . . 18

2.4 Energy-level diagram and relevant excitation and decay

processes of an atomic three-level laser system. . . . . . 19

2.5 Energy-level diagram and relevant excitation and decay

processes of a four-level laser system. . . . . . . . . . . 21

3.1 Chemical structure of some common dyes: (a) Rhodamine

6G, (b) Coumarin 2 . . . . . . . . . . . . . . . . . . . . 22

3.2 Molecular transitions . . . . . . . . . . . . . . . . . . . 23

3.3 UV/VIS absorption and fluorescence spectra of the laser

dye pyrromethene 567 in methanol solution . . . . . . . 24

3.4 Typical energy levels for a dye in solution . . . . . . . 26

3.5 Mechanism for dye laser action . . . . . . . . . . . . . 27

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