LASERS AND HOLOGRAPHY

Transcription

1 LASERS AND HOLOGRAPHY

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3 LASERS AND HOLOGRAPHY P C MEHTA Instruments Research and Development Establishment Defence Research and Development Organisation Dehra Dun, India VVRAMPAL Department of Science and Technology New Delhi, India World Scientific Singapore New Jersey * London Hong Kong

4 Printed in Singapore. Published by World Scientific Publishing Co. Pte. Ltd. P O Box 128, Fairer Road, Singapore 9128 USA office: Suite IB, 1060 Main Street, River Edge, NJ UK office: 73 Lynton Mead, Totteridge, London N20 8DH LASERS AND HOLOGRAPHY Copyright 1993 by World Scientific Publishing Co. Pte. Ltd. All rights reserved, This book, or parts thereof, may not be reproduced in any form orby any means, electronic ormechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher. For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 27 Congress Street, Salem, MA 01970, USA. ISBN ISBN Printed in Singapore.

5 Dedicated to BHAPPO "The Candle burns and brightens those that cause it to burn"

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7 PREFACE The coming of lasers and their use for holography marked an important era in the advancement of physical sciences. This generated diverse fields of activity and gave new life to well researched areas like Raman spectroscopy. Holography provided an excited medium for three dimensional display. Lasers and holography continue to find new areas of applications. Their use in industry, medicine, communication and instrumentation for analysis and measurement are now well established. Individually, the two subjects, Lasers and Holography, have been treated at length in the literature and excellent reviews are available. The present book covers both the areas in a comprehensive manner. It is not always easy to get an overall view of a modern discipline in the presence of vast literature scattered in journals, books, reports and conference proceedings. Our effort of presenting both lasers and holography in a single volume may therefore appear rather ambitious but we hope it will achieve its purpose of providing the essentials of the topics and application update in a fairly reasonable extent. The subject of holography is still evolving and a number of new applications such as computer interconnects and in medicine are emerging fast. It simply depends on ones imagination to exploit the unique features of holograms. A complete treatment of such applications and their thorough understanding therefore need further developments in architectures, techniques and materials. The first three chapters discuss the physics and technology of lasers, while chapter 4 deals with the principles and techniques of holography. The chapters 5 to 9 describe the applications. The applications in the areas of medicine, information processing, nondestructive testing and interconnections have been included for their relevance in the context of recent developments. In writing the book a large number of original publications have been used. However, the references cited do not represent the complete bibliography on the subject. Only those references are listed which have been used for writing the book. It is natural in such a book that many important publications may have been left unintentionally, for which

8 viii PREFACE the authors regret. The book aims for a readership of those studying for a Master's degree in Applied Optics, Lasers and Holography and requiring an understanding of the generation and use of coherent optical radiation. The book will be useful to students, researchers and professionals actively involved in the development of lasers, holography and their applications. It is hoped that the students and researchers would find it useful and interesting. One of the authors (PCM) is grateful to Dr O.P. Nijhawan, Director, IRDE, Dehra Dun for helpful suggestions. The authors are also thankful to Mr. Devendra Mohan, Mr. K.S.S. Rao, Mr. Chandra Bhan and Mr. Pritam Lai for providing some of the photographs used in the book. We take great pleasure in acknowledging the valuable help of Dr R.K. Tyagi and Mr. A.K. Musla for their critical reading of the manuscript. We wish to specially thank Mr. R.K. Kukreti for his patience and skill in typing. We are obliged to Mr. A.K. Musla for his painstaking efforts in type setting all the equations and tables, and formatting the manuscript in the computer for laser printing. Finally, we express our appreciation to the World Scientific Publishing Company for the high quality of publication. The authors acknowledge the patience and moral support of their spouses, Dr. Mrs. P. Mehta (PCM) and Mrs. S. Rampal (WR) during the writing of the book. May 19, p.c. Mehta V.V. Rampal

9 CONTENTS PREFACE vii 1. OPTICAL RADIATION AND PHOTONS Nature of light Quantum description of radiation Fluctuation properties Power flow of electromagnetic radiation Interaction of radiation with matter- Emission and absorption of radiation Transition probability Emission and absorption of radiation by bound electrons Spontaneous and stimulated radiation Einstein coefficients Optical gain Gain saturation Optical resonators Resonant modes of optical cavity Theoretical methods for analyzing the modes Gaussian beams Design of open resonator cavity X Q' of optical resonator Unstable resonators Threshold condition for laser oscillation Cavity coupling Frequency of resonant modes Frequency selection of laser oscillation Transverse modes selection Longitudinal mode selection Mode competition Hole burning Mode pulling Frequency stability of laser output Single mode operation of a laser Coherence of laser radiation Time coherence 75

10 X CONTENTS Spatial coherence Time and space coherence Transient coherence Higher order coherence functions Factors responsible for imparting coherence to laser radiation Laser noise General treatment of laser oscillation SPATIAL, TEMPORAL AND SPECTRAL CHARACTERISTICS OF LASER Introduction Mode locking Methods of mode locking Mode locking with saturable absorber- Passive mode locking Active mode locking Acousto-optic and electro-optic modulators as mode locking devices Self mode locking Experimental arrangement of an active mode\ locked laser Stabilization of mode locked lasers Measurement on mode locked pulses Generation and measurement of ultrashort pulses Colliding Synchronous pulse mode locking mode locking Self phase modulation and pulse compression Measurement of ultrafast pulses Mode locking of transverse modes Q-switching and cavity dumping Cavity dumping Q-switching Relaxation oscillation SPECIFIC LASER SYSTEMS Solid state lasers The Ruby laser Neodymium lasers Tunable solid state lasers Sensitized solid state laser materials Eye safe solid state lasers 164

11 CONTENTS xi Diode laser pumping of solid state lasers The slab lasers Colour centre lasers Semiconductor lasers The p-n junction laser diode Heterojunction lasers Recent advances Quantum well lasers Distributed feedback lasers Dye lasers The dye as laser medium Spectra of organic dyes Requirements for starting oscillation Cavity arrangements Output characteristics Specific purpose developments Gas lasers He-Ne laser Argon ion laser Carbon dioxide laser TEA CO laser Gas dynamic CO laser Chemical lasers HF/DF laser Carbon monoxide (CO) laser Excimer lasers Nitrogen laser Metal vapour lasers He-Cd laser Hg-Br laser Copper vapour laser Plasma recombination laser Far infrared (FIR) lasers Free electron laser (FEL) Harmonic generation of laser radiation through nonlinear processes Second order effects in nonlinear crystals- Generation of second harmonics Third order nonlinear processes in gaseous media- Generation of tunable UV and IR 245

12 xii CONTENTS 4. HOLOGRAPHY:PRINCIPLES AND TECHNIQUES Introduction Characteristics of a hologram In-line Holography: Gabor holography Off-axis Holography: Leith-Upatnieks holography Holographic imaging equations Image magnification Hologram aberrations Orthoscopic and pseudoscopic images Classification of holograms Amplitude and phase holograms Classification based on hologram thickness Classification based on direction of reconstructed image Classification according to recording arrangement Practical holography Laser Reference-to-object intensity ratio Angle between reference and object beams Polarization of light beams Vibration isolation table Optical components and mounts Hologram recording geometries Hologram of a moving object Efficiency of a hologram Refractive index modulation Signal-to-Noise Ratio (SNR) Holographic recording materials Modulation transfer function Nonlinear recording Silver halide emulsion Hardened dichromated gelatin (DCG) Photopolymers Photoresists Photothermoplastics Photochromic materials Photorefractive crystals (Electrooptic materials) Summary of recording materials Health hazards of hologram processing chemicals Display holography Requirements of a display hologram 378

13 CONTENTS xiii hologram Rainbow hologram Holographic stereogram Viewing zone Change of size Dispersion compensation Sources for reconstruction Hologram display systems Holographic 3D printer Holographic television Holographic cinematography Colour holography Chromaticity diagram Recording of colour holograms Volume colour holograms Recording geometry Pseudocolouring Special techniques Local reference beam hologram Multiple-exposure holography (Scanning object beam holography) Multiplexed hologram Multifaceted hologram Pinhole hologram Edge-lit hologram Hologram replication Optical interferometric techniques Mechanical replication technique (Embossed holograms) Polarization holography Depolarization effects Polarization recording Evanescent wave holography (Waveguide holography) Holographic lithography HOLOGRAPHIC INTERFEROMETRY Introduction Double-exposure holographic interferometry Single-exposure real-time holographic interferometry Time-average holographic interferometry Stroboscopic holographic interferometry Temporally modulated holography 488

14 xiv CONTENTS 5.7. Fringe linearization holographic interferometry Desensitized holographic interferometry Digital holographic interferometry Fringe localization Pure translation Pure rotation about an axis in the surface Sandwich hologram interferometry Applications Holographic nondestructive testing (HNDT) Holographic contouring Two wavelength holographic contouring Two refractive index holographic contouring Contouring by change in the illuminating angle Holographic interferometry with fibre optics HOLOGRAPHIC OPTICAL ELEMENTS What is a HOE? Hologram of a point Resolution of a HOE Design aspects Fabrication Holographic gratings/mirrors Applications of HOEs Spectral filters Applications in optical communication HOEs in compact disks Holographic laser beam attenuator HOE based fibre optic gyroscope Holographic scanner Diffractive-refractive telescope Applications in architecture Beam combiners Fingerprint sensor HOEs in Art INTERCONNECTS Introduction Optical interconnects Classification of holographic interconnects HOE size Desirable characteristics 558