The introduction of innovative light sources, fibre laser sources and light emitting diodes, is opening unexpected perspectives into optical techniques and is promising new exciting applications in the field of biomedicine. Lasers and Current Optical Techniques in Biology aims to provide an overview of light sources, together with an extensive and authoritative description of the optical techniques in bio-medicine. This book is designed to give biomedical researchers a strong feel for the capability of physical approaches, promote new interdisciplinary interests and persuade more practitioners to take advantage of optical techniques. Current developments in a variety of optical techniques, including Near-Infra Red Spectroscopy, and traditional and advanced fluorescence techniques are covered, ranging from those that are becoming common practice to those that need much more experimentation before they can be accepted as real breakthroughs. Further topics include optical coherence tomography and its variations, polarised light imaging and, principle laser and lamp sources- a usually fragmentary topic, often dispersed among specialist publications. The wide range of topics covered make Lasers and Current Optical Techniques in Biology of interest to a diverse range of scientific communities.
Lasers and Current Optical Techniques in Biology
By Giuseppe Palumbo, Riccardo PratesiThe Royal Society of Chemistry
Copyright © 2004 European Society for Photobiology
All rights reserved.
ISBN: 978-0-85404-321-7Contents
Part I: Lasers and Lamps,
Chapter 1 Gas state lasers Terry A. King, 3,
Chapter 2 Liquid state lasers Terry A. King, 33,
Chapter 3 Solid state lasers Willy Lüthy and Heinz Weber, 57,
Chapter 4 Semiconductor lasers Peter Unger, 77,
Chapter 5 Diode pumped solid state lasers Holger Zellmer and Andreas Tünnermann, 97,
Chapter 6 Incoherent light sources Brian L. Diffley, 105,
Chapter 7 Solid state lamps Roland Diehl, 117,
Chapter 8 Fibre lasers Terry A. King, 133,
Chapter 9 Methods for the generation of light pulses: from nanoseconds to attoseconds Mauro Nisoli, 157,
Part II: Spectroscopic and Imaging Techniques (Non-microscopic),
Chapter 10 Autofluorescence spectroscopy of cells and tissue as a tool for biomedical diagnosis Giovanni Bottiroli and Anna Cleta Croce, 189,
Chapter 11 Reflectance and transmittance spectroscopy Enrico Gratton and Sergio Fantini, 211,
Chapter 12 Fluorescence spectroscopy and imaging (non-microscopic), 259,
Part I: Paola Taroni and Gianluca Valentini,
Part II: Laura Marcu,
Part III: Microscopy Techniques,
Chapter 13 Optical microscopy Herbert Schneckenburger, 331,
Chapter 14 Wide-field autofluorescence microscopy for imaging of living cells Franco Fusi, Monica Monici and Giovanni Agati, 357,
Chapter 15 Scanning probe microscopy Cesare Ascoli, Riccardo Gottardi and Donatella Petracchi, 375,
Chapter 16 Confocal and multiphoton microscopy Alberto Diaspro, 429,
Part IV: Advancing Imaging Techniques and Novel Ultrasensitive Fluorescence Detection Techniques,
Chapter 17 Optical coherence tomography David Sampson and Timothy R. Hillman, 481,
Chapter 18 Laser optoacoustic imaging Steven L. Jacques, 573,
Chapter 19 Polarized light imaging of tissues Steven L. Jacques and Jessica C. Ramella-Roman, 591,
Chapter 20 Ultrasensitive fluorescence detection at surfaces: instrument development, surface chemistry, and applications in life science and medicine Stefan Seeger, 609,
Subject Index, 641,
CHAPTER 1
Gas state lasers
Terry A. King
Table of contents
Abstract 05
1.1 Introduction 05
1.2 Basic principles 06
1.2.1 Line broadening mechanisms in gases 07
1.2.2 Saturation irradiance 09
1.2.3 Threshold operation 09
1.3 Basic structures of gas state lasers 10
1.3.1 Gas laser media 10
1.3.2 Optical resonators 12
1.3.3 Pumping techniques 13
1.3.4 Emission characteristics 13
1.3.4.1 Coherence 13
1.3.4.2 Divergence 13
1.3.4.3 Coherence length 14
1.3.5 Pulsewidth control 14
1.3.6 Wavelength selection and frequency control 15
1.4 Types of gas lasers 16
1.4.1 Helium-neon 16
1.4.2 Ion gas lasers 16
1.4.3 Excimer lasers 20
1.4.4 Molecular lasers 23
1.4.4.1 Carbon dioxide 23
1.4.4.2 Carbon monoxide 25
1.4.4.3 Nitrogen 26
1.4.4.4 F2 27
1.4.5 Metal vapour lasers 27
1.4.5.1 He-Cd 27
1.4.5.2 Copper and gold vapour 27
1.5 Perspectives 29
References 30
Abstract
A brief review of the structures and operation of gas lasers of particular interest in photobiology is given in this chapter along with details of their emission characteristics. Gas lasers provide laser wavelengths over a very broad range from the vacuum UV to the far-IR in continuous wave and pulsed operation and from low to high powers. Many of these wavelengths have found valuable application in photobiology, particularly in the several forms of fluorescence technique, microscopy, imaging and Raman spectroscopy, as well as in such techniques as optical trapping and tweezers, micromanipulation and microdissection. Extensive use has been made of the He-Ne laser (wavelength 632.8 nm), argon ion laser (488.0 and 514.5 nm), krypton ion (647.1 nm), He-Cd laser (441.6 and 325.0 nm), excimer lasers (ArF 193 nm, KrF 248 nm, XeCl 308 nm) and nitrogen laser (337.1 nm). The ion and excimer lasers have application in the pumping of tunable dye and titanium-sapphire lasers. Since the discovery of the first gas laser in 1961 many gas lasers have been devised, a detailed understanding built up of their operation and performance and the commercial technology has reached a highly developed and mature state.
In recent years solid-state alternatives to several of the common gas lasers have been developed based on diode lasers, diode pumped solid-state lasers and fibre lasers which offer advantages of compactness and efficiency and operation from low voltage power supplies. However, solid-state substitutes are not presently available at many of the useful gas laser wavelengths, such as the high power pulsed output from excimer lasers in the UV, high power continuous wave output in the near UV, visible and near IR, and mid-and far-IR wavelengths from molecular gas lasers.
1.1 Introduction
The interaction of laser light with biological samples gives an optical signal which carries information on the composition, structure and function of the sample. The probe laser light may be used in the basic measurements of absorption, fluorescence and phosphorescence emission, and Rayleigh and Raman scattering. In this there is a remarkable variety of techniques which have evolved with important applications in photobiology: spectral microscopy and imaging, scanning confocal microscopy, optical labelling, ultrafast pulse and fluorescence lifetime spectroscopy, fluorescence probe (marker) spectroscopy, fluorescence recovery after photobleaching (FRAP), fluorescence in situ hybridization (FISH), fluorescence resonance energy transfer (FRET) and optical trapping and tweezers [1–4]. Special attention can be drawn to the use of fluorescence in several of these techniques with the use of spectral (continuous), dynamic (pulsed) and imaging methods. These applications include laser scanning confocal fluorescence microscopy, time-correlated single-photon counting lifetime studies, total internal reflection fluorescence, near-field scanning fluorescence optical microscopy (NSOM), fluorescence correlation spectroscopy and multi-photon fluorescence microscopy [4]. The Raman scattering technique in its various forms has widespread application in photobiology through its sensitivity to molecular vibrations. Surface enhanced Raman scattering derives an enhanced Raman signal from molecules attached to surfaces to give molecular structural information. Coherent anti-Stokes Raman scattering microscopy enables the identification of molecular constituents of cells without the use of dye markers.
Gas lasers provide source radiation for many of these techniques. In particular, these include the argon (514.5 and 488 nm) – and krypton (647.1 nm) – ion lasers at medium power levels and which provide UV, visible and near-IR wavelengths; the He-Cd laser (441.6 and 325.0 nm), excimer lasers (ArF 193 nm, KrF 248 nm, XeCl 308 nm), N2 lasers (337.1 nm) and F lasers (157 nm). The ion lasers and excimer lasers are also used as pump sources for the tunable liquid dye and solid-state titanium-sapphire lasers. In addition there are several gas lasers which have more specialised applications in photobiology.
In this chapter the basic principles of laser operation are briefly reviewed and some of the laser...
