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Journal ArticleDOI

Stimulated emission in a periodic structure

15 Feb 1971-Applied Physics Letters (American Institute of Physics)-Vol. 18, Iss: 4, pp 152-154
TL;DR: In this paper, the authors investigated laser oscillation in periodic structures in which feedback is provided by backward Bragg scattering, and showed that the feedback mechanism is distributed throughout and integrated with the gain medium.
Abstract: We have investigated laser oscillation in periodic structures in which feedback is provided by backward Bragg scattering These new laser devices are very compact and stable as the feedback mechanism is distributed throughout and integrated with the gain medium Intrinsic to these structures is also a gratinglike spectral filtering action We discuss periodic variations of the refractive index and of the gain and give the expression for threshold and bandwidth Experimentally we have induced index periodicities in gelatin films into which rhodamine 6G was dissolved The observed characteristics of laser action in these devices near 063 μm are reported
Citations
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Journal ArticleDOI
TL;DR: In this article, an analysis of laser action in a periodic structure is presented, where the resonant frequencies and threshold criteria for the modes of oscillation have been determined for both index and gain periodicities.
Abstract: An analysis of laser action in a periodic structure is presented. A model of two counter‐running waves coupled by backward Bragg scattering is used. The resonant frequencies and threshold criteria for the modes of oscillation have been determined for both index and gain periodicities. Analytical approximations are given for both the high‐ and low‐gain cases, and computational results for the intermediate regimes.

2,090 citations

Journal ArticleDOI
TL;DR: This paper is a review of recent progress made in organic thin films grown in ultrahigh vacuum or using other vapor-phase deposition methods and describes the most important work which has been published in this field since the emergence of OMBD in the mid-1980s.
Abstract: During the past decade, enormous progress has been made in growing ultrathin organic films and multilayer structures with a wide range of exciting optoelectronic properties. This progress has been made possible by several important advances in our understanding of organic films and their modes of growth. Perhaps the single most important advance has been the use of ultrahigh vacuum (UHV) as a means to achieve, for the first time, monolayer control over the growth of organic thin films with extremely high chemical purity and structural precision.1-3 Such monolayer control has been possible for many years using well-known techniques such as Langmuir-Blodgett film deposition,4 and more recently, self-assembled monolayers from solution have also been achieved.5 However, ultrahighvacuum growth, sometimes referred to as organic molecular beam deposition (OMBD) or organic molecular beam epitaxy (OMBE), has the advantage of providing both layer thickness control and an atomically clean environment and substrate. When combined with the ability to perform in situ highresolution structural diagnostics of the films as they are being deposited, techniques such as OMBD have provided an entirely new prospect for understanding many of the fundamental structural and optoelectronic properties of ultrathin organic film systems. Since such systems are both of intrinsic as well as practical interest, substantial effort worldwide has been invested in attempting to grow and investigate the properties of such thin-film systems. This paper is a review of recent progress made in organic thin films grown in ultrahigh vacuum or using other vapor-phase deposition methods. We will describe the most important work which has been published in this field since the emergence of OMBD in the mid-1980s. Both the nature of thin-film growth and structural ordering will be discussed, as well as some of the more interesting consequences to the physical properties of such organic thin-film systems will be considered both from a theoretical as well as an experimental viewpoint. Indeed, it will 1793 Chem. Rev. 1997, 97, 1793−1896

1,809 citations

Journal ArticleDOI
14 Apr 2005-Nature
TL;DR: Polymers containing cinnamic groups can be deformed and fixed into pre-determined shapes—such as elongated films and tubes, arches or spirals—by ultraviolet light illumination and can recover their original shape at ambient temperatures when exposed to ultraviolet light of a different wavelength.
Abstract: Materials are said to show a shape-memory effect if they can be deformed and fixed into a temporary shape, and recover their original, permanent shape only on exposure to an external stimulus. Shape-memory polymers have received increasing attention because of their scientific and technological significance. In principle, a thermally induced shape-memory effect can be activated by an increase in temperature (also obtained by heating on exposure to an electrical current or light illumination). Several papers have described light-induced changes in the shape of polymers and gels, such as contraction, bending or volume changes. Here we report that polymers containing cinnamic groups can be deformed and fixed into pre-determined shapes--such as (but not exclusively) elongated films and tubes, arches or spirals--by ultraviolet light illumination. These new shapes are stable for long time periods, even when heated to 50 degrees C, and they can recover their original shape at ambient temperatures when exposed to ultraviolet light of a different wavelength. The ability of polymers to form different pre-determined temporary shapes and subsequently recover their original shape at ambient temperatures by remote light activation could lead to a variety of potential medical and other applications.

1,807 citations

Book
27 Aug 2012
TL;DR: In this paper, the authors present a survey of the most commonly used line-broadening and line-switching techniques for laser beams, including the following: 1.1.1 Semiclassical approach, 2.2.2 Allowed and Forbidden Transitions, and 3.3.3 Pumping Schemes.
Abstract: 1 Introductory Concepts.- 1.1 Spontaneous and Stimulated Emission, Absorption.- 1.1.1 Spontaneous Emission.- 1.1.2 Stimulated Emission.- 1.1.3 Absorption.- 1.2 The Laser Idea.- 1.3 Pumping Schemes.- 1.4 Properties of Laser Beams.- 1.4.1 Monochromaticity.- 1.4.2 Coherence.- 1.4.3 Directionality.- 1.4.4 Brightness.- Problems.- 2 Interaction of Radiation with Matter.- 2.1 Summary of Blackbody Radiation Theory.- 2.2 Absorption and Stimulated Emission.- 2.2.1 Rates of Absorption and Stimulated Emission.- 2.2.2 Allowed and Forbidden Transitions.- 2.2.3 Transition Cross Section, Absorption and Gain Coefficient.- 2.3 Spontaneous Emission.- 2.3.1 Semiclassical Approach.- 2.3.2 Quantum Electrodynamic Approach.- 2.3.3 Einstein Thermodynamic Treatment.- 2.3.4 Radiation Trapping, Superradiance, Superfluorescence, and Amplified Spontaneous Emission.- 2.4 Nonradiative Decay.- 2.5 Line Broadening Mechanisms.- 2.5.1 Homogeneous Broadening.- 2.5.2 Inhomogeneous Broadening.- 2.5.3 Combined Effect of Line Broadening Mechanisms.- 2.6 Saturation.- 2.6.1 Saturation of Absorption: Homogeneous Line.- 2.6.2 Gain Saturation: Homogeneous Line.- 2.6.3 Inhomogeneously Broadened Line.- 2.7 Degenerate Levels.- 2.8 Relation between Cross Section and Spontaneous Radiative Lifetime.- 2.9 Molecular Systems.- 2.9.1 Energy Levels of a Molecule.- 2.9.2 Level Occupation at Thermal Equilibrium.- 2.9.3 Radiative and Nonradiative Transitions.- Problems.- References.- 3 Pumping Processes.- 3.1 Introduction.- 3.2 Optical Pumping.- 3.2.1 Pumping Efficiency.- 3.2.2 Pump Light Distribution.- 3.2.3 Pumping Rate.- 3.3 Electrical Pumping.- 3.3.1 Electron Impact Excitation.- 3.3.2 Spatial Distribution of the Pump Rate.- 3.3.3 Pumping Efficiency.- 3.3.4 Excitation by (Near) Resonant Energy Transfer.- Problems.- References.- 4 Passive Optical Resonators.- 4.1 Introduction.- 4.2 Plane-Parallel Resonator.- 4.2.1 Approximate Treatment of Schawlow and Townes.- 4.2.2 Fox and Li Treatment.- 4.3 Confocal Resonator.- 4.4 Generalized Spherical Resonator.- 4.4.1 Mode Amplitudes, Diffraction Losses, and Resonance Frequencies.- 4.4.2 Stability Condition.- 4.5 Unstable Resonators.- Problems.- References.- 5 Continuous Wave and Transient Laser Behavior.- 5.1 Introduction.- 5.2 Rate Equations.- 5.2.1 Four-Level Laser.- 5.2.2 Three-Level Laser.- 5.3 CW Laser Behavior.- 5.3.1 Four-Level Laser.- 5.3.2 Three-Level Laser.- 5.3.3 Optimum Output Coupling.- 5.3.4 Reasons for Multimode Oscillation.- 5.3.5 Single-Line and Single-Mode Oscillation.- 5.3.6 Two Numerical Examples.- 5.3.7 Frequency Pulling and Limit to Monochromaticity.- 5.3.8 Lamb Dip and Active Stabilization of Laser Frequency.- 5.4 Transient Laser Behavior.- 5.4.1 Spiking Behavior of Single-Mode and Multimode Lasers.- 5.4.2 Q-Switching.- 5.4.2.1 Methods of Q-Switching.- 5.4.2.2 Operating Regimes.- 5.4.2.3 Theory of Q-Switching.- 5.4.2.4 A Numerical Example.- 5.4.3 Mode Locking.- 5.4.3.1 Methods of Mode Locking.- 5.4.3.2 Operating Regimes.- 5 5 Limits to the Rate Equations.- Problems.- References.- 6 Types of Lasers.- 6.1 Introduction.- 6.2 Solid-State Lasers.- 6.2.1 The Ruby Laser.- 6.2.2 Neodymium Lasers.- 6.3 Gas Lasers.- 6.3.1 Neutral Atom Lasers.- 6.3.2 Ion Lasers.- 6.3.2.1 Ion Gas Lasers.- 6.3.2.2 Metal Vapor Lasers.- 6.3.3 Molecular Gas Lasers.- 6.3.3.1 Vibrational-Rotational Lasers.- 6.3.3.2 Vibronic Lasers.- 6.3.3.3 Excimer Lasers.- 6.4 Liquid Lasers (Dye Lasers).- 6.4.1 Photophysical Properties of Organic Dyes.- 6.4.2 Characteristics of Dye Lasers.- 6.5 Chemical Lasers.- 6.6 Semiconductor Lasers.- 6.6.1 Photophysical Properties of Semiconductor Lasers.- 6.6.2 Characteristics of Semiconductor Lasers.- 6.7 Color-Center Lasers.- 6.8 The Free-Electron Laser.- 6.9 Summary of Performance Data.- Problems.- References.- 7 Properties of Laser Beams.- 7.1 Introduction.- 7.2 Monochromaticity.- 7.3 First-Order Coherence.- 7.3.1 Complex Representation of Polychromatic Fields.- 7.3.2 Degree of Spatial and Temporal Coherence.- 7.3.3 Measurement of Spatial and Temporal Coherence.- 7.3.4 Relation between Temporal Coherence and Monochromaticity.- 7.3.5 Some Numerical Examples.- 7.4 Directionality.- 7.5 Laser Speckle.- 7.6 Brightness.- 7.7 Higher-Order Coherence.- Problems.- References.- 8 Laser Beam Transformation.- 8.1 Introduction.- 8.2 Transformation in Space. Gaussian Beam Propagation.- 8.3 Transformation in Amplitude: Laser Amplification.- 8.4 Transformation in Frequency: Second-Harmonic Generation and Parametric Oscillation.- 8.4.1 Physical Picture.- 8.4.1.1 Second-Harmonic Generation.- 8.4.1.2 Parametric Oscillation.- 8.4.2 Analytical Treatment.- 8.4.2.1 Parametric Oscillation.- 8.4.2.2 Second-Harmonic Generation.- Problems.- References.- 9 Applications of Lasers.- 9.1 Introduction.- 9.2 Applications in Physics and Chemistry.- 9.3 Applications in Biology and Medicine.- 9.4 Material Working.- 9.5 Optical Communications.- 9.6 Measurement and Inspection.- 9.7 Thermonuclear Fusion.- 9.8 Information Processing and Recording.- 9.9 Military Applications.- 9.10 Holography.- 9.11 Concluding Remarks.- References.- Appendixes.- A Space-Dependent Rate Equations.- B Physical Constants.- Answers to Selected Problems.

1,483 citations

Journal ArticleDOI
25 Sep 1997-Nature
TL;DR: In this article, a solgel-based dip-coating method for the rapid synthesis of continuous mesoporous thin films on a solid substrate is presented, which can be used for membrane-based separations, selective catalysis and sensors.
Abstract: Thin films of surfactant-templated mesoporous materials1,2 could find applications in membrane-based separations, selective catalysis and sensors. Above the critical micelle concentration of a bulk silica–surfactant solution, films of mesophases with hexagonally packed one-dimensional channels can be formed at solid–liquid and liquid–vapour interfaces3,4,5. But this process is slow and the supported films3,5 are granular and with the pore channels oriented parallel to the substrate surface, so that transport across the films is not facilitated by the pores. Ogawa6,7 has reported a rapid spin-coating procedure for making transparent mesoporous films, but their formation mechanism, microstructure and pore accessibility have not been elucidated. Here we report a sol–gel-based dip-coating method for the rapid synthesis of continuous mesoporous thin films on a solid substrate. The influence of the substrate generates film mesostructures that have no bulk counterparts, such as composites with incipient liquid-crystalline order of the surfactant–silica phase. We are also able to form mesoporous films of the cubic phase, in which the pores are connected in a three-dimensional network that guarantees their accessibility from the film surface. We demonstrate and quantify this accessibility using a surface-acoustic-wave nitrogen-adsorption technique. We use fluorescence depolarization to monitor the evolution of the mesophase in situ, and see a progression through a sequence of lamellar to cubic to hexagonal structures that has not previously been reported.

1,390 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a coupled wave analysis of the Bragg diffraction of light by thick hologram gratings is given, analogous to Phariseau's treatment of acoustic gratings and to the dynamical theory of X-ray diffraction.
Abstract: A coupled wave analysis is given of the Bragg diffraction of light by thick hologram gratings, which is analogous to Phariseau's treatment of acoustic gratings and to the “dynamical” theory of X-ray diffraction. The theory remains valid for large diffraction efficiencies where the incident wave is strongly depleted. It is applied to transmission holograms and to reflection holograms. Spatial modulations of both the refractive index and the absorption constant are allowed for. The effects of loss in the grating and of slanted fringes are also considered. Algebraic formulas and their numerical evaluations are given for the diffraction efficiencies and the angular and wavelength sensitivities of the various hologram types.

5,244 citations

Journal ArticleDOI
TL;DR: In this article, the authors report theory and experiment on modes of propagating light waves in deposited semiconductor films, where the modes are excited by a prism-film coupler which is also used for the measurement of their phase velocities.
Abstract: We report theory and experiment on modes of propagating light waves in deposited semiconductor films. The modes are excited by a novel prism‐film coupler which is also used for the measurement of their phase velocities. Up to 50% of the incident laser energy has been fed into a single mode of propagation. The positions and linewidths of the modes, the wave intensity inside the film, and a dramatic view of the mode spectrum displayed by the scattered light are discussed in detail.

751 citations

Journal ArticleDOI
TL;DR: In this article, a miniature form of laser beam circuitry is proposed, where the index of refraction changes of the order of 10−2 or 10−3 in a substrate such as glass allow guided laser beams of width near 10 microns.
Abstract: This paper outlines a proposal for a miniature form of laser beam circuitry. Index of refraction changes of the order of 10−2 or 10−3 in a substrate such as glass allow guided laser beams of width near 10 microns. Photolithographic techniques may permit simultaneous construction of complex circuit patterns. This paper also indicates possible miniature forms for a laser, modulator, and hybrids. If realized, this new art would facilitate isolating the laser circuit assembly from thermal, mechanical, and acoustic ambient changes through small overall size; economy should ultimately result.

600 citations

Journal ArticleDOI
TL;DR: In this article, a single-crystal lithium niobate has been used as a holographic storage medium and the high resolution obtained suggests that such material may be useful in high capacity, changeable optical information storage, processing and display devices.
Abstract: Single‐crystal lithium niobate has been used as a holographic storage medium. The material undergoes a change in refractive indices upon exposure to suitably intense light thus allowing it to act as a pure‐phase, volume‐holographic medium requiring no processing. The holograms formed have high diffraction efficiencies and are thermally erasable. The high resolution obtained suggests that such material may be useful in high‐capacity, changeable optical information storage, processing and display devices.

455 citations

Journal ArticleDOI
T. A. Shankoff1
TL;DR: The gelatin-dichromate photosensitive system has been shown to be very efficient as a recording medium for both two- and three-dimensional holographic gratings.
Abstract: The gelatin–dichromate photosensitive system has been shown to be very efficient as a recording medium for both two- and three-dimensional holographic gratings. Upon development, as much as 33% of incident reading light is diffracted into the first order for the unmodulated thin phase gratings and 95% for the thick holograms. The material can record a grating spacing at least as small as 2600 A, and gives reconstructions comparable with those obtained in 649F film. The air–gelatin index differential of 0.54 is considered responsible for the high diffracted powers found. Exposures vary from 3 mJ to 150 mJ at 4880 A. Certain films have speeds within two orders of magnitude of 649F holographic film.

250 citations