A laser diode emits a narrow range of frequencies. However, drifts infrequency occur over time due to many factors like changes in laser temperature, current, mechanical vibrations in the apparatus, etc. These frequency drifts make the laser unsuitable for experiments that require high frequency stability. We have used an atomic transition in rubidium as a frequency reference and used Dopplerfree saturated spectroscopy to observe the reference peak. We have designed an electronic locking circuit that operates the diode laser at a specific frequency. It keeps the laser at that frequency for a long period of time with very few or no drifts. We have constructed and characterized an extended cavity diode laser that costs significantly less than a commercial unit. It is much more compact with performance comparable to that of a commercial unit. It can be used in undergraduate and graduate optics laboratories where commercial units are cost prohibitive. The various components of the set-up are discussed, and the basicprinciples behind the function and operation of this versatile device are explained. We designed a servo loop filter circuit, which is used to stabilize the frequency of the laser to an atomic reference frequency. We also generated an error signal using a technique similar to the Pound Hall Drever technique and then feedback the error signal in the loop filter circuit.

This is the first book on tunable external cavity semiconductor diode lasers, providing an up-to-date survey on the physics, technology, and performance of widely applicable coherent radiation sources of tunable external cavity diode lasers. The purpose is to provide a thorough account of the state-of-the-art of tunable external cavity diode lasers which is achieved by combining this account with basic concepts of semiconductor diode lasers and its tunability with monolithic structures. The practical and accessible information in this volume will enable the reader to study external cavity diode laser, to build up the systems of external cavity diode laser as well as to develop advanced systems for their particular applications. This book will appeal to undergraduate and graduate students, scientists and engineers alike.

Advances in optical fibre based communications systems have played a crucial role in the development of the information highway. By offering a single mode oscillation and narrow spectral output, distributed feedback (DFB) semiconductor laser diodes offer excellent optical light sources as well as optical filters for fibre based communications and dense wavelength division multiplexing (DWDM) systems. This comprehensive text focuses on the basic working principles of DFB laser diodes and optical filters and details the development of a new technique for enhanced system performance. Considers the optical waveguiding characteristics and properties of semiconductor materials and the physics of DFB semiconductor lasers. Presents a powerful modelling technique based on the transfer matrix method which can be used to improve the design of laser diodes, optical fibres and amplifiers. Examines the effect of the various corrugation shapes on the coupling coefficients and lasing characteristics of DFB laser diodes. Technical advice to improve immunity against the spatial hole burning effect. Extensive referencing throughout and a comprehensive glossary of symbols and abbreviations. Suitable for both introductory and advanced levels This is an indispensable textbook for undergraduate and postgraduate students of electrical and electronic engineering and physics as it consolidates their knowledge in this rapidly growing field. As a technical guide for the structural design of DFB laser diodes and optical filters, the book will serve as an invaluable reference for researchers in opto-electronics, and semi conductor device physics.

A huge number of applications require coherent radiation in the visible spectral range. Since diode lasers are very compact and efficient light sources, there exists a great interest to cover these applications with diode laser emission. Despite modern band gap engineering not all wavelengths can be accessed with diode laser radiation. Especially in the visible spectral range between 480 nm and 630 nm no emission from diode lasers is available, yet. Nonlinear frequency conversion of near-infrared radiation is a common way to generate coherent emission in the visible spectral range. However, radiation with extraordinary spatial temporal and spectral quality is required to pump frequency conversion. Broad area (BA) diode lasers are reliable high power light sources in the near-infrared spectral range. They belong to the most efficient coherent light sources with electro-optical efficiencies of more than 70%. Standard BA lasers are not suitable as pump lasers for frequency conversion because of their poor beam quality and spectral properties. For this purpose, tapered lasers and diode lasers with Bragg gratings are utilized. However, these new diode laser structures demand for additional manufacturing and assembling steps that makes their processing challenging and expensive. An alternative to BA diode lasers is the stripe-array architecture. The emitting area of a stripe-array diode laser is comparable to a BA device and the manufacturing of these arrays requires only one additional process step. Such a stripe-array consists of several narrow striped emitters realized with close proximity. Due to the overlap of the fields of neighboring emitters or the presence of leaky waves, a strong coupling between the emitters exists. As a consequence, the emission of such an array is characterized by a so called supermode. However, for the free running stripe-array mode competition between several supermodes occurs because of the lack of wavelength stabilization. This leads to power fluctuations, spectral instabilities and poor beam quality. Thus, it was necessary to study the emission properties of those stripe-arrays to find new concepts to realize an external synchronization of the emitters. The aim was to achieve stable longitudinal and transversal single mode operation with high output powers giving a brightness sufficient for efficient nonlinear frequency conversion. For this purpose a comprehensive analysis of the stripe-array devices was done here. The physical effects that are the origin of the emission characteristics were investigated theoretically and experimentally. In this context numerical models could be verified and extended. A good agreement between simulation and experiment was observed. One way to stabilize a specific supermode of an array is to operate it in an external cavity. Based on mathematical simulations and experimental work, it was possible to design novel external cavities to select a specific supermode and stabilize all emitters of the array at the same wavelength. This resulted in stable emission with 1 W output power, a narrow bandwidth in the range of 2 MHz and a very good beam quality with M²<1.5. This is a new level of brightness and brilliance compared to other BA and stripe-array diode laser systems. The emission from this external cavity diode laser (ECDL) satisfied the requirements for nonlinear frequency conversion. Furthermore, a huge improvement to existing concepts was made. In the next step newly available periodically poled crystals were used for second harmonic generation (SHG) in single pass setups. With the stripe-array ECDL as pump source, more than 140 mW of coherent radiation at 488 nm could be generated with a very high opto-optical conversion efficiency. The generated blue light had very good transversal and longitudinal properties and could be used to generate biphotons by parametric down-conversion. This was feasible because of the improvement made with the infrared stripe-array diode lasers due to the development of new physical concepts.

Excerpt from Toward Extended-Cavity Grating-Tuned Mid-Infrared Diode Laser Operation We have investigated an extended-cavity technique which utilizes tunable lead-salt diode lasers, emitting in the spectral region around 3 pm. We have developed a special liquid nitrogen cryostat that enables us to place both the collimation optics and the optics for the extended cavity within the vacuum chamber. The external reflector is a diffraction grating for wavelength-selective optical feedback. This scheme promises to overcome two major drawbacks of tunable diode lasers, their large spectral width and their incomplete spectral coverage. Progress with the coating efforts, problems with the collimation optics. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.

The thesis describes growth and characterization of nitride-based quantum well structures for laser diodes emitting in the wavelength range between 400 nm and 450 nm. In order optimize the epitaxial growth process by metal organic vapor phase epitaxy and thus the performance of the laser diode structures, the material properties of the indium gallium nitride (InGaN) active region were correlated with device characteristics. By analyzing optically pumpable laser structures in a first step, growth conditions and growth schemes were revealed that prevent 3D growth and the formation of additional defects in the active region. In the next step, using growth parameter that provide a high material gain broad area current injection laser diodes emitting around 400 nm were realized on sapphire substrate. These devices feature threshold current densities in the range of 6 kA/cm² in pulsed operation. For laser diodes emitting at longer wavelengths, the heterostructure layout was optimized by comparing optical pumping results with device simulation. Using a layer sequence with increased modal gain, first broad area current injection laser diodes emitting around 440 nm were demonstrated. The structures were grown on low defect density bulk GaN substrates and exhibit threshold current densities of ~10 kA/cm² in pulsed operation. On the basis of these results further device and process development was started aiming for ridge waveguide laser structures operating continuous wave in the wavelength range between 400 and 450 nm.