Relaxation Oscillation Dynamics in AlGaInP Diode Lasers

Laser operation relies on two conditions, stimulated emission of the amplifying medium and feedback by an optical resonator. The threshold of laser operation is obtained if the gain in the resonator compensates for the overall losses, i.e., the propagation losses and the apparent losses due to the extraction of light [2.1]. Both common laser conditions are satisfied in diode lasers in another way than in typical gas or solid-state lasers. The resonator is given by the semiconductor structure itself using the crystal facets as mirrors. The gain in diode lasers involves a whole crystal structure and not only excited single atoms, ions, or molecules. Modern semiconductor lasers restrict the excited volume to reduce the threshold current by applying quantum wells or quantum dots. Technically, this is achieved by growing very thin layers consisting of different crystal compositions for quantum wells or by applying two-dimensional growth for quantum dots. A scheme of a diode laser is shown in Fig. 2.1. The following chapter takes a short tour through the excitation of high-power semiconductor lasers by examining the current injection of carriers, the optical gain, and appropriate resonator structures. More detailed descriptions of several aspects can be found in several textbooks [2.2, 2.3]. The electronic states of crystals form energy bands (Fig. 2.2). At zero temperature , Pauli's principle results in band filling up to a certain level, the Fermi energy level. The status at finite temperatures is described by the Fermi function [2.4]. In semiconductor crystals, the Fermi level is always between two energy bands, the valence band and the conduction band. The minimum gap between both energy bands is called band gap. Semiconductors without impurities and distortions exhibit no allowed states in the band gap. For optoelectronics, direct semiconductors are normally used where the minimum energy of the conduction band and the maximum energy of the valence band are at the-point, i.e., at the center of the Brillouin zone. If an electron is lifted into the conduction band, e.g., by absorption of a photon, it will leave a hole in the valence band. The optical gain within a semiconductor laser 5

IEEE International Frequency Control Symposium, 1995

As they apply to frequency standards and precision spectroscopy the characteristics and technology of tunable diode lasers are briefly reviewed. It is now possible to use nonlinear optical techniques and high quality diode lasers to extend the useful wavelength coverage of semiconductor lasers into the UV, the IR and even millimeter-wave spectral regions. Progress in developing an all diode-laser system

Optics & Laser Technology, 2014

The invention of first laser in 1960 triggered the discovery of several new families of lasers. A rich interplay of different lasing materials resulted in a far better understanding of the phenomena particularly linked with atomic and molecular spectroscopy. Diode lasers have gone through tremendous developments on the forefront of applied physics that have shown novel ways to the researchers. Some interesting attributes of the diode lasers like cost effectiveness, miniature size, high reliability and relative simplicity of use make them good candidates for utilization in various practical applications. Diode lasers are being used by a variety of professionals and in several spectroscopic techniques covering many areas of pure and applied sciences. Diode lasers have revolutionized many fields like optical communication industry, medical science, trace gas monitoring, studies related to biology, analytical chemistry including elemental analysis, war fare studies etc. In this paper the diode laser based technologies and measurement techniques ranging from laboratory research to automated field and industry have been reviewed. The application specific developments of diode lasers and various methods of their utilization particularly during the last decade are discussed comprehensively. A detailed snapshot of the current state of the art diode laser applications is given along with a detailed discussion on the upcoming challenges.

1981

This report is a .study of the dynamic properties of semiconductor laser diodes. The measurement of some important lc;ser diode parameters necessary for dyn?mic behaviour prediction is described. The relc;xation oscillation behaviour for laser diodes pumped with nanosecond time scale current pulses is predicted using both an approximate an~lytic solution c;nd computer simulations. This predicted behaviour is compared with experimental results. DynC~mic experiments with c;n externc;l cavity for extra optical feedb2ck and a regenerativE loop for optoelectronic feedback are also described and discussed. Details of the experimental setups and techniques used are given. iii and B.L.C. for their support. Special thanks to John Goodwin for numerous discussions and immeasurable help throughout this work.

IEEE Journal of Selected Topics in Quantum Electronics, 2019

Optics Communications, 2001

This paper describes the diode laser system we use for our fast-beam laser experiments. The air-tight housing, temperature controller, and current controller are described in detail. Data are given for the temperature stability and current noise of the system. A contour map shows the dependence of laser wavelength on temperature and injection current, from which laser frequency scan rates are determined. Fluorescence and absorption spectra of the 133 Cs 6s 2 S 1a2 3 6p 2 P 1a2 and 6p 2 P 3a2 resonances are shown for a fast beam, a thermal beam, and a room temperature cell, demonstrating the laser tuning capabilities and spectral width. A radio-frequency sideband technique with a Cs absorption cell is used to demonstrate robust absolute laser frequency stabilization suitable for fast beam applications. Ó

IEEE Journal of Selected Topics in Quantum Electronics, 2000

High-brightness laser diode technology is progress-7 ing rapidly in response to competitive and evolving markets. The 8 large volume resonators required for high-power, high-brightness 9 operation makes their beam parameters and brightness sensitive 10 to thermal-and carrier-induced lensing and also to multimode op-11 eration. Power and beam quality are no longer the only concerns 12 for the design of high-brightness lasers. The increased demand for 13 these technologies is accompanied by new performance require-14 ments, including a wider range of wavelengths, direct electrical 15 modulation, spectral purity and stability, and phase-locking tech-16 niques for coherent beam combining. This paper explores some 17 of the next-generation technologies being pursued, while illustrat-18 ing the growing importance of simulation and design tools. The 19 paper begins by investigating the brightness limitations of broad-20 area laser diodes, including the use of asymmetric feedback to 21 improve the modal discrimination. Next, tapered lasers are consid-22 ered, with an emphasis on emerging device technologies for applica-23 tions requiring electrical modulation and high spectral brightness. 24 These include two-contact lasers, self-organizing cavity lasers, and 25 a phase-locked laser array using an external Talbot cavity. The brightness is also related to M 2 and the beam parameter 81 product Q (product of the minimum beam diameter ω 0 and its 82 divergence θ f ). The current state of the art for power and bright-83 ness of diode lasers and systems is shown in Fig. 1. The com-84 parison with other high-power lasers (e.g. CO 2 and diode/lamp 85 pumped solid-state lasers) in Fig. 1 shows that diode lasers are 86 approaching the level of power and brightness achievable by the 87 other laser systems. 88 As the variety of applications for high-brightness laser diodes 89 increases, so does the range of performance specifications, 90 which generally depend upon the intended application. For 91 example, most high-brightness diode lasers operate at 808 or 92 980 nm, but other wavelengths are emerging for appli-93 cations such as medicine, displays, printing, and mark-94 ing/cutting/welding of plastics. Display and optical wireless ap-95 plications also require that the laser has a controlled emission 96 spectrum and beam quality during high-frequency modulation 97 (0.1-1 GHz) and a large modulation efficiency (power/current 98 ratio). Applications requiring frequency doubling (e.g., blue and 99 green lasers for displays, blue/near-UV lasers for fluorescence 100 155 Numerous laser models have been reported in the literature. 157 These models vary in complexity and have typically been de-158 veloped to target specific applications. Early models ignored 159 current spreading in the cladding layers of the device and typ-160 ically solved the 1-D unipolar diffusion equation in the lateral 161 direction. These tools were used to explain spatial hole burn-162 ing and carrier lensing effects and were also applied to explain 163 the filamentary nature of broad-area lasers [19]. Later, full 2-D 164 cross-sectional models were introduced, which were borrowed 165 from modeling techniques developed for silicon device simula-166 tors [20]-[22]. These 2-D cross-sectional laser models solved 167 the electrical, thermal, and optical problems self-consistently, 168 making them more accurate-especially for ridge waveguide 169 (RW) lasers. However, since they only considered a single cross 170 section, they were unsuitable for longitudinally nonuniform 171 structures and high-power operation, where longitudinal spa-172 tial hole burning and carrier/thermal lensing effects are signifi-173 cant. Early models based on beam propagation methods (BPMs) 174 were developed to handle nonuniform structures, but typically 175 only solved the 1-D electrical problem in the lateral direction 176 [23]-[25]. Sophisticated models were also introduced that 177 solved the spatiotemporal dynamics of the lasers, but these 178 models also used a 1-D electrical model in the lateral di-179 rection [26], [27]. Quasi-3-D models were introduced in [28] 180 and [29], with the optical model separated into 1-D in the lon-181 gitudinal direction and 2-D in the transverse cross section. The 182 combination of the 2-D cross-section electrothermal model with 183 the BPM was then introduced [30], [31]. By including the longi-184 tudinal direction and accounting for current and heat spreading 185 effects, these models have become predictive and useful design 186 tools for high-brightness lasers. By including the spectral and/or 187 the dynamic properties of the laser, design tools are reaching 188 new levels of accuracy and reliability.

Surface Engineering, 2007