Showing papers on "Quantum dot laser published in 1980"

Quantum-well heterostructure lasers

Abstract: The various features peculiar to the operation of quantum-well semiconductor lasers are described and illustrated with data on single- and multiple-quantum-well Al x Ga 1-x As-GaAs heterostructures grown by metalorganic chemical vapor deposition (MO-CVD). Photo-pumped and p-n diode lasers (injection lasers) are described that are capable of continuous room temperature (CW 300 K) operation. The basic problems of carrier collection, thermalization, and quantum-well band filling are considered and have made clear the limits on single quantum-well laser operation and how these can be overcome with multiple quantum-well active regions. The idea that the steplike density-of-states of a quantum-well heterostructure can improve the operation of a semiconductor laser is shown to be valid. Also, it is shown that phonon participation in the operation of a quantum-well laser, which was not anticipated, is a major (even dominant) effect, with perhaps the phonon emission itself in the compact active region being stimulated. Besides the obvious freedom that quantum-well layers offer in how the active region of a semiconductor laser can be designed, quantum-well lasers are shown to exhibit a lesser sensitivity of the threshold current density on temperature, which is explained in terms of the step-like density-of-states and the disturbed electron and phonon distributions in the quantum-well active regions. Values as high as \sim437\deg C have been obtained for T 0 in the usual expression J_{th}(T) = J_{th}(0) \exp (T/T_{0}) . Since photopumped multiple-quantum-well MO-CVD Al x Ga 1-x As-GaAs heterostructures have operated as CW 300 K lasers with only 5-10 mW of photoexcitation (uncorrected for focusing and window losses, \lambda \sim 5145 A), it is suggested that quantum-well laser diodes can be made that will operate at ∼1 mA or even less excitation.

Semiconductor diode laser array

Abstract: An integrated laser array is disclosed in which a plurality of semiconductor lasers are integrated on a semiconductor multi-layer crystal that includes an active layer in which the band gap energy varies in one direction By means of this arrangement a plurality of semiconductor lasers, which differ in their respective oscillating wavelengths over a relatively broad range, can be formed on a common substrate

Intrinsic noise of semiconductor lasers in optical communication systems

Abstract: The upper limit of the achievable signal-to-noise ratio in optical communication systems is determined by the intrinsic laser noise due to quantum fluctuations inside the laser cavity. This achievable signal-to-noise ratio depends on the way in which different lasing modes are detected; wavelength filtering and material dispersion may yield a significant deterioration of the signal-to-noise ratio. It is concluded from theoretical calculations and from measurements on V-groove lasers that a d.c. signal-to-noise ratio of about 70 dB may be achieved for a noise bandwidth of 10 MHz.

Single-mode stabilization by traps in semiconductor lasers

Abstract: Recently it has been observed that certain single-transverse-mode semiconductor lasers continue to emit light predominantly in a particular longitudinal mode even after the optical gain peak has shifted by one or more mode spacings due to changes in bias current or temperature [1], [2]. The purpose of this paper is to show that this type of mode stabilization can be caused by the saturable optical absorption resulting from deep-level states or traps, which have been observed in AlGaAs laser structures [3]-[7]. The mode-selection mechanism is due to the spatial variation in the optical loss created by the standing-wave pattern of the single predominant mode. This loss pattern results in a lower average loss for the creating mode and a higher loss for all other modes. It is possible that laser devices with greatly improved single-mode stability can be made by introducing traps of the proper type and density during fabrication.

Multiwatt operation of Cu II and Ag II hollow cathode lasers

Abstract: We report multiwatt pulsed (120 μs pulsewidth, 40Hz) laser operation of silver and copper hollow cathode lasers. Peak output powers of 65 mW at 224 nm, 500 mW at 248 nm, 1.3 W at 318.1 nm, and 2.3 W at 478.8 nm have been achieved. Measurements of small-signal gains of selected laser transitions and new laser lines in Cu, Ag, Kr, and Ar are presented.

Active media of exciplex lasers (review)

Abstract: A review is given of experimental data on exciplex lasers. An analysis is made of the optical characteristics of lasing transitions, experimental conditions for achieving laser action, mechanisms of formation of the active level populations, character of nonequilibrium of the active medium, and proposed new active media. Detailed tables are presented with data on optical transitions, exciplex quenching rates, and characteristic parameters of the media and pump sources of existing lasers.

Pb 1-x Sn x Te/PbTe 1-y Se y lattice-matched buried heterostructure lasers with CW Single mode output

Abstract: The first successful realization of buried heterostructure diode lasers in the PbSnTe/PbTeSe system is reported. This has resulted in routine cw operation above 80 K with threshold currents as low as 60 mA in 5 µm wide stripe lasers. CW operation has been achieved to 120K. In addition, these lasers operate in the fundamental transverse mode up to as much as four times threshold.

Effects of high density pumping on relaxation oscillations and mode spectra in lasers

Abstract: Effects of high density pumping on relaxation oscillations and mode spectra are investigated in LiNdP 4 O 12 (LNP) lasers. It is shown that high density pumping reduces the spatial population inhomogenuity, which is due to periodic inversion saturation by a first lasing mode in the crystal, and results in spontaneous single longitudinal mode oscillations even at high excitation rates. Physical interpretations are given for single-mode operations on the basis of Auger recombination (annihilation) process for 1.048 and 1.32 μm quantums in LNP lasers. An effective diffusion parameter of excited states is shown in an increase with absorbed pump power density through the Auger process. Observed relaxation oscillation waveforms, which disagreed with the traditional laser dynamic theory, are found to be explained well by the rate equations, including the effective diffusion constant.

Development of self-pulsations due to self-annealing of proton bombarded regions during aging in proton bombarded stripe-geometry AlGaAs DH lasers grown by molecular beam epitaxy

Abstract: Experimental observations indicate that the occurrence of optical self-pulsation in proton delineated stripe-geometry double-heterostructure junction lasers is related to the degree of gain guiding inherent in individual lasers. We show that an aging process occurs during lasing operation which has the effect of partially annealing the proton induced carrier removal concentration at the edges of the active stripe of the laser. In some lasers, the magnitude of this annealing effect is sufficiently large to flatten the active stripe carrier concentration profile thus reducing filament stability leading ultimately to optical self-pulsation. It is shown that the carrier concentration profile modification is due to the dual effects of decreasing the n = 2 nonradiative current component at the active stripe-proton bombarded interface as well as the geometric effect of increasing the laser active stripe width. This latter effect may be also responsible for some portion of laser threshold current increase observed during device operation.

A new design concept for hollow-cathode white light laser

Abstract: A white light laser has been constructed which employs a concentric cylinder type laser tube and embodies the novel concept of separating the functions of confining the negative glow providing for diffusion of Cd vapor. The main source preventing the white light oscillation in previous designs is not a lack of Cd vapor in lasing zone but a decrease of the hollow-cathode effect due to many holes of large diameter.

New far infrared CW optically pumped cis-C 2 H 2 F 2 laser

Abstract: Lasing on 6 FIR lines is reported for the new laser molecule cis-C 2 H 2 F 2 with high conversion efficiencies up to 7 percent of the maximum theoretical limit. A set of molecular selection criteria was used to predict efficient FIR lasing from this molecule, and analysis of the laser performance has increased the basic understanding of the molecular parameter contribution to high conversion efficiency. From this work a refined set of selection criteria has evolved that may be used to predict additional efficient laser molecules.

Field effect semiconductor lasers

Abstract: A new semiconductor laser, the field-effect semiconductor (FES) laser, in which the both sides of the active region are surrounded by the burying layers with the reverse-biased p-n junctions is proposed. The proposed FES laser is a Q -switching device based on the direct control of laser beam intensity by the internal loss modulation through the field effect. The structure design and the operating principles of the device are discussed. Numerical solution shows that a pulsewidth shorter than 30 ps can be obtained.

Active Q-switching of lateral field coupling control d.h. laser

Abstract: Active Q-switching of d.h. semiconductor lasers is proposed and analysed. The method is based upon the coupling switch of a lateral evanescent field coupled laser with superposition of the simultaneous injection current change. This novel method relaxes greatly the required condition for realisation of a Q-switched semiconductor laser.

Self saturating semiconductor lasers

Abstract: A double heterostructure semiconductor laser having the configuration of its optical cavity arranged to impose a constraint on the lasing filament as the spatial distribution of the lasing filament changes from that occuring at the start of the lasing regime, so that the optical flux emitted by the laser has self-saturating properties. This protects the laser from catastrophic facet erosion and enables a simpler control circuit to be used to drive this laser when it is used as a light source for an optical communications system.

A new design of hollow cathode lasers with multiple electrodes

Abstract: A new design for hollow cathode lasers, using multiple electrodes excited with an alternating power supply, is introduced and a report on their preliminary performance is given. Laser action was observed on the 781 nm transition of the Cu ion.

Future Developments In Laser Technology And Their Applications

Abstract: One of the many areas in which lasers are beginning to play an important role is that of chemistry. One application of great significance is the use of low average power tunable lasers as an analytical tool to measure or study reaction kinetics and products. The other application of equal or greater importance is the use of high average power tunable lasers as a manipulative tool to control or drive chemical reactions in industrial processes. Here the cost of photons is the most important factor and a new device called the "Free Electron Laser" is under development which promises to reduce the photon cost to less than one dollar per pound of material, thus including a wide range of industrial products.TextSoon after the invention of the laser in 1961, predictions were made that the laser would produce a new technological revolution similar to that due to the rapid development of solid state electronics after the invention of the transistor. However, these predictions were slow in being realized due to the much great complexity and cost of lasers and their associated technology, and due to the lack of well-developed need in the optical industry which the laser could satisfy. In fact, the laser was referred to as a solution looking for a problem.Today, these early predictions are coming to pass as both the laser technology and its applications in the scientific and industrial field are developing at a rapid pace. The laser is finding broad uses in such diverse areas as communications, chemistry, biology and medicine, cutting drilling and welding for hardware fabrication, fusion research, isotope separation, metrology, pollution monitoring, surveying, industrial process instrumentation and control, and military uses, to name a few, and the list still is expanding. To a great extent, the applications are limited by the capability of well engineered laser hardware which can be used reliably without being a laser physicist, but this area is improving rapidly.One of the most interesting of the areas just mentioned, in which lasers are starting to play an excit­ ing role, is that of chemistry. Some of the laser tools needed are now available as off-the-shelf items and new ones now in the development process will become available in the next several years as the demand increases.The two general types of laser applications in chemistry are the laser's use as an analytical tool and its use as a manipulative agent, whose object is to induce chemical change. Both applications have been made possible through the development of tunable lasers. In the infrared, this has been achieved through the use of diode lasers, line tunable and high pressure gas lasers and by parametric oscillators, in the visible by dye lasers and in the UV by eximer lasers, and a recent addition, the color center lasers. For very high power applications, a new candidate on the horizon is the free electron laser which can, in principle, be constructed to operate over continuously tunable wide frequency bands from millimeter wave­ lengths to far ultraviolet wavelengths.The extremely high resolution spectroscopy obtainable with lasers is illustrated in Figure 1, where a single P branch rotational line of the complex molecule, uranium hexafluoride, is resolved into its 11 sub­ components due to Coriolis splitting of its degeneracy. Not only are such measurements able to obtain the force constants of the molecule, and give structural information, but they have also permitted the selec­ tion of the correct theoretical model1 and allowed an extension of the theory which permitted accurate predictions of the line intensities as shown by the bars. These measurements were taken in absorption us­ ing a diode laser on flow cooled UFe. The laser intensity available also permits saturation of the medium, which, with the addition of a second tunable laser permits spectroscopy of excited states.Mode-locked dye lasers operating in the visible, and parametric oscillators, (pumped by mode-locked yag lasers) operating in the infrared, are used to produce very short, high intensity pulses at tunable wave­ lengths. These probes permit the study of chemical kinetics by observing fluorescent radiation from the reaction products. Again, a second tunable probe laser can be used to obtain information on the rate at which excitation energy from a single mode is transferred to other modes in the same molecule or is trans­ ferred to other molecules.