Investigation of practical high repetition rate copper vapour lasers with external heating

The characteristics of high repetition rate CVL devices incorporating passive external heating have been investigated. Pre-heating of the CVL plasma tube using external heating has been shown to significantly reduce CVL warm-up time, while supplementary heating of the CVL plasma tube using external heating allows efficient CVL operation with reduced discharge power input without any degradation in output power.     

FM dye lasers

We have investigated the detailed operation of a frequency modulated dye laser (FML). The FML consists of a standing wave Rh6G dye laser with an intracavity transverse ADP phase modulator which is driven at a frequency close to the cavity mode spacing. An ideal FML output consists of a laser beam which is constant in amplitude but sinusoidally varying in frequency. This provides a source of many laser modes which are equally spaced by the modulation frequency. Several dye laser configurations have been investigated. Measurements of the mode intensities, total power, amplitude modulation and rf beat amplitudes have been made as a function of the rf driving frequency of the phase modulator. The FM laser obtained has been frequency stabilised by locking it to a reference interferometer and also by frequency offset locking it to a single-frequency dye laser.     

Lifetime tests of rf-excited atomic xenon lasers

In this article we have, for the first time, performed a series of lifetime tests for the continuous wave radiofrequency-excited atomic xenon laser in the 1.7–3.9 μm regime. Different constructions and electrode materials are used to investigate the usefulness of this laser during long-term sealed-off operation. The influence of electrode material on wall–plasma interactions and the effect of gas impurities on the long-term operation of the laser are investigated and discussed. Received: 30 August 1999 / Published online: 23 February 2000     

Recent progress in semiconductor lasers — cw GaAs lasers are now ready for new applications

Semiconductor lasers, first demonstrated in 1962, have spent a long time in development without finding many applications. (GaAl)As double heterostructure diode lasers with stripe structure have distinctive characteristics for cw operation with a pure mode, in addition to their compactness and ease of operation. Quick degradation of these lasers has been investigated and it was found that the degradation was caused by local crystalline defects produced by internal stresses and local weakness. Improvements based on the study have provided reliable lasers with an operating life of over several thousand hours. These new generation lasers will be useful for optical communications and other optical systems.     

Valley density profile for highly efficient x-ray lasers with good beam quality

A plasma with a valley density profile at the required electron density for high-gain operation of an x-ray laser could be obtained using a normally incident 300 ps laser pulse followed by a grazing-incident 300 ps laser pulse. Sudden heating of the valley plasma region by another grazing-incident 300 fs laser pulse would then yield a highly efficient x-ray laser beam with a deflecting angle of 2 mrad and a divergence angle of 4 mrad. Saturation operation of the x-ray laser beam at 32.6 nm could be achieved with a total pump energy of less than 100 mJ.     

Multiple pulse passive mode locking in lasers with spectrally inhomogeneous gain

A new mechanism of formation of multiple pulse operation, multistability, and hysteresis in lasers with spectrally inhomogeneous gain media such as ion-doped glasses has been discovered. The multistability manifests itself as a dependence on the initial conditions of the number of pulses in the laser operation that is established after the transient process. It has been found that the dependence of the number of pulses in the established operation on the pumping power is hysteretic in character. The mechanism revealed is connected with a change in the frequency dispersion of the active medium caused by the spectrally inhomogeneous saturation of the gain. Analysis and numerical simulation have been carried out on the basis of the modified Ginzburg-Landau equation, which takes into account the change in the spectral profile of the gain during laser operation.     

光纤激光器的偏振开关操作

本文阐述了采用光子注入法实现光纤激光器的偏振开关操作.这种新颖的全光开关器件具有极低的阈值(0.1μW).对操作机理、实验实现和器件特性.     

Lead salt quantum well diode lasers

Lead-salt diode lasers are useful for spectroscopic applications in the 2.5–30 μm wavelength range. These devices have previously required cryogenic cooling <100 K) for CW operation. The use of quantum well, large optical cavity structures has improved the operating temperatures to 174 K CW (at 4.39 μm) and to 270 K pulsed (at 3.88 μm). These diodes have a single PbTe quantum well with lattice-matched Pb_1?xEu_xSeyTe_1?y confinement layers grown by molecular beam epitaxy. The emission energy shifts have been calculated using a finite square well with nonparabolicity effects included. Initial work has also been done on multiple quantum well lasers. The maximum operating temperatures were comparable to those of single quantum well lasers, with leakage current and possibly Auger recombination limiting device performance.     

GaInAsP/InP double-heterostructure lasers for fiber odtic communications

This paper reviews the performance of GaInAsP/InP double-heterostructure diode lasers prepared by liquid-phase epitaxy. These lasers have the advantage that exact lattice-matching between the GaIn-ASP active region and the InP substrate is possible for quaternary alloy compositions giving emission wavelengths over a range that includes 1.1-1.3 μm, the optimum region for optical communication systems utilizing fused silica fibers. Continuous operation at room temperature has been achieved in this region for proton-defined stripe (PDS), oxide-defined stripe (ODs), and junction-defined, buried-stripe (JDBS) lasers. The first three PDS devices to be life-tested have already logged over 6,000, 5,700, and 4,000 h, respectively, of cw operation at room temperature without any degradation.     

GaInAsP/InP double-heterostructure lasers for fiber odtic communications

Abstract

This paper reviews the performance of GaInAsP/InP double-heterostructure diode lasers prepared by liquid-phase epitaxy. These lasers have the advantage that exact lattice-matching between the GaIn-ASP active region and the InP substrate is possible for quaternary alloy compositions giving emission wavelengths over a range that includes 1.1–1.3 μm, the optimum region for optical communication systems utilizing fused silica fibers. Continuous operation at room temperature has been achieved in this region for proton-defined stripe (PDS), oxide-defined stripe (ODs), and junction-defined, buried-stripe (JDBS) lasers. The first three PDS devices to be life-tested have already logged over 6,000, 5,700, and 4,000 h, respectively, of cw operation at room temperature without any degradation.     

Novel colliding plasma pulse clipper and optical isolator for high power infra-red lasers

The properties of a high density plasma focus produced inside a ring target with an Nd laser have been investigated. Studies of the axial propagation of a CO₂ laser beam through the plasma focus have shown that the device can be used either as a fast pulse clipper or as an optical isolator for high power infra-red lasers. Self-focussing, strong refraction and defocussing and non-classical absorption of the CO₂ laser beam have all been observed.     

Flashlamp pumped color center lasers

Flashlamp pumped tunable operation of F_A(II) and F_B(II) center lasers is reported. Threshold pump energies as low as 400 mJ, output energies of nearly 70 mJ and an efficiency of 0.1% have been achieved. The width of the emission spectrum of initially 70 GHz with a Littrow grating tuner was reduced to 1.5 GHz using a grazing incidence grating configuration. The scalability of the system is discussed.     

Optimization studies of single-transverse-mode 980 nm ridge-waveguide lasers

The paper presents a simple and efficient Mode-Solver-based method for determining the ridge profile that ensures stable single-transverse-mode operation in ridge waveguide lasers. A quantitative figure of merit, easily derived from the Mode Solver analysis of the structure, indicates the likelihood of single transverse modal behavior over the whole bias range. The transverse mode analysis performed with the in-house developed software has been compared with the results of the commercial simulation package LASTIP and with experiments. The simulation and experimental results have been used to derive processing guidelines for achieving a stable single-transverse-mode operation in ridge waveguide lasers.     

Analysis of short-wavelength charge-exchange lasers via plasma-gas beam clashing

The coupled particle and radiation rate equations have been solved for the population inversion and laser intensity which result when a plasma is incident on a vapor target. For the specific case of a helium plasma incident on a cesium vapor target, a laser intensity of order 10⁶W/cm² at 584A?is calculated. The numerical results are in basic agreement with a simple analytical model. Experimental considerations and progress are discussed.     

Efficacite des systemes unidirectionnels utilisables dans les lasers en anneau

A new dye for cw laser operation has been found which can be tuned as low as 390.4 nm. A low threshold and a good efficiency have been observed. The dye showed no photochemical degradation even at high pump laser levels.     

Research on chemical and discharge oxygen-iodine lasers

Novel methods and device configurations for singlet oxygen and atomic iodine generation were proposed and investigated for operation of the chemical or discharge oxygen-iodine lasers (COIL/DOIL). A chemical centrifugal spray generator of singlet oxygen was developed, based on the conventional chlorine-basic hydrogen peroxide chemistry. Results of theoretical and experimental investigation of the generator parameters are presented and compared with parameters of other generator types. A design of experimental device for singlet oxygen generation by means of the hybrid DC arc and RF plasma jet is presented. An alternative method of atomic iodine generation by a radiofrequency discharge decomposition of iodine compounds like CH₃I or CF₃I is described employing advanced experimental configuration. Some representative experimental results of this investigation are presented.     

A review of external cavity-coupled quantum dot lasers

Since the external cavity quantum dot laser was first demonstrated, the performances have been improved in terms of operation temperature, output power, pulse generator and tuneability based on the naturally size fluctuation of quantum dot. Nowadays, the external cavity quantum dot sources have been successfully used in different absorption spectroscope techniques, in industry, biomedical and research. In this paper we reviewed the recent developments of quantum dot lasers operated in a grating-coupled external cavity system where a single frequency and wide tunable wavelength range were easily obtained by adjusting the grating angle. In all cases, we mainly stressed the significant progresses in understanding of basic optical and electronic properties to enable the importance steps forward. The prospects for further progress directed towards stability, mode-hoping-free tuning range, miniaturization and integration of the external cavity quantum dot lasers also reviewed.     

High power self-controled volume discharge based molecular lasers

An investigation was made of the characteristics of the formation of a selfcontroled volume discharge for the pumping of CO₂ lasers, i.e. self-sustained volume discharge (SSVD), which involved a preliminary filling of a discharge gap by an electron flux from an auxiliary-discharge plasma. We have found that this method was suitable for large interelectrode gaps, that distortion of the electric field in the gap by the space charge of the electron flux played an important role in the formation of the discharge and that the electrodes could be profiled dynamically during propagation of an electron flux through the discharge gap and a SSVD could form in systems with a strongly inhomogeneous field. High power SSVD based CO₂ laser systems have been created and investigated. Another type of self-controled volume discharge without pre-ionization, i.e. a selfinitiated volume discharge (SIVD), in nonchain HF lasers with SF₆−C₂H₆ mixtures was investigated as well in our review. We have established that, after the primary local electrical breakdown of the discharge gap, the SIVD spreads along the gap in directions perpendicular to that of the electric field by means of the successive formation of overlapping diffuse channels under a discharge voltage close to its quasi-steady state value. It is shown that, as new channels appear, the current flowing through the channels formed earlier decreases. The volume occupied by the SIVD increases with increase in the energy deposited in the plasma and, when the discharge volume is confined by a dielectric surface, the discharge voltage increases simultaneously with increase in the current. The possible mechanisms which explain the observed phenomena, namely the dissociation of SF₆ molecules and electron attachment SF₆ molecules, are examined. A simple analytical model, which makes it possible to describe these mechanisms at a qualitative level, was developed. High power SIVD based HF(DF) lasers have been developed and tested.     

Effective-mass superlattice as an injector in quantum cascade lasers

In this paper, we have developed new design of the injector for quantum cascade structures based on the effective mass superlattice. The transmission spectra of the conventional injector and effective-mass injector have been compared. Advantage of the effective-mass injector is more uniform spectrum of pass-band. This feature allows to improve controllability of the quantum cascade laser, to increase stability of its operation and to decrease sensitivity to noise in applied voltage bias. Also, we have computed geometrical parameters for effective-mass injector which is appropriate to provide inverted population in existing quantum-cascade lasers. Such injector should be characterized by 15–25 numbers of layers with widths of layers up to 2 nm.     

A novel structure of visible semiconductor lasers

Terraced substrate inner current stripe lasers emitting in the range of 750–780 nm are developed with very simple fabrication processes. The lasers have good performance of cw room temperature, linear light-current output over 30 mW per facet and maintain stable fundamental transverse and longitudinal mode of 2–4 times current threshold. The current threshold of 25 mA under cw room temperature operation has been achieved.