Rate equations for modelling of short-pulse rare-gas halide excimer lasers

In this work, on the basis of the analysis of data relating to relaxation processes and emission spectra of excimer molecules, the rate equations for modelling short-pulse rare-gas halide excimer lasers are formulated and discussed. The equations take into account relaxation processes important for short-pulse generation, such as decay of B-, C- and X-states, vibrational relaxation in these states, and B-C mixing. As a special case for these equations, simplified equations for KrF and XeCl lasers are introduced. The gain recovery curves and the dependences of saturation energy on pulse duration, computed both for KrF and XeCl, coincide well with the experimental data. Discussion of the factors influencing the gain dynamics and the saturation energy of these media, is also presented.     

Rate equations and transient phenomena in semiconductor lasers

This contribution attempts to review certain resonance effects which occur in the dynamic behaviour of semiconductor lasers. To study these effects theoretically, a rate equation approach is used for single-mode operation in the region of lasing threshold.The two basic rate equations are given and their transient solutions discussed. The existence of two time constants in these equations, viz. the electron lifetime _e and the photon lifetime _e; gives rise to a characteristic resonance frequency in the GHz region. This resonance manifests itself in transient spiking effects, in quantum noise phenomena, and in high-frequency modulation experiments. In a modified form the resonance frequency may also be studied in lasers with external cavities and in double-diode configurations (or, equivalently, conventional devices with non-uniform excitation along the cavity length).In the latter two examples mentioned above, the resonance is excited by optical feedback of the laser radiation into the active medium via a lossy or insufficiently inverted region. In the spiking oscillations commonly observed at the commencement of laser operation, the initial population overshoot is the cause of the resonance. For the case of quantum noise it is the requirement that the photon and electron populations have integer values which supplies the driving force-a true quantum effect. High-frequency modulation experiments directly reveal the same resonance frequency where a strong maximum in modulation intensity occurs.A part of this work was reported at the Conference on Semiconductor Injection Lasers and their Applications, Cardiff, March 1972.     

Prospects for vapor-phase dye lasers

This review covers the field of vapor-phase dye lasers (VPDL) with special emphasis on prospects of gas lasers with optical pumping. Some peculiarities of the gaseous active medium and a possibility to control its density near the critical point are discussed. High specific laser energies (0.3J/cm^–3), low thresholds, and high efficiencies (20–40%) made it possible to construct a powerful tunable VPDL.     

Irreversible circulation and the undampled spiking in lasers

Our new theory of fluctuation was applied to the undamped spiking in lasers with single mode saturable absorption. It was found that the irreversible circulation α diverges at the thresholds of hard mode instabilities, which leads to limit cycle.     

Irreversible circulation and the undamped spiking in lasers

Our new theory of fluctuation was applied to the undamped spiking in lasers with single mode saturable absorption. At the marginal points, which lead to limit cycles, it was found that the irreversible circulation α and the residual circulation α′ diverge together with the variance σ. The model system of this article has effectively three degrees of freedom; however, it was demonstrated that the dominant motion and the fluctuation have two dimensional character in the neighbourhood of a hard mode instability.     

The effect of dye photodegradation on the performance of dye lasers

Detailed experimental study of laser dye stability and the subsequent effects of photodegradation products on the operation of a Nd:YAG laser pumped Rhodamine-6G pulsed dye oscillator has been carried out. Deterioration of laser output on account of dye photodegradation resulting in the loss of active dye molecules and the generation and accumulation of reaction products that introduce a loss at the laser and pump wavelengths has been theoretically simulated in terms of a time dependent rate equation model. Our experimental observations have been found to be in good agreement with our theoretical estimates. We have also investigated the deterioration in the performance of a copper vapour laser pumped tunable dye laser with a high average power and a high repetition rate operating over an extended period of time. Our theoretical model, when suitably modified, provided useful estimates for the extent of deterioration in laser performance of such a dye laser with a high average power and a high repetition rate on account of photodegradation of the active dye molecules. PACS 42.55.Mv; 42.60.By; 42.70.Hj     

Rate equations studies on coherently combined fiber lasers connected by an optical coupler

Attempt has been made to apply the steady-state rate equations to study two coherently combined Er³⁺-doped fiber lasers joined by an optical fiber coupler. In order to establish the boundary conditions, which are necessary for solving the equations, we have taken into consideration the fact that a constructive interference at the coupler assures that the laser radiations from both constituent lasers are directed to the coupler output port to which a reflection mirror defining both lasers is attached. Consequently, effective reflectivity, provided by the coupler-mirror combination, can be specified in terms of the laser powers of both laser signals, and the rate equations describing the compound system can be solved. Using the derived solutions, quantitative investigations can be made on the influences of different laser parameters. For example, the influence of the length difference between doped fibers, the splitting ratio of the coupler and power difference between the two pump radiations have been given in this report.     

Water-soluble coumarin dyes for flashlamp-pumped dye lasers

New coumarin derivatives have been prepared that are soluble in water, a solvent with superior thermo-optical properties. The new dyes, flashlamp-pumped, lase with high effeciency between 450 and 520 nm (untuned).     

New dye solutions for mode-locking infrared lasers

The recovery time of saturable absorbers is shortened externally by electronically active solvents, e.g., iodoethane, methyl sulfoxide, or ethyl sulfide. With a highly stable dye in such a solvent, very reproducible mode-locking of the neodymium-glass laser is achieved. The recovery time of the dye and hence the degree of mode-locking can be varied readily through the choice of solvent or solvent mixture.     

A magnetic tuning system for dye lasers

A new device for magnetically displacing the output mirror of a laser resonator and synchronously tilting an etalon in order to obtain single-mode tuning of a dye laser over a tuning range of at least 10 GHz is described. Comparatively large displacements with good linearity of a coil mounted on a membrane and placed inside the strong magnetic field of a ring magnet are obtained for currents in the order of several hundred milliamperes. Together with etalon flats of appropriate thickness and reflection mounted in the resonator of the laser a versatile instrument for application in intra and extra cavity spectroscopy has been developed.     

Optimization of pulse lamps for dye lasers

We carry out investigations of the generation efficiency of a dye laser in which, as a source of pumping, tubular lamps are used that are enclosed in shells to withstand the pressure of the xenon filling them. It is found that the optimum pressure is 60–80 torr, which ensures the greatest luminous efficiency of the lamps in the short-wave region of the spectrum at standard electrical parameters of the power supply system. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 134–137, January–February, 1998.     

New jet stream technique for dye lasers

We report on a novel technique for generating large area flowing sheets of viscous fluids for use in dye lasers. The proposed technique allows one to control the shape, size and thickness of the fluid sheets of excellent optical quality. Rhodamine 6G/ethylene glycol jet streams have been investigated. Application to other dye/solvents, to saturable absorbers or to other fluids is straightforward.     

Precise rf tuning for cw dye lasers

Laser beams are rf amplitude modulated to generate side frequencies which are used to tune a cw dye laser with rf accuracy. In a laser spectroscopic test experiment a precision of ±15kHz has been realized.     

A double-prism beam expander for pulsed dye lasers

The design of a pulsed dye laser cavity incorporating a double-prism beam expander is described and operating characteristics compared with those of single-prism systems. Narrow spectral linewidths (δλ = 0.008 Å) are achieved at relatively high efficiency (> 10%) for coumarin 500 dye solutions. Background superfluorescence in the output is low and the cavity is free from external coupling effects.     

Extending the solvent palette for cw jet stream dye lasers

The use of viscosity-raising additives (VRAs) for jet stream dye lasers is proposed and examples for all common organic solvents given. The use of water-based dye solutions with polyvinyl alcohol as a VRA offers substantial advantages for high stability and high power applications.     

Flashlamp-excited dye lasers in the near infrared

The laser emission of flashlamp-excited polymethine dyes is investigated. The spectral shift towards longer wavelengths due to relatively slow pumping is discussed in terms of transient triplet-triplet absorption. First results concerning mode locking and tuning on the 785–805 nm and 872–880 nm ranges of two tricarbocyanine dyes are presented.     

Rate equation approach for diode lasers

The light output and the electron density within the active layer of a semiconductor laser have been calculated from the steady state solution of a rate equation approach. The assumed rate equation model takes into account the spontaneous emission into the lasing modes. Simple analytical approximation formulae have been found under the assumption of a power-law dependence between optical gaing and electron densityn (g ∞n′). The approximations are compared with numerical results from the rate equations. With the exception of a small region near the lasing threshold good agreement has been found. The theoretical results are compared with experimentally measured light outputs from single and double heterostructure lasers. From the comparison below threshold the power law exponent/may be evaluated. The comparison at threshold suggests that the spontaneous emission term decreases at threshold. This decrease is in agreement with experimentally measured changes of the emission bandwidth at threshold.     

A basic property of dye lasers: Spectral evolution

We have derived an analytical equation which is found to be useful in understanding injection locking, progressive narrowing, enhancement of intracavity absorption and amplification, dual-wavelength dye lasers, broad band shift and coupled cavities. The basic property of the dye laser emission, i.e. the spectral evolution, is described without explicit reference to the molecular populations and the excitation time shape. The concept of spectral evolution is expressed in terms of new parameters such as the evolution length of the amplifier and the evolution time of the oscillator.     

Fast rise air spark pump for organic dye lasers

A specially constructed capacitor with low inductance is used to produce an air spark with short rise time, which is able to pump organic dye lasers with high efficiency. For Rhodamin 6 G we observed a threshold energy for stimulated emission of 3 Ws.