Regime Of Laser Operation Research Articles

Stimulated emission, gain, and coherent oscillations in II-VI semiconductor microcavities

The large oscillator strength for excitons in ZnSe-based quantum wells (QW's) is reflected in a normal-mode (Rabi) splitting which exceeds 10 meV per QW at low temperatures when measured by conventional linear optical probes or by four-wave mixing technique. The dominating impact of the electron-hole Coulomb interaction extends to high pair densities, including the regime of vertical cavity laser operation. Measurement of gain spectra shows how the composite photon-exciton oscillator supplies the optical gain for a laser operating beyond the perturbative regime.

Investigation of a He-Eu+ laser excited by short pumping pulses

A gas-discharge collisional He-Eu laser (λ=1.0019 µm, atmospheric pressure) has been investigated. The laser has been pumped by short pulses (150 and 80 ns). We have shown the advantages of the laser construction and operation regime under conditions in which the metal vapor pressure does not depend on the thermal regime of the active volume. In this case it is possible to optimize independently the metal vapor pressure and the power pumping the discharge. It is shown that the average laser output powerP l and efficiency η are increased up on an increase of the pumping pulse repetition rateF in the whole studied range ofF (up to 30 kHz). We have attainedP l ≈ 13 W and η ≈ 0.15%.

The role of excitation parameters in high repetition-rate N2-TE lasers

We have studied the effects of decreasing the excitation duration on the pulse-repetition-rate (PRR) capabilities of a low-pressure (P<200 Torr) N2-TE laser. It was found that maximum PRR increases with decreasing duration of the discharge current. PRR as high as 1000 Hz has been obtained in the sealed-off non-flowing regime of laser operation. These findings are adequately explained by the time dependence of the arc-discharge formation.

Ultralow-threshold-current lasing in inversion channel lasers

A new regime of semiconductor laser operation was observed in quantum-well inversion channels of double heterostructure optoelectronic switches. The quantum-well active region operated with substantial excess negative charge imbalance due to the proximity of a high-density depleted donor charge sheet. Threshold current densities as low as 15 A/cm/sup 2/ in as-cleaved 400- mu m-long devices were measured, and unusual high-frequency operation under low power operation was observed. These qualities may be of great significance for optical interconnections and optoelectronic integrated circuits. >

High efficiency 33.3 GHz free electron laser amplifier with a reversed axial guide magnetic field

Abstract We report on a new regime of free electron laser operation using a helical wiggler field and a reversed axial guide magnetic field. The orientation of the axial field is such as to oppose the rotation of the electrons imparted by the helical field. The 33.3 GHz free electron laser amplifier is driven by a mildly relativistic electron beam (750 kV. 300 A. 30 ns) and generates 61 MW of radiation with a 27% conversion efficiency. The results are compared with those obtained when the axial guide field is in its conventional orientation where considerable loss of power and efficiency is observed.

Amplification and superradiant emission from a 33.3 GHz free electron laser with a reversed axial guide magnetic field

A new regime of free-electron laser (FEL) operation using a helical wiggler field and a reversed axial guide magnetic field is reported. The orientation of the axial field is such as to oppose the electron rotation imparted by the helical field. The 33.3-GHz FEL amplifier is driven by a mildly relativistic electron beam (750 kV 300 A, 30 ns) and generates 61 MW of radiation with a 27% conversion efficiency. The results are compared with those obtained when the axial guide field is in its conventional orientation, where considerable loss of power and efficiency is observed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spectral regimes of an XeF laser

A detailed investigation was made of the emission spectra of an electric-discharge XeF laser pumped by short high-power pulses and operating in the buffer-gas (He and Ne) pressure range 0.01–0.8 MPa. The experimental results were explained on the basis of a model of relaxation processes in an excited electronic state. Several spectral regimes of laser operation were identified. Laser emission spectra were obtained for mixtures containing Ar and excited by an electron beam. It was necessary to take into account the population of the ground state in explaining these spectra.

Selection of the resonator type

A discussion is given of the factors involved in employing different types of resonator, in accordance with the properties of the amplifying medium, the active zone dimensions, and the laser operating regime.

Time structure of iodine laser pulse in the free running mode of operation

Time structure of iodine laser pulse in the free running mode of operation was studied using the power amplifier of laser system PERUN as the laser oscillator. Two characteristic shapes of laser pulse correspond to different regimes of laser operation, the existence of which is ascribed to the critical concentration of I2 molecules. Simultaneously an additional chemical pumping was proved at least in the initial phase of photodissociation and in a late-time lasing after the end of flashlamps pumping light.

Use of low-power ionizers in the excitation of the active media of excimer lasers

The characteristics of XeF and XeCl lasers stabilized by an external low-power ionizer were considered. Two laser operating regimes were investigated, one with a buildup of negative ions and the other with a discharge stabilized by an external low-power ionizer. The temporal, spectral, and energy characteristics of these lasers were investigated. The minimum ion concentration in the negative-ion buildup regime was found to be [F−]=1011cm−3 and [Cl−]=1012cm−3, while the use of a discharge stabilized by a low-density electron beam made it possible to reduce the current density of the electron beam to ~0.1mA/cm2 in the case of the XeCl laser. A value of 10 J/liter was achieved for the maximum specific output energy of the XeCl laser.

Optimisation of the process of laser-induced thermochemical image recording

The process of image recording by laser-induced oxidation of thin metal films has been mathematically modelled. A numerical simulation of the recording process has been carried out by a computer. In this experiment the optimum conditions for distortionless thermochemical image recording have been established. It has been shown that the nano-second laser operation regime is the most suitable one for recording of complex images at high resolution.

Mechanism of surface breakdowns of materials for ir optics by radiation from a pulsed CO2 laser

A procedure is developed for measuring the breakdown thresholds on the surfaces of IR-optics materials. It is shown that the decisive role in the onset of the breakdown under pulsed CO= laser radiation is the water absorbed in this surface layer. Successive stages of the breakdown development are investigated. Its main regularities as functions of the parameters of the acting laser radiation, of the surface state, and of the external conditions are determined. Different methods of decreasing the breakdown threshold on the surface of IR-optics materials both by increasing the technology of the surface finish and as a result of a corresponding choice of laser operating regimes are investigated.

Divergence of radiation from an electric-discharge CO2laser having an unstable resonator

The results are presented of an experimental investigation into the divergence of radiation from a quasi-cw CO2 laser having an unstable resonator. It was found that the onset of inhomogeneity in the active medium, caused by instability of the self-sustained gas discharge, led to a substantial increase in the divergence of the laser radiation before its power fell. This effect must be taken into account when optimizing laser operating regimes. Laser radiation entering the resonator after reflection from an irradiated target can greatly influence the power, stability, and divergence of the radiation, leading to disruption of the normal intensity distribution in the focal plane. This effect is observed even when the target is rotated through large angles relative to the direction of the incident radiation.

Characteristics of a CO2laser excited by a capacitative ac discharge

An experimental study was made of a model of a steady-state fast-flow CO2 laser excited by a 10 kHz ac capacitative discharge. The results of an optimization of the laser operating regimes agree with those obtained from calculations. According to these results a commercial laser with a power of ~20 kW, an overall efficiency of ~15%, and a specific output energy of ~40?45 J/g can be made utilizing the specific parameter levels achieved in this work.