Output Radiation Parameters Research Articles

Towards the “dream pulsed laser”

It is an obvious trend that more and more technology devices are approaching the stage of computer-controlled black box, and lasers cannot escape this either. Generally, users do not want to understand the operation of a black box. They just want to set the output radiation parameters through their computer and have a magic black box deliver the desired radiation. In addition, they expect this technology to be reliable and inexpensive. The most fitting laser platforms for this type of technology are semiconductor and fibre-optical, which do not require optical alignment of laser cavities and have been performing very well in a numerous applications. Here, we analyse the fibre laser platform from the viewpoint of using it as a base for implementation of a “dream pulsed laser” and discuss limitations and prospects of such implementation.

Contrasting the performance capabilities of urban radiation field between three microclimate simulation tools

Radiation heat in urban areas has detrimental effects on outdoor environments and building energy consumption. A better method for quantifying solar radiation in cities is very important. In order to compare the performance differences between three urban microclimate simulation softwires in the urban radiation field, ENVI-met, RayMan, and SOLWEIG were selected as the research objects. The output radiation parameters and the radiation calculation models were analyzed. Effects of underlying surface and enclosure modes of buildings on the radiation field were simulated separately. The differences in radiation field performance simulations of the three tools were compared from several aspects, including long-wave, short-wave, direct, and reflected radiation. It was found that all three softwires can calculate the effect of space enclosure on direct and diffuse radiation. RayMan has the highest sensitivity and fastest simulation speed, but it has few output radiation parameters, and it cannot simulate reflected radiation very well. ENVI-met can calculate the most radiation parameters and has the lowest errors; it can also calculate long- and short-wave radiation between building surfaces. SOLWEIG can be used for simulation in large outdoor spaces, but it has the highest errors.

Change in the Generation Mode of the Plasma Relativistic Microwave Oscillator

Time evolution of the parameters of output radiation of a plasma relativistic microwave oscillator (PRMO) based on the Sinus 550-80 accelerator during a single relativistic electron beam (REB) pulse was studied experimentally. Analysis of the experimental data was accompanied by numerical simulations under conditions close to the experimental ones. It is shown that qualitative changes in the parameters of the PRMO output radiation are associated with a change in the generation mode. The first half of the REB pulse is characterized by the maximum output radiation power and a broadband spectrum consisting of a great number of harmonics. The nonlinear beam–plasma interaction limits the growth of the field amplitude, decreases the number of plasma electrons, and leads to the emergence of longitudinal plasma inhomogeneity. The appearance of an ion background in the drift tube volume and the formation of a radially nonuniform plasma waveguide alter the conditions of beam–plasma interaction in the second half of the pulse. The second half of the REB pulse is characterized by a decrease in the output microwave power and the narrowing of the generation frequency band. Spectral analysis demonstrates preservation of a stable narrow spectral component throughout the microwave pulse.

Dual-wavelength generation of picosecond pulses with 9.8 GHz repetition rate in Nd : YAG waveguide laser with graphene

We report a new solid-state waveguide laser generating picosecond pulses with a GHz repetition rate, based on the use of graphene as a saturable absorber. Lasing at the main transverse mode is provided by the geometry of a cylindrical waveguide formed in the active crystal volume by the method of direct writing with a femtosecond laser beam. Fine tuning of the intracavity interferometer formed between the active medium and output mirror makes it possible to control the spectral-temporal parameters of output radiation and to smoothly tune the repetition rate of pulses having a duration of less than 20 ps. In particular, the possibility of dual-wavelength generation in the regime of continuous passive mode locking using a single saturable absorber based on graphene is demonstrated. By amplifying laser output radiation in the ytterbium fibre amplifier, an average output power of 530 mW is obtained.

Comparative analysis of simulation of urban radiation field

In order to compare the differences between various outdoor environmental simulation software in the urban radiation field, ENVI-met, RayMan and SOLWEIG were selected as the research objects. The multiple types of urban radiation intensities that can be obtained by each software are compared, and the calculation method of types of these radiations was analyzed. Effects of underlying surface on the radiation field were simulated separately. The differences in radiation field performance simulations of three softwares were compared from several aspects such as short wave, direct radiation and reflected radiation. It is found that Rayman has the high sensitivity and fast simulation speed, but the output radiation parameters are less; ENVI-met can calculate the most radiation parameters and calculate the long-short wave radiation heat transfer process between building surfaces; the SOLWEIG can be used for simulation in large outdoor space, and has more calculated radiation parameters, but has large error. All three softwares can calculate the effect of space enclosure on direct and scattered radiation.

Single-Frequency TEA CO2 Laser for Experiments on Non-Resonant Radiation Interaction with Matter

The design philosophy and output radiation parameters of single frequency TEA CO2 laser with bleaching intracavity longitudinal modes selector (cell filled with SF6) are described. At cavity tuning to 10P(16) line and choosing optimum SF6 pressure in the cell the stable single frequency lasing is realized with scatter of radiation peak power in a series of “shots” less than ±7% of average value. The radiation energy density and intensity gradually tuned in the ranges 0.36–12.5 J/cm2 and 2.9–100 MW/cm2 correspondingly were realized in the focal plane of a lens with f = 127 mm.

ЭФФЕКТИВНАЯ СХЕМА НАКАЧКИ ЭРБИЕВОГО ВОЛОКОННОГО ЛАЗЕРА С РАСПРЕДЕЛЕННОЙ ОБРАТНОЙ СВЯЗЬЮ ДЛЯ ПОДАВЛЕНИЯ РЕЛАКСАЦИОННЫХ КОЛЕБАНИЙ

The scheme of erbium-doped distributed feedback fiber laser is proposed, which combines pumping schemes of the single frequency oscillator and optical signal amplifier. The scheme provides maximum efficiency of pump to signal conversion while minimizing the effect of relaxation oscillations on the output radiation parameters. In this scheme single-frequency fiber laser radiation power up to 30 mW achieved at the pump power of 600 mW at 980 nm. Amplified spontaneous emission was at the level of 0.08%. The magnitude of the relative intensity noise is — 140dB/Hz at frequencies more than 10 MHz and — 100dB/Hz at the peak of relaxation oscillations. The linewidth of the laser radiation is less than 1 kHz.

Equivalent Schemes of a Resistive Hot-Carrier Sensor for Measurements of the Parameters of Output Radiation of Relativistic Microwave Generators

We have developed equivalent schemes of high-frequency hot-carrier detectors, which allow one to measure the parameters of output radiation of relativistic microwave generators with higher accuracy, as well as to solve the problems of optimization of the design of such detectors and the ways of connecting them into external circuits.

The Investigation of Properties of Copper Vapor Pulsed Power Active Medium in Time and Development of Operational Control Methods of Output Radiation Parameters on Their Basis

The Investigation of Properties of Copper Vapor Pulsed Power Active Medium in Time and Development of Operational Control Methods of Output Radiation Parameters on Their Basis

Estimation of output beam characteristics of laser with unstable resonator and turbulent active medium

In this paper we present calculations of the three-dimensional mode structure and output beam characteristics of unstable resonator with turbulent active medium. The calculations of the output beam are carried out in the Fresnel approximation using the well-known iterative method [1]. The active medium is modeled as a series of phase screens with Kolmogorov statistics. The dependence of output radiation parameters of the gas flow laser with unstable resonator on the strength of turbulence in active medium and parameters of resonator is under consideration.

Features of neodymium laser epilation

The efficiency and features of the use of the Nd:YAG laser for epilation in comparison with ruby, alexandrite, diode lasers and a broadband light source were studied. Procedures for calculating the temperature distribution of the hair follicle over the entire depth of its position in the skin and temperatures of undesirable heating of surrounding skin regions under exposure to Nd:YAG laser radiation were developed. The heating temperature of hair follicles with black, brown, and light hair was calculated. The heating temperature of follicles of biological tissues for patients with light, swarthy, and dark skin was calculated. The ranges of the neodymium laser applicability to hair and skin colors during epilation procedures were determined. The ways of optimization of the output radiation parameters (pulse energy and duration, light spot sizes) for removing variously colored hair of patients with various skin phototypes were directed. The ways of epilation technology improvement (active skin cooling, injection of special dyes into hair follicles, and others) were proposed.

Effect of inductive-plasma UV preionization on the parameters of XeCl laser radiation

A XeCl laser with a double plasma electrode providing automated inductive-plasma UV preionization has been experimentally studied. Ways to increase the laser efficiency by selecting a proper regime of excitation of the active medium based on various buffer gases (helium, argon, and neon) are considered, depending on the parameters of a two-stage pumping source. It is shown that the scheme of pumping with an inductive-plasma UV preionization source is effective only with a XeCl laser using neon as a buffer gas excited in a fast regime, which can provide a significant increase in the energy parameters of output radiation and, accordingly, in the laser output efficiency.

Study of an electric-discharge molecular fluorine VUV laser

The effect of the discharge voltage, composition and pressure of the He—F2 gas mixture on the output radiation parameters of a VUV F2 laser is studied. It is shown that reaction of dissociative attachment of electrons to fluorine molecules plays a significant role in the process of active medium excitation. The condition for choosing the optimal mixture composition is determined. The use of a pump generator with multistage magnetic compression of high-voltage pulses and preionisation system with a barrier discharge at the surface of a ceramic tube ensures a high homogeneity of the gas discharge (without cathode spots). A small-size 2.5-mJ F2 laser (with an active volume of ∼9 cm3) with a pulse repetition rate of up to 1 kHz operating on a He—F2 mixture at a pressure of up to 3500 mbar is developed.

Peculiarities of active medium formation in a short-pulse electric-discharge XeCl laser

The effect of the conditions of discharge on the output radiation parameters and efficiency of an electric-discharge XeCl laser pumped by 20 ns pulses is studied experimentally. It is shown that the highest specific energy extraction ∼3.9 J L-1 atm-1 from the active medium is realised in a discharge formed by pronounced macroinhomogeneities. The maximum laser efficiency of 2.7% is attained for discharge current densities of 1.2–1.4 kA cm-2.

Phase Correlations and Polarization Characteristics of Dye-Solution Laser Radiation

The influence of phase correlations of components on the energy and polarization parameters of output radiation have been calculated within the framework of the formalism of polarization components. It is shown that these correlations have a marked effect only on the energy characteristics. At the same time, an analysis of the polarization characteristics of a probe wave provides rich information for the analysis of the phase-polarization structure of radiation. An analysis of experimental data allows the inference that the correlation of components is relatively weak even for lasers with a high-Q resonator and at a high excess of threshold values.

Efficiency of an unstable resonator with an active medium containing small-scale phase inhomogeneities

Properties of an unstable resonator with small-scale periodic inhomogeneities of the refractive index in an active medium are considered. It is shown that the parameters of output radiation depend on the structure of a phase inhomogeneity. The methods for increasing the resonator efficiency are analysed.

Selection of a Master-Oscillator Scheme for a Chemical IR-Initiated Laser

The results of experimental and theoretical studies of operation regimes of a pulsed chemical D2–F2–CO2 UV initiated laser are presented. The influence of particular mixture components, the power of the UV radiation source, and the resonator's characteristics on the output radiation parameters are experimentally studied on the “Kaiman” setup. The results of theoretical simulation obtained using the proposed scheme correspond sufficiently to those obtained experimentally. A description is given of the pulsed D2–F2–CO2 UV initiated laser “Flash-1” that provides for radiation pulses of 18 J with a 2.6–3.5 μs duration in the 10-micron range. A detailed description is given of the precision diagnostics of dark reactions occurring during the mixture preparations and affecting the efficiency of energy extraction in the course of generation.

Effect of argon buffer and the UV preionization regime on the electric-discharge XeCl laser parameters

The gas discharge and output radiation parameters were studied in XeCl lasers with various buffer gas compositions (argon vs. neon) and different types of excitation regimes (fast vs. quasi-stationary) in the preionization source. The intervals of specific energy for the neon-and argon-based buffer gas mixtures are 10–125 and 45–360 J/(l atm), respectively. The specific parameters of radiation in the neon-and argon-based buffer gas mixtures depend on the energy required for the UV preionization. For high-power UV preionization sources, the output parameters of lasers using argon-based gas mixtures may exceed those obtained with neonbased mixtures.

Approximate analytical calculation of the beam characteristics of a laser with aperture-truncated cavity mirrors

A method for the approximate analytical calculation of the parameters of laser output radiation is considered. The aperture truncation of the optical cavity mirrors is taken into account within the framework of the Gaussian formalism. The influence of the aperture constraints is described with the aid of equivalent Gaussian stops. The distances from the focusing lens to the beam waist, measured experimentally and calculated by the proposed analytical method, are compared. Analytical expressions are proposed for the Gaussian beam parameters, approximating the beam from a laser with aperture-truncated cavity end mirrors.

Automatically controlled system for stabilisation of the output power of an Nd : YAG laser with intracavity frequency doubling

An automatically controlled system for stabilisation of the output power of an Nd : YAG laser with intracavity frequency doubling was constructed. This system applied to an industrial laser of the LG-402A type. Active stabilisation of the output radiation was performed by personal-computer control of the pump current and of the thermal conversion regime in the nonlinear element. Algorithms developed for control of the output radiation parameters make it possible to avoid the use of a probe perturbation and to achieve a relative instability of less than 0.5% for the integral intensity of the second-harmonic radiation.