Length Of Active Medium Research Articles

Study of Active Medium Length Effect on Characteristics of Passive QSwitching and Stokes with Anti-Stokes Pulse

Objective: To study the effect of active medium length on the characteristics of passive Q-switching pulses, Stokes pulses, and anti-Stokes pulses generated by laser-Raman medium interaction in optical systems, theoretically. Methods: The optical system consists of Nd+3:YVO4, PbWO4, and Cr+4:YAG as active mediums, Raman medium, and saturable absorber materials, respectively. The rate equations model has been used in the study, and the Rung-Kutta-Fehelberg numerical method was used to solve the rate equations. Finding: The result shows that, decreasing of the active medium length leads to emit high power pulses at advanced time. It also leads to increase in initial value and the maximum value of population inversion density, and leads to increase in the energy of passive Q-switching pulses, Stokes pulses, and anti-Stokes pulses. So the decreasing of the active medium length leads to decrease in the pulses duration and the final population inversion density. To increase the power of the three generated pulses, the length of the active medium used in the system must be decreased. Novelty: The characteristics of two pulses generated by Laser-Raman interaction (passive Q-switching pulse and Stokes pulse) have been of interest in some studies. This study investigates the effect of the active medium length on the characteristics of three pulses generated (anti-Stokes pulse with Stokes pulse as well as the passive Q-switching pulses) by the optical system rather than two pulses. Keywords: Laser; Nd+3 :YVO4; passive Q-­switching pulse; Stokes and anti-­Stokes pulses 1

Investigation of optical amplification of Cu II 224.7 nm spectral line in multiple segmented Grimm discharge

In this study the resonance energy transfer from metastable argon ion to copper atom in an argon glow discharge is used to investigate posibility of inverse population of the upper energy level of the line Cu II 224.7 nm. This resonance energy transfer is very efficient due to small difference between the energy levels of Ar II (3p5,2P1/2) and Cu II (4p,3P2). In order to examine the possibility of obtaining the inverse population of this copper ion level, arrangement of eight aligned catodes of Grimm-type abnormal glow discharges has been assembled. The length of the active medium is changed, by varying the number of the active discharges while the intensity of the Cu II line is monitored. It has been found that the increase of the line intensity is not a linear function of the active medium length. This can be considered as the first indication of an optical amplification of mentioned Cu II line and a possibility to achieve an inverse population on Cu II (4p,3P2) level. Since the intensity of this copper ion line depends on the discharge current, dependence of the Cu II line intensity on the plasma length for different currents is recorded. In order to achieve higher line intensity of Cu II 224.7 nm line, instead of DC power supply, a laboratory made pulse generator has been used. The device enables high intensity current pulses through the discharge and consequently increased the population of the excited level of copper ion. To determine parameters of the most efficient pulse regime, dependence of the Cu II line intensity on pulse duration has been studied.

Investigation of operational parameters on copper bromide laser output power

In this work, a copper bromide laser with an active medium length of 58 cm and an inner diameter of 20 mm designed and constructed. He and Ne used as buffer gases. The effect of reservoir temperature, He and Ne buffer gas pressure, frequency and electrical input power on the output power investigated. The result of experiments shows that an optimum laser efficiency obtained at the electrical input power of 2.1kW and corresponding operational temperature of 510 oC. The maximum output powers, 4 and 6 W, with use of He and Ne buffer gases, were determined at pressures 11 and 24 torr, respectively.

Numerical optimization of the electrical characteristics of an EUV laser on 3p–3s transition in neonlike argon ions in low-inductance capillary-type discharge

Electrical characteristics of low-inductance capillary-type discharge have been determined by numerical model calculations, which ensure high efficiency of energy supply to a plasma column with an aspect ratio of 1: 100. The EUV argon laser based on this discharge provides a gain of g+ > 1 cm–1 on the operating transition and ensures single-pass spontaneous lasing with g+l > 25 (where l is the active medium length).

Buffer gas effects on output power of a copper vapor laser

A copper vapor laser with an active medium length of 60 cm and bore of 16 mm was operated and optimized using different buffer gases to investigate the effect of pressure and gas flow rates on the laser output power. It was shown that a special interval of operational pressure and an optimum gas flow rate associated with the type of buffer gas were obtained.

The energy and spectral characteristics of a room-temperature pulsed laser on a ZnS:Fe2+ polycrystal

The energy and spectral characteristics of a laser on a ZnS:Fe2+ polycrystal operating at room temperature have been studied. The laser was pumped by a non-chain electro-discharge HF laser with a full-width at half-maximum pulse duration of ~140 ns. The diameter of the pumping radiation spot on the crystal surface was 3.8 mm. The two-sided diffuse doping of a polycrystalline CVD-ZnS sample with the surfaces preliminarily coated by high-purity iron films was performed in the process of hot isostatic pressing (HIP) in an argon atmosphere at a pressure of 100 MPa and temperature of 1290 °С. Increasing the duration of the HIP treatment from 54 h to 72 h made it possible to obtain twice the doping depth, and correspondingly, twice the length of active medium. As a result, the slope laser efficiency with respect to the absorbed energy was raised by a factor of 1.75 as compared to the value obtained in our earlier work with a polycrystalline sample. The generation energy was 25 mJ at a slope efficiency of ηslope = 35%. It was established that the generation spectra of the laser with a non-selective resonator have a linear structure with intervals between the neighboring lines of δλ ≈ 6 ÷ 8 nm, which is spurious for solid-state lasers. The spectral structure observed is not related to the elements inside the resonator, which might form Fabry–Perot interferometers.

Experimental Optimization of the Output Power of a Copper Vapor Laser Using Air as a Buffer Gas

In order to investigate the effect of the pressure buffer gas and frequency on the output power, a copper vapor laser with active medium length of 60 cm and bore of 16 mm has been operated and optimized using air as a buffer gas. The observed oscillatory behavior of the output power versus frequency is in good agreement with the previous reports. The measured results show the maximum output power of ~1.6W at the optimum pressure of 3.8 torr and frequency of 17 kHz. Abundance of the air and reduction of the system volume due to elimination of the gas handling system as well as the economically benefits are the advantages of the employing air as a buffer gas in the copper vapor laser operation.

Experimental Study of Buffer Gas Flow Rate Effect on Output Power of a Copper Vapor Laser

A copper vapor laser with active medium length of 60 cm and bore of 16 mm has been operated and optimized using different buffer gases to investigate the effect of the gas flow rates on the output power. It is found that there is a special optimum gas flow rate associated with the type of buffer gas.

High-energy room-temperature Fe2+:ZnS laser

Characteristics of a room temperature laser on polycrystalline ZnS:Fe2+ subjected to diffuse doping from two sides were investigated. The sample was pumped by a non-chain electrodischarge HF laser with the FWHM duration of the radiation pulse of ~140 ns. The diameter of the pumping radiation spot on the surface of the crystal was 3.8 mm. Further increases in the size of the pumping spot were limited by parasitic generation arising due to a high concentration of Fe ions in the near-surface layer of the sample at a relatively small depth of doping (short length of active medium). The generation energy of 25.5 mJ was obtained at a slope efficiency of 12% with respect to the energy incident on the sample. Characteristics of lasers on polycrystalline ZnS:Fe2+ and ZnSe:Fe2+ have been compared in equal pumping conditions. The slope efficiencies of ZnSe:Fe2+ and ZnS:Fe2+ lasers with respect to the absorbed energy were 34% and 20%, respectively. At equal pumping energy absorbed in the samples, the duration of the ZnSe:Fe2+ laser radiation pulse was longer than that of the ZnS:Fe2+ laser. Possibilities of increasing the efficiency of ZnS:Fe2+ laser operation at room temperature by improving the technology of sample manufacturing and reducing the duration of the pumping pulse are discussed in this letter.

A new approach for describing amplified spontaneous emission in a KrF excimer laser using z-dependency of gain-coefficient

Based on our recent realization concerning the geometrically dependent gain coefficient in self-terminating gas lasers, where it is shown that in one-dimensional approach it is z-dependent, we applied the gain formulation to explain, both numerically and analytically, the behavior of the amplified spontaneous emission (ASE) output energy vs. excitation length of the active medium. As an example, we used experimental measurements reported for a KrF excimer laser. In the approach it was realized that it is needed to present a gain-profile slightly lower than the gain-profile deduced from different reports appeared in the literature, where it is also indicating that the contribution of the ASE on the laser output is significant and it is the active medium length dependent. The present analytical presentation of the ASE output energy behavior, also, introduces a generalized formulation compared to that appeared in the literature. With this approach it is possible to remove most of the present ambiguities existing on understanding of the ASE behavior.

Optimization of Yb-Er microchip laser parameters

Output parameters of microchip lasers based on Yb:Er co-doped phosphate glasses have been numerically calculated using a simplified 4-level model in order to optimize the Yb and Er concentrations and active medium length. It was shown that active media with Yb concentration ~2·1027 m–3 and length of the order of 1 mm were most appropriate to obtain the practically maximum slope efficiency and minimum threshold power. Simulation results indicated that the Er concentration could be much lower than those currently used in practice. The obtained results were in good agreement with available experimental data.

Small-signal gain dependence on active medium length and axial thermal profile in metal-vapor lasers

We measure the small-signal gain coefficient g0 of a gold vapor laser for a 627.8 nm transition through the implementation of a discharge-driven oscillator-amplifier configuration. We study the gain dependence on the length of the laser active medium. In addition, we measure the output power of a copper-vapor laser for two different thermal insulator distributions and simulate the thermal-length profile to determine the effective length of the active medium. We show that the small-signal gain coefficient depends on the effective length of the active medium and do not depend on the physical (actual) length of the active medium.

Intracavity SRS conversion in diode-pumpedmultifunctional Nd3+:SrMoO4 laser crystal

Lasing of a miniature all-solid-state SRS laser based on a Nd3+:SrMoO4 crystal with a LiF:F2−-passive Q-switch is studied. The dependences of the laser and SRS self-conversion parameters on the initial transmission of the passive Q-switch are studied experimentally and theoretically. Simulation of the lasing kinetics has shown the possibility of nonlinear cavity dumping upon highly efficient SRS self-conversion of laser radiation. An increase in the active medium length from 1 to 3mm resulted in an increase in the energy of the output 1.17-μm SRS radiation from 20 μJ to record-high 60 μJ at the absorbed multimode diode pump energy of 3.7 mJ.

Dependences of small-signal gain and saturation-energy intensity on laser active length, buffer-gas type, and pressure variations in gold-vapor lasers

We measure the small-signal gain coefficient g0 and the saturation-energy intensity Es of a gold-vapor laser by implementing an oscillator-amplifier on the base of the gold-vapor laser. The dependence of the gain and saturation properties of the laser on the length of the laser active medium, the buffer-gas pressure, and the buffer-gas type are studied. The measurements of g0 for the amplifier for different lengths of the laser active medium (60 and 75 cm) show that with increase in the active-medium length, g0 increases while Es, vice versa, decreases. Such behavior of g0 and Es is observed in the whole range of changing the total pressure of buffer gas in the He-Ne mixture.

Enhancement of the efficiency and control of emission parameters of an unstable-resonator chemical oxygen—iodine laser

The outlook is considered for the development of a high-power supersonic flowing chemical oxygen—iodine laser operating as an amplifier and controlled by radiation from a master oscillator by using an unstable resonator with a hole-coupled mirror. The influence of the seed radiation intensity, the coupling-hole diameter, the active-medium length, and the magnification factor on the parameters of laser radiation is analysed. It is shown that the use of such resonators is most advisable in medium-power oxygen—iodine lasers for which classical unstable resonators are inefficient because of their low magnification factors. The use of unstable resonators with a hole-coupled mirror and injection provides the control of radiation parameters and a considerable increase in the output power and brightness of laser radiation.

The comparative analysis and optimization of the free-running Tm3+:YAP and Tm3+:YAG microlasers

The thulium microlasers based on yttrium-aluminium perovskite and yttrium-aluminium garnet crystals are considered as coherent light sources at the wavelength near 2 μm. The comparative analysis of these lasers is carried out by means of the lasers’ parameters optimization for each value of the pumping power taking into consideration the cross-relaxation and up-conversion processes as well as heating of the active medium. The optimal values of the active medium length, activator concentration and the output mirror reflectivity are determined both for Tm:YAP- and Tm:YAG-laser. The pulse generation of Tm:YAP- and Tm:YAG-lasers is also considered, the parameters of this regime are determined. The comparison shows the suitability of Tm:YAP laser crystal both for cw and pulse generation. The up-conversion influence on the laser characteristics is also analyzed.

A repetitively pulsed HF laser with a large discharge gap operating on the F2—H2 mixture

An efficient repetitively pulsed (RP) HF laser pumped by a barrier electric discharge with a 10-cm discharge gap is developed. A specific output energy E/V=3 and 23 J L-1 and a technical efficiency η equal to 3.4% and 26%, respectively, were obtained in the single-pulse regime for non-chain and chain processes. An average output power of 43 W (E/V∼10 J L-1 and η=11.3%) was obtained in the RP mode of the laser with a pulse repetition rate of 10 Hz for a depleted fluorine—hydrogen mixture (20% F2, 5% H2). Numerical simulation of laser operation under the conditions corresponding to the RP regime for an active medium length of about 0.5 m showed that a specific output energy of 15 J L-1 and a technical efficiency right up to 20% can be attained in a single pulse. A specific output energy ∼14 J L-1 attained under such conditions in the single-pulse mode for an active medium length of 0.37 m is found to be in good agreement with the theoretical values.

Theoretical search for optimal pump parameters for observing spontaneous radiation amplification on the λ=41.8-nm transition of Xe IX in plasma

Based on a collisional-radiative model, an atomic-kinetic calculation of the gains on the 41.8-nm transitions of Pd-like xenon was performed for the plasma produced due to the interaction of a femtosecond laser pulse with gaseous xenon. The gains g(z,τ) averaged over the spatial and temporal coordinates were compared with the known gains which had been measured experimentally in Xe8+. The amplification was shown to occur under the conditions of ionisation of the working ions, and the time of output radiation saturation depends on the time of Xe8+ transformation to higher-ionised ions. Our theoretical investigation enables determining the optimal pump parameters, at which the product of the gain g by the active medium length L is about 20, which exceeds the experimental gL value.

A continuous-wave DF chemical laser on an ethylene-based fuel composition

The consequences of replacing the primary fuel, hydrogen, as a part of the conventional F2 — H2 — He DF-laser fuel composition by ethylene are studied experimentally. During comparative tests of the laser with different primary fuels, the completeness of combustion of the fuel mixtures is assessed and their optimal chemical compositions, at which the energy and spectral characteristics of laser radiation are measured, are determined. It is shown that, when C2H4 is used instead of H2, an increase in the specific laser energy yield of 37 % without a change in the active-medium length is ensured and radiation within the range of 3.75 — 4.18 μm is generated.

Formation of a narrow beam from an excimer laser pumped by gamma rays

A laser pumped by a travelling gamma-radiation wave and consisting of a cylindrical part forming spontaneous superradiation and a conical amplifier is considered. The energy parameters of an excimer conical KrF amplifier are investigated. The factors influencing the divergence of induced radiation at the output of the conical amplifier are analysed for various durations of a pump pulse. It is shown that the divergence of radiation emitted by the laser with an active medium length of 10 m may be as high as 10-4 rad. The scheme of laser-beam focusing on the target for the purposes of laser-induced fusion is considered.