Energy Characteristics Of Lasers Research Articles

Window Fabrication of Zinc Selenide Nanostructures: Synthesis and Properties

Zinc selenide (ZnSe) nanostructure’s optical and structural characteristics were investigated in this study. Pulse laser deposition of thin films on glass substrates was achieved using an Nd:YAG laser (wavelength 1064 nm) at different laser powers (100, 200, 300, 400 and 500 mJ) with fixed pulses 100 pulses, repetition rate 6 Hz and distance 10 cm between laser and the substrate with a thickness of films 200 nm. An atomic force microscope (AFM) and X-ray diffraction method were used to research the impact of altering the laser intensity on the structural characteristics. A branched (100) polycrystalline type and a plane (111) and branched (100) polycrystalline type are prevalent (002). In addition, AFM measurements further revealed that the smallest granular size achieved at high laser power was 48.40 nm at 100 mJ. The findings showed that it is possible to construct nanostructures with medium grain sizes of alumina (72.99 nm). The study of the relationship between laser energy and nanostructure optical characteristics was explored and it was discovered that the transitions had a specific range of 2.83–3.10 eV.

Bragg order effect on ultrashort pulse generation by distributed feedback dye lasers under subnanosecond excitation: Numerical study

A comparative numerical study of the 1st- and 2nd-order distributed feedback (DFB) dye lasers pumped with 0.5 ns, 532 nm laser pulses is performed. A dynamic model of the gain-coupled DFB dye laser based on a coupled-wave theory and taking into account Bragg diffraction order is used. Due to the periodical distribution of the pump field and stimulated emission intensities along the excited dye volume, the rate equations of the population densities are turned into the equations of the Fourier coefficients. To simulate the DFB lasing, coupled-wave equations of optical fields are used. Effect of the pumping intensity on the temporal and energy characteristics of DFB dye lasers is studied depending on the dye concentration and the length of the excited dye volume. Influence of the lasing seed type (constant or noise-like) on the simulation results is also analyzed. A special emphasis is on the characteristics of single ultrashort (US) picosecond pulses generated by the relaxation oscillations mechanism. The results obtained indicate that for both types of DFB dye lasers the temporal course of the output intensity is governed by the pumping strength. Depending on the excess above the threshold (high or low), either US pulse trains or single US pulses are generated. The influence of the active medium parameters on their characteristics has been studied in detail. In addition, it was established that unlike the 1st-order DFB lasing, where the simulation results are independent of the seed type and smooth US pulses are always obtained, for the 2nd-order regime, to get smooth rather than structural single US pulses, a noise-like seed should be used. However, the most important finding is that the changeover from the 1st to the 2nd order leads to ∼1.1–3.2 (∼1.13–1.46) times reduction in duration, ∼1.4–3.4 (∼1.4–3.0)-fold increase in energy and ∼2.8–9.7 (∼1.5–4.8)-fold growth in peak power of single US pulses for the case of constant (noise-like) lasing seed. Hence, the use of the 2nd-order regime represents a simple and convenient way to improve the energy characteristics of single US pulses of DFB dye lasers generated by the relaxation oscillations mechanism.

Economical generation regime of a supersonic continuous-wave chemical DF laser

We have performed experimental and computer-aided theoretical studies of the effect of the dilution degree ψ2 of a secondary fuel (deuterium) by an inert gas (helium) on the output characteristics of a supersonic cw chemical DF laser with a flat nozzle array, constructed in accordance with the nozzle – nozzle reagent mixing scheme. It is shown that an increase in the dilution degree in the range of 0 ⩽ ψ2 ⩽ 20 leads to a monotonous increase in the lasing zone length (a decrease in the radiation load on the resonator mirrors) and a drop in the laser specific energy output. With an increase in the optical path length (a decrease in the threshold gain), the sensitivity of the laser energy characteristics to the dilution degree decreases. Consequently, for a high-power DF laser (with a long nozzle array) with partial replacement of expensive deuterium with cheaper helium, a potential possibility for the implementation of an economical generation regime with acceptable specific energy output is achieved. The conditions for the implementation of this regime are identified.

Upgrade the Evaluation of the Contribution of the Active Element Cross Section Geometry to the He-Ne Laser Energy Characteristics

The models for estimating the contribution of the cross section geometry to the active medium gain of the He-Ne laser have been considered in this work. Expanding the range of studied cross sections it has been found that these models were not analytical and demand the approximate calculations. Modern methods and computing tools should clarify the results of 1960–1970 and it will bring to more accurate results. Some the experimental verification was carried out only in a rectangular cross section. Our model have to complicate taking into account the field intensity distribution in the resonator.

Gas laser energy characteristics with different active element cross section geometry

The models for estimating the contribution of the cross section geometry to the active medium gain of the gas laser have been considered. A testing of our method for the solving of the Helmholtz equation with different boundary conditions have been fulfilled. The next step is the complication of the model taking into account the distribution of the field intensity in the resonator.

КОГЕРЕНТНОЕ РАСПРОСТРАНЕНИЕ ЛАЗЕРНЫХ ПУЧКОВ В МАЛОРАЗМЕРНОЙ СИСТЕМЕ СЛАБОСВЯЗАННЫХ СВЕТОВОДОВ

The successful development of fiber-optic technologies in recent decades has stimulated research on the replacement of components of solid-state laser systems with fiber components, which can drastically change the attractiveness of the corresponding applied developments. Yielding on the energy characteristics of solid-state systems, fiber lasers and nonlinear optical devices have high efficiency of conversion of pump energy to radiation energy associated with waveguide geometry, high quality of the spatial profile of the laser beam, as well as low cost, compactness, lack of alignment in work process. Note that the maximum achievable radiation power in a single fiber is limited primarily by the process of self-focusing, which leads to fiber damage. The use of a multi-core fiber (MCF), consisting of identical equidistant weakly coupled optical fibers, makes it possible to realize initially coherent propagation of laser radiation with a total power noticeably higher than it can be transmitted in a single optical fiber. However, as theoretical and experimental studies have shown, such systems have its own critical power (Balakin et al., 2016) whereby the self-focusing of the quasihomogeneous distribution of the wave field and its separation into a set of incoherent structures occurs. Therefore, we have considered a small-sized optical system of 2N identical weakly coupled optical fibers arranged in a ring (Balakin et. al., 2018). In such systems, it is possible to find stable distributions of intense wave beams, which allow coherent radiation transport over long distances. The total radiation power in the found distributions can significantly (up to 2N times) exceed the critical self-focusing power in continuous media. This manifests itself most clearly for the distribution of un ~ (-1)n with antiphase fields in neighboring waveguides, which is stable at an arbitrary wave beam power. Direct numerical simulation of a nonlinear wave equation confirms the stability of the field distributions found. The research was supported by the RAS Presidium Program «Nonlinear dynamics: fundamental problems and applications».

Influence of Peaking Capacitance on the Output Power of Capacitive-Discharge-Pumped Metal Halide Vapor Lasers

This paper presents the study of the energy characteristics of CuBr and CuCl lasers pumped by a longitudinal capacitive discharge. It is shown that with the peaking capacitor connected to the electrodes of a gas-discharge tube of capacitive-discharge-pumped metal halide vapor laser, the lasing power can significantly increase. The optimum value of peaking capacitance varies from 25% to 60% of the value of the capacitive electrodes serial connection. The introduction of HBr additive into the active volume significantly improves laser performance and requires greater peaking capacitance than operation without active additive. The most increase in the output power corresponds to small diameter tubes and amounts 50%, in tubes of large diameter an increase amounts 20%-40%. Currently, the maximum average lasing power of 15 W has been achieved for the capacitive-discharge-pumped metal vapor laser.

Resonanсe nonlinear optical properties of dye-doped liquid crystals under pulse excitation: Insight into early experiments

The results of studies of the nonlinear optical properties of dye-doped nematic (NLCs) and cholesteric liquid crystals (CLCs) under powerful laser excitation are presented. The invariability of the structure of a planar-oriented NLC as a result of the conservation of the absorption dichroism of an impurity dye under the control over the lasing threshold is shown. A method to reduce the threshold for the stimulated Raman scattering (SRS) in the isotropic phase of NLC at frequencies that overlap with the amplification band of a dissolved dye is proposed. The peculiarities of the energy characteristics of CLC lasers are studied in detail. A variation of the lasing efficiency and the nonlinear dependence of the lasing energy on the pumping are explained within a model of lasing systems with distributed feedback. The dynamics of the optical destruction of a planar texture of a dye-doped CLC at critically high levels of laser irradiation is studied.

Analytical model of a transversely diode-pumped alkali metal vapour laser

The previously presented analytical model of a transversely diode-pumped alkali metal vapour laser (A.I. Parkhomenko, A.M. Shalagin, Quantum Electronics, 2015, Vol. 45, No. 9, pp 797 – 806) is refined and expanded. Analytical formulas are derived describing the operation of a high-intensity laser at an almost arbitrary buffer gas pressure and taking into account radiation losses in the resonator. Comparison of the results of calculations of the laser energy characteristics by analytical formulas with the results of numerical calculations of other authors shows very good agreement.

On a Mechanism for Limiting the Frequency and Energy Characteristics of Lasers on Self-terminating Transitions of Metal Atoms

Electrophysical approach to estimation of conditions for efficient pumping of active medium of lasers on selfterminating transitions of metal atoms in a gas discharge tube with electrodes in cold buffer zones is used. Existence of processes that enhance the effect of the well-known mechanism of limitation of radiation frequency and energy characteristics caused by the presence of a pre-pulse electron concentration in the discharge circuit of lasers on self-terminating transitions of metal atoms is demonstrated. The mechanism of influence of these processes on frequency and energy characteristics of lasers on self-terminating transitions of metal atoms and the technical methods of neutralization of these processes are considered. It is shown that the practical efficiency of a copper vapor laser can attain ~10% under conditions of neutralization of these processes.

National Primary Standard for the Unit of Average Laser Radiation Power Get 28–2013

The improved national primary standard for the unit of average laser radiation power GET 28–2013 is described. It can be used to provide metrological support for unity of measurements of the energy characteristics of semiconductor lasers and laser diodes that have high divergences and fairly high output radiation instability.

Effect of radiation field inhomogeneity on energy characteristics of intracavity-pumped steady-state Raman lasers

The steady-state generation power of a Raman laser with Raman and laser media located inside a common cavity was calculated taking into account field inhomogeneities in the active media. Dependences of the laser and Stokes power on the cavity, active media, and pump parameters were derived and analyzed over a wide range of their values. Validity conditions for a homogeneous (averaged) field model that is widely used in the theory of laser energy characteristics were determined. It was shown that the Stokes power dependence on the reflection coefficients of the laser radiation from the active medium surfaces or an intermediate mirror can be neglected.

A stabilized copper bromide laser with computer-controlled operating modes and a mean lasing power of 20 W

A copper bromide vapor laser with a mean lasing power of 20 W and the computer-controlled pulse-periodic, pulse train, and waiting modes is described. The laser power-supply unit has a modular structure. The effect of operating parameters on the lasing characteristics is shown. The mutual influence of the power-supply units is determined. The laser design and energy characteristics are presented.

Linear energy control of laser drilling and its application in the repair of TFT-LCD bright pixels

Laser drilling is an energy dependent process in which energy consumption is linearly proportional to the thickness of the material being drilled. Thus, providing linear output power from the laser can provide considerable advantages in the repair of devices such as TFT-LCD pixels. Unfortunately, the non-linear energy characteristics of lasers require compensation to achieve linear power output. Conventional compensation schemes use laser power meters that require repeatedly switching the laser system off and on again. This study developed a software-based energy compensation method to provide optimized energy output and continuous linear laser energy. This software solution enables the measurement of laser energy in a fixed period and its manipulation using a compensation table, which eliminates the need for a laser power meter and enables the system to remain in operation during laser power calibration. The proposed method provides linear output in which the linear energy proportion (R2) reaches 0.9988 and provides a very stable power source. We applied this method to repair bright pixels in LCD panels, achieving a success rate of 86 %. In addition, the proposed method eliminates the need to remove the LCD casing from the fabrication module, thereby increasing the efficiency of production.

Continuous chemical HF laser with a modified radially expanding nozzle unit

dium. It was shown that the process of laser radiation generation involves only that part of the active medium that has fairly low values of the static pressure and temperature. Obviously, the creation of conditions for involving the entire volume of the active medium in the generation process is promising for further enhancement of HF laser energy parameters. This can be achieved, in particular, by adding an additional quantity of inert diluent to the active medium of the laser. In [2], we proposed a method for such addition. This method was realized in practice in an autonomous HF laser with a modified radially expanding nozzle unit of original design operating according to the "nozzle–injector–injector" scheme of mixing the reactants. The modified nozzle unit is equipped with a special injector for injecting a cold inert diluent at the inlet to the nozzle and thus realizing the above mixing scheme. Such injection permits separated supply of atomic fluorine and inert diluent into the nozzle, as well as two-region mixing of reactants with subsequent low-temperature flow of the oxidizing gas (mixture F+DF+He) in the supersonic parts of the nozzles. We have modified two available models of the laser under consideration. One of them is a small-size laser (the size of the outlet section of the nozzle unit is 18 × 3.9 cm) with a total mass flow of reactants m Σ 30 g ⁄ s. The other model ia a medium-size laser (the outlet section of the nozzle unit is 35 × 10 cm) with a total mass flow of reactants m Σ 140 g ⁄ s. The results of experiments with the small-size laser with a design power N = 5 kW [2, 3] have shown convincingly that the use of the new method of obtaining oxidizing gas makes it possible to enhance considerably the HF laser energy characteristics. For example, if 95% of the inert diluent (helium) is transferred from the first mixing zone (combustion chamber) to the second one (inlet part of the nozzles), then the laser power can increase by a factor of 2.5 and the specific energy of the laser can increase by a factor of 1.6 as compared to the characteristics of the base model. In the course of experiments with the medium-size HF laser (design power N 20 kW), its workability has been demonstrated. However, the energy characteristics of such a laser turned out to be lower than in the base model.

Effect of longitudinal pump inhomogeneity on the energy characteristics of steady-state raman lasers

The energy characteristics of externally pumped Raman lasers are calculated taking inhomogeneities in the active medium into account. Equations for the power and steady-state lasing threshold in these systems as function of the parameters of the cavity, pump, and Raman active medium are obtained over the entire ranges of their possible variations. The conditions for applicability of the model of averaged (uniform) fields, which is widely used in the theory of Raman lasers, are determined and interrelations among the cavity parameters favor unidirectional lasing in ring cavity Raman lasers are identified.

CuBr Laser Excited by a Capacitively Coupled Longitudinal Discharge

The paper presents the study of the CuBr laser energy characteristics using capacitively coupled discharge excitation. We have studied the effect of the addition of HBr on laser performance for gas discharge tubes of different bore diameter at various input power conditions. When adding HBr pulse and average output power as well as laser efficiency more than double increase due to the shortening of the current pulse rising time and its duration. The total maximum average lasing power of 3.7 W was obtained at 0.27% efficiency. In the paper, we also notice that when adding admixtures capacitively coupled discharge pumping is superior to traditional glow discharge pumping.

High-pressure pulsed CO2 lasers

This paper presents a large body of data allowing one to determine the energy, time, and spectral characteristics of high-pressure pulsed CO2 lasers over wide ranges of parameters.

Influence of the edge effect on the energy characteristics of a supersonic cw chemical HF laser

The energy characteristics of large-scale cw chemical lasers can be predicted on the basis of the results obtained for small-scale models (modules). This is demonstrated by an experimental investigation of the influence of the edge effect on the output power of an HF laser with a radial-expansion nozzle array of 10 × 35 cm dimensions. An approach is proposed for estimating the degree of influence of the edge effect and identifying the boundaries of the zones in the active medium subject to this influence. The results obtained are used to formulate recommendations on the geometric dimensions of a module.

Ways of increasing the specific energy characteristics of self-contained supersonic cw chemical HF lasers

An experimental investigation was made of ways of increasing the specific energy characteristics of a self-contained supersonic cw chemical HF laser with a radial-expansion nozzle array 18 cm long. Optimisation of the chemical composition of the fuel (which was a F2—D2—He—H2 mixture) improved the energy characteristics by 10–25% and made it possible to reach a specific output energy of 305 J g-1. A 1.4-fold reduction in the size of the reactant mixing zone at the entry to the cavity increased the specific power by 50% and its maximum value was 180 W cm-2. Possible further improvements in the specific energy characteristics are suggested.