Design and performance of a transverse discharge, UV-preionized mercury-bromide laser

The design, construction, and operating characteristics of a pulsed, transverse discharge-pumped HgBr laser, capable of operation at pulse repetition frequencies as high as 100 Hz, are presented. Having an active length of 53 cm, this laser system is preionized by two sets of spark arrays and average single pulse energies of 55 mJ are produced from Ne/N₂/HgBr₂ (natural abundance) vapor mixtures, with an output coupling of 50% and 17 J of energy stored in the pulse forming network. Based on measurements of the laser pulse energy for several values of cavity output coupling, the small signal gain coefficient and saturation intensity for the laser were determined to be 4.7% cm^–1 and 260 kW cm^–2, respectively. The single pass gain-to-loss ratio is 12.4.     

Study of Direct Amplification of Ultrashort Light Pulses in a Laser Amplifier with a View to Obtaining High Radiation Contrast

An amplification scheme for ultrashort laser pulses of high radiation contrast was used to perform experiments on ablation pressure symmetrization using a prepulse upon acceleration of thin foils. It is shown that the spontaneous radiation of the regenerative amplifier restricts the energy contrast in the amplification of chirped pulses at a level of 10^-4–10^-3. The possibility of direct amplification of a short pulse with a view to increasing the energy contrast ratio was considered. Experiments were performed on the PICO laser facility to demonstrate that a 10-ps pulse amplification achieved an intensity 100 GW/cm², a gain factor of 1.2, and an inversion dumping factor >30%.     

Mathematical modeling of hybrid CO2 laser

A Teller–Landau six-temperature model describing the dynamic emission of single-mode TEA CO₂ laser has been adapted. This model has been also used to describe the mechanism of obtaining relatively high-power output pulses from hybrid TE-TEA or CW-TEA CO₂ laser consisting of high- and low-pressure sections. The suggested mathematical model allows to investigate the mechanism which limits the TEA oscillation to single longitudinal mode (SLM) due to the narrow gain bandwidth of low-pressure section, and also to study the effect of the laser input parameters on the smooth output laser pulse parameters. In addition, numerical solutions of non-linear rate equation system of the suggested model are quantitatively discussed. The solutions describe the radiation field intensity, the population inversion, and the energy transfer processes. The calculated values of maximum peak power, total energy in pulse, pulse width, etc. are in a very good agreement with the observed experimental values.     

Method of Measuring Electron Density in Pulse Metal Vapor Lasers Using Microwave Technique

A method of measuring the electron density kinetics in the plasma of pulse-periodic metal vapor and metal compound vapor lasers using microwave technique within the wavelength region of 78–142 GHz is realized. The method is based on the dependence of the absorption efficiency of a probe microwave radiation on the frequency of electron collisions and also on the dependence of the cut-off or the critical density on the frequency of the probe radiation. In a quasioptical translucence scheme the plasma of a copper bromide vapor laser is studied within an interpulse time interval in a gas-discharge tube of 20 mm in inner diameter and with a 300 mm long active heated region excited by a capacitor discharge with a pulse repetition rate of 10 kHz. It is shown that under operational conditions typical for metal vapor lasers the absorption of the probe radiation within the interpulse intervals is totally determined by Coulomb electron–ion collisions. This allows one to measure both the density kinetics and the electron temperature. Probable measurement errors are analyzed and it is shown that they result in a systematic error for the absolute value of the electron density but have a slight influence on the density kinetics.     

Effect of the amplitude of excitation pulses on the shape of photon-echo signals in two-level systems

It is theoretically established that multiple photon-echo signals reflect the oscillatory structure of the primary echo signal, which arises under the conditions of collinear excitation of two-level active centers by laser pulses having the same width but different amplitudes. It is shown that the oscillatory structure of the primary photon echo exists within the intervals (?t ₁, t ₁) and (?2t ₁, 2t ₁), where t ₁ is the pulse width. It is found that, when the pulse width is of the same order of magnitude as the delay between the pulses and the amplitudes of the excitation pulses obey certain relations, the oscillatory structure of the primary photon-echo signal becomes asymmetric. In the mode of quadratic detection of the primary photon-echo signal, the asymmetric oscillatory structure of the primary echo manifests itself as a manifold of isolated signals (multiple photon echoes), with the time intervals between these signals being equal to the pulse width.     

224 nm segmented hollow-cathode silver ion laser

The segmented hollow-cathode discharge arrangement is used the first time to excite the 224 nm Ag II laser transition. Quasi-continuous output power of 45 mW is obtained during the 300 s current pulses at optimal discharge conditions (10 hPa of He+4% Ar buffer gas) for discharge current of 3 A. No power saturation is observed up to this current value. An average output power of 0.75 mW is reached using pulse repetition frequency of 190 Hz. The longitudinal mode structure of the TEM₀₀ transversal mode is measured by means of a scanning confocal Fabry–Perot interferometer. Two-mode operation is found to be dominant at high current values. Attempts and suggestions are made to prolong the lifetime of the laser tube. PACS 42.55.Lt; 42.60.Lh; 52.80.-s     

Numerical calculations of intracavity dye Q-switched ruby laser

A mathematical model describing the dynamic emission of the Q-switched ruby laser has been adapted. The suggested model allows the investigation of the effects of a dye cell on the mode characteristics of the ruby laser and, moreover, the study of the effect of the laser input parameters on the output laser pulse. This model simulates the nonlinear effects of dye pulse modulation on the laser emission.In addition, a numerical solution of a nonlinear rate equation system of the adapted model is discussed. The solution estimates the density of the emitted radiation, population inversion and energy transfer processes of the ruby laser rod and dye cell for different emission regimes (one pulse regime, free running pulses, repetition periodic pulses). The estimated results of the laser output pulse characteristics are in a good agreement with the other calculated and experimental results.     

Modeling the plasma kinetics mechanisms of CuBr laser with neon–hydrogen additives

A mathematical model describing the discharge kinetics and lasing characteristics of copper bromide vapor laser with neon and hydrogen additives has been developed. The suggested model is based on a “zero-dimensional” model and offers simple mechanisms to explain discharge kinetics mechanisms, different physical processes and hydrogen additive effects on the copper bromide vapor laser.The model estimates the temporal evolution of discharge voltage and current, population densities, laser beam density, electron temperature and radial distribution of pressure and buffer gas temperature. The suggested mechanism assumes that the electron detachment from negative hydrogen ions does not contribute to the copper ionization process.Numerical solutions of a nonlinear rate equation system predict the generation of nanosecond pulses. The calculated maximum values of discharge voltage, current, average output laser power, electron temperature, etc. are in good agreement with other reported calculated and experimental data.     

毛细管放电软X光激光预-主脉冲延时电路

 以预-主脉冲方式工作的激励软X光激光毛细管放电装置，其预-主脉冲先后触发时间间隔的控制，直接影响了泵浦能量转换为X射线激光能量的效率。运用光电耦合及脉冲变压器隔离等技术，将集成芯片构成的延时电路用于快速高压放电装置中。实验结果表明，预-主脉冲协调工作，延时触发2～50μs，为产生软X光激光提供了条件。     

ArF-excimer-laser annealing of 3C–SiC films—diode characteristics and numerical simulation

We fabricated Schottky barrier diodes using 3C–SiC films deposited on Si(1 1 1) by lamp-assisted thermal chemical vapor deposition and annealed with an ArF excimer laser. Improvement in both the reverse current and the ideality factor was obtained with 1–3 pulses with energy densities of 1.4–1.6 J/cm² per pulse. We solved a heat equation numerically assuming a transient liquid phase of SiC. The calculated threshold energy density for melting the surface was 0.9 J/cm². The thermal effects of Si substrate on SiC film were also discussed. The experimental optimum condition was consistent the numerical simulation.     

铜蒸气激光脉冲终止机理的数值研究

建立了一个反映纵向脉冲放电激励铜蒸气激光动力学过程的自洽物理模型并进行了数值求解. 根据模拟结果深入分析了铜蒸气激光脉冲的终止机理，表明受激辐射跃迁、激光下能级的电子碰撞激发和激光上能级的铜原子经电子碰撞被抽运到更高激发能级这三个过程，是导致激光脉冲终止的重要因素. 关键词： 铜蒸气激光 激光脉冲终止机制 电子碰撞 更高激发能级     

New Series of Dyes for Flashlamp-Excited Lasers

A new series of laser compounds which are derivatives of 7H-benzo[4, 5]imidazo[1, 2-c]chromeno[3, 2–e]pyrimidine have been developed and their working characteristics are presented. It is shown that the new compounds fluoresce with a high quantum yield (0.83–0.97) in the green spectral region; their methanol solutions gave effective lasing upon flashlamp excitation with a pulse duration of about 2.0 sec at the level 0.5. In a nonselective cavity they emit laser radiation in the range 540–570 nm. The influence of the molecular structure of the investigated dyes on their fluorescence and laser characteristics is discussed.     

Pulsed power modeling of very-large-aperture,transverse-discharge CO2 lasers

Discharge behavior of large-aperture (10–70 cm) CO₂ lasers is computed using a coupled particle kinetics-equivalent circuit model. Pulsed power systems that produce a single excitation pulse are only able to satisfy the preionization, ignition, and impedance matching conditions for interelectrode gaps 40–50 cm. Double-pulse systems are required for larger gaps, not only to optimize electrical efficiency, but to avoid oscillatory behavior which can lead to arc formation during the second cycle.     

Scaling and performance of CO2 lasers at supra-atmospheric pressure

The performance of a compact uv photo-preionized TE laser is studied in the pressure range 1–5 bar. As the pressure is increased, the laser pulse shape is little altered, but both the peak power and the total output pulse energy increase significantly with pressure, even for constant input electrical energy. For various gas mixtures and excitation source capacitors the measurements suggest approximate output energy scaling with the product of the source charge per unit electrode area [C.m^–2] and the molecular partial pressure [CO₂+N₂+CO]. This is explained in terms of the pressure-dependent discharge impedance. An input-energy-related discharge instability limits the optimum laser pressure to 1.5–2.5 bar, and we show that, at constant input energy, the instability boundary depends on the molecular partial pressure alone. The pre-ionization photo-electron yield varies negligibly with pressure, but the discharge tolerance to added oxygen decreases asp ^–3 top ^–4, dependent on gas mixture. Nevertheless sealed operation for >10⁵ shots has been obtained with a 5% CO₂5% CO3% N₂2% H₂85% He gas mixture at a total pressure of 5 bar.     

Output characteristics of a cataphoresis He–Sr recombination laser

A cataphoresis discharge tube of 7 mm inner diameter and 38 cm active length was designed and made for the He–Sr⁺ laser. The cataphoretic input of uniform distribution of strontium vapor concentrations along the active region was realized by the cataphoresis effect and the slow flowing (0.5 nl/h) of helium buffer gas. The strontium ionic recombination laser at 430.5 nm and the R–M transition laser at 1.03 μm were obtained with the modified Blumlein circuit by high-frequency longitudinal pulsed discharge. The laser components are concentrated on the 430.5 nm wavelength. Dependences of working parameters such as the pulse frequency, the supply voltage, and the helium pressure on laser output characteristics were measured and discussed. The maximum laser output power of 819 mW and specific power of 56 mW/cm³ were obtained, respectively.     

Numerical solution of Boltzmann tranport equation for TEA CO2 laser having nitrogen-lean gas mixtures to predict laser characteristics and gas lifetime

Selective laser isotope separation by TEA CO₂ laser often needs short tail-free pulses. Using laser mixtures having very little nitrogen almost tail free laser pulses can be generated. The laser pulse characteristics and its gas lifetime is an important issue for long-term laser operation. Boltzmann transport equation is therefore solved numerically for TEA CO₂ laser gas mixtures having very little nitrogen to predict electron energy distribution function (EEDF). The distribution function is used to calculate various excitation and dissociation rate of CO₂ to predict laser pulse characteristics and laser gas lifetime, respectively.Laser rate equations have been solved with the calculated excitation rates for numerically evaluated discharge current and voltage profiles to calculate laser pulse shape. The calculated laser pulse shape and duration are in good agreement with the measured laser characteristics. The gas lifetime is estimated by integrating the equation governing the dissociation of CO₂. An experimental study of gas lifetime was carried out using quadrapole mass analyzer for such mixtures to estimate the O₂ being produced due to dissociation of CO₂ in the pulse discharge. The theoretically calculated O₂ concentration in the laser gas mixture matches with experimentally observed value. In the present TEA CO₂ laser system, for stable discharge the O₂ concentration should be below 0.2%.     

Actively mode-locked dual-wavelength fiber laser with close wavelength spacing using a fiber Bragg grating

A simple actively mode-locked fiber ring laser is proposed and successfully demonstrated to generate dual-wavelength picosecond pulses with close wavelength spacing using one Bragg grating in standard single-mode fiber. The proposed laser can be made to operate in stable dual-wavelength at room temperature, due to the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled. Generation of stable dual-wavelength pulses with a pulsewidth of 212–234 ps and a tunable wavelength separation from 0.2 to 0.44 nm at a pulse rate of 1.05 GHz was demonstrated.     

磁脉冲压缩器在卤化铜激光器上的应用

在卤化铜激光器脉冲放电电源系统中，为减轻闸流管的工作负担并同时保证电路的快放电激励，采用了单级磁脉冲压缩器.分析了磁脉冲压缩器的工作机理，介绍了所采用磁脉冲压缩器的设计考虑及参数选用. 关键词： 磁脉冲压缩器 闸流管 CuBr激光器     

The strontium-vapor laser pumping efficiency under running-wave excitation

The effect of the design features of the gas-discharge tube on the processes proceeding in the discharge circuit of a metal-vapor laser has been investigated. The position of electrodes in the gas-discharge tube has been found to significantly affect the processes at work in the discharge circuit and the energy characteristics of the laser. For instance, gas-discharge tubes with electrodes placed in the hot region of the discharge channel are typified by high metastable-population rates at the leading edge of the excitation pulse, whereas with electrodes positioned in cold buffer regions, the leading edge of the voltage pulse across the resistive component of the tube impedance is seen to peak. Conditions for running-wave generation in the active media of lasers on self-terminated transitions of metal atoms and the running-wave use efficiency for laser pumping are discussed, considering a strontium-vapor laser as an illustration. It is shown that the running wave is generated as the result of the breakdown in the anode end of the gas-discharge tube and is maintained by the energy stored in the capacitive component of the impedance of the gas-discharge tube. The lasing pulse duration under running-wave excitation corresponds to the time it takes an ionization wave to propagate from the anode to the cathode of the gas-discharge tube, with pumping efficiency being ~6–8% for a strontium-vapor laser. The average lasing power varies within 10–15% depending on whether the totally reflecting cavity mirror is placed near the anode or the cathode of the tube. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 79–87, December, 2008.     

Alternate oscillations of self-terminating and recombination lasers in univalent calcium and strontium ions

The univalent calcium and strontium ions have been confirmed as ideal lasing substances both for self-terminating laser and recombination laser by theoretically analysing their energy level structures and lasing mechanisms. With the optimization of the excitation circuit and the improvement of the laser cavity as well as the laser discharge tube, thealternate laser oscillatlons of the two laser mechanisms were suceessfully realized by longitudinal pulsed discharge in mixture vapours of helium and univalent ions of calcium or strontium, respectively. The dependences of laser performance on working parameters, together with the characteristics of the photoelectric pulse waveforms were elementally studied and analysed.