Measurement of temporal behavior of electron density in adischarge-pumped ArF excimer laser

Time-resolved number densities of electrons in a discharge-pumped ArF excimer laser are measured by an interferometric method. The peak electron density is 6.7×10¹⁵ cm^-3 at a total gas pressure of 2.5 atom, a gas mixture ratio of F₂-Ar-He=0.2-10.0-89.8, and a charging voltage of 24 kV for a 68-nF storage capacitor bank. The dependences of the electron density and laser output power on the Ar and F₂ fractions in Ar-F₂-He mixture and on the Ne-He mixing ratio in Ar-F₂ -He-Ne mixture are investigated, and the effects of Ar-F₂ -He-Ne mixing ratio on the ArF laser discharge are discussed. The experimental data of the peak electron density are also compared with the results of a computer simulation. A good agreement between them was obtained by considering the fact that the actual discharge volume occupied only part of the electrode width     

Density measurements of excited components in a longitudinaldischarge excimer laser

Time-dependent particle number densities of the excited components (Xe^+*, He^*) in a longitudinal-discharge XeCl excimer laser have been measured by laser absorption probing with a CW dye laser. The densities are compared with those in transversal-discharge XeCl excimer lasers. The formation dynamics of the XeCl excimer molecules, excited atoms, and excited ions are discussed. The dependence of the particle number densities of the Xe^+* ions on the buffer gas pressure, the Xe gas pressure, and the HCl gas pressure is investigated     

Theoretical high-efficiency extraction study of a short-pulseelectron-beam-pumped ArF laser amplifier with atmospheric pressureAr-rich mixtures

The single-pass (50 cm) amplifier performance of an atmospheric-pressure ArF laser pumped by a 65-ns full-width-at-half-maximum short-pulse electron beam was investigated theoretically for a wide range of excitation rates (0.1-2.0 MW/cm³ ). Atmospheric mixtures of Ne, Ar, and F₂ (three mixtures of Ar=40%, 70%, and Ne-free) were studied. A kinetic numerical model of the ArF amplifier with a Ne buffer system was constructed. A one-dimensional propagation treatment considered the gain depletion and saturation absorption spatially and temporally along the optical axis. In this model the rate constants for electron quenching of ArF* of 1.6×10^-7, 1.9×10^-7, and 2.4×10 ^-7 cm³/s were used for Ar concentration of 40, 70 percent, and Ar/F₂ mixture, respectively     

Formation dynamics of excited components in discharge XeCl laser plasma from the data of dye laser absorption probing

The absorption spectra in the 335-610 nm spectral range and the time dependences of the concentrations of Xe^*, He^*, Ne^*, Ar^*, Xe+*, Cl-, and XeCl* were measured by the pulse dye laser absorption (gain) probing of the active medium of a XeCl discharge laser for different buffer gas mixtures. The formation dynamics of excited atoms, ions, and excimer molecules is discussed. It is shown that at the initial stage of discharge the dominant process in the formation of XeCl* molecules is the "harpooning" reaction, whereas at the following stages the ion-ion recombination gains predominance. The rate constants of the ionic XeCl* formation reaction are determined for He, Ne, and Ar buffer gases.     

Efficiency characterization of vacuum ultraviolet molecularfluorine (F2) laser (157 nm) excited by an intense electricdischarge

Detailed experimental results of a discharge-excited high-pressure F₂ laser are compared with a model prediction. Special emphasis is placed on the output performance of the discharge-pumped F ₂ laser at extremely high excitation rates (10~35 MW/cm³ ) by using high-pressure laser mixtures up to 8 atm. The kinetics model predicts fractional contributions of excited F₂ formation channels, relaxation channels, and absorption channels together with the formation and extraction efficiencies at the experimental conditions. Although the only experimental quantity compared with the model prediction is laser output energy, it is enough to obtain a better understanding of major F₂ laser kinetics and key issues for improving the efficiency     

Plasma chemistry of the closed-cycle 1 kHz transversely excitedatmospheric CO2 laser with an efficient catalytic CO2 regenerator

A high-power closed-cycle 1 kHz transversely excited atmospheric (TEA) CO₂ laser with an efficient catalytic CO₂ regenerator was used to investigate the variations of the average laser output power and the concentrations of the CO₂, CO, and O₂ molecules in the laser gas mixture with the operational performance of the CO₂ regenerator. It was experimentally shown that for the laser gas mixture of CO₂-N₂-He=15-15-70% and the output coupler reflectivity of 70%, η of 0.1 was required to maintain the laser output power greater than 90% of the initial laser output power of 570 W at an input energy density and a clearing ratio of 150 J/L and 3.0, respectively     

1.27μm atomic argon laser parameters in fission-fragment excitedHe/Ar and He/Ne/Ar gas mixtures

The authors examine the power efficiency of the fission-fragment-excited atomic argon laser operating on the 1.27-μm (3d'[3/2]₁-4'_p[3/2]₁) argon transition as a function of pump power, gas mixture, and pressure. The maximum measured power efficiency was 1.1±0.3% for a gas pressure of 1300 torr and a He/Ar ratio of 99.88/0.12. Neon addition to the He/Ar gas mixture increased both the energy deposited in the gas and the energy output without decreasing efficiency for a neon gas fraction of less than 0.5. Small-signal gain and saturation intensity are between 0.15-0.27%/cm and 25-200 W/cm² for pump rates of 7.5-30 W/cm ³ in He/Ar and He/Ne/Ar gas mixtures. The laser threshold as a function of total pressure and argon concentration is presented     

Frequency stabilization of laser diodes using 1.51-1.55 μmabsorption lines of 12C2H2 and 13C2

Frequency stabilization of a 1.55 μm DFB laser diode is demonstrated using vibrational-rotational absorption of ¹²C ₂H₂ and ¹³C₂H₂ molecules (named VRAM). Frequency stability within 2 MHz peak to peak fluctuation can be achieved in the wavelength region of 1.51-1.55 μm. Frequency-stabilized DFB laser compact modules have been constructed. Frequency stabilities are evaluated by measuring the beat spectrum of the two lasers. In addition, the temperature and pressure dependences of the acetylene absorption lines are characterized     

High-power narrow-band operation and Raman frequency conversion ofan electron-beam pumped krypton excimer laser

A Kr excimer laser pumped by a relativistic electron beam has generated high-power output by using a cavity composed of a Si mirror and M_gF₂ mirror. The threshold gas pressure for laser oscillation is 10 atm, and the maximum output power achieved so far is 6.6 MW at 15 atm. The maximum power is limited by the surface damages on the mirrors. This laser output, oscillating at 145.7 nm, has a spectral width of 0.8 nm (FWHM). Efficient spectral narrowing down to 0.1 nm has been achieved with a 32° apex angle MgF₂ prism inserted in the cavity giving 3.5 MW peak power at 15 atm of Kr gas pressure. Wavelength conversion by stimulated Raman scattering in high-pressure H₂ has been demonstrated for efficient extension of the laser wavelength     

Subnanosecond multi-gigawatt CO2 laser

A semiconductor switching technique has been utilized to produce 30-300 ps variable duration CO₂ laser pulses of 0.5-MW peak power. Eight passes through a 1.2-m long, UV-preionized, 3-atm TE CO₂ amplifier raise the output laser peak power to the 10¹⁰ W level. Sampling the amplifier gain in linear and saturated regimes using CO₂ laser radiation ranging from CW to 30 ps pulse length permits comparison with computer modeling of picosecond CO₂ pulse amplification. The potential for further peak power scaling of picosecond molecular lasers is discussed     

Scaling characteristics of the XeF (C→A)excimer laser

The scaling characteristics and medium properties of an injection-controlled XeF(C→A) laser pumped by a 10-ns-high current density electron beam have been investigated. A five-component laser gas mixture, consisting of F₂, NF₃ , Xe, Kr, and Ar was optimized for the scaled laser conditions, resulting in 0.8-J output pulses at 486.8 nm, corresponding to an energy density of small-signal-gain measurements combined with kinetic modeling permitted the characteristics of the dependence of net gain on the electron-beam energy deposition and gas mixture composition, resulting in an improved understanding of XeF(C→A) laser operation     

Average-power scaling of self-heated Sr+ afterglowrecombination lasers

The performance of a large-bore (25-mm) self-heated Sr⁺ (430.5-nm) recombination laser with longitudinal excitation is discussed in relation to the prospects for scaling average output power to the 5-10-W regime. Average-power scaling is found to be limited in large-bore laser tubes by slow interpulse thermal relaxation in the laser gas mixture with strong radial gradients in species' densities and temperatures at only modest pulse repetition frequencies, leading to premature termination of the population inversion on the tube axis. Proposals for circumventing these limitations in order to permit generation of multiwatt average laser output power at 430.5 nm from Sr ⁺ are discussed     

Optical absorption and fluorescence studies in high pressure cesium-xenon mixtures

The pressure and temperature dependent absorption and fluorescence spectra of the cesium-xenon (CsXe) molecule have been examined. In contrast to previous investigations of the alkali-rare gas molecules, cesium atomic states that have weakly allowed optical transitions have been studied and have been shown to form excimer levels that are attractive for application as potential dissociation lasers. In particular, the (Cs[7^{2}S]Xe)* excimer appears promising as a source of high-energy laser radiation due to 1) its large dissociation energy (0.132 eV), 2) its stimulated emission cross section ofsimeq10^{-17}cm², and 3) its small population threshold inversion densities (simeq10^{13}cm^-3).     

Generation of extreme ultraviolet radiation at 79 nm by sum frequency mixing

High brightness tunable coherent extreme ultraviolet (XUV) radiation at 79 nm with a peak power of ∼200 mW has been generated in H2gas by sum frequency mixing of two quanta from a high spectral brightness ArF* (193 nm) source with one quantum from a tunable dye laser (∼436 nm). Spectroscopic application of this radiation has been demonstrated by observation of a broad (∼160 cm^-1) autoionizing structure in Ar and narrow (∼2 cm^-1) autoionizing features in D2. An analysis is given which identifies the dominant molecular states involved in the nonlinear susceptibility of the medium (H2). The frequency independent tuning behavior of the 79 nm output power observed over ∼300 cm^-1is related to the molecular structure and response of the nonlinear medium in the intense optical field.     

A CW CO2 laser with DC-discharge preionization

The application of the plasma-injection technique (involving DC-discharge preionization) to a CW CO₂ laser operating with recirculated gas is described. Measured characteristics of the discharges, the gain, and the output power are presented. An output of 110 W was obtained with a specific efficiency of 1.0 J/l^-1 of flowed gas at a pressure of 10 kPa. A simplified model to calculate a characteristic length of the main discharge, which is useful for design purposes, is developed. This type of laser may be scaled simply to higher output powers, requires a gas mixture with only 20% He, is compact and robust, and yet is simple in its electrical and mechanical requirements     

Nd:Y2O3透明陶瓷4F3/2-4I11/2跃迁光谱及高效激光输出

报道了采用真空烧结法结合热等静压技术制备的Nd:Y₂O₃透明陶瓷的荧光光谱特性及相关激光输出。通过与Nd:YAG透明陶瓷的荧光光谱对比,表明Nd:Y₂O₃透明陶瓷的4F_3/2-4I_11/2跃迁光谱存在着多个增益相当的谱线,这更有利于实现同时双波长段激光振荡;不同斯塔克子跃迁光谱的离散特性有利于通过腔镜镀膜控制不同波长损耗,获得丰富的1.0~1.1 μm波段激光。利用简单的平平两镜腔结构完成进一步的实验,通过选择的输出镜片镀膜获得了输出功率3.62 W、转换效率40.4%的1074.6 nm和1078.8 nm的双波长输出和输出功率1.7 W、转换效率19.4%的1130.3 nm波长输出。     

Simultaneous emission of the HF and N2 lines from aplasma cathode TEA laser

Simultaneous laser action from HF and N₂ is obtained, from a plasma cathode TEA laser, for the first time. The sliding discharge along the surface of a dielectric is used as a plasma cathode, for the main volumetric discharge. The laser operates at atmospheric pressure, with a gas mixture of SF₆:C₃H₈:N₂:He. For a typical flow rate ratio of 0.27:0.024:0.2:19.8 1 min^-1, it produces simultaneously 160 mJ HF and 0.6 mJ N₂ laser outputs at 0.43% and 1.4×10^-3% efficiencies respectively, at the moderate charging voltage of 28.5 kV. These output characteristics are obtained from a small active discharge volume and length of 10⁶ cm³ and 38 cm respectively. These values extend the performance, recently reported in the literature, of a sliding discharge HF/N₂ laser with corresponding simultaneous energy outputs of 12 mJ HF and 1.1 mJ N₂, to a higher energy output level, thus making the device suitable for a broader range of applications. This novel dual wavelength HF/N₂ laser system presented, can be particularly convenient for medical experiments, where the IR beam can be used for tissue ablation, while the UV beam can be used as the excitation source for fluorescence spectroscopic measurements, for the evaluation of the ablation process. Details are presented on the dependence of the laser performance parameters, such as output energy, discharge voltage and current and structure of the laser output pulses on the mixture composition and the circuit parameters     

A parametric study of the output of the optically pumped continuouswave CF4 laser

A parametric study of laser output versus CF₄ pressure and temperature was performed and correlated with a model for the gain in the system, which includes the relevant relaxation processes. Lasing in CF₄ was observed at temperatures below 170 K. Cooling the CF₄ gas, the output power of the laser increased from 3 mW at 142 K to 5 mW at 113 K, when 4% of the radiation was coupled out. Chopping the pump, the 16-μm signal consisted of a peak decaying in approximately 2 ms, superimposed on a CW background. This decay is caused by the slow relaxation in the CF₄ laser, resulting in filling of the lower laser level. For the CW CF₄ laser, vibrational relaxation from the laser lower level is even slower than diffusion to the cold cell walls. To increase the relaxation rate, HD was added. In this molecule, the J=1→3 rotational transition at 447 cm^-1 is almost resonant with the ν₂ vibration in CF₄. Maximum CW output was increased by 25% in a mixture containing 10% HD. At the same time, the lasing pressure range was extended     

High peak power and high repetition rate characteristics in acurrent-pulsed Q-switched CO2 laser with a mechanical shutter

An electro-mechanical Q-switched (EMQ) CO₂ laser is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current. Such a system can produce pulses with high peak powers (>10 kW) and high repetition rates (>1 kpps). In order to analyze the output characteristics, the peak power and the duration of the output pulses have been measured experimentally in detail over a wide range of Q-switching times up to 250 ns. For a low-pressure (<4 kPa) CO₂ gas system, the standard rate equations adequately explain the experimental results by introducing a new switching function for the form of the cavity loss for the mechanical chopper. In an EMQ-laser with a high initial inversion density (4.5·10¹⁵ /cm³ at 150 mA peak current), multiple peak pulses or pulse distortion have been observed. This is due to the plasma screening effect induced by the burning of the metal shutter blades placed inside the cavity. It is found that tungsten metal shutter blades can be used up to a power density of 259 MW/cm² for a focused beam without this effect occurring, The solutions of the rate equations show that optimum coupling can prevent the plasma screening effect even for a Q-switching time longer than the pulse buildup time. The EMQ-laser configured for optimum coupling has produced a peak output power of 30 kW for the 9P20 transition branch in the CO₂ spectrum without any pulse distortion. This value has been obtained even though the discharge length was only 1.3 meters     

High-power operation of an argon excimer laser with a MgF2 and SiC cavity

An intense coherent light pulse whose energy, height and width (FWHM) were 80 mJ, 16 MW, and 5 ns, respectively, was obtained as 126 nm from an argon excimer laser. A superpoished SiC mirror was used in combination with a MgF₂ output coupler for an electron-beam-pumped argon excimer laser. The SiC mirror had a reflectivity at 126 nm as high as 47% and was highly damage resistant. Laser mirror materials for high-power short-wavelength lasers are discussed. Surface damage on the MgF₂ output mirror could not be avoided; this prevented stable operation of the argon excimer laser. In order to obtain such high power from the argon excimer laser, it is necessary to construct the resonator without a MgF₂ coupler. An unstable resonator is considered as the best candidate for the stable operation of the argon excimer laser