The mathematical models and computational tools for design, analysis and predictions of supersonic jet and nozzle flows in the aerodynamic windows of high-power gas lasers are considered. The ...steady-state Euler equations describing strong shock waves, contact discontinuities, rarefaction waves and their interactions are solved with the finite-volume solver and space-marching method. The results of numerical simulation of steady-state supersonic flows of inviscid compressible gas in nozzles and under- and over-expanded jets are obtained and analyzed for different pressure ratios in the laser cavity and ambient atmosphere. The flowfields corresponding to the uniform velocity profile and free-vortex velocity profile in the outlet nozzle boundary are compared. Nozzle profiling tools are developed on the basis of numerical solution of a sequence of direct problems. The aerodynamic performance of the window is evaluated in terms of the simulated laser cavity pressure and plenum pressure of the free-vortex supply nozzle. The pressure support characteristic for the aerodynamic window is established by determining the ambient to cavity pressure ratio over a range of aerodynamic window supply pressures.
•Simulation of supersonic jet flows in aerodynamic windows is performed.•Results are presented for under-expanded and over-expended jets.•Aerodynamic performance is evaluated for free-vortex supply nozzle.•Study provides information for design of aerodynamic windows.
Liquid crystal (LC) device has high tunability with low power consumption and it is important not only in visible region but also in terahertz region. In this study, birefringence and absorption ...losses of hydrogen-bonded LC was estimated at 2.5 THz. Our results indicate that introduction of alkoxy chain to hydrogen-bonded LC is effective to increase birefringence in terahertz region. These results indicate that hydrogen-bonded LCs are a strong candidate for future terahertz devices because of their excellent properties in the terahertz region.
A steady-state kinetic model of argon-helium high-pressure radio frequency dielectric barrier discharge is developed using a simplified reaction rate package appropriate for pressures ranging from ...200 to 500 torr. Electron production and loss rates are analyzed as a function of pressure and Ar-He mixture, highlighting the importance of the Ar 2 * dimer for higher pressures and Ar rich mixtures. As pressure increases, the primary ionization mechanism shifts between ionization of ground state Ar to dimer ionization, which affects the steady-state reduced electric field due to the electron energy required for the two dominant ionization mechanisms. The resulting reduced electric field profile controls the metastable Ar(1s 5 ) production, which, combined with the Ar(1s 5 ) loss rates, reveals the metastable density as a function of pressure and Ar-fraction. This simplified 0-D steady-state model shows close agreement with previous time-dependent simulations using a robust reaction rate package.
Motivated by recent work in the area, we consider the behavior of solutions to a nonlinear PDE model of a two-state gas laser. We first review the derivation of the two-state gas laser model, before ...deriving a non-dimensional model given in terms of coupled nonlinear partial differential equations. We then classify the steady states of this system, in order to determine the possible long-time asymptotic solutions to this model, as well as corresponding stability results, showing that the only uniform steady state (the zero motion state) is unstable, while a linear profile in space is stable. We then provide numerical simulations for the full unsteady model. We show for a wide variety of initial conditions that the solutions tend toward the stable linear steady state profiles. We also consider traveling wave solutions, and determine the unique wave speed (in terms of the other model parameters) which allows wave-like solutions to exist. Despite some similarities between the model and the inviscid Burger’s equation, the solutions we obtain are much more regular than the solutions to the inviscid Burger’s equation, with no evidence of shock formation or loss of regularity.
•A non-dimensional PDE system for a two-state gas laser is derived.•Steady states of this PDE system are classified showing a linear profile in space is stable.•Numerical simulations are performed and resulting solutions tend to the linear steady state.•Solutions maintain regularity and do not show signs of turbulence.•Traveling wave solutions are also considered.
Tunable diode laser spectroscopy technique was employed to determine pressure broadening coefficients for the (n+1)s3/22→(n+1)p5/23 transitions in Ar and Kr in RF discharge plasma. The widths of ...Gaussian and Lorentian components of the absorption lines were determined simultaneously by fitting absorption line profiles obtained in experiments to a Voigt profile. The technique was validated in measurements of pressure broadening coefficient for 811.5nm Ar absorption line in the pressure range of 15–75Torr. The obtained values for these coefficients reduced to 300K are ξAr–Ar=(2.8±0.1)×10−10s−1cm3 for broadening in the parent gas and ξAr-He=(3.2±0.2)×10−10s−1cm3 in helium.
For krypton, isotope abundance was accounted for and appropriate fit function was constructed permitting to determine pressure broadening coefficients using the natural mixture of isotopes. For krypton 811.3nm line these coefficients are ξKr-Kr=(2.4±0.2)×10−10s−1cm3 and ξKr-He=(3.1±0.2)×10−10s−1cm3.
•A technique was developed to measure pressure broadening in glow discharge plasma.•Pressure broadening coefficients for a transition in Ar and Kr were determined.•The technique is applicable for natural mixture of Kr isotopes.•The technique is insensitive to temperature gradients in plasma.
The historical aspect, present status, and future prospects of diode-pumped alkali lasers (DPAL) are discussed. DPAL is a relatively new laser, first reported in 2003. It is characterized by ...extremely high scalability, good beam quality by virtue of its gaseous laser medium, and intrinsically high efficiency because it is a three-level laser with a small Stokes defect. Because of these features, DPAL is being studied as a directed energy weapon and is also expected to find applications in industry and space. We propose the use of DPAL for space debris removal. Some of the research results of our group are also introduced.
Optically pumped all-rare-gas laser (OPRGL) with unique properties were recently proposed with a possibility to obtain the laser power on the order of hundreds of Watts from a cubic centimeter. To ...provide high laser efficiency, the pumping radiation has to match the absorption spectrum of the rare gas metastables. To meet this condition a reliable diagnostics of the key parameters of the active medium is required and knowledge of the broadening and shift coefficients for corresponding transitions of rare gases is necessary. In this paper, the diode-laser absorption spectroscopy was employed to determine the pressure shift coefficient for 811.5 nm Ar line. The value of obtained coefficient in pure argon reduced to 300 K is -(2.1 ± 0.1) × 10-10 s-1cm3. In the course of the study the pressure broadening coefficient was also evaluated and found to be (2.4 ± 0.5) × 10-10 s-1cm3.
•A longitudinally excited CO2 laser had a large discharge tube.•The discharge tube had an inner diameter of 16 mm and a length of 80 cm.•The discharge tube did not have a preionization system or a ...fast gas flow system.•The CO2 laser produced short laser pulses at a repetition rate of 700 Hz.
A longitudinally excited CO2 laser with a large discharge tube having an inner diameter of 16 mm and a length of 80 cm produced short laser pulses with an energy of 38.1 mJ at a repetition rate of 700 Hz. The CO2 laser did not have a preionization system or a fast gas flow system. The dependence of the laser output and discharge voltage on the repetition rate, the gas pressure and the structure of the discharge tube in 1:1:4 and 1:1:2 mixtures of CO2/N2/He gas was investigated. At a repetition rate of 300 Hz or more, the laser energy decreased as the repetition rate increased. The 1:1:4 mixture of CO2/N2/He gas produced a higher laser energy than the 1:1:2 mixture of CO2/N2/He gas. At a repetition rate of 300 Hz or less, the laser beam profile was doughnut-shaped. At a repetition rate of 400 Hz or more, the center of the laser profile had a high energy. At a high repetition rate, the fast discharge may have collected in the center of the discharge tube. Moreover, an increase in the repetition rate decreased the discharge formation time and the energy of a pulse tail part of the laser pulse waveform.
•Cheap multi-mode diode lasers can be tailored for spectroscopy needs.•Pressure shift and broadening rates of spectral lines’ in rare gases were measured.•Natural krypton requires specially designed ...spectral line profile.•Starters for fluorescent lamps can produce reference optical frequency.
In this work simultaneous measurements of pressure broadening and shift coefficients for 811.5 nm Ar and 811.3 nm Kr spectral lines of the 4s3/22 → 4p5/23 transition were performed. Assessment of gas temperature was done by determining Doppler width components of the lines’ Voigt profiles. Pressure shift coefficients for the mixtures Ar:Ne, Kr:Ne and Kr:Ar were determined for the first time. Their values in units of 10-10 s-1 cm3, reduced to 300 K are: βAr:Ne = -0.51 ± 0.05, βKr:Ne = -0.65 ± 0.01, βKr:Ar = -2.07 ± 0.08. Additionally we demonstrated the use of easily available starters for fluorescent lamps as sealed Ar discharge cells for reference optical frequency.
•Large volume CuBr laser with the continuous control pulse energy was developed.•The ratio of excitation and preionization pulses energy for full lasing suppression was determined.•The control ...characteristics for different active media operation mode were obtained.
The paper presents the results of the research and development of the CuBr laser with continuous control of each pulse energy. The prototype consists of a large volume CuBr active element with an unstable cavity, two high voltage pulses generators and control system. The HBr additive was used to increase the laser energy-frequency characteristics. Control of laser pulses energy has been provided by high-voltage preionization pulses. The linear control of output power from 5 W to 0 have been demonstrated. The metastable atom population is the major factor in the energy control. The dependence of the preionization pulse energy for full suppression on the active media operating mode (CuBr concentration, pumping energy etc.) was studied. The ratio between excitation pulse energy and preionization pulse energy for full suppression of the lasing changing from 18 to 25.
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