Laser Gas Mixture Research Articles

Spectral characterization of a Cryo-Cooled CO laser operating with CO2 laser gas mixture

This study explores the emission spectra and performance characteristics of a cryo-cooled CO laser system operating with CO2 laser gas mixture under various operating conditions, viz., N2 free gas mixture, different coolant temperatures and in grating tuned configuration. The narrow operational window in case of N2 free gas mixture, increased output power and richer emission spectrum obtained with the addition of N2 gas indicates enhanced discharge stability and efficient excitation in presence of Nitrogen. The emission spectrum revealed shifting of the trapping levels towards lower vibrational quantum number with reducing coolant temperature and the same was also corroborated by theoretical calculations. No lasing was observed for vibrational levels V>15 which is attributed to the higher partial pressure of oxygen inherently present in the gain medium formed due to dissociation of CO2. The system lased on more than 20 transitions in grating tuned configuration with power exceeding 100mW on several lines. The presence of higher concentration of O2 in the discharge prevents carbon deposition − a common issue in CO lasers. This study underscores the significance of this unconventional CO laser system offering reliable operation in the 5 µm wavelength region without the usage of extraneous CO gas.

Experimental estimation of CO concentration in LN2 cooled CW CO laser operating with CO2 laser gas mixture

The lasing medium of cryo-cooled CW-CO laser operated with CO2 laser gain medium (CO2–N2–He mixture) resulting in 5 µm emission is formed in-situ in the discharge and its composition, that is sensitively dependent on the discharge temperature, is not known a priori. The composition of the CO lasing gas mixture here was successfully arrived at by way of sampling the gas mixture at the exhaust and measuring the wavelength dependent absorbance by a Fourier Transform Infrared Spectrophotometer. This enabled us to determine the CO and CO2 concentrations in the lasing mixture accurately while the other major constituents were estimated from the initial partial pressures. The composition of the lasing gas mixture was studied for various discharge wall temperatures starting from no cooling condition (∼351 K) to LN2 cooled conditions (79 K). While the concentrations of both, CO2 and CO were found to decrease for temperatures below the freezing point of CO2 at the operating pressure of 11 mbar, the relative concentration of CO with respect to CO2 also increased with reducing temperature accompanied by a steady increase in the CO laser power output. The onset of lasing in 5 µm region was found to occur at a discharge wall temperature of 212 K.

Development of a dielectric corona pre-ionized TEA CO2 laser with CO2-rich gas mixture suitable for second harmonic generation

A simple dielectric corona pre-ionized TEA CO2 laser, which is suitable for SHG applications, has been developed with the help of high concentration of carbon dioxide. The intense, very uniform UV pre-ionization and low-inductance discharge circuit permit the best laser performance with a gas mixture rich in CO2. In order to achieve the most acceptable combination of the peak power, output energy and pulse duration, not only N2:CO2 ratio varies in favor of CO2 but also helium concentration is significantly reduced. When CO2 concentration varied from 20 to 53% in the experiment, a more symmetrical, shorter output pulse (a FWHM of ∼60 ns) with a significantly lower tail and a lower energy (∼700 mJ) was obtained with a rich gas mixture of CO2:N2:He = 10:1:8 than a lean gas mixture of 1:1:3 while the peak output power was virtually kept constant (∼5.8 MW). The effect of the laser gas mixture on optimizing the energy and time parameters of SH waveform has been studied numerically. The calculations show that for the rich gas mixture the residual tail of the SH pulse is completely eliminated by the nonlinear conversion and the corresponding waveform has a lower total duration (∼600 ns). Moreover, the energy conversion efficiency can be increased by 29% with the rich mixture compared to the lean mixture.

Development of a broad bandwidth 193 nanometer laser driver for inertial confinement fusion

The U.S. Naval Research Laboratory (NRL) has built a 137 J electron beam pumped argon fluoride (ArF) laser operating at 193 nm utilizing the Electra facility. This paper highlights initial ArF oscillator measurements in the context of significant benefits of ArF laser characterization for inertial confinement fusion target performance and development of a kinetics code with predictive capabilities. Other aspects of NRL's ArF laser development program, including large scale electron beam pumped ArF amplifier development and ArF optical transport, are discussed. Initial measurements were made utilizing a quadruple pass oscillator configuration constructed in the Electra facility with a nominal 100 cm2 aperture. Laser yields between 80 and 100 J, time-dependent laser intensity, and amplified spontaneous emission (ASE) are reported over a range of gas pressure (0.8–1.4 atmospheres). Higher laser yields, 137 J, were attained in a non-optimized dual ArF oscillator configuration wherein the optical axis was rotated to conform to the measured electron beam deposition in the laser gas mixture.

Cryogenically cooled CW electric discharge CO laser operated with CO2 laser mixture

We report lasing on multiple wavelengths in the 5 µm region from a non-selective CW-CO laser cavity utilizing the CO2 laser gas mixture when its gain length was maintained at LN2 temperature. The inversion obtained in the CO medium formed by the dissociation of CO2 gas in the discharge made this possible. The findings are significant as the handling of the toxic CO gas that is conventionally employed in the generation of wavelength in the 5 µm region has been dispensed with. A maximum CW output power of 8 W was obtained at an electro-optic efficiency of 8%. The cascading lasing transitions have been identified and matched with known transitions available in the literature.

Radiation power control of the industrial CO2 lasers excited by a nonself-sustained glow discharge with regard to dissociation in a working gas mixture

The action of a working gas mixture degradation related to the plasma chemical reactions in a glow discharge on the laser output power of the molecular laser excited by a nonself-sustained glow discharge has been studied by the example of an industrial laser of “Lantan” CO2 laser series. It was found that the laser power overshoot when operating on a fresh gas mixture may exceed 3 times power level set in a steady-state regime. The working algorithm for the control system was proposed and developed setting standard fresh CO2/N2/He laser gas mixture to plasma chemical equilibrium composition during the laser turn-on procedure after full refill of a working gas mixture.

High-power gas-discharge excimer ArF, KrCl, KrF, and XeCl lasers on buffer-gas free gas mixtures

Results of experimental studies of the gas mixture (laser active medium) effect on the lasing energy and overall efficiency of excimer discharge ArF (193 nm), KrCl (222 nm) KrF (248 nm), and XeCl (308 nm) lasers operating in buffer-free gas mixtures are presented. The optimal (in terms of maximum radiation energy) ratios of the gas components of the excimer laser active media are found, at which efficient operation is achieved with a sufficiently high power of the laser radiation. It is confirmed experimentally that for the rare gas halide discharge pumped excimer lasers the presence of a buffer gas in the active medium is not required for efficient laser operation. For example, in two-component excimer laser gas mixtures, containing working rare and halogen-containing gases, laser pulse energy of up to 170 mJ and high pulsed power of laser radiation of up to 24 MW have been attained for the first time for pulsed gas-discharge excimer lasers operating on electronic transitions at excimer ArF*, KrCl*, KrF*, and XeCl* molecules pumped by a transverse electric volume discharge of a low-pressure buffer-free gas mixture. A overall efficiency maximum of up to 0.8% was experimentally attained for binary gas mixture of KrF and XeCl lasers.

Temporal controlling of a bifurcated dual-band two-line TEA CO2 laser

The influence of N2 and He ratios in laser gas mixture on the pulse shape and onset delay time of the 10P(20) and 9P(20) lines in a bifurcated dual-band two-line TEA CO2 laser was investigated. It was shown that the pulse shape as well as delay in onset time of 9P(20) line is strongly dependent on the ratios of N2 and He components. So that, duration and onset delay time of the 9P(20) line can be respectively controlled in 100–400 ns range and 0.1 up to several µs, by varying the N2:He ratio in the gas mixture.

Benefits of cryogenic cooling on the operation of a pulsed CO2 laser

The paper presents results of a theoretical model of a pulsed electron beam controlled CO2 laser (EBCL) to investigate the effect of cooling on the laser gas mixture. It is shown that cryogenic cooling can significantly improve the performance of the laser. The efficiency of an EBCL improved from 20% to 25.3% by cooling it to 200 K. The improvement is mainly due to the decrease of thermal population of the CO2 (0 1 0) vibration level.

Acoustic Plasma Effects in the Diffusion-Cooled Working Medium of an Electric-Discharge CO2 CW Laser*

We have studied the effect of shallow modulation of the discharge current on the burning regime and the plasma parameters of a diffusion-cooled glow discharge in CO2/N2/He laser gas mixtures. We have established that modulation of the discharge current leads to excitation in the discharge of pulsations in the acoustic pressure, the electric current, and the intensity of the generated laser radiation, with the frequency of standing acoustic waves arising in the discharge tube and also with the frequencies of the current modulation, its harmonics, and combinations of all these frequencies with the frequency of the current pulsations in the power supply. We have shown that when self-sustaining resonant oscillations in the discharge current are excited or when the current is modulated, the IR luminescence intensity from the upper laser level of the CO2 molecule and the power of the radiation generated by the laser vary because of plasma heating in the positive column of the discharge, due to its contraction in the acoustic wave field initiated by the current pulsations.

New Circulation System of Laser Gas Mixtures

The electrohydrodynamic flow in air, being formed at issue of ions from plasma of the high-frequency barrier discharge is investigated. It is shown that velocity of a flow is proportional to intensity of electric field between the emitter and a collector of ions. All solid-state pulse generator with voltage of U f = 0-12 kV and pulse repetition rate of f = 10-25 kHz is applied to feed the plasma emitter. It is experimentally established that the increase in high voltage and frequency of the plasma emitter feeding leads to increase velocity of a gas flow. The circulation system with a gas flow rate more than 15 L s–1and velocity more than 1.6 m s–1 was proposed for electric-discharge lasers.

Development of laser-plasma generator for injector of C4+ ions

AbstractThe results of the development of the ITEP accelerator carbon ion injector based on a repetition-rate CO2 laser ion source are described. The improvement includes a modified pulsed HV-feeding generator for the discharge formation in the laser gas mixture. The advanced discharge module ensures essential increase of the laser active volume and specific electrical deposition energy. The comparative computer simulations of the discharge characteristics for the improved and the prototype lasers are applied. The design and the output spatial-temporal parameters of the free-running laser “Malish-M” are shown, so the significant increase of the laser power is reached. The spatial characteristics of the laser beam obtained with diffraction calculations are compared to measured radial distribution of the energy density. The target laser intensity and the different channels of the energy loss of the laser beam in the optical scheme are estimated. Finally, the output C4+ current trace of heavy ion injector as well as the injector scheme are shown.

Carbon dioxide laser with an e-beam-initiated discharge produced in the working gas mixture at a pressure up to 5 atm

A high-pressure CO2 laser with a discharge initiated by an electron beam of sub-nanosecond duration in the laser gas mixture at a pressure up to 5 atm is fabricated. For the 20-ns pulses the energy from the active volume ∼ 4 cm3 amounted to 40 mJ. The laser operation at a pulse repetition rate up to 5 Hz is demonstrated. In the gas mixture CO2:N2:He = 1:1:6 at a pressure 5 atm, the specific energy deposition of ∼ 0.07 J cm-3 atm-1 is obtained in the process of a non-self-sustained discharge with ionisation amplification.

热带连续波CO2激光器

The paper describes the design and construction of an intracavity intensity enhanced hot band CW CO2 laser with the line selected by concave grating. In this laser, using a gas mixture of 13% CO2, 15% N2 and 72% He (volume fraction) at a total pressure of 1074, 9 Pa and a discharge current of 25mA, more than 100 laser lines are observed from R(56) to P(60) in the regular hand 00^0 1-[10^00, 02^00](subscript Ⅰ, Ⅱ), besides, another 18 lines in 11μm wavelength region with 9 lines in the 01^11-03^10 band and 9 lines in the 01^11-11^10 band, are also observed under the condition of no hot CO2 absorption cell in the cavity. In the experiment, it is found that the laser output power decreases when more helium gas is added to the laser gas mixture. The one-way intracavity power of every line is above 35 W. which is adequate for most intracavity photochemistry.

A miniature electron beam pumped laser

The 1.73 μm XeI laser has been operated in a fully continuous mode using a table-top electron beam pumped laser setup. A 12 keV electron beam sent through a 300 nm thick silicon nitride membrane into a laser gas mixture of typically 600 mbar gas pressure was used for pumping. A low loss cavity was installed, resulting in a very low pumping power of 37 mW to reach laser threshold. The geometrical conditions for the laser setup such as the shape of the beam pumped volume and its overlap with the optical mode volume are discussed. The laser scheme has been clearly identified as a recombination laser scheme by operating the laser in pulsed mode and observing the time structure of the laser pulse.

Temporal extension of stable glow discharges in fluorine-based excimer laser gas mixtures by the addition of xenon

The effect of addition of xenon on the long term homogeneity of discharges in F2and ArF excimer laser gas mixtures was investigated in a small-volume discharge chamber. The gas mixture in the discharge chamber was preionized by X-rays. A special electrical excitation circuit containing a pulse forming line provided a long, square-shaped current pumping pulse of a predetermined duration to the discharge electrodes. The initiation and the development of the discharge was monitored via its fluorescence signal with an intensified CCD camera. We found that adding Xe up to partial pressures of 0.53 mbar extended the homogeneous phase of the discharge from 80 ns to approximately 200 ns in He/F2as well as in He/Ar/F2and Ne/Ar/F2excimer laser gas mixtures. Monitoring of the ArF and XeF spontaneous emission signals showed that the formation of ArF excimers remained unaffected by the addition of xenon (up to 1.3 mbar) to the laser gas mixture.

Laser gain measurements at 193 nm in a small discharge cell containing ArF excimer laser gas mixtures

Spatial and temporal gain profiles as well as the peak net gain at 193 nm have been measured in X-ray preionized discharges excited by a single pulse electrical system working in the charge transfer mode. Ar- and F2-containing laser gas mixtures with He or Ne as a buffer gas have been used. With a pumping pulse duration of ∼ 100 ns (FWHM) and a specific peak power deposition of ∼ 1 MW cm-3 bar-1 in a gas mixture containing F2 : Ar : He (0.1%:5%:94.9%), at 2 bar total pressure, a very high peak net gain coefficient of ∼ 30% cm-1 was measured in the gas discharge. The FWHM of the gain waveform was ∼ 60 ns.

Effect of preionization, fluorine concentration, and current density on the discharge uniformity in F2 excimer laser gas mixtures

The discharge homogeneity in F2-based excimer laser gas mixtures and its dependence on various key parameters, such as the degree of preionization, preionization delay time, F2 concentration and current density, is investigated in a small x-ray preionized discharge chamber. The spatial and temporal evolution of the discharges is monitored by taking photographs of the discharge fluorescence with a fast intensified CCD camera. It is found that a preionization electron density of about 107 cm−3 bar−1 is sufficient to initiate a streamer-free homogeneous discharge in gas mixtures of helium and fluorine with multiatmospheric gas pressure. The accompanying optimum time delay between the application of the x-ray pulse and voltage across the discharge electrodes is determined to be about 20 ns. It is shown that in spite of these optimum initial conditions, a homogeneous glow discharge eventually transforms into an inhomogeneous discharge containing numerous filaments. Our experiments show that the higher the initial F2 concentration, the initial current density or the pump power density, the shorter the time interval over which the discharge stays homogeneous. By a quantitative characterization and defining a detailed measure of the observed discharge inhomogeneity we find that halogen depletion, as suggested from the theory, is responsible for the temporal instability of discharges in such laser gas mixtures, as the experimental results are in good agreement with the theory on the halogen depletion instability mechanism.

Triggered Spark Gap Command Charger for High Repetition Rate Applications

A normal dc resonant charger was transformed into a command-mode charger by connecting a spark gap at its output terminal, prior to the load circuit. This charging spark gap was triggered by a transformer connected in series, pulsed by a fast spark gap circuit. Noise suppression schemes were implemented throughout the command charger, in particular around the charging spark gap to order prevent misfiring. The ringing noise and spikes from the capacitor discharge and those of the stray capacitance of coaxial cable were strongly suppressed by a simple LCR circuit so that these would not induce self-breakdown in the charging spark gap. This triggered spark gap command charger was tested to 2 kHz and < 10 kV with a resistive load. A transversely excited atmospheric CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser was operated up to 300 Hz and (10-15) kV that was limited only by the flow rate of the laser gas mixture

Current filamentation in discharge-excited F2-based excimer laser gas mixtures

Discharge instabilities in x-ray preionized F2-doped excimer laser gas mixtures are investigated using an intensified charge coupled device camera with a gating time of 300ps. In contradiction with earlier theories and observations, it is found that the discharges in He∕F2 mixtures are homogeneous only at very low concentration of F2 (0.025%). We present experimental results, which prove that in He∕Kr∕F2 mixtures the appearance of discharge filaments is coupled with the presence of F2 rather than Kr.