Electric-discharge XeCl Laser Research Articles

Spontaneous and stimulated emission spectra for 124Xe35Cl molecules

Abstract. The influence of the isotopic composition of active medium on a lasing spectrum of a XeCl laser has been investigated. Spectra of spontaneous and stimulated emissions for monoisotopic 124 Xe 35 Cl molecules were measured. The frequencies in lasing spectrum were determined. The frequencies of vibrational edging in the luminescence spectra of the molecule 124 Xe 35 Cl were also measured. We showed that varying the isotopic composition of the active medium one can get the lasing on frequencies different from the lasing ones in the natural XeCl laser. Keywords: excimer laser, isotopic composition, emission spectra, fine structure. Manuscript received 17.03.05; accepted for publication 18.05.05. 1. Introduction The electric discharge XeCl laser is one of the most powerful sources of coherent UV radiation now. This laser has wide applications for different scientific and technological branches. Many applications need for a narrow spectrum, whereas the XeCl laser spectrum is quite wide. It is well known that, under common lasing conditions and if there are no additional selecting elements, there are four electron-vibrational transitions: 0-0, 0-1, 0-2, and 0-3 in the vicinity of 308 nm. Different schemes were used for narrowing the lasing spectrum. Some papers reported that, under the low pressure of a working medium (0.3–0.5 atm), there is a line structure caused by rotation of molecules [1, 2]. While the frequency is tuned in a laser with the selective resonator, this structure becomes apparent at the high pressure (2-3 atm) [3], which makes the tuning discrete in the tuning range. The identification of the rotational spectrum of the XeCl laser has to be performed with taking into account the great number of overlapping lines from different rotational branches. One of the ways for simplification of the spectrum structure for its study is usage of mixtures enriched with isotopes [4]. Furthermore, usage of a mixture enriched by isotope, the concentration of which in the natural mixture is low, makes it possible to obtain new lasing lines. This paper shows spectra of luminescence and lasing for molecules

Peculiarities of active medium formation in a short-pulse electric-discharge XeCl laser

The effect of the conditions of discharge on the output radiation parameters and efficiency of an electric-discharge XeCl laser pumped by 20 ns pulses is studied experimentally. It is shown that the highest specific energy extraction ∼3.9 J L-1 atm-1 from the active medium is realised in a discharge formed by pronounced macroinhomogeneities. The maximum laser efficiency of 2.7% is attained for discharge current densities of 1.2–1.4 kA cm-2.

Electric-discharge XeCl laser emitting 10-J, 300-ns pulses

The development of a long-pulse electric-discharge XeCl laser with the 9 × 6 × 100 cm active volume is reported. Laser is excited by using a double circuit with a pulsed charged storage capacitor consisting of paper-oil capacitors forming the pulse-shaping line. The storage capacitor is switched by a multichannel extended gap. The laser mixture was preionised by X-rays. The laser generated the 10-J output pulses with the FWHM of 300 ns, and a uniform intensity distribution over the exit aperture.

Pulse generator for pumping electric-discharge excimer lasers

A pulse generator is developed for pumping electric-discharge excimer lasers in which the capacitive energy storage is connected with the gas-discharge chamber of the laser with the help of a multichannel spark switch via a low-inductive strip line. This scheme of the generator reduces energy losses in the switch and the inductance of the discharge circuit of the capacitive storage. For the pump power equal to 800 MW, the efficiency of the stored energy transfer to a load achieves 85%. To ignite a homogeneous volume discharge, the generator produces a prepulse, which initiates a low-current volume discharge in the gas-discharge chamber. Upon excitation of an electric-discharge XeCl laser with the 3 × 5.4 × 80-cm active region and the Ne : Xe : HCl= 2000 : 2.5 : 1 mixture at a pressure of 4 atm, radiation pulses with energies up to 3.4 J and the FWHM duration up to 260 ns were obtained with a homogeneous energy distribution over the laser aperture.

Effect of the degree of preionisation of a gas on the homogeneity of a volume discharge and generation of radiation in a wide-aperture XeCl-laser

The results of investigation of an electric discharge XeCl laser with active region apertures 8 × 11, 10 × 15, and 15 × 15 cm are presented. The preionisation of the Ne — Xe — HCl working mixture was performed by soft X-rays and a low-current electron beam, which provided the initial concentration n0 of electrons in the gas from 106 to 2 × 1013 cm-3. For n0 < 1012 cm-3, the homogeneity of the initial electron concentration and of an electric field in the discharge gap have a considerable effect on the homogeneity of the volume discharge and output characteristics of the laser. For n0 ≥ 1012 cm-3, a homogeneous volume discharge is ignited and is stable if the inhomogeneity of the electric field in the discharge gap does not exceed 10%. A storage capacitor charged to double the voltage of the quasi-stationary discharge operation is sufficient for discharge formation. It is shown that an improvement of the volume discharge homogeneity and a decrease in the size of the discharge chamber make it possible to increase the efficiency of a wide-aperture XeCl laser.

Effect of inhomogeneities of an active medium on the divergenceof radiation from a long-pulse electric-discharge XeCl laser

The effect of optical inhomogeneities of the activemedium of an electric-discharge XeCl laser excited by 300-nspulses on the divergence of amplified radiation is experimentally studied. The possibility of obtaining the diffraction-limited divergence of radiation at the output of the amplifieris shown. Under our conditions, for the pump power densityexceeding 400 kW cm-3 , the radiation divergence in mainlydetermined by the nonuniformity of the gain profile of theactive medium that appears at a certain stage of the dischargeburning. This property of the active medium is caused by thedevelopment of macro- and microinhomogeneities of the discharge current.

Efficient long-pulse XeCl laser with a prepulse formed by an inductive energy storage device

An efficient electric-discharge XeCl laser is developed, which is pumped by a self-sustained discharge with a prepulse formed by a generator with an inductive energy storage device and a semiconductor current interrupter on a basis of semiconductor opening switch (SOS) diodes. An output energy up to 800 mJ, a pulse length up to 450 ns, and a total laser efficiency of 2.2% were attained by using spark UV preionisation.

Electric-discharge XeCl laser with 4% efficiency and 14 J output energy

An investigation was made of an electric-discharge XeCl laser with an active region of 5.5 cm × 7 cm × 100 cm dimensions. This laser was pumped by a voltage generator based on capacitance storage lines. A multichannel spark-discharge gap was used as a fast-response switch. An Ne—Xe—HCl working mixture was preionised with soft x-rays. When the charging voltage applied to the capacitance lines was constant, an output radiation energy of 10.5 J and an efficiency of 3% (in terms of the stored energy) were achieved. When the capacitance lines were subjected to pulsed charging, the energy per pulse was 14 J and the efficiency was 4%.

Influence of vibrational kinetics of HCl on the growth of microinstabilities and the characteristics of an electric-discharge XeCl laser under inhomogeneous preionisation conditions

A one-dimensional model of an electric-discharge XeCl laser was used in an investigation of the growth of microinstabilities induced by perturbations both of the initial electron density and of the electric field under homogeneous field and inhomogeneous preionisation conditions. A mechanism of attachment—vibrational stabilisation of a discharge in mixtures containing HCl molecules was proposed and investigated. It was found that dissociative attachment to vibrationally excited HCl molecules delays considerably the growth of microinstabilities and contraction in a selfsustained discharge. This accounts for the well-known experimental observation that a discharge in a mixture containing HCl is more stable than a discharge in a mixture containing F2. A full description of this effect could be given in the one-dimensional approximation only when one effective level was replaced by four vibrational levels (υ = 0–3). A study was made of the influence of microinstabilities on the energy characteristics of the laser. Critical perturbations of the electric field, which suppressed lasing, amounted to ~0.15% and ~1% for the KrF and XeCl laser models. These values were nearly two orders of magnitude less than the critical microperturbations of the electron density (~5% and ~100%, respectively). In the case of mixtures containing HCl there were ranges of perturbations of the initial electron density and of the electric field (up to 20% and 0.2%, respectively) in which the discharge was stable. However, there were in practice no such ranges for mixtures containing F2. The experimental results obtained for a 10-litre XeCl laser were explained when the influence of microinstabilities and contraction of the discharge current on the operational characteristics of the laser was taken into account.

Investigation of an electric-discharge XeCl laser with a radiation energy of 5 J per pulse

An investigation was made of an electric-discharge XeCl laser with the active region of 4 cm × 5.5 cm × 100 cm dimensions. The laser was pumped by one of two pulse generators: a generator with a two-circuit configuration, a peaking capacitor, and a spark switch or a thyratron magnetic generator. An Ne(He, Ar)—Xe—HCl working mixture was preionised by x rays of 25–30 keV energy. A study was made of the conditions needed for the initiation of a homogeneous volume discharge. When the buffer gas in the mixture was neon, the radiation energy per pulse was 5 J, in a mixture with helium it was 2.5 J, and in a mixture with argon it was 1.2 J.

Active-medium inhomogeneity and beam divergence of the electric discharge XeCl laser

Active-medium inhomogeneity and beam divergence of the electric discharge XeCl laser

Long-pulse (0.5 ?sec) electric-discharge XeCl laser continuously tunable in the 307.00?308.93 nm range

Long-pulse (0.5 ?sec) electric-discharge XeCl laser continuously tunable in the 307.00?308.93 nm range

Modeling of a 10-liter electric-discharge XeCl laser

Theoretical models developed independently by groups in Russia and Italy were used to describe the operation of a 10-liter electric-discharge XeCl laser. The calculations gave similar results for an HCl pressure of 1.5 Torr, but diverged strongly at low (0.5 Torr) and high (4 Torr) HCl pressures. The reasons for this discrepancy were determined. It was found that homogeneous models cannot describe the experimental data satisfactorily.

Control of the divergence of radiation from an XeCl laser amplifier

The results are presented of experimental studies of the divergence of narrow-band radiation from an electric-discharge XeCl laser operating in an injection-locked regime and as a single-pass amplifier. It is shown that the radiation brightness under injection-locking conditions is twice that after single-pass amplification.

Influence of a time delay between a prepulse and the main discharge pulse on the characteristics of an electric-discharge XeCl laser

The results are given of an experiment in which the active mixture of an XeCl laser was excited in the following sequence: preionization, prepulse, main discharge. The mixture was preionized by ultraviolet radiation from an array of sparks through a planar grid electrode. The mixture consisted of Ne (He), Xe, and HCl at pressures of respectively 2.2 atm, 6 Torr, and 0.6 Torr. A study was made of the influence of the time delay τ of the main discharge pulse, relative to the prepulse, on the laser characteristics. For zero time delay, the laser spot was a 4 × 2.5-cm rectangle. For τ > 100 ns, a marked reduction was observed in the laser pulse energy; lasing ceased in the center of the beam and the beam was split into two luminous bands whose separation widened as τ was increased. The observed change in the intensity profile was well described by a model allowing for the inhomogeneous distribution of the vibrationally excited HCl molecules (ν = 1, 2, 3, ...) formed after the passage of the prepulse. The rate of attachment of electrons to HCl (ν = 1, 2, 3, ...) molecules was two orders of magnitude higher than that to unexcited molecules, so that the electron attachment processes were considerably faster in the center of the discharge region than at its edges. Numerical estimates were made. A comparison of the experimental with the calculated dependences demonstrated a good qualitative agreement. The possibilities for using the observed phenomenon in practice were analyzed.

Modeling of the spatial and temporal characteristics of the active medium of an electric-discharge XeCl laser

An analysis was made of a model of an electric-discharge XeCl laser with a one-dimensional spatial description of the discharge. The concentrations of the components of the laser-active medium and the lasing pulse were simulated both in time and in space in a direction perpendicular to the electric field lines. The results of calculations of the spatial and temporal dynamics of the laser plasma components, the lasing pulse, and also the discharge voltage and current were compared with the experimental results. An analysis was made of the influence of the degree of homogeneity of the electric field and of the preionization on the spatial characteristics of an XeCl laser-active medium.

Pulse-periodic electric discharge XeCl laser

A wide-aperture pulse-periodic electric-discharge XeCl laser was constructed having an energy per pulse of 10 J and a pulse repetition frequency of 50 Hz. The active volume was pumped using an electrical circuit employing a rail spark gap and a double artificial pulse-shaping line charged from a pulsed power supply of up to 70 kV.

Narrow-band XeCl laser with an amplifier

An investigation was made of an electric-discharge XeCl laser consisting of a narrow-band master oscillator and an amplifier with an unstable resonator. Narrow-band radiation tunable in the 307.5–308.5 nm range with a line width of up to 1 pm and an angular divergence of 0.1 mrad was obtained. Up to 70% of the laser output power was concentrated in a narrow line.

Evolution of spatial distributions of charged and excited particles in the plasma of an electric-discharge XeCl laser

Interferometric techniques were used to measure spatial distributions of electrons. A one-dimensional model of an electric-discharge XeCl excimer laser is described. Measured and calculated space–time distributions of electron densities are compared. It is found that the spatial distributions of excited particles and electrons may differ substantially.

Divergence of radiation from an electric-discharge XeCl laser operating in the pulse-periodic regime

Investigations were made of a pulse-periodic electric-discharge XeCl laser with two types of resonator. When an unstable confocal resonator with a magnification of M = 12 was used, the divergence exceeded the diffraction limit by a factor of only 2?3 and there was only a slight ( ? 30%) reduction in the output energy relative to that from a laser with a plane?plane resonator. The influence of the pulse repetition frequency on the radiation divergence was investigated for helium- and neon-containing gas mixtures. A dependence of the divergence on the pulse repetition frequency was discovered. A theoretical interpretation is given of the results of the experiments.