Preionization Source Research Articles

Investigation of sliding sparks by the schlieren method

The authors study the optical perturbations of the medium when sliding sparks (SS) are employed for preionization or optical pumping of the active medium in lasers. The experiments were performed on a Schlieren setup. A series of photographic frames are shown of the channel of an incomplete SS. It is shown that the SS are a source of perturbations of the gaseous medium in both the completed and incompleted stages of the discharge. The perturbations appear because of the nature of the formation of the SS and the form of the voltage applied to the discharge gap. The characteristic propagation velocities of these perturbatins range from 0.4 to 1 km/sec. This circumstance should be taken into account when employing SS as a source of preionization of laser media or as a source for optical pumping.

High-power pulsed CO2laser with plasma electrodes

Plasma sheets formed by a creeping discharge on the surface of an insulator were used as a preionization source and as electrodes in atmospheric-pressure CO2 lasers with a cross section of the active medium channel amounting to 150 × 150 mm. The output energy parameters of such lasers were not inferior to those of lasers with electron-beam preionization.

Low energy x-ray preionization source for discharge excited lasers

A low voltage (50 kV), low energy (3 J) x-ray preionization source has been developed specifically for avalanche discharge laser preionization. The new device uses a single stage high-voltage capacitor switched by a gradient grid hydrogen thyratron that drives a cold-cathode electron beam. Intense x-ray emission is produced by allowing the e beam to impact a high Z target foil. The entire system can operate up to 35 Hz repetition rate and produce an electron preionization density of ∼108 cm−3 in most rare-gas/halide laser gas mixtures.

CW X-RAY PREIONIZED PULSED GAS LASERS

We have successfully demonstrated that the cw x-ray generator can work as a preionization source for a pulsed H F laser. The preionization effect of cw x radiation was revealed by a comparative study of with and without applying x-ray photons to the H F laser. Since dose rate of the cw x-ray generator is easily controllable, the laser output could be measured as a function of initial electron number density produced. The cw x-ray preionizer has many advantages for actual gas laser systems compared with other preionizers. There are attributable to its high-energy photons and its characteristics of the cw x-ray generator. Applicability of the cw x-ray preionizer for actual laser systems, especially for high-repetition-rate pulsed laser systems is discussed.

Pulsed discharge N2/SF6 laser with cw x radiation as a preionization source

A cw x-ray generator was used as a preionizer for a pulsed-discharge uv N2/SF6 laser. We revealed experimentally that cw x radiation was effective for preionization of a N2 laser discharge. We observed that the N2 laser energy increased linearly with increasing initial electron number density generated by a cw x-ray preionizer when the electron number density was below 6×107 cm−3 and the input energy loading was kept at 35 J/l. In the case of x-ray illumination, the N2 laser energy increased by a factor of 12 over that of pure N2 gas when SF6 was added.

Effect of preionization of a copper vapor laser

It is shown that the operation of a copper vapor laser (CVL) in exeptionaly low <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E/P</tex> is due to preionization. By introducing a wire preionization to a CVL we demonstrate its influence on the laser performance. In a repetitively pulsed CVL a previous pulse can be the preionization source.

Construction and performance characteristics of a rapid discharge TEA CO 2 laser

A novel excitation technique is described for molecular gas lasers. A specially constructed electrode configuration is activated by a rapid Marx generator. A very homogeneous selfsustained discharge can be obtained although no separate preionization source is present. The construction is applied to a CO2 system. Details of the operating characteristics are given. We found the maximum energy production to be over 60 J per liter and a small-signal gain of 6% per cm could be reached.

Use of a surface discharge for preionization of gases in discharge lasers

The results are reported of a comparative study of ultraviolet spectra emitted from preionization sources designed for gas-discharge lasers. A comparison is made of the emission spectra of a complete surface (guided) discharge, a free spark, and a spark in the presence of an insulator in the discharge region. It is shown that the radiation energy can be concentrated in the required wavelength range by exciting the emission lines of the insulator. The strongest concentration effect is observed for a surface discharge on insulating substrates containing silicon.

Efficient self-sustained pulsed CO laser

In this paper a simple sealed-off TEA CO laser is described with a self-sustained discharge without an external UV preionization source. At 77 K this system yields more than 600 mJ from a lasing volume of about 60 cm 3 CO-N 2-He mixture (45 J/ℓ atm. with 15.6% efficiency).

Multiple preionization discharge TEA CO2 laser

A new concept in utilizing preionization in the TEA CO2 laser is presented. The variable adjustment of the delay between the preionization and the main discharge in a pin-grid double discharge TEA CO2 laser permits the use of low He concentrations (?60%), and different CO2/(CO2+N2) ratios (ranging from 1 to 0) at relatively high main discharge storage energy density (150 J/liter). The addition of a different preionization source (Lamberton–Pearson type) to this laser type leads to further increase in overall performance. This permits a completely variable TEA CO2 laser operation over the gas mixture [100–45% He, and CO2/(CO2+N2) ratio from 1 to 0] and the pump energy (to more than 200 J/liter) without the use of any sophisticated discharge circuit configuration or any seeded gas in the laser mixture. We propose a qualitative explanation based on the comprehension of the different electron production–electron loss processes in the laser discharge. This contribution opens up a new point of view in using more profitably the different preionization schemes proposed to date.

A Small Microwave Plasma Source for Long Column Production without Magnetic Field

A new HF device is described. It allows the production, without the use of a magnetic field, of long plasma columns from a small HF coupling structure situated at one end of the column. Its operation is based on the propagation of a cold plasma surface wave. This device can work (in argon for example) at pressures from 2 mTorr to 20 Torr with electron densities from 1010 cm-3 to 1013 cm-3, depending on plasma diameter and HF power. Typically, 80W of 500 MHz HF will produce a 25 mn diameter column of 1.8 m length. The plasma is quiescent (low electron density fluctuations), efficient (~ 100% absorbed power), and perfectly reproducible. It can be used as a substitute for a positive column, and some practical applications are foreseen in ion production, laser excitation, gas preionization and spectroscopic sources.