Electric-discharge Laser Research Articles

Lasers developed in the Institute of Atmospheric Optics of the SB RAS (a review)

The results of research on the development of the first electric discharge lasers on active media N2, CO2, Cu, CuBr and excimer molecules at the Institute of Atmospheric Optics named after V. E. Zueva SB RAS are given. It created one of the world's first Cu-lasers with a pulse production of copper vapors due to the explosion of conductors and a transverse excitation discharge. For a copper laser, record specific generation parameters were obtained almost equal to the limit: radiation energy 2.4 J/l, peak power 120 MW/l with an efficiency of 0.16 %. For the CuBr laser operating in frequency mode, for the first time, an average radiation power of more than 100 W was obtained. In the dual pulse excitation mode, conditions were found that limit the growth of the efficiency of the CuBr laser. For him, a record efficiency of 2.7 % was obtained. For the first time, a nitrogen laser was developed with a maximum efficiency of 0.27 % with an
 energy of 0.8 mJ, a peak power of 160 kW. For the first time, a miniature XeCl laser with a longitudinal excitation discharge was developed, which worked both with and without buffer gases He, Ne and Ar.

The effect of external visible light on the breakdown voltage of a long discharge tube

The breakdown characteristics of a discharge tube with a configuration typical of gas-discharge light sources and electric-discharge lasers (a so-called “long discharge tube”) filled with argon or helium at a pressure of 1 Torr have been investigated. A breakdown has been implemented using positive and negative voltage pulses with a linear leading edge having a slope dU/dt ~ 10–107 V/s. Visible light from an external source (halogen incandescent lamp) is found to affect the breakdown characteristics. The dependences of the dynamic breakdown voltage of the tube on dU/dt and on the incident light intensity are measured. The breakdown voltage is found to decrease under irradiation of the high-voltage anode of the tube in a wide range of dU/dt. A dependence of the effect magnitude on the light intensity and spectrum is obtained. Possible physical mechanisms of this phenomenon are discussed.

Studying the Effects of Internal and External Microstructure on Fatigue Strength of Materials by Electromagnetic Excitation Technique

A fatigue testing setup based on electromagnetic excitation was built to apply cyclic stresses to the specimens near their resonance frequency. A test near the resonance frequency has the advantage that higher stresses can be applied to test specimens at a reduced input power. Stress amplitude up to 1000 MPa can be applied to the test specimens and up to four specimens can be tested simultaneously. The setup can test specimens at high fatigue cycle regime i.e. 100 million stress cycles can be achieved in 48 hours.The setup has been used to study the effects of internal and external microstructure on the fatigue strength of materials. Specimens especially stainless steel-304 was prepared by different techniques i.e. electric discharge machining EDM, etching and laser cutting. Specimens prepared by these techniques were tested and their fatigue strengths were compared. To probe the material endurance limit, tests were also performed on the above mentioned steel specimens in very high stress cycle regime i.e. > 109 cycles. In order to investigate the effect of internal microstructure on fatigue strength of material, CuZn37 fabricated by etching was tested and the effect of different grain size on fatigue strength was compared. SN curves have been plotted for materials with no prior fatigue strength data. Stainless steel-1.4404 specimens prepared by Rapid Prototyping (RP) has been tested for fatigue analysis. The test results showed higher degree of scattering when compared to the traditionally manufactured steel. Fractography revealed the existence of inherent material flaws which was the main reason of higher degree of test point scattering. In addition to these data, the SN curve was plotted for Innolot which is an important soldering alloy and prompts to fatigue failure in electronic assemblies.

A2B6 electric-discharge semiconductor focon laser

The working principle of the electric-discharge semiconductor focon laser is considered. CdS, CdxZn1−xSe, and CdSxSe1−x plates were used as active medium. In the case of CdS, lasing at λ = 525 nm was observed. The radiation power reached 3 kW, the pulse duration being 3 ns. The conditions of generation initiation in the streamer regime are considered. The spectral characteristics of discharge channel radiation in CdxZn1−xSe and CdSxSe1−x plates are investigated. The spectrum is shown to consist of discrete lines occurring upon discharge propagation and corresponding to the change in the composition of the ternary compound obtained in the course of single crystal growth. The application of ternary solid solutions A2B6 is supposed to help in obtaining a successive laser pulse generation within the range of 480 to 700 nm.

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.

Gas mixture circulation system in lasers using a high-frequency barrier discharge

Electrohydrodynamic flow in gas for a high-frequency barrier discharge distributed over the surface of a dielectric was investigated. An electric-discharge laser circulation system with a gas flow rate higher than 15 L s-1 was proposed.

Increase of process reliability in the micro-machining processes EDM-milling and laser ablation using on-machine sensors

In micro production micro electric discharge machining (μEDM) and laser ablation are two established manufacturing methods. Due to the thermal material removal mechanism there are some challenges to provide the needed process reliability. In both cases it is important to ensure a precise manufacturing process by the correct positioning of the tool, e.g. the laser spot, relative to the work piece and the measurement and elimination of geometrical deviations. Using the EDM-milling process to manufacture small cavities a deviation of the manufactured depth and a waviness of the surface may appear if the compensation of the tool wear does not work correctly. A confocal white-light sensor can be used to measure the surface of the machined cavity after the EDM process. An on-machine system provides the possibility to rework the work piece without unclamping it. Combining these two procedures in an automatic working quality loop the accuracy of the manufactured depth can be improved down to a maximum deviation of less than 2 μm. Regarding the laser ablation process using ultra short pulsed Nd:YAG lasers problems arise if the focal plane is not on the surface of the work piece. Due to the manufacturing in layers occurring deviations in the surface remain until the end of the machining process. In this work an acoustical sensor is used to provide a correctly adjusted focal plane at the beginning of the first manufacturing step. Acoustic emissions are detected during the ablation process. A signal analysis of the airborne sound spectrum emitted by the process enables specific conclusions about the focal position of the laser beam. Based on this correlation an acoustic focus positioning is built up and tested on a ceramic work piece. The focal plane can then be adjusted automatically before the ablation.

Fabrication Technology of Involute Micro Gear Based on Two-Photon of Femtosecond Laser

Microfabrication is a kind of critical technology for the development of Micro Electro-Mechanical Systems (MEMS). The frequently-used microfabrication technologies are electric discharge machining, photoetching, LIGA and laser fabrication, et al. Micro structures may be fabricated by these technologies. The polymerization principle of two-photon of femtosecond laser is different from that of single-photon. Photoinitiator of photosensing material absorbs two photons simultaneously to accomplish energy level transition and to induce the material to occur photochemical reaction. For the material absorbing two photons, the energy of each photon is equivalent to half of the energy that needed by the material transiting from ground state to excited state. It is also equal to half of the energy needed by the material occurring single-photon absorption. Therefore, the photonic frequency of two-photon excitation light source is half of the single-photon light source. According to two-photon fabrication principle, machining system of two-photon of femtosecond laser is set up. Which includes light path transmission equipment, three dimensional micro displacement scanning stage and control software, et al. Involute micro gear is fabricated by two-photon of femtosecond laser generated by the system.

Numerical simulation of the mixing kinetics of an iodine-containing flow and the oxygen flow excited in the electric-discharge oxygen-iodine laser

A parametric analysis has been carried out to discover how the concentration of atomic oxygen in the O2: O2 (1Δg): O flow and the degree of predissociation and concentration of molecular iodine in the I2: He mixture affect the temperature regime and the formation of the inverse population at the atomic iodine laser transition at elevated pressures of P = 5–10 Torr in a simulated system with the axial injection of an I2: He mixture in the EDSOG-excited oxygen flow.

A wide-aperture x-ray source with high intensity and uniformity of radiation

The results of experimental research on an x-ray source intended for preionizing the laser mixture in wide-aperture electric-discharge excimer lasers are presented. An experimental prototype of the source in which an x-ray radiation pulse is formed in an inverted-type vacuum diode during braking of accelerated electrons in a tantalum foil has been developed. It is shown that the use of a metal-dielectric cathode allows generation of x rays with nonuniformity of the intensity distribution within limits of 10% at an energy of quanta no higher than 55 keV and a radiation exposure dose 160 mR.

Using infrared laser to enhance field emission of carbon nanotube

Infrared laser has been used to irradiate carbon nanotube (CNT) powders and the performance of CNT emitter was enhanced. The CNTs were prepared by conventional electric arc discharge method and laser irradiation was processed by Nd:YAG infrared laser with a wavelength of 1064nm. It was found that the turn-on electric field was significantly decreased for laser treated sample. As compared to the sample of no laser treatment, the emission current density was enhanced by a magnitude of 16.56 for 225J∕cm2 treated plus annealing one. Possible mechanism is discussed here.

Combination of electric discharge machining and laser ablation in microstructuring of hardened steels

Improving the efficiency of manufacturing processes becomes more and more important. This paper describes a new approach where two technologies are combined to manufacture wear-resistant mold inserts for powder injection molding. By combining laser ablation and electrical discharge machining (EDM) specific advantages of the respective technology can be utilized while drawbacks can partially be eliminated.In the following machining results of die-sinking EDM, EDM milling and laser ablation with structure sizes down to 20 μm are presented and a concept for a new type of electrode for EDM is introduced. Furthermore the combined machining center is presented.

Compact 4-kHz XeF laser with a multisectional discharge gap

A XeF electric-discharge laser with a pulse repetition rate f of up to 4 kHz is developed. The laser electrode unit is based on plate electrodes with inductive—capacitive discharge stabilisation. He and Ne are used as buffer gases, and NF3 serves as a fluorine donor. A narrow (∼1 mm) discharge is achieved; the specific energy deposition per unit length of the active volume is as high as 2 J m-1. The maximum energy in a laser pulse is ∼3 mJ for NF3—Xe—He and NF3—Xe—Ne mixtures at total pressures of 0.8 and 1.2 atm, respectively, and the maximum lasing efficiency is ∼0.73%. The maximum gas velocity in the working gap is 19 m s-1. The laser-pulse energy at a high pulse repetition rate (4 kHz) virtually coincides with that obtained at a low repetition rate. The mean output pulse power at f = 4 kHz reaches 12 W, and the rms deviation of the laser-pulse energy is ∼2.5%.

Formation of the beam profile in a plate electrode HF laser

The near-field energy-density distribution of a beam from an HF electric-discharge laser with an inductively stabilised discharge, an SF6- and H2-based active medium, and interelectrode gaps of 34 and 52 mm is studied. Plates 1-mm thick and 60- or 120-mm wide oriented at an angle of 30° to the optical axis serve as 60-mm-wide electrodes. Electrodes 30-mm wide are formed by 60-mm-wide plates also oriented at an angle of 30° to the optical axis. The distributions of the laser-radiation density in a resonator with flat mirrors and the discharge-emission intensity over the resonator cross section are studied. The distributions of the laser-radiation density in the near-field zone and the discharge-emission intensity have similar profiles. The arrangement of the electrode plates at an angle of 30° provided a considerable increase in the width of the lasing region. The FWHM of the laser-radiation distribution is ∼80% of the electrode width for the both interelectrode gaps.

Intracavity scanning of the radiation of an electric-discharge nonchain DF laser

This paper presents the results of a study of the possibility of using an electrically controlled space-time light modulator based on the transparent electrooptic ceramic PLZT for intracavity scanning of the radiation of a chemical nonchain DF laser (lasing-wavelength range 3.5-4.0 µm). The radiation pulses are scanned in space in the pulsed and pulse-frequency operating modes of the laser. © 2005 Optical Society of America

Effect of the pump intensity on the efficiency of a KrF excimer electric-discharge laser on a He—Kr—F2 mixture

The effect of the pump parameters on the efficiency of operation of a KrF gas-discharge excimer laser on a He—Kr—F2 mixture is studied. A theoretical model of the excitation system and the kinetic processes in the plasma of this laser is developed. A pump system based on an LC inverter with a spark gap as a high-voltage switch, automatic UV preionisation, and a low-inductance discharge circuit is created. To increase the efficiency and the output energy of the KrF laser based on a He—Kr—F2 mixture, it is proposed to enhance the pump intensity to 4 MW cm-3 by increasing the inductance between the LC inverter and the discharge circuit to 100 nH. An output energy of 1 J at an efficiency of 2% is achieved for the first time for the KrF laser operating on this mixture.

On the Efficiency of Nonchain Electric-Discharge HF (DF) Lasers

An important operating parameter of any laser which determines the field of application for the laser is its efficiency. Therefore, to increase the efficiency is a practically significant problem. Nonchain electric-discharge HF (DF) lasers have been studied for a long time, and high energies and average radiation powers have been achieved with an electrical efficiency of ~3–4% [1–5]. However, no work has been performed with the goal to increase the efficiency of nonchain HF (DF) lasers and to reveal the factors that affect the efficiency. The maximum electrical efficiency of an HF laser (up to 6.3%) has been obtained for mixtures of elegas with hydrogen pumped with short (20 ns) pulses from a strip line; the pulse energy was not over 0.14 J [6]. For SF6–С2Н6 mixtures, a specific lasing energy of about 9 J/l has been obtained with an electrical efficiency of up to 4.7% [7]. Earlier we have shown that if the discharge is maintained homogeneous, the intrinsic efficiency of an HF laser can be as high as up to 10% over a wide range of the conditions of its initiation [8]. In the work under consideration, the pumping parameters have been determined that provide the highest efficiency of electric-discharge nonchain HF and DF lasers, and the processes that affect the lasing efficiency are considered. Nonchain HF and DF lasers with a radiation pulse energy over 1 J and an electrical efficiency of up to 6 and 5%, respectively, have been developed and built for the first time. For pumping the lasers, inductor or LC generators were used; the capacitance of the primary capacitive store was С0 = 13–370 nF; the store was charged to 35 kV. The design of the laser and the measurement techniques are described in detail elsewhere [8]. The following factors that mainly affect the operating efficiency of HF (DF) lasers have been revealed: 1. Uniformity of the electric field in the discharge gap of the laser. When the uniformity of the field was violated, the efficiency of the laser was not over 1% even for mixtures with pentane, and integrated photos of the discharge showed numerous spark channels. 2. Illumination. Illumination of gas mixtures of SF6 with H2 (D2) and C5H12 with uv radiation increases the lasing energy of a nonchain laser. The effect of illumination becomes especially pronounced as the pressure of the mixture is increased. 3. The pumping pulse duration should not be over ~100 ns. In our experiments, as the duration of the discharge current in mixtures with hydrogen was increased from 100 to 250 ns, the radiation energy was observed to halve because of the constriction of the discharge. A reduced stability of the discharge and a decrease in lasing efficiency with increasing the duration of the discharge current was observed earlier for mixtures with hydrocarbons [5] and deuterium [2]. 4. Composition of the working mixture and the specific input energy. It has been revealed that if the conditions of the formation of a volumetric discharge are violated, the lasing energy and efficiency of a nonchain laser are higher for mixtures with hydrocarbons. However, when the pumping conditions are optimized, the highest efficiency of HF and DF lasers is achieved for mixtures of SF6 with H2 (D2). It has been found that the maximum intrinsic efficiency of an HF laser, ηint = 9–10%, was achieved with an input energy Ein = 30–70 J/l (the specific radiation energy was Ql ~ 3–7 J/l) and a storage capacitance С0 = 13–39 nF. Further increasing Ein and С0 reduced the lasing efficiency. For a DF laser, the intrinsic

Spectral characteristics of nonchain HF and DF electric-discharge lasers in efficient excitation modes

The spectral characteristics of efficient nonchain HF and DF chemical lasers are studied. It is found that the emission spectra of nonchain lasers operating with high efficiency are strongly broadened. Almost 30 emission lines of an HF laser and cascade lasing on the v(3-2) → v(2-1) → v(1-0) vibrational transitions of HF molecules for a number of rotational lines are obtained. It is shown that the development of discharge inhomogeneities significantly reduces the number of lasing lines in the spectra of nonchain chemical lasers. For an SF6 — D2 mixture excited by a generator with an inductive storage, about 40 lasing lines are observed on four vibrational transitions of DF molecules and the v(4-3) → v(3-2) → v(2-1) → v(1-0) cascade lasing is obtained at several rotational lines. Nonchain HF and DF electric-discharge lasers with a total and intrinsic efficiency of up to 6% and 10%, respectively, pumped from capacitive and inductive generators are developed.

Excimer laser with highly coherent radiation

Experimental studies aimed at the optimisation of an unstable resonator of an ArF electric-discharge laser are performed. Several optical schemes of an unstable resonator of a single-module laser are proposed and investigated. It is shown that the laser developed on the basis of these schemes is characterised by a high coherence (the spatial coherence length is 1 — 10 mm and the temporal coherence length is 0.5 — 30 mm at a pulse energy of 40 — 290 mJ).

Scaling of repetitively pulsed electric-discharge wide-aperture lasers

The main reasons that hamper an increase in the energy and average output power of wide-aperture electric-discharge lasers are analysed. The physical and technical requirements imposed on the laser chamber design and a pump source of the laser for the attainment of high technical characteristics are formulated. A laser design is proposed, which involves separate, electrically uncoupled modules arranged along the optical axis. A new design of the electrode unit underlies the working principle of the laser chamber of an individual module, wherein both electrodes are made of sets of plates electrically insulated from each other and connected to the common busbars of the pump source via stabilising inductors. Technical efficiencies of 3.5 % and 2.4 % for specific energy outputs of 4.2 and 2.9 J L-1, respectively, were obtained in HF and DF chemical lasers with the above electrode units and electrode gaps of 12 cm. A design of wide-aperture electric-discharge lasers based on carrying cylindrical shells was proposed.