Copper vapor laser (CVL) devices of 60 mm bore have been developed for atomic vapor laser isotope separation, and recently an average power per device of over 200W (211W maximum) has been achieved by expanding the discharge length to 3000 mm. In order to further improve the power output by increasing the discharge volume, it is important to supply discharge energy efficiently to the laser tube and to maintain the optimum copper vapor density in the larger volume. Now a CVL discharge circuit has been designed using a CVL discharge simulation code able to calculate time-dependent plasma resistance. In addition, a thermal insulation structure that effectively maximizes the laser gain volume has been designed using a thermal simulation code that takes thermal conduction and emission loss from the tube ends into account. This code yields results which show good agreement with experimental data. The results demonstrate that codes which simulate electrical and thermal characteristics are effective tools in the design of high-power CVL devices. In this paper, the methods of designing CVL electrical circuits and laser head structures using CVL simulation codes are reported, and some resulting high-power devices are discussed.
The authors have observed multiphoton induced emission from supersonic nozzle beams of Cr(CO)6 and (C6H6)Cr(CO)3 which is extremely intense and longlived. Certain types of emission lasting many tens of microseconds, which the authors have definitively assigned as due to transitions originating at a 7D manifold of J levels in neutral chromium atoms, can only be observed using (C6H6)Cr(CO)3 and other arene chromium tricarbonyls. This situation only occurs because of structure dependent intramolecular dynamics in (C6H6)Cr(CO)3 which occur during the multiphoton dissociation and which do not occur during multiphoton dissociation of Cr(CO)6. Taken together; the precise wavelength needed to produce these levels, the very low amount of focusing needed to observe the emission, and the high vapor pressures attainable using organometallics strongly suggest that this discovery could lead to the development of a new class of lasers, optical amplifiers and parametric oscillators. In this case, lasers operating near 465 nm and 1.3 micrometers may be feasible. The scheme could also be utilized to produce 'metal vapor' type lasers using a wide variety of refractory metal atoms as the basis of the gain media.
Pointing stability, beam divergence and beam generating mode have been studied in a copper vapor laser equipped with a modified off-axis unstable resonator. In the modified cavity design, the convex mirror is coupled via the edge of a flat scraper mirror, in contrast to the common resonator design where the edge of a convex mirror is used for feedback. As a result, the pointing stability improved, and day to day fluctuations were as small as 200(mu) rad. The beam divergence was about nine times the diffraction limit for the green laser line. The relatively high beam divergence, as well as spatial and temporal analysis of the beam generating mode, shows that a beam traversing the active medium only three times constitutes the useful laser radiation. Possible mechanisms causing the dominance of the triple-pass beam are discussed. An explanation for the impact of the beam generating process on the pointing stability and its improvement in the new cavity design is suggested.
Efficient source of visible laser light produced by metal vapor laser technology is serving and creating a variety of new applications in industry. Copper, gold, manganese, lead and strontium lasant-based metal vapor lasers (MVLs) have all been made commercially available in recent years. They are reliable laser systems with different visible wavelengths that serve different applications in science, medicine, military and commercial developments. This article summarizes the present status and future goals of MVL applications and their respective metal vapor laser packaging and performance requirements.
The authors have developed a magnetic-pulse-compression type solid-state pulse power supply. The lifetime of a solid-state device is expected to be much longer than that of a thyratron. Two parallel connected gate-turn-off thyristors generated a long pulse, which was compressed to 0.27 microsecond(s) ec by a three-stage magnetic pulse compression circuit. The average power of 8.2 kW was able to be obtained when a dummy load was connected instead of copper vapor laser (CVL). This pulse power supply has been applied to a CVL with a plasma tube of 70 mm inner diameter and 1.5 m discharge length, and has been successfully operated.
Pre-charging of peaking capacitors has been tested on a high-repetition-rate transversely excited atmospheric CO2 laser. The peaking capacitors, connected to the discharge electrodes, were divided into two blocks in series. One part was pre-charged by a DC voltage source and another part was pulse-charged. An efficiency of over 6% was obtained by only 7 kV pulse voltage, and was higher than that obtained in a charge-transfer-type circuit. A high repetition rate operation up to 1 kHz was demonstrated.
Copper vapor laser (CVL) was designed on the basis master oscillator (MO) - spatial filter - amplifier (AMP) system which is placed in thermostable volume. Processing material is moved by means of CNC system GPM-AP-400 with +/- 5 micrometers accuracy. Several cutting parameters are considered which define the quality and productivity of vaporization cutting: efficiency, cutwidth, height of upper and lower burr, roughness, laser and heat affected zones. Estimates are made for some metals with thickness 0.02 - 0.3 mm and cutwidth 0.01 - 0.03 mm. The examples of workpieces produced by CVL are presented.
The multiple spectral structure of the 578.2 nm copper laser line of a discharge heated copper vapor laser has been found under a fixed operating condition. The multiple structure can be classified into three cases. The structure changes as the neon buffer gas pressure increases. In addition, the stero-relation among the relative peak intensity difference of the line shape, the peak frequency difference, and the neon pressure, have been measured and explained qualitatively.
The dissociated bromine in CuBr laser has serious effects on the life-time of CuBr laser and the stability of the discharge plasma so it is important for the long-lived sealed-off CuBr lasers. The adsorption of bromine on the surface of the copper around the electrodes was measured by an X-ray Energy Dispersive Spectrometer. It is found that the dissociated bromine from CuBr molecule after collision in the laser discharge plasma is negative bromine ion, no positive bromine ion existed. On the average the atomic percentage of the adsorbed bromine is about 20%. The radial distribution of the atomic percentage of bromine around anode copper is given and has been explained qualitatively.
Parameters of output diffraction-limited beam from copper vapor laser are investigated for different unstable resonators: self-imaging, self-filtering and modified self-filtering. Three types of intensity distribution (uniform, Gaussian and Bessel) in near-field (output beam) and far-field (focal plane) zones are considered with 20 mm active medium diameter. Divergence of these beams depends on phase and amplitude distortions by active medium gain saturation. Angle beam position dependencies are considered versus position of more curves mirror and field-limiting aperture of unstable resonators.
The electron-beam pumped XeF(C yields A) excimer has been investigated as a novel gain medium for ultrashort pulse, high power amplification in the visible spectral region over a wide range of laser pulse durations. Gain measurements for 100 ps and 800 fs pulses resulted in a small signal gain coefficient of 3%/cm and a saturation energy density of 80 mJ/cm2. For 250 fs pulses, a saturation energy density of 50 mJ/cm2 was observed. Narrowband absorbers in the XeF(C yields A) spectrum could be bleached out, yielding a smooth gain profile of 60 nm bandwidth. An unstable resonator was designed with particular consideration of the small XeF(C yields A) gain coefficient and optimized energy extraction in a single pulse output. A maximum pulse energy of 275 mJ was obtained by amplification of 250 fs pulses at 490 nm wavelength, generating laser powers in the terawatt range. The beam quality of the amplified pulses was within 1.3 times the diffraction limit, making possible focused intensities in the 1018 W/cm2 range.
Rare-gas halide gas mixtures such as helium, xenon and hydrogen-chloride were investigated using L-band microwave excitation techniques. For the experiments a magnetron generator with a pulsed power of 2.5 MW, a pulse duration of 4 microsecond(s) and a repetition frequency of 10 Hz, a klystron transmitter with a pulsed power of 10 MW, a variable pulse duration from 500 to 6000 ns, and a maximum repetition frequency of 430 Hz were applied. In a gas mixture consisting of He/Xe/HCl equals 1000/10/0,5 at a total pressure of 1 bar two laser transitions were observed to operate simultaneously. One in the UV, i.e. the XeCl laser, and the second in the IR, i.e. the Xe laser at 2.03 micrometers . It was found the HCl content is important for the Xe laser performance. Up to a factor of 5, more IR laser pulse energy was measured when the HCl concentration of the mixture was optimized. For both lasers almost the same pulse energies were obtained, 15 (mu) J respectively. The pulse duration was 65 ns for the UV and 150 ns for the IR laser. In all experiments the discharge tube had an inner diameter of 2.6 mm and an outer diameter of 10.3 mm. The excited discharge length was 438 mm. However, when a larger cross-section of the discharge tube was chosen, a maximum UV pulse energy of 1.8 mJ in a 16 ns long pulse was obtained.
Real-time analysis of XeCl gas mixtures are described using mass, infrared, and ultraviolet spectrometry while monitoring output power from the laser. In separate experiments, the effects of dominant gaseous impurities are measured individually. Combining these data into a model, power loss from the XeCl laser can be predicted.
A laser output power control system which has an ability to realize high stability of the laser output power in long-term operation is proposed for high-power rare-gas halide excimer lasers. The system has a function of maintaining laser gas conditions, mainly the halogen gas concentration, constant against the gas degradation in the laser tube. As a result the laser output power is stabilized at near maximum available power. The system has been applied to a 20-W UV-preionozed XeCl excimer laser and the laser output power has been stabilized for 8 hours successfully with a fluctuation less than +/- 2% at 20 W.
Precision openings for construction of an optical backplane have been machined in an optical fiber using an excimer laser operating at a wavelength of 193 nm. The openings were made by imaging the laser beam onto the polymer fiber cladding with a telescope, then ablating the cladding with a sufficient number of pulses to expose the core. Circular openings measuring 250 and 625 microns and elliptical openings measuring 650 X 350 microns have been made in the cladding of a 1 mm polymer-clad silica fiber. Examination by scanning electron microscopy reveals that the best quality openings are obtained with either the smaller circular geometry or the elliptical geometry. For various reasons, elliptical openings, with the major axis oriented along the longitudinal axis of the fiber, appear more suitable for tap construction. Individual optical fiber taps have been constructed by attaching a tap fiber to a laser machined opening in a central fiber using an ultraviolet-curable acralate. Individual tap measurements were made on the elliptical and the 250 micron circular openings. In addition, a triple tap assembly was made using elliptical tap openings. These results indicate that the excimer laser machining technique may be applicable to the construction of a linear tapped bus for optical backplanes.
The results of comprehensive investigations of a compact UV-preionized XeCl laser are presented. It has been shown that the gas lifetime increased to more than three times if BCl3 was used as a halogen donor instead of HCl. The analysis of chemical degradation products suggests the possibility of a 'self-regeneration' of BCl3-containing gas mixtures, where volatile contaminants can be converted into solid products. The temporal and spatial dependences of the densities for several plasma components: Ne*, Xe*, Xe+*, Cl-, XeCl* and boron atoms were measured by the dye laser absorption (gain) probing. The halogen donor depletion in volume and constricted phases of the discharge was traced by the temporal dependence of the ground-state boron atoms density. The evolution of filamentary instabilities in the discharge was monitored from the Stark broadening of Xe* absorption lines.
A large scale pulsed laser system with heated tantalum foils as the blackbody pumping source was built in the laboratory. A deeper understanding of the effects of pumping configurations and laser modes on the blackbody pumped CO2 laser has been achieved through parametric studies using this system. Theoretical analysis and experimental investigation show the feasibility of a slab pumping scheme which may be applied to large scale transverse flow laser systems. The use of an 8 mm tube with waveguide quality enables generation of both gaussian and waveguide modes in the same structure with different optics setup. The experiment demonstrates that high waveguide cavity losses can be prevented with large bore structure (> 4 mm) and the advantage of better filling of the laser gain region by waveguide modes is clearly observed. The size scaling studies also indicate that there are similarity relations of the optimum laser parameters between different sizes of tube in optically pumped gas lasers.
The motivation in initiating these calculations is to allow observation of the frequency evolution of a laser pulse as it propagates through an amplifier and then through a sequence of amplifiers. The question this paper tries to answer is what pulse shape must be produced out of a front-end oscillator so that after it propagates through the whole Aurora KrF fusion amplifier chain it will result in high energy, broad-band laser fields of a given bandwidth that can be focused onto a fusion target. The propagation of single frequency source through an amplifier with distributed loss was considered by Rigrod and was significantly expanded by Hunter and Hunter. The latter included amplified spontaneous emission [ASE] considerations both in the direction of and transverse to the coherent field. Analytic solutions that include forward and backward propagating fields and ASE were derived which were transcendental in nature but allowed for fairly easy computer calculations. Transverse ASE were calculated using the saturated gain resulting from longitudinal fields and were used to compare this with the longitudinal fields. Thus, the influence of the transverse ASE were not folded back into the longitudinal field equations. Large computer programs are now available at LANL which include the influence of transverse ASE on the longitudinal fields. However, none of these considerations have worried about the changes in the frequency characteristics of the propagating field or of how each of the frequency field components contributes to the saturation of the gain. The inclusion of full frequency characteristics to the analytic solutions of Hunter and Hunter proved impossible at least for this author and a new calculation technique was developed and is the subject of this talk.
Principal chemical reactions in the electric discharge CO-laser plasma, preventing the efficiency and output power increase, are analyzed. It was found that the negative influence of CO2-impurity is manifested due to the picking of CO-molecule vibration energy by CO2 molecules and following fast V-T relaxation of these molecules. The density of CO-molecules in plasma can be reduced by conversion of these molecules into radiating molecules on the surface of the plasma-activated carbon. The applied technique provided the fast chemical reactions that preserve CO molecules in the plasma. The conversion of oxygen-bearing impurities on carbon surface is used for cleaning and maintaining the optimum laser mixture in sealed-off electric discharge CO-lasers featuring high-efficiency and linear power. This technique turned out to be effective for producing a high-power multibeam laser with long-term laser mixture quality up-keep and can be useful for powerful electric discharge CO-lasers operating at fast flowing and room temperature cooling.
Data on the laser generation at (eta) equals 585.3, 703.2, and 724.5 nm on pumping of He-Ne-Ar and Ne-H2 mixtures with a short electron beam and on the generation on Xe atomic transitions are presented.
The CO-CO2 laser, operating at laser transitions belonging to both CO and CO2 molecule spectra, are described. The multiple alternate changes of spectrum regions have been obtained due to chemical transformations of CO2 molecules to CO and vice versa. The transformations of radiating molecules are provided by volume and surface plasma-chemical reactions of CO and CO2 molecules with oxygen and carbon respectively. The device needs no low temperature cooling or flowing facilities. Also, both laser wavelength regions can be realized simultaneously.
In this paper an originally designed TEA CO2 Laser with simple construction and easy assembly/disassembly as its design advantages is introduced. Double continuously adjusting photo-pulses with 0~150 microsecond(s) time separations under a single excitation can be obtained by the laser. The characteristics of control circuits and the experimental results are also described.
In the present study, the optimal design of CO2 laser was investigated and a mathematical model developed for this purpose. The mathematical model covers energy levels, transitions of molecules between these levels and molecular collisional decay mechanism. The effect of gas mixture ratios on molecular population at excited states and on efficiency are interpreted as results.
On-line process control equipment for CO2 laser cutting is not available for industrial applications today. The majority of the industrial cutting machines are regulated off-line by highly-educated staffs. The quality inspection of the samples often is visual, and referred to different quality scales. Due to this lack of automatization, potential laser users hesitate to implement the cutting method and hereby to benefit from the advantages offered by the method. The first step toward an automatization of the process is development of a process monitoring system, and the investigation described in this paper is concentrated in the area of on-line quality detection during CO2 laser cutting. The method is based on detection of the emitted light from the cut front by photo diodes. The detection is made co-axial with the laser beam to assure independence of the chosen processing direction. ZnSe mirrors have been placed in the beam path, reflecting the laser beam but transmitting the visible light emitted from the process. Cut series of 2, 6 and 8 mm mild steel have been performed. Fourier Analyses and statistical analyses of the signals have been undertaken, and from these analyses it is possible to estimate the surface roughness in the cut kerf, dross attachment at the backside of the work piece and the penetration of the laser beam.
In industry, a large number of mechanical pieces need a specific treatment in order to improve their behavior towards aggressions such as erosion, corrosion, fatigue and high temperature. These treatments consist in transformation hardening, surface melting, surface alloying or surface cladding. High power continuous-wave C02 laser has been pointed out as one of the most attractive way to carry out such surface treatments.With respect to other conventional ones, this method has got many advantages such as energy transport without any material support, adaptable beam shaping, precise localization of the energy deposit, very thin thermal affected zone, etc... In this paper, surface melting of cast irons and of 304 L stainless steel are principally studied. The case of cast iron surface melting is of great interest because of the widespread use of this material in industry. In particular, in automotive industry, cast iron has been used for the manufacturing of camshafts, diesel motor cylinders, etc In the case of surface melting, the liquid region may be the seat of very important motions due to high temperature gradients at the surface of the melted pool. This convection has a great influence on the final structure of the thin treated layer of the metal specimens. In order to improve our knowledge on laser-material interaction, a new method for the visualization of the melt geometry and of the melt dynamics is necessary. This method involves an analysis of the temporal stability of the melted pool and velocity measurements of solid particles at the surface of the bath as well. The thermal field at the surface of the pool is also obtained by means of an optical method. In the first part, a brief overview of the main physical processes which take place during laser-matter interaction is presented. In the second part, the experimental set-up is described, and then, the first results are analyzed in the last part of the report.
A pulsed gas laser with a plasma cathode and a metal anode in CO2:N2:He mixture has been experimentally studied. It was found that the discharge sliding along the surface of a dielectric can be used simultaneously as a UV-preionizer, a plasma cathode, and a laser radiation source in the UV band. In this way, it is possible to design a two-frequency laser emitting in the UV and IR spectral bands, with the capability of controlling the delay between the two laser pulses.
A modeling scheme is presented for an iodine monofluoride chemical laser (IFCL) within the F-NH3-IF system which comprises 14 kinetic processes. The number densities of IF(B) and relevant excited species, and gain coefficients of the IF(B, v' equals 0, J' equals 21)yields(X, v' equals 5, J' equals 20) transition are obtained together with the influence of cavity pressure thereon by using Gear's auto-integration method on a PDP 11/73 Computer. Numerical calculation gives a small negative gain for a cavity pressure Pe < 4 Torr and a small positive gain for Pe > 6 Torr, respectively. It is predicted that Pe > 10 Torr would be necessary for lasing. The major energy transfer channels for IF(B) production are also analyzed.
The application of excimer lasers for processjng of polymers is well established. PMMA, e.g., (poly methyl metacrylate) does not exhibit any trace of thermal stress like discoloration or bubbles, not even loss of elasticity, thus cutting or punching operations can be performed with increased quality and speed as compared with CNC-lathe. Poly imide, e.g., can be drilled or machined to micrometer precision levels, and there is no known alternative to excimer laser processing. These two polymers are presently already machined commercially by excimer lasers. The reason of the superior results are, of course, determined by the properties of the laser beam. These are: photons in the ultraviolet spectral region, high power density, and the temporal form of short pulses. The absorption of UV-photons leads to fragmentation of the long molecular chains, which constitute the polymer. Of course, the energy of the absorbed photons needs to be above the onset of this process. If the concentration of the fragments is sufficiently large, they burst out from the irradiated surface, carrying away the laser beam energy before it can migrate to and affect the remaining substrate. Material removal will begin only if the internal pressure becomes large enough. This is the explanation, why the effect requires a threshold energy density to be overcome. The subtrate receives only a negligible amount of heat. The expansion of the vapor cloud is so rapid that the created shock wave is clearly audible. The loudness of the 'click" increases with increasing energy density. To distinguish this effect of material removal from the normal photon induced heating, it was given the name "ablative photodecomposition". Choosing the wavelength and adjusting the energy density are the main preparations for production. Due to the efficiency of fragmentation, in the case of poly imide carbon is formed in the vapor and deposited as black debris around the processed areas, regardless which excimer wavelength is applied. If it is unwanted on the final product, and a cleaning step is undersired, the use of processing gas (e.g. a mild stream of Helium during irradiation) will leave a clean surface . On PMMA beam scanning is recommendable to keep the surface cool; irradiating this polymer at one spot at high repetition rate would otherwise allow energy transfer from the hot vapors to the substrate. Today the collection of data on most polymers of technical importance and their appropriate processing parameters is finished. Until recently, there was only one polymer of high importance with no excimer laser beam parameters to achieve comparable quality: poly tetra fluoro ethylene PTFE (brand name: Teflon).
A thermionic X-ray generator using Philips scandate cathodes is described for the preionization of a high repetition rate XeCl laser. Currents as high as 40A from an 8 cm long line source can be extracted from an array of 10 cathodes each having an emitting surface of 0.011 cm2 (360 A/cm2).
The paper presents investigation results on amplification and generation in supersonic flow of laser medium, flowing along laser axis, namely: 1. Opportunity to suppress laser amplifier self-oscillation and to increase maximum permissible gain is demonstrated. 2. It is shown that in supersonic flow medium splitting of gain line takes place and for that reason oscillation is double frequency in a flat resonator laser and single-frequency in each direction in a ring laser. 3. The efficiency of flowing medium laser as a master oscillator for high power lasers with phase conjugation mirror is demonstrated.
At present opportunity to apply phase conjugation phenomenon to laser facilities is widely investigated. High power nanosecond laser designs with SRS mirrors are considered as well. To discuss such designs it is very important. to obtain experimental data on performance of kilojoule class lasers, having aperture > 0.5 m, with phase conjugation. However, there is no publications in literature about experiments of such level. In our paper we present first experimental data, having been obtained on gas iodine laser with (0.4 - 1.2) m aperture and 6 kJ radiation energy in a nanosecond pulse in a single channel, using SBS mirror.