Proceedings Volume 3268

Gas and Chemical Lasers and Intense Beam Applications

Ernest A. Dorko, Jeffrey L. Moler
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Proceedings Volume 3268

Gas and Chemical Lasers and Intense Beam Applications

Ernest A. Dorko, Jeffrey L. Moler
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 12 May 1998
Contents: 5 Sessions, 44 Papers, 0 Presentations
Conference: Optoelectronics and High-Power Lasers and Applications 1998
Volume Number: 3268

Table of Contents

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Table of Contents

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  • CO and CO2 Lasers and Applications
  • COIL and Applications I
  • COIL and Applications II
  • Gas Lasers and Applications
  • Poster Session
  • CO and CO2 Lasers and Applications
  • Poster Session
  • Gas Lasers and Applications
  • Poster Session
  • COIL and Applications II
CO and CO2 Lasers and Applications
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Phase conjugation at intracavity degenerate four-wave mixing of frequency-selective pulsed CO laser radiation
Andrei A. Ionin, Andrei A. Kotkov, Alexander K. Kurnosov, et al.
Energetic, temporal and spectral characteristics of the process of phase conjugation (PC) at intracavity degenerate four wave mixing (DFWM) of frequency selective pulsed e-beam controlled discharge CO laser radiation have been studied both experimentally and theoretically. Maximum PC reflectivity (PCR) on energy comes up to 1.5% being independent of specific input energy. The dependencies of PCR on energy have quite different behavior for various selected spectral lines. An influence of lasing and PC process in adjacent vibrational bands on PCR for the selected spectral line has been experimentally demonstrated, PCR decreasing at switching on adjacent vibrational bands. The numerical model has been formulated to simulate the temporal behavior of PC process on large scale gain (amplitude) and refraction (phase) gratings formed in the active medium of CO laser. The trend in the calculated temporal behavior of PCR is the same as for the experimental result, the theoretical PCR being higher as compared to experimental one. The resonance (amplitude) mechanism of PC process seems to be a prevailing one for DFWM of CO laser radiation.
Parametric study of a first overtone CO laser with supressed fundamental band lasing: experiment and theory
Andrei A. Ionin, Andrei A. Kotkov, Alexander K. Kurnosov, et al.
Parametric study of first overtone (FO) CO laser was carried out both experimentally and theoretically. Special optical filter was used for suppression of fundamental band lasing. The theoretical model is in satisfactory agreement with the experiment for the laser operating on He-containing gas mixture. The maximum FO CO laser efficiency of 5.5% and specific output energy of approximately 20 J/I Amagat were obtained for laser resonator with rather high useless optical losses, FO CO lasing taking place from 13 yields 11 up to 30 yields 28 vibrational transitions ((lambda) equals 2.7 - 3.6 micrometers ). Important influence of intracavity water vapor on output characteristics of FO CO laser and its spectrum, in particular, is discussed. Both theoretical and experimental results indicate that FO CO laser efficiency up to 15 - 20% and SOE up to 50 - 80 J/I Amagat can be obtained.
High-power CO2 blending-mode laser beam propagation and focus due to phase shifts
Zhiyong Wang, Tao Chen, Yue Ding, et al.
In laser materials processing, the transverse intensity distribution of focus affects processing quality greatly. In this paper, phase shifts is used to analyze high-power CO2 laser beam propagation and focus, especially the change of transverse intensity distribution along beam propagation path. From theory, the phase shifts of high-power blending laser beam determines the transverse intensity distribution. It is also found that if there contains odd mode in blending laser beam, the asymmetry of laser beam is broken. Moreover the high-power laser beam focus and unfocused diagnosis system UFF100 is used to test the beam transverse intensity distribution. Theory is accord with measurement. According to the theory, two optical transformation system is designed to attain the minimum intensity changes.
Interference effects on the efficiency of an intracavity Raman-Nath mode locker in a TE CO2 laser
Richard S. Eng, Victor H. Hasson, Yu-Lin Wang, et al.
The axial separation distance between an intracavity resonant Raman-Nath acousto-optic modulator and the secondary mirror of an unstable resonator of a TE CO2 laser has strong effects on the mode-locking efficiency. Experimental measurements showed that the mode-locker laser pulse width was a periodic function of the separation distance with a period of about 18 mm. Preliminary simple analyses using a two-beam interference model yield a periodic sine-squared acousto-optic diffraction intensity distribution as a function of separation distance with the mode-locked pulse width varying as the inverse of sine to the fourth power of the diffraction intensity. The observed pulse width was in good agreement with the calculated value using the above interference theory.
Problems that flying optics faced and their solutions
Tiechuan Zuo, Zhiyong Wang, Kai Chen, et al.
In this paper, the influence of beam quality, transverse intensity distribution and atmospheric thermal lens upon laser materials processing quality is studied. And the demand of flying optics on beam quality is analyzed. A new concept--laser processing range is proposed on account of beam quality. In order to gain the maximum laser processing area, the beam waist should be transformed to the center of the processing area. Or a good quality laser beam or optical path compensation and focusing system should be used. As well as the method of eliminate the atmospheric thermal lens is also obtained.
High-power 5-um-band CO laser and its new hollow waveguides for industrial applications
Shunichi Sato, Kouki Shimizu, Yi-Wei Shi, et al.
Recent progress in the developments of the 5-micrometers -band high-power CO laser and its flexible beam delivery system is reviewed. At a room temperature, a specific laser output of 4.0 W/cm3 is achieved with an rf-to-optical efficiency of 17%, based on a fast-axial-flow, rf discharge excitation scheme. The performance is compared with that taken when the device was operated as a CO2 laser. It is shown that the output performance of the CO laser is comparably high to that of the CO2 laser and a high slope efficiency of 28% is achieved. The output has been scaled to over 1 kW. For flexible beam delivery of the CO laser, cyclic-olefin- polymer (COP)-coated hollow fibers are newly developed. The initial power transmission experiment shows that the COP- coated hollow fibers are capable of transmitting a CO-laser power of > 200 W at a low transmission loss of approximately 0.4 dB/m.
High-speed thin metal sheet welding with high-power CO2-lasers
Arnold Braunsteiner, Markus Bohrer, Dieter Schuoecker
Welding of thin metal sheet is an application, which is more and more often applied in the field of material processing with laser. In many of these applications it is necessary to weld the thin metal with high speed. A new coaxial high power CO2-laser concept offers the possibility to weld these metals. The presented welding has been realized with sheet steels, which are coated with a zinc layer. The results of the experiments are presented with pictures of the application station and pictures of the weldseam. What is furthermore demonstrated, are the quality and the cross section of the welded materials.
Experimental research on the influence of laser-induced plasma on beam focusing during high-power CO2 laser materials processing
Tiechuan Zuo, Rongshi Xiao, Robert Volz
During high power CO2 laser materials processing, the process will be disturbed or interrupted when the propagation plasma generates and detaches from the workpiece. This phenomenon is called the shielding of plasma to the incident laser beam. It is usually considered that the plasma absorption contributes to the plasma shielding. In fact, the plasma just absorbs only about 50% incident laser energy when plasma shielding occurs. Therefore, several theoretical modes have been presented concerning on the plasma refraction and defocusing effect. However, the results presented are not verified by experiments. In this paper, we develop a simple but effective experimental method to verify the effects of plasma on the focused beam propagation according to the basic fact that plasma sustains for a while even when laser beam moves out of the workpiece at high power. It is found that the focus spot enlarges and the position of the focus shifts due to the effects of the plasma. This `Lensing Effect' of the laser induced plasma becomes more serious with the increase of the distance of plasma propagation. We conclude that the `Lensing Effect' of plasma, other than plasma absorption, is the main mechanism for plasma shielding. Due to the `Lensing Effect', the power density on the workpiece decreases seriously which causes the process be interrupted.
COIL and Applications I
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Power extraction for a supersonic chemical oxygen-iodine laser
Lutz v. Entress-Fuersteneck, Karin M. Gruenewald, Juergen Handke, et al.
The design of an optimized resonator for a supersonic chemical oxygen iodine laser (COIL) requires detailed information of the saturated gain distribution. By using diaphragms with slit apertures of various sizes at different positions in a stable resonator configuration it was possible to work out detailed information on the coupling characteristics and the influence of iodine repumping and deactivation processes. The measurements were performed at the DLR Lampoldshausen 10 kW supersonic COIL. A high Fresnel number stable resonator is coupled to the active medium and extends about 40 mm downstream from the exit plane of the expansion nozzle array. Apertures with slit widths ranging from 14% to 100% of the full resonator width were introduced into the cavity directly in front of the outcoupling mirror at a fixed z-position of 17 mm downstream of the nozzle exit. The center of another aperture with a fixed slit width of 10 mm could be positioned in flow direction from near the nozzle exit plane to about 29 mm downstream. The optical alignment was controlled with respect to the laser beam size and power density distribution at the outcoupling mirror. As a function of slit aperture the laser output power saturates well before the aperture of the resonator is fully opened. The experimental results are compared with calculations based on the theoretical model of Hager et al. Measured pressure values along the flow direction from the nozzle exit plane to well beyond the laser cavity show a strong dependence on position and width of the diaphragm, resulting from deactivation of unexploited singlet delta oxygen. After taking these pressure effects into account good agreement is found between theory and experiment. The data highlight the significance of deactivation processes for the achievable output power.
Performance characteristics of a high-pressure jet generator
Over the last several years, Rocketdyne has conducted a number of experiments on advanced jet generators. A number of these experiments were described last year at this conference. In this paper, additional detail describing the experiments are presented and new analyses are included. The experiments show that the jet generator is operating in the kinetic limited regime. A nozzle power flux of almost 400 watt/cm2 was demonstrated at a 20 kW power level.
Airborne laser (ABL) - A legacy and a future for high-energy lasers
Jeffrey L. Moler, Steven E. Lamberson
The Airborne Laser (ABL) is being built by the USAF as the primary weapon system for boost-phase defense against theater ballistic missiles. The ABL is a legacy of the Airborne Laser Laboratory built in the late 70's that demonstrated the viability of high-energy laser platforms for the future. The ABL is the first airborne laser weapon system for the 21st century, and will be the stepping stone to future high-energy laser systems.
Advanced technologies in chemical oxygen-iodine lasers for industrial applications
Masamori Endo, Syoji Nagatomo, Shuzaburo Takeda, et al.
A new concept of energy network system, `optical power system', was proposed. In this system, optical power is generated at a laser facility and it is distributed to users through optical fiber such as electric power system. The authors have started a feasibility study of this concept based on the latest chemical oxygen-iodine laser technology. 23.4% of chemical efficiency was obtained using nitrogen as buffer gas. Buffer gas cooling remarkably increased chemical efficiency. Liquid-jet type singlet oxygen generator (SOG) and twisted aerosol SOG (TA-SOG) were compared with the same setup. TA-SOG showed good performance especially in the high gas flow velocity range.
Zeeman spectra of atomic iodine in a 0- to 400-gauss B field
Ralph F. Tate, Brian T. Anderson, Philip B. Keating, et al.
A high-resolution, continuously tunable 1.3 micrometers diode laser is used as a small signal probe to investigate the Zeeman spectra of atomic iodine. A heated quartz cell containing a small amount of I2 is placed in a 0 to 400 gauss B field transverse to the axis of the laser probe. Hyperfine spectral scans are recorded as a function of B- field strength and laser polarization and are compared to theory with very good agreement.
Quantitative determination of oxygen yield in a chemical oxygen-iodine laser
Kip R. Kendrick, Charles A. Helms, Brian Quillen, et al.
With the advent of the Airborne Laser program, the emphasis of chemical oxygen-iodine laser (COIL) research has shifted toward improving the overall efficiency. A key component of COIL is the singlet-oxygen generator (SOG). To asses the efficiency of the SOG an accurate method of determining the yield of O2((alpha) 1(Delta) g),[O2((alpha) 1(Delta) g)]/[O2(total)] where [O2(total)]equals[O2((alpha) 1(Delta) g)]+[O2(X3(Sigma) g-)], has been developed. Absorption measurements of ground-state oxygen utilizing the magnetic-dipole transition, O2(X3(Sigma) g-) at 763 nm, have been obtained using a diode laser in conjunction with a multiple-pass Herriot-cell on a 10 kW class supersonic SOIL (RADICL). When RADICL is configured with a 0.35' throat, 15' diskpack, and a medium volume transition duct, with a diluent ratio (He:O2) of 3:1, the yield of O2((alpha) 1(Delta) g) in the diagnostic duct is 0.41 +/- 0.02.
Cutting performance of a chemical oxygen-iodine laser
W. Pete Latham, James A. Rothenflue, Charles A. Helms, et al.
Chemical Oxygen-Iodine Laser (COIL) is a member of the class of high power lasers for industrial applications, including the materials processing tasks of high speed cutting and drilling. COIL technology has received considerable interest over the last several years due to its short, fiber- deliverable wavelength (1.315 microns), scalability to very high powers (tens of kilowatts, cw), and demonstrated nearly diffraction-limited optical quality. Its material interaction characteristics are similar to the Nd:YAG laser since the wavelengths of these lasers are comparable. This paper documents the cutting performance of a high power, good optical quality COIL. In this experiment different types of materials were cut with the COIL, and the cut depth and width are presented here as a function of various process parameters.
COIL performance modeling
Charles W. Clendening, Jeffrey Hartlove
ICONOS (Integrated COIL Optics Nozzle SOG Model) is an end to end performance model that was developed to predict the performance of Chemical Oxygen Iodine Laser (COIL) systems. The model includes coupled routines to model the singlet oxygen generator (SOG) including ducting, the nozzle, and the laser cavity and resonator. Aerosol SOG concepts can be modeled with both one and two dimensional model versions. The model is described and experimental results obtained using a transverse uniform droplet singlet oxygen generator are compared with model predictions.
COIL and Applications II
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Parametric studies of a small-scale chemical oxygen-iodine laser/jet generator system: recent achievements
Recent results of parametric studies of an efficient supersonic chemical oxygen-iodine laser are presented. The laser is energized by a jet type singlet oxygen generator, operated without primary buffer gas and applies simple nozzle geometry and transonic mixing of iodine and oxygen. Output power of 190 W with chemical efficiency of 18% was obtained in a 5 cm gain length for Cl2 flow rate of 11.8 mmole/s. The power is studied as a function of the distance between the optical axis and the supersonic nozzle exit plane, the molar flow rates of various reagents, the BHP and gas pressures in the generator, the type of the secondary buffer gas (N2 or He) and the stagnation temperature of the gas. It is found that the power under the present operation conditions is almost unaffected by water vapor in the medium. The role of buffer gas under different conditions is discussed.
Comparative analysis of the different methods of preparing active media in a supersonic COIL
Five major methods of preparing active medium in supersonic COIL are analyzed: (1) `classical' case with upstream SOG primary buffer gas and chlorine premixing, injection and dissociation iodine vapor in the subsonic region of the supersonic nozzle; (2) mixing oxygen stream with primary buffer gas (may be cooled) downstream of SOG; (3) iodine vapor injection into boundary layers of the trans-sonic region of the small-scale grid nozzle; (4) mixing of the coflowing supersonic jets of pure oxygen and N2 + I2 mixture at close static pressures and Mach numbers; (5) mixing of co-flowing sonic (or supersonic with small Mach number) pure oxygen jets and high velocity head supersonic N2 + I2 jets for reaching very high active medium recovery pressure.
Experimental measurements of two-dimensional distribution of small signal gains in a supersonic COIL
Liping Duo, Bailing Yang, Fengting Sang, et al.
A dedicated continuous wave chemical oxygen iodine mini- laser is constructed and used to probe the 2D distribution of small-signal gains in a supersonic continuous wave chemical oxygen iodine laser. The uneven lateral gain distribution may possibly be explained by boundary layer effects.
Fluid dynamic effects on uniform droplet oxygen singlet-delta generator output
Richard D. Romea, Scott O'Brien, William J. Thayer III
Comparison of high chlorine molar flow rate tests of the Transverse Uniform Droplet Oxygen Generator (TUDOG) with a detailed numerical model reveal important fluid dynamic effects that greatly affect the device performance. These insights relative to the physics and chemistry of the TUDOG have resulted in improvements to the agreement between our TUDOG model and the experimental data.
Simple models of optical phase distortion for shock waves and turbulent boundary and shear layers
Victor Quan, Sergio E. Rodriguez
Simple analytical models are presented for assessment of the phase distortions on circular optical beams caused by shock waves, turbulent boundary layers, and turbulent shear layers. The shock wave formulas are applicable for wedge- shaped vehicles traveling at supersonic or hypersonic speeds. The boundary layers analysis is formulated for turbulent flow along on optical window surface. The shear layer solution is developed mainly for aerowindows; but it is also useful for wake flow behind obstructions, for jet flow from plumes, etc., that interfere with an optical beam. For the optical phase distortion associated with shocks, the flow conditions are evaluated using oblique shock relations and the beam deflection is based on Snell's law. On turbulent flow, both ordered and random phase variations are treated. The density fluctuations is considered to be driven by the temperature gradient. For turbulent flow over a surface, the turbulent eddy size distribution and the mean flow property profiles are based on empirical correlations. The numerical results obtained for turbulent boundary layer at various Mach numbers and altitudes are found to be in fair agreement with reported measurements from a subsonic aircraft. For the shear layer formed between two fluid streams, the method formulated is similar to those commonly employed. In the present work, however, a simple approach is applied to account for the fluid composition difference, and hence the Gladstone-Dale coefficient variation, between the two streams. Expansion waves and laminar flow conditions are also indicated.
Characterization and optimization of a rotating disk singlet oxygen generator
Frank R. Duschek, Wolfgang O. Schall
A small type of rotating disk generator (Autodisk) for O2(1(Delta) )--based on the chemical reaction between basic hydrogen peroxide (BHP) and chlorine--has been examined with respect to the variation of several parameters: the type of inert gas (Ar, He, Ne) added to the chlorine, the flowrate of chlorine at a constant ratio nCl(subscript 2)/nHe, the flowrate of helium at a constant chlorine flow rate and the composition of the BHP. In addition the material of the disks (nickel, polycarbonate, plexiglass) and the number of disks was varied in order to estimate the influence of surface effects on the O2(1(Delta) )-yield. The type of buffer gas did not affect the O2(1(Delta) )-yield (up to 55%) with a 7.4/0.6 BHP mixture (i.e. 7.4 M KOH and 0.6 M H2O2 in excess) and flowrates of chlorine and buffergas of 1 mmol/s and 3 mmol/s, respectively. Here, the chlorine utilization of 86%. Long time operation of 25 min has been achieved with BHP concentration of 6.8/0.6 resulting in the same O2(1(Delta) )-yield but in lower chlorine utilizations (78%). Replacement of the heavy nickel disks by lighter plastic disks with lower moment of inertia made the operation of the Autodisk much more flexible. The chlorine utilization was slightly affected by the material of the disks and dropped about 2% (Cl2/He-flowrates: 1/3). The variation of the reacting surface had a nonlinear influence on the utilization of chlorine (1 mmol/s; 6 polycarbonate disks: 69%, 10 disks: 84%, 17 disks: 93%). It is assumed that the smaller separation of the disks increased the amount of BHP in the free space between the disks. This reduced the available reaction surface and the chlorine transit time in the generator.
Water-vapor measurement via cavity ring down spectroscopy in the visible
Fuge Sun, Dongxu Dai, Lu Kang, et al.
Using cavity ring down spectroscopy, we recorded high resolution spectra of water overtones in the visible region. While the system is simple, experimental results have shown that the detection sensitivity is better than 2 X 10-8 cm-1. We have also studied the effects of cavity mirror reflectivity and cavity length on the detection sensitivity. The observed spectrum agrees well with the standard reference spectrum. Thus, this highly sensitive, quantitative, and widely applicable absorption spectroscopy technique proves to be capable of water vapor measurement, especially in Chemical Oxygen Iodine Laser.
Damage effect of cw COIL to PV InSb detector
Jinbao Chen, Qisheng Lu, Zhongfu Jiang, et al.
The performance change of photovoltaic (PV) indium stibium (InSb) detector illuminated by continuous wave (CW) chemical oxygen iodine laser (COIL) with different power density was measured and the damage threshold interval of the detector was achieved to be 26(0.89S) approximately 113(1.4S)W/cm2. Using the integrating sphere technology, the thermal coupling coefficient of InSb crystal material to CW COIL was measured to be 0.664 +/- 0.004. Compared with the theoretical result, the thermal coupling coefficient measured was a little bigger due to the effect of the surface defect of InSb material. The principle and damage mechanism of PV InSb detector was reviewed. The temperature rise and performance change of PV InSb detector illuminated by CW COIL were calculated with 1D thermal model. The calculated results was consistent with the experimental results.
Gas Lasers and Applications
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Efficient nonchain chemical HF lasers initiated by e-beam and self-sustained discharge
Victor F. Tarasenko, Evgenii H. Baksht, Mikhail I. Lomaev, et al.
Non-chain HF lasers initiated by electric discharge and e- beam are described. A generator with an inductive energy storage and semiconducting opening switch was used for discharge formation. The generator was shown to be very promising for development of efficient discharge HF lasers with high output energy. It produces very uniform discharge in SF6-H2(C3H8) gas mixtures at elevated pressure and increases its stability. Discharge HF laser efficiency up to 5.5% was demonstrated. Radially convergent e-beam was used to pump 30 1 HF laser. Optimal gas mixture SF6:H2 equals 8:1 under pressure of 0.45 atm was chosen to provide no more than two-fold specific output power variations across the laser beam area. Output energy as high as 115 J and efficiency with respect to e-beam energy deposited into gas mixture up to 7-8% were demonstrated. Total laser energy and efficiency with respect to deposited energy at pressure of 1.1 atm when the output distribution was non-uniform were found to be up to 200 J and 11%, respectively. The `jump' of pressure in SF6-H2 mixture at the instance of e-beam injection was found to be lower than that in excimer laser mixtures due to SF6 high density. This simplifies creation of wide-aperture e- beam HF-lasers. We expect that the use of pulse generators and wide-aperture laser setup available at HCEI enable us to develop 1 kJ non-chain HF laser initiated either by self- sustained discharge or e-beam.
Acceleration of electrons in thin metal films by strong ultrashort laser pulses
Andrey V. Lugovskoy, Alexander V. Zinoviev, Timurbek Usmanov
The possibility of effective electron acceleration in a thin solid film exposed to irradiation by two power ultrashort laser pulses are discussed. The acceleration effect is caused by resonant action of the radiation on electrons oscillating across the film with frequencies close to the laser frequency. The numerical analysis of the relativistic equations of electron motion is conducted.
Closed-cycle 1-kHz-pulse-repetition-frequency HF(DF) laser
Michael R. Harris, A. V. Morris, Eric K. Gorton
We describe the design and performance of a closed cycle, high pulse repetition frequency HF(DF) laser. A short duration, glow discharge is formed in a 10 SF6:1 H2(D2) gas mixture at a total pressure of approximately 110 torr. A pair of profiled electrodes define a 15 X 0.5 X 0.5 cm3 discharge volume through which gas flow is forced in the direction transverse to the optical axis. A centrifugal fan provides adequate gas flow to enable operation up to 3 kHz repetition frequency. The fan also passes the gas through a scrubber cell in which ground state HF(DF) is eliminated from the gas stream. An automated gas make-up system replenishes the spent fuel gases removed by the scrubber. Total gas admission is regulated by monitoring the system pressure, whilst the correct fuel balance is maintained through measurement of the discharge voltage. The HF(DF) generation rate is determined to be close to 5 X 1019 molecules per second per watt of laser output. Typical mean laser output powers of up to 3 watts can be delivered for extended periods of time. The primary limitation to life is found to be the discharge pre- ionization system. A distributed resistance corona pre- ionizer is shown to be advantageous when compared with an alternative arc array scheme.
Powerful eximer laser systems with gamma-pumping for plasma physics and ICF research in the 0.1- to 1.0-MJ energy range
Evgeni K. Bonyushkin, R. I. Ilkaev, A. P. Morovov, et al.
Results of experimental and calculation and theoretical investigations on eximer laser pumping by (gamma) -radiation powerful source is presented. Based on the results of investigations there are proposed laser systems for study of thermonuclear targets compression physics.
Mathematical means of the process data acquisition for sensor engineering
Georg Hutflesz, Markus Bohrer, Stephan Fazeny, et al.
Economical considerations in the industrial manufacturing of technical components force for improvement of established material machining processes. In the field of laser cutting and welding as a young technology, higher decollating and welding rates do always require quality inspection with new sensor combinations. Higher mathematical means are used to find relations between quality and measured signals with its aid the process is to be controlled. Combination of derivatives, integrals or statistical data give information of the quality. Even knowledge about the material weighted with rules of fuzzy-logic helps to control cutting speed and laserpower. In addition to different algorithms, those lead to evaluation offline the process, means of the online check are developed and presented.
Process monitoring for laser welding using a quality sensor for cutting
Stephan Fazeny, Andreas Penz, Markus Bohrer, et al.
In typical optical sensor setups for CO2 laser material processing there are scraper mirrors or beam selectors used to allow sensor positions, which have an coaxial path for both the laser beam and the monitored visible or near- infrared signal. For the monitoring and controlling of the laser welding process it is of interest to get information on the plasma stability. A two color photodiode sensor which has been successfully tested for quality monitoring of both cutting and ablation has been used for welding in order to find correlations between the sensor signal and the quality of the weld seam. Results and comparisons between cutting and welding will be presented.
Poster Session
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Features of self-action of an optical beam with screw dislocation propagating through a near-resonant saturated medium
Vladimir L. Derbov, Olga M. Priyutova
Near-resonance self-action of an initially Gaussian CW beam having a screw dislocation of the wavefront of its center is studied by means of numerical modeling. Peculiar features of the induced lens manifestations associated with the beam topology are revealed.
Microcomputer-based automatic laser measurement system for circular parts
Gonghe Feng, Qingming Chen, Mao-hua Zhou, et al.
This article introduces a system which utilizes the Fourier transform of laser beam to extract defect data from part, and then carries out optical information processing under microcomputer control. Automatic measurement and classification of axial and radial jitters on precision parts, automatic feeding and printing of statistical parameters are implemented. Finally, the measurement error of this system is analyzed theoretically. Constructional simplicity, low cost, highly automatic, and good measurement reliability are features of this system. Practical measurement on a large amount of parts shows that the proposed system effectively alleviates worker's laboring tension and increases the production rate.
Novel self-switched high-repetition-rate HF(DF) laser
Michael R. Harris, David J. Jackson, Philip K. Milsom
We present results obtained from a new class of self- switching, high repetition rate, HF (DF) laser. The laser utilizes a magnetically stabilized longitudinal discharge, transverse to a high velocity gas flow. The gas mixture is pre-mixed, and consists of He, SF6 and H2(D2) in the ratio 1000:9:2 at a total pressure of around 52 torr. A centrifugal fan recirculates the gas and provides a linear flow velocity of 80 ms-1 in the gain region. Permanent magnets provide the stabilizing magnetic field of approximately 1400 Gauss. This magnetic field ensures that the discharge and optic axes are co-linear. The discharge length is 30 cm, and the gas flow channel 0.5 cm in height. Conventional stable resonators were used to extract the laser energy. We show that the self-switching behavior is a result of the negative I-V characteristic in the positive column of a constricted SF6 discharge, coupled with the current limitations imposed by the external electrical circuit. It is found that the switching frequency, and therefore lasing repetition rate, can be controlled via either the applied discharge current or the RC time constant for the external circuit. Higher discharge currents and shorter time constants both result in higher pulse repetition frequencies. We have demonstrated self-switched lasing at repetition rates from 400 Hz up to 17 kHz.
Three-electrode CO2-laser with a middle control electrode
Valeriy V. Borovkov, Sergey L. Voronov, Boris V. Lazhintsev, et al.
There was developed a three-electrode discharge CO2- laser of atmospheric pressure. The discharge in the gaps was ignited sequentially in time at the application of high- voltage pulse to the middle control electrode. A storage capacitor of the main discharge is connected directly to the other two electrodes. The system and the operation method allow to form the discharge with the input energy up to 250 J/I-atom with 11,5% laser efficiency. The voltage on the main laser electrodes before the discharge ignition was in the range of 0.6...0.9 of the static breakdown voltage for the laser medium. The energy for the discharge formation was only 1...3% of the stored pump energy. Such system and the operation method can reduce by tens of times the load on the switches in the CO2-laser.
CO and CO2 Lasers and Applications
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Pulse selection from a mode-locked TE CO2 laser output using a resonant acousto-optic modulator
Yu-Lin Wang, Richard S. Eng, Michael Groden, et al.
The pulse separation and associated range ambiguity of a CO2 laser radar using a pulse burst waveform consisting of 1.3 ns mode-locked pulses spaced 40 ns apart was successfully doubled to 80 ns and 12 m respectively by suppressing every alternate pulse. This was done by sending the mode-locked laser output beam with 40 ns pulse spacing through a resonant Raman-Nath acousto-optic modulator driven at 18.75 MHz which is 1.5 times the drive frequency used to intracavity mode-lock the CO2 laser transmitted. The spatial filtering of the diffracted pulses results in the suppression of the alternate pulses to better than 15 dB. The throughputs for the unsuppressed pulses were greater than 95%. The laser radar capability in detecting large targets,
Poster Session
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XeCl laser based on a three-electrode system of a double discharge formation
Valeriy V. Borovkov, V. V. Voronin, Sergey L. Voronov, et al.
The paper describes a three-electrode electric-discharge XeCl-laser, in which the discharge ignition takes place, when a high-voltage pulse is delivered to a middle control electrode, a capacitor bank of the main discharge is connected directly to two other electrodes. The three- electrode system of a double discharge formation provides a sequential in time breakdown of two discharge gaps followed by a general discharge current. The laser reached the high efficiency up to 3.7% with the fast commutation < 5% from the pump energy and a significant decrease of the load on the elements of the electric system of the laser pump supply.
Intracavity wide-angle beam pointing in mid-IR gas lasers
Oleg B. Danilov, Vladimir V. Danilov, Aleksandr I. Sidorov, et al.
The present work is the further evolution of our studies on wide-angle intracavity beaming in 3-10.6-micron gas lasers by space-time light modulators.
Use of a fast ionization wave for laser pumping
Oleg V. Boutine, Leonid M. Vasilyak
The effective laser generation depends greatly on pumping conditions. To provide fast uniform atomic or molecular levels excitation special mechanisms are often required. One of them is the use of a fast ionization wave (FIW) which gives high-excited uniform plasma due to its high propagation velocity and great values of E/p in it. In experimental works carried out at our laboratory, where we investigated both cathode and anode -directed waves, it was fo,.md dependence of ionizing wave velocity on an electrical potential of the high voltages electrode and gas pressure. There are several works in which FIW has been successfully used for laser pumping especially for lasers on self-terminated transitions. For example in our laboratory such wave was successfully applied for nitrogen laser pumping. Here investigation is focused on several phenomena in such waves and on theoretical models of FIW. The mechanism of wave propagation is closely connected with ionization processes inside the narrow structure of the wave front where the electrical field has the typical shape of solitary wave. The several models of ionizing wave are discussed. Using cross-section averaging of the basic equations a numerical code is developed for investigation of super - high velocity wave propagation. Our numerical model is based on the continuity equation for electron and on the modernized non-linear equations describing evolution of the electrical potential. Equations for electron energy and drift velocity are significantly improved. With the help of this model it is possible to investigate evolution of wave and to trace dependence of the propagation velocity, energy absorption and different atomic levels excitation on main parameters: voltage, gas pressure, radius of discharge tube, initial electron concentration. The model can be also applied to backward shock of lightning. Typical values of breakdown parameters in modeling were V=32 kV. p=l-SO ton, potential growth duration on high-voltage electrode of 10 ns.
CW deuterium fluoride chemical laser with reactant combination C2H4/NF3
The characters of combustion driven cw deuterium fluoride (DF) chemical laser with C2H4/NF3 reactant were numerically investigated. The numerical simulation was carried out using compressibility scaling method--a finite difference technique for the numerical integration of the steady and unsteady Navier-stokes equations for reactive flow. The small signal gain and the flow field were calculated. The numerical results shown that active zone length of the cw DF chemical laser with C2H4/NF3 is very long, which is about 6 cm, and the average cavity pressure is about 7 torr as the combustion pressure is about 1.5 atm. These results shown that the DF chemical laser with C2H4/NF3 is suitable for high cavity pressure performance.
Gas Lasers and Applications
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Possibilities of continuously tuning a CO laser at high pressure
Guangyu He, Yuxing Chen, Jun Guan
On the basis of gain coefficient calculation it is shown that the frequency of the CO laser can not be continuously tuned over 5 - 8/tm region by means of increasing its pressure beacause of the resonant absorption of the R and P branches. Keywords: gain coefficient, continuously tuning, resonant absorption
Poster Session
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Output characteristics and applications of multi-electrode-pair laser
Xiangyen Li, Shibao Wu, Yongqin Zhang
A TEA CO2 laser with multi-electrode-pair in one optical resonant cavity is being studied. This kind of laser can obtain the output of multi-light pulse-pairs of high- intensity, and time interval of the pulses can be continuously regulated. Measure of the velocity of high- speed moving objects and objective detection are analyzed in principle according to the technology of pulse coding. Applications in this kind of laser in holography interferometry is also introduced in this paper.
Fluoride thin films for reflective coatings at 157 nm
An overview of the excimer laser market shows the trend towards shorter operating wavelengths. The optical properties of vacuum ultraviolet materials are described and the design of a reflective fluoride multilayer coating for 157 nm is given. Practical considerations and techniques used for the coating manufacture are discussed. Results on coating performance and film properties are presented. Finally, a summary reviews the relevant aspects and salient points encountered during the project with an indication of the direction of any subsequent follow-up work.
COIL and Applications II
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Chemical oxygen-iodine laser (COIL) beam quality predictions using 3D Navier-Stokes (MINT) and wave optics (OCELOT) codes
Alan I. Lampson, David N. Plummer, John H. Erkkila, et al.
This paper describes a series of analyses using the 3-d MINT Navier-Stokes and OCELOT wave optics codes to calculate beam quality in a COIL laser cavity. To make this analysis tractable, the problem was broken into two contributions to the medium quality; that associated with microscale disturbances primarily from the transverse iodine injectors, and that associated with the macroscale including boundary layers and shock-like effects. Results for both microscale and macroscale medium quality are presented for the baseline layer operating point in terms of single pass wavefront error. These results show that the microscale optical path difference effects are 1D in nature and of low spatial order. The COIL medium quality is shown to be dominated by macroscale effects; primarily pressure waves generated from flow/boundary layer interactions on the cavity shrouds.
Collisional broadening coefficients for oxygen and water absorption lines used in COIL diagnostics
Steven J. Davis, William J. Kessler, Matthew Bachmann, et al.
For the past several years we have been developing diode laser-based diagnostics for the Chemical Oxygen Iodine Laser (COIL). These systems operate by scanning a tunable diode laser over complete absorption lines in species such as water and oxygen. In this paper we describe measurements of the collisional broadening and shifts of absorption transitions in both water and oxygen. These results have implications for the interpretation of data such as the flow temperature when the diagnostics are used on COIL systems.