Very early in the history of lasers it was recognized that the high power beam from a ruby laser could perform a variety of practical tasks. It could weld and drill holes easily; enthusiasm for exploitation of these capabilities ran very high. However, it took many years before lasers were employed in a practical sense by industry. The early lasers were not reliable and durable enough. Even though a laser could perform many useful tasks well, it was often unfeasible economically.
Recent advances in laser technology have resulted in the development of multikilowatt lasers which have been engineered for industrial applications. This paper will review these developments for CW CO2 lasers and the application of these lasers in the metal-working industry. The physics and engineering problems associated with obtaining a uniform electric discharge at the required high power densities will be reviewed. The applications of multikilowatt lasers in the metal-working industry reviewed in this paper will highlight the newer processes of surface hardening and surface alloying. These are processes which have recently impacted the automobile industry to replace conventional hardening and hard facing techniques.
High power lasers are cost-effective tools for material processing. These industrial machines are being introduced and used in an increasing number of metalworking applications. High power lasers can provide improved processing when compared with other metalworking methods and offer advanced techniques for the future. A laser beam can produce a deep, narrow weld zone at high rates and with low distortion. Transformation hardening can achieve depths of 0.5 mm at rates of 1100 mm2/sec. Laser cladding can melt cladding or hardfacing metal onto a selected surface with dilutions as low as two percent. Laser alloying can modify the surface chemistry of a localized area on a part to resist wear and corrosion.
The ability of lasers to produce very high power densities is the key characteristic which has led to the recent emergence of the laser as an important manufacturing tool. The general areas of industrial material processing which are discussed here are 1) welding, 2) cutting and drilling, and 3) surface hardening. The basic mechanisms involved in these processes are discussed and both theoretical and experimental results are described. In each case specific examples are discussed to further demonstrate the nature of the process, as well as to give an indication of the wide variety of successful industrial applications.
Current high power laser welding technology is reviewed. The nature of the beam-material interaction, the influence of laser, process and material parameters on welding response and the unique characteristics of the process are discussed. Examples are given of representative laser welding performance in ferrous and nonferrous alloys and selected illustrations are presented of weld mechanical properties. A relationship is noted for the dependence of maximum single-pass laser weld penetration on power and a range of laser welding applicability is delineated. Laser welding efficiency is identified and process advantages and disadvantages are compared. The potential for future utilization of lasers in welding is discussed.
Thick film resistors cannot be printed and fired to their final value because of the large number of processing variables involved. Resistors are "trimmed" to value by removing material from the conducting path. In the last decade the YAG laser has become the most important production tool for this operation. The trimming process is described, available equipment reviewed, and a procedure is described for optimizing the parameters.
Of all the problems which must be solved when designing or using a high power CO2 laser, those dealing with transmissive optical components (output mirrors, lenses, windows, and beam splitters) can be the most troublesome and costly. This paper discusses a number of topics meant to help the user avoid problems and cut expenses. Some practical reasons to choose one substrate material over another are presented. The physical phenomena which degrade performance of an optic when it becomes overheated are examined, and a simplified figure of merit analysis is used to predict which substrate material will perform best in a given application. Examples of common field problems and ways to control these problems are given. Finally, some specifications important to the selection of lenses and beam splitters for lasers are reviewed.
This paper presents information on the special systems integration requirements of laser, beam delivery and work handler sub-systems. It is aimed to acquaint manufacturing and tooling engineers with the special problems associated with safety; facilities and space; fume removal; laser configurations; accumulated and tolerance control; applications engineering inputs; and other special interface requirements.
The high capital investment necessary to investigate the use of laser technology provides the laser job shop with a role not common to job shops in other industries. It may act as a transfer agent of the new technology into the manufacturing world by laser processing parts on the contract basis, by training the staffs of companies who purchased their own equipment, and by becoming a "second source" to those companies. Two case histories, complete with technical details, are used as examples. Precision hole drilling in metals and alumina substrates was investigated and refined in just a few days, resulting in considerable gain both technically and economically for the companies involved. A checklist is also provided as a guide to help an engineer determine if job shopping is applicable to his particular situation.
Advanced Lasers subsystems performance requirements for a fusion power reactor are presented and analyzed in the context of an energy-storage laser medium. Three types of energy-storing laser media are identified: 1) the Group VI atoms, 2) selected rare-earth doped solids, and 3) rare-earth molecular gases. The operating principles, basic parameters, and conceptual designs for high energy amplifiers are outlined for 1) atomic selenium pumped photolytically with rare-gas excimer radiation, 2) thulium-doped glass pumped with XeF excimer radiation, and 3) terbium chelate vapor pumped with KrF excimer radiation. The use of energy nonstoring laser media, particularly the rare-gas monohalide excimers, are discussed in the context of short-pulse fusion applications. The concept of backward wave Raman pulse compression is introduced as one attractive means toward this end. The basic parameters and a conceptual design of a KrF pumped methane (CH4 ) Raman compressor laser are presented. On the basis of exploratory experiments and computer modeling of amplifier devices and systems, all of the systems discussed here appear scientifically and technologically scalable in energy to hundreds of kilojoules. Systems efficiencies are projected to be in the range of 1-5%, subject to favorable resolution of a few remaining physics and technological issues.
In a variety of laser applications there are requirements for devices which shorten laser pulses, emphasize the peaks, or act as a limiter to suppress peaks in the intensity. In this paper we consider several types of devices which can perform all these functions with subnanosecond response times. The emphasis in this paper is on the limiting function, however. All the devices are based on the concept of a dual-beam interferometer with a non-linear element in one or both beams. The nonlinear component can be either a saturable absorber or a medium exhibiting the optical Kerr effect. In the former case, the transmission of the absorber increases with increasing incident intensity; in the latter case, a phase shift is introduced as the intensity increases. By combining both beams at the output port of the interferometer with an appropriate static phase difference, these nonlinear effects can be made to produce either pulse peaking or limiting. In the same way, using two orthogonal polarizations and one beam, rather than two physically separated beams, one can construct a nonlinear polarization interferometer with the same characteristics but with reduced sensitivity to vibration and temperature changes. Theoretical and experimentally determined characteristics of several nonlinear interferometers are presented here. Of particular interest is a simple, inexpensive limiter with excellent shaping characteristics which we have demonstrated using a Nd:YAG laser at 1064 nm. This device operates for days without adjustment and can be designed for use with a wide range of laser wavelengths.
Characteristics, fabrication, and write-read-erase procedure of a thermoplastic data recording medium are presented with experimental results describing diffraction efficiency, signal-to-noise ratio, residual image, sample surface condition, fatiguing, and infrared spectrum.
The PROM is a solid-state, rapidly recyclable, image storage device having a number of applications in image and signal processing. Some of its important characteristics include 1/10-wave optical surface quality, 100-1p/mm three-bar resolution, 10 ergs/cm2 light sensitivity, and image plane contrast of 10 4 :1. One of the unique features of the PROM is that the bias level of stored patterns can be adjusted through application of an external voltage, resulting in image contrast inversion or enhancement. This same operation (baseline subtraction) is used to null the zero order in an optical Fourier transform, achieving a Fourier plane signal-to-noise ratio approaching 106:1. This paper reports on the current status of this device and a number of applications for which it has been tested in several areas of image and signal processing. Results are shown for coherent optical processing by computer-controlled Fourier plane filtering and real-time image correlation, and signal processing systems are described which couple the PROM with an acousto-optic raster recorder to perform spectrum analysis and correlation on radio frequency signals.
This paper deals with certain nonlinear effects that can directly generate a wavefront which is the phase conjugate of the incident field. These phenomena can be exploited in pulsed laser systems to remove aberrations in the optical train as well as ab-errations arising from turbulence in the atmosphere. We discuss our measurements of the effectiveness of this conjugation process using a ruby laser and stimulated Brillouin scattering in a CS2 waveguide device. Measurements are made of the divergence angle of the beam after correction. The application of conjugate processes realizable in SBS, SRS, parametric downconversion, and four-wave mixing is considered for typical CO2 laser systems. System gain, backscatter limitations and parasitic oscillation are discussed for typical pulsed amplifier systems. Amplified spontaneous emission and unwanted glint returns from optical defects appear to be the most serious limitations.
The application of communication theory and linear systems concepts to the analysis of photographic images and imaging systems is well established. These techniques include the use of the Wiener spectrum to characterize photographic granularity and to determine the transfer functions for photographic imaging and printing; the standard methods of measurement that have been developed use essentially incoherent optical techniques. Recently, however, coherent optical processors have been applied to image analysis. A series of experiments is described which allows comparison of the spectra and the transfer functions generated by the incoherent and the coherent techniques.
A new photorefractive effect, resulting from the interaction of high-intensity, short-duration laser pulses with propagating acoustic waves, has been found in LiNbO3. The acoustic wave pattern is stored as changes in the index of refraction (on). The On is proportional to the rf amplitude, and increases sublinearly with the number of laser pulses and as the 1.3 power of the incident laser energy density. The decay time varies from a few hours, when only green illumination (530 nm) is used, to several weeks when combined green and infrared illumination (1060 nm) are used. The On can be erased by exposure to ultraviolet radiation or by annealing at 250 C. This acousto-photorefractive effect has been utilized to construct an acousto-optic memory correlator wherein both the stored On and the On produced by a "live" propagating acoustic wave simultaneously modulate a low-power cw laser beam. The resultant detected signal is pro-portional to the correlation integral. The memory correlator operated at a center frequency of 10 MHz with a 1 MHz band-width. A large variety of complex signals, such as chirps and Barker codes, was stored and subsequently correlated. The stored signal strength is about 30 dB below that of the original live signal. Successful correlation with a live signal was achieved several weeks after storage.
The real-time functional features of optically addressed electrooptical spatial modulators such as the Pockels Readout Optical Modulator (PROM) are described and applied to hybrid optical/digital processing of photographic information. The current and predicted performance of developed hardware and R&D devices for optical image sampling, incoherent-to-coherent conversion, stored image manipulation and computer-controlled Fourier plane filtering are presented. The utility in image exploitation of adjusting the dynamic range of a stored image under interactive
The use of a shearing plate provides a simple and convenient technique for the alignment of optical collimating systems. A quantitative analysis of this technique is outlined. The effects of optical system aberrations are discussed.
A novel square Fresnel lens is described which illuminates a circular solar cell. The square lens can be close-packed in a large photovoltaic array to help minimize system cost. The novel design is accomplished by forming the Fresnel facets in the corners of the lens with different focal lengths than the central portion of the lens. Acrylic lenses were compression molded from a master cut according to the design and were determined to be 79.4% efficient in the solar cell spectral response range.
Academic Responsibilities in the Development of Knowledge - Education is a many-faceted process. Probably, the greatest responsibility of an educator is instruction of students. A second facet (of possible equal importance) is the necessity to keep abreast of the developments in scientific discovery. A third responsibility imposed upon the academic community is that of participating in the development of new scientific knowledge.