The National Laser-Fusion Program has grown into a maturing but still rapidly advancing major research and development program of the ERDA. The LASER, once a solution looking for a problem has found a viable place in the pattern of search for solutions to energy and military problems. The program has grown from less than $1 million in 1963 to a projected total of $101 million in fiscal year 1977. Several existing advances have occurred and several milestones will be passed in the next two years. A projection of our program through the turn of the century is outlined. The hardest obstacles as we see them are presented.
The Nd:Glass laser is used extensively throughout the world for laser fusion and laser plasma interaction studies. Its popularity, to a large extent, stems from the fact that it is capable of operating reliably in the subnanosecond-terawatt power regime. In addition, the technology necessary to combine a large number of laser chains to produce a system capable of multi-terawatt performance currently exists and is being applied.
The mechanisms which cause a damaging interaction between laser light and optical materials are reviewed. Their dependence on laser pulse duration and wavelength is discussed and available experimental results for short pulse damage thresholds are presented. It is shown that localized absorption in coatings, surface defects, or impurity inclusions generally determines the practical irradiance limit. Intrinsic non-linear processes such as avalanche breakdown or two photon absorption set the upper limit to the safe irradiance level.
The rare-gas halogen and diatomic halogen molecular gases are relatively efficient, narrowband radiators in the ultraviolet spectral region when excited by electron beams. We have recently demonstrated production of 1.315 micron stimulated emission in atomic iodine by photolyzing C3F7I vapor with fluorescence emission from the XeBr exciplex. The use of spontaneous and superfluorescent emission from selected rare gas halogen exciplex systems to pimp high average power atomic iodine lasers for fusion applications is explored with emphasis on the pump source kinetics in relation to amplifier design.
The atomic iodine photodissociation laser has developed into a system capable of producing nanosecond or shorter pulses of near infrared radiation with energies well in excess of a hundred joules. Discussed are the operating characteristics, advantages, and potential problem areas associated with this laser.
High-power, fast-rising pulses of hydrogen fluoride laser energy suitable for laser-fusion target interaction experiments can in principle be generated by directing an electro-optically shuttered oscillator pulse through one or more electron-beam driven amplifiers. We have constructed and successfully tested a three-stage HF master oscillator-power amplifier (MOPA) configuration using SF6-C2H6 in which an E-0 generated 4-ns-FWHM pulse was amplified in an electron-beam-excited third stage and subsequently isolated with a Brewster angle splitter. Independent experiments in which a 100-ns-FWHM pilot pulse interacted with the power amplifier demonstrated for the first time complete extraction of the available laser energy. These two results provide strong evidence that with upgrading to H2-F2, it should be possible to obtain nanosecond duration pulses with power levels sufficient for meaningful laser fusion target coupling experiments.
Recent experiments show that pulsed HF lasers are capable of producing high energy with good efficiency. Preliminary experiments show that the laser radiation from the high-gain medium can be controlled with a low-power probe laser beam or with low-level feedback. These results indicate that the HF laser may have potential for second-generation laser fusion experiments.
This article summarizes the current performance and understanding of deuterium fluoride (DF) cw chemical lasers. The fundamental principles of the laser are explained. The advantages and disadvantages of the laser system are discussed. The characteristics of the DF laser beam, the performance parameters and operating characteristics are enumerated.
This paper reviews the characteristics of high power electric discharge CO lasers with emphasis on the unique properties which differentiate CO EDLis from competitive systems. The operational principles and design constraints are discussed. The results of investigations into some of the most promising approaches to the development of high power devices are summarized. Projections for device performance and technology development are presented. Consideration is given to the impact that the potential advantages of the CO EDL may have in enhancing the performance and/or simplifying the design of laser systems for practical applications. Although the first CO EDL was demonstrated more than a decade ago (making it a contemporary of the CO2 EDL), it is only within the last few years that the potential advantages of the CO system have been fully appreciated, and attention has been focused on the development of practical devices. Of particular significance are the demonstrated advantages in power conversion and volumetric efficiency, the development of low loss optical components for the CO laser wavelength (~5μ) which show remarkable resistance to laser damage, and projections of favorable atmospheric propagation characteristics. A high energy pulsed electric discharge laser has demonstrated efficiencies in excess of 60%, and a small (~1 liter) CO EDL utilizing supersonic flow has produced over 100 kW in a short run (~2 ms) experiment which simulated the conditions for continuous operation. Balanced against the advantages are a number of technological problems which must be addressed before truly practical devices can be realized. However, device technology is progressing rapidly and CO electric discharge lasers should be considered serious contenders for future high power laser applications.
Kinetics of electron beam pumped and electron beam controlled discharge pumped lasers are discussed. Device scaling criteria are given for window foil survival, electron beam pinching, electron beam pulse length, discharge pulselength, and discharge-electron beam interaction.
Programs at the Army Missile Command on strategic and tactical applications of laser radar center around determination of the target signatures and cross sections which drive laser power requirements. The strategic concepts use the narrow beam width, short pulses, and short wavelengths to achieve high spatial and doppler resolution. Candidate lasers include CO2, CO, HF, DF, and Nd. Power, coherence length, pulse to pulse coherence, ability to chirp, and good beam quality are of interest. The tactical concepts use high power 10.6 micron pumped extreme infrared lasers in the 100 to 1000 micron band to enable the Army to see through bad weather with imaging laser radar. The driving problem in sizing laser requirements is the lack of target information. This paper will describe some early predictions of laser power requirements.
Present rangefinder technology status is discussed and future technology trends are presented. Specifically, well established existing technology, using neodymium laser cartridges, advanced integrated electronics and detectors, well established, will satisfy most medium range determination requirements. Implementation of the concept of modular standardized components and subsystems will permit low cost production and integration of rangefinder-functions in many optical systems. Mini-rangefinders for short ranges with low weight-size-cost factors are also technically oossible using integrated laser cavities and concomitantly miniaturized peripheral components. Base technology being actively pursued addresses mainly 2 micron eye-safe rangefinders (medium range class) and 10 micron rangefinders, commensurable with thermal imaging device requirements.
The basic principles behind the operation of the thermally pumped CO2 gas dynamic laser are developed. Experimentally demonstrated performance is compared to theoretical upper limits and approaches for performance improvement toward these limits are reviewed. Relative efficiency and utility vis-a-vis electrically pumped CO2 lasers are discussed. Investigations towards a thermally pumped laser based on the HCl molecule are reported.
CO2 Electric Discharge Lasers have proven themselves to be efficient sources of high power, high quality laser output energy. This paper describes the basic concepts behind molecular gas discharge lasers concentrating on the CO2 system. A summary of the three classes of electric laser systems is presented as well as examples of operating devices in each class.
The transfer chemical laser has been shown to provide efficient performance under three modes of operation. Specific powers as great as 47 kj/lb and pressure recovery potential up to 0.6 atmospheres have been achieved. The potential development of the device has been directed towards short chain operation.
The need for expanded sources of energy in the immediate future is of worldwide concern, and in the near term, nuclear energy is one of the few methods having the proven capability of fulfulling these needs. A brief review of existing projections of national energy demand and the resulting requirements for expanded uranium enrichment capacity, coupled with a comparison of the economics of providing this addtional enrichment capacity [by methods of gaseous diffusion, centrifugation and laser isotope separation (LIS)], in-dicates potential savings of billions of dollars between now and the year 2000 if LIS performs as predicted. Laser methods also appear to offer solutions in the equally important fuel cycle problem areas of deuterium enrichment and nuclear fuel reprocessing. We have reviewed recent experimental LIS results obtained using the methods of single- and multiple-photon dissociation and laser-induced chemical reaction employing a single laser. Also discussed are recent experiments on several- and multiple-photon methods that employed more than one laser wavelength. For each of these processes, methods are given for estimating the minimum laser requirements. Also discussed are the projected it and uv laser requirements to proceed from scientific proof-of-principle, through medium-size scaling experi-ments, to the full-sized uranium enrichment plant for a two-step photodissociation process currently under investigation in our laboratory.
A brief review of recent research in novel UV lasers is given. Special emphasis is placed on those lasers which have recently shown potential for high efficiency. A new class of lasers, the rare gas monohalides, is reviewed in detail. A kinetically complementary set of lasers operating on halogen molecules is discussed since these species have demonstrated very high fluorescence efficiencies.
Interest in laser isotope separation and laser induced chemistry is now creating a large demand for tunable lasers throughout the frequency spectrum. In the visible and near uv these demands have generally been met with tunable dye lasers and frequency doubled dye lasers. However, development of tunable lasers operative throughout the ir has proven to be much more difficult. The difficulty is greatly enhanced by the strict wave-length requirements dictated by isotope separation. In this presentation the status of various experimental approaches being pursued for solution of this problem will be reviewed. These approaches may be grouped under the general headings of: optical pumping, non linear optics in gases and solids, electrical discharges in gases, and excitation transfer. In addition, because of the large number of known ir laser transitions, there may be near coincidences between a particular line of an existing laser and the desired absorption feature. In this case one would like to have a fine tuning capability that is continuous over a range of ~ ± .5 cm-1 comparable to spacings between rotational lines. Several possible solutions to this problem will also be discussed.
Following a brief discussion of uranium isotope separation using lasers, the delayed coincidence method of measuring atomic mean lives with pulsed electron beams utilized here is described along with the beam source used to supply the free uranium atoms for measurement. Experimental details involved in the lifetime measurement are next discussed followed by the effect of resonance radiation imprisonment on the measured lifetimes. Finally, lifetime measurements involving the 3584.9 Å and 5915.4 Å transitions in natural uranium are described, and the previously reported result of 7.3 ± 1.1 ns ior the mean life of the upper level of the 3584.9 Å transition (27886.99 cm -1 ) is presented.