<title>Neodymium Glass Lasers - A Status Report</title>

Abstract

AbstractProgress on high peak power short pulse glass lasers has been rapid. Prospects for reaching the 1013 - 1014 watt level required for laser fusion appear reasonable. Progress in the control of the onsetself- focusing effects offers the hope of the realization in the near future of laser systems which operateat output intensities of 30 CW/cm4 at overall efficiencies approaching 0.1 %.Very high peak power lasers are needed forlaser fusion compared to what exists at present. Presentsolid state and gas laser systems operate with well controlled beams at power levels of 1011 - 1012 watts per beam. Laser fusion has been estimated to require the symmetric irradiation of targets by pulses of1013 - 1014 watts for a breakeven experiment(1). Even higher laser powers may be required for a fusionreactor, but here the real problem will be that high high efficiency is also necessary.A first reaction to the gap between present technology and the peak power requirement might be todismiss the idea out of hand, as simply too difficult to achieve especially when other projected require-ment on a breakeven experiment such as a precise pulse shape and very uniform illumination are considered.This is too simplistic an attitude. The benefits of fusion power if it can be harnessed are so enormousthat the question of whether such lasers can be built deserves the closest and most intensive study.This is likely to be money well spent as high peak power lasers will have many other uses even if fusionproves impractical by this route. Examples of this exist now; experiments at NRL on laser and electronbeam targets have provided a wealth of atomic physics data on the spectra of highly ionized atoms. Theselaboratory astrophysics experiments are being used to analyze the solar flare data obtained from theSkylab space station.The real question involves how possible it is to achieve the desired output powers and how soon.This depends on where on the learning for a particular technology we are at a given time. Thisconcept is useful because historical knowledge provides useful insight as to whether innovation orengineering will advance the technology. Figure 1 shows the achieved peak power vs time for solidstate laser systems, and gas lasers. Clearly any projections before 1967 were likely to be in error sinceat that point we were still on the exponentially rising part of the curve for both technologies. At thispoint in time however we are on a much more slowly rising portion of the curve for solid state lasersystems and we can hope to project future progress more exactly. This unscientific exercise would lead usto project peak powers of '