Jon E. Sollid

The Aurora Project: Optical Design For A Kilojoule Class KrF Laser

Aurora is a 248-nm,10-kilojoule laser system being built at Los Alamos National Laboratory to demonstrate the feasibility of large KrF laser systems for laser fusion. It was designed as a test bed to demonstrate: 1) efficient energy extraction at 248 nm; 2) an angularly multiplexed optical system that is scaleable to large system designs; 3) the control of parasitics and ASE (amplified spontaneous emission); 4) long path pulse propagation at uv wavelengths; 5) alignment systems for multibeam systems; and 6) new or novel approaches to optical hardware that can lead to cost reduction on large systems. In this paper only issues pertinent to the optical system are addressed.

Single-Point Diamond-Turned Mirror Performance Before And After Polishing

The surface finish of a single-point diamond-turned (SPOT) mirror produced in 1977 on the large (2-meter swing) Excello lathe at the Union Carbide Corporations Y-12 Plant in Oak Ridge, Tennessee, was such that it was not possible to do visible alignment using it. Therefore, it was necessary to polish the mirror by hand. This was done at the University of Arizona. The intent was to remove the high ridges in the SPDT mirror but not to degrade the figure. Both interferometric and encircled energy measurements were made on the mirror before and after polishing. The mirror was an f/2 off-axis parabola 39.37 cm in diameter. The equation describing the generator of the mother parabola is y2 = 309x(cm2) and the center of each off-axis sister mirror is at x = 7.64 cm, and y = 48.59 cm. After polishing it was possible to align it using techniques which employed visible light. Furthermore, the polished mirror was about 20% better as far as the rms surface figure was concerned, although cosmetically the surface finish appeared visibly degraded after polish.

Calorimetry At 10.6 µm For Large Aperture Beams (Up To 2 M) And High Powers (Up To 20 Tw)

Three kinds of calorimeters, differing in their absorption mechanisms, will be described. Included are surface absorbing calorimeters constructed of beryllium oxide, volume absorbing calorimeters of kapton and copper laminate, and box calorimeters of various shapes constructed of electroformed copper enclosures blackened by the commercial Ebanol* process. In all cases, devices are constructed so that the dominant heat loss mechanism is radiation. That is, they are carefully insulated from their environment. In some cases, drift produced by the background is subtracted by using the twin technique. The heat capacities of the calorimeters are known and the temperature rise is sensed using thermopiles. This gives the energy absorbed. Each device is also calibrated in such a way that it is traceable to the NBS Laser Measurements Standards.

Evaluation of Single-Point Diamond-Turned Copper Mirrors For the Los Alamos Scientific Laboratory Eight-Beam CO2 Laser: Helios

This paper describes the best large-aperture single-point diamond-turned copper mirrors currently available. The state of the art is progressing rapidly. At present, for 400-mm diam, f/16.5 spherical surfaces, the peak-to-valley figure can be held to two visible fringes in a center of curvature test, and the surface roughness is better than 50 mm peak-to-valley. Since the time of Galileo attempts have been made to machine optical components. With very few exceptions these attempts have failed. Recently 1,2 however, much careful atttention has been paid to the numerous fine details such as vibration isolation, uniformity of spindle and tool drive, temperature control, tool shaprness, etc. Components of infrared quality are being produced in large numbers. The advantages of machined optics are a generally lower price, a higher production rate, a higher damage threshold (on the order of 11 J/cm2, the intrinsic limit, for 1-ns, 10-um pulses),3 and greater resistance to corrosion and tarnishing than can be achieved through conventional optic production. It is the combination of these advantages which made single-point diamond-turned (SPDT) optical components a key element in the current and projected Los Alamos Scientific Laboratory (LASL) CO2 laser systems. There are two operating large pulsed CO21 lasers at LASL; the TBS or Two-Beam System, and Helios, the Eight-beam System. Helios has a nominal energy of 10 kJ at 1 ns, while the TBS has a nominal energy of 2.5 kJ at 1 ns. The Antares CO2 laser at LASL will have an energy of 105 J in 1 ns and consist of 6 beams of 12 segments, each of which is essentially an independent beam train. In addition to numerous smaller optics, a single segment of the beam train will contain nine elements with a characteristic diameter of 40 cm or larger. There will be 72 such beam trains and 1500 elements. Completion of the laser is scheduled for 1982. Timely and reliable fabrication will be essential. Thus, single-point diamond turning forms an integral part of the CO2 lase