Technique using axicons for generating flat-top laser-beam profiles

In certain fusion experiments using CO/sub 2/ lasers, like Helios, it is desired to produce a focal spot several times larger than the nominal focal spot, with a flat beam profile. The typical focal spot in Helios is roughly 70 ..mu..m and just defocussing the beam produces beam breakup, with several hot spots with roughly the original diameter, and a gaussian distribution. A number of schemes were tried to achieve a large spot with desired characteristics. These are described in the article. Axicons were found to produce spots with desired characteristics. Axicons are lenses or mirrors having a cone-shaped surface. The various schemes are described, as well as an experiment in Helios which confirmed that axicons produced the spots with desirable characteristics. Helios is an 8-beam CO/sub 2/ laser which produces 10 kJ at power in excess of 20 TW. It is currently being used for Laser Fusion studies at the Los Alamos National Laboratory

Optical design and analysis of carbon dioxide laser fusion systems using interferometry and fast Fourier transform techniques

The optical design and analysis of the LASL carbon dioxide laser fusion systems required the use of techniques that are quite different from the currently used method in conventional optical design problems. The necessity for this is explored and the method that has been successfully used at Los Alamos to understand these systems is discussed with examples. This method involves characterization of the various optical components in their mounts by a Zernike polynomial set and using fast Fourier transform techniques to propagate the beam, taking diffraction and other nonlinear effects that occur in these types of systems into account. The various programs used for analysis are briefly discussed

An "Intelligent" Optical Design Program

Described is a general approach to the development of computer programs capable of designing image-forming optical systems without human intervention and of improving their performance with repeated attempts. The approach utilizes two ideas: (1) interpretation of technical design as a mapping in the configuration space of technical characteristics and (2) development of an intelligent routine that recognizes global optima. Examples of lens systems designed and used in the development of the general approach are presented, current status of the project is summarized, and plans for the future efforts are indicated

Resonator Optical Designs For Free Electron Lasers

The output beam from free-electron lasers tends to be a thin, pencil-like beam because of the nature of the gain volume. For moderate power devices, mirror damage considerations imply that the beam has to travel many meters before it can expand enough to allow retro-reflection from state-of-the-art mirrors. However, use of grazing incidence optics can resolve the problem of damage to the optical elements and result in a cavity of reasonable dimensions. The optical design considerations for such resonators are addressed in this paper. A few of the practical resonator designs approaching diffraction limited performance are presented

Global Coordinates and Exact Aberration Calculations Applied to Physical Optics Modeling of Complex Optical Systems

Historically, wave optics computer codes have been paraxial in nature. Folded systems could be modeled by ''unfolding'' the optical system. Calculation of optical aberrations is, in general, left for the analyst to do with off-line codes. While such paraxial codes were adequate for the simpler systems being studied 10 years ago, current problems such as phased arrays, ring resonators, coupled resonators, and grazing incidents optics require a major advance in analytical capability. This paper describes extension of the physical optics codes GLAD and GLAD V to include a global coordinate system and exact ray aberration calculations. The global coordinate system allows components to be positioned and rotated arbitrarily. Exact aberrations are calculated for components in aligned or misaligned configurations by using ray tracing to compute optical path differences and diffraction propagation. Optical path lengths between components and beam rotations in complex mirror systems are calculated accurately so that coherent interactions in phased arrays and coupled devices may be treated correctly

Cloning and sequencing of the trpE gene from Arthrobacter globiformis ATCC 8010 and several related subsurface Arthrobacter isolates

Tryptophan dependent mutants of Arthrobacter globiformis ATCC 8010 were isolated and trp genes were cloned by complementation and marker rescue of the auxotrophic strains. Rescue studies and preliminary sequence analysis reveal that at least the genes trpE, trpC, and trpB are clustered together in this organism. In addition, sequence analysis of the entire trpE gene, which encodes component I of anthranilate synthase, is described. Segments of the trpE gene from 17 subsurface isolates of Arthrobacter sp. were amplified by PCR and sequenced. The partial trpE sequences from the various strains were aligned and subjected to phylogenetic analysis. The data suggest that in addition to single base changes, recombination and genetic exchange play a major role in the evolution of the Arthrobacter genome

Interferogram reduction and interpretation as applied to the optical analysis of the 10 kJ LASL laser fusion system

The LASL 10 kJ Eight-Beam CO/sub 2/ Laser Fusion System, currently under construction, has approximately one hundred optical elements per beam. The nominal system is diffraction limited and degradations in performance are primarily caused by imperfect components as well as alignment errors. Consequently, analysis and predictions for the system are very much dependent on the proper description of the imperfect components. The approach taken at LASL has been to characterize the components interferometrically. Interferograms of the various components are made at the 633 nm He--Ne wavelength. Detailed results of the analysis for one complete leg of the eight-beam system is presented