Laser-induced damage initiation on fused silica optics can limit the lifetime of the components when used in high power UV laser environments. For example in inertial confinement fusion research applications, the optics can be exposed to temporal laser pulses of about 3 nsec with average fluences of 8 J/cm<SUP>2</SUP> and peak fluences between 12 and 15 J/cm<SUP>2</SUP>. During the past year, we have focused on optimizing the damage performance at a wavelength of 355-nm (3(omega) ), 3-nsec pulse length, for optics in this category by examining a variety of finishing technologies with a challenge to improve the laser damage initiation density by at least two orders of magnitude. In this paper, we describe recent advances in improving the 3(omega) damage initiation performance of laboratory-scale zirconium oxide and cerium oxide conventionally finished fused silica optics via application of processes incorporating magnetorheological finishing (MRF), wet chemical etching, and UV laser conditioning. Details of the advanced finishing procedures are described and comparisons are made between the procedures based upon large area 3(omega) damage performance, polishing layer contamination, and optical subsurface damage.
Design of experiment (DOE) methods were employed to optimally develop thin films with respect to optical absorption and mechanical stress performance. The goal of the experiment was to identify key deposition characteristics which would yield very low optical absorption and minimized film stress characteristics. A fractional factorial matrix was utilized for the preliminary portion of the experiment. Key deposition parameters with respect to low absorption and low film stress were identified as a result of the DOE effort. In addition, the interaction effects of each key deposition parameter with other key deposition parameters as a function of performance were identified. Details of the DOE setup, analysis, and evaluation are presented. Subsequent application of statistical process control methods to control these optimized critical parameters during production to ensure consistent, high quality production yields are discussed.
Development of better, larger, and more dense focal plane arrays has stimulated the design of lens systems of larger aperture, longer focal lengths, and nearly diffraction limited performance over larger fields of view. As performance requirements, and the number of optical elements increase, the process of aligning lens elements during assembly rapidly becomes a critical issue. Tolerances on spacing, centration, and tilt become very challenging, as do the requirements on stability over extreme ambient excursions. This paper is intended to give a top level, general treatment of the subject, while describing certain techniques that incorporate precision alignment and measurement of critical lens parameters during assembly. These methods also allow monitoring during the accompanying bonding and curing cycles used throughout the build process. Examples serve to illustrate some of these techniques, and results are presented for specific cases. It is shown that centering, as evidenced by axial runout, can be set to the ten microinches level with a few microinches accuracy and maintained to about 50 microinches through the assembly and bonding process. With the use of computer data logging and analysis techniques, this can be extended to below five microinches.
The application of advances in a variety of disciplines, has made significant impact on the area of optical sensing technology. This impact has not evolved so much from new optical designs, component prescriptions, or revolutionary coating designs, although there have been substantial innovations in certain areas. Instead, progress has resulted from the combined mix of a variety of ideas including the areas of advanced materials and material forming processes, coatings that do their job more efficiently, the application of computer control to manufacturing, wavefront correction, and alignment, as well as the collection, integration, and display of relevant data in a format that makes possible interpretation at-a-glance.
The Solar-A Soft X-Ray telescope will be launched aboard the Japanese Solar-A Satellite in 1991, to
study the sun during the next period of sunspot activity. The mechanical and optical design of this
monolithic, near 2 arc-sec image quality Nariai Telescope was developed previously as explained in reference
1 and depicted in Figure 2.0. Successful achievement of the aggressive performance goals for this design
required precision manufacturing and assembly, and accurate metrology to verify results. In fact, more
than three-fourths of the error budget was allocated to manufacturing and meirology errors because of the
recognized difficulty in producing and measuring the precision grazing-incident optical surfaces. To
obtain the anufacturing precision and metrology accuracy desired, specialized tooling had to be designed to
support and mount the optical substrate during the fabrication, surface metrology, alignment and assembly
processes. The design considerations, the substantiating structural analyses performed and the resulting
successful application of this specialized tooling are reported here in to show the difficulties often
encountered in developing "support" equipment to achieve desired results in the final product.
The process of accommodating extreme measurement geometries, including aspheric cylindrical surfaces, is considered, and an absolute calibration technique for linear surfaces capable of 0.0067 wavelength (42 A) p-p with a precision (1-sigma) of 0.0008 wavelength 5 A is described. The technique was used to measure the absolute axial sag on the inside of a X-ray telescope.