Hyperspectral imaging systems are finding broader applications in both the commercial and aerospace markets. It is becoming clear that to optimize the performance of these systems, their instrument transfer function needs to be tailored for each application. Vis-SWIR systems in the full 400nm to 2500nm waveband present particular design and manufacturing challenges. A single blazed grating is inadequate for a system operating in the full vis-SWIR wavelength range. In addition, optical materials and broad band coatings present a challenge for non-reflective systems. An understanding of the application and wavelengths of interest, combined with a judicious choice of a focal plane array, can then lead to an optimized system for the specific application. The ability to tailor the grating and manufacture a wide variety of grating profiles and substrate shapes becomes a significant performance enabler. This paper will discuss how the use of optical, coating, and grating design/analysis software, combined with grating manufacturing techniques assure meeting high performance requirements for different applications.
An ultra-low surface finishing process for 6061 T6 type aluminum has been developed by Corning Incorporated, Specialty Materials Division, and has been successfully applied to mirrors up to 13 inches in diameter. This paper presents finish and figure data achieved from the mirror finishing process. Mirror stability is demonstrated through Pre and post thermal cycle surface figure measurements; temperature range of cycle -55°C to +70°C. As an added benefit, the process enables the use of deterministic finishing and enhances the reflective optics resistance to corrosion. Survivability of the reflective optic is evaluated through extended humidity testing.
Laser durable multiband high reflective optics can be realized by depositing densified HfO<sub>2</sub>/SiO<sub>2</sub> multilayers on aluminum alloy substrates. To further understand the impact of surface finishing and cleaning on laser-induced damage of multiband high reflective optics, 1” diameter witness samples were characterized by means of spectrophotometry, atomic force microscopy, confocal laser scanning microscopy, white light interferometry, scanning electron microscopy, and laser-induced damage threshold tests performed at 1064 nm, 20 ns, 20 Hz, and near normal angle of incidence. Laser-induced damage thresholds of 12.5 J/cm<sup>2</sup> and 47 J/cm<sup>2</sup> were obtained on a stained witness and unstained witness, respectively. A two-step laser damage process was proposed based on the post-damage analysis. The results suggest that nodule defects are the limiting factor for laser-induced damage thresholds. There exists the potential in aluminum-based dielectric coated multiband reflective optics for extremely high power laser applications.
Extreme light-weighting is important in many aerospace and defense applications but the cost associated with beryllium or other exotic materials can be prohibitive. The current standard for producing cost effective, high performance mirrors is to diamond machine mirror blanks from aluminum alloy stock. About 80% material removal is the limit for geometrical lightweighting while still retaining the structural integrity required for optical fabrication. To reduce weight further requires alternative materials. This paper summarizes the status of diamond machined finishing and coating of magnesium alloys to produce cost effective, lightweight mirrors with high, broadband reflectivity and low scatter finish.
HfO<sub>2</sub>/SiO<sub>2</sub> multilayers were deposited on single point diamond turned aluminum substrates via
modified reactive plasma ion assisted deposition to form a laser durable and environmentally
stable dielectric enhanced IR mirror at a wavelength of 1064nm. The effect of the surface quality
of the diamond turned aluminum on the optical performance of the dielectric enhanced mirror was
assessed. A laser-induced damage threshold up to 11 J/cm<sup>2</sup> was obtained from the enhanced
aluminum mirror tested in pulse mode at 1064nm with a pulse length of 20ns and a repetition rate
of 20Hz. Laser damage morphology was revealed by a scanning electron microscopy. The damage
mechanism was attributed to nodule defects generated by particle embedded on the aluminum