In this paper, edge filters including short pass (SP) filters and long pass (LP) filters are reviewed in terms of definition and features. The necessity of SP and particularly LP filters and their functions in an optical system are addressed in depth. Principles of defining the OD level in the blocking band are elaborated for different spectra ranges, particularly for long wavelength LP filters. For SP filters, the filter design, performance, and potential applications are discussed. An example is given on a DUV filter via reactive plasma ion assisted deposition of HfO2/SiO2 that suppresses solar background at wavelengths above 300 nm and transmits 260-290 nm radiation. For LP filters, the design principles of the blocking band for the LP filter using the substrate, absorption material in coating, and interference type reflective coating are discussed. Semiconductor materials and doping levels for different bandgap energies and cut-on wavelengths are proposed for blocking band solutions. Examples of design practices cover a broad spectra range including short wavelength infrared (SWIR), mid-wavelength infrared (MWIR), and long wavelength infrared (LWIR). Coating challenges, for example element segregations in the deposition of a compound semiconductor, are discussed. Finally, quality control and related issues are also addressed.
We recently completed a preliminary design of a novel illumination system. The concept of this design is to integrate the incident irradiance from a small source such that an otherwise non-uniformly iluminated target is uniformly illuminated, while maintaining high radiometric throughput. Our design incorporates a collector to efficiently gather flux from the source, two multi-element faceted arrays, and a flux relay. We explore the concept behind our design and show a preferred embodiment and its predicted peformance.
The performance of an optical system can be degraded by the intrusion of stray light form sources both inside and outside of the system field of view. Stray light, or 'veiling glare,' can be particularly distracting in visual systems such as Helmet Mounted Display (HMD) systems. This paper describes techniques used by the authors to map stray light sources positions in the far field for HMD systems and to quantitatively define their impact. The mapping can be performed over 4(pi) steradians both inside and outside the system field of view. Monte-Carlo ray tracing algorithms are utilized for determining that separates the veiling glare component from the desired optical signal components. Once the major veiling glare source positions are identified, methods to reduce veiling glare can be determined. A technique for reducing noise in the calculation due to the statistical nature of the Monte Carlo ray trace is also discussed.
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