Wescam (Canada)

DriveFlamborough, OntarioCanada, L9HMartin High & Vladimir StrnadApplied Physics Specialties17 Prince Andrew PlaceDon Mills, OntarioCanada, M3C 2H2ABSTRACTMany infrared lenses include Diffractive Optical Elements (DOEs) which have been incorporated toreduce the lens complexity and/or the tolerance sensitivity. In many cases the diffractive surface includesan asphere to achieve further aberration correction. For complex lens systems such as infrared multi-FOVand infrared zoom lenses there is a strong motivation to use multiple diffractive optical elements. Thispaper reviews the performance impact and producibility advantages of using multiple diffractive opticalelements in an infrared lens.Key Words: Infrared Lens, Diffractive Optical Elements, Lens Design1. INTRODUCTIONDiffractive optical elements have been incorporated into infrared lenses for over ten years. These hybridlenses can be used to replace a conventional doublet by providing both chromatic and aspheric correctionusing a single diamond turned surface. The advantages offered by these elements are well known. Studieshave shown that lens complexity can be reduced, the manufacturing tolerance sensitivity can be lowered

In this paper, the design and performance of an airborne long range thermal imaging system, operating in the 3 - 5 micrometer spectral band, is described. Comparisons of predicted and measured performance are provided. The system, which contains a dual field-of-view telescope, is stabilized to better than 5 microradians rms jitter and provides high quality thermal images with a spatial frequency resolution greater than 8 cycles per mradian.

The slit diaphragm is a useful type of flexure for producing small rotations or translations. This type of flexure is easily fabricated using modern technique such as electro-discharge machining, and provides a convenient solution for certain types of precision motion problems. There are two types of slit diaphragms used in optomechanics: a two axis gimbal for rotation and a linear flexure for translation. Closed form solutions are discussed for determining rotational and radial stiffness of the two axis gimbal slit diaphragm flexure. Similar equations are given for finding the linear and radial stiffness of the linear translation slit diaphragm flexure. A design example of a focus mechanism employing a pair of linear translation slit diaphragm flexures is discussed.

The upper and lower volumes of the violin cavity are treated as acoustical capacitances coupled by an internal inertance. This leads to the development of a simple acoustical network that takes into account the noncentral position of the f-hole system and has two degrees of freedom representing the Helmholtz mode A0 and the primary longitudinal mode A1. The initial choice of values for the network elements is based in part on wave-acoustical considerations. These values are then adjusted under the guidance of new experimental data. In particular, when the violin is operating in the A0 mode, it is found that the acoustic pressure in the upper volume is 30% greater than that in the lower volume. The presence of rib holes around the upper and lower volumes is represented by additional network elements shunting the acoustical capacitances. The characteristics of the modified instrument, with and without rib-hole damping, are presented in terms of the calculated values of the resonance frequencies ν0 and ν1 , the Q factors, and the volume velocity ratios (φ) of the A0 and A1 modes as functions of the number of rib holes. (The parameter φ provides an indication of the volume velocity passing through the rib holes in comparison with that associated with the f-hole system.) The calculated values are compared with experimental data for the special instrument known as ‘‘Le Gruyère’’ [C.M. Hutchins, J. Acoust. Soc. Am. Suppl. 1 73, S84(1983); 87, XXX–XXX (1990)].