How special reflective devices reduce the angle of incidence of a laser beam irradiating a surface with the ability to decrease the incidence angle over a wide range of angles is described. To optimize the diffraction efficiency of a focusing holographic optical element (HOE), spread of the angle of incidence of an incoming laser beam about a preferred angle should be small. There is a constraint with thick HOEs in which a Bragg effect condition must be satisfied to achieve high diffraction efficiency. Angle reduction and applications of military interest are discussed. Ways to couple a reflection angle reducer component and an HOE to a photographic or TV camera are suggested.
The use of holographic optical elements (HOEs) to discriminate between coherent irradiation and
broadband, noncoherent light has been experimentally demonstrated under adverse scattering and
attenuating conditions. As a passive sensor component in a laser irradiation detection system, an HOE can
be used in several application areas, e.g., data transmission systems, aircraft warning system, underwater
communications, and alignment systems, where wavelength and direction of arrival information can be
The efficient concentration or focusing of laser light by an HOE onto a detector stage and, of equal
importance, the ability to form bright, unique geometric patterns are characteristics that establish the
HOE's use as a readily compatible irradiation sensor component. In addition, there is a considerable size
and weight advantage over other functionally comparable optical components. Finally, as a passive
element, an HOE can fmd use with CW or pulsed illumination.
The properties and advantages, pros and cons, of the use of HOEs as sensor elements are
discussed in the paper and illustrated in several laboratory experiments and a field test.