Showing papers on "Signal beam published in 1975"

Optical information storage system

Abstract: A wideband holographic information storage system records Fourier holograms on film in rapid succession, each hologram storing 128 bits of data. The hologram fringe pattern is held stationary by varying the reference beam frequency to track the variations of frequency of the signal beam that are caused by acoustic-optic modulation of the signal beam. Holograms are successively recorded in adjacent positions by scanning a light beam across a photosensitive film with a rotating polygonal mirror, the recording light beam being wide enough to cover two facets of the mirror so as to achieve nearly 100% scanning duty cycle. During readout, a readout light beam is steered to compensate for prismatic deflection effects caused by variations in thickness of the film. The direction of the output beam is maintained constant despite a scanning motion of the incident readout beam, by reflecting the output beam a second time from a different facet of the polygonal mirror to compensate the rotational component of beam motion. Clocking of output data is self-synchronized, based upon modulation signals. Acoustically caused defocusing of the light beam is optically corrected. Methods are employed to reduce crosstalk.

The optically gated dye cell - A high-speed shutter and pulse shaper

Abstract: This paper discusses characteristics of a class of devices that use a saturable absorber irradiated by an optical control pulse, or gating pulse, to alter the shape of a transmitted optical signal. We consider two device geometries: a longitudinally gated cell, in which signal and gate beams are nearly parallel, and a transverse cell, in which the medium is bleached by a gating pulse applied at right angles to the signal beam. The longitudinal device permits synthesis of rising exponential signal pulses with arbitrary, subnanosecond time constants. The transverse geometry can provide pulses of complex shape and permits independent optimization of several device parameters. The dynamics of the saturable absorber (with particular emphasis on liquid dye systems) is analyzed in detail, and a pulse-shape synthesis procedure is outlined. Spurious nonlinear effects are considered, and an example of pulse shaping for laser-driven fusion is given.