A novelty filter utilizes self-nulling and self-aligning of reflection and transmission phase conjugate beams. A photorefractive crystal is arranged so that the contributions to the phase conjugate are equal and opposite in the steady state to produce destructive interference when the input image is stationary, and thus no output image is displayed. If the image moves, then the gratings will rewrite and erase themselves, each with their own response times, total destructive interference will not occur, and transient enhancement and surpression of the phase conjugate output signal will indicate the direction of motion of the input image.

A gas discharge laser with a pulse multiplier. In the pulse multiplier, short pulses from the laser are divided into portions and all or all but one of these portions are delayed in delay legs by different time periods and recombined to provide a stretched output pulse having substantially reduced intensity and longer duration as compared to the pulse from the laser. Focusing optics are included in each delay leg to assure that beam size and angular spread of each portion of the combined pulse is not substantially different from other portions of the pulse.

Achromatic volume holograms are attained for broad band phase conjugation and image reconstruction having bandwidths of 250 nanometers. The holograms are generated by means of a diffraction grating having a predetermined angle of tilt. Achromaticity is achieved by tilting the holographic recording medium at the same predetermined angle.

A compound semiconductor that is suitably doped to exhibit the DX effect is irradiated with an optical beam of spatially varying intensity whereby localized regions of persistently higher conductivity and lower refractive index are created in the semiconductor where sufficient intensity of the beam was incident. The persistently higher conductive region can be used to bridge selected gaps in conductive paths on a support member use in memory device and the regions of lower refractive index can be used to providing guiding in a wave guide, to form high resolution gratings, or to form holograms.

The present invention provides an apparatus and method for non-invasively monitoring turbulent fluid flows including anisotropic flows. The present invention uses an optical technique to filter out the rays travelling in a straight line, while transmitting rays with turbulence induced fluctuations in time. The output is two dimensional, and can provide data regarding the spectral intensity distribution, or a view of the turbulence in real time. The optical monitor of the present invention comprises a laser that produces a coherent output beam that is directed through a fluid flow, which phase-modulates the beam. The beam is applied to a temporal filter that filters out the rays in the beam that are straight, while substantially transmitting the fluctuating, turbulence-induced rays. The temporal filter includes a lens and a photorefractive crystal such as BaTiO.sub.3 that is positioned in the converging section of the beam near the focal plane. An imaging system is used to observe the filtered beam. The imaging system may take a photograph, or it may include a real time camera that is connected to a computer. The present invention may be used for many purposes including research and design in aeronautics, hydrodynamics, and combustion.