Noise elimination technique in holography.

A method has been described for reducing speckling and the noise arising due to cosmetic defects present in the elements of the hologram recording geometry by using a multifrequency grating-diffuser-lens combination for object illumination at the time of recording the hologram. The averaging of the speckling is simulated at the plane of the object. The experimental results show that this method of object illumination is quite effective for noise reduction and may be applied to recording noise-free holograms of shortlived events. It may also be useful in holographic microscopy.

Elimination of depolarization effects in holography.

The polarization of a scattered beam from any object depends on the nature of the surface of the object. Depolarization of the laser beam can occur as a result of reflections from metallic and dielectric surfaces; it can also be due to multiple scattering in some of the medialike aerosol particles when the laser beam passes through them. While recording a hologram this fact is altogether ignored, and it is assumed that object and reference beams are polarized linearly and parallel to each other. We have studied the variation of diffraction efficiency of a hologram with the degree of polarization of the object beam. There is a 43% decrease in the efficiency value when the degree of polarization falls from 1 to 0.9. A method for minimizing the effects of depolarization is suggested.

Frequency-modulated zone plate for coherent noise reduction.

Laser images and holographic reconstructions are highly affected by dust and imperfections present in various optical components of the imaging system, which create noiselike structures in the final images. To reduce this speckle noise, a phase plate based on a frequency-modulated zone plate is proposed. It can be fabricated by holographic techniques, and it does not require a separate Fourier transforming lens. Experimental results are presented showing the capabilities of the phase plate.

Compact optical data processor employing holographic reflective lenses.

A compact optical data processor is described that employs holographic reflective lenses. The processor is inexpensive and requires one-half of the length of the optical bench as that required for using glass lenses. The fabrication of the holographic lenses is described, and the results of optical processing reported. The results show that an inexpensive data processor employing holographic lenses is a feasible project. The processor may find use for onboard optical processing on spacecrafts and satellites. The most distinguishing characteristic of such a processor is its extreme light weight. The angular alignment tolerances for holographic lenses are very low. The processor must, therefore, be made rugged, designed, and mounted to withstand vibrations, shocks, and other environmental problems associated with spacecrafts and satellites.

Higher order aberrations in holographic lenses.

Third-, fifth-, and seventh-order aberrations have been analyzed for in-line and off-axis holographic lenses of different f/No. The seventh-order wave aberrations and the corresponding aberration coefficients are reported here for the first time. It has been concluded that when the holograms are to be used as optical elements, fifth- and seventh-order aberrations should also be considered along with the third order to achieve ideal imagery as both the chromatic and nonchromatic aberrations are quite large even when only small deviations from the recording geometry are present in the reconstruction step.

Measurement of the coherence length of a laser using a holographically generated phase-conjugated wave front.

A simple and quick method is reported for measurement of the coherence length of a laser by using a holographically generated phase-conjugated wave front employing realtime recording material.