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Kim, D. M.

Publications and source records attributed to Kim, D. M..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Characterization of iron-doped lithium niobate for holographic storage applications

A comprehensive characterization of chemical and holographic properties of eight systematically chosen Fe:LiNbO3 crystals is performed in order to determine optimum performance of the crystals in holographic storage and display applications. The discussion covers determination of Fe(2+) and Fe(3+) ion concentrations in Fe:LiNbO3 system from optical absorption and EPR measurements; establishment of the relation between the photorefractive sensitivity of Fe(2+) and Fe(3+) concentrations; study of the spectral dependence, the effect of oxygen annealing, and of other impurities on the photorefractive sensitivity; analysis of the diffraction efficiency curves for different crystals and corresponding sensitivities with the dynamic theory of hologram formation; and determination of the bulk photovoltaic fields as a function of Fe(2+) concentrations. In addition to the absolute Fe(2+) concentration, the relative concentrations of Fe(2+) and Fe(3+) ions are also important in determining the photorefractive sensitivity. There exists an optimal set of crystal characteristics for which the photorefractive sensitivity is most favorable.

Shah, R. R.↗
NASA NTRS1976

Nonlinear dynamic theory for photorefractive phase hologram formation

A nonlinear dynamic theory is developed for the formation of photorefractive volume phase holograms. A feedback mechanism existing between the photogenerated field and free-electron density, treated explicitly, yields the growth and saturation of the space-charge field in a time scale characterized by the coupling strength between them. The expression for the field reduces in the short-time limit to previous theories and approaches in the long-time limit the internal or photovoltaic field. Additionally, the phase of the space charge field is shown to be time-dependent.

Kim, D. M.↗
NASA NTRS1976

Photorefractive materials for optical storage and display

Real-time data storage and processing using optical techniques have been considered in recent years. Of particular interest are photosensitive electro-optic crystals which permit volume storage in the form of phase holograms, by means of a charge transfer process. A survey of the state of the art of such holographic memories is presented. The physical mechanism responsible for the formation of phase holograms in such crystals is discussed. Attention is focused on various aspects of materials characterization, development and utilization. Experimental reversible holographic read-write memory systems with fast random access and high storage capacity employing this new class of photosensitive materials have already been demonstrated.

Shah, R. R.↗
NASA NTRS1972

A study of compressed spatially non-Gaussian optical pulses from mode-locked lasers.

The effect of the grating-induced phase and spatial modulations by multiple transverse modes simultaneously present in mode-locked laser pulses is investigated. Our analysis shows that the dispersions of the grating pair become strongly dependent on wavelength because of the energy exchanges occurring among transverse modes. As a result, the maximum-intensity trace at the output of the grating is shown to be curved and the grating-induced pulse-compression rate is shown to vary significantly across the beam cross section. Also, a discussion is presented relating our analysis to existing experimental data on the wavelength-dependent chirping rates of mode-locked laser beams.

Kim, D. M.↗
NASA NTRS1972

Effect of saturated frequency chirping on mode-locked laser pulses.

A dye-induced nonlinear frequency chirping is analytically shown to have significant modifications on the nature of the output mode-locked lasers. It is shown that the saturated frequency sweeping is responsible for substantial pulse broadening as well as substructures.

Kim, D. M.↗