D. von der Linde

High‐voltage bulk photovoltaic effect and the photorefractive process in LiNbO3

Photocurrents in doped LiNbO3 crystals are shown to be due to a bulk photovoltaic effect with saturation voltages in excess of 1000 V (∼105 V/cm). This effect accounts for the light‐induced index changes in LiNbO3. An explanation of the photovoltaic effect, based on the asymmetry of the lattice, is proposed.

Excited state polarization bulk photovoltaic effect, and the photorefractive effect in electrically polarized media

Optical absorption in pyroelectric crystals is accompanied by electrical effects (in addition to the well-known pyroelectric effect) which are not present in other materials. Optical excitation between localized states gives rise to an instantaneous macroscopic polarization change due to the change of dipole moment at the absorbing center. Excitation of free carriers from localized states will in general result in a bulk photovoltaic effect due to asymmetric charge transfer. Thus spatially non-uniform illumination gives rise to internal fields, resulting in refractive index variations. Studies of these effects for fast detection, optical logic, memories, and microwave generation will be described.

Photorefractive effects for reversible holographic storage of information

Optical storage of information offers great potential for high capacity and speed. A very promising approach to the embodiment of an optical memory is based on volume storage in the form of phase holograms. Attractive storage materials for such a system are electrooptic crystals. The storage mechanism in these materials is based on light induced permanent changes of the refractive index-the photorefractive effect. In this article the physical processes underlying photorefractive hologram recording are outlined, and some of the advantages and limitations of this method are discussed.

High-sensitivity optical recording in KTN by two-photon absorption

Birefringence changes are induced in a cubic potassium tantalate niobate crystal with an external electric field by two−photon absorption of picosecond optical pulses. The recording sensitivity of 100 μJ/cm2 for elementary holograms with a few percent reconstruction efficiency is comparable to the sensitivity of holographic silver halide emulsions. The high sensitivity of KTN is shown to be due to efficient charge transport of photoexcited carriers.

Optical storage using refractive index changes induced by two‐step excitation

Multiphoton excitation allows reversible photorefractive recording without the disadvantage of erasure during readout. The light intensity required for two‐photon storage can be drastically reduced if two‐step excitation via long†lived real intermediate states is used. Experimental results for LiNbO3:Cr3+ and LiTaO3:Cr3+ demonstrate the advantages of the two‐step process. The energy and intensity requirements for optical two‐step recording are within reach of presently available repetitively pulsed lasers.

Observation of superheating during picosecond laser melting

Abstract The surface temperature of GaAs during pulsed laser heating is obtained from the measured velocity distributions of evaporated atoms. For nanosecond pulses the observed solid-liquid transition temperature agrees with the equilibrium melting point. It is shown that with picosecond pulses the solid is superheated by several hundred degrees.

Recovery time of saturable absorbers for 1.06 u

The recovery time of a new saturable absorber suitable for mode locking of neodymium lasers has been measured and compared with the recovery of two commonly used saturable dyes (Eastman 9740 and 9860).

Suppression of the spectral narrowing effect in lasers mode-locked by saturable absorbers

Abstract A gain profile with a very flat top is produced by incorporating a Fabry-Perot interferometer in the cavity of a mode-locked Nd-glass laser. With proper adjustment of the interferometer parameters, the spectral narrowing effect is significantly reduced, and bandwidth-limited pulses as short as 1.5 psec have been observed.

Mode-locked lasers and ultrashort light pulses

This article reviews some aspects of the generation of very short optical pulses using mode-locked lasers, with the emphasis laid on pulsed laser systems. Active and passive mode-locking is discussed, and the problem of measuring ultrashort light pulses is considered. A survey of some commonly used sources and techniques for the generation of ultrashort light pulses follows. The paper concludes with a short account of limitations in the generation and propagation of these pulses.

Photovoltaic, photoconductive and excited state dipole mechanisms for optical storage in pyroelectrics

Abstract The electronic transport mechanisms in pyroelectrics which give rise to light induced polarization changes are examined with a view to maximizing the sensitivity of materials for optical storage. Experiments demonstrating diffractive scattering due to localized excitation of Cr3 + ions in LiNbO3 are reported.