RESUMEN
Holographic gratings are recorded in colloidal suspensions of silver nanoparticles by utilizing interfering nanosecond pulses. The diffraction efficiency is measured with continuous-wave light. An instantaneous response together with a transient grating are observed: the nanoparticles absorb the pump light and heat up. Heat is transferred to the solvent, and a delayed thermal grating appears. The final decay time constant of this grating depends quadratically on the period length and has a typical value of 1 micros for grating spacings of several micrometers.
RESUMEN
Photorefractive gratings are recorded in lithium niobate crystals in the presence of externally applied electric fields close to the coercive field. After optical erasure a voltage pulse above the poling threshold is applied, and by these means a photorefractive grating reappears that can be erased optically. The results point to electrical fixing, i.e., ferroelectric domain reversal induced by a space-charge field.
RESUMEN
Infrared holographic recording in a two-step process is demonstrated in stoichiometric iron-doped lithium tantalate crystals. Through absorption of two intersecting infrared pulses (A = 1064 nm) a temperature grating and thus a modulated pyroelectric field build up. Free electrons, excited by homogeneous light of a shorter wavelength (lambda = 532 nm) drift in this field, and a phase hologram is stored that can be read nondestructively. The change in refractive index depends mainly on the absorption coefficient at the wavelength of the recording light and on the intensity of the infrared light. The proposed method may be extended to telecommunication wavelengths by choice of suitable dopants.