Paraxial energy transport of an intensity-modulated and focused Gaussian beam is studied in ruby. Deformations of the temporal profiles are observed under different conditions and explained by the interplay among a nondegenerate two-wave couplinglike mechanism, the population oscillations, and the Fraunhofer diffraction. Experimental evidence is provided for the existence of a nondegenerate two-wave couplinglike mechanism. The self-superluminal can be observed under proper conditions. A group velocity of −83m∕s is achieved with a Gaussian-like-modulated pulse of 30ms with background illumination. Based on these results, a method to control the group velocity of a single beam in such media is proposed.

Paraxial energy transport of a focused Gaussian beam in ruby with nondegenerate two-wave couplinglike mechanism

Spectroscopic characteristics of 1.54 μm emission in Er/Yb:LiNbO3 crystals tridoped with In3+ ions

This paper investigates the temporal behaviour of open-circuit bright photovoltaic spatial solitons by using numerical techniques. It shows that when the intensity ratio of the soliton, the ratio between the soliton peak intensity and the dark irradiance, is small, the quasi-steady-state soliton width decreases monotonically with the increase of ?, where ? is the parameter correlated with the time, that when the intensity ratio of the soliton is big, the quasi-steady-state soliton width decreases with the increase of ? and then increases with ?, and that the formation time of the steady-state solitons is not correlated with the intensity ratio of the soliton. It flnds that the local nonlinear efiect increases with the photovoltaic fleld, which behaves as that the width of soliton beams is small and the self-focusing quasi-period is short. On the other hand, we also discuss that both the time and the temperature have an efiect on the beam bending.

Temporal development of open-circuit bright photovoltaic solitons ⁄

The slowing down of light in Ce:BaTiO3 at room temperature via degenerate two-wave mixing for chopped pulses is reported. Delay of 0.9 ms is observed for chopped pulses of duration 8 ms, corresponding to a group velocity of 5.5 m/s. Effect of pulse width of signal beam and pump intensity onto the slowing down action of light in the crystal is studied. The building up and decay time of photo grating is also recorded as a function of pump beam intensity.

Effect of Pump Intensity on Slowing Down of Light in ${\rm Ce{:}BaTiO}_{3}$ Crystal via Degenerate Two-Wave Mixing Using Chopped Pulses

Observation of superluminal and slowdown light propagation in doped lithium niobate crystals

We show theoretically that the group velocity of light pulses can be reduced significantly by use of the steep dispersion properties of the phase coupling effect in the photorefractive two-wave mixing process. The group velocity of light pulses of the order of 0.1 m/s can be achieved in typical photorefractive BSO crystals with an appropriate externally applied electric field and moving gratings of appropriate speeds. It is also shown that the slowly propagating light pulses can be set to be amplified after passing through the photorefractive material.

Group Velocity Reduction of Light Pulses in Photorefractive Two-Wave Mixing

We show that the refractive index change induced by a focused incident beam with an additional incoherent uniform illumination in photovoltaic-photorefractive crystals under open-circuit condition has a saturable nonlinearity form. The incoherent uniform background illumination can be used to increase the effective dark irradiance. The formation time of the photovoltaic soliton can be decreased by keeping the intensity of the soliton at a higher value without over-saturation by use of the background illumination.

Saturable Nonlinearity in Photovoltaic-Photorefractive Crystals Under Open-circuit Condition

We solve the Kukhtarev's nonlinear equations of the photorefractive effect with the participation of diffusion, drift and the photovoltaic effect without the approximation of linear generation and linear recombination, and especially discuss in detail the effects of photovoltaic field on the photorefractive grating and its equivalence to an applied electric field in the photovoltaic photorefractive materials.

http://iopscience.iop.org/article/10.1088/0256-307X/12/10/011/pdf

Influence of Photoveltaic Effect on Photorefractive Phase Gratings

Experimental studies of light amplification with dynamic multiwave gratings recorded in an acceptor-donor-substituted azobenzene-doped poly(methyl methacrylate) thin film by multiwave mixing are reported. The amplification gain was measured to be as high as 6.7, and the operation at red light wavelength decreases the absorption losses.

Light Amplification in Non-photorefractive Doped Polymer Film at Red Light Wavelength

By studying the ultraviolet-red two-color holographic storage performances of Mg-, Zn- and In-doped lithium niobate crystals, we found that the response time of the two-color recording could be shortened by as much as 3 orders of magnitude compared to that of one-color recording, and the two-color recording sensitivity was improved significantly, which was measured to be 11 cm/J in the crystal doped with Mg of 5 mol.%. Nonvolatile holographic storage was achieved in the crystals with doping concentrations above the damage-resistant threshold value. However, gratings on the deep centers and the shallow centers were out of phase in Mg- or Zn-doped lithium niobate, while those in In-doped lithium niobate were in phase. We consider that different defects induced by different dopants are responsible for the observed results.

Zhang Guo-Quan

Papers

Group Velocity Reduction of Light Pulses in Photorefractive Two-Wave Mixing

Saturable Nonlinearity in Photovoltaic-Photorefractive Crystals Under Open-circuit Condition

Influence of Photoveltaic Effect on Photorefractive Phase Gratings

Light Amplification in Non-photorefractive Doped Polymer Film at Red Light Wavelength

Influence of dopants on nonvolatile holographic storage in lithium niobate