Bulk Photorefractive Semiconductors

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Time-resolved buildup of a photorefractive grating induced in Bi12SiO20 by picosecond light pulses

International audiencePhotorefractive gratings are induced with picosecond light pulses in a BSO crystal. Both experiment and calculations show a buildup of the effect governed by a diffusion of the excited charge carriers that occurs after illumination

Characterization and optimization of a ring self-pumped phase conjugate mirror at 1.06 Μm with BaTiO3:Rh

International audienceWe optimize the ring self-pumped phase-conjugate mirror at 1.06 mm. With cw as well as nanosecond illumination the photorefractive efficiency is higher than 90%. Therefore the reflectivity (79%) is limited only by the transmission of the loop. Another relevant characteristic is the time needed to increase the reflectivity from 10% to 90% of its maximum value, which is as little as 12 s at 5 W cm22 in the cw regime. In the nanosecond regime, 90 J cm22 is needed. We study the response to an abrupt change in the incident wave front, taking into account the three-prism system inserted in the loop

Two-wave mixing in photorefractive BaTiO3:Rh at 1,06 µm in the nanosecond regime

International audienceWe present two-beam coupling experiments in the nanosecond regime at 1.06 mm, using photorefractive BaTiO3:Rh. The maximum observed exponential gain coefficient is 14.2 cm-1. No intensity-dependent electron-hole competition and no strong saturation of the photoionized charge carriers are observed for intensities of less than 20 MW cm-2. The energy required for recording the photorefractive grating is not significantly different in the nanosecond and the cw regimes

Saturation of the Raman amplification by self-phase modulation in silicon nanowaveguides

We experimentally show that the self-phase modulation of picosecond pump pulses, induced by both the optical Kerr effect and free-carrier refraction, has a detrimental effect on the maximum on-off Raman gain achievable in silicon on insulator nanowaveguides, causing it to saturate. A simple calculation of the Raman gain coefficient from the measured broadened output pump spectra perfectly matches the saturated behavior of the amplified Raman signal observed experimentally at different input pump powers.Comment: Accepted for publications in Applied Physics Letter

Balanced homodyne detection of Bragg microhologramms in photopolymer for data storage

Wavelength multiplexed holographic bit oriented memories are serious competitors for high capacity data storage systems. For data recording, two interfering beams are required whereas one of them should be blocked for readout in previously proposed systems. This makes the system complex. To circumvent this difficulty and make the device simpler, we validated an architecture for such memories in which the same two beams are used for recording and reading out. This balanced homodyne scheme is validated by recording holograms in a Lippmann architecture

Photoinduced magneto-optic Kerr effects in asymmetric semiconductor microcavities

Giant photoinduced magneto-optic Kerr effects are predicted and measured in asymmetric semiconductor microcavities with a totally reflecting rear mirror operated in the limit of the strong coupling regime. Themicrocavity is modeled by two coupled Fabry-Perot cavities and use is made of the optical scattering matrices to derive its characteristics. The giant photoinduced rotations and phase changes are traced to the saturation, blueshift, and pseudo-Zeeman splitting of the exciton transition. Modeling the lower and upper polariton transitions by two different two-level systems qualitatively accounts for the main spectral features: the photoinduced Kerr rotations and phase changes are due to the modifications of the coupling existing between the cavity and exciton modes, due to the photoinduced changes of the exciton characteristics. The influence of spin relaxation on the rotation and ellipticity spectra is also analyzed; it confirms the gyrotropic nature of the interaction which depends strongly on the difference between the densities of counter-rotating circularly polarized excitons and only weakly on their sum as is the case in previous isotropic studies. Measurements of photoinduced Kerr rotations performed at a temperature of 50 K in a microcavity containing a single semimagnetic semiconductor quantum well confirm the effectiveness of the effect with polarization rotations of 10° around the lower polariton frequency at a pump fluence of only 2 μJ/cm2

High power multimode fiber amplifier with wavefront reshaping for high beam quality recovery

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