Robert W. Hellwarth

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We write and read a refractive-index grating in a photorefractive crystal BaTiO(3) with a single 20-nsec laser pulse at 532 nm. The grating formed is erasable with similar pulses. Diffraction efficiency decreases exponentially with the cumulative erasing light energy for 20-nsec pulses at intensity levels of 5-30 MW/cm(2). Optical energies required to write(More)
We discuss exact solutions of Maxwell's equations that describe the evolution of single-cycle electromagnetic pulses. The solutions are applied to recent observations of the diffraction transformation of terahertz pulses. In particular, we elucidate the role of the Gouy shift in the temporal reshaping and polarity reversals of single-cycle terahertz pulses.
We report tributary channel data traffic grooming/exchange of pol-muxed DPSK signal based on Kerr-induced nonlinear polarization rotation. 8 tributary channel data grooming between two pol-muxed 80-Gbit/s DPSK channels is demonstrated with a penalty of <4 dB.
We demonstrate optical-beam phase conjugation by the process of two-beam coupling in photorefractive barium titanate. The incident, image-bearing beam causes exponential gain for counterpropagating waves, which are fed by noise and emerge with a power of the order of 10% of the incident beam and phase conjugate to it. This is expected from the calculated(More)
We measure the optical two-beam coupling gain in three nominally undoped cubic n-type Bi(12)SiO(20) crystals as a function of the beam frequency difference Omega and the beam intensity. The crystal geometry is chosen so that the beam coupling through the ordinary photorefractive effect is absent. From the dependence of the gain on Omega the full complex(More)
A method is introduced that measures the spatial-migration rate of electronic excitation in condensed media over distances of the order of 0.1 microm. Two volume holographic gratings of widely differing modulation periods are simultaneously produced, using a phase-conjugate wave geometry of degenerate four-wave mixing. Spatial migration results in a reduced(More)