Christopher Barsi

Dispersive shock waves with nonlocal nonlinearity

We consider dispersive optical shock waves in nonlocal nonlinear media. Experiments are performed using spatial beams in a thermal liquid cell, and results agree with a hydrodynamic theory of propagation.

Diffraction from an edge in a self-focusing medium

We experimentally demonstrate diffraction from a straight edge in a medium with self-focusing nonlinearity. Diffraction into the shadow region is suppressed with increasing nonlinearity, but mode coupling leads to excitations and traveling waves on the high-intensity side. Theoretically, we interpret these modulations as spatially dispersive shock waves with negative pressure.

Increased field of view via nonlinear digital holography

All imaging systems have limitations to their field of view. Here, we experimentally demonstrate that wave mixing due to spatial nonlinearity can increase this parameter.

Peakon profiles and collapse-bounce cycles in self-focusing spatial beams

We study the over-focusing of spatial light beams due to self-focusing nonlinearity, in both local and nonlocal nonlinear media. Numerical simulation of both cases reveals a peaked profile, with a near-cusp at the center surrounded by exponentially-decaying tails, at a critical self-focusing power. The profile is a local effect, occurring as diffraction counteracts nonlinearity. Nonlocality, however, is needed to prevent modulation instability of the initial beam and to prevent catastrophic collapse in 2D. The peaked profile remains for weak nonlocality but disappears for wide nonlocal responses. Beyond the critical power for a peaked solution, or for longer propagation distances, competition between nonlinearity and diffraction causes oscillatory collapse-bounce behavior. The numerical results are confirmed by observing these dynamics in a self-focusing glass with a nonlocal, thermal response.

Digital reconstruction of optically-induced potentials

The holographic reconstruction of optically-induced objects typically assumes that the object is axially thin. Here, we demonstrate a simple approach that works for axially thick objects which evolve dynamically. Results are verified by reconstructing linear scattering experiments in a self-defocusing photorefractive crystal.

Spatially Dispersive Shock Waves in Nonlinear Optics

We discuss recent experimental work demonstrating spatial dispersive shock waves (DSWs). These structures occur whenever nonlinearity enhances diffraction so that wave spreading becomes intensity-dependent. The mechanism of this spreading follows naturally from a hydrodynamic description of light flow, in which wave steepening from phase gradients allows faster parts of a beam to overtake slower parts. Scaling relationships are developed for this spreading and experimentally observed, in both local and nonlocal media.

Observation of the condensation of classical waves

We report a theoretical, numerical and experimental study of condensation of classical optical waves. The condensation of observed directly, as a function of nonlinearity and wave kinetic energy, in a self-defocusing photorefractive crystal.

Digital reconstruction of nonlinear beam propagation

We extend the technique of digital holography to the case of propagation through nonlinear media. We experimentally verify the technique by reconstructing nonlinear wave dynamics within a self-defocusing medium and nonlinearly imaging through it.

Phase Retrieval through Nonlinear Media

We extend the Gerchberg-Saxton algorithm to the phase retrieval through nonlinear media. We experimentally verify the technique by reconstructing a phase distribution from intensity measurements in two image planes with different positions.

Super-resolution via Nonlinearity in Computational Optics

All computational methods suffer from resolution limits due to finite-aperture effects. Using digital holography, we show that nonlinearity surpasses linear limits, as formulated by Abbe, as high-frequency spatial modes mix with low-frequency ones.