Energy transfer between two filaments and degenerate four-photon parametric processes

Four photon parametric amplification

Energy transfer between laser filaments in liquid methanol.

We demonstrate energy exchange between two filament-forming femtosecond laser beams in liquid methanol. Our results are consistent with those of previous works documenting coupling between filaments in air; in addition, we identify an unreported phenomenon in which the direction of energy exchange oscillates at increments in the relative pulse delay equal to an optical period (2.6 fs). Energy t...

Efficient energy transfer between four-wave-mixing and six-wave-mixing processes via atomic coherence

We demonstrate efficient energy exchange during propagation between four-wave-mixing FWM and sixwave-mixing SWM signals generated in a four-level inverted-Y atomic system, which fall in the electromagnetically induced transparency window. After an initial growth distance for both FWM and SWM fields in the atomic medium, these two nonlinear optical processes compete and exchange energy between t...

Two-step four-photon absorption.

We report a theoretical investigation of effective four-photon absorption (4PA) process and propose a two-step 4PA model of three-photon- induced excited-state absorption (ESA). Based on three-level rate-equation theory, we find an analytical result for the effective 4PA coefficient that depends on the three-photon absorption (3PA) cross-section, excited-state photophysical properties, and lase...

Experimental filtering of two-, four-, and six-photon singlets from a single parametric down-conversion source

Invariant entangled states remain unchanged under simultaneous identical unitary transformations of all their subsystems. We experimentally generate and characterize such invariant two-, four-, and six-photon polarization entangled states. This is done only with a suitable filtering procedure of multiple emissions of entangled photon pairs from a single source without any interferometric overla...