We present an alternative description of nonlinear cross-phase modulation based on the kinetic equation for photons. The most relevant feature of this new approach is that phase itself is completely ignored. Formal exact solutions and approximate analytical solutions are discussed. Experimental measurements of cross-phase modulation of two-color ultrashort laser pulses propagating in a highly nonlinear photonic crystal fiber reveal a good agreement with the analytical results.
We demonstrate highly-efficient generation of green-blue light using 20-fs femtosecond laser pulses propagating in short highly-nonlinear photonic crystal fibres. Three 5-mm-long fibres with different zero dispersion wavelengths were pumped by Ti:Sapphire pulses centred around 800-nm, and the relevant spectral characteristics of the generated radiation were studied as a function of pulse energy and chirp. In addition to the non-solitonic green-blue light, a well-defined infrared peak was simultaneously observed that follows the same power and wavelength dependence found on the green-blue peak. This work shows that short photonic crystal fibres can be used as an efficient source of ultrashort blue-green pulses (and possibly near-IR pulses) since linear dispersion (and consequent temporal broadening) and absorption of fused silica are minimized when using short fibres.
We report on the efficient spectral control of ultrashort sub-nanojoule violet laser pulses by means of cross-phase modulation (XPM) with a pump pulse in a highly nonlinear photonic crystal fiber (PCF). Spectra of the output pulses were recorded as a function of pump-probe delay for different pump central wavelengths. For fiber lengths that are much longer than the pulse walk-off distance, we consistently observe simultaneous downshifted and upshifted bands in the output pulses, associated with the frequency shift induced by both the leading and trailing edges of the pump as it sweeps over the probe pulses. These features can only be observed with pump pulses propagating in the anomalous dispersion region of the PCF, where pump pulse compression occurs and provides the necessary pump asymmetry.
The aim of this paper is to implement the self-imaging phenomenon by utilizing an incoherent to coherent conversion in a non-holographic approach. This is materialized by using a photorefractive BSO crystal to encode as modulation of birefringence an incoherently projected Ronchi grating that will be coherently read out by collimated laser light which is outside of the spectral sensitivity range of the crystal. The transmitted output through the analyzer is written in terms of: a component of the linear polarized part of the readout wavefront exiting the crystal, and a component of the elliptically polarized part of it. In this way, the incoherent input is converted in a coherent output that repeats itself under free propagation. By rotating the analyzer the contrast of the replicated grating is controlled. Experimental results are presented and possible applications are discussed.