Showing papers on "Supercontinuum published in 1989"

Picosecond relaxation path of ethyl violet

Abstract: Steady-state and time-resolved spectroscopy of a triphenylmethane dye (ethyl violet) exhibiting a fast electronic relaxation is studied. Transient transmissions were probed with a supercontinuum in the 1-20 ps range and fluorescence decays were monitored with a streak camera. Delayed bleaching is observed in solution at room temperature when probing in the short wavelength edge of the main ground state absorption band (530–560 nm). The various shapes of the transmission curves measured at wavelengths where transient absorption, ground state bleaching or amplification dominates are explained by a model involving one absorbing intermediate state. The existence of two electronic transitions in the visible ground state absorption is confirmed as well as non-exponential fluorescence decay. The relaxation mechanism is discussed in terms of internal twisting with charge redistribution.

Chapter 4 – SELF-PHASE MODULATION

Abstract: Publisher Summary This chapter considers SPM as a simple example of the non-linear optical effects that can occur in optical fibers. It is devoted to pure SPM as it neglects the GVD effects and focuses on spectral changes induced by SPM. The combined effects of GVD and SPM are discussed with emphasis on the SPM-induced frequency chirp. The chapter presents two analytic techniques and uses them to solve the NLS equation approximately. The analysis to higher-order non-linear effects such as self-steepening is also included and the chapter illustrates the SPM-broadened spectra for an unchirped Gaussian pulse and contains a graph of experimentally observed spectra for a nearly Gaussian pulse at the output of a 99-m-long fiber. The chapter summarizes that the SPM and other non-linear effects such as stimulated Raman scattering and four-wave mixing, occurring simultaneously inside optical fibers, can broaden the spectrum of an ultrashort pulse so much that it may extend over 100 nm or more. Such extreme spectral broadening is called supercontinuum, a phenomenon that has attracted considerable attention in recent years because of its potential application. Pulse spectra extending over as much as 1000 nm have been generated using the so-called highly non-linear fibers.

Phase Modulation of Ultrashort Laser Pulses

Abstract: Supercontinuum generation, i. e., the production of intense ultrashort broadband pulses by passing picosecond laser pulses through condensed media is reviewed. The generation mechanism includes self-phase modulation, four-photon parametric generation, cross-phase modulation, and induced-phase modulation.

On the Origin and Optical Properties of the Supercontinuum Generation

Abstract: Publisher Summary Intense picosecond pulses propagating in nonlinear media can produce frequency broadened output beams with a nearly white spectrum called supercontinuum (SC). SC generation is correlated with self-focusing (SF) and self-trapped filament formation. This chapter discusses the effect in solids, liquids, and gases. Supercontinuum cone emission (SCCE) has the same circular or linear polarisation as that of the input laser beam. Any light of circular polarisation contains a small portion of counter rotating polarisation radiation. The weaker polarisation should be self-trapped before the stronger one, resulting in light changing its polarisation into a linear. That change occurs inside the filaments where the saturation degree is maximal. The SCCE angle is independent on the lens focal length in the range 5–20 cm. The SCCE, similar to conical emission in alkali metal vapors and class II radiation, is a radiation formed on the surface of the self-trapped filaments—a process involving longitudinal momentum conservation only. The supercontinuum conical emission is generated at the surface of self-trapped filaments, and it shares its optical characteristics with other Cherenkov-type processes—conical emission in alkali metal vapors and class II Raman radiation.