Self-reconstruction of a distorted nondiffracting beam

In this article, we review the phenomenon of dispersion, paying particular attention to its impact in the optics of ultrashort pulses, as well as its measurement and management. At present, lasers generating coherent bandwidths of several hundred nanometers have been demonstrated and correspondingly short pulses of 10 fs or so are quite usual. The limits to the breadth of optical spectra and brevity of pulse durations that may be achieved are often set by the dispersive properties of the linear optical elements of which the source is constructed. Progress in ultrafast optics to date has therefore relied extensively on the development of ways to characterize and manipulate dispersion. The means by which this can be accomplished are significantly different for laser oscillators and laser amplifiers, as well as for nonlinear interactions that are used to extend the range of frequencies at which short optical pulses are available, but in all cases it is this phenomenon that determines the output of current optical sources.

The role of dispersion in ultrafast optics

We demonstrate the possibility of a 52-fs pulse single-shot measurement by using the spatial analysis of the second harmonic beam produced in an optical autocorrelator. We show that this method gives a reliable means of optimizing low repetition rate femtosecond amplifiers. Since the introduction of femtosecond laser systems in 19811 much progress has been made toward reducing the duration of the produced pulses. These lasers are able to produce pulses shorter than 70 fs and with a peak power up to 10 GW. 2 3 Moreover, one always uses the classical background-free autocorrelation scheme 4 (modified Michelson interferometer with a scanning arm) to measure the pulses. There have not been significant advances in obtaining a real time measurement (i.e., made with a single pulse) of femtosecond pulses. In the picosecond domain, streak cameras with 0.4-ps rise time exist, but they cannot be used for 100-fs pulses. At this time, there is much theorizing about new measurement systems for femtosecond pulses 5 - 7 but few experimental demonstrations of their capabilities. The problem is to transform the temporal information (shape of the pulse) into a more convenient form (spatial or slowly varying signal). In a classical autocorrelator the delay between the two pulses is slowly swept, and the autocorrelation function is built from a large number of successive pulses. In the picosecond domain, single-shot measurements have been demonstrated using two-photon fluorescence (TPF) 8 or second harmonic generation. 9 In a recent paper, Sperber and Penzkofer 8 show that TPF traces could be decorrelated to determine the approximate temporal shape of modulated pulses. Nevertheless, the continuous background signal produced by each individual beam gives a maximum contrast ratio of 3:1 between the maximum value of the autocorrelation function and the background level. In 1981, Wyatt and Marinero 9

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Single-shot measurement of a 52-fs pulse.

Focusing of Laguerre–Gaussian beams by axicon

“Non-diffracting” beams do not spread as they propagate. This property is useful in many areas. Here, the theory, generation, properties, and applications of various “non-diffracting” beams, including the Bessel beam, Mathieu beam, and Airy beam is reviewed. Applications include imaging, micromanipulation, nonlinear optics, and optical transfection.

Light beats the spread: ``non-diffracting'' beams

Background-free measurement of time behaviour of an individual picosecond laser pulse

We report on a novel pumping scheme for stimulated Raman scattering (SRS) that uses a Bessel beam. We have used this scheme for SRS from molecular vibrations in acetone and from a polariton mode in a LiIO3 crystal. A nearly diffraction-limited Stokes beam was observed along the cone axis of the Bessel beam. The generation mechanism of the Stokes beam is identified as being due to noncollinear scattering of the component plane waves that constitute the Bessel beam. Frequency tuning of SRS from polaritons in LiIO3 by variation of the Bessel beam cone angle is demonstrated.

S. Sogomonian

Papers

Background-free measurement of time behaviour of an individual picosecond laser pulse

Tunable stimulated Raman scattering by pumping with Bessel beams.

Self-reconstruction of a Bessel beam in a nonlinear medium

Stimulated Raman scattering of femtosecond Bessel pulses

Propagation dynamics of phase dislocations embedded in a Bessel light beam