S. L. Shapiro

Bio: S. L. Shapiro is an academic researcher. The author has contributed to research in topics: Picosecond & Raman scattering. The author has an hindex of 9, co-authored 15 publications receiving 1147 citations.

Observation of Self-Phase Modulation and Small-Scale Filaments in Crystals and Glasses

Abstract: Frequency broadening and small-scale filaments were observed in calcite, quartz, sodium chloride, and several glasses under picosecond pulse excitation. The physical mechanism responsible for these processes is the change in refractive index resulting from electronic distortion.

Optical Phonon Lifetime Measured Directly with Picosecond Pulses

Abstract: The lifetime of the 1086-${\mathrm{cm}}^{\ensuremath{-}1}$ optical phonon in calcite is measured directly to be 8.5 \ifmmode\pm\else\textpm\fi{} 2 psec at 297\ifmmode^\circ\else\textdegree\fi{}K and 19.1 \ifmmode\pm\else\textpm\fi{} 4 psec at 100\ifmmode^\circ\else\textdegree\fi{}K by using a picosecond laser beam to create the phonons by stimulated Raman scattering, and then observing Raman scattering off the phonons at various delay times with a weaker picosecond beam at another frequency.

Establishment of a Molecular-Vibration Decay Route in a Liquid

Abstract: The decay route of the methyl vibrations in ethanol excited by stimulated Raman scattering is shown to be a splitting into daughter vibrations of half the frequency. Measurements of the growth and the decay of these daughter vibrations are reported for the first time using picosecond probe techniques.

Supercontinuum generation in photonic crystal fiber

Abstract: A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Intense few-cycle laser fields: Frontiers of nonlinear optics

Abstract: The rise time of intense radiation determines the maximum field strength atoms can be exposed to before their polarizability dramatically drops due to the detachment of an outer electron. Recent progress in ultrafast optics has allowed the generation of ultraintense light pulses comprising merely a few field oscillation cycles. The arising intensity gradient allows electrons to survive in their bound atomic state up to external field strengths many times higher than the binding Coulomb field and gives rise to ionization rates comparable to the light frequency, resulting in a significant extension of the frontiers of nonlinear optics and (nonrelativistic) high-field physics. Implications include the generation of coherent harmonic radiation up to kiloelectronvolt photon energies and control of the atomic dipole moment on a subfemtosecond $(1{\mathrm{f}\mathrm{s}=10}^{\mathrm{\ensuremath{-}}15}\mathrm{}\mathrm{s})$ time scale. This review presents the landmarks of the 30-odd-year evolution of ultrashort-pulse laser physics and technology culminating in the generation of intense few-cycle light pulses and discusses the impact of these pulses on high-field physics. Particular emphasis is placed on high-order harmonic emission and single subfemtosecond extreme ultraviolet/x-ray pulse generation. These as well as other strong-field processes are governed directly by the electric-field evolution, and hence their full control requires access to the (absolute) phase of the light carrier. We shall discuss routes to its determination and control, which will, for the first time, allow access to the electromagnetic fields in light waves and control of high-field interactions with never-before-achieved precision.

Femtosecond laser micromachining in transparent materials

Abstract: Femtosecond laser micromachining can be used either to remove materials or to change a material's properties, and can be applied to both absorptive and transparent substances. Over the past decade, this technique has been used in a broad range of applications, from waveguide fabrication to cell ablation. This review describes the physical mechanisms and the main experimental parameters involved in the femtosecond laser micromachining of transparent materials, and important emerging applications of the technology. Interactions between laser and matter are fascinating and have found a wide range of applications. This article gives an overview of the fundamental physical mechanisms in the processing of transparent materials using ultrafast lasers, as well as important emerging applications of the technology.

Vibrational dynamics of liquids and solids investigated by picosecond light pulses

Abstract: With well-defined coherent light pulses of several ${10}^{\ensuremath{-}12}$ sec duration we are in a position to investigate a variety of ultrafast vibrational processes in liquids and solids. Several new experimental techniques have been devised to study directly the dynamics of different vibrational modes and molecules in the electronic ground state. A first light pulse excites the vibrational system via stimulated Raman scattering or by resonant infrared absorption. A second interrogating pulse allows one to determine the instantaneous state of the excited system. Using a coherent probing technique one can measure the dephasing time of homogeneously broadened vibrational transitions and a collective beating of multiple isotope levels. In addition, one can investigate inhomogeneously broadened vibrational modes and observe the dephasing time of a small molecular subgroup. Different information is obtained when the coherent anti-Stokes Raman scattering of the probe pulse is measured. The population lifetime of known vibrational modes can be investigated and evidence for inter- and intra-molecular interactions is obtained. In a third probing technique, the vibrationally excited jolecules are promoted to the first electronic state by a second pulse and the fluorescence is measured. In this way it is possible to see the very rapid change of population of the primary excited vibrational mode. The article gives a detailed theoretical treatment of different excitation and probing processes. Several experimental techniques successfully applied in the authors investigations are outlined and a variety of results is presented and discussed. New information, not available from other experimental methods, is obtained.