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.

Intense few-cycle laser fields: Frontiers of nonlinear optics

Group velocity dispersion in prisms and its application to pulse compression and travelling-wave excitation

Femtosecond time-resolved measurements of optic phonon dephasing by impulsive stimulated raman scattering in α-perylene crystal from 20 to 300 K

Femtosecond time-resolved observations of coherent molecular vibrations are carried out through impulse-stimulated Raman scattering (ISRS). Individual cycles of vibrational oscillation, as well as vibrational dephasing, are time resolved. ISRS therefore provides a means through which time-resolved spectroscopy of vibrationally distorted molecules can be carried out. Several experimental configurations involving either crossed excitation pulses or a single excitation pulse are discussed theoretically and demonstrated experimentally. >

Coherent molecular vibrational motion observed in the time domain through impulsive stimulated Raman scattering

Time‐resolved observations of coherent molecular vibrational motion and the general occurrence of impulsive stimulated scattering

In high-gain dye amplifiers, the effective storage time of the gain medium is only a few hundred picoseconds. Therefore, efficient amplification of ultrashort pulses places a stringent requirement on the synchronization between the pump pulse and the pulse to be amplified. We present a technique of short pulse generation using a dye laser synchronously pumped by a frequency-doubled CW mode locked Nd:YAG laser. Pulses as short as 70 fs are produced. The short optical pulses are subsequently amplified with two different synchronous amplification schemes using 100 ps pulses to establish the gain in the dye amplifier stages. Subpicosecond pulses with energies from a few hundred nanojoules at 500 Hz to a few hundred microjoules at 7 Hz can be obtained.

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Synchronous amplification of subpicosecond pulses

Pulse compression by stimulated Brillouin scattering (A)

With the exception of picosecond photoelectron switching recently demonstrated, streak camera tubes have been used exclusively as a fast optical and x-ray diagnostic tool. However, some of the most beautiful features of the image converter device used in the streak camera have been only partially exploited with this application. The image converter device produces a temporal and spatial monoenergetic photoelectron replica of the incident optical pulse. This replica is ultimately limited by the temporal and spatial resolution of the particular streak tube employed. Temporal and spatial resolution can be as good as subpicosecond and 100 μm respectively. It is also worth noting that this replica is accurately synchronized with the incident optical pulse. We have used this electron burst to generate an electron diffraction pattern, inferring that picosecond snap shots of laser induced structural changes in laser annealing or in the field of surface physics, can now be taken not only with a picosecond exposure, but also in picosecond synchronization with the laser induced kinetics. In the experiment (Fig.1) a demountable photochron II streak camera tube is used. The Al specimen of 150 Angstroms thickness is located in the drift space 1 cm behind the anode. The diffraction pattern is captured on a phosphor sreen and photographed using an image intensifier with a gain of 3×104 lens coupled to the film.

Electron Diffraction in the Picosecond Domain Steven Williamson and Gerard Mourou and Synchronous Amplification of 70 fsec Pulses Using a Frequency-Doubled Nd: YAG Pumping Source

Conger W. Gabel

Papers

Synchronous amplification of subpicosecond pulses

Pulse compression by stimulated Brillouin scattering (A)

Electron Diffraction in the Picosecond Domain Steven Williamson and Gerard Mourou and Synchronous Amplification of 70 fsec Pulses Using a Frequency-Doubled Nd: YAG Pumping Source

Picosecond electrooptic sampler