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.

Supercontinuum generation in photonic crystal fiber

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

Femtosecond filamentation in transparent media

We review the field of femtosecond pulse shaping, in which Fourier synthesis methods are used to generate nearly arbitrarily shaped ultrafast optical wave forms according to user specification. An emphasis is placed on programmable pulse shaping methods based on the use of spatial light modulators. After outlining the fundamental principles of pulse shaping, we then present a detailed discussion of pulse shaping using several different types of spatial light modulators. Finally, new research directions in pulse shaping, and applications of pulse shaping to optical communications, biomedical optical imaging, high power laser amplifiers, quantum control, and laser-electron beam interactions are reviewed.

Femtosecond pulse shaping using spatial light modulators

Diffraction characteristics of general dielectric planar (slab) gratings and surface-relief (corrugated) gratings are reviewed. Applications to laser-beam deflection, guidance, modulation, coupling, filtering, wavefront reconstruction, and distributed feedback in the fields of acoustooptics, integrated optics, holography, and spectral analysis are discussed. An exact formulation of the grating diffraction problem without approximations (rigorous coupled-wave theory developed by the authors) is presented. The method of solution is in terms of state variables and this is presented in detail. Then, using a series of fundamental assumptions, this rigorous theory is shown to reduce to the various existing approximate theories in the appropriate limits. The effects of these fundamental assumptions in the approximate theories are quantified and discussed.

Analysis and applications of optical diffraction by gratings

We obtain gigawatt white-light continuum pulses that permit spectroscopic measurements with a time resolution of 80 fsec. These pulses extend continuously from 0.19 to 1.6 μm and have time sweeps as small as 10 fsec/1000 A. We find temporal, spatial, and spectral properties that are consistent with self-phase modulation having a prominent role in generation of the continuum.

Femtosecond white-light continuum pulses.

We describe the generation and measurement of optical pulses as short as 30 fs. The pulses are produced using self‐phase modulation in a short 15‐cm optical fiber followed by a grating compressor.

Compression of femtosecond optical pulses

We report a technique for amplifying pulses as short as 70 fs to gigawatt power levels while retaining the short duration of the incident pulse. Pulse recompression by a dispersive delay line is used to compensate temporal broadening by group velocity dispersion.

Amplification of 70‐fs optical pulses to gigawatt powers

Picosecond dynamics of hot carrier relaxation in highly excited multi-quantum well structures

Considerable progress has taken place in the last decade and a half in the generation of ultrashort optical pulses. A steady progression of developments has led to ever shorter optical pulses and subsequent improvements in our ability to resolve fast spectroscopic events. In this discussion I will describe progress that has taken place in our laboratory which has led to the generation of optical pulses of less than 0.1 picoseconds in duration, pushing well into the femtosecond time regime. Three significant advances have taken place in the last two years which have made possible experimental investigations on a femtosecond time scale. The first key advance was the improvement of the passively modelocked dye laser [1] using the colliding pulse modelocked dye laser configuration [2]. With this laser the first pulses with a duration of less than 0.1 picoseconds were generated. The second important result is an improvement in amplification technique which has permitted the generation of femtosecond optical pulses of gigawatt intensities. The final point of discussion will be the use of pulse compression techniques to generate a 30 femtosecond optical pulse, the shortest optical pulse duration yet reported.

R. Yen

Papers

Femtosecond white-light continuum pulses.

Compression of femtosecond optical pulses

Amplification of 70‐fs optical pulses to gigawatt powers

Picosecond dynamics of hot carrier relaxation in highly excited multi-quantum well structures

Moving from the Picosecond to the Femtosecond Time Regime