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

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

Ultrafast lasers, which generate optical pulses in the picosecond and femtosecond range, have progressed over the past decade from complicated and specialized laboratory systems to compact, reliable instruments. Semiconductor lasers for optical pumping and fast optical saturable absorbers, based on either semiconductor devices or the optical nonlinear Kerr effect, have dramatically improved these lasers and opened up new frontiers for applications with extremely short temporal resolution (much smaller than 10 fs), extremely high peak optical intensities (greater than 10 TW/cm2) and extremely fast pulse repetition rates (greater than 100 GHz).

Recent developments in compact ultrafast lasers

Intracavity semiconductor saturable absorber mirrors (SESAM's) offer unique and exciting possibilities for passively pulsed solid-state laser systems, extending from Q-switched pulses in the nanosecond and picosecond regime to mode-locked pulses from 10's of picoseconds to sub-10 fs. This paper reviews the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime. The combination of device structure and material parameters for SESAM's provide sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence, in a compact structure with low insertion loss. We have been able to demonstrate, for example, passive modelocking (with no Q-switching) using an intracavity saturable absorber in solid-state lasers with long upper state lifetimes (e.g., 1-/spl mu/m neodymium transitions), Kerr lens modelocking assisted with pulsewidths as short as 6.5 fs from a Ti:sapphire laser-the shortest pulses ever produced directly out of a laser without any external pulse compression, and passive Q-switching with pulses as short as 56 ps-the shortest pulses ever produced directly from a Q-switched solid-state laser. Diode-pumping of such lasers is leading to practical, real-world ultrafast sources, and we will review results on diode-pumped Cr:LiSAF, Nd:glass, Yb:YAG, Nd:YAG, Nd:YLF, Nd:LSB, and Nd:YVO/sub 4/.

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Semiconductor saturable absorber mirrors (SESAM's) for femtosecond to nanosecond pulse generation in solid-state lasers

The evolution of the theory of mode-locking over the last three and a half decades is reviewed and some of the salient experiments are discussed in the context of the theory. The paper ends with two-cycle pulses of a mode-locked Ti:sapphire laser.

Mode-locking of lasers

We introduce a new low-loss fast intracavity semiconductor Fabry-Perot saturable absorber operated at anti-resonance both to start and sustain stable mode locking of a cw-pumped Nd:YLF laser. We achieved a 3.3-ps pulse duration at a 220-MHz repetition rate. The average output power was 700 mW with 2 W of cw pump power from a Ti:sapphire laser. At pump powers of less than 1.6 W the laser self-Q switches and produces 4-ps pulses within a 1.4-micros Q-switched pulse at an approximately 150-kHz repetition rate determined by the relaxation oscillation of the Nd:YLF laser. Both modes of operation are stable. In terms of coupled-cavity mode locking, the intra-cavity antiresonant Fabry-Perot saturable absorber corresponds to monolithic resonant passive mode locking.

https://www.ulp.ethz.ch/content/dam/ethz/special-interest/phys/quantum-electronics/ultrafast-laser-physics-dam/research/Overview2005/19.pdf

Solid-state low-loss intracavity saturable absorber for Nd:YLF lasers : an antiresonant semiconductor Fabry-Perot saturable absorber

We report time-to-space mapping of femtosecond light pulses in a temporal holography setup. By reading out a temporal hologram of a short optical pulse with a continuous-wave diode laser, we accurately convert temporal pulse-shape information into a spatial pattern that can be viewed with a camera. We demonstrate real-time acquisition of electric-field autocorrelation and cross correlation of femtosecond pulses with this technique.

/pdf/time-to-space-mapping-of-femtosecond-pulses-5cupy86wl0.pdf

Time-to-space mapping of femtosecond pulses

Semi‐insulating multiple quantum well photorefractive devices using GaAs/Al0.29Ga0.71As with an electric field applied perpendicular to the layers are demonstrated. Semi‐insulating behavior is obtained by doping with Cr(1016/cm3) during epitaxial growth of the material. Diffraction efficiencies as high as 3% with an applied voltage of 20 V and microsecond response times are obtained in a 2 μm thick device. These devices are of importance for implementation of fast and sensitive two‐dimensional optical information processing systems at wavelengths compatible with current diode lasers without the spatial‐bandwidth limitations of thick photorefractive materials.

Cr‐doped GaAs/AlGaAs semi‐insulating multiple quantum well photorefractive devices

We produced transform-limited pulses as short as 130 fs with 160-mW average output power from a passively mode-locked Nd:glass laser. This is to our knowledge the first demonstration of an intracavity semiconductor antiresonant Fabry–Perot saturable absorber continuously starting a Kerr-induced passively mode-locked laser. The antiresonant Fabry–Perot saturable absorber, even with dispersion compensation, produced only picosecond pulses, and femtosecond performance was observed only with the addition of an intracavity long-pass wavelength filter. We propose a new mode-locking mechanism, which we refer to as Kerr-shift mode locking, in which the wavelength-dependent intracavity aperture and self-phase modulation in Nd:glass combine to produce a self-wavelength shift that reduces intracavity losses for femtosecond pulses.

Self-starting femtosecond mode-locked Nd:glass laser that uses intracavity saturable absorbers.

We demonstrate a compact real-time optical image correlator using diode lasers and a semi-insulating GaAs/AlGaAs multiple-quantum-well (SI-MQW) device as the holographic element With only 3 mW of power incident upon the SI-MQW device, the correlation is obtained in 1 microsec and can be erased in as fast as 2 microsec, which presents the possibility of a system capable of 3 x 10 exp 5 correlations/s We also show that images can be stored for a controllable length of time (2-25 microsec), which presents possibilities for the use of the SI-MQW device as a data or image buffer memory

T. H. Chiu

Papers

Solid-state low-loss intracavity saturable absorber for Nd:YLF lasers : an antiresonant semiconductor Fabry-Perot saturable absorber

Time-to-space mapping of femtosecond pulses

Cr‐doped GaAs/AlGaAs semi‐insulating multiple quantum well photorefractive devices

Self-starting femtosecond mode-locked Nd:glass laser that uses intracavity saturable absorbers.

High-speed joint-transform optical image correlator using GaAs/AlGaAs semi-insulating multiple quantum wells and diode lasers