A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Femtosecond filamentation in transparent media

Summary form only given. Fundamental processes in atoms, molecules, as well as condensed matter are triggered or mediated by the motion of electrons inside or between atoms. Electronic dynamics on atomic length scales tends to unfold within tens to thousands of attoseconds (1 attosecond [as] = 10-18 s). Recent breakthroughs in laser science are now opening the door to watching and controlling these hitherto inaccessible microscopic dynamics. The key to accessing the attosecond time domain is the control of the electric field of (visible) light, which varies its strength and direction within less than a femtosecond (1 femtosecond = 1000 attoseconds). Atoms exposed to a few oscillations cycles of intense laser light are able to emit a single extreme ultraviolet (XUV) burst lasting less than one femtosecond. Full control of the evolution of the electromagnetic field in laser pulses comprising a few wave cycles have recently allowed the reproducible generation and measurement of isolated sub-femtosecond XUV pulses, demonstrating the control of microscopic processes (electron motion and photon emission) on an attosecond time scale. These tools have enabled us to visualize the oscillating electric field of visible light with an attosecond "oscilloscope", to control single-electron and probe multi-electron dynamics in atoms, molecules and solids. Recent experiments hold promise for the development of an attosecond X-ray source, which may pave the way towards 4D electron imaging with sub-atomic resolution in space and time.

Attosecond Physics

Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.

A compact X-ray free-electron laser emitting in the sub-ångström region

Modern laser sources nowadays deliver ultrashort light pulses reaching few cycles in duration and peak powers exceeding several terawatt (TW). When such pulses propagate through optically transparent media, they first self-focus in space and grow in intensity, until they generate a tenuous plasma by photo-ionization. For free electron densities and beam intensities below their breakdown limits, these pulses evolve as self-guided objects, resulting from successive equilibria between the Kerr focusing process, the chromatic dispersion of the medium and the defocusing action of the electron plasma. Discovered one decade ago, this self-channeling mechanism reveals a new physics, widely extending the frontiers of nonlinear optics. Implications include long-distance propagation of TW beams in the atmosphere, supercontinuum emission, pulse shortening as well as high-order harmonic generation. This review presents the landmarks of the 10-odd-year progress in this field. Particular emphasis is laid on the theoretical modeling of the propagation equations, whose physical ingredients are discussed from numerical simulations. The dynamics of single filaments created over laboratory scales in various materials such as noble gases, liquids and dielectrics reveal new perspectives in pulse shortening techniques. Far-field spectra provide promising diagnostics. Attention is also paid to the multifilamentation instability of broad beams, breaking up the energy distribution into small-scale cells along the optical path. The robustness of the resulting filaments in adverse weathers, their large conical emission exploited for multipollutant remote sensing, nonlinear spectroscopy and the possibility of guiding electric discharges in air are finally addressed on the basis of experimental results.

https://iopscience.iop.org/article/10.1088/0034-4885/70/10/R03/pdf

Ultrashort filaments of light in weakly ionized, optically transparent media

We demonstrated the energy scaling of phase matched high-order harmonics using a self-guiding beam. By adjusting the gas density and the pump laser focusing, we generated the 27th harmonic with an output energy as high as 0.5 /spl mu/J at wavelength 30 nm.

Generation of sub-/spl mu/J high-order harmonics in the soft x-ray region

A total output energy exceeding 30 mJ has been achieved in the infrared region by dual-chirped optical parametric amplifier for generating soft x-ray harmonic pulses. Obtained spectrum supports a pulse duration shorter than 40 fs.

High-energy infrared femtosecond pulses by dual-chirped optical parametric amplification

Generation dynamics of high order harmonies in a selfguided beam

We discuss the feasibility of an efficient laser wakefield acceleration driven by an intense mid-infrared pulse. TW-scale 1.5 μm laser pulse can improve the number of accelerated electrons as an order of magnitude, compared with that driven by a Ti:sapphire laser (0.8 μm).

Efficient laser wakefield acceleration by using mid-infrared pulses

One of the most crucial issues for the present attoscience is to increase the energy of isolated attosecond pulses (IAP's). Typical pulse energy of IAP's reported before is order of pJ, which is enough for streaking-type experiments[1], but not for fundamental pump-and-probe-type experiments using IAP's only. For this purpose, there are two crucial experimental challenges to demonstrate; one is to develop a multi-mJ few cycle laser with a stabilized carrier-envelope phase (CEP) and the other is the phase-matching between the few cycle pulses and high harmonics of them.

Eiji J. Takahashi

Papers

Generation of sub-/spl mu/J high-order harmonics in the soft x-ray region

High-energy infrared femtosecond pulses by dual-chirped optical parametric amplification

Generation dynamics of high order harmonies in a selfguided beam

Efficient laser wakefield acceleration by using mid-infrared pulses

Direct generation of highly phase-matched isolated attosecond pulses using multi-mJ, carrier-envelope phase stabilized, few-cycle laser pulses