Journal of Nonlinear Optical Physics & Materials

We discuss applications of coherent four-wave mixing in the plasma of optical breakdown produced by an additional laser pulse (laser-preproduced plasma) for the generation of short-wavelength radiation and the investigation of spatial distribution of atoms and ions. The use of an additional laser for the generation of laser-produced plasma on the surface of a metal target makes it possible to optimize the efficiency of frequency conversion and to implement plasma diagnostics at various stages of plasma expansion. An experimental technique based on hyper-Raman-resonant four-wave mixing is developed for two-dimensional mapping of relative populations of excited atomic and ionic states in laser-produced plasma.

A finite number of color centers in the region of sharp crystal needle's tip has been recently observed by laser resonance photoelectron projection microscopy technique. Hereby we present a new result in the field: only one single color center was observed on the tip region of lithium fluoride and calcium fluoride needles. Due to the high fluorescence yield of these color centers such needles can be treated as one-atom light sources, and perspectives of their application in Scanning One-Atom Fluorescence Resonance Energy Transfer Microscopy are briefly discussed.

An analytical model has been developed to describe both drift and diffusion mechanisms of nonlinear response (local and nonlocal components of nonlinearity) of photorefractive crystals (PRCs) on a microscopic level. Some types of stable self-consistent distributions of light intensity — bright and dark photorefractive spatial solitons — have been considered. Paths of their propagation (self-bending) have been calculated and a possibility of formation of a new type of soliton-like distributions — spatial shock waves — has been shown. Analysis of plane wave modulation instability has been performed and specific spatial scales of light distribution, resulting from self-action processes (fanning), have been calculated. All the analytical results have been confirmed using computer simulation.

An original approach to constructing special type symmetries for boundary value problems, RENORMGROUP SYMMETRIES, is reviewed here. It is applied to a system of geometric optics equations. New solutions to the laser beam self-focusing problem are presented.

The influence of losses and thermal noise on the polarization-squeezed light formation in a medium with third order nonlinearity has been analysed. A method of analysis based on the delta-correlation property of noise was developed. Mean values and variances of some Stokes parameter of the light was calculated. It was shown that optimal interaction length for effective fluctuation suppression in the Stokes parameters is determined by damping constants, noise level, and radiation intensity.

The potentialities of fabricating large-size monosectorial crystals for powerful laser systems are discussed. Two types of technologies used for high-rate growth of profiled crystals and some results attained in crystal growth in the Institute of Applied Physics of the Russian Academy of Science are described briefly. It is concluded that the growth technique developed may be used for producing large-size optical elements (about 400 × 400 mm²) for laser systems intended for nuclear fusion experiments.

The new self-similar solutions to the problem of bichromatic field interaction with medium of three-level atoms or molecules have been found. The solutions are explicit and hence very helpful to discover the new properties of soliton-like pulses discovered in different experiments.

We demonstrated how the moving focus model developed for condensed media should be modified for the explanation of experiments on filamentation of high-power femtosecond laser pulses in air. This modification is based on the consideration of gas ionization in high-intensity laser field. Numerical simulations based on this modified model allow for the explanation not only of filamentation itself but also the accompanying phenomena such as refocusing and conical emission.

Two new types of targets: ultrathin freely suspended carbon films and porous Si, both revealing thermoconductivity restriction leading to plasma overheating upto electron temperature above 1 keV under "moderate" intensities 10¹⁵ - 10¹⁶ W · cm^-2 has been investigated experimentally. For the ultrathin carbon film of 20–30 nm X-ray yield threefold increase has been observed. Computer simulations decribe well the observed behaviour of the X-ray yield, and the electron temperature of 700 eV was deducted for the film of 10 nm in thickness. Por-Si produces greater X-ray flux under intensity of 10¹⁶ W · cm^-2 as compared to the solid Si. If the intensity increased the total X-ray yield from por-Si undergoes "saturation", while the X-ray yield from solid Si fits as ≈ I². Simple model to describe the "overheating" of Si plasma using a set of ultrathin films is developed. Some promising advantages of new targets are discussed.

The ultimate goal of worldwide research in inertial confinement fusion (ICF) is to develop fusion as an inexhaustible, economic, environmentally safe source of electric power. Following nearly thirty years of laboratory and underground fusion experiments, the next step toward this goal is to demonstrate ignition and propagating burn of fusion fuel in the laboratory. The National Ignition Facility (NIF) Project is being constructed at Lawrence Livermore National Laboratory (LLNL) for just this purpose. NIF will use advanced Nd-glass laser technology to deliver 1.8 MJ of 0.35 μm laser light in a shaped pulse, several nanoseconds in duration, achieving a peak power of 500 TW. A national community of U.S. laboratories is participating in this project, now in its final design phase. France and the United Kingdom are collaborating on development of required technology under bilateral agreements with the US. This paper presents key aspects of the laser design, and descriptions of principal laser and optical components. Follow-on development of lasers to meet the demands of an inertial fusion energy (IFE) power plant is reviewed.

In parallel with the NIF Project and IFE developments, work is proceeding on ultrashort pulse lasers with peak power in the range of 100–1000 TW. A beamline on the Nova laser at LLNL recently delivered nearly 600 J of 1 μm light in a 0.5 ps duration pulse, for a peak power in excess of a petawatt (10¹⁵ W). This beamline, with advanced adaptive optics, will be capable of focused intensities in excess of 10²¹ W/cm². Its primary purpose will be to test technological and scientific aspects of an alternate ignition concept, called the "Fast Igniter", that has the potential to produce higher fusion gain than conventional ICF.

Progresses in nonlinear optical materials research and laser pump source development have led to rapid advances in many areas of optical parametric device technology in recent years. One particularly active area has been broadly tunable femtosecond sources. This tutorial begins with a review of the fundamentals of parametric processes. It is followed by a brief review of some of the more recent advances in femtosecond optical parametric oscillators, covering the spectral range from the visible to the mid-infrared.

The field of nonlinear optics began nearly simultaneously in the United States and in Russia in 1962. The early years of discovery led to an understanding of nonlinearity in materials, phasematching, and nonlinear device performance. In the second decade of the 1970s, tunable parametric oscillators driven by high-peak-power Q-switched lasers made the transition to tools useful for spectroscopy and remote sensing. In the late 1980s engineered nonlinear materials were introduced with the successful implementation of quasi-phasematching by periodic inversion of ferroelectric domains in lithium niobate. Lithographic processing techniques enabled the fabrication of quasi-phasematched nonlinear "chips" using electric field poling of lithium niobate at the wafer scale.