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

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Two types of photomodulation of orientations of liquid crystals (LCs) are reviewed: 1) order–disorder phase transitions of LCs induced by photochemical reactions of photochromic molecules and 2) order–order alignment change of LCs (change in LC directors) induced by photochemical reactions or without photochemical events. Both processes produce a large refractive-index modulation, which forms the basis of a range of photonic applications. Various modes of photomodulation of orientations of LCs with plausible mechanisms and their possible applications in photonics are described.

Photomodulation of liquid crystal orientations for photonic applications

Numerical simulations of the onset phase of continuous wave supercontinuum generation from modulation instability show that the structure of the field as it develops can be interpreted in terms of the properties of Akhmediev Breathers. Numerical and analytical results are compared with experimental measurements of spectral broadening in photonic crystal fiber using nanosecond pulses.

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Modulation instability, Akhmediev Breathers and continuous wave supercontinuum generation.

The year 2009 marks the tenth anniversary of the first report of white-light supercontinuum generation in photonic crystal fibre. This result had a tremendous impact on the field of nonlinear fibre optics and continues to open up new horizons in photonic science. Here we provide a concise and critical summary of the current state of nonlinear optics in photonic crystal fibre, identifying some of the most important and interesting recent developments in the field. We also discuss several emerging research directions and point out links with other areas of physics that are now becoming apparent.

Ten years of nonlinear optics in photonic crystal fibre

We analyze propagation in a nonlinear, birefringent optical fiber with twist. The results show that the polarization evolution is periodic, and they are applied to the analysis of a Sagnac interferometer. The period is calculated by using perturbation theory, and we find a condition for it to be independent of the initial polarization state. We derive a simplified set of equations to describe the nonlinear evolution of the phase. We give a useful way to visualize the behavior of the nonlinear optical loop mirror (as a function of birefringence, twist, length, and input polarization) in terms of the Poincare sphere.

Theory of nonlinear loop mirrors with twisted low-birefringence fiber

We present novel results on thermocavitation using a CW medium-power near infrared laser (lambda=975 nm) focused into a saturated copper nitrate saline solution. Due to the large absorption coefficient at the laser wavelength, the solution can be heated to its superheat limit (T(sh) approximately 270-300 degrees C). Superheated water undergoes explosive phase transition around T(sh) producing approximately half-hemispheric bubbles (gamma approximately 0.5) in close contact with the substrate. We report the temporal dynamic of the cavitation bubble, which is much shorter than previously reported under similar conditions. It was found that the bubble radius and pressure wave amplitude emitted on bubble collapse decreases exponentially with the power laser. Thermocavitation can be a useful tool for the generation of ultrasonic waves and controlled ablation for use in high-resolution lithography.

Time-resolved analysis of cavitation induced by CW lasers in absorbing liquids.

The influence of a high light absorption on the photoelectromotive force excited by moving interference fringes in photoconductive crystals is considered. It is shown that due to a deep penetration of the electric field pattern into the sample volume, the absolute magnitude of the output signal and its dependence on the spatial frequency of the grating may practically be the same as for low absorption. This conclusion is confirmed experimentally for semi‐insulating GaAs:Cr for λ=633, 840–900, and 1064 nm. This means, in particular, that films or thin specimens of photoconductive materials can be used for fabrication of adaptive detectors of phase‐modulated optical signals with the same efficiency as bulk specimens.

Non‐steady‐state photoelectromotive force in semiconductor crystals with high light absorption

We report the observation of a non-steady-state photo-EMF generated in a semi-insulating GaAs: Cr crystal by vibrating speckle patterns. The experimentally observed basic dependences of the output signal on the vibration frequency and amplitude as well as on the light intensity are in reasonable agreement with those observed earlier for vibrating sinusoidal light patterns. Using this novel technique, lateral vibrations of diffusely scattering objects can be easily detected over a wide range of frequencies and amplitudes.

Measurement of small lateral vibrations of speckle patterns using a non-steady-state-photo-EMF in GaAs:Cr

Experimental results on self-diffraction of periodically phase-modulated laser beams from a relief grating formed on a free surface of a cubic photorefractive Bi12TiO20 crystal due to the piezoelectric effect are reported. Periodic intensity modulations of the reflected beams up to 10−2 due to energy exchange at this unshifted phase grating are measured. The modulation depends linearly on the fringe spacing and on the amplitude of an externally applied electric dc field. The observed self-diffraction process is independent of the light polarization.

Nikolai Korneev

Papers

Theory of nonlinear loop mirrors with twisted low-birefringence fiber

Time-resolved analysis of cavitation induced by CW lasers in absorbing liquids.

Non‐steady‐state photoelectromotive force in semiconductor crystals with high light absorption

Measurement of small lateral vibrations of speckle patterns using a non-steady-state-photo-EMF in GaAs:Cr

Self-diffraction from free surface relief gratings in a photorefractive Bi12TiO20 crystal