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

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

Recent observations show that the probability of encountering an extremely large rogue wave in the open ocean is much larger than expected from ordinary wave-amplitude statistics. Although considerable effort has been directed towards understanding the physics behind these mysterious and potentially destructive events, the complete picture remains uncertain. Furthermore, rogue waves have not yet been observed in other physical systems. Here, we introduce the concept of optical rogue waves, a counterpart of the infamous rare water waves. Using a new real-time detection technique, we study a system that exposes extremely steep, large waves as rare outcomes from an almost identically prepared initial population of waves. Specifically, we report the observation of rogue waves in an optical system, based on a microstructured optical fibre, near the threshold of soliton-fission supercontinuum generation--a noise-sensitive nonlinear process in which extremely broadband radiation is generated from a narrowband input. We model the generation of these rogue waves using the generalized nonlinear Schrodinger equation and demonstrate that they arise infrequently from initially smooth pulses owing to power transfer seeded by a small noise perturbation.

Optical rogue waves

We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.

Optical properties of ZnO nanostructures.

Current medical imaging technologies allow visualization of tissue anatomy in the human body at resolutions ranging from 100 micrometers to 1 millimeter. These technologies are generally not sensitive enough to detect early-stage tissue abnormalities associated with diseases such as cancer and atherosclerosis, which require micrometer-scale resolution. Here, optical coherence tomography was adapted to allow high-speed visualization of tissue in a living animal with a catheter-endoscope 1 millimeter in diameter. This method, referred to as "optical biopsy," was used to obtain cross-sectional images of the rabbit gastrointestinal and respiratory tracts at 10-micrometer resolution.

In Vivo Endoscopic Optical Biopsy with Optical Coherence Tomography

We present an overview of our recent achievements on fabrication, characterization and CW and passively Q-switched laser operation of Thulium and Holmium depressed-cladding waveguide lasers operating at ~2 μm and inscribed in anisotropic crystals by femtosecond direct laser writing. Variable waveguide geometries (buried and surface guides; circular, rectangular and hexagonal channels; Y-splitters) are described.

Near-Infrared Femtosecond Direct Laser Written Waveguide Lasers [Invited]

The recent surge of interest in ytterbium-based lasers is focused on high-power diode-pumped all-solid-state laser sources. One of the advantages of the Yb3+ ion are the relatively broad absorption and emission bands. They are much smoother and display less structure in glass host materials than those of %:YAG, a promising feature for tunable operation and generation of ultrashort laser pulses. Efficient diode pumping of %:glass has already been demonstrated under continuous-wave conditions.'32 The first attempt to modelock the %:YAG laser by a passive method (A-FPSA) resulted in 540-fs-long pulses at 1.03 I J . ~ . ~ Here we demonstrate cw passive modelocking of an %:glass laser for the first time to our knowledge, based entirely on the Kerr effect in the active medium in a resonator with dispersion compensation. The glass sample used was doped with 6 X 10' cm-3 Yb3+ and exhibits a fluorescence lifetime of 1.2 ms. In our experiments a cw Tksapphire laser acts as the pump source. The output of the pump laser (3 W at 940 nm) was focused into the 4-mm-thick %:glass sample by a 60 mm lens. The active material was positioned at the Brewster angle between two folding mirrors in a standard astigmatically compensated type-Z laser configuration (Fig. 1). The cavity could be operated as a free-running cw laser by use of M, (Fig. 1) yielding >350 mW ofoutput power near 1035 nm at 1.2 W of absorbed pump radiation with a threshold of -150 mW. Essential for the achievement of pure passive modelocking was the minimization of all losses at the maximum pump power available. After optimization in the cw free-running regime modelocked operation was achieved then by precise adjustment of the two prisms, the %:glass sample and the 3-mm-wide vertical slit employed as an aperture near the output coupler Mi. Starting of the laser was accomplished through slow translation of one of the

Self-modelocked femtosecond Yb:fluoride phosphate glass laser

The parametric generation of 2.5 mJ ultrashort pulses at 5 μm is reported using a 2-μm pump source which delivered pulses with 43 mJ energy and 2.8 ps duration at a 1 kHz repetition rate.

Multi-mJ sub-100 fs Midwave-infrared OPCPA at a 1 kHz Repetition Rate

Multi-μJ 12 μm Femtosecond GaSe-based OPCPA at 1 kHz Repetition Rate

A passively mode-locked semiconductor disk laser employing a graded-gap-barrier design in the gain section is presented. The all-semiconductor laser generates transform-limited pulses as short as 290 fs at 1036 nm.

Uwe Griebner

Papers

Near-Infrared Femtosecond Direct Laser Written Waveguide Lasers [Invited]

Self-modelocked femtosecond Yb:fluoride phosphate glass laser

Multi-mJ sub-100 fs Midwave-infrared OPCPA at a 1 kHz Repetition Rate

Multi-μJ 12 μm Femtosecond GaSe-based OPCPA at 1 kHz Repetition Rate

290-fs Passively Mode-Locked Semiconductor Disk Laser