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

Transversely guided pumped Yb:YAG laser

We report on the first laser operation of a novel double molybdate compound, Yb:KY(MoO4)2. Single-crystals were grown by the Low Temperature Gradient (LTG) Czochralski method. The crystal structure (orthorhombic, sp. gr. Pbna – D142h) was refined with the Rietveld method. Yb:KY(MoO4)2 exhibits a layered structure leading to a strong optical anisotropy and a perfect cleavage along the (100) plane. The stimulated-emission cross-section for Yb3+ ions is 3.70×10-20 cm2 at 1008.0 nm and the emission bandwidth is 37 nm (for light polarization E || b). Continuous-wave laser operation is achieved in a 3 at.% Yb:KY(MoO4)2 crystal plate (thickness: 286 μm) under diode pumping. The microchip laser generated a maximum output power of 0.81 W at 1021-1044 nm with a slope efficiency of 76.4% and linear polarization. Yb:KY(MoO4)2 crystal films / plates are attractive for sub-ns passively Q-switched microchip lasers and thin-disk lasers.

Efficient laser operation in cleaved single-crystal plates of Yb:KY(MoO4)2: A novel molybdate compound

The femtosecond regime of mode-locked InGaAs/AlGaAs disk lasers was investigated, resulting in almost chirpfree sub-220-fs pulses. Pulse picking using a tapered diode amplifier is demonstrated, reducing the pulse rate from 3 GHz to 47 MHz.

InGaAs-AlGaAs Disk Laser Generating sub-220-fs Pulses and Tapered Diode Amplifier with Ultrafast Pulse Picking

Yb:YGG, Yb:LuGG and Yb:CNGG lasers are Q-switched by a graphene-based saturable absorber. 190 ns/1.9 μJ pulses are generated at 1045.1 nm using Yb: CNGG and the maximum output power is 440 mW with 24 % slope efficiency.

Q-Switching of Ytterbium Lasers by A Graphene Saturable Absorber

We demonstrate the first thin disk epitaxial Tm-laser based on the monoclinic KLu(WO4)2 with 15 at. % doping. The
doped epitaxial layer serving as an active medium is only 80 μm thick. The large absorption enables efficient pumping
with only a single double pass of the pump radiation from the diode-laser. For output coupling between 0.4% and 2.8 %,
the slope efficiency in the continuous-wave regime is in the 7-11% range and the laser threshold is 1.5...2.5 W of
absorbed pump power. The laser emission spectra are centered at ~1850, 1915 and 1940 nm for output couples of 2.8%,
1.6% and 0.4% transmission, respectively. In all cases the emission spectra are "structured", consisting of a number
(typically 5...10) of narrow emission lines spread irregularly over 15...30 nm.

Uwe Griebner

Papers

Transversely guided pumped Yb:YAG laser

Efficient laser operation in cleaved single-crystal plates of Yb:KY(MoO4)2: A novel molybdate compound

InGaAs-AlGaAs Disk Laser Generating sub-220-fs Pulses and Tapered Diode Amplifier with Ultrafast Pulse Picking

Q-Switching of Ytterbium Lasers by A Graphene Saturable Absorber

CW laser operation of a highly-doped Tm:KLu(WO 4 ) 2 /KLu(WO 4 ) 2 thin disk epitaxial laser