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

Simultaneous lasing of Ho3+ at 2061 nm and Tm3+ at 1937 or 1919 nm is observed in co-doped monoclinic (Ho,Tm):KLu(WO4)2 at room temperature with output power and slope efficiency reaching 218 mW and 27%, respectively.

Simultaneous Dual-Wavelength Laser Operation in Co-Doped (Ho,Tm):KLu(WO4)2 Crystal

Waveguide lasing of monoclinic KY(WO4)2:Tm3+ grown by liquid-phase epitaxy is demonstrated in the 2 mum spectral range. The maximum continuous-wave output power achieved was 32 mW in the fundamental mode.

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KY(WO 4 ) 2 :Tm 3+ planar waveguide laser

A diode-pumped Q-switched Tm:KLu(WO 4 ) 2 microchip laser generated a maximum average output power of 310 mW with M2 < 1.2 at 1947 nm. The shortest pulse duration was 285 ns at a pulse repetition rate of 190 kHz.

Graphene-based saturable absorber for passive Q-switching of Tm:KLu(WO 4 ) 2 microchip laser

We report on mode-locking of a Cr:YAG laser at 1516 nm with a monolayer-graphene-based saturable absorber of transmission type generating ∼90-fs pulses at an average output power exceeding 100 mW.

Sub-100-fs mode-locking of the Cr:YAG laser using monolayer graphene saturable absorber

In recent years, the development of compact all solid-state lasers has attracted the scientific community because of their vast scientific and technological applications. In particular, ytterbium (Yb3+) laser sources have been developed with a great number of hosts, due to the promise of the Yb3+ ion related to the very simple energy level structure and absence of higher energy levels, as well as a small quantum defect. However, at room temperature (RT) these materials behave as quasi three-level lasers due to a finite population of the ground state leading to reabsorption limited power scaling [1]. To overcome this issue, the material has to be cooled to cryogenic temperatures, where four-level operation is accomplished. The monoclinic potassium lutetium double tungstate crystal, KLu(WO 4 ) 2 , considered here exhibits favourable spectroscopic properties when doped with Yb3+, characterized by large absorption and stimulated-emission cross sections and attractive thermo-optic properties for certain “athermal” crystal cuts (e.g., along the Ng-axis). It is very suitable for moderate power levels as demonstrated with Yb3+ and Tm3+ doping at RT [2]. In this work, we studied the continuous-wave laser characteristics of Yb:KLu(WO 4 ) 2 (Yb:KLuW) at cryogenic temperatures pumped by a VBG-stabilized fiber coupled diode laser at 981 nm.

Uwe Griebner

Papers

Simultaneous Dual-Wavelength Laser Operation in Co-Doped (Ho,Tm):KLu(WO4)2 Crystal

KY(WO 4 ) 2 :Tm 3+ planar waveguide laser

Graphene-based saturable absorber for passive Q-switching of Tm:KLu(WO 4 ) 2 microchip laser

Sub-100-fs mode-locking of the Cr:YAG laser using monolayer graphene saturable absorber

Diode-pumped cryogenic Yb:KLu(WO 4 ) 2 laser