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

Yb3'-doped germanosilicate fibre has been demonstrated to be a versatile host for laser action at wavelengths from 1 to 1.2 pm.' It can be pumped at wavelengths from 800-1064 nm, and the emission band extends from 970-1200 nm, including wavelengths of interest for specific applications, e.g., 1020 nm for pumping of 1.3 pm Pr3'-doped fibre amplifiers, 1140 nm for pumping of Tm3'doped fluoride fibre upconversion lasers, and 1083 nm for optical pumping of 3He. The availability of fibre gratings has been a major element in expanding the potential of Yb3'-doped fibre devices.2 The present work is based on Yb3'-doped germanosilicate fibres, fabricated by the MCVD technique. This host is photosensitive so that gratings can be written directly into the Yb3'-doped fibre core. We have previously reported efficient (up to 60% slope efficiency with respect to absorbed power) operation at 1020 nm and 1140 nm using fibre gratings and pumped respectively at 840 nm (with the output from a Ti:sapphire laser) and 1047 nm (with the output from a Nd:YLF laser). While the efficiency with respect to absorbed power was high (-6O%), the overall conversion efficiency of pump light for these devices is -30-40%, limited largely by the launch efficiency of the pump beam into the doped fibre core. A large improvement in the overall conversion efficiency has been demonstrated through the use of a claddingpumping scheme; it is envisaged that this fibre laser will ultimately enable very efficient pumping with a semiconductor MOPA. The fibre designed for this work consists of a single-mode doped inner core of 4.25 pm diameter and an outer core (inner cladding) of 12.75 pm diameter. The N A for the inner and outer guides are 0.16 and 0.15, respectively. Ytterbium was added by solution doping and the concentration was measured to be -500 ppm. The pump source was a Ti: sapphire laser operating at 974 nm, launched into the fibre using a X5 microscope objective, in order to simulate the focal spot size, which would be produced by a semiconductor MOPA focussed within the acceptance angle of this fibre. Very efficient performance (up to 80% slope efficiency with respect to incident power) at 1020, 1040, and 1140 nm was obtained. Single-longitudinal mode operation of Yb fibre lasers has also been demonstrated, at 1083 nm. The fibre used for this work had an Yb3' concentration of -2000 ppm, NA 0.28, and cutoff wavelength -1000 nm. Stable single-frequency operation at 1083 nm was obtained using a 5.6-cm-long cavity formed by two gratings with 92% and 60% reflectivity. The grating bandwidths at full-width half maximum were 0.25 nm. Pump light at 970 nm was launched into the cleaved end of the 92% reflectivity grating pigtail (-1 cm long) and laser action at 1083.0 nm on a single longitudinal mode occurred with a threshold of -12 mW pump light incident on the launch objective. Single-frequency operation was verified using a scanning confocal FabryPerot interferometer with 7.5 GHz free spectral range (FSR) and instrument-limited bandwidth of -200 MHz. The FSR of the laser was -1.8 GHz. The slope efficiency for these initial measurements was -6% with respect to launched pump power, and significantly improved efficiency is anticipated in an optimised system.

http://ieeexplore.ieee.org/iel3/5030/13794/00636634.pdf

Passively Q-switched flashlamp-pumped ND:glass fiber-bundle laser

Summary form only given. We report on a study of autocorrelation and frequency doubling of thin polycrystalline ZnO films using 20 fs pulses. These films show an effective second order nonlinearity larger than that of beta-barium borate (BBO) and negligible group velocity dispersion (GVD) for input wavelengths around 800 nm.

Zinc oxide thin films for autocorrelation studies of femtosecond pulses

Monoclinic double tungstate (DT) crystals, due to their maximum absorption and emission cross sections and minimum concentration quenching, seem ideal as hosts for thin-disk lasers with simplified geometry (number of pump passes). The first diode-pumped thulium thin-disk laser based on Tm:KY(WO4)2 generated CW output power of 4.9 W at 1950 nm using 4 pump passes [1]. The power handling capability of the thin-disk concept scales inversely proportional to the thickness and the high absorption of the monoclinic DTs reveals another important advantage of these anisotropic materials - enormous scaling potential, which, however, could be technically exploited by only relying on doped epitaxial layers. Recently, employing Tm-doped epitaxial layers grown on un-doped KLu(WO4)2 (KLuW) and 4 pump passes, we achieved 47% slope efficiency and CW output power of 5.9 W [2]. Here, we study the power scaling potential of this laser in the quasi-CW (QCW) mode.

Power scaling of thin-disk Tm-lasers based on Tm:KLu(WO 4 ) 2 /KLu(WO 4 ) 2 epitaxy

We investigate the cw laser performance of Tm:LuVO4 crystals pumped with tunable polarized source and report roughly 2 times improvement of the efficiency with 1 W of output power and broad tunability at room temperature.

Continuous-wave laser performance of Tm:LuVO4 under Ti:sapphire laser pumping

Mode-locking of the Yb:NaY(WO4)2 laser is reported. Pulse durations as short as 53 fs are achieved using a semiconductor saturable absorber mirror (SESAM) and additional extracavity compression. Autocorrelation trace of the shortest pulse is obtained.

Uwe Griebner

Papers

Passively Q-switched flashlamp-pumped ND:glass fiber-bundle laser

Zinc oxide thin films for autocorrelation studies of femtosecond pulses

Power scaling of thin-disk Tm-lasers based on Tm:KLu(WO 4 ) 2 /KLu(WO 4 ) 2 epitaxy

Continuous-wave laser performance of Tm:LuVO4 under Ti:sapphire laser pumping

Mode-locking of the Yb:NaY(WO 4 ) 2 laser