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

A channel waveguide (propagation loss: ∼0.1 dB/cm) laser femtosecond-laser-written in monoclinic Tm:MgWO 4 generated up to 320 mW slightly above 2 μm (slope efficiency up to 71%) and vibronic laser emission extending up to ∼2.08 μm.

Highly-Efficient Femtosecond-Laser-Written Waveguide Lasers at ∼2 μm in Monoclinic Tm:MgWO 4

We review the recent progress in passively mode-locked Tm- and Ho-lasers operating near 2 μm, comparing saturable absorbers based on carbon nanostructures (SWCNTs and graphene) with SESAMs, employed in lasers based on different active media.

2D Materials for Mode-Locking of Bulk 2 Micron Lasers: Alternatives to SESAMs

Contouring of dynamic phase changes of a piezoelectrically driven fluidic lens with a temporal resolution of 410 frames/s is presented. Using a dual-wavelength few-ps source, optical path differences of several 10 µm are unambiguously detected.

High-Speed Contouring of an Adaptive Fluidic Lens with Two-Wavelength Single-Pulse Digital Holography

A novel method for contouring of optical surfaces with unprecedented dynamic range is presented. At an object depth ≫50 µm, surface deformations of a MEMS of some 10 nm are still unambiguously detectable.

High-precision contouring of rapidly oscillating optical surfaces with two-wavelength single-shot digital holography

A long-wave infrared OPCPA containing a front-end based on a femtosecond Cr:ZnS oscillator without additional nonlinear stages is presented, delivering idler pulses at 11.8 µm with a 14 µJ energy at a 1-kHz repetition rate. 

Uwe Griebner

Papers

Highly-Efficient Femtosecond-Laser-Written Waveguide Lasers at ∼2 μm in Monoclinic Tm:MgWO 4

2D Materials for Mode-Locking of Bulk 2 Micron Lasers: Alternatives to SESAMs

High-Speed Contouring of an Adaptive Fluidic Lens with Two-Wavelength Single-Pulse Digital Holography

High-precision contouring of rapidly oscillating optical surfaces with two-wavelength single-shot digital holography

LWIR OPCPA based on a fs Cr:ZnS front-end