Compact 85 fs frequency doubled 810 nm fiber system with 60 mW of average power

We demonstrate a sub-100 fs frequency doubled fiber laser operating at 810 nm. The laser produces 60 mW of average power at a repetition rate of 50 MHz. Extremely low amplitude noise (below 0.1%) and compact size makes this source ideal replacement for low power ultrafast Ti:Spphire lasers

Depressed clad hollow optical fiber with fundamental LP01 mode cut-off

We propose a depressed clad hollow optical fiber with fundamental (LP01) mode cut-off suitable for high power short-wavelength, especially three-level, fiber laser operation by introducing highly wavelength dependent losses at longer wavelengths. The cut-off characteristic of such fiber structure was investigated. A Yb-doped depressed clad hollow optical fiber laser generating 59.1W of output power at 1046nm with 86% of slope efficiency with respect to the absorbed pump power was realised by placing the LP01 mode cut-off at ~1100nm

Ethnicity and Consumption South Asian food shopping patterns in Britain, 1947-75

Authors' draft version also available on University of Surrey e-print repository. Final version published by Sage and available at http://joc.sagepub.com/This article reviews the literature that explores the relationship between ethnic identities and food consumption, with particular reference to business management studies. It focuses on the food shopping practices of south Asians in Britain in the period 1947 to 1975, to illustrate the need for more historically contextualized studies that can provide a more nuanced exploration of any interconnections between ethnic identity and shopping behaviour. The article draws on a reasonably long-standing interest in ethnicity and consumption in marketing studies, and explores the conceptual use of acculturation within this literature. The arguments put forward are framed by recent interdisciplinary studies of the broader relationship between consumption and identity, which stress the importance of contextualizing any influence of ethnic identifications through a wider consideration of other factors including societal status, gender and age, rather than giving it singular treatment. The article uses a body of empirical research drawn from recent oral histories, to explore how these factors informed everyday shopping practices among south Asians in Britain. It examines some of the shopping and wider food provisioning strategies adopted by early immigrants on arrival in Britain. It considers the interaction between the south Asian population and the changing retail structure, in the context of the development of self-service and the supermarket. Finally, it demonstrates how age, gender and socioeconomic status interacted with ethnic identities to produce variations in shopping patterns

Fiber design for high-power low-cost Yb:Al-doped fiber laser operating at 980nm

We investigated an Yb:Al-doped depressed-clad hollow optical fiber (DCHOF) for cladding-pumped 980nm laser operation. With a careful design, the nonzero fundamental-mode cutoff characteristics of a DCHOF allows the competing 1030-1060nm emission to be filtered out, despite being quite close to 980nm. The laser yielded over 3W of output power in a diffraction limited beam (M -parameter degrades to 2.7, as a result of increased cladding-mode lasing, as the cladding thickness is reduced

Tunable single-frequency ytterbium-sensitized erbium-doped fiber MOPA source with 150W (51.8 dBm) of output power at 1563 nm

A single-frequency, single-mode ytterbium-sensitized erbium-doped fiber master-oscillator power-amplifier generated 150 W of continuous-wave output power at 1563 nm with 33% slope efficiency and was tuned in the range of 1546 to 1566 nm at >125 W

Efficient femtosecond pulse generation using a parabolic amplifier combined with a pulse compressor. II. Finite gain bandwidth effect

A derivation of an analytical expression for the propagation of a parabolic pulse in an optical fiber amplifier with a finite Lorentzian gain bandwidth is presented. Through a separation of variables combined with the method of stationary phase, we derive equations in both time and frequency spaces to obtain the analytical solution. This results in a compact analytical form that has a number of physical meanings. It shows that the finite gain bandwidth seriously limits the performance of parabolic amplification by distorting both the chirp and the frequency envelope, thus preventing efficient pulse compression required for high-power femtosecond pulse generation. The validity of the analytical derivation is verified through numerical simulations using the split-step Fourier method, showing an excellent agreement with the derived analytical solution, in pulse shape, chirp, and the optical spectrum

Geometrical factor modification of helical-core fiber radiation loss formula

A strict consideration of the geometry of helical-core fibers leads to a modification of a previously published formula for radiation loss in such fibers. We derive an expression for the radiation loss of the fundamental mode, and find that it differs from the previous expression by a simple modification factor, which depends on the geometric parameters of the helix (pitch and offset). The derived expression predicts a loss which is of the order of 40% lower for typical helix parameters

Neodymium-doped cladding pumped aluminosilicate fiber laser tunable in the 0.9 micron wavelength range

A tunable high-power cladding-pumped neodymium-doped aluminosilicate fiber laser is demonstrated. The maximum power reached was 2.4 W with a slope efficiency of 41% and a threshold pump power of 1.68 W, both with respect to launched pump power, when cladding pumped by two 808 nm diode pump sources at both fiber ends. The dependence of the tuning range on the fiber length is investigated. The tuning range changed from 922 to 942 nm for a 25 m-long fiber to 908-938 nm with a 14 m-long fiber, because of reabsorption effects. The output linewidth was 0.26 nm in a diffraction-limited beam. Operation on the challenging 0.9 µm three-level transition in neodymium-doped double-clad fiber laser was facilitated by a W-type core refractive index profile. This filtered out the unwanted and competing strong transition at 1.06 µm while guidance of 0.9 µm remained intact

Core area scaling of Nd:Al-doped silica depressed clad hollow optical fiber and Q-switched laser operation at 0.9 microns

We demonstrate a Q-switched, cladding-pumped, Nd:Al-doped silica depressed clad hollow optical fiber (DCHOF) laser, which generated up to 133 µJ of pulse energy at a repetition rate of 5 kHz and 0.9 W of average output power at a high repetition rate (>20 kHz) in a diffraction-limited beam (M=1.08) at 927 nm. The laser was tunable from 919 to 935 nm. This result shows the potential of the DCHOF structure for the suppression of unwanted long-wavelength radiation in large-area cores suitable for high-power Q-switched laser operation

High-power tunable single-frequency single-mode erbium:ytterbium codoped large-core fiber master-oscillator power amplifier source

We present a cladding-pumped single-frequency, single-mode erbium:ytterbium co-doped fiber master-oscillator power amplifier source generating up to 151 W of continuous-wave output power at 1563 nm with 33% slope efficiency and 20 dB gain. This source was also tunable and had a stable operation range of 1546 to 1566 nm at an output power level in excess of 125 W. The doped fiber exploited a large-core design for improved power handling and mitigation of stimulated Brillouin scattering. There was no sign of having stimulated Brillouin scattering even at the highest power. Despite a large core (V = 12), the output beam was nearly diffraction-limited (M = 1.1). The source showed slight roll-over at over 100 W of output power because of the onset of emission from ytterbium, centered at 1060 nm