Ultra-short pulse compression using photonic crystal fibre

A short section of photonic crystal fibre has been used for ultra-short pulse compression. The unique optical properties of this novel medium in terms of high non-linearity and relatively small group velocity dispersion are shown to provide an ideal platform for the standard fibre pulse compression technique used directly on the nano-Joule output pulses from a commercial laser system. We report an order of magnitude reduction of the pulse width to 25 fs FWHM but predict a substantially improved performance with a dedicated fibre design. Good agreement is obtained with a simple model for the spectral broadening in the fibre

Characterisation of periodically poled materials using nonlinear microscopy

Periodically poled crystalline materials are extremely attractive for processes such as second harmonic generation and optical parametric generation due to their very high conversion efficiency. For optimal performance, fabrication of poled regions with sub-micron tolerance is required. In this paper we introduce multi-photon laser scanning luminescence microscopy as a powerful minimally-invasive measurement technique which provides information about internal device structure with high spatial resolution that cannot be easily obtained with existing methods. A comparative study of confocal and multi-photon imaging of periodically poled crystalline materials is also performed

Radio sources near the core of globular cluster 47 Tucanae

We present ATCA radio images of the globular cluster 47 Tucanae made at 1.4 and 1.7 GHz and provide an analysis of the radio sources detected within 5 arcmin of the cluster centre. 11 sources are detected, most of which are clustered about the core of 47 Tuc. Both of the pulsars in 47 Tuc whose positions are known can be identified with sources in the 1.4 GHz image. The source distribution has a characteristic radius of ~100 arcsec, larger than the 23 arcsec radius of the cluster core. We compare source positions with the positions of nine X-ray sources and find no correspondence.Comment: 6 pages, 4 postscript figures, LaTeX with MNRAS macro; Accepted by MNRA

Relaxed damage threshold intensity conditions and nonlinear increase in the conversion efficiency of an optical parametric oscillator using a bi-directional pump geometry

A novel bi-directional pump geometry that nonlinearly increases the nonlinear optical conversion efficiency of a synchronously pumped optical parametric oscillator (OPO) is reported. This bi-directional pumping method synchronizes the circulating signal pulse with two counter-propagating pump pulses within a linear OPO resonator. Through this pump scheme, an increase in nonlinear optical conversion efficiency of 22% was achieved at the signal wavelength, corresponding to a 95% overall increase in average power. Given an almost unchanged measured pulse duration of 260 fs under optimal performance conditions, this related to a signal wavelength peak power output of 18.8 kW, compared with 10 kW using the traditional single-pass geometry. In this study, a total effective peak intensity pump-field of 7.11 GW/cm(2) (corresponding to 3.55 GW/cm(2) from each pump beam) was applied to a 3 mm long periodically poled lithium niobate crystal, which had a damage threshold intensity of 4 GW/cm(2), without impairing crystal integrity. We therefore prove the application of this novel pump geometry provides opportunities for power-scaling of synchronously pumped OPO systems together with enhanced nonlinear conversion efficiency through relaxed damage threshold intensity conditions

Fast wavelength-tunable ultra-violet laser source for confocal Fura-2AM imaging

We report a novel wavelength-flexible laser source for three-dimensional ultra-violet imaging. Based on supercontinuum generation in photonic crystal fiber, the resultant broadband laser source extended from A = 331 nm into the visible region of the spectrum. Using an electronically-controlled filter wheel and filter set with a response time of approximately 50 ins, rapid wavelength selection was performed. The described scheme is capable of exciting the current range of ultra-violet-excited fluorophores and the simple and rapid wavelength control also provides a new approach for fast ratiometric imaging of Fura-2AM, facilitating an easy method of performing quantitative intracellular calcium concentration measurements

Energy shedding during nonlinear self-focusing of optical beams

Self-focusing of intense laser beams and pulses of light in real nonlinear media is in general accompanied by material losses that require corrections to the conservative Nonlinear Schrödinger equations describing their propagation. Here we examine loss mechanisms that exist even in lossless media and are caused by shedding of energy away from the self-trapping beam making it to relax to an exact solution of lower energy. Using the conservative NLS equations with absorbing boundary conditions we show that energy shedding not only occurs during the initial reshaping process but also during oscillatory propagation induced by saturation of the nonlinear effect. For pulsed input we also show that, depending on the sign and magnitude of dispersion, pulse splitting, energy shedding, collapse or stable self-focusing may result

Inertial measurement unit pre-processors and post-flight STS-1 comparisons

The flight results show that the relative tri-redundant Inertial Measurement Unit IMU performance throughout the entire entry flight was within the expected accuracy. Comparisons are presented which show differences in the accumulated sensed velocity changes as measured by the tri-redundant IMUs (in Mean Equator and Equinox of 1950.0), differences in the equivalent inertial Euler angles as measured with respect to the M50 system, and finally, preliminary instrument calibrations determined relative to the ensemble average measurement set. Also, differences in the derived body axes rates and accelerations are presented. Because of the excellent performance of the IMUs during the STS-1 entry, the selection as to which particular IMU would best serve as the dynamic data source for entry reconstruction is arbitrary

The radio luminosity distribution of pulsars in 47 Tucanae

We have used the Australia Telescope Compact Array to seek the integrated radio flux from all the pulsars in the core of the globular cluster 47 Tucanae. We have detected an extended region of radio emission and have calibrated its flux against the flux distribution of the known pulsars in the cluster. We find the total 20-cm radio flux from the cluster's pulsars to be S = 2.0 +/- 0.3 mJy. This implies the lower limit to the radio luminosity distribution to be L_1400 = 0.4 mJy kpc^2 and the size of the observable pulsar population to be N < 30.Comment: 7 pages, 4 figures, MNRAS in pres

Simultaneous evaluation of multiple PEMS using an engine dynamometer emissions test cell

Portable emission measurement systems (PEMS) are taking center stage as in-use testing programs are getting underway. EPA-mandated manufacturer-run in-use testing programs require a PEMS, and currently there is one commercially available and widely used, the SEMTECH-D built by Sensors, Inc. The SEMTECH-D was first unveiled in 2002, and numerous software and hardware upgrades have given way to the SEMTECHDS. The manufacturer claims this system is fully compatible with all new Code of Federal Regulations (CFR) including part 1065 subpart J (which addresses field testing and PEMS). Yet, while West Virginia University (WVU) was using the SEMTECH-D during the summer of 2005, problems were encountered that prompted further insight into its performance. A ten month study ensued to study SEMTECH-D\u27s behavior compared to an EPA certified engine test cell on the campus of WVU at Morgantown, WV. After multiple test days, exhaust configurations, and comparisons to both the heavy-duty engine dynamometer laboratory (compliant with CFR40 Part 86 Subpart N) at WVU, and another PEMS, the SEMTECH-D was found to consistently exhibit high discrepancies. Over a twenty minute Federal Test Procedure (FTP) transient test the total NOX mass emitted error was as high as 25%, while the CO2 total mass emitted error was as high as 15% compared to the engine dynamometer laboratory