Fiber laser systems shine brightly

Describes the advancements in active fiber laser systems. Outline of cladding pumping technique for enhanced power scaling; Improved energies and peak powers; Extended wavelength range; Frequency doubling with fiber sources

Contact electrode method for bulk periodically poled LiNbO₃

Over the past few years, there has been increasing interest in the use of quasi-phase-matched (QPM) nonlinear crystals, which permit noncritical-phase-matching for any wavelengths in the transparency range of the crystal, and have the advantage of using the largest component of the nonlinear susceptibility tensor, one that is not available in birefringent phase matching without walk-off problems. QPM can be achieved by an appropriate periodic modulation of the nonlinear coefficient, which corresponds to periodic domain reversal in ferroelectric materials. In particular, the application of QPM to bulk nonlinear optics has been revolutionised by the emergence of electric field poling techniques for patterning the domain structure of ferroelectric and polar crystals. In all the reported fabrication processes the periodic electrode (consisting of resist and/or metal layers) has been fabricated on the surface of the crystal substrates by conventional photolithography.We report here a new fabrication process for PPLN - the contact electrode method (CEM) - in which the periodic electrode is pressed onto one of the substrate surfaces with a uniform electrode on the other. CEM does not need any photolithographic processes on the substrate surface which may lead to greatly reduced fabrication cost. Furthermore, CEM would be applicable for fabrications of periodically poled glass fiber

Teaching UbiComp with Sense

Modern computer science education has to take account of the recent changes towards smart ubiquitous computing devices. In addition, existing programming languages are needlessly difficult for novice programmers to learn concepts. We have developed Sense, an extension to the graphical programming language Scratch, and an associated sensor/actuator board. Together, these will allow novice undergraduate students to quickly develop their own smart devices while learning the fundamentals of programming. Students will first study with Sense in 2011 but developmental feedback has been positive

Efficient superfluorescent light sources with broad bandwidth

We demonstrate various efficient broad-band light sources at ~1µm wavelength with a 3dB bandwidth of up to 65nm at 108mW output power, based on rare-earth doped silica fibers and a simple adjustable spectral filter

Saturation and tuning behaviour of stimulated electronic Raman scattering

The saturation behavior of stimulated electronic Raman scattering (SERS) in atomic vapors is studied theoretically and experimentally. Limits to the SERS output energy are imposed by both pump depletion and saturation of the Raman transition. The effects of these on the performance of tunable infrared lasers based on SERS are examined

Comprehension of wh-questions in a case of mixed dementia

We investigated processing of wh-questions and declarative sentences with differing syntactic complexity in a case of mixed dementia (FA). FA was impaired in her ability to understand syntactically complex declarative sentences and syntactically complex wh-questions beginning with which but not complex who questions. This profile, novel in dementia, is similar to that reported for people with agrammatic aphasia and discerns a ‘‘fault line’’ of the language system along a syntactic/semantic paramete

Lifetime quenching in Yb doped fibres

We have discovered that in ytterbium-doped silica fibres the excited state lifetime of a fraction of the Yb ions can be quenched to a very small value, leading to a strong unbleachable loss. This unexpected behaviour seems to be caused by some, yet unidentified, impurity or structural defect. It is of considerable relevance for various Yb doped lasers and-amplifiers including Er:Yb codoped fibres as used in telecommunication amplifiers although it should also be emphasized that fibres can be produced that are free from the quenching effect

Stabilisation of single longitudinal mode operation in a Q-switched Nd:YAG laser

Detection of the reflected laser beam power from the mode-selecting etalon in a prelase-Q-switched laser provides an indicator of mode-frequency drifts. The detected signal can be used to control a piezo-mounted resonator mirror, thus correcting the drift and providing a means for maintaining single longitudinal mode operation on every shot

High gain Nd:YLF amplifier end-pumped by a beam-shaped broad-stripe diode laser

The output from a 1W broad-stripe diode, reshaped by a two-mirror beam-shaper, is used to end-pump a Nd:YLF amplifier. In a double-pass configuration a small-signal gain of 240 has been obtained

A high power synchronously-pumped dye laser with diffraction-limited and transform-limited performance

The design and performance of a high-power synchronously pumped dye laser is described. Emphasis has been given to achieving bandwidth-limited and diffraction-limited performance so that efficient, reproducible nonlinear frequency conversion can be achieved. Pulses of 1 mJ from Rhodamine 6G and 250 µJ from DCM with tuning ranges of 557-584 nm and 609-676 nm, respectively, have been obtained. Second harmonic generation with 40 percent efficiency to ~280 nm and efficient multiple Stokes Raman shifting to cover the range 1.1-1.2 µm has been demonstrated. Blue dyes, pumped by third harmonic of Nd:YAG, have been operated. Typically, for Stilbene 3 (peak at 420 nm), pulses of 160µJ were obtained