1,720,986 research outputs found
Performance of a CW pumped Nd:YVO4 amplifier with kHz pulses
No full textUntil recently, simple and reliable high repetition-rate laser sources with nanosecond pulses much shorter than from conventional A-O Q-switch lasers were not available. However over the past 2 years we have developed such lasers based on proprietary fast E-O switching technology, which allows designs delivering pulses and subnanosecond jitter for good synchronisation. The technology provides pulses with multi-kW peak power and repetition-rates to .Most recently, the performance of these short pulse lasers has been developed further by implementing oscillator/amplifier (master oscillator and power amplifier, MOPA) technology which increases the output to average power. Here we report on a simple model that has been used to predict the performance of the CW pumped Nd:YVO4 amplifier used in the MOPA laser. The model is based on the well-known expressions for the saturated gain applying to laser pulses, but more usually applied to pulse-excited amplifiers. The model is shown to allow a good interpretation of the amplifier behaviour for kHz pulses and to be a useful tool for predicting the performance of the MOPA laser
Solid-state Raman laser generating
No full textA new Raman oscillator is described based on a diode end-pumped Nd:YAG laser and an intra-cavity rubidium titanyl phosphate (RTP) crystal that serves as the active Q-switch. This compact and robust laser generates <1 ns, kilohertz pulses at 1096 nm with a 1064 nm pump and has potential for ?1480 nm eye-safe operation using a 1340 nm pump. Based on rate equation modelling a Raman gain of ?1.7–2.2 cm/GW at 1064 nm is estimated for RTP
Simplified analysis of double pass amplification with pulse overlap and application to Nd:YVO<sub>4</sub> laser
No full textWe derive simple and convenient expressions for two-pass saturated amplification with pulse overlap. These have the same form as the single-pass Franz–Nodvik equations but with a factor of two in front of the cross-section for stimulated emission. The predicted decrease in energy extraction efficiency when there is pulse overlap compared with sequential passes agrees well with earlier numerical modelling. This approach has been extended to analyse a two-pass Nd:YVO4 amplifier (diode pumped 2 mm long 1% doped crystal) operated with nanosecond pulses delivered at rates up to 20 kHz and taking account of the Gaussian beam profile. An estimate of γ = 1 × 10-15 cm3 s-1 for the up-conversion macro-parameter was found to provide a consistent value for the length-averaged gain coefficient and the effective gain lifetime of the amplifier for the pump conditions used
Properties of rare earth doped thin film dielectric layers for upconversion laser waveguides
No full textStructural and optical properties of different dielectric thin films for planar waveguiding applications
No full textReactive dual magnetron sputtering of Ta2O5 and Al2O3: Optical and structural properties and thin film applications
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Efficient, high-power, repeatable, cryogenic Yb:YAG MOPA system
No full textA diode-pumped laser system in joule-class energy has been developed at 100 Hz in nano-second to pico-second. A feasibility study has shown high slope efficiency of 44% and optical efficiency of 30% at 150 mJ pulse energy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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