1,720,979 research outputs found
Numerical model for a widely tunable self-similar oscillator
No full textWe propose a design for a widely tunable oscillator operating over the wavelength range 1µm to 2µm. Numerical simulations show that the pulses evolve self-similarly in each stage of the oscillator maintaining a hyperbolic secant form
Dataset for: Short single-frequency self-pulsing Brillouin-Raman distributed feedback fiber laser
No full textDataset for the paper: 'Short single-frequency self-pulsing Brillouin-Raman distributed feedback fiber laser' accepted in Optics Express.
Dataset contains raw data for all the optical/eletronic spectra and oscioscope graphs presented in the paper.</span
Fabrication and characterisation of few mode DBR Brillouin-Raman lasers
No full textStimulated Raman scattering (SRS) fiber lasers remain an area of interest as they provide a simple and compact method of creating lasers at wavelengths beyond the rare-earth ion bands. The authors and others have demonstrated that short π-phase shifted distributed-feedback (DFB) cavity structures can be used to create single-frequency lasers [1–3]. To reach longer wavelengths, cascading SRS cavities are typically used, which usually involve many-meter-long distributed Bragg reflector (DBR) Fabry–Pérot cavities with 100s or 1000s of longitudinal modes. However, to keep the laser system compact, these cavities must be as short as possible, which results in few longitudinal modes and a different behaviour. Siekiera et al. have reported such short DBRs which consist of two 50 mm gratings separated by 120 mm in a high germania fiber with an effective area of 7.3 μm2 [4]. This produced a laser with a threshold of 4 W with a maximum output of 700 mW for 8 W of pump with the expected 607 MHz beat frequency between the few longitudinal modes and 20 dB side mode suppression.Our DBRs were fabricated in the same manner as the previous π-phase shifted DFB laser using UHNA3 fiber again for its high germania content and small effective area of 5.4 μm2 [3]. The DBR’s 241 mm long cavity is formed from two 22 mm gratings at 1116 nm which are 99.9 % reflective. The cavity is pumped with a freespace linearly polarised 1064.4 nm pump setup as shown in Fig. 1a. Unlike Siekiera et al., the lack of an output coupler grating leads to a much higher finesse cavity which, along with the smaller effective area, leads to a lower threshold of 2.2 W, higher maximum output powers of 900 mW at 5 W pump power, and the presence of stimulated Brillouin scattering (SBS) as we saw in our DFB laser, as shown in Fig. 1b. We also see a much reduced broadening with a FWHM of 23 pm for the SRS and 18 pm for the SBS with 70 dB sidemode suppression. Given the similarities to our DFB we expected a low lasing threshold, which we believe is increased by larger loss in the gratings due to the higher fluence required (1 kJ compare to 0.03 kJ). As with the DFB, we see pulsing of the DBR laser, as shown in Fig. 1c. However, most of this is as expected for longitudinal mode beating (repetition rate matches the expected free spectral range) with occasional single-frequency SBS pulses and massive pulse bursts which always lead to pump depletion. It should also be noted that if these lasers are run near threshold they can enter stable CW single or at slightly higher powers quasi-CW dual mode lasing with no SBS. We will report on our latest findings into DBR lasers, optimisation of grating fabrication to improve lasing parameters, further investigations into pulsed behaviour, and potentially cascading using DFB cavities
Diode seeded parametric amplifier pumped by a picosecond all-fibre system
No full textSeveral recent advances in fibre source development have greatly increased the output powers and energies available from compact fibre laser systems,[1,2,3]. Suitable levels are now achievable for pumping of parametric devices that use highly nonlinear materials such as periodically poled lithium niobate (PPLN). This powerful combination of fibre sources and PPLN promises a whole range of efficient, widely tunable, practical, all solid state optical sources and devices [ 4 ,5, 6, 7]. Fibre-laser-pumped optical parametric amplifiers ( 0 P As) constitute one such nonlinear device type offering gains in excess of 80d.B. With such high gains OP As can be used to amplify parametric noise to appreciable power levels so as to efficiently provide high power, broadband parametric fluorescence. An OPA operated in such a fashion is called an Optical Parametric Generator (OPG), [8]. A fibre-laser-pumped OPG has already been demonstrated by Galvanauskas et al. [7] who used a femtosecond erbium-fibre-based chirped based amplification (CPA) system with bulk gratings combined with PPLN to obtain broadband emission on a femtosecond timescale tunable in the wavelength range 1.05-2.9µm. However, due to the noise initiated nature of the process and broad gain bandwidth the generated pulses were far from transform-limited. The same authors also demonstrated a high gain OPA, using millijoule energy pump pulses from a bulk amplifier and a chirped nanosecond pulsed seed [9]. In the following we describe PPLN-based OPA (and OPG) experiments performed using a picosecond allfibre CPA system as a pump source, i.e. achieving pulse compression using fibre gratings rather than the bulk gratings of RefI7]. We have demonstrated the high gain achievable with OP A systems using engineered quasi-phase-matched PPLN. Additionally we show that seeding of a high gain OPA with a low-power, continuous-wave beam (e.g. from a laser diode) provides a convenient means to obtain near transform-limited high power pulses at the seed wavelength, thus greatly enhancing the pulse quality relative to that achievable using a simple OPG. Our approach, assuming a PPLN sample of suitable period and an appropriate temperature allows one to use established fibre laser technology to obtain high-quality, high-power pulsed output at any signal/idler wavelengths for which a seed laser, (e.g. a semiconductor diode laser), is available
Self-pulsing of Brillouin-Raman distributed feedback fiber lasers
No full textWe report on self-pulsing in distributed-feedback single-frequency Raman fibre lasers. We see a periodic reduction in intra-cavity power associated with each pulse and propose that this self-pulsing arises from parasitic Brilluoin scattering cavity dumping the Raman
Real-time observation of hidden multi-soliton dynamics in a few-cycle Ti:Sapph oscillator
No full text
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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