We report on the development of what we consider to be a practical and highly stable stretched-pulse laser based on Yb 31 -doped silica fiber. The Fabry -Perot cavity uses nonlinear polarization rotation as the mode-locking mechanism, and a semiconductor saturable-absorber mirror to ensure robust self-starting and incorporates a diffraction grating pair to compensate for the normal dispersion of the fiber. Use of a single-mode grating-stabilized telecommunications-qualified pump laser diode ensures reliable, low-noise operation (ϳ0.05% amplitude f luctuations at 10-Hz measurement bandwidth). The laser generates high-quality, 60-pJ pulses of ,110-fs duration at a repetition rate of ϳ54 MHz (3-mW average power Stable, low-noise sources of ultrashort pulses are important for a wide range of applications including ultrafast spectroscopy, multiphoton microscopy, and the pumping of parametric devices. Passively mode-locked, stretched-pulse fiber laser cavities based on Er 31 -doped fiber can operate with low amplitude noise and timing jitter, 1 and such lasers are now available commercially. Yb 31 -doped silica fiber, with its broad gain bandwidth, represents an attractive medium for the generation and amplification of ultrashort optical pulses. However, constructing a stretched-pulse cavity operating at 1 mm requires the inclusion of a prism/grating dispersive delay line (DDL) to compensate for the normal dispersion of the f iber. Here we report the development of a compact and highly stable stretched-pulse laser operating at 1.06 mm, based on Yb 31 -doped fiber. The system's stability is attributable largely to the use of a grating-stabilized, telecommunications-qualified 976-nm laser-diode pump laser. Pump coupling is both conveniently and reliably achieved with a 976͞1050-nm fused-tapered wavelength-division multiplexer coupler. We believe that this oscillator will prove attractive for use in a wide range of scientif ic and industrial applications.In our first demonstration of an ultrashort pulse ͑ϳ65-fs͒ Yb 31 silica f iber oscillator in 1996, 2 we used a unidirectional cavity design incorporating an optical circulator arrangement and an intracavity prism-based DDL. Nonlinear polarization evolution in the f iber acted as the fast saturable absorber. The laser exhibited good self-starting performance and generated ,100-fs pulses. However, the cavity was large and complex and was pumped with a Ti:sapphire laser. A passively mode-locked stretched-pulse laser based on a Nd-doped fiber in a Fabry -Perot cavity with a prism-based DDL was reported in 1993. 3 Nonlinear polarization evolution was used as a fast saturable-absorber mechanism, and a semiconductor saturable-absorber mirror (SESAM) was used to induce self-start mode locking. 4 Although the laser's performance in terms of pulse duration and quality seemed good, no data were presented on system stability and reliability. Moreover, this system was end pumped with two polarization-multiplexed 150-mW laser diodes (808 nm) or with a Kr 31 laser (to produce the short...
The role of spectral shaping in the production of subpicosecond, high-contrast pulses by using chirped-pulse amplification in Nd:glass lasers is described. Spectral shaping has been used to produce 3.2-TW pulses at 750 fsec with an energy contrast of better than 10(3):1. In the absence of shaping, compression of the 1053-nm pulses yielded only 1.5 psec and a contrast ratio of approximately 10:1.
The energy transfer by stimulated Brillouin backscatter from a long pump pulse (15 ps) to a short seed pulse (1 ps) has been investigated in a proof-of-principle demonstration experiment. The two pulses were both amplified in different beamlines of a Nd:glass laser system, had a central wavelength of 1054 nm and a spectral bandwidth of 2 nm, and crossed each other in an underdense plasma in a counter-propagating geometry, off-set by 10 • . It is shown that the energy transfer and the wavelength of the generated Brillouin peak depend on the plasma density, the intensity of the laser pulses, and the competition between two-plasmon decay and stimulated Raman scatter instabilities. The highest obtained energy transfer from pump to probe pulse is 2.5%, at a plasma density of 0.17n cr , and this energy transfer increases significantly with plasma density. Therefore, our results suggest that much higher efficiencies can be obtained when higher densities (above 0.25n cr ) are used.
• Summary: This paper uses research from American, Australasian and UK-based perspectives to examine supported employment as an enabling strategy to support disabled people with complex needs to access mainstream employment. Supported employment is analysed in the context of models of disability and employment policy. Factors underlying and hindering successful provision are identified from research. • Findings: Supported employment is successfully supporting some people with complex needs into mainstream employment. However, aspects of employment policy, the benefits system, a lack of funding, and geographical variation in provision act as barriers to success. • Applications: The implications of supported employment for people with complex needs are identified for social services and social work departments.
The design and performance of a Nd:YAG-dye-laser system capable of producing synchronized peak powers approaching 10 GW is described. The output of the amplified dye-laser system is several millijoules with fully tunable pulses as short as 300 fsec and is optically synchronized with the 3-GW output of an amplified Nd:YAG laser system, permitting a new class of high-intensity pump-probe experiments. By using short ( approximately 70-psec) pulses to pump the dye amplifier, the energy of amplified spontaneous emission is reduced to less than 10(-5) of that contained in the main subpicosecond pulse.
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