1,721,022 research outputs found
Generation of femtosecond pulses down to 166nm by sum-frequency mixing in KB(5)O(8.)4H(2)O
No full textAn all solid-state laser system based on sum-frequency mixing the signal wave from an optical parametric generator and the fourth harmonic of a Ti:sapphire regenerative amplifier produced similar or equal to 200fs long nearly bandwidth-limited pulses tunable from 172 down to 166n
Laser-diode-seeded single and double stage femtosecond optical parametric amplification in the mid-infrared
No full textTunable mid-infrared pulses are generated with a MgO:LiNbO3-based traveling-wave optical parametric amplifier in single and double stage operation regime pumped by a 1-kHz Ti:sapphire regenerative amplifier system. For the first time to our knowledge a pulsed laser diode is successfully used in the femtosecond regime as a compact seed source at the signal wavelength where the tunability of the generated idler pulses can be realized by tuning the seed wavelength. Almost transform limited mid-infrared pulses as short as 130 and 160 fs with pulse energies as high as 5 and 15 mu J are produced near 3.5 mu m by the single and double stage scheme, respectively. The pulse to pulse fluctuations in both cases do not exceed 2% which corresponds to the stability of the pump sourc
Characterization of ZnGeP2 for parametric generation with near-infrared femtosecond pumping
No full textValues for the nonlinear refractive index (n(2) approximate to 5.4 X 10(.5) cm(2)/GW) are reported as well as the two-photon absorption coefficient (beta approximate to 0.25 cm/GW) in ZnGeP02 at wavelengths near half the band edge of this semiconductor nonlinear optical crystal. The Z-scan measurements were performed with a mode-locked femtosecond Cr:forsterite laser at 1.26 mum and 83 MHz, and the nonlinear transmission measurements were accomplished by a near infrared traveling wave optical parametric generator providing powerful femtosecond pulses at 1 kHz. In both cases, ZnGeP2 samples with reduced anomalous absorption were used. The parametric fluorescence in these 2-mm thin ZnGeP2 samples was studied with near infrared pumping and the optimum pump wavelength established lies between 1.9 and 2.1 mum. The femtosecond signal and idler pulses generated could be tuned between 2.5 and 12 mum at a maximum single pass internal conversion efficiency of 2.5
Femtosecond regenerative amplification in Cr : forsterite at 5-10 kHz
No full textWe developed a high-power oscillator-regenerative amplifier femtosecond laser system. Based on chromium-doped forsterite. The system is operating near 1.25 mum at a 5-10 kHz repetition rate. Chirped-pulse amplification produced 0.86 W (0.75 W) of average power, or 465 mW (400 mW) after compression at 5 kHz (10 kHz). Nearly bandwidth-limited pulses of duration 135 fs (shortest) and 150 fs; (typical) are available with an energy of 93 muJ and 40 muJ at 5 and 10 kHz, respectivel
Generation of high-power femtosecond light pulses at 1 kHz in the mid-infrared spectral range between 3 and 12 mu m by second-order nonlinear processes in optical crystals
No full textWe review methods for frequency conversion of amplified femtosecond laser pulses from the near- to the mid-infrared. The potential of all commercially available optical crystals is evaluated on the basis of the specific requirements in the high-power femtosecond regime. A comparative experimental study of a number of materials (birefringent and quasi-phase-matched) employed in a seeded optical parametric amplifier pumped near 800 nm is presented, where the generated idler is tunable between 3 and 4 mum. Internal conversion efficiencies as high as 40% and pulse energies as high as 20 muJ are achieved in this spectral range. Wavelength tunability up to 12 mum with energies exceeding 1 muJ is demonstrated by pumping optical parametric amplifiers and generators near 1.25 and 2 mum, as well as by difference frequency generation with a quantum efficiency of 40-80%. In all cases the generated mid-infrared pulses are almost bandwidth limited with a duration of 100-200 f
Femtosecond noncollinear parametric amplification in the mid-infrared
No full textWe demonstrate the potential of noncollinear parametric interaction in a traveling wave MgO:LiNbO3 optical parametric amplifier operating in the mid infrared near 3 mu m. Our calculations indicate that for pump wavelengths below 816 nm (the wavelength near which collinear group matching is achieved at a fixed signal wavelength of 1064 nm), the group velocity mismatch can be reduced and the parametric gain can be increased by noncollinear propagation of the three beams. Experimentally we verify this by producing approximate to 2.5 times higher energy and shorter pulse duration (125 fs against 180 fs) at the idler wavelength by noncollinear interaction as compared to collinear interaction. (C) 1999 Elsevier Science B.V. All rights reserve
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
Femtosecond parametric generation in ZnGeP2
No full textWe report traveling-wave optical parametric generation in short (2-mm) ZnGeP2 samples with reduced anomalous absorption, using femtosecond pump pulses near 2 mu m. The signal and the idler waves generated could be tuned from 2.5 to 10 mu m, and they extend the tunability of the beta-barium berate optical parametric generator used as a pump source to the mid-infrared. At a single-pass internal conversion efficiency of 2.5% we estimate pulse durations of 75 fs (signal near 3 mu m) and 200 fs (idler near 6 mu m). (C) 1999 Optical Society of Americ
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