19 research outputs found
HV discharge acceleration by sequences of UV laser filaments with visible and near-infrared pulses
We investigate the triggering and guiding of DC high-voltage discharges over
a distance of 37 cm by filaments produced by ultraviolet (266 nm) laser pulses
of 200 ps duration. The latter reduce the breakdown electric field by half and
allow up to 80% discharge probability in an electric field of 920 kV/m. This
high efficiency is not further increased by adding nanosecond pulses in the
Joule range at 532 nm and 1064 nm. However, the latter statistically increases
the guiding length, thereby accelerating the discharge by a factor of 2. This
effect is due both to photodetachment and to the heating of the plasma channel,
that increases the efficiency of avalanche ionization and reduces electron
attachment and recombination.Comment: 12 pages, 6 figure
High-Power Hybrid Mode-Locked External Cavity Semiconductor Laser Using Tapered Amplifier with Large Tunability
We report on hybrid mode-locked laser operation of a tapered semiconductor amplifier in an external ring cavity, generating pulses as short as 0.5 ps at 88.1 MHz with an average power of 60 mW. The mode locking is achieved through a combination of a multiple quantum well saturable absorber (>10% modulation depth) and an RF current modulation. This designed laser has 20 nm tuning bandwidth in continuous wave and 10 nm tuning bandwidth in mode locking around 786 nm center wavelength at constant temperature
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Short- and long-term gain dynamics in N2+ air lasing
Air lasing in the nitrogen molecular ion is not well understood because the complex physics responsible for gain is interwoven with pulse propagation in an extreme environment. Here we use a short gas jet to limit the interaction length, thereby removing the propagation effects. We report on several mechanisms that contribute to the decay of gain in different conditions, and experimentally isolate two decay timescales: the decay of long-term gain due to collisional state mixing, and short-term gain that cannot be explained by population inversion. To test the former, we control the inelastic electron scattering rate by varying the gas concentration while keeping the propagation length fixed, and predict the change of the decay using a model of collisional state mixing. We show that the same mechanism causes the decay of rotational wave packets in the states of the ion. Finally, we simulate the complex modulations of gain due to rotational wave packets and the propagation of the probe pulse through the evolving rotationally excited and inverted medium.U.S. Army Research Office [W911NF-14-1-0383]; National Research Council of Canada; National Science and Engineering Research Council of Canada; Government of Ontario; Xerox Canada Inc.; U.S. AFOSR under MURI [FA9550-16-1-0013]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]