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Interferometric measurements of submicrosecond gas density dynamics following passage of an intense ultrashort pulse are presented for single- and multi-lobed beams at 10 Hz and 1 kHz. Results are in excellent agreement with hydrodynamic simulations.
We demonstrate that long-lived air waveguides can efficiently collect remote, isotropically emitted optical signals. Signal-to-noise enhancements of ∼104 are possible for standoff measurements at 100 m, with even higher increases possible at longer distances.
We show that femtosecond filament arrays can generate robust, very long-lived optical waveguides in air. These guides have millisecond lifetime and should be suitable for the transmission of high average power beams.
We show that the deposition of energy in nitrogen by a train of ultrafast pulses can be greatly enhanced or diminished using multiple pulses spaced near the molecular rotational revival or half revival period.
The plasma-induced phase shift of a probe is measured in 2D spatially with ∼3 µm resolution and temporally with ∼5 fs resolution. From this ionization rates for the noble gases are found for a 40 fs, 800 nm pulse, for intensities up to nearly full depletion of the neutral population.
Recent exciting results from research in femtosecond laser pulse filamentation in transparent media are presented, with an emphasis on experiments in gases.
The nonlinear refractive index in air components and noble gases is measured absolutely using spectral interferometry in a thin gas target. Contributions from bound electronic states, molecular alignment, and free electrons from ionization are observed.
We show that a localized and long-lived quasi-stationary gas density depression exists after filament-generated-plasma recombination. Its millisecond timescale dynamics is governed by thermal diffusion and has strong effects on high-repetition-rate filamentation and supercontinuum generation.
The two-photon Franz-Keldysh effect in bulk GaAs is calculated using a 14-band model for the band structure. Strong effects are predicted for both two-photon absorption and quantum interference control of carrier injection.
We measure the polarization dependence of the Kerr effect in air using single-shot supercontinuum spectral interferometry, enabling separation of the instantaneous and rotational components of the nonlinearity.
A static electric field enables 1 + 2-photon coherent control of the photoexcited carrier population in semiconductors. A theory based on the Franz-Keldysh effect is compared to results of an experiment in (100) GaAs.
We measure two-color quantum interference control of photocurrent injection in erbium-doped GaAs. The signal size is the same order of magnitude as from a low-temperature grown GaAs sample, and much larger than in a semi-insulating GaAs sample. Thus erbium-doped GaAs could be useful for fabrication of monolithic optical carrier-envelope phase detectors. We also describe a prism-based two-color interferometer...
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