Femtosecond laser-induced damage and filamentary propagation in fused silica.

Bulk damage induced by fs IR laser pulses in silica is investigated both experimentally and numerically. In a strong focusing geometry, a first damage zone is followed by a narrow track with submicron width, indicating a filamentary propagation. The shape and size of the damage tracks are shown to correspond to the zone where the electron density created by optical field ionization and avalanche is close to 10(20) cm(-3). The relative role of avalanche and photoionization is studied. The plasma density produced in the wake of the pulse is shown to saturate around 2-4x10(20) cm(-3).

Nonlinear propagation of subpicosecond ultraviolet laser pulses in air.

We report filamentation of subpicosecond UV laser pulses with only millijoule energy in atmosphere. The results are in good agreement with a numerical simulation using a quasi-three-dimensional propagation code.

Formation of a conducting channel in air by self-guided femtosecond laser pulses.

We report a drastic reduction of air resistivity following the passage of a self-guided femtosecond pulse from a Ti:sapphire laser system at 800 nm with energies per pulse between 1 and 14 mJ and a pulse duration of 120 fs. Connected plasma filaments with a length that can exceed 150 cm are created by these pulses. The presence of a conducting plasma channel results from multiphoton ionization of air molecules in the filament core.

Anomalous long-range propagation of femtosecond laser pulses through air: moving focus or pulse self-guiding?

Self-guided propagation of femtosecond laser pulses is studied for a converging-beam configuration. Channeling of the pulse energy through various gases is observed over distances well beyond the lens focal point, a fact that cannot be explained by the moving-focus model. The results are in good agreement with three-dimensional numerical simulations.

Kerr effect in all-fiber cavities of optical gyros.

The transmission spectrum of an all-fiber cavity is theoretically analyzed, in order to evaluate the perturbation induced in the eigenfrequency measurement by the Kerr effect. Existence of a threshold separating the bistable operation region from the monostable is shown. In the weakly nonlinear operation, the asymmetry of the line is evaluated and the resulting error in the frequency measurement is analytically derived.

Continuous laser amplification in a monomode fiber longitudinally pumped by evanescent field coupling.

Amplification of continuous laser radiation propagating in a monomode optical fiber was obtained by evanescent field coupling within a pumped dye solution deposited in the neighborhood of the fiber core. A factor-of-25 signal gain was recorded for 632.8-nm He-Ne radiation and DCM dye solution.

Polarization effect in optical-fiber ring resonators.

The effect of birefringence on the resonance frequency of a closed-loop fiber-optic resonator is calculated.

Elastooptical antenna for detection of gravitational radiation.

Using the photoelastic effect in transparent solids to detect stresses induced by a gravitational wave is proposed. The induced birefringence is measured by a polarimeter. The phase difference is amplified by a Fabry-Perot cavity containing the medium. The sensitivity of this optical strain sensor is discussed, and that of the antenna is estimated.

Automatic measurement of the Stokes vector of light.

A system which measures the Stokes parameters of light automatically over a wide range of wavelengths is described. The method requires two piezooptic modulators, three lock-in amplifiers, and an on-line minicomputer for data processing. The absence of a static retardation plate provides an unprecedented insensitivity to beam wandering. Typical performance parameters such as response time, accuracy, and detectivity as a function of the incident polarization are given.

Capacity of polarization and amplitude modulated links in the presence of atomospheric scintillation.

A transmission channel may be characterized by its capacity, i.e., the largest quantity of mean mutual information transmitted between the emitter and the receiver. The channel we have studied is a light beam traveling in the low atmosphere, and the capacity has been calculated for polarization (PCM/PL) and intensity (IM) modulation, assuming a Poisson detection process and log-normal fluctuations for scintillation. The depolarization of light has been neglected, and the polarizers have been considered perfect. The appended graphs show that PCM/PL modulation has a greater capacity in all investigated cases.