Marc Châteauneuf

Microwave guiding in air by a cylindrical filament array waveguide

Microwave guiding was demonstrated over 16cm in air using a large diameter hollow plasma waveguide. The waveguide was generated with the 100TW femtosecond laser system at the Advanced Laser Light Source facility. A deformable mirror was used to spatially shape the intense laser pulses in order to generate hundreds of filaments judiciously distributed in a cylindrical shape, creating a cylindrical plasma wall that acts as a microwave waveguide. The microwaves were confined for about 10ns, which corresponds to the free electron plasma wall recombination time. The characteristics of the plasma waveguide and the results of microwave guiding are presented.

512-channel vertical-cavity surface-emitting laser based free-space optical link

A vertical-cavity surface-emitting laser based bidirectional free-space optical interconnect has been implemented to interconnect two printed circuit boards. A total of 512 clustered channels with a density of 2844 channels/cm2 are transmitted over a distance of 83 mm. The optical interconnect is a combination of refractive microlenses and diffractive minilens relays.

Ultrabroadband conical emission generated from the ultraviolet up to the far-infrared during the optical filamentation in air

Ultraviolet and infrared conical emissions were observed during the filamentation in air of powerful femtosecond laser pulses produced by a portable terawatt laser system. The broadband spectrum was measured from 200 nm up to 14 microm and covered the complete optical transmission window of the atmosphere. The angularly resolved spectrum showed some X-wave structure across the frequency range analyzed. However, we demonstrated that the strong conical emission observed in the mid- and far-infrared is mainly owing to the four-wave mixing between the pump pulse and its blueshifted conical emission.

Toward remote high energy terahertz generation

Remote terahertz (THz) generation from a two-color femtosecond laser-induced filament in air was experimentally demonstrated. A record of remote THz emission at 16 m was achieved. THz pulse energy more than 250 nJ in the frequency range below 5.5 THz was recorded; this is two orders of magnitude stronger than that from single-color excitation. Back-scattered nitrogen (N2) fluorescence signal remotely measured with a lidar is linearly proportional to the THz emission, which would provide a more practical method to characterize the THz pulses.

Characterization of terahertz emission from a dc-biased filament in air

We demonstrate that the terahertz emission from a dc-biased filament can be regarded as a sum of an elliptically polarized terahertz source (generated by a filament without external electric field) and a linearly polarized terahertz source induced by the external electric field applied to the filament. The peak frequency and linewidth of the linearly polarized terahertz source are related to the average plasma density of the filament.

High energy terahertz emission from two-color laser-induced filamentation in air with pump pulse duration control

Two-color laser-induced femtosecond filamentation was employed to generate high energy terahertz emission in air with high energy pump. By controlling the pump pulse duration, more than four times enhancement in terahertz pulse energy has been obtained when compared with a Fourier transform-limited pump. Multiple filaments’ dynamics might be responsible for the terahertz enhancement. Superbroadband terahertz pulse with energy up to 2 μJ was generated using loose focusing condition, while the maximum terahertz pulse energy in the frequency range below 5.5 THz was around 60 nJ.

Elliptically polarized terahertz emission in the forward direction of a femtosecond laser filament in air

Elliptically polarized terahertz emission from a femtosecond laser filament in air in the forward direction was discovered by using a wire grid polarizer and electro-optic sampling technique. The generation mechanism could be through four-wave optical rectification or second-order optical rectification inside the filament zone where the inversion symmetry of air is broken.

Ultrafast birefringence induced by a femtosecond laser filament in gases.

We demonstrate that a femtosecond-laser filament in both molecular and atomic gases is birefringent for a copropagating probe pulse. Any input-probe polarization is decomposed into two orthogonal components, the optical axis being in the pump polarization direction. In molecular gases, the birefringence is mainly due to the delayed rotational molecular-wave packet; the probe pulse thus experiences several revivals in time. The two probe components end up spatially separated in the far field. In atomic gases such as argon, the effect is weaker and is attributed to the instantaneous electronic cross-phase modulation.

Experimental and numerical analyses of misalignment tolerances in free-space optical interconnects

A comparison of numerical analyses with experimental measurements suggests that both the ray-tracing and the Gaussian beam-propagation models overestimate the misalignment tolerances for on-axis beams and fail to predict the large longitudinal focal shift that occurs for off-axis beams propagating in free-space optical interconnects.

Remote THz generation from two-color filamentation: long distance dependence.

Remote terahertz (THz) generation from two-color filamentation is investigated as a function of the onset position of filaments. THz signals emitted by filaments produced at distances up to 55 m from the laser source were measured. However, from 9 m to 55 m, the THz signal decayed monotonically for increasing onset positions. With a simple calculation, the dominant factors associated to this decay were identified as group velocity mismatch of the two-color pulses and linear diffraction induced by focusing and propagating the second harmonic pulse.