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.

Infrared generation by filamentation in air of a spectrally shaped laser beam.

We demonstrated the generation of infrared radiation by filamentation of a spectrally shaped femtosecond laser beam. The spectrum is divided in two distinctive parts using an acousto-optic programmable dispersive filter (AOPDF) as a pulse shaper, resulting in two pulses of different colors. One pulse is frequency doubled and the beams are then focused to produce an optical filament. Efficient infrared generation occurred in the filament zone through the four-wave mixing interaction. This in-line setup allowed perfect spatial overlap of the pulses, fine control of the relative delay and the remote control of the infrared spectral distribution through spectral shaping of the initial femtosecond laser beam via the AOPDF.

Non-radially polarized THz pulse emitted from femtosecond laser filament in air.

Femtosecond laser filament could produce THz wave in forward direction. In our experiment, THz pulse emitted from a femtosecond laser filament has been investigated. It was found that the polarization of the studied THz pulse mainly appears as elliptical. This observation supplements the previous conclusion obtained by C. D'Amico et al. that THz wave emitted by a filament is radially polarized. The mechanism of generating elliptically polarized THz wave has been interpreted by either four-wave optical rectification or second order optical rectification inside the filament zone where centro-symmetry of the air is broken by the femtosecond laser pulse.

Six-Degrees-of-Freedom Alignment of Two-Dimensional Array Components by Use of Off-Axis Linear Fresnel Zone Plates.

A novel six-degrees-of-freedom (six-DOFs) alignment technique for assembling two-dimensional array components is presented. The technique uses off-axis linear Fresnel zone plates on one component that are combined with alignment targets on the other. The technique is compact and sensitive to all six DOFs; it was used to package an array of microlenses with a 32 x 32 array of GaAs multiple-quantum-well modulators flip-chip bonded to a 9 mm x 9 mm complementary-metal-oxide-semiconductor chip. By use of interference fringes to control the tilt misalignment, the worst-case misalignment of the microlenses relative to the chip is calculated to be as follows: lateral = 3.0 mum, rotational = 0.023 degrees , longitudinal = 13 mum, and tilt = 0.022 degrees . We also propose alternative implementations of the technique, including one that uses on-chip photodetectors to automate this six-DOF alignment technique.

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.