Intracavity frequency-doubled degenerate laser.

We develop a green light source with low spatial coherence via intracavity frequency doubling of a solid-state degenerate laser. The second-harmonic emission supports many more transverse modes than the fundamental emission, and exhibits lower spatial coherence. A strong suppression of speckle formation is demonstrated for both fundamental and second-harmonic beams. Using the green emission for fluorescence excitation, we show the coherent artifacts are removed from the full-field fluorescence images. The high power, low spatial coherence, and good directionality make the green degenerate laser an attractive illumination source for parallel imaging and projection display.

Angular dependence of filament-induced plasma emission from a GaAs surface.

Quantitative measurements of the angular distribution of the plasma line emission from a gallium arsenide (GaAs) target irradiated by a single laser-air filament are reported. These enable reliable estimates of the stand-off ranges possible with single-filament-induced laser-induced breakdown spectroscopy materials detection.

Multiple beam splitter using volumetric multiplexed Fresnel zone plates fabricated by ultrafast laser-writing.

A simple approach to producing a 1×N beam splitter is demonstrated by fabricating a volumetric multiplex phase Fresnel zone plate in bulk transparent material. This comprised four layers of zone plates created in borosilicate glass by femtosecond laser direct-writing, each shifted laterally relative to the illumination axis, creating four separate beamlets. Since the power transmitted in each beamlet is proportional to the diffraction efficiency of the corresponding zone plate, the power ratios can be customized by adjusting the fabrication parameters of each layer. This approach demonstrates the potential of femtosecond laser direct-writing for the fabrication of complex optical elements in transparent media as components of integrated monolithic photonic devices.

Refractive index modification using fs-laser double pulses.

Buried waveguides in glass are manufactured by irradiation with femtosecond laser double pulses. The refractive index change Deltan is determined by measuring the numerical aperture NA of the waveguides and by through light microscopy. The value of Deltan shows a significant dependency on the time delay Deltat of the fs-laser double pulses. A Deltan of up to 2x10(-3) in fused silica is reached at a Deltat between 400 and 800 ps. Based on the results of the double pulse experiments the initial effects of the refractive index change are discussed, taking into account thermal effects and the formation of self trapped excitons (STE) and transient color centers and their interaction with the next laser pulse.