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We present results of 2D real-time imaging of terahertz (THz) beam generated by a photoconductive antenna driven by a femtosecond oscillator. The detector, operating at room temperature, is a 320 x 240 array of antenna-coupled microbolometers with integrated CMOS read-out electronics delivering 25 images per second. High quality images of broadband THz beams covering the 0.1-2 THz range are recorded while maintaining a signal-to-noise ratio of 10 for detected THz power as low as 25 nW. The compactness of the easy-to-use uncooled camera makes it very useful for the alignment of systems such as THz time-domain spectrometers and for the characterization of emitters, optics and other components.

The dynamical electrical properties of annealed low-temperature-grown GaAs layers moderately doped with beryllium are studied using photoconductive sampling. Picosecond electrical pulses are sampled using an interdigitated metal-semiconductor-metal structure. These time-resolved experiments supported by numerical simulation allow us to determine electron and hole mobilities of, respectively, 540 and 90 cm 2 /V/s. We also demonstrate that the free-electron trapping process is saturating under high-optical-density excitation. From these experiments, we get an electron trapping cross section of n =1ϫ 10 −13 cm 2 .

Diffraction gratings can be used to achieve phase matching between the fundamental modes of a slab or confined waveguide. Compared with the usual techniques such as quasi-, Cerenkov, and intermodal phase matching, the matching method used here involves spatial harmonics of the guided electromagnetic field that are generated by the corrugated grating. This grating acts simultaneously as a linear waveguide coupler at both the pump and harmonic frequencies. Using the third spatial harmonic, we report what we believe to be the first observation of grating-assisted phase-matched second-harmonic generation between counterpropagating TM(0) modes of an organic waveguide.

Using femtosecond time resolved reflectivity, we have characterized the dynamics of photoinduced generated carriers in a polycrystalline low-temperature-grown GaAs sample. Our measurements are fitted with an analytical expression reliable for low pump power experiments. The sample, which presents no As precipitates, shows an ultrafast subpicosecond response together with a longer picosecond tail that we attribute to the midgap defect states. Moreover, we have observed the influence of surface roughness on the differential reflected signal.