We demonstrate room temperature coherent generation and control of a directional photocurrent in bulk GaAs via simultaneous one-and two-photon interband absorption processes using phase-related 1 ps or 175 fs pulses at 0.775 and 1.55 mm. Electrical currents generated in low-temperature-grown (LT) and normal bulk GaAs are collected via gold electrodes. Current densities as high as 3 nA͞mm 2 in LT-GaAs are measured for injected carrier densities as low as 10 14 cm 23 and for peak irradiances of 18 MW cm 22 (1.550 mm) and 3 kW cm 22 (0.775 mm).
A label-free optical biosensor based on a one-dimensional photonic crystal microring resonator with enhanced light-matter interaction is demonstrated. More than a 2-fold improvement in volumetric and surface sensing sensitivity is achieved compared to conventional microring sensors. The experimental bulk detection sensitivity is ~248nm/RIU and label-free detection of DNA and proteins is reported at the nanomolar scale. With a minimum feature size greater than 100nm, the photonic crystal microring resonator biosensor can be fabricated with the same standard lithographic techniques used to mass fabricate conventional microring resonators.
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