We observe intense pulses of far-infrared electromagnetic radiation emitted from arrays of InAs nanowires. The THz radiation power efficiency of these structures is about 15 times higher compared to a planar InAs substrate. This is explained by the preferential orientation of coherent plasma motion to the wire surface, which overcomes radiation trapping by total-internal reflection. We present evidence that this radiation originates from a low-energy acoustic surface plasmon mode of the nanowire. This is supported by independent measurements of electronic transport on individual nanowires, ultrafast THz spectroscopy and theoretical analysis. Our combined experiments and analysis further indicate that these plasmon modes are specific to high aspect ratio geometries.Comment: 12 pages, 7 figure

Recent developments in cooling thulium-doped heavy-metal fluoride glass are presented. Thulium-doped fluorozirconate (ZBLANP) is cooled to 19 K below ambient with a multiple-pass pump scheme. This represents over an order of magnitude increase from the previously reported single-pass geometry. The results agree with a simple model for anti-Stokes fluorescence cooling that includes considerations of quantum efficiency and parasitic heating mechanisms. Issues relating to a practical optical refrigerator are examined, including a general model for the effects of multiple pump passes.

Photoluminescence of GaAs passivated with GaInP is studied over the temperature range 7-450 K. Different photocarrier recombination mechanisms are identified as the temperature changes. An interface recombination velocity of less than 0.6 cm/ s is measured at 300 K. Lift-off processing inhibits but does not preclude laser cooling of GaAs.

Femtosecond mid-infrared laser pulses that are continuously tunable in the wavelength range from 9 to 18mum are demonstrated. These nearly bandwidth-limited pulses are generated by phase-matched difference-frequency mixing within the broad spectrum of 20-fs pulses from a mode-locked Ti:sapphire laser in GaSe. A direct determination of the pulse duration at 11.5mum gives a value of 140 fs. The average mid-infrared power of 1muW is ~100 times greater than that for infrared generation by non-phase-matched optical rectification.

Coherent electromagnetic radiation is generated by the oscillation of longitudinal modes associated with optical phonons and bulk plasmons in InAs. Dramatic changes to the radiation spectra occur when the plasmon and phonon frequencies are in close spectral proximity, i.e., when the modes become strongly coupled.