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This letter reports the fabrication and demonstration of an ErAs:GaAs interdigitated photomixer as a tunable THz source ranging from ∼20 GHz to ∼2 THz, with 12 μW maximum power typically around ∼90 GHz. Each photomixer is coupled to a composite dipole-spiral planar antenna that emits a Gaussian-type beam into free space. The beam switches from dipole to spiral antenna behavior as the frequency increases. A distributed Bragg reflector is embedded in the device beneath the photomixer to increase its external quantum efficiency. The photomixer has a 900 Å thick silicon nitride coating which serves as an antireflection and passivation layer, and also improves the reliability and heat tolerance of the device. [ABSTRACT FROM AUTHOR]

This letter reports the use of a photomixing sweep oscillator to characterize samples of B. subtillis spores at room temperature between 200 and 1200 GHz. Dilute (10% by mass) and concentrated samples were tested, the former using fine-grained polyethylene powder as a low-loss dielectric matrix. The dilute sample displays many weak transmission undulations, but the three centered at 418, 1037 and 253 GHz were strong enough to remain after normalization. The concentrated sample displays a much stronger broadband attenuation, precluding accurate measurements above ∼500 GHz. Two broad signatures remain between 250 and 290 GHz, and between 410 and 440 GHz, respectively. The results suggest that single-bioparticle electromagnetic resonance, perhaps from surface phonons, occurs in the dilute sample but is smeared in the concentrated sample. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]