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The interaction between waves in an idealized saturable absorber is discussed. It is shown that the presence of a strong wave will cause the line to appear to be ``hole-burned'' when probed by a second wave, even though the broadening mechanisms are conventionally homogeneous. This effect would be expected to work against the tendency of dye-switched ruby lasers to operate in a single mode. Related effects should play a role in optical pulse generators and in other devices using saturable absorbers.

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We describe a novel room-temperature detector for the wavelength range 10–1000 μm. This detector consists of a thin bismuth bolometer film with dimensions much smaller than a wavelength. The small size of the detector results in reduced NEP and faster response. A video NEP of 1.6×10−10 W/Hz1/2 is obtained at 119 μm, remaining within a factor of 10 of this value for modulation frequencies up to 25 MHz. When used as a mixer, the device is predicted to have an NEP of 3.5×10−18 W/Hz. It is easily fabricated with conventional planar processing techniques and can be replicated in arrays. The device is expected to be most useful when the radiation to be detected is spatially coherent.

A theoretical study has been made of the use of antennas to couple radiation to infrared detectors. It is shown in general that for any detector characterized by a specific detectivity D, noise-equivalent power (NEP) can be reduced until the background blackbody fluctuation limit is reached. The reduction in NEP is expected to be on the order of b/λ, where b2 is the area of the detector. In the case of far-infrared bolometers away from the blackbody limit, significant reductions of NEP appear to be possible. Alternatively the antenna may be used to increase the temperature at which the bolometer can be operated or to reduce its response time. The possible use of antennas with various other infrared detectors is also considered, and some criteria for suitability are described.