A sensitive, spatially uniform photodetector for broadband infrared spectrophotometry.

We describe the design and performance of a liquid helium-cooled As:Si blocked-impurity-band photodetector system intended for spectrophotometry in the thermal infrared (2 to 30 mum) spectral region. The system has been characterized for spectral sensitivity, noise, thermal stability, and spatial uniformity, and optimized for use with a Fourier-transform infrared spectrophotometer source for absolute goniometric reflectance measurements. Its performance is evaluated and compared to more common detector systems used in this spectral region, including room-temperature pyroelectric and liquid-N(2)-cooled photoconductive devices.

Resolving an anomaly between measured spectral linewidths of n=3 transitions in N II and O III spectra.

A reported anomaly in the experimental scaling of the widths of Stark broadened n=3, Delta n=0 spectral lines along the carbon isoelectronic sequence is not observed in the present experiments. The ratio omega(N)/omega(O) of widths for N II lines compared to those for the narrower O III lines for the same transitions is now measured as lying between two theoretical predictions, both of which show a value omega(z-1)/omega(z) greater than unity continuing throughout the sequence. In the earlier measurements, the widths (in frequency units) were actually measured as being smaller for N II than for O III, i.