Terahertz Spectroscopy of Dilute Gases Using Bi2Sr2CaCu2 O8+δ Intrinsic Josephson-Junction Stacks

Abstract

We report on spectrometric gas detection using terahertz waves radiated from Bi2Sr2CaCu2O8+δ (BSCCO) intrinsic Josephson-junction stacks. The emission frequency is varied by changing the bias current through and thus the voltage across the emitter. For the terahertz detection, both bolometric and heterodyne detection methods are employed. Clear absorption dips of water and ammonia vapor on the terahertz spectrum are obtained with both detection methods. With the bolometric scheme, we achieve a frequency resolution of about 1 GHz, which is on the order of the frequency resolution of systems employing terahertz time-domain spectroscopy. With the more stable heterodyne detection scheme, the minimum detectable gas pressure is around 0.001 mbar for H2O and about 0.07 mbar for NH3. The smallest observable absorption linewidths are in the range of 4 to 5 MHz. Our results suggest that the frequency-tunable BSCCO emitters can be convenient sources for potential terahertz applications in spectroscopy for frequencies between roughly 0.4 and 2 THz. © 2017 American Physical Society.