  While mid-infrared radiation can be used to identify and quantify numerous
chemical species, contemporary broadband mid-IR spectroscopic systems are often
hindered by large footprints, moving parts and high power consumption. In this
work, we demonstrate multiheterodyne spectroscopy using interband cascade
lasers, which combines broadband spectral coverage with high spectral
resolution and energy-efficient operation. The lasers generate up to 30 mW of
continuous wave optical power while consuming less than 0.5 W of electrical
power. A computational phase and timing correction algorithm is used to obtain
kHz linewidths of the multiheterodyne beat notes and up to 30 dB improvement in
signal-to-noise ratio. The versatility of the multiheterodyne technique is
demonstrated by performing both rapidly swept absorption and dispersion
spectroscopic assessments of low-pressure ethylene (C$_2$H$_4$) acquired by
extracting a single beat note from the multiheterodyne signal, as well as
broadband multiheterodyne spectroscopy of methane (CH$_4$) acquired with all
available beat notes with microsecond temporal resolution and an instantaneous
optical bandwidth of 240 GHz. The technology shows excellent potential for
portable and high-resolution solid state spectroscopic chemical sensors
operating in the mid-infrared.
