Demonstration of long-wave infrared Virtually Imaged Phased Array (VIPA)

Earth-like planets emit thermal radiation predominantly in the mid- to far-infrared, spanning roughly 4 μm to 100 μm, with a peak near 11 μm. Despite the scientific importance of this spectral region for habitable world surveys, there are currently very few spectrometers capable of operating in this regime. To address this gap, we present the design, fabrication, and experimental characterization of an air-gapped, silicon-based virtually imaged phased array (VIPA) optimized for mid-IR spectroscopy. The device consists of a 1″ wide, 3″ tall high-purity silicon plate pair with two coating configurations, gold (Au) and titanium nitride (TiN). Using quantum cascade lasers at wavelengths of 14 μm and 17 μm, paired with a THz microbolometer detector array, we characterize the VIPA’s dispersion and evaluate its resolving power. We also develop computational models to simulate the VIPA’s dispersion and expected resolving power, enabling direct comparison with the measured performance.