PLX Inc. has developed an interferometer for FTIR spectroscopy. The single monolithic structure contains two mirrors and a beamsplitter fused with top and bottom glass plates of the same material. The uniform coefficient of thermal expansion of the device affords greater stability under high temperature and vibration. Used with a single PLX hollow retroreflector, the assembly separates and recombines beams for a double-pass configuration that accommodates any wavelength. The interferometer is available for OEM applications in quartz or BK 7 for visible or near-infrared applications, or with a KBr beamsplitter for far-infrared.