Compact Mid‐Infrared Spectrometer Using Continuously Variable Infrared Filter and Microbolometer Array for Simple and Fast Measurement of Molecular Mid‐IR Spectra

The mid-infrared (mid-IR) region is attractive for spectroscopy because this range has molecular fingerprint information. Existing FTIR-based systems are limited by their complex optical systems, highlighting the ongoing necessity to advance miniaturization and simplify these systems. Here, a compact mid-IR spectroscopy is introduced in the mid-IR range, utilizing a continuously variable mid-IR filter. This filter is made from Germanium (Ge) and BaF2 and is produced using physical vapor deposition. Continuously varying wavelengths of mid-IR light are transmitted from different areas of the filter. These different wavelengths of light enter each pixel of the microbolometer array. Calibration is conducted using a sample material to match each pixel of the microbolometer array to its corresponding wavelength. Additionally, a deconvolution algorithm is applied to sharpen the acquired spectrum. This results in acquisition of high signal-to-noise ratio mid-IR spectra in the LWIR region. Using this technology, mid-IR spectroscopy for several types of samples like polymer film, and gas molecules is possible. In addition, by adopting total internal reflection, it is possible to measure non-uniform thickness samples, such as liquid droplets.