Si: As Focal-Plane Array Detection for Fourier Transform Spectroscopic Imaging in the Infrared Fingerprint Region

Abstract

An instrument is described that simultaneously records images and spectra of materials in the infrared fingerprint region using a long-wavelength infrared focal-plane array detector, a step-scan Michelson interferometer, and an infrared microscope. With the combination of step-scan Fourier transform (FT) Michelson interferometry and arsenic-doped silicon (Si: As) focal-plane array image detection, an infrared spectroscopic imaging system has been constructed that maintains both an instrumental multiplex and multichannel advantage and operates from approximately 4000 to 400 cm−1. With this method of mid-infrared spectroscopic imaging, the fidelity of the generated spectral images recorded through the microscope is solely determined by the number of pixels on the focal-plane array detector, and only a few seconds of data acquisition time are required for spectral image acquisition. This seamless combination of spectroscopy for molecular analysis and the power of visualization represents the future of infrared microscopy. Step-scan imaging principles, the operation and characteristics of long-wavelength array detectors, and instrument design details are outlined, and infrared chemical imaging results are presented. The results are discussed with respect to their implications for the chemical analysis of a variety of solid-state materials.