Instrumentation and Applications of Cascade Laser Spectroscopy

Abstract

Owing to recent technological advances in mid‐infrared (MIR) laser sources, cascade laser spectroscopy (CLS) has evolved to a promising modern technique for high selective and sensitive quantification of trace gases in many sensing scenarios. High output power, narrow linewidths, single‐mode operation, low power consumption besides compactness are just some of the outstanding features of cascade lasers. Since their discovery, quantum cascade lasers (QCL) and interband cascade lasers (ICL) have made rapid progress and has established themselves as the most important MIR laser sources. In this article, we provide a brief overview of state‐of‐the‐art spectroscopic techniques in cascade laser spectroscopy associated with their fundamental principles, including direct absorption spectroscopy (DAS), wavelength modulation spectroscopy (WMS), photoacoustic spectroscopy (PAS), and optical cavity enhanced spectroscopy (OCES). A number of selected spectroscopy applications of QCL‐ and ICL‐based optical systems for industrial process control, medical applications, and standoff detection for security are reviewed.