Quantum Cascade Lasers in Infra-red Absorption Spectroscopy

The primary emphasis of this research paper centers on advancing spectroscopic methods utilizing midinfrared Quantum Cascade Lasers (QCLs). The aim is to apply these techniques in accurately measuring trace gases for environmental science, breath analysis, and determining absolute spectroscopic parameters. In the field of gas-phase analysis, the use of infrared molecular absorption spectroscopy is critical. This technology excels at detecting and tracking minute molecular entities with pinpoint accuracy and selectivity. The study of how electromagnetic (EM) radiation interacts with molecules or atoms, including processes like as absorption, emission, and scattering, is referred to as molecular absorption spectroscopy. Atomic spectroscopy is primarily concerned with quantum transitions manifested as changes in electron configuration. Molecular spectroscopy, on the other hand, studies transitions that occur within a molecule as a result of internal motions such as nuclei vibrations, rotations, and nuclear spin alignment. Because of their intricacy, molecular spectra are more intricate than their atomic counterparts. Furthermore, molecular spectroscopy provides useful information about the molecular framework, such as bond strength, length, the relative arrangement of its constituent atoms, transition dipole moment, and energy levels. These discoveries are made possible by the use of quantum mechanical models that describe the discrete distribution of energy levels within a molecule. This work aims to improve understanding of infrared spectroscopy (IR) by providing a foundational introduction to the principles of molecular spectroscopy. Furthermore, it provides a thorough explanation of commonly used spectroscopic detection techniques for tracking minute air components and trace chemicals in exhaled human breath.