Because of their small size, the possibility to operate at room temperature and high spectral power density, MIR QCLs can find widespread applications in stable process analyzers. For instance, these lasers are able to be used for liquid phase measurements as measuring total petroleum hydrocarbons in water or the determination of glucose and lactate in aqueous solutions [34].
Another important application of QCLs is sensitive nanosecond time-resolved spectroscopy to probe chemical reactions [35]. External Cavity QCLs are a functional infrared source for time-resolved infrared instrumentation and can be used to obtain high sensitive nanosecond spectra in order to detect short lived reaction intermediates and the clarification of reaction mechanisms.
Absorption spectroscopy systems are based on widely tunable QCLs. They are able to detect and measure substances on surfaces, which allows them to identify bulk materials and detect sub-micron films based on their absorption characteristics [36]. This enables to analyze vapors and liquids. Fast analysis, and the ability to work at a distance either through free space or a fiber are key factors for the ability of these systems to analyze trace amounts of explosives.
QCL based optical methods in chemical sensing have many advantages such as high selectivity and real-time detection. This allows the determination of the local concentration of a species with high accuracy and sensitivity. Industrial applications include combustion diagnostics in the power and automobile industries as well as medical diagnostics such as breath analysis for the early detection of ulcer and other diseases, and additionally process control. In the atmospheric science, spectral data are used to determine chemical concentration profiles, which are important for the development of climate models.