Fast Detection of Multispecies Liquid Evaporation by Mid-IR Broadband Supercontinuum Source and Upconversion Spectrometer

Evaporation, the phase transition of a liquid into its gaseous state, is a fundamental process that plays a pivotal role in several scientific and engineering applications in environmental science, chemistry, medicine, and agriculture. The evaporation rate of liquids varies depending on several internal or external factors: vapour pressure, external temperature, humidity, concentration, and exposure surface area. Real-time monitoring techniques could provide a better understanding and control over the evaporation procedure. Broadband absorption spectroscopy is a good candidate for studying liquid evaporation due to its non-invasive, highly sensitive and real-time detection capabilities. In absorption spectroscopy, the mid-infrared (mid-IR) range is frequently used as it contains the molecular absorption fingerprint region. While FTIR spectrometers are commonly used for mid-IR absorption spectroscopy, their time resolution is limited due to the mechanical movement of the scanning mirror(s). Grating-based spectrometers can provide much shorter detection times (although at the expense of spectral range/resolution). Meanwhile, optical components are much more mature in the near-infrared (near-IR) wavelength range. Therefore, nonlinear upconversion of mid-IR light into near-IR and using a near-IR grating-based spectrometer can provide high detection sensitivity and temporal resolution [1].