Unveiling the properties of liquids via photothermal-induced diffraction patterns

Laser-liquid interactions trigger various thermal and optical responses the characteristics of which are unique to a given liquid. Here, the authors employ femtosecond laser pulses to investigate the formation of diffraction patterns in hydrogen-bonded liquids that can be used to identify the target liquid. The interaction of a laser with a liquid can cause temperature changes in the liquid from which some properties of the latter can be indirectly obtained. However, from just temperature changes, a sample cannot be identified. Here, we report on the interaction of tightly focused femtosecond infrared light into secondary hydrogen-bonded liquids like water, organic compounds, and binary mixtures. Such interaction induces a local change in the sample's index of refraction. The latter alters the wavefront of a white-light probe beam, giving rise to unique diffraction patterns that can be observed in the far field. The specific diffraction patterns may be considered as the optical signatures or fingerprints of the liquids studied. The technique proposed here is noninvasive and simple to implement with commercially available supercontinuum sources and digital cameras. Thus, it may be useful for the development of compact thermal lens spectroscopic instruments for a number of practical applications.

Automated summary

The authors use femtosecond laser pulses to study the formation of diffraction patterns in hydrogen-bonded liquids, which can be used to identify the target liquid. The interaction between laser and liquid can cause temperature changes and alter the index of refraction, resulting in unique diffraction patterns. This noninvasive and simple technique may be useful for practical applications in developing compact thermal lens spectroscopic instruments.