Remote chemical sensing and recognition by acoustic mapping of photothermal fields

A remote chemical sensing and recognition approach is developed based on the acoustic mapping of photothermal fields, which has been verified in transmission and reflection modes using a system with ultrasonic transducers, a light source, and light filters. Light absorption increases sample temperature, which changes the phase angle of reflected or transmitted ultrasonic waves. The chemical natures of samples are determined from the wavelength dependent phase change spectrum. The method does not require resonance chambers to amplify photogenerated signals. The light source and ultrasonic transducers can be arranged to enable compact device construction and remote field operation in stand-off manner.