Non-contact reflection-mode optical absorption spectroscopy using photoacoustic remote sensing.

A method of remote optical absorption spectroscopy is described that utilizes the photoacoustic remote sensing detection technique. A nanosecond tunable excitation source is used to excite thermo-elastic pressure-induced elasto-optic modulations within targets across a wide wavelength range from 210 to 680 nm, providing optical absorption contrast. These modulations are read remotely as back-reflected intensity variations within a continuous-wave 1310 nm detection beam. The absorption spectra of several samples including dyes and biological macromolecules are captured with an 8 mm working distance in reflection-mode without the use of containment chambers or acoustic detection. This represents an initial investigation into the characteristics of this technique, which may facilitate optical absorption measurement within previously inaccessible sample types due to their size or opacity.