US Patent 10955335 Non-contact photoacoustic spectrophotometry insensitive to light scattering

A non-contact photoacoustic spectrophotometry system is configured to measure an absorption spectrum of a material. The system includes a modulated light source such as tunable pulsed laser that generates laser pulses to produce photoacoustic signals in the material. A non-contact detector monitors the surface of the container for the material. The detector includes a second light source, such as a continuous wave laser, focused on the surface of the container, and transmits reflected light to an interferometer, for example, a Sagnac interferometer. The interferometer produces an interference signal from the received light that is proportional to the acoustic pressure, which is transmitted to a computer to calculate an absorption coefficient. Using a plurality of wavelengths from the tunable pulsed laser, an absorption spectrum may be generated.