This can benefit from another molecular-absorption technique, optoacoustic (OA) spectroscopy[16] and [17]. It is based on the conversion of the absorbed electromagnetic radiation into local nonstationary heating of the sample, which generates pressure pulses, OA signals. When nanosecond laser pulses are used, thermal diffusion from the heated zone can be neglected (so called thermal confinement condition [18]) for most of dielectric media. OA spectroscopy is the unique method for direct measurements of the laser fluence distribution providing the determination the optical properties and optical inhomogeneity of a medium