Dependences of the parameters of an optoacoustic signal on the radius of the excited region

Experimental and theoretical investigations were made of the dependence of the amplitude of an optoacoustic signal on the radius of a region excited by a focused beam. A linearized equation for the pressure was solved to show that the acoustic signal profile was governed primarily by the beam radius and that for r₀ < cτ (r₀ is the beam radius, τ is the heat evolution time, and c is the velocity of sound) the amplitude rises as r₀^3/2, whereas for r₀ > cτ it is proportional to r₀^1/2. A series of experiments was carried out on the absorption in ozone and these experiments confirmed the r₀^3/2 dependence for r₀ < cτ.