Use of colloidal monolayers of glass spheres for the improvement of the optoacoustic ultrasound generation

New type of optoacoustic transducer containing monolayer of dielectric spheres is presented. Experiments of the ultrasound generation by the single nanosecond laser pulses (2nd harmonic of Nd:YAG) in a liquid absorbing ink were carried out. It was found that the irradiation of the liquid through a mask containing the monolayer of glass spheres result in the greater ultrasound intensity and the broader spectrum compared to the same setup without the mask. The effect is explained by the focusing of the laser light by the spheres. The laser intensity is being concentrated into the multitude of the 'hot spots' where the high-frequency ultrasound is generated.