PbWO$_4$ Acoustic Properties Measurement by Laser Ultrasonics with the Aim of Optical Damage Recovery

The paper, at first, discusses theoretical aspects of acoustic wave propagation in lead tungstate (PWO). After that, it introduces the application of laser ultrasonics to PWO crystals with the aim of measuring the acoustic properties and the absorbed energy. A specific set-up has been developed to deposit energy in the crystals by means of shock waves generated by a pulsed Nd-YAG laser. We measured the acoustic properties of the PWO crystals along the crystallographic c axis and measured the acoustic energy absorption. Calculations confirmed that the majority of the energy has been absorbed in the samples. Since in scintillating crystals the radiation damage leads to a decrease in the optical transmission, the paper formulates the hypothesis that the laser energy absorbed can sustain recovery of the optical transmittance properties. Preliminary tests of light transmittance measurements showed a systematic improvement of optical transmittance after laser treatment in a series of PWO samples. These results are consistent and in agreement with the hypothesis, and they support the feasibility of a laser-based method to recover radiation-damaged crystals.