OPTICAL CREATION OF RADIOPHOTOLUMINESCENCE CENTERS IN DOSIMETER GLASSBY 2-PHOTON ABSORPTION

In recent years considerable progress has been achieved in the field o f phosphate glass dosimetry through the evolution of improved glass ma terial with good batch uniformity, newly designed dosemeter encapsulat ion and automatic readout techniques based on pulsed UV laser excitati on. The peak intensity of the laser pulses exceeds the range of intens ity available with conventional UV light sources. This paper reports o n effects that may occur when an intense light source is used for RPL readout. In a specially designed reader unirradiated flat RPL glasses and a scanning focused laser beam for RPL readout were used. The influ ence of intense UV laser excitation on RPL readout intensity has been studied for dependence on the intensity and duration of excitation. Th e experimental arrangement, the scanning procedure for laser excitatio n, the dosemeter glass handling and the method of RPL readout are desc ribed. The observed RPL intensity is attributed to the optical creatio n of RPL centres by two-photon absorption in the focal region of the l aser beam. By means of beam profile and power measurements an estimati on of the lower limit of excitation intensity is given where two-photo n absorption becomes important.