光音響分光法による測定可能深さに関する基礎検討

抄録

A measurable depth of the blood glucose level by using photoacoustic spectroscopy (PAS) was discussed experimentally in order to improve detection sensitivity. Since a measurable depth of the PAS based on a modulation frequency of the chopped light irradiated to a sample, the relationship between modulation frequency and the thickness of a sample was evaluated. In our experiments, the photoacoustic detector consisted of an acoustic resonant pipe and an optical microphone, and a two-layer model composed of silicone sheets with the different optical absorption were used. We varied the thickness of the upper-layer for the two-layer model from 0.50 to 5.00 mm at each modulation frequencies to investigate the relationship between the measurable depth and the modulation frequency. As results, it is shown that the measurable depth was 2-3 mm with modulation frequency of 1.6-1.9 kHz. Furthermore, the reason for the measurable depth to be deeper than the thermal diffusion length of a sample was discussed. From these analyses of thermoelastic wave, the relation between the photoacoustic signal propagation and the measurable depth in a tissue was clarified.