Photo-acoustic sensor for diagnostic laser absorption spectrometer

摘要

A photo-acoustic sensor for a diagnostic laser absorption spectrometer has a sound activated ceramic piezo element (16,17,18) and the system is energised by a variable intensity, frequency modulated laser source (not shown) supplying the fibre optic (7). An optical unit (9,10,11) enables the laser beam (2) to be focused (13) at a variable depth below the central exit aperture of the instrument to produce acoustic excitation at a controlled depth and frequency within the tissue under examination. An aluminium cylinder (20) which forms a masking stop (24) to minimise the entry of stray light also provides Faraday cage screening against electrical interference external to the region (20').