Crystallographic analyser for geological investigations - has laser optical system lowered into borehole to test reflection characteristics of rock under investigation

摘要

The crystallographic analyser for geological investigations comprises a capsule (11) which is lowered into a bore-hole, the capsule containing a tunable infra-red laser (16). The wavelength of the laser emission is selected to match the reflection characteristics of the rock under investigation. The laser beam is split (18) and reflected onto the wall of the bore-hole through a window (13). The reflected ray is split, part being focused onto an optical detector (41). A direct reference beam (21) is reflected back by a series of mirrors (22, 23) through a lens (20) to the detector. Both measuring beam and reference beam are chopped by a motor-driven disc (24) so that both are modulated. The separate electrical signals from the detector lock-in amplifier are fed to a ratio meter so that the absolute value of the amplitude of the laser beam can be eliminated. The intensity of the beam, which varies with the frequency then has no effect on the result.