Remote subsurface water temperature measuring apparatus with Brillouin scattering

DETAILED DESCRIPTION A general object of the invention is the provision of apparatus for measuring the subsurface temperature of a transparent substance remotely and substantially instantly.
A further object is the provision of such apparatus that is relatively compact and highly portable.
Another object is the provision of a measurement technique that has a high signal-to-noise ratio and therefore produces highly accurate measurements.
A further object is the provision of such apparatus in which the irradiance of the received return signal from the target substance is relatively high.
These and other objects of the invention are achieved with apparatus consisting of a pulsed laser having a highly intense output beam capable of producing stimulated Brillouin scattering (SBS) in the medium under test.
A beam splitter splits this pulsed beam into two sub-beams and directs one sub-beam designated the probe beam, into the transparent medium of unknown temperature to produce a phase-conjugate beam from the medium.
The return phase-conjugate sub-beam and the other sub-beam are optically mixed in a photodetector to derive a difference frequency proportional to the unknown temperature of the medium.
And, a frequency converter translates the difference frequency to a value corresponding to the unknown temperature.