Acousto-optical ultrasonic flowmeter

DETAILED DESCRIPTION The flowmeter of the present invention includes an optical window in a wall of a fluid conveyance such as a pipe.
A pulsed laser apparatus is positioned to project a laser beam into the fluid, through the optical window to cause a rapid thermal expansion of the fluid in the path of the beam.
The rapid thermal expansion generates a corresponding pressure wave such that the beam path in effect acts as a line source of the pressure wave which is transmitted axially downstream and upstream of the source.
A first detecting means displaced from the beam is operable to detect the pressure wave as it passes to provide a corresponding output signal, and similarly a second detecting means is so positioned to provide a corresponding output signal.
A signal processing means is responsive to both output signals to provide flow related data.
In a preferred embodiment the first and second detecting means are low power continuously operating lasers with beams which are projected through respective optical windows in the pipe wall toward respective optical detectors, the output signal of which is modulated due to the modulation of the low power laser beam caused by pressure variations of the acoustic signal wavefront.