Krautkramer Branson, Inc.

Erik Primbsch

Walter Kaule

Wolf Bickel

An apparatus for sensing the acoustic energy responsive deformation of a workpiece surface by optical means, that is without physical contact with the workpiece surface, comprises the use of a laser light beam illuminating the workpiece surface portion along which the acoustic energy responsive deformation is manifest. The laser light incident upon the workpiece surface is reflected at the workpiece surface and, modulated responsive to the surface deflection, is transmitted to an optical phase interferometer and to a photoelectric means associated therewith. The output from the photoelectric means is transmitted to an evaluation unit. The improvement shown in this invention concerns means for maintaining the reflected light intensity at a predetermined level by comparing the reflected light intensity with a preset level and feeding a control signal to a light control means controlling the laser light intensity incident upon the workpiece surface.

Apparatus for sensing ultrasonic waves by optical means

An apparatus for maintaining the adjustment of coincidence and relative phase relationship of light beams in an optical interferometer comprises the passing of a measuring light beam and of a control beam through substantially the same paths of the interferometer. Any change in optical alignment of interferometer components from a set condition is manifest as a change of the electrical signal produced by photoelectric sensing means which receive the control beam. The change of the electrical signal is processed by an electrical circuit and fed to one or more positioning means supporting an optical component of the interferometer for causing a repositioning of such component to thereby restore the set condition. In a typical embodiment, the component is a reflective surface mounted on a set of piezoelectric positioning means.

Apparatus for maintaining adjustment of coincidence and relative phase

Laser light for producing acoustic waves in a specimen to be examined is carried to the specimen from a single laser by a plurality of fiber optic cables. The fiber optic cables have different path lengths to cause a specific time delay between adjacent fiber optic cables to focus and steer the sonic waves in a desired direction.

Apparatus for producing ultrasonic waves in a workpiece

The acoustic energy responsive deformation of a workpiece surface is sensed in a contact-free manner by optical means using a laser which illuminates the surface at which deformation is expected. The reflection light energy is transmitted to an optical interferometer as previously shown in the art. The present improvement comprises the use of a multi-wavelength laser beam light and separating the light after passing through the interferometer into the distinct wavelengths. Each light signal corresponding to a specific wavelength is converted individually to an electrical signal, each electrical signal is rectified, and the plurality of rectified signals are then averaged in an electrical summing means.

Method and apparatus for sensing ultrasonic energy

This invention relates to an interferometric laser method and apparatus for sensing the acoustic wave responsive deformation of a workpiece surface. A laser provides a coherent beam of light which after reflection at the workpiece surface is split into a first measuring beam portion and a second reference beam portion, the latter portion being delayed by being transmitted over a long delay path. The optical length of the delay path is dimensioned to be a multiple integer of the optical length of the resonator of the laser.

Method and apparatus for measuring deformation of a workpiece surface

Focussed acoustic waves are generated free of physical contact in a light absorbing workpiece by the use of laser beam means providing a coherent light beam which in a pulsed manner impinges upon the surface of the workpiece in a Fresnel zone pattern. The zoned pattern is caused in a typical example by a suitable mask interposed between the laser source and workpiece surface. The thermal effect responsive to the laser beam energy produces in the workpiece a plurality of acoustic waves having a common focal point.

Method and apparatus for producing acoustic waves by laser pulses

A method and apparatus for producing on the surface of a workpiece free of contact with a source of energy a pulse shaped ultrasonic shock wave comprise the use of laser means. A plurality of strip-shaped equidistantly spaced surface portions of the workpiece are pulsed with coherent light from the laser means in time delayed sequence. The angle of propagation of the ultrasonic wave is determined by the center-to-center distance between the strip-shaped surface portions illuminated with coherent light, the time delay between the light pulses and the velocity of propagation of the ultrasonic wave in the workpiece.

Method and apparatus for producing pulse-shaped acoustic waves on a

In order to stabilize the acoustic wave amplitude in a workpiece, where such acoustic wave is generated by a laser beam pulse transmitted upon the workpiece surface, laser pulses preceding the laser pulse used for acoustic evaluation are utilized to clean the workpiece surface from contamination. Cleaning of the workpiece surface to the bare metal provides a normalized surface condition in respect to absorbed pulsed laser beam energy and, hence, produces acoustic waves of substantially constant amplitude. Either the same laser producing the acoustic wave or a separate laser is used for vaporizing contamination at the workpiece surface where an acoustic wave is subsequently to be produced.

Method and apparatus for producing ultrasonic waves in light absorbing

A receiver probe for ultrasonic energy is described in which the surface deformation caused by compressive wave energy affects a thin gas-filled gap, its width being in the order of 10.sup.-7 meter. The gap is formed by opposing surfaces of an optical prism and an optical interference means. A beam of light is conducted to the boundary surface between the prism and gas. Changes in reflected and/or transmitted light beam portions resulting from compressive wave energy induced changes in gap width are sensed by opto-electric means.

Ultrasonic energy receiver probe utilizing opto-electrical sensing

A method and apparatus for producing on the surface of a workpiece an ultrasonic pulse wave without physical contact comprise the use of a laser beam illuminating a small, striplike, portion of the workpiece surface and such portion being moved with uniform motion along a linear axis over a predetermined distance. The angle of propagation of the resulting ultrasonic wave is a function of the propagation velocity of sound in the workpiece and the velocity of the illuminated portion along the linear axis.

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Cologne, Germany

Erik Primbsch