Abstract: Apparatus for nondestructive detection of subsurface defects in a continuously moving workpiece of sheet material by using an infrared thermal imager. The temperature of a portion of the surface of sheet material is altered and the presence of subsurface flaws is indicated by development of discontinuities in the surface temperature distribution above the defects. In order to avoid problems due to changes in the infrared emissivity of the surface of sheet material, such as caused by grease patches or oxidized areas as well as errors caused by reflections of other sources of infrared radiation from the surface, the thermal image of the portion is first transferred by contact to a surface of a thermal transfer device whose surface has a high infrared emissivity and a low infrared reflectivity. Then the thermal image of the portion is obtained from the surface of the thermal transfer device.

Abstract: A method of modulating the output of a solid state diode laser by directly straining the laser chip. The chip is mechanically coupled to a transducer such as a piezoelectric crystal in such a manner that a dimensional variation in the transducer is translated into a corresponding variation in the chip. It is contemplated that the modulated output will have application in communication systems and in particular a hydrophone system.

Abstract: The surface acoustic waves are generated by laser beam that is focussed onto a surface to irradiate it in an arcuate pattern as a partial annulus or as a still or moving fringe pattern. The arcuate pattern may be formed by a transmitting or a reflecting axicon, while the fringe pattern may be formed by splitting the laser beam into two beams and directing the two beams to the surface. In addition, a lens or a frequency shifting device may be placed in the path of one of the split beams to form a circular fringe or a moving fringe, respectively.

Abstract: An optical fiber hydrophone system in which a single optical fiber is used for all of the acoustical sensors in the system. A signal source and detector provides an optical signal in selected form, such as continuous or pulsed and detects and extracts an identifiable output signal. Each sensor is in the form of a sensing portion of the single optical fiber. Each sensing portion includes two optical reflectors separated one from another by a predetermined length of said optical fiber. Variations in acoustical pressure incident on the sensing portion causes a change in the predetermined length. This causes reflected portions of the optical signal to interfere with one another. Such interference is detectable for extraction of the identifiable output signal. In one form each sensing portion has two terminal branches of a mechanically deformable material, deformable in response to the fluctuations in acoustical pressure.

Abstract: The apparatus for analyzing the surface of a fibrous web, such as a paper or a textile, includes a prism structure in which one surface is placed in contact with the fibrous web under a predetermined pressure. A collimated beam of light is directed into the prism on the contact surface. The light reflected from the contact surface through the prism is directed to a detector. The detector senses the light reflected by the contact surface as well as the light diffracted at the contact surface to indicate the surface condition of the fibrous web.

Abstract: The laser-surface coupler is used to uniformly irradiate a well defined surface area with a laser beam. The coupler includes a lower masking section and an upper section to form a cavity. The masking section has inner surfaces which are highly reflective and lustrous, and an aperture to define the surface area to be irradiated. The upper section has an opening to receive the laser beam into the cavity, and a highly reflective and diffuse inner surface to reflect and diffuse any radiation reflected to it from the irradiated surface. The coupler recycles any reflected radiation from the laser beam increasing the absorption coefficient and the irradiated surface is precisely defined by the masking section without loss of energy.

Abstract: A tunable optical fiber reflector is described, together with a method of making the same. A length of optical fiber has a core of a first light transmitting material, and a cladding of a second light transmitting material covering the core. The cladding is etched away to a predetermined thickness over a portion of the fiber. A layer of photoresist material is applied either to the etched away portion of the fiber or to a thin metal blade, i.e., mask, and then exposed to beams of light which optically interfere and generate a standing wave pattern in said material. The photoresist material is then developed to fix said wave pattern therein. An optical discontinuity is formed in one of the core and cladding by that fixed wave pattern, said discontinuity representing a quasi-periodical fluctuation in the refractive index and causing evanescent waves in the cladding to be reflected. Such discontinuity forms a distributed-feedback reflector.