Apparatus for maintaining adjustment of coincidence and relative phase relationship of light beams in an interferometer

The method for automatically maintaining an adjustment of the coincidence and of the relative phase relationship of beams of light in the field of view of an interferometer in which beams of laser light are so delayed in time relative to one another over the different optical paths as to satisfy the interference condition required for producing an amplitude modulated signal from a beam which has been frequency modulated by ultrasonic deformations manifest on a workpiece surface comprising:

• illuminating the workpiece surface on which ultrasonic wave deformations are manifest with a beam of laser light and passing the light reflected at said workpiece surface as a measuring beam, frequency modulated by said deformations, to an optical interferometer;
• separating a portion of said laser light from said laser beam before it is incident on the workpiece surface and passing said non-incident portion as a control beam during control time intervals to said interferometer superposed on said measuring beam;
• causing said measuring beam and said control beam to traverse said interferometer through substantially the same optical paths in the same direction;
• sensing by means of first photoelectric means said measuring beam after it has traversed said interferometer and providing a corresponding amplitude modulated electrical signal;
• disposing in the field of view plane of the control beam second photoelectric means which responsive to the control beam illumination thereupon provide an electrical control signal adapted to indicate a change of the alignment of the optical paths of the interferometer from a set condition, and
• applying said control signal from said second photoelectric means to electromechanical positioning means supporting an optical component of the interferometer to cause a positioning adjustment of said optical component for restoring said set condition responsive to said control signal being indicative of such change.

The method for automatically maintaining an adjustment of the coincidence and of the relative phase relationship of beams of light in the field of view of an interferometer in which beams of laser light are so delayed in time relative to one another over the different optical paths as to satisfy the interference condition required for producing an amplitude modulated signal from a measuring beam which has been frequency modulated by ultrasonic deformations manifest on a workpiece surface comprising:

• illuminating the workpiece surface on which ultrasonic wave deformations are manifest with a beam of laser light and passing the light reflected at said workpiece surface as a measuring beam, frequency modulated by said deformations, to an optical interferometer;
• separating a portion of said laser light from said laser beam before it is incident on the workpiece surface and passing said non-incident portion as a control beam to said interferometer;
• causing said measuring beam and said control beam to traverse said interferometer through substantially the same optical paths but in opposite directions;
• sensing by means of first photoelectric means said measuring beam after it has traversed said interferometer and providing a corresponding amplitude modulated electrical signal;
• disposing in the field of view plane of the control beam second photoelectric means which responsive to the control beam illumination thereupon provide an electrical control signal adapted to indicate a change of the alignment of the optical paths of the interferometer from a set condition, and
• applying said control signal from said second photoelectric means to electromechanical positioning means supporting an optical component of the interferometer to cause a positioning adjustment of said optical component for restoring said set condition responsive to said control signal being indicative of such change.

The method for automatically maintaining an adjustment of the coincidence and of the relative phase relationship of beams of light in the field of view of an interferometer in which beams of laser light are so delayed in time relative to one another over the different optical paths as to satisfy the interference condition required for producing an amplitude modulated signal from a measuring beam which has been frequency modulated by ultrasonic deformations manifest on a workpiece surface comprising:

• illuminating the workpiece surface on which ultrasonic deformations are manifest with a beam of laser light;
• providing a focussing lens for receiving the light reflected at the workpiece surface and passing the reflected light as a measuring beam, frequency modulated by said deformations, to an optical interferometer which includes focussing optical elements for processing divergent light rays, said focussing lens causing an intermediate image of the illuminated workpiece surface on a reflective surface disposed in said interferometer;
• separating a portion of said laser beam before it is incident on the workpiece surface;
• focussing said non-incident beam portion to cause it to have a focal point disposed in or in proximity to the principal plane of the focussing lens focussing said light reflected at said workpiece surface and causing said non-incident beam portion to become superposed on said measuring beam as a control beam at or in proximity to the focal point of said control beam;
• causing said measuring beam and said control beam to traverse said interferometer through substantially the same optical paths;
• sensing by means of first photoelectric means said measuring beam after it has traversed said interferometer and providing a corresponding amplitude modulated electrical signal usable for measuring said deformations;
• disposing in front of said first photoelectric means an optical element for separating said control beam from said measuring beam;
• transmitting said separated control beam to second photoelectric means disposed in the field of view plane of the control beam and said second photoelectric means responsive to the illumination thereupon by said control beam providing an electrical control signal adapted to indicate a change of the alignment of the optical paths of the interferometer from a set condition, and
• applying said control signal from said second photoelectric means to electromechanical positioning means supporting an optical component of the interferometer to cause a positioning adjustment of said optical component for restoring said set condition responsive to said control signal being indicative of such change.

An apparatus for automatically maintaining an adjustment of the coincidence and of the relative phase relationship of beams of light in the first of view of an interferometer in which beams of laser light are so delayed in time relative to one another over different optical paths as to satisfy the interference condition required for producing an amplitude modulated signal from a measuring beam which has been frequency modulated by ultrasonic deformations manifest on a workpiece surface comprising:

• a laser disposed for illuminating with a beam of laser light the workpiece surface on which ultrasonic wave deformations are manifest;
• beam splitting means disposed in said beam of laser light for separating a portion of said laser light before it is incident upon said workpiece surface;
• an optical interferometer disposed for receiving the laser light reflected on said workpiece surface as a measuring beam;
• means disposed for receiving said separated laser light portion and superimposing it as a control beam on said measuring beam for causing said measuring beam and said control beam to traverse said interferometer along substantially the same paths;
• first photoelectric means disposed for receiving said measuring beam after it has traversed said interferometer for providing a corresponding amplitude modulated electrical signal usable for measuring said deformations;
• second photoelectric means disposed in the field of view plane of said control beam after said control beam has traversed said interferometer for providing an electrical control signal adapted to indicate a change of the alignment of the optical paths of the interferometer from a set condition;
• electromechanical positioning means supporting at least one optical component forming a part of the optical paths of said interferometer, and
• means for causing said control signal to be effective upon said positioning means for providing a positioning adjustment of said optical component responsive to said control signal being indicative of a change of the optical paths from a set condition.

An apparatus for automatically maintaining an adjustment of the coincidence and of the relative phase relationship of beams of light in the field of view of an interferometer in which beams of laser light are so delayed in time relative to one another over different optical paths as to satisfy the interference condition required for producing an amplitude modulated signal from a measuring beam which has been frequency modulated by ultrasonic deformations manifest on a workpiece surface comprising:

• a laser disposed for illuminating with a beam of laser light the workpiece surface on which ultrasonic wave deformations are manifest;
• beam splitting means disposed in said beam of laser light for separating a portion of said laser light before it is incident upon said workpiece surface;
• an optical interferometer disposed for receiving the laser light reflected on said workpiece surface as a measuring beam;
• means disposed for receiving said separated laser light portion and transmitting it as a control beam to said interferometer and causing said control beam to traverse said interferometer along substantially the same paths as said measuring beam but in opposite direction;
• first photoelectric means disposed for receiving said measuring beam after it has traversed said interferometer for providing a corresponding amplitude modulated electrical signal usable for measuring said deformations;
• second photoelectric means disposed in the field of view plane of said control beam after said control beam has traversed said interferometer for providing an electrical control signal adapted to indicate a change of the alignment of the optical paths of the interferometer from a set condition;
• electromechanical positioning means supporting at least one optical component forming a part of the optical paths of said interferometer, and
• means causing said control signal to be effective upon said positioning means for providing a positioning adjustment of said optical component responsive to said control signal being indicative of a change of the optical paths from a set condition.

An apparatus for automatically maintaining an adjustment of the coincidence and of the relative phase relationship of beams of light in the field of view of an interferometer in which beams of laser light are so delayed in time relative to one another over different optical paths as to satisfy the interference condition required for producing an amplitude modulated signal from a measuring beam which has been frequency modulated by ultrasonic deformations manifest on a workpiece surface comprising:

• a laser disposed for illuminating with a beam of laser light the workpiece surface on which ultrasonic wave deformations are manifest;
• beam splitting means disposed in said beam of laser light for separating a portion of said laser light before said light is incident upon said workpiece surface;
• a first converging lens disposed for receiving the laser light reflected at the workpiece surface and transmitting said reflected light as a measuring beam to an interferometer;
• optical means disposed for receiving said non-incident portion of laser light and bringing it to a focus at a focal point disposed in or in proximity to the principal plane of said first converging lens and transmitting said non-incident laser light portion as a control beam to said interferometer for causing said control beam to traverse said interferometer along substantially the same paths as said measuring beam;
• intermediate image forming means disposed in said interferometer for receiving and reflecting said measuring beam and said control beam;
• a second converging lens disposed in said interferometer for receiving said images from said intermediate image forming means;
• first photoelectric means disposed for receiving said measuring beam after traversing said interferometer and said second converging lens for providing a corresponding amplitude modulated electrical signal usable for measuring said deformations;
• said second converging lens causing said control beam to be focussed at a focal point disposed in front of said first photoelectric means;
• beam deflecting means disposed substantially at said focal point in front of said first photoelectric means for separating said control beam from said measuring beam;
• second photoelectric means disposed in the field of view plane of said control beam for receiving said control beam from said beam deflecting means and for providing an electrical control signal adapted to indicate a change of the alignment of the optical paths of the interferometer from a set condition;
• electromechanical positioning means supporting at least one optical component forming a part of the optical paths of said interferometer, and
• means causing said electrical control signal to be effective upon said positioning means for providing a positioning adjustment of said optical component responsive to said electrical control signal being indicative of a change of the optical paths of said interferometer from a set condition.