Scanning heterodyne acousto-optical interferometers

A scanning spot heterodyne optical interferometer comprising:

• means for providing a first coherent light beam and a second coherent light beam having a frequency different from said first coherent light beam;
• light combining means for combining said first and said second light beams into a collinear beam composed of two wavelengths;
• first means for splitting said collinear light beam into fixed beams unaffected by said first means and test beams varying in spatial position in a first direction in accordance with a signal input to said first means and producing a frequency shift in said test beams relative to the fixed beams;
• a first light deflector for deflecting said fixed and test beams in a second direction perpendicular to said first direction;
• a test medium onto which said test beams impinge as they vary in spatial position in said first and said second directions perpendicular to an optical axis of said interferometer, said test medium imparting a further frequency shift onto said test beams;
• second means for recombining said fixed beams and said test beams from said first means and providing said test beams with a further frequency shift relative to said fixed beams, wherein said fixed beams and said test beams are collinear and unmoving in at least said first direction;
• and
• means for detecting test medium phase information from said test beam.

A scanning heterodyne optical interferometer comprising:

• means for providing a coherent light beam;
• first means for splitting said coherent light beam into a fixed beam unaffected by said first means and a test beam varying in spatial position in accordance with a signal input to said first means and producing a frequency shift in said test beam relative to the fixed beam;
• a test medium onto which a first part of said test beam impinges as it varies in spatial position in a first direction perpendicular to an optical axis of said interferometer, said test medium imparting a further frequency shift onto said first part of said test beam but not a second part of said test beam;
• second means for recombining said fixed beam from said first means and said test beam and providing said test beam with a further frequency shift relative to said fixed beam, wherein said fixed beam and said test beam are collinear and unmoving in at least said first direction;
• and
• means for detecting test medium phase information from said first and second parts of said test beam.

A scanning heterodyne optical interferometer comprising:

• means for providing a coherent light beam;
• first means for splitting said coherent light beam into a fixed beam unaffected by said first means and a first scanning beam shifting in spatial position and frequency;
• second means for splitting said first fixed beam into a second fixed beam unaffected by either first or second means and a second scanning beam shifting in spatial position and frequency, and for splitting said first scanning beam into a third scanning beam shifting in spatial position and a third fixed beam unaffected by said second means, said second and third fixed beams being collinear and said second and third scanning beams being collinear;
• first and second polarizing beam splitters for splitting polarized light components of said collinear second and third fixed beams and said second and third scanning beams, components of each passing through a test medium and the other components of which acts as a reference;
• and
• detecting means for determining phase differences between respective components.