Abstract: The present invention relates to apparatus for providing orthogonally polarized light beams for use in precision metrology applications such as in the measurement of length or length changes using interferometric techniques. An input beam is introduced to a multifaceted anisotropic optically active acousto-optical crystal for travel through an interactive region where it experiences two acoustic beams that diffract it via small angle Bragg diffraction to form two orthogonally polarized internal beam components that are separated by a small angle of divergence and subsequently become external beam components available outside of the acousto-optical crystal for use in anticipated downstream applications. The acousto-optical crystal preferably is a uniaxial crystal comprising TeO.sub.2.

Abstract: Interferometric apparatus and method for measuring and monitoring intrinsic optical properties of a gas, especially the reciprocal dispersive power of the gas, so that information about the gas properties can be used in downstream applications, such as interferometric distance measuring instruments, to increase accuracy by correcting for refractive index of the gas and especially environmental and air turbulence effects in the measurement path. The apparatus comprises a concentric measurement cell having an inner chamber containing a vacuum surrounded by an outer occupied by the gas. Wavelength selective mirrors are arranged at each end of the measurement cell and operate in conjunction with plane mirror interferometers to change the phase of orthogonally polarized components of light beams of different wavelength introduced in the measurement cell from opposite ends of the cell.

Abstract: Electro-optical devices comprising a multifaceted anisotropic acousto-optical crystal for transforming a single-frequency beam comprising two individual linearly-orthogonally, polarized input beams into an output beam having two linearly-orthogonally, polarized principal output beams having frequencies that differ from each other and the input beam where the input beam preferably is a laser of frequency, f.sub.L. While the directions of propagation of the individual input beams are preferably parallel, and the directions of propagation of the principal output beams are preferably parallel, they need not be and instead the individual input beams and the principal output beams may beneficially have their own predetermined angle of divergence or convergence, respectively.

Abstract: Electro-optical devices for transforming a single-frequency, linearly polarized input beam from a light source introduced into a multifaceted anisotropic acousto-optical crystal into an output beam having two orthogonally polarized, output beam components that differ in frequency from each other and may be parallel or have a predetermined angle of divergence between them. The energy flux profiles of the output beam components may be spatially separated, partially coextensive, or substantially coextensive in accordance with the birefringence, acoustical, and optical properties of the acousto-optical crystal and/or the use of external elements for particular device embodiments.

Abstract: An electro-optical apparatus transforms a single frequency, linearly polarized laser input beam (18) from a light source (10) into an output beam (36) having two collinear orthogonally polarized output beam components (32,33) differing in frequency from each other by the frequency of a stabilized electrical signal (40) provided from an electronic oscillator (38). The output of the oscillator (38) is provided to a power amplifier (42) which is used to drive a piezoelectric transducer (46) affixed to an acousto-optical Bragg cell (52) through which the input beam (18) passes and is transformed into the output beam (36) composed of two beam components (32,33). The electrical output (44) of the power amplifier (42) is adjusted so that each of the output beam components (32,33) has approximately a preselected fraction of the intensity of the input beam (18).

Abstract: A method and apparatus for measuring fluctuations in the refractive index of a gas, such as air, in a measurement path (66) may be used to measure displacement of an object (67) independent of these fluctuations. A coherent source light (1,4) provides two source light beams (11,12) having source wavelengths (.lambda..sub.1, .lambda..sub.2) along the measurement path (66) which are substantially harmonically related to each other. Beams (11, 12) make multiple passes over measurement path (66) where the number of passes for the respective light beams are harmonically related, the relationship of harmonics being substantially the same as said substantially harmonic relationship between the wavelengths to provide heterodyne phase shifts based on the provided source wavelengths and the number of passes over the measurement path (66) for providing a superheterodyne modulation phase substantially insensitive to motion along the measurement path (66).