An interferometer system for measuring the wavelength of laser light or and other optical radiation comprises an interferometer with a radiation input for a reference beam of a given wavelength, a sample radiation input for a sample beam of unknown wavelength, and a beam splitter for splitting up an incoming beam into two part-beams, and a system for changing the optical lengths of two part-beam optical paths as used by the reference beam and, parallel to it, the beam whose wavelength is to be measured. There is furthermore a detector for converting output beams from the interferometer into representative electrical signals and a signal processing circuit coupled to the detector means. Furthermore in the part-beam paths there is an optical part in the form of a parallelepipedic transparent body able to be rotated for the changing of the lengths of the paths of the beams in relation to each other, and a reflector system for reflecting back the part-beams, coming from the turning part, back into themselves.
An interferometer/spectroradiometer that uses a beamsplitter means for dividing an input beam into two separate beams and presents the resultant beams to a rotary refractive window from symmetrically oriented optical elements such that the optical path differences through the refractive window as it rotates are additive and non-linearities are subtracted. The beams are returned through the refractive window to the beamsplitter for dividing the input beam, where fringes are generated for application to appropriate detectors. The detector output is applied to Fourier transform computer equipment for digitizing and processing for presentation on a spectrum display device.
A twin-arm interferometer spectrometer having a tiltable reflector assembly, which includes a pair of mutually facing parallel reflective elements, varies the path length of both interferometer arms simultaneously to achieve high resolution in a small, low maintenance design. Collimated electromagnetic radiation is split by a beamsplitter into first and second arm beams. Both arm beams impinge on the tiltable reflector assembly, to retroreflectors, and back to the beamsplitter wherein they recombine to form an exit beam. The exit beam is directed to a sample and then to a suitable detector. Modulation of the exit beam is produced by tilting the reflector assembly about an axis parallel to the reflective elements in the reflector assembly. This tilting causes a simultaneous variation in the path length of both interferometer arms, and thereby yields a large total path difference with a relatively small movement. Symmetry between the paths of the reference beam and test beam results in greater stability and greater immunity to thermal expansion.
In the claimed invention for an improved AC type interferometric metrology apparatus, a change in position of an item disposed in a rotating reference frame is measured. The rotating reference frame accumulates a rotation angle over a time period with respect to a fixed reference frame. A quarter wave plate and an interferometer comprising a polarizing beam splitter, a reference path reflector, and a measurement path reflector are all mounted in the rotating reference frame. The measurement path reflector is mounted to item so that changes in its radial position along an axis orthogonal to the axis of rotation of the rotating reference system are measurable. In one preferred embodiment, the components in the fixed reference frame are a two-frequency laser light source, a stationary quarter wave plate, a receiver, for producing a measure signal containing information representing the change in optical path length between the measurement and reference paths of the rotating interferometer, the difference in the two frequencies of the beams from the laser source, and the rotation angle, and a signal processor. The signal processor receives the measure signal, a reference signal representing the difference frequency of the laser light source, and a signal from a rotary encoder containing information proportional to the rotation angle. The signal processor produces a signal representing the measurement of the change in position. In another embodiment, the rotary encoder is replaced by added optical components which automatically produce optical signals that contain information about the rotation angle and the difference in the two frequencies of the beams from the laser source.
The structure of the invention serves to support mirrors defining a reflective channel, which can dynamically be reciprocally widened and narrowed, as in a two-beam interferometer. It is effectively divided, by pivot points on an intermedial axis, into two opposite portions of equal mass, thus affording to the structure immunization against translational forces transmitted through those points. The opposite portions also have their centers of gravity remotely located, so as to generate a counteracting torque in response to moments of rotational inertia transmitted through the pivot points. In the structure, integrally formed planar pieces are assembled to provide contiguous elongate elements and an interposed connecting web element, a plurality of which web elements produce a flexure joint.
A reference mirror (50) in an interferometer is fixed in position with respect to a laser (34). A refractive block (40) having parallel upper and lower surfaces is mounted for pivoting about a pivot axis (60) parallel to the reference mirror (40). The refractive block (40) is disposed in the path of the light beam (36) produced by the laser (34), and it includes a partially reflective surface (42) on its lower face that divides the incident beam (36) into two components (44 and 46), which travel along different paths, in which they are reflected from different portions (48 and 54) of the surface of the reference mirror (50) and from different portions (52 and 56) of a reflective surface on the upper face of the refractive block (40). A second partially reflective coating (58) rejoins portions of the two components to form an exit beam (32) in which the radiation from the two beams interferes in accordance with the angle of the refractive block (40). The angle that the exit beam (32) makes with the surface of the reference mirror (50) is independent of the angle of the refractive block (40).
