Abstract: A stable scanning or non-scanning Fabry-Perot interferometer and a method for stabilising the interferometer. The interferometer is composed of two plane mirrors arranged parallel to one another with a preselected optical distance between the optical surfaces of the mirrors. The interferometer radiates an output light signal in response to a light input signal applied parallel to the optical axis of the interferometer. The interferometer is stabilised by providing an arrangement for passing a plurality of reference light beams through the interferometer, the reference light beams being inclined at a preselected angle to the optical axis of the interferometer.

Abstract: A stable scanning or non-scanning Fabry-Perot interferometer and a method for stabilising the interferometer. The interferometer is composed of two plane mirrors arranged parallel to one another with a preselected optical distance between the optical surfaces of the mirrors. The interferometer radiates an output light signal in response to a light input signal applied parallel to the optical axis of the interferometer. The interferometer is stabilised by providing an arrangement for passing at least one reference light beam through the interferometer, the reference light beam being inclined at a preselected angle to the optical axis of the interferometer.

Abstract: Isolating a load from a source of vibrations includes detecting vibrations from that source, and controlling a displacement transducer stage with these detected vibrations through a feedforward loop. Isolation is increased with a resilient mount between the displacement transducer stage and the load. Residual movements of the load may be detected and the displacement transducer stage may additionally be controlled with these detected residual movements through a feedback loop.

Abstract: An object to be isolated from vibrations is supported by a structure having a curved surface which contacts the object. The support structure is in turn coupled to a resilient spring-like support frame which allows the structure to move in response to vibrations. Also contacting the support structure are three isolation elements which sense the vibration forces and produce forces to counter the vibrations.

Abstract: Machines and work surfaces may be isolated from vibration effects by coupling them to a vibration damping device. A bracket is connected to the object to be isolated. An accelerometer which supports a mass is coupled to the bracket and senses the acceleration of the mass. An electromechanical transducer is connected between the bracket and the floor on which the object rests. The transducer responds to the sensed acceleration of the mass to generate forces to counter the acceleration.

Abstract: A given type of authenticating device operates as a diffractive subtractive color filter that exhibits a reflectivity spectrum that includes a peak occurring at a wavelength that varies as a substantially linear function of the angle of incidence of polychromatic illuminating light having a particular polarization. The verification technique involves simultaneously illuminating a sample device over a range of angles of incidence by the polychromatic light, and then employing the reflected light from the sample to illuminate a reference device known to be genuine over the same range of angles of incidence. A sample device is indicated as being genuine only if both the respective intensity ratios of the light reflected from the reference device to the polychromatic light and to the light reflected from the sample device exceed respective threshold values.

Abstract: A thin film thickness monitor uses the successive reflection of polychromatic light from a reference or standard thin film having a varying optical thickness (n.sub.1 t.sub.1) and then from a thin film of unknown thickness (t.sub.f) or optical thickness (n.sub.f t.sub.f). The reflected intensity of light from the thin film is detected to provide a signal indicating when the optical thickness of the unknown film is equal to the optical thickness of the reference.

Abstract: A vernier tandem Fabry-Perot interferometer includes a first pair of plane mirrors forming a first interferometer and a second pair of plane mirrors forming a second interferometer which is receptive of the output signal of the first interferometer. One mirror of each pair is mounted on a common movable support in positions such that when the support is moved in a given direction the spacing between one pair of mirrors remains in the same ratio to the spacing between the other pair of mirrors as the original ratio between these spacings. With this ratio maintained constant, the system continues to exhibit a single pass band at frequencies of interest corresponding to different spacings between mirror pairs. A deformable parallelogram maintains mirror parallelism while a transducer provides mirror motions. Other features are also disclosed.