Abstract:
There is disclosed an interference spectrophotometer which collects data while monitoring the position of a movable mirror by providing quadrature control to accurately perform coherent addition of data. The spectrophotometer includes a main interferometer, a control interferometer, a sliding controller controlling movement of the movable mirror, an A/D converter converting analog data obtained by the main interferometer into digital form, a register for holding data obtained by one scan of the movable mirror, a memory for accumulating data obtained by numerous scans of the movable mirror, an up/down counter receiving the output signals from two detectors included in the control interferometer, and a decision part. When the counter's value varies, the counter causes the A/D converter to perform its A/D conversion. Then, the decision part checks the counter's value after the A/D conversion. If this value differs from the count value obtained prior to the A/D conversion, the data held in the register is discarded.
Abstract:
A short scan passive infrared remote sensor for detecting a target chemicalpecies, located some distance from the center burst, includes a telescope for targeting a remote gas, a beam splitter means for splitting a beam from the target gas and sending one portion along a first path to an infrared detector and sending a second portion along a second path longer than the first path to the infrared detector. The second path is variable by providing a moving mirror a first distance away from the beam splitter which is 0.5 mm farther away from the beam splitter than the fixed mirror. By this arrangement, a mirror movement of only 0.5 mm is required to obtain an equivalent of 8 cm.sup.-1 spectral information for processing with time domain digital filters. The information from the infrared detector is converted from analog to digital and fed to a digital signal processor. The resulting interferogram is then filtered by a microprocessor using a FIR linear digital filter.
Abstract:
In an interferometer comprising a beam splitter made up of a parallel planar plate and translucent (that is, semi-reflecting) films formed on both sides thereof, and a pair of reverse reflectors disposed at predetermined distances from the two surfaces of the beam splitter, an incident beam is split into two beams by one of the translucent films, and the two beams are reflected by the reverse reflectors, thus interfering with each other at the other translucent film.
Abstract:
An interferometer bearing assembly including a fixed glass rail, a movable carriage that carries both the movable interferometer mirror and the drive coil for the linear motor, and a mechanism for biasing the carriage onto the rail. The glass rail has two optically flat faces defining a normally horizontal line of intersection. The carriage is a rigid structure with plastic surface portions that provide a bearing interface for contacting the flat faces of the glass rail. To improve stability and reduce the possibility of any transverse movement, the carriage is downward biased, preferably by providing an overlying glass plate with a downwardly-facing flat surface, and mounting a spring-loaded plastic element to the top of the carriage. The plastic element contacts (and slides along) the flat glass surface and transmits a downward force to the carriage.
Abstract:
To reduce the data rate of a digitalized measuring signal produced in Fourier spectroscopy, the analog signal representing the interferogram is mixed with a second electrical signal whose frequency is modulated in proportion to the deviation of the instantaneous actual speed of the moving mirror of a double beam interferometer from its constant desired speed. Only the difference frequencies produced as a result of the frequency mixing are digitalized and supplied to an associated computer for analysis of the interferogram. The digital measuring signal thus obtained is distinguished by a substantially reduced data rate without giving rise to additional errors in the frequency transformation. To produce the second frequency modulated electrical signal, a laser source is used which supplies a laser beam into the interferometer parallel to the measuring beam. The interferogram of the laser beam produced in the interferometer is converted by a second optoelectrical converter into an electrical signal frequency modulated in a desired manner and is supplied to a frequency mixer.
Abstract:
An improved mirror scan control for driving a movable mirror in an interferometer with a constant scan velocity comprises a closed loop servo control which provides constant velocity mirror scan in response to a phase comparison of a signal derived from the beat frequency of a two frequency laser beam passing through the interferometer and a selected frequency reference signal, wherein the difference in frequencies or beat frequency of the two frequency laser beam is stabilized at a specified difference in frequencies. The mirror scan control employs a phase lock control loop which locks the frequency of the referenced signal with the frequency of the signal derived from the laser beam to provide precise mirror velocity control.
Abstract:
A continuous drive type Michelson interferometer system for use in Fourier spectroscopy, having a main Michelson interferometer for obtaining the interferogram of a sample, an auxiliary Michelson interferometer for detecting the moving speed of a movable mirror of said main Michelson interferometer, and a control section for controlling the driving speed of said movable mirror. In said control section, the AC output signal of a photodetector is converted into a voltage corresponding to the frequency of the signal, said voltage is compared with a preset voltage by a voltage difference detection means, the phase of said AC output of said photodetector is compared with a phase of a reference signal by a phase comparison means, and said driving speed is controlled by both the outputs of said voltage difference detection means and said phase comparison means.
Abstract:
A spectrometer is disclosed having an interferometer in which: (a) the variable-length arm has a moving retroreflector (copy A to A in summary). The pivoted linkage comprises three or more arms each having its upper end pivotally connected to a supporting structure and its lower end pivotally connected to a carrier for the retroreflector. The stationary folding mirror blocks approximately half of the open face of the retroreflector, causing the radiation which enters the unblocked half of the retroreflector to be reflected back to the retroreflector after it has traveled diagonally across the retroreflector and then been reflected toward the folding mirror.
Abstract:
An interferometer for analyzing electromagnetic frequency spectra including a movable mirror supported on two air bearings such that the center of support of the bearings continuously coincides with the center of gravity of the movable mirror during the motion of the mirror. The air bearings engage two parallel, spaced apart lateral rods that maintain the optical alignment of the mirror. To facilitate making spectral measurements, the interferometer also incorporates a laser for producing monochromatic light that is directed through a primary beam splitter to provide a periodic fringe pattern as the mirror moves and a white light directed through a secondary beam splitter to provide a reproducible reference point.
Abstract:
In a Fourier interference spectrometer of the double-pass retroreflector type, a single mirror is employed in the path of both split beams of an incoming ray to cause them to double back through separate retroreflectors. Changes in optical path length are achieved by linear displacement of both retroreflectors using a motor driven lead screw on one for large, low-frequency changes, a moving-coil actuator on the other for smaller, midfrequency changes and a piezoelectric actuator on one of these two for small, high-frequency changes.