摘要:
A sample placed under a microscope is illuminated by light from a laser beam. Raman scattered light is passed back via a dichroic filter to various optical components which analyse the Raman spectrum, and thence to a CCD detector. The optical components for analysing the Raman spectrum include tunable dielectric filters in a filter wheel; a Fabry-Perot etalon; and a diffraction grating. These various components may be swapped into the optical path as desired, for example using movable mirrors, enabling the apparatus to be used very flexibly for a variety of different analysis procedures. Various novel analysis methods are also described.
摘要:
A laser inteferometer system is disclosed which is able to make measurements of any deviations in the movement of a machine component which is moving along a main movement axis. The system can measure roll, pitch, yaw, straightness, and parallelism of two tracks using a single laser beam. FIG. 1 shows an arrangement for measuring roll of a vertical machine column (2) during movement of the column along the x-axis of a machine. A straight mirror (6) is positioned on the machine bed with its longitudinal axis aligned with the x-axis, and its reflecting surface normal to the x-axis. An optical component including a polarizing beam splitter is mounted for movement with the machine column and generates from a laser beam (A), a measuring beam (B1) and a reference beam (B2) both directed at the mirror, but laterally separated in the direction of the Z axis. The reflected beams from the mirror are re-combined in the optical device to form a return beam (C) directed towwards a detector adjacent the laser (9). Any change in relative length of the beams (B1) and (B2) give a meausre of roll. Yaw can be measured by producing beams (B1) and (B2) laterally separated in the direction of movement, i.e. along the x-axis. Straightness is measure using a fixed length reference arm within the optical device. Parallelism is meausured by taking straightness measurements of both pillars (2) and (2a). Pitch can be measured by producing four beams.
摘要:
A scale is fixed to one part of a position determining apparatus, and a read head is relatively movable on the other part of the apparatus. Incremental scale marks are regularly spaced along the scale and are counted in a counter to give an indication of relative position of the scale and read head. The marks may for example be recorded magnetically. Some scales are distinguishable from the other, e.g., by having different amplitudes. Positioning information can then be encoded in a binary word. This can either be absolute position values, or error correction information.
摘要:
In an optical detection system a plurality of photodiode detectors are placed in an enclosure. The enclosure has an aperature through which is directed a light beam to be analyzed. To eliminate the effect which ambient light entering the aperture would have on the detector signals, each of the detectors are arranged to be at equal distances from the aperture so that they all have the same acceptance cone angle for the light entering the aperture. Thus the ratio of signal to ambient light in the portion of the light beam reaching each detector is the same and the d.c. component of the signal produced by the detector can be easily removed in the signal conditioning electronics. The equal spacing of the detectors from the aperture is achieved in accordance with the invention by using beam splitters in the path of the beam to deflect portions of the beam to detectors which are offset from the base axis.
摘要:
A laser interferometer uses an acousto-optically modulated laser (100) to produce a pair of orthogonally polarized frequency-shifted beams. The beams are passed down a monomode, polarization preserving optical fiber (110) in order to transmit the beams to a cavity (148). The beams are separated at polarizing beam splitter (128) and directed down measuring arm (130) and reference arm (132) of an interferometer. The beat frequency between the reflected beams is detected at photo-detector (146) which outputs a measuring signal (152). This beat frequency is compared to the beat frequency of the beams before entering the interferometer, which is derived by providing a semisilvered mirror (114) and interfering polaroid (116) in the path of the beams up-beam of the interferometer to produce a reference signal (126). The measuring and reference signals are compared to determine the movement of the measuring arm of the interferometer. This method of determining the reference signal makes the apparatus less susceptible to temperature changes.
摘要:
A rotable object table which has a stator (112) a rotor (114), and positioning servo and measuring system (16). The system (16) is calibrated using an angular interferometer and an intermediate table having stator 122 and rotor 124. Values of angular displacement of stator 124 are determined by the interferometer by solving 3 orthogonal simultaneous equations derived from the equation R+R.sub.o =K sin (.THETA.-.THETA..sub.o), and are compared with corresponding angular displacement as determined by the system (16).
摘要:
The invention relates to a straightness interferometer system, for measuring transverse deviations in the relative movement of machine parts. The preferred embodiment comprises a laser (30) which directs a single frequency laser beam, polarized in two orthogonal modes, along a principal axis P onto a beam splitter (24) which splits the beam into its two modes to provide two secondary beams (26,28). One of the secondary beams (26) is undeviated from the principal axis, the other (28) is deviated through a small angle. A roof-top reflector-prism combination (30/40) is positioned in the paths of both secondary beams in a plane normal to the principal axis, the prism being arranged to deflect the deviated beam into a direction parallel to the principal axis so that both beams are reflected back to the beam splitter where they re-combine to form a combined beam. The combined beam is passed to a detector sytem (38) for detecting interference fringes reproduced from the combined beam caused by relative change in the path lengths of the two secondary beams as the reflector undergoes movements transverse to the principal axis. Three types of beam splitter are specificaly disclosed, two of which show a further preferred feature of displacing one of the beams transversely to solve the dead path problem of a prior art system. A variety of combinations of the varous elements of the preferred system are discussed but not all are illustrated.
摘要:
The output frequency of a semiconductor laser beam is stabilized using a grating or another optical device which has an interaction with the beam whose parameters are sensitive to the beam frequency. The grating (130) generates positive and negative first order diffracted beams (132, 134), whose angle of diffraction is sensitive to the beam frequency, and is detected by split photodetectors AB, CD respectively. In the event of a change in beam frequency the outputs from the photodetectors AB, CD will vary to provide an error signal for the laser frequency. This error signal is insensitive to variations in angular alignment between the beam and the diffraction grating. This is because variations in frequency and variations in angular alignment cause different changes in the outputs of the photodetectors AB, CD.
摘要:
A system for calibrating a rotary table (10) includes an indexing table (20) (which is a Hirth coupling table) and an angular interferometer (100), together with a control (200). The indexing table is mechanically coupled to the rotary table (this being the only connection between the rotary table to be calibrated and the calibration system), and the interferometer is set up to measure rotation of the indexing table. During rotation of the rotary table (10) to a target angle, the control (200) monitors the interferometer reading, and when this reading exceeds a predetermined threshold, actuates a drive motor (240) of the table (20) to counter rotate the table, thereby to maintain the optics (106) of the interferometer in alignment with the laser beams (L2, L3) and thus enable continuous measurement of the position of the indexing table.
摘要:
The presence of Semtex plastic explosive in a sample such as a fingerprint is detected by Raman spectroscopy. RDX and PETN, the active chemical ingredients of Semtex, have strong Raman peaks at 885 cm.sup.-1 and 874 cm.sup.-1 respectively. Consequently, both these peaks can be detected in a Raman spectroscopic system by employing a filter having a narrow passband centered on 880 cm.sup.-1 and with a bandwidth of 20 cm.sup.-1. Such a filter is used in a Raman system used to scan airport boarding cards, or in a Raman microscope which produces images of fingerprints.