Abstract: 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.

Abstract: 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.

Abstract: In a Raman spectrometer having a charge-coupled device (CCD) detector (24), an incoming beam (36) containing a spectrum of Raman scattered light is dispersed by a diffraction grating (44). Different parts of the spectrum are split into separate optical paths (48A-C) by edge filters (38A, 38B) and a mirror (46). These components are tilted at different vertical angles, so that after the beams (48A-C) have been dispersed by the diffraction grating (44), they form partial spectra (50A-C), one above the other on the CCD (24). This enables several consecutive parts of a widely dispersed spectrum to be viewed simultaneously on the CCD (24) at high resolution.

Abstract: In a Raman microscope, Raman scattered light from an illuminated area on a sample 10 is collected by an objective 12 and imaged by a lens 18 onto a detector in an image plane 20. A filter 16 selects only light of a desired Raman wavenumber shift. Since the tuning of this filter is sensitive to the angle of incidence, it is placed after the lens 18 instead of before it, and the distance from the objective 12 to the lens 18 is made substantially equal to the focal length of the lens 18. This ensures that chief rays 14A',14B' from different points on the sample 10 pass through the filter 16 at the same angle of incidence. The wavenumber selected by the filter is therefore the same for light from all points on the sample, which it would not be if the filter were placed before the lens 18.

Abstract: A spot of a sample is illuminated by laser light. Raman scattered light is collimated in a parallel beam by a microscope objective, and analyzed by a dispersive or non-dispersive analyzer (such as a diffraction grating or filter). A lens then focuses the Raman scattered light onto a two-dimensional photodetector array in the form of a charge-coupled device (CCD). A confocal technique is described to eliminate light scattered from outside the focal plane of the objective. This may be done by binning together a few pixels of the CCD at the focal point of the lens, or by image processing techniques in a computer.

Abstract: 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.

Abstract: A sample (14) is illuminated by light from a laser source (16), which is reflected to it by a dichroic filter (18) and passed through a microscope objective (20). The microscope objective (20) focusses a two dimensional image of the illuminated area onto a detector (22). On the way to the detector (22), the light passes through an interference filter (26), which selects a desired line from the Raman spectrum scattered by the sample (14). The filter (26) can be tuned to any desired Raman line by rotating it through various angles of incidence (.THETA.), about an axis (28) perpendicular to the optical axis.

Abstract: An optical sensor device uses surface plasmon resonance to detect the presence of a specific material. A transparent body (12) is coated with a thin gold film (14) which film may be coated e.g. with an antibody material. The arrangement is illuminated with a divergent light beam and light internally reflected from the gold film is detected by a photodiode array (16). The dielectric conditions adjacent the gold film determine the position of the surface resonance angle, this being indicated by a dark area on the detector array.

Abstract: An arrangement for the remote actuation of a controlled device, e.g. a hydraulic valve, in situations with stringent safety requirements, uses optical power. The optical power, e.g. from a high-power laser, is conveyed via an optical fibre (1) to the controlled device. Here it falls on a heat-absorbent surface (2), as a result of which a volatile fluid (e.g. freon) is evaporated. This via a bellows (4) drives an output rod (5), which operates the controlled device.Alternatives include a bimetallic strip, a thermostat-type capsule, and a memory metal strip, as the heat responsive device.

Abstract: In order to determine the vortex shedding frequency, from which the fluid flow rate may be calculated, an optical beam, such as produced by a laser, is passed through a fluid, transversely to a vortex street therein, and modulated in dependence on the alternate high and low velocity regions comprising the vortex street. The modulated signal is detected and "cleaned" of noise by filtering with a first (high) band-pass filter of a center frequency f.sub.c, such that the first filter output comprises an amplitude modulated signal of carrier frequency f.sub.c modulated by the vortex shedding frequency, that is the frequency of oscillation of the power spectra between the respective curves for the high and low velocity regions. The first filter output is demodulated and filtered by a second (low) band-pass filter, whose output is of a frequency comprising the vortex shedding frequency.

Abstract: A vortex flowmeter having a double bluff body arrangement whereby vortices are generated at a rate corresponding to the fluid flow velocity. The upstream body and the downstream body together interact with the fluid stream to generate vortices. The arrangement introduces a relatively low blocking factor in comparison to simple bluff body arrangements. Vortex sensors are located between the bodies and downstream of the second body a distance between three and five times the diameter of that body.

Abstract: A bluff body is placed in a fluid pipe with one flat face facing the oncoming fluid. Vortices are then generated and shed alternately from opposite edges of the body. This body is of a scalene triangle cross section, and in one version a hole extends transversely therethrough. A longitudinal hole intersects the first hole at right angles thereto. The vortices cause oscillations in the transverse hole. A light beam is provided in the longitudinal hole. The light beam is modulated as it crosses the path of the transverse hole. Hence by measuring the frequency at which the beam is modulated and by suitable calibration, one gets a good and reliable indication of fluid flow rate. In a second version the transverse hole is formed into a blind hole at the foot of which is an etalon (a Fabry-Perot interferometer). The effect of the fluid oscillations due to vortex generation influences the etalon so that its output is a measure of the fluid flow rate.