Abstract: A system for determining the condition of an optical signal includes a first refractive material having an interface with a second refractive material. The first refractive material receives an optical signal. A portion of the optical signal reflects off the interface between the first refractive material and the second refractive material as a reflection signal. A signal monitoring circuit determines the condition of the optical signal using the reflection of the optical signal at the interface between the first refractive material and the second refractive material.

Abstract: The invention relates to an optical phantom that is suitable for simulating the optical properties of biological material and to a method of producing said phantom. The phantom is comprised of a matrix of poly(vinyl alcohol) (PVA) and spherical particles whose refractive index differs from that of the PVA. Preferably the PVA has a level of hydrolysis of >98%. Preferably the spherical particles are hollow polystyrene particles. In addition, light-absorbing and light-scattering substances may be added to the matrix.

Abstract: A method for monitoring the interaction of molecular species utilizes a sensor device comprising a substrate (1) with a waveguide (2) formed on the surface thereof. A grating (3) is formed in one of the surfaces of the waveguide (2). A beam of light (6) is incident on the grating (3) and the angle of incidence at which maximum reflection occurs is monitored. A first molecular species is immobilized on the waveguide (2). Changes in the angular position of the reflection maximum provide an indication of interaction of the first molecular species with a second molecular species contained in a sample brought into contact with the sensor device.

Abstract: A technique for increasing the excitation and collection of evanescent fluorescence radiation emanating from a fiber optic sensor having a high refractive index (nr), dielectric thin film coating has been disclosed and described. The invention comprises a clad optical fiber core whose cladding is removed on a distal end, the distal end coated with a thin, non-porous, titanium dioxide sol-gel coating. It has been shown that such a fiber will exhibit increased fluorescence coupling due in part by 1) increasing the intensity of the evanescent field at the fiber core surface by a constructive interference effect on the propagating light, and 2) increasing the depth of penetration of the field in the sample. The interference effect created by the thin film imposes a wavelength dependence on the collection of the fluorescence and also suggests a novel application of thin films for color filtering as well as increasing collected fluorescence in fiber sensors.

Abstract: A refractometer and a method for measuring the refractive index of a lens, wherein a thin insert in the form of a pad of a flexible transparent material attached to a rigid transparent sheet, is lightly pressed onto a surface of the lens under test, such that the pad surface effectively acquires the same profile as the lens surface. The focal length or power of the lens is first measured without the insert, and the measurement is then repeated with the insert positioned first in contact with one surface of the lens, and then in contact with the other surface. The use of equations derived from the classical lens formula then enables the refractive index of the lens to be easily and quickly determined. The apparatus and method also enables the measurement of the refractive index of lenses of low power.

Abstract: A method of fabricating a semiconductor device includes the steps of illuminating a structure formed on a surface of a substrate by an incident optical beam incident to the structure with a predetermined incident angle with respect to the surface, measuring a polarization state of an exiting optical beam exiting from the structure in response to an illumination of the structure by the incident optical beam, and evaluating a size of the structure in a direction parallel to the surface from the polarization state of the exiting optical beam, and adjusting a parameter of production of a semiconductor device in response to the size.

Abstract: A refractometer, comprising a light source arranged in a frame structure, an optical window to be positioned in a process solution, means for directing a beam of rays from the light source to an interface between the optical window and the process solution, part of the beam of rays being absorbed partly into the solution and part of it being reflected back from the solution entirely and creating an image, in which the location of a borderline between a light area and a dark area depends on the refractive index of the process solution, and an image detector, by means of which the image created in said manner is observed.

Abstract: A refractometric apparatus and method for monitoring the percentage of water in hydraulic fluids employ a temperature sensitive device allowing a user to obtain accurate and correct readings of various measured properties. In particular, the temperature sensitive member comprises a prism-wedge-mirror combination in conjunction with a bimetallic strip. The combination ensures the proper angular displacement of a light beam inside the refractometric apparatus and, therefore, the correct reading of a parameter to be measured.

Abstract: A dry zeroing assembly is provided for zeroing a gun-sight implemented on a gun having a barrel.

Abstract: A compact portable instrument for determining the percentage concentration of a material in a solution such as the amount of concentrate in an output from an Aqueous Film Forming Foam generator used to extinguish fires. The instrument comprises a refractive index sensor with a reflective type refractometer prism having a measuring surface in contact with liquids placed in a sample holder formed by an opening through a retainer plate. The measuring surface of the prism covers that opening and presses the retainer plate towards an outer surface of the instrument, that outer surface having entrance and exit ports for sample liquids at that opening. The refractometer senses the refractive index of liquid in the sample holder and, when properly calibrated, provides an output to a digital display that directly indicates the percentage concentration of material in the liquid.

Abstract: Improved crop yields are obtained by determining total dissolved solids (TDS) in a representative sample of transplants to determine strike rate as a logarithmic function of TDS before transplanting. Juvenile plants with high strike rate readings are transplanted. A refractometer having a logarithmic scale showing low, medium, and high strike rates as a direct readout from a juice sample is used. A bioregulator can be used to induce high TDS levels prior to transplanting. Particular application is to transplanting strawberry runners.

Abstract: An optical sensor for determining an index of refraction of a substance being monitored includes a light source (20). An optical element (24) having a coupling surface (30) and a measuring surface (26) is arranged such that light directed into the optical element (24) through the coupling surface (30) is partially reflected twice from the measuring surface such that it is directed to and exits through the coupling surface (30). The measuring surface (26) is preferably spherical. An input optical fiber (22) having first and second ends directs light emitted from the light source to the coupling surface of the optical element. The first and second ends of the input optical fiber (22) are optically coupled to the coupling surface (30) of the optical element (24) and the light source, respectively. An output optical fiber (28) has first and second ends and directs light expelled from the coupling surface (30) of the optical element (24) to a photodetector (50).

Abstract: A dielectric dispersion determining method applying a transient grating method. The transient response of a sample is observed by the transient grating method using a femtosecond ultrashort visible optical pulse. A vibrational waveform b(t) is determined such that its square b(t).sup.2 replicates vibrational components observed in the transient response. The vibrational waveform b(t) is converted into b(.omega.) through the Fourier transform. The dielectric constant .epsilon.(.omega.) is obtained by substituting the converted value for b(.omega.)/.omega..sup.2 on the right-hand side of the following equation (1) derived from Maxwell's equations. The dielectric constant and/or refraction index can be directly obtained from the transient response to the femtosecond ultrashort visible optical pulse without passing through the dispersion relation which leaves some ambiguity in its definition.

Abstract: A capillary tube used to transfer a liquid sample into a detection cell following separation by a chromatographic system is modified by plugging or otherwise severely restricting its flow. Near its plugged end, said tube is drilled to provide a plurality of holes or ports perpendicular thereto and penetrating to the central flowing core of said tube so as to direct outflow from the tube perpendicularly therefrom. The outer diameter of this somodified capillary tube is selected to be of a size comparable to, though smaller than, the detection cell diameter into which it transfers the flowing sample. In this manner, fluid transferred into a detection cell by said modified capillary tube will be split into a plurality of smaller streams flowing outwardly therefrom and striking the adjacent detector cell walls almost immediately.

Abstract: A system for analyzing a sample is disclosed. The system includes a light-transmitting probe with a light emitting tip having a diameter that is less than one-wavelength of light. The system is adapted to place the probe in close proximity to the sample without physically contacting the sample with the probe, and to move the sample relative to the probe such that light transmitted from the probe is directed onto the desired portion of the sample surface. The system further include a light source which transmits light into the probe tip. The system also includes a detector which detects a portion of the light transmitted through the sample. The detector is configured to detect that portion of the light that was incident on the sample surface at an angle greater than the critical angle. The detector is equipped with an aperture through which passes substantially all of the light that was incident on the surface at an angle less than the critical angle and which was transmitted through the sample.

Abstract: A refractometer comprising an optical pattern-beam projection system for projecting a pattern,light beam onto the fundus of a tested eye to measure refractive power of the tested eye, and an optical light-receiving system for receiving the pattern light beam reflected at the fundus to compute the refractive power of the tested eye. A deflecting member is inserted into an optical path of the optical pattern-beam projection system for deflecting the pattern light beam with respect to an optical axis of the optical pattern-beam projection system and then projecting the deflected pattern light beam onto the fundus.

Abstract: A method and apparatus for fluid analysis includes a sensor for determining the index of refraction of a fluid. Advanced methods of fluid analysis relate index of refraction and other measured physical characteristics of the fluid.

Abstract: A low-cost refractometer for determining whether or not a beverage has been sweetened with sugar. The refractometer has an elongated transparent body with a prism at one end and either an eye piece or a light source at the other end. A drop of the beverage to be tested is put on the face of the prism and a diffuser is closed over it to spread the liquid into a thin sheet and to diffuse the light entering the prism face. The user looks through the eye piece at the remote end and because of a light block, light only shows through at the eye piece if there is sugar in the drink. Alternatively, a light may be directed at the eye piece end and if light is visible through the diffuser, the sample has sugar and if there is no light showing at the diffuser, the sample is essentially sugar-free.

Abstract: A target molecule at a binding site is detected using an optical waveguide having a surface proximate to the binding site, and a waveguide detector coupled to the optical waveguide. An incident light beam is applied to the binding site along an axis transverse to the surface of the optical waveguide. The incident light beam impinges an optical indicator associated with the target molecule to form secondary light which is coupled into the optical waveguide. The secondary light is detected by the waveguide detector to thereby detect the target molecule.

Abstract: An optical scintillometer is provided which is operative to measure atmospheric wake vortex turbulence intensity up to a distance of ten kilometers. The optical scintillometer provides real time continuous measurements of aircraft generated wake vortex turbulence intensity in the field of operations employing a transmitter, receiver, and digital processing circuitry. The signal is digitized before comparison with a threshold to eliminate events attributable to objects moving through the path of the optical transmitter and receiver. The system is thereby able to perform calculations to adjust the first order log-amplitude variance function in the saturation regime. An extremely important aspect of the invention is the digitization of the signal and its comparison with the threshold signal. Because a digital signal is compared with a threshold signal level, invalid signal inputs are excluded from the calculation of path-averaged turbulence intensity.

Abstract: The proposed fibre-optic sensor is based on surface plasmon resonance and consists of a monomode fibre with multiple angled facets at its end face and suitable coatings. A first partial face is preferably metal-coated, a second is provided with a conventional detection layer, and the angle between the two partial surface is 30.degree., 45.degree. or 90.degree..

Abstract: Detection apparatus for use with a carbon dioxide jet spray cleaning system that determines whether liquid carbon dioxide is flowing between a storage tank and a jet spray nozzle. The detection apparatus determines whether carbon dioxide snow is generated by the jet spray nozzle, which is produced by expansion of liquid carbon dioxide through the jet spray nozzle. The apparatus comprises a transfer tube coupled between the storage tank and the jet spray nozzle that has transparent input and output windows and which permits liquid carbon dioxide to flow from the storage tank to the jet spray nozzle. A light source produces light that is focused on a pinhole in an aperture stop. A collimating lens images collimated light on the input window of the transfer tube, and a light detector detects light that is refracted by liquid carbon dioxide in the transfer tube that exits through the output window and is incident thereon, and generates an output signal indicating light detection.

Abstract: The invention relates to a system for monitoring a fiber optic cable (2) connected between optical signal transmitting (TX) and receiving (RX) equipment, and comprising first (3) and second (4) electro-optical devices for measuring optical power being both connected to a central control unit (14) over a bus (13) and permanently connected to the beginning and the end, respectively, of the fiber optic cable (2), at said transmitting (TX) and receiving (RX) equipment.The invention also relates to a compact electro-optical device (3) for measuring the operating optical power (P) of a fiber optic cable (2), having an optic input (5) and optic output (7), as well as an electric input (9) and electric output (11) and being of the type which comprises an optical power measuring circuit (20) having an input (19) connected to the optic input (5) and an output (21) connected to the electric output (11).

Abstract: The separations resulting from capillary electrophoresis performed in a microbore capillary tube are detected on-line by focusing a light beam in the form of a line or sheet of light on the capillary passage in which the separations take place so that the width of the sheet of light encompasses the length of the passage in which separations of interest are expected to take place. The separations form concentration gradients in the capillary passage encompassed by the light beam and cause refraction of portions of the light beam and variations in the intensity of the light beam due to such refraction. Alternately, the separated components may absorb light of certain frequencies so if the light beam includes light of the certain frequencies, variation in the intensity of the light beam is caused by such absorbance.

Abstract: The invention relates to non-contact methods of examining physical and chemical parameters of various media, particularly, gases or liquids. It can be used to determine properties and compositions of media including those containing various chemical or biological components with applications in scientific research, technology and environmental monitoring.

Abstract: Fluorescence measuring methods and apparatus use planar optical waveguides to excite fluorescence in the evanescent field of the waveguides and photodetectors to sense the fluorescence produced. Chemically sensitive fluorophores are bound to the evanescent regions of the planar optical waveguides. Substrates support the waveguides. Photodetectors, positioned in the substrates with fields of view normal to the waveguides, detect the fluorescence. Wavelength-selective material coating surfaces of the photodetectors allow fluorescence to be detected while restricting entry of light at the excitation wavelengths. The photodetectors have high aspect ratios for detection of fluorescence generated by the optical waveguides. Preferably, the photodetectors are closely coupled to the fluorescence generated in the evanescent field of the waveguide.

Abstract: A scanning mode sensor and method is provided for detection of flow inhomogeneities such as shock. The field of use of this invention is ground test control and engine control during supersonic flight.Prior art measuring techniques include interferometry, Schlieren, and shadowgraph techniques. These techniques, however, have problems with light dissipation.The present method and sensor utilizes a pencil beam of energy which is passed through a transparent aperture in a flow inlet in a time-sequential manner so as to alter the energy beam. The altered beam or its effects are processed and can be studied to reveal information about flow through the inlet which can in turn be used for engine control.

Abstract: A measuring beam is incident upon a triangular cell storing a liquid sample, and transmitted light thereof is received by a linear sensor so that both transmitted light intensity and a position of the beam are detected. A refractive index calculating part calculates refractive indices from the position detected by the linear sensor, while an absorbance calculating part calculates absorbance values dependent on component concentration values correcting influence by transmittance change at the triangular cell through the transmitted light intensity values and the refractive indices of the sample calculated at the refractive index calculating part. A component concentration calculating part performs a multivariate analytical operation on the basis of the absorbance values dependent on the component concentration values at a plurality of measuring wavelengths calculated at the absorbance calculating part.

Abstract: A sensor system including a first layer having first and second surfaces and a first index of refraction, a second layer having a second index of refraction which is less than the first index of refraction, a mechanism for generating a first diffuse light beam which passes through the first layer from the first surface to the second surface, and a mechanism for sensing a portion of the first diffuse light beam reflected back through the first layer to the first surface as an incident of the first diffuse light beam impinging upon the second layer.

Abstract: A capillary tube used to transfer a liquid sample into a detection cell following separation by a chromatographic system is modified by plugging or otherwise severely restricting its flow. Near its plugged end, said tube is drilled to provide a plurality of holes or ports perpendicular thereto and penetrating into the central flowing core of said tube so as to direct outflow from the tube perpendicularly therefrom. The outer diameter of this so-modified capillary tube is selected to be of a size comparable to, though smaller than, the detection cell diameter into which it transfers the flowing sample. In this manner, fluid transferred into a detection cell by said modified capillary tube will be split into a plurality of smaller streams flowing outwardly therefrom and striking the adjacent detector cell walls almost immediately.

Abstract: A target molecule at a binding site is detected using an optical waveguide having a surface proximate to the binding site, and a waveguide detector coupled to the optical waveguide. An incident light beam is applied to the binding site along an axis transverse to the surface of the optical waveguide. The incident light beam impinges an optical indicator associated with the target molecule to form secondary light which is coupled into the optical waveguide. The secondary light is detected by the waveguide detector to thereby detect the target molecule.

Abstract: In a method of determining the refractive index of a gaseous, liquid or solid sample, preferably a gaseous or liquid sample, there is used a waveguide resonator (1) which includes an open waveguide (4) and a closed waveguide (5) located adjacent the open waveguide. The sample is brought to the vicinity of the closed waveguide (5) so as to influence the proximal surroundings of the waveguide and therewith its effective refractive index. Light derived from a light source (9) is coupled to one end of the open waveguide (4) and transmitted light is measured at the other end of the open waveguide to establish the influence of the sample on the resonance wavelength and therewith determine the refractive index of the sample or a sample-related refractive index difference. A device for carrying out the method includes a waveguide resonator having a sample contact area (12) adjacent the closed waveguide (5) of the waveguide resonator.

Abstract: A light beam is sent onto a wafer, at different angles of incidence, thus giving rise to fluctuations in the transmittance of the wafer, as the angle of incidence varies, because of interference due to multiple reflections of the beam inside the wafer. The transmittance of the wafer is measured as the angle of incidence varies. The angular positions of transmittance maxima and minima are determined with respect to a maximum or minimum corresponding to normal incidence. The refractive index is obtained from these positions and from the number of maxima and minima in the different angles.

Abstract: To determine the polymerization profile of a layer of polymeric material, particular a coating of an optical waveguide, a source sends a light radiation towards the layer under test at different angles of incidence, and both the portion of radiation reflected by the layer and the portion transmitted by the layer are converted into electrical signals. The electrical signals are supplied to devices for measuring their intensity, and a processing system processes the intensity values to obtain a value of the refractive index at a different depth inside the layer and to obtain the degree of polymerization at each depth by comparison with the values of the refractive index of a precursor of the polymer and of the fully polymerized material.

Abstract: Disclosed and claimed is an optical sensor for the detection of chemical species. The optical sensor includes an optical waveguide having a guiding thin film. The thickness of the refrative index of the guiding thin film changes due to adsorption or absorption of the chemical species or reaction of the chemical species with the guiding thin film. The thickness of the guiding thin film is above the cutoff thickness in the presence of gaseous or liquid chemical species to be detected. And, the thickness of the guiding thin film is below the cutoff thickness in the absence of such chemical species.

Abstract: Apparatus for the measurement of optical properties of a quasi cylindrically symmetric transparent object (2), which apparatus comprises source means (11) for providing a source of electromagnetic radiation, illumination forming means for forming an illuminating beam (41), region selecting means for selecting a localised radial region (42), region scanning means for scanning the localised radial region (42) through a range of radial positions, reflection detecting means for detecting a reflected beam (43), beam measuring means for measuring the component of the position where the reflected beam (43) leaves the transparent object (2), supporting means which causes the illuminating beam (41), the reflected beam (43) and an axis of rotational symmetry (1) of the transparent object (2) to lie in a measurement plane, and angle altering means for altering the angle of incidence of the illuminating beam (41) on the transparent object (2).

Abstract: A optical analytical method and apparatus for measuring concentrations of materials in liquids and gases is described. The method is based upon measurements of light reflection from diffraction gratings in contact with the sample. Features in the reflection spectrum are directly related to the complex dielectric constant of the sample solution. By examining the reflection spectrum, the concentration of materials in the liquid or gas can be determined.

Abstract: In order to measure the optical quality of the surface of a transparent sheet, the second surface of the sheet is placed in contact with a flexible material which is wetted with an index liquid. In the case of soda lime glass, water is suitable. The optical measurement can be carried out by traditional methods, ombroscopy in particular.

Abstract: The present invention relates to a refractive index detector for a dynamic liquid sample having a fiber optic filament of a predetermined diameter with an unclad sensor region, wherein the sensor region comprises a longitudinally tapered zone wherein the diameter continuously decreases from the predetermined diameter to a minimum diameter.The invention finds use as a detector for high performance liquid chromatography and capillary zone electrophoresis.

Abstract: A Brewster angle refractometer, based on the principal that reflectivity of light polarized parallel to the plane of incidence is minimized at the Brewster angle, is used to determine the refractive index of a material. The refractometer has a precision mechanical drive arrangement for precisely determining the refractive index over a range of 1.4 to 3.0, with an accuracy of at least .+-.0.02.

Abstract: A refractive index sensor of a total-reflection type comprises a waveguiding layer of a cladding/core/cladding waveguide structure formed on a substrate. The waveguiding layer has an input face connected to either a single optical fiber or a plurality of optical fibers for injecting a light(s) into the layer, a detection face which, obeying Snell's law, totally reflects/transmits the light beam or beams that have arrived there with an expansion angle from the optical fiber or fibers and which constitutes a surface with which a material whose refractive index is to be measured comes in contact, and an output face which outputs the light reflected from the detection face and is connected to an optical detector. The refractive index of the material of interest is detected from a bright-dark boundary of the presence of the corresponding total reflected light from the detection face. With no need of a bulk prism or lamp-type light source, the sensor is small in size and high in sensitivity.

Abstract: An optical sensor for detecting gaseous or liquid chemical species including a sensing element having a flat light reflecting substrate and one or more transparent thin films which are organic or inorganic films or high-polymer films and are formed on the substrate. The detection of the gaseous or liquid chemical species is effected by measuring a change in the light reflection characteristic of the sensing element based on swelling of the thin film or a change in its thickness or refractive index or changes in both parameters.

Abstract: An arrangement for cleaning an optical window in an instrument such as a refractometer located in-line in a continuous or batch process, comprising a nozzle for spraying under high pressure a harmless cleaning medium onto the optical window. The nozzle is firmly fixed in a nozzle frame, the frame itself being firmly attached to the instrument in the vicinity of the optical window. The nozzle is recessed in the frame. The invention achieves cleaning of the optical window without mechanical parts or strong solvents, and does not require removal of the instrument from its in-line position.

Abstract: An optical fourier transform image representative of characteristics of a liquid sample and particles within the fluid sample is quickly and inexpensively generated by an optical fourier transform system. A small liquid sample is received in a lenticular array liquid sample container with the fluid sample entering open-ended microchannels in the container preferably by capillary action. The container is formed of an optical material such that the fluid sample in the microchannels forms a grating when placed into an optical fourier transform system. Accordingly, the fourier transform image generated within the system is characteristic of the liquid sample forming the grating for the system. The liquid sample container is formed of two plates of optical acrylic, which may be coated or otherwise treated to make it non-hydrophobic to prevent the loss of moisture from liquid samples. A first one of the plates has an array of microgrooves formed into a first surface of the plate.

Abstract: Characteristic values of transparent layers in the nanometer range, such a layer thickness and refractive index, can be determined with a spectro-ellipsometer. The task is to determine these values even with a less elaborate ellipsometer which only operates at one or a few wavelengths. In accordance with the invention, first at least one pair of the ellipsometric angles psi and delta are measured with at least one angle of incidence of the light beams on the sample for at least one ellipsometer wavelength, from which at least one characteristic value is determined for one ellipsometer period. Furthermore, the wavelength-dependent reflection of the probe in the wavelength range of interest is photometrically measured and from this the spectral dependency of the characteristic value is determined with the ellipsometrically measured characteristic value.

Abstract: A optical analytical method and apparatus for measuring concentrations of materials in liquids and gases is described. The method is based upon measurements of light reflection from diffraction gratings in contact with the sample. Features in the reflection spectrum are directly related to the complex dielectric constant of the sample solution. By examining the reflection spectrum, the concentration of materials in the liquid or gas can be determined.

Abstract: Apparatus for the determination of a chemical or biochemical species comprises a resonant optical biosensor (1-4) disposed in a light path between a pivotally-mounted source (5) of monochromatic light and a stationary detector (12) adapted to monitor some characteristic of the light. There is provided means (7) for causing pivotal motion of the light source (5) so as to vary the angle of incidence of the light on the sensor (1-4). Also provided is means for monitoring the instantaneous angle of incidence. The means for varying the angle of incidence of the light on the sensor may be a cam arrangement (7) acting on a pivoting member (6) carrying the light source (5), and the means for monitoring the instantaneous angle of incidence of the light on the sensor (1-4) may comprise means for monitoring the number of steps performed by a stepper motor driving the cam arrangement (7).

Abstract: The invention relates to the measurement of the difference between refractive indexes of two media, traversed by a light beam the beams produce an interference figure consisting of fringes having a displacement which is measured.According to the invention, the displacement of the fringes of the interference figure is detected with a photosensitive device and a phase modulation is performed on at least one of the beams and the modulation is controlled in order to obtain a movement of the fringes of the interference figure.

Abstract: Apparatus for analysing the optical properties of a transparent object (118) comprises a light source, an analyser cell comprising a body of solid transparent material (110) having a cavity (112) formed therein for receiving the object (118) to be analysed, and arranged so as to allow a light beam from the light source to pass through the object (118), said body (110) having an entrance surface (114) through which the light beam enters the cell from the ambient medium and an exit surface (116) through which the light beam leaves the cell, and analysing means for analysing the light beam after passage through the object (118), and is characterised in that the cavity (112) in the analyser cell is of substantially circular section in at least the region through which the light beam passes in use.

Abstract: The present invention relates to a fluid detection system which can be adapted for use in applications including liquid-level detection, pipeflow monitoring, and interstitial leakage in double-walled containers. The system operates on principles of optics and provides the capability of remotely differentiating between fluids having different refractive indices including liquids and vapors. The present detector uses a unique light pulsation technique which increases permissible operating ranges over existing optical detection systems.