Abstract: A non-invasive system for detection of explosives and contraband in a vehicle includes at least one laser vibrometer for measuring vehicle vibrations at one or more points on the vehicle while the vehicle is operating. One laser vibrometer can be sequentially directed to various points on the vehicle according to a predetermined single point or pattern. Or, a plurality of laser vibrometers could be used to simultaneously illuminate the vehicle. After measurement, the vehicle vibrations are compared to a database of reference vibrations, which that were taken of similar vehicles that were known to be contraband-free. The measured vibrations are compared to the vibrations pattern for the same type of vehicle. If the vibration patterns exhibit differences in frequency peaks that exceed predetermined parameters, the system alerts the operator. A more detailed inspection of the vehicle can then be accomplished.

Abstract: An object information acquiring apparatus has: a holding unit which holds an object; a probe which receives an acoustic wave generated in the object via the holding unit and converts the acoustic wave to an electrical signal; a force measuring unit which measures a force applied to the object when the object is held by the holding unit; a sound speed acquiring unit which determines a sound speed in the object by using the force measured by the measuring unit and a contact area between the object and the holding unit; and a generating unit which generates object information data from the information about the sound speed determined by the sound speed acquiring unit and the electrical signal.

Abstract: A photoacoustic imaging apparatus is used that comprises a light source capable of irradiating light onto an object from a plurality of directions, a detector that detects acoustic waves generated by the object irradiated with light, a calculator that calculates object information from detected acoustic waves, and a generator that generates image data from the object information. The calculator calculates a plurality of object information pieces corresponding to irradiation in respective directions on the basis of acoustic waves at a time of irradiation of light at dissimilar timings from the plurality of directions. The generator selects, for each region and according to a predetermined criterion, image data of increased contrast in a case where a plurality of image data items on the object are generated on the basis of the plurality of object information pieces, and generates image data by combining the image data selected in each region.

Abstract: A photoacoustic wave measuring apparatus, having: a probe including a plurality of devices which detect an acoustic wave generated by irradiating light onto an object; and a signal processor which acquires information about the object on the basis of an acoustic wave received by the devices, wherein the light is irradiated onto the object from the probe side; the probe includes: bright-field devices having a view angle covering a bright-field illumination area, which is an area where the light is irradiated, on the probe-side surface of the object; and dark-field devices having a field of view which does not cover the bright-field illumination area; and the signal processor uses an acoustic wave received by the dark-field devices when acquiring information about the object on the basis of a acoustic wave received before a predetermined time period is elapsed since the irradiation of light onto the object.

Abstract: Provided is a technique capable of changing resolution or an imaging area during imaging, in an acoustic wave acquiring apparatus using a Fabry-Perot probe. An acoustic wave acquiring apparatus includes a measurement light source emitting measurement light, a probe having a Fabry-Perot interferometer including a first mirror, upon the side of which the measurement light is incident, and a second mirror, upon the side of which an elastic wave from an object is incident, an optical system changing a beam diameter of the measurement light, a controller controlling change in the beam diameter performed by the optical system, a photosensor measuring a light intensity of the measurement light reflected on the Fabry-Perot interferometer, and a processor acquiring intensity of the elastic wave on the basis of change in the light intensity measured by the photosensor due to incidence of the elastic wave.

Abstract: A pulse laser oscillator (11) outputs a first laser beam, a beam splitter splitting the first laser beam into split beams, optical paths (12, 13, 14, 15, 16) propagating light of split beams split, respectively, taking different times for light propagation thereof, a condenser superimposing light of split beams propagated through the optical paths, respectively, on an identical spot of a measuring material (100), for irradiation therewith, a laser interferometer (30) irradiating the measuring material (100) with light of a second laser beam, having light intensity variations resulted from interferences between reference light and light of the second laser beam reflected or scattered, as bases to detect ultrasonic waves energized by light of the first laser beam and transmitted in the measuring material (100), a waveform analyzer (32) calculating a metallic microstructure or a material property of the measuring material (100) based on ultrasonic waves.

Abstract: Micro-opto-mechanical chemical sensors and methods for simultaneously detecting and discriminating between a variety of vapor-phase analytes. One embodiment of the sensor is a photonic microharp chemical sensor with an array of closely spaced microbridges, each differing slightly in length and coated with a different sorbent polymer. The microbridges can be excited photothermally, and the microbridges can be optically interrogated using microcavity interferometry. Other actuation methods include piezoelectric, piezoresistive, electrothermal, and magnetic. Other read-out techniques include using a lever arm and other interferometric techniques.

Abstract: An apparatus and method for detecting gunfire is provided which uses distributed acoustic sensing to provide the gunfire detection. The method comprises interrogating an optical fibre with electromagnetic radiation to provide a distributed acoustic sensor comprising a plurality of sensing portions of the optical fibre, and analysing a measurement signal from said sensing portions to detect gunfire events. A gunfire event will typically be relatively intense but of short duration and affect multiple sensing channels. The method may detect a characteristic 602 of a muzzle blast and/or a characteristic 601 of pressure wave from a supersonic round and may determine the location of the gunfire and the location at which the round crosses the sensor.

Abstract: An optical microphone includes: a propagation medium portion; a light source to output a light wave passing through the propagation medium portion across the acoustic wave propagating through the propagation medium portion; a reflecting section to retroreflect the light wave having passed through the propagation medium portion; and a photoelectric conversion section to receive the light wave having been reflected by the reflecting section and passed through the propagation medium portion to output an electric signal. 0th-order, +1st-order and ?1st-order diffracted light waves are respectively produced on outward and return paths, by virtue of a refractive index distribution across the propagation medium portion caused by the propagation of the acoustic wave therethrough. The photoelectric conversion section detects interference light between the +1st-order or ?1st-order diffracted light wave of the outward path and the ?1st-order or +1st-order diffracted light wave of the return path.

Abstract: An object of the present invention is to provide a noninvasive constituent concentration measuring apparatus and constituent concentration measuring apparatus controlling method, in which accurate measurement can be performed by superimposing two photoacoustic signals having the same frequency and reverse phases to nullify the effect from the other constituent occupying large part of the object to be measured. The constituent concentration measuring apparatus according to the invention includes light generating means for generating two light beams having different wavelengths, modulation means for electrically intensity-modulating each of the two light beams having different wavelengths using signals having the same frequency and reverse phases, light outgoing means for outputting the two intensity-modulated light beams having different wavelengths toward a test subject, and acoustic wave detection means for detecting an acoustic wave generated in the test subject by the outputted light.

Abstract: An acoustic wave detector includes: a transducer; and a light reflecting member which is positioned between the transducer and a subject surface that is irradiated with the light, and which reflects scattered light on the subject surface. The light reflecting member includes a first reflecting surface and a second reflecting surface positioned closer to the transducer than the first reflecting surface, and a distance between the first reflecting surface and the second reflecting surface is an odd multiple of a half wavelength of a predetermined wavelength included in an acoustic wave generated from the light reflecting member by the scattered light.

Abstract: A long-distance fiber optic monitoring system having a sensing unit and an analyzer that is remotely located from the sensing unit is provided. The sensing unit comprises a source of optical energy for injecting optical energy into the fiber optical cable and an optical detector configured to detect an optical return signal from the optical fiber. The detected optical return signal is associated with an acoustic signal impinging on the optical fiber. The analyzer receives a signal from the remote sensing unit via the optical fiber that is representative of the optical return signal, and determines a location of a disturbance based at least on the received signal. The representative signal can be transmitted from the remote sensing unit to the analyzer as an optical signal or via a metallic wired included with the optical fiber.

Abstract: An optical fiber type vibration meter including a light source, an incident side optical fiber guiding light from the light source, a vibration probe to which a guided light is made incident, an optical receiver photoelectric-converting light modulated by a vibration of a weight and a movable coil arranged in the vibration probe to output the light as an electrical signal, a processor processing the electrical signal to output a state of the vibration as an output voltage value, a velocity pickup converting a velocity of the weight and the movable coil arising from the vibration of the weight and the movable coil into an electrical current, a solenoidal coil generating a magnetic field by the electrical current, and a magnetic field sensor attenuating an amount of light guided to the vibration probe according to an intensity of the magnetic field.

Abstract: Provided is a photoacoustic apparatus capable of recognizing light quantity unevenness, which occurs on a surface of an analyte, and decreasing image unevenness resulted from the light quantity unevenness. A photoacoustic apparatus includes a light source configured to irradiate an analyte with light; an optical system configured to guide the light from the light source to the analyte; a detecting unit including a receiving element configured to receive an acoustic wave generated in the analyte by the light; a signal processing unit configured to acquire information about the inside of the analyte from a detected signal acquired from the detecting unit; an optical absorber configured to absorb the light from the light source; and a calculation unit configured to calculate an irradiation intensity distribution of the light on the basis of a detected signal acquired when the receiving element receives the acoustic wave generated from the optical absorber.

Abstract: An optical detection system for monitoring a pipeline. The optical detection system includes a host node in the vicinity of or remote from, a pipeline to be monitored. The optical detection system includes (a) an optical source for generating optical signals, and (b) an optical receiver.

Abstract: Methods and systems used to perform sweep-free stimulated Brillouin scattering-based fiber optical sensing are described. In one aspect, a method includes interrogating different parts of a Brillouin gain spectrum using multiple optical tones in an optical fiber. The interrogating includes sending at least two pump tones into the optical fiber from one end of the optical fiber, such that a frequency spacing between the pump tones is larger than a width of the Brillouin gain spectrum. The interrogating also includes sending at least two probe tones into the optical fiber from another end of the optical fiber, such that a frequency spacing between the probe tones is different from the frequency spacing between the pump tones. The method further includes generating a sensing output based on the interrogating.

Abstract: A vibration detection apparatus for, for example, ultrasound/AE, with Fiber Bragg Grating (FBG), is used for elastic wave detection generated by a material impact and ultrasonic defect detection. Disadvantageously, the apparatus cannot detect ultrasound and has degraded performance at variable temperatures and strains. In response, a highly sensitive, small and light vibration detection apparatus is provided. FBG reflection light is lased by using a fiber laser. The intensity of the lased reflection light from the FBG is converted into an electrical signal. Thus, the ultrasound vibration or the like is detected. A vibration detection system includes an optical amplifier 42, an optical circulator 43, and an optical coupler 45. An FBG 44 and an entry/exit port of the optical circulator are connected by an optical fiber. The optical coupler and the optical amplifier are inserted between an entry port and an exit port of the optical circulator. The entry port and the exit port are connected by an optical fiber.

Abstract: An apparatus and a method that achieve physical separation of sound sources by pointing directly a beam of coherent electromagnetic waves (i.e. laser). Analyzing the physical properties of a beam reflected from the vibrations generating sound source enable the reconstruction of the sound signal generated by the sound source, eliminating the noise component added to the original sound signal. In addition, the use of multiple electromagnetic waves beams or a beam that rapidly skips from one sound source to another allows the physical separation of these sound sources. Aiming each beam to a different sound source ensures the independence of the sound signals sources and therefore provides full sources separation.

Abstract: A gyroscope sensor includes a gyro disk. A first light source is configured to provide a first light beam. A first light receiver is configured to receive the first light beam for sensing a vibration at a first direction of the gyro disk. A second light source is configured to provide a second light beam substantially parallel with the first light beam. A second light receiver is configured to receive the second light beam for sensing a vibration in a second direction of the gyro disk. The second direction is different from the first direction.

Abstract: A measuring apparatus includes: laser sources; and a control unit for outputting an excitation start signal that instructs the laser light sources to start excitation, and outputting an oscillation start signal to instruct the laser light sources to start oscillation after a predetermined time has elapsed from the output of the excitation start signal, so as to generate pulsed light from the laser light sources. The laser sources include a first laser source and a second laser source of which preparation time from the start of the excitation to the generation of the pulsed light is longer than that of the first laser source. The control unit sets timing to output the excitation start signal to the first laser source to follow timing to output the excitation start signal to the second laser source according to a difference of the preparation time between the first and second laser sources.

Abstract: The present invention employs a photoacoustic measuring apparatus including: a laser light source; a forming unit for forming a second light beam by dividing or deforming a laser light beam; an optical member for guiding the second light beam to the surface of a subject; a probe for obtaining a photoacoustic wave generated when the subject is irradiated with the second light beam; and a buffering member that contacts the surface of the subject and transmits light, wherein the optical member overlaps areas of the second light beam having a small light intensity on the surface of the subject, the probe and the optical member are positioned on an identical side of the buffering member relative to the subject, and the optical member refracts the second light beam such that the second light beam enters the subject through the buffering member while avoiding the probe.

Abstract: An acoustic sensor includes at least one photonic crystal structure and an optical fiber in optical communication with the at least one photonic crystal structure. The at least one photonic crystal structure has at least one optical resonance with a resonance frequency and a resonance lineshape, wherein at least one of the resonance frequency and the resonance lineshape is responsive to acoustic waves incident upon the acoustic sensor. The acoustic sensor further includes an optical fiber in optical communication with the at least one photonic crystal structure. The optical fiber is configured to transmit light which impinges the at least one photonic crystal structure and to receive at least a portion of the light which impinges the at least one photonic crystal structure.

Abstract: A system for imposing and analyzing surface acoustic waves in a substrate to determine characteristics of the substrate is disclosed. Optical elements and arrangements for imposing and analyzing surface acoustic waves in a substrate are also disclosed. NSOM's, gratings, and nanolight elements may be used to impose surface acoustic waves in a substrate and may also be used to measure transient changes in the substrate due to the passage of surface acoustic waves therethrough.

Abstract: The present invention relates to distributed acoustic sensing using fiber-optic system. More particularly, the present invention describes use of frequency pulse labeling techniques and wavelength pulse labeling techniques for providing high bandwidth acoustic sensing in applications such as infrastructure monitoring. In one embodiment, a segmented sensing fiber is used with corresponding circulators in an architecture that controls the interrogation of each segment of the fiber. In another embodiment, a single continuous length of sensing fiber is used, but a plurality of pulse sequences with different wavelengths are used to interrogate. In both configurations, heterodyne beat frequency components are rejected by a processing scheme, resulting in a simple direct measurement of baseband phase information.

Abstract: A laser ultrasonic device is disclosed. The laser ultrasonic device comprises an ultrasonic generation system capable of generating ultrasonic waves on a surface of a sample, said system comprising a first collection of optical fiber output ends arranged in a first pattern.

Abstract: A method and system are provided for inspecting a surface of an object with an optical scanner and a laser vibrometer. The method includes the steps of: (a) mapping at least a portion of the object surface using the optical scanner; (b) projecting a beam of light from the laser vibrometer onto the object surface at a measurement point; (c) locating the measurement point relative to the object surface using the optical scanner; and (d) measuring a position of the object surface using the laser vibrometer to determine, for example, a deflection of the object surface.

Abstract: An apparatus and a method that achieve physical separation of sound sources by pointing directly a beam of coherent electromagnetic waves (i.e. laser). Analyzing the physical properties of a beam reflected from the vibrations generating sound source enable the reconstruction of the sound signal generated by the sound source, eliminating the noise component added to the original sound signal. In addition, the use of multiple electromagnetic waves beams or a beam that rapidly skips from one sound source to another allows the physical separation of these sound sources. Aiming each beam to a different sound source ensures the independence of the sound signals sources and therefore provides full sources separation.

Abstract: An optical probe comprising an elongate hollow body having an internal chamber for receiving an optical sensor and/or an light emission device, such as one or more optical fibres, an optical window being provided at a first end of the hollow body, said optical window defining a wall of said internal chamber for transmitting light therethrough, and an ultrasonic transducer provided at a second end of the elongate body opposite said first end for cleaning said optical window via ultrasonic vibrations, wherein said ultrasonic transducer is provided with an entry aperture extending through the ultrasonic transducer, through which entry aperture optical fibres, cables or wires may pass to enter said internal chamber.

Abstract: The spatial resolution of a fiber optical Distributed Acoustic Sensing (DAS) assembly is enhanced by: arranging an optical DAS fiber (1) with a series of contiguous channels (C1-C14) that are sensitive to vibration in a U-shaped loop (U1) such that substantially parallel fiber sections (IA, IB) comprise pairs of channels (C1&C14, C2&C13,C3&C12 . . . etc) that are arranged at least partially side by side; transmitting a series of light pulses (5A, 5B) through the optical fiber (1) and receiving back reflections (6A, 6B) of said light pulses (5A, 5B) by a light transmission and receiving assembly (7); and processing the received back reflections (6A, 6B) such that back reflections stemming from at least one pair of channels (C1, C14; C2,C13) that are arranged at least partially side by side are correlated to each other.

Abstract: A fiber optic acoustic sensor system. The fiber optic acoustic sensor system includes an optical source, and a fiber optic acoustic sensor array configured to receive an optical signal from the optical source. The fiber optic acoustic sensor array includes a core, a first polymer layer disposed on the core, an optical fiber wound around the first polymer layer, and a second polymer layer disposed on the first polymer layer such that the optical fiber is between the first polymer layer and the second polymer layer.

Abstract: Fibre optic cables with improved performance for use in distributed sensing, for instance in distributed acoustic sensors, are disclosed. In one embodiment a fibre optic cable (210) comprises a core (208) and cladding (206) disposed within a buffer material (202) and surrounded by a jacket (204) and arranged so that the core is offset from the centre of the cable. By offsetting the core from the centre of the jacket any bending effects on the core can be maximised compared with the core being located at the centre of the cable.

Abstract: A method and a device for spectroscopic detection of molecules, containing a resonance body, an apparatus for identifying a vibration of the resonance body and at least one laser light source, the laser light of which interacts with the molecules to be detected and which is designed to emit light pulses with a duration of less than 200 fs, the device also containing apparatus for pulse shaping the light pulses emitted by the laser light source by modulating the amplitude and/or the phase, to generate sequentially different pulse shapes of the light pulses.

Abstract: A sensor includes a housing adapted to be secured to a component within a system to be monitored by the sensor, an optical fiber, and a membrane spring assembly. The optical fiber includes a sensing portion containing a fiber Bragg grating that is able to undergo expansion and contraction resulting from movement of the optical fiber at a second location relative to a first location. The membrane spring assembly includes a membrane disc, wherein movement of a central portion thereof causes corresponding displacement of the optical fiber at the second location to cause expansion and contraction of the sensing portion of the optical fiber containing the fiber Bragg grating, which expansion and contraction effects a change in a light wavelength reflected by the fiber Bragg grating. The light wavelength reflected by the fiber Bragg grating can be used to measure movement of the central portion of the membrane disc.

Abstract: An ultrasonic probe for optical detection of ultrasonic waves includes a membrane integrated into the probe for contact with a body, the membrane being excited to vibration by reflected ultrasonic waves, leading to a change in optical path length of a beam of light directed at the membrane, which change is determined interferometrically.

Abstract: A rig for studying a component has a component support for mounting the component. A speaker applies sound energy to airfoils in the component. A vibrometer studies the effect of the applied sound on the airfoils. At least two of the vibrometer, the component support, and the speaker are rotatable relative to each other. In a separate feature, a vibrometer for studying the effect of sound energy on airfoils in a component is provided with a vision system. The vision system is operable to identify the exact location at which the laser is studying the effect on the airfoil. Methods are also disclosed.

Abstract: An apparatus and method for testing composite structures in which ultrasonic waves are used to detect disbonds in the structures are described. The apparatus comprises a flexible structure carrying acousto-optical transducers such as fiber Bragg gratings. During use, the apparatus is mechanically and conformally coupled to the structure under test.

Abstract: A kit for detecting the presence of an explosive includes a pulsed focused energy source located at a target distance away from a substrate, the energy having a magnitude sufficient to release the internal energy of an explosive if present on the substrate and thereby generate an acoustic wave. The kit also includes a detector adapted to detect the acoustic wave at a detection distance away from the substrate.

Abstract: An acoustic sensor includes at least one photonic crystal structure and an optical fiber in optical communication with the at least one photonic crystal structure. The at least one photonic crystal structure has at least one optical resonance with a resonance frequency and a resonance lineshape, wherein at least one of the resonance frequency and the resonance lineshape is responsive to acoustic waves incident upon the acoustic sensor. The acoustic sensor further includes an optical fiber in optical communication with the at least one photonic crystal structure. The optical fiber is configured to transmit light which impinges the at least one photonic crystal structure and to receive at least a portion of the light which impinges the at least one photonic crystal structure.

Abstract: A liquid delivery apparatus is provided for depositing liquid materials onto prescribed areas. The apparatus includes a sensing and delivery pin and a photo sensor. The apparatus is sized to deliver a droplet of liquid material to the surface of a target area without coming into contact with the target surface. The apparatus is also capable of drawing geometric features, such as lines and grids of liquid material. The photo sensor measures the intensity of light during a processing cycle. Measured reflected-light intensity can be compared in real-time to a reference curve which is based on test process cycles representing the light intensity expected when the process proceeds in the preferred fashion to produce a normal spot having an expected droplet size. The light intensity measurements can also be fitted with a mathematical function such as an asymmetric double sigmoidal curve.

Abstract: A device of testing a vibrating device includes a housing, a connector, an indicator, and a vibrating sensing apparatus. The connector, the indicator, and the vibrating sensing apparatus are mounted with the housing, and electronically connected in series. When the test device is vibrated by a portable electronic device received in the housing, the vibrating sensing apparatus forms a closed circuit with the connector and the indicator to activate the indicator to indicate whether the vibrating performance of the portable electronic device is normal or not.

Abstract: The invention relates to a device for a spatially-resolved measurement of mechanical parameters, in particular mechanical vibrations, comprising at least one optical fiber (3) for measuring at least one mechanical parameter with spatial resolution, at least one laser light source (1), the light from which can be coupled into the optical fiber (3), wherein in the optical fiber (3), backscattered portions of the light generated by the laser light source (1) can be coupled out of the optical fiber (3), tuning means (2) that can tune the laser light source (1) within a time period of less than 50 ms, detection means that can detect the portions of the backscattered light that are coupled out of the optical fiber (3), and analysis means that can determine at least one mechanical parameter of the optical fiber (3) in a spatially-resolved manner from the captured portions of the backscattered light.

Abstract: An acoustic wave measuring apparatus includes a light source for radiating a light having a wavelength component in wavelength areas, light filters arranged in a light path from the light source to a subject and each to shut off or transmit the light in one of the wavelength areas, a detector for detecting an acoustic wave generated by the radiation, a controller for generating conditions having different combinations of the wavelength components contained in the light, and a signal processor for calculating an optical absorption coefficient of the subject for the light in each wavelength area based on a pressure of the acoustic wave detected under each of the conditions and a strength of the radiated light for each wavelength area under conditions.

Abstract: Methods and apparatus for sensing fluid flow within a conduit using a Distributed Acoustic Sensing (DAS) system. The DAS system may lower production costs and may offer some technical advantages over fiber Bragg grating (FBG)-based flowmeters such as auxiliary measurement of strain from the wellhead down to the flowmeter. The DAS system may also simplify multiplexing multiple flowmeters on a single fiber.

Abstract: This invention relates to the fibre optic distributed acoustic sensing to detect P and S waves in a solid medium. Distributed acoustic sensing can be achieved using an unmodified fibre optic by launching optical pulses into the fibre and detecting radiation which is Rayleigh backscattered there from. By analysing the returns in analysis bins, acoustic disturbances can be detected in a plurality of discrete longitudinal sections of the fibre. The present invention extends such fibre distributed acoustic sensing to detection of S and P waves.

Abstract: Method and apparatus for noise reduction in ultrasound detection with the steps of: an optical interferometer having a reference arm and a signal arm that includes a polarization-maintaining probing fiber having a reflective coating at a distal end, a way to couple the probing fiber to ultrasound, a way to generate two output beams from the interferometer, a device to modulate the polarization state of the light in the probing fiber, and a detection mechanism responsive to the ultrasonic signals at the distal tip of the probing fiber.

Abstract: An acoustic sensor includes at least one structure including at least one photonic crystal slab and an optical fiber optically coupled to the at least one photonic crystal slab, and having at least one optical resonance with a resonance frequency and a resonance lineshape. The acoustic sensor further includes a housing mechanically coupled to the at least one structure. At least one of the resonance frequency and the resonance lineshape is responsive to acoustic waves incident upon the housing.

Abstract: According to one embodiment, a system for measuring vibration includes multiple spatially separated detectors coupled to a differential signal analyzer and a light source. The light source generates a coherent light beam onto a target that is reflected as backscattered light. The differential signal analyzer receives signals from each of the detectors indicative of backscattered light from the target. The differential signal analyzer then applies a phase shift to a subset of the received signals and combines the phase shifted signals with signals from other detectors to form a differential signal representative of physical vibration of the target.

Abstract: The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

Abstract: An interferometer includes a cavity including a pair of mirrors defining a cavity length. An input beam and a counter-propagating reference beam are directed into the cavity. The interferometer generates a feedback control signal and an ultrasound signal for optimal performance and measurement of a target, respectively.

Abstract: In a schlieren optical system, a laser beam is passed through the jet flow and the ambient around the jet flow, and a high speed sampling is performed using a high speed photo sensor while displacing measurement points. The value obtained by sampling represents a result of the optical path caused curved by a density gradient generated in an arc-shape from the center of the jet flow. The value is subjected to a high speed discrete Fourier transform and decomposed into frequency components which constitute the noise. Thereafter, Abel inversion is performed on data belonging to a particular frequency to obtain a density gradient in the radial direction from the center of the jet flow. The obtained density gradient is visualized in a graph display, so that the position of the sound source and the state of the jet flow can be accurately grasped.