Abstract: In an embodiment, an edge extraction method includes: emitting, toward an object, an electromagnetic wave polarized only in one direction perpendicular to a propagation direction; receiving a transmitted electromagnetic wave that has been transmitted through the object, using a receiving antenna; calculating an intensity in the propagation direction of the transmitted electromagnetic wave based on an intensity of the transmitted electromagnetic wave received by the receiving antenna; and obtaining a spatial distribution of the intensity in the propagation direction of the transmitted electromagnetic wave.

Abstract: Techniques of measuring vibrations from an object surface using LIDAR includes grouping beams having similar vibration velocity values over a specified time window and replace outlier vibration velocity values with a vibration velocity value based on the similar vibration velocity values over the specified time window. Advantageously, replacing outlier vibration velocity values with a value based on vibration velocity values of similar beams results in a more accurate profile of the vibration velocity field over the surface.

Abstract: Methods, systems, and apparatuses are disclosed for non-destructively inspecting a substrate by measuring the Doppler effect in sound waves comprising wide bandwidth ultrasound wavelengths generated from a piezoelectric polymer coating material with the sound waves read by a laser in communication with a Doppler velocity meter.

Abstract: Systems and methods are provided for performing OCT vibrography based on the synchronization of components of the OCT vibrography system. An A-scan trigger is employed to synchronize the operation of the scanning subsystem that scans the sample beam and an acoustic stimulus source that generates an acoustic stimulus for vibrographic measurements. The acoustic stimulus source is controlled such that when the scanning subsystem dwells on an imaging line selected for vibrography measurements, the acoustic stimulus is generated over a plurality of A-scans and the phase of the acoustic stimulus is locked to the A-scan trigger, such that the phase of the acoustic stimulus is incrementally modified with each A-scan. The accumulation of the acoustic phase is therefore synchronized to the A-scan trigger. The synchronization, providing synchronized acoustic phase evolution during each acoustic phase waveform cycle, permits the use of the OCT vibrography system for simultaneous anatomical and functional imaging.

Abstract: A vibration measurement system comprises an image capturing apparatus, a distance measuring apparatus, a sensor that outputs a signal according to an inclination of the image capturing apparatus relative to the vertical direction, and a vibration measurement apparatus. The vibration measurement apparatus includes calculating an angle formed by the normal of an image capturing surface of the image capturing apparatus and the normal of the measurement target surface that the image capturing apparatus shoots, based on the signal output by the sensor, converting the image obtained that the image capturing apparatus shoots into an image that would be obtained were the normal of the measurement target surface coincident with the normal of the image capturing surface of the image capturing apparatus, using the calculated angle, and measuring vibration of the structure, using the converted image and the measured distance from the image capturing apparatus to the measurement target surface.

Abstract: In a photoacoustic measurement probe including an acoustic wave detector and an amplifier for amplifying a detection signal of a photoacoustic wave and a probe unit and a photoacoustic measurement apparatus having such a probe, heat is efficiently dissipated from the probe. In a probe having an acoustic wave detector and an amplifier, there are provided a first heat conductive member that is in contact with a part of a side plate of a housing and the amplifier to transfer heat generated by the amplifier to the side plate and a second heat conductive member that is in contact with a part different from the part of the side plate and the acoustic wave detector to transfer heat generated by the acoustic wave detector to the side plate.

Abstract: This disclosure is related to devices, systems, and techniques for determining, using an electro-opto-mechanical accelerometer system, a frequency value in order to determine an acceleration value. For example, an accelerometer system includes a light-emitting device configured to emit an optical signal and a circuit. The circuit is configured to determine a frequency value corresponding to the optical signal and determine an acceleration value based on the frequency value. Additionally, the accelerometer system includes a housing that encloses the light-emitting device, the circuit, and Helium gas, where the Helium gas defines a partial pressure within a range between 0.1 torr and 760 torr.

Abstract: Systems and methods are provided for performing OCT vibrography based on the synchronization of components of the OCT vibrography system. An A-scan trigger is employed to synchronize the operation of the scanning subsystem that scans the sample beam and an acoustic stimulus source that generates an acoustic stimulus for vibrographic measurements. The acoustic stimulus source is controlled such that when the scanning subsystem dwells on an imaging line selected for vibrography measurements, the acoustic stimulus is generated over a plurality of A-scans and the phase of the acoustic stimulus is locked to the A-scan trigger, such that the phase of the acoustic stimulus is incrementally modified with each A-scan. The accumulation of the acoustic phase is therefore synchronized to the A-scan trigger. The synchronization, providing synchronized acoustic phase evolution during each acoustic phase waveform cycle, permits the use of the OCT vibrography system for simultaneous anatomical and functional imaging.

Abstract: An interferometric vibration observation device includes a transmitting unit, a receiving unit and a signal processing unit. The transmitting unit transmits a transmission signal toward an observation object. The receiving unit receives a reflection wave from the observation object with a plurality of receiving antennas and generates a reception signal for each of the receiving antennas. The signal processing unit obtains a phase plane of the reflection wave to an antenna plane from a phase difference between the reception signals, identifies an arrival direction and a signal strength of the reflection wave, calculates a phase variation of the reflection wave from a certain direction, and generates an observation signal representative of a vibration of the observation object or a certain site of the observation object.

Abstract: Systems and methods are provided, which use at least two coherent light sources with known phase relations between them, which are configured to illuminate a target with at least two corresponding spots, an optical unit comprising a mask and configured to focus, onto a sensor, interfered scattered illumination from the spots of the target, passing through the mask, to yield a signal, at least one shifter configured to shift a frequency of at least one of the coherent light sources to provide a carrier frequency in the signal, and a processing unit configured to derive a vibration frequency of the target from the sensor signal with respect to the carrier frequency. The vibration frequency of the target is separated from the carrier frequency and speckle disturbances may be attenuated or avoided.

Abstract: A system and method are disclosed for interrogating a liquid in a container. In one embodiment, methods are provided to interrogate and identify a container material type and a liquid within a container.

Abstract: A system and method are disclosed for interrogating a liquid in a container. In one embodiment, methods are provided to interrogate and identify a container material type and a liquid within a container.

Abstract: A system and method for noncontact ultrasound imagery capable of generating images in a manner that is safer for eyes and skin is provided. A photoacoustic excitation source may be employed to direct light signals with wavelengths of 1400-1600 nanometers into the patient to generate acoustic disturbances that induce propagating photoacoustic waves. The acoustic disturbances may be translated in defined directions to cause coherent summation of the propagating photoacoustic waves and, thereby, generate a resultant acoustic and/or elastic wave to probe structures within the patient. Vibrations created by the scatter of the resultant wave are detected at the surface of the patient and ultrasound images of the structures within the patient may be generated. Detection of the vibrations may be performed using a laser vibrometer. The excitation and detection systems may be used separately or in combination. Ultrasound images can be generated without physically contacting the patient.

Abstract: Provided is a transmitter which can maximize the efficiency of rectification in a power-receiving electronic device irrespective of the distance therebetween. The transmitter transmits electric power to the electronic device through use of a microwave. The electronic device receives the microwave, converts the microwave to DC power, and uses the DC power as operation power.

Abstract: A flow rate measurement device of the present invention includes a flow rate signal detection unit for detecting a flow rate signal of a fluid to be measured flowing through flow path, flow rate calculation unit for calculating a flow rate from the flow rate signal detected by the flow rate signal detection unit, and oscillation circuit for generating a reference clock. Furthermore, the flow rate measurement device includes temperature calculation unit for calculating a temperature from a frequency change resulting from a temperature change of oscillation circuit, and flow rate correction unit for correcting the flow rate calculated by the flow rate calculation unit by obtaining an offset flow rate at a desired temperature based on the temperature calculated by temperature calculation unit. Thus, accuracy of flow rate measurement can be improved.

Abstract: A system for aerially surveying an area where a plane may have crashed in water and locating pings from the plane's black box using a laser on an aerial platform that produces laser pulses; using a launch telescope to direct the laser pulses to the water producing scattering from the laser pulses and a continuous stream of backscatter; using a receiving telescope to collect the continuous stream of backscatter; using an interferometer operatively connected to the receiving telescope to produce two outputs, wherein one output is the continuous stream of backscatter, and wherein the other output is a delayed replica of the first output; and using a data collection and analysis unit operatively connected to the interferometer to produce a measurement of the sound.

Abstract: A method for generating vibration and measuring vibration properties of a structure, such as information equipment, micro-electrco/mechanical systems, and large-equipment, using a non-contact type laser excitation in a non-contact type vibration property measurement system.

Abstract: A laser beam having a single wavelength emitted from a laser light source is converted at a wavelength shifter into a laser beam having at least two wavelengths, which is further demultiplexed at a beam splitter into a laser beam having a first wavelength and a laser beam having a second wavelength. The output power and pulse width of the laser beam having the first wavelength are adjusted by a first controller so as to reach levels appropriate for generating ultrasonic vibrations without causing damage to an inspection object. The output power and pulse width of the laser beam having the second wavelength are adjusted by a second controller so as to reach appropriate levels for detecting the above-described ultrasonic vibrations. These laser beams are multiplexed by a multiplexer into a single laser beam to be focused onto a surface of the inspection object.

Abstract: An apparatus for testing a test specimen, the apparatus comprising a first fixture comprising a first mounting filament tensionably secured thereto, a second fixture comprising a second mounting filament tensionably secured thereto, and a vibratory energy source adapted to apply vibrational energy to the test specimen. In use the test specimen is mounted to the first and second mounting filaments so that each of the first and second mounting filaments is aligned with a nodal line on the test specimen.

Abstract: A motion/vibration detection system and method therefore are provided. The system includes a transmitter and a receiver. The transmitter includes a transmit/receive antenna unit and a first oscillator. The receiver includes a receiving unit and a demodulation unit. The transmit/receive antenna unit receives an output signal from the first oscillator and transmits a detection signal. The detection signal is reflected from at least one object under detection into a reflected detection signal, which is received by the transmit/receive antenna unit. The transmit/receive antenna unit injects the reflected detection signal into the first oscillator and accordingly the first oscillator is under a self-injection locking mode. The receiving unit receives the detection signal. The demodulation unit demodulates the detection signal received by the receiving unit into a baseband output signal, to extract at least one motion/vibration information of the objection under detection.

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: An imaging apparatus for generating photoacoustic images and ultrasound images that is capable of generating both types of images with high resolution is provided. An ultrasound probe includes a plurality of probe elements. A first phase matching adding section reads out photoacoustic signals from a photoacoustic element data memory, and administers phase matching addition within a first phase matching range. An image processing section generates a photoacoustic image based on phase matched and added data. A second phase matching adding section administers phase matching addition on reflected acoustic signals sampled by a signal obtaining section within a second phase matching range. An image processing section generates an ultrasound image based on phase matched and added data. The first phase matching range is greater than the second phase matching range.

Abstract: A laser vibrometer makes non-contact measurements of vibrations of a target. A laser produces a laser beam, and a beamsplitter splits the laser beam into a reference beam and a first target beam. A first frequency shifter/splitter splits the first target beam into a pair of target beams each having a frequency different than a frequency of the other target beams. The target beams are reflected from the target to a detector, and the reference beam is combined with the target beams such that the detector receives the target beams and reference beam together.

Abstract: Disclosed herein are a system and method for three-dimensional vibration measurement. The method includes measuring vibration components and shape information at a vibration measurement point of a measurement target by sequentially emitting laser beams to the vibration measurement point of the measurement target at each of three measuring positions for measuring vibration of the measurement target; obtaining transformation matrices between first to third coordinate systems with respect to each of the measuring positions and a local coordinate system with respect to the vibration measurement point of the measurement target, based on the shape information; measuring angles between unit vectors of respective axes of the local coordinate system and direction vectors of the laser beams emitted with reference to the first to third coordinate systems upon measuring the vibration components; and measuring three-dimensional vibration of the measurement target based on the vibration components and the angles.

Abstract: An acoustic-wave sensor (10) is constructed by a membrane (11) adapted to be displaced by an acoustic wave, a first waveguide (16a) for transmitting light therein, an optical coupling part (15) to which the light transmitted through the first waveguide (16a) is adapted to be optically coupled, and a second waveguide (16b) through which the light coupled from the optical coupling part (15) transmits. When the membrane (11) is displaced by its reception of the acoustic wave, at least one of an optical coupling coefficient between the first waveguide (16a) and the optical resonator (15) and an optical coupling coefficient between the second waveguide (16b) and the optical resonator (15) is changed to output a corresponding optical signal.

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: In accordance with various aspects of the disclosure, a method and apparatus is disclosed for optically resolving one or more vibrating objects at an unknown distance using a vibrometer. The vibrometer includes a processor, a memory, and an optical device including a transmitter and a receiver. The method includes transmitting a first optical waveform having a linear frequency modulated chirp from the transmitter towards a region of space. At the receiver, a second optical waveform reflected from the one or more vibrating objects in the region of space is received. The vibrometer determines both a vibration frequency and a range information associated with the one or more vibrating objects based upon one or more characteristics of the second optical waveform. The determined vibration frequency and range information are stored in the memory for processing by the processor.

Abstract: A laser vibrometer makes non-contact measurements of vibrations of a target. A laser produces a laser beam, and a beamsplitter splits the laser beam into a reference beam and a first target beam. A first frequency shifter/splitter splits the first target beam into a pair of target beams each having a frequency different than a frequency of the other target beams. The target beams are reflected from the target to a detector, and the reference beam is combined with the target beams such that the detector receives the target beams and reference beam together.

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: 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 photoacoustic imaging system comprising a coded laser emitting apparatus and a photoacoustic signal receiving apparatus is provided. The coded laser emitting apparatus comprises an encoding unit, a signal generating unit and a laser light source. The encoding unit is used for generating a coded signal. The signal generating unit is used for generating a modulated signal according to the coded signal. The laser light source is used for generating a laser pulse having a specific coded waveform according to the modulated signal. The photoacoustic signal receiving apparatus comprises a photoacoustic signal receiving unit and a decoding unit. The photoacoustic signal receiving unit is used for receiving a photoacoustic signal generated by an object having received the laser pulse and converts the photoacoustic signal into an electrical signal.

Abstract: An acoustic field in a body of water is monitored using a coherent light field emitter applying a distributed light field across the surface of the water to be reflected, and a sensor is used to sense reflected components of the light field above the surface and to provide a signal representing information in the reflected light and related to movements in the water and caused by the acoustic field. The signal is provided from an interferometry technique and useable to derive information on the underwater acoustic field in a useful form.

Abstract: A laser vibration sensor, system and method of vibration sensing employ a nanostructured resonance interactor. The sensor includes a resonator cavity of a laser and the nanostructured resonance interactor. The resonator cavity has a resonance deterministic of a characteristic of an output signal of the laser. The nanostructured resonance interactor modulates the resonance of the resonator cavity in response to a vibration. A change in the output signal characteristic induced by a resonance modulation is representative of the vibration. The system further includes an output signal detector. The method includes modulating a resonance characteristic of the resonator cavity using a nanostructure that responds to the vibration being sensed.

Abstract: A surface acoustic wave sensor detects a mass load on a resonator-type surface acoustic wave filter on the basis of a change in frequency and includes an IDT electrode arranged on a piezoelectric substrate to excite surface waves, an insulating film arranged so as to cover the IDT electrode, and a reaction film which is disposed on the insulating film and which reacts with a target substance to be detected or a binding substance that binds to a target substance to be detected. The reaction film is composed of a metal or a metal oxide.

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: A mid infrared range laser source for ultrasound inspection having a high energy laser coupled with one or more harmonic generation devices. The high energy laser may be a CO2 laser and tuned to emit laser light at a single wavelength. The harmonic generation devices convert the laser beam into the mid infrared range for optimal ultrasound inspection.

Abstract: An imaging apparatus for generating photoacoustic images and ultrasound images that is capable of generating both types of images with high resolution is provided. An ultrasound probe includes a plurality of probe elements. A first phase matching adding section reads out photoacoustic signals from a photoacoustic element data memory, and administers phase matching addition within a first phase matching range. An image processing section generates a photoacoustic image based on phase matched and added data. A second phase matching adding section administers phase matching addition on reflected acoustic signals sampled by a signal obtaining section within a second phase matching range. An image processing section generates an ultrasound image based on phase matched and added data. The first phase matching range is greater than the second phase matching range.

Abstract: A surface acoustic wave (“SAW”) sensor includes; a first signal generator which generates a first signal having a predetermined frequency bandwidth using a pseudo random sequence, a second signal generator which generates a second signal with a predetermined frequency, a signal blender which blends the first signal with the second signal to generate a blended signal having the predetermined frequency bandwidth with the predetermined frequency as a center frequency, a wave generator which generates a surface acoustic wave using the blended signal, which converts the surface acoustic wave into a third signal after the surface acoustic wave travels a predetermined distance, and which outputs the third signal, and a signal detector which detects a change in the third signal from the wave generator to sense a substance bound to the wave generator.

Abstract: A method for determining the topography of a static surface (305) of an object (301) comprises the steps of: (a) selecting a region (301a) on the static surface (305) of the object (301); (b) directing an incident monochromatic electromagnetic wave (302) onto the region (301a) while the surface (305) and the incident monochromatic electromagnetic wave (302) are moved relative to one another, the incident monochromatic electromagnetic wave (302) being characterised by a frequency f0, an amplitude A0 and a propagation direction, the direction of movement (304) being substantially not parallel to the propagation direction of the incident monochromatic electromagnetic wave (302), wherein the surface (305) reflects the incident monochromatic electromagnetic wave (302) thus generating a reflected monochromatic electromagnetic wave (303), the movement (304) being characterized by a movement frequency (F) and a movement amplitude (A); (c) determining properties of the monochromatic electromagnetic wave (303) reflecte

Abstract: An optical sound detection system including: a laser source to generate a laser beam; an optical fiber; an optical sensor aligned to detect a detected portion of a diffraction pattern formed by the laser light emitted from the output coupling port of the optical fiber; and a signal processor to process the signal produced by the optical sensor. The optical fiber includes: a core that includes a photoelastically active material; an input coupling port optically coupled to the laser source to couple the laser beam into the core of the optical fiber; and an output coupling port from which the laser light is emitted after propagating through the core. The optical sensor is adapted to produce a signal corresponding to the detected portion of the diffraction pattern.

Abstract: A technique for acoustic detection of a disbond within a bonded structure involves thermal excitation of the surface of the bonded structure to induce a lifting and membrane vibration and is applicable to laminates and coated structures, as well as foam core structures or a honeycomb structures. The technique does not require access to both sides of the bonded structure. A large etendue interferometer is used to provide surface displacement measurement. The surface displacement measurement can be analyzed both by frequency or amplitude to determine existence of a disbond by membrane vibration, and further a thickness of the disbond can be determined using traditional pulse-echo time analysis. The technique may allow detection of stick bonds.

Abstract: This disclosure relates in general to a method and system for acoustic monitoring using a fibre optic cable. More specifically, but not by way of limitation, embodiments of the present invention provide for using an optical fiber as a distributed interferometer that may be used to monitor a conduit, wellbore or reservoir. In certain aspects, the distributed interferometric monitoring provides for accurate detection of acoustic occurrences along the fibre optic cable and these acoustic occurrences may include fluid flow in a pipeline or wellbore, processes taking place in a wellbore or pipeline, fracturing, gravel packing, production logging and/or the like.

Abstract: An apparatus and method for non-determination of the surface velocity of a target using optical interference and Doppler shifting of the light reflected from the target are disclosed. It may be used to measure small-amplitude, acoustic frequency surface vibrations as well as non-periodic surface vibration.

Abstract: The present invention relates to an arrangement (1) for detection of a first resonance frequency (F1), related to a mass (1b?) loaded carrier means (1b), and to compare said first resonance frequency (F1) with a second, as a reference used, resonance frequency (F2), related to said carrier means (1b), by using frequency comparing and/or calculating means (3, 4) to evaluate, by a noted frequency shift (F2-F1), a mass weight (1b?). An array of individual carrier means (1a, 1b . . .

Abstract: Method and optical device for measuring the rotation of an object, include a light source emitting a collimated incident light beam, a reflecting plane optical interface to be fastened to the object, and capable of forming a first reflected beam. The device includes a corner reflector fastened to the object, and having reflecting plane faces capable of forming a second reflected beam, a detection system capable of measuring the displacement ?1 of the first reflected beam, and the displacement ?2 of the second reflected beam (16). A processing system calculates, as a function of the measurement of the displacement ?1 and of the distance D1 between the detection system and the reflecting plane optical interface, and of the measurement of the displacement ?2 and of the distance D2 between the detection system and the corner reflector, a measurement of the rotation ? of the object between an initial position and a measurement position.

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: A laser Doppler vibrometer for vibration measurement that employs active feedback to cancel the effect of large vibration excursions at low frequencies, obviating the need to unwrap phase data. The Doppler shift of a reflective vibrating test object is sensed interferometrically and compensated by means of a voltage-controlled oscillator driving an acousto-optic modulator. For frequencies within the servo bandwidth, the feedback signal provides a direct measurement of vibration velocity. For frequencies outside the servo bandwidth, feedback biases the interferometer at a point of maximal sensitivity, thus enabling phase-sensitive measurement of the high-frequency excursions. Using two measurements, one with a low bandwidth and one with a high bandwidth, more than five decades of frequency may be spanned.

Abstract: Disclosed is a method for characterizing a sample having a structure disposed on or within the sample, comprising the steps of applying a first pulse of light to a surface of the sample for creating a propagating strain pulse in the sample, applying a second pulse of light to the surface so that the second pulse of light interacts with the propagating strain pulse in the sample, sensing from a reflection of the second pulse a change in optical response of the sample, and relating a time of occurrence of the change in optical response to at least one dimension of the structure.

Abstract: A system, program product, and method to perform automated three-dimensional image registration of a part within an inspection cell, are provided. The system can include a laser-ultrasound inspection device having a scanning head to generate ultrasonic surface displacements in a part, an inspection laser, and an interferometer to collect phase modulated light reflected by the part. The system can also include a part position locator positioned to measure a distance between points on a surface of the part and a scanning laser reference location. The system can also include a database containing computer-aided design models for each part of interest, and a model of the inspection cell. The system can further include a laser ultrasound inspection computer communication with the laser-ultrasound detection device and the part position locator, and laser ultrasound inspection program product adapted to perform automated three-dimensional image registration of the part.

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.