Abstract: The present invention relates to a method and apparatus used to calculate at least one velocity component for a target within the region. The invention employs an energy source which is activated using an activation system in a cyclic pattern with a selected source frequency. A receiver is also employed in conjunction with a shielding system where this shielding system is configured to block the sensing of reflected energy from the target in a cyclic pattern with a selected receiver frequency. The invention operates through measuring a frequency change in the source frequency of the energy source signal when received by the receiver and determines a velocity component for a target based on a measured frequency change for a known direction of travel. The invention may also be extended to provide a two or three dimensional velocity vector through the addition of further energy sources.

Abstract: A radar device has a wave projecting part for projecting pulsed electromagnetic waves to a target object in a specified direction at specified time intervals, a wave receiving part for receiving reflected waves reflected by the target object, an intensity measuring part for measuring the intensity of the reflected waves, a distance measuring part for measuring the distance to the target object based on elapsed time from when the pulsed electromagnetic waves are projected until when the reflected waves are received and also serving to determine a maximum reflection point at which the intensity of the received reflected waves is the largest, and a scanning part for varying the direction of the projected electromagnetic waves and the received reflected waves in horizontal and vertical directions respectively within a specified angular scan range.

Abstract: Sensing results from moving objects, e.g. from photosensing emanating light or from impedance-based sensing, can indicate sensed time-varying waveforms with information about objects. For example, a sensed time-varying waveform can be compared with another waveform, such as a reference waveform produced by objects of a certain type, to obtain comparison results indicating motion-independent information about the object; time-scaling can adjust for displacement rate such as speed. Also, a modulation periodicity value can be obtained from a sensed time-varying waveform and used in obtaining information about an object; for example, a periodic modulation frequency can be used with a given time's chirp frequency to obtain phase information about an object's position. Or, where periodic modulation frequency indicates displacement rate, time scaling during comparison can use a scaling factor based on the frequency.

Abstract: A technique for adapting an optical navigation device for navigation on a transparent structure such as a glass plate involves establishing a navigation window for navigation tracking, detecting reflected light within the navigation window, generating an output signal in response to the detected light, and adjusting a characteristic of the navigation window in response to the output signal. An optical navigation device includes an illumination system configured to output light, an image sensor configured to generate an output signal related to a detected portion of the light, and a transparent structure adapter module configured to adjust a navigation window of the image sensor in response to the output signal to adapt the optical navigation device for use directly on an opaque surface or for use on a transparent structure that is located between the optical navigation device and the opaque surface.

Abstract: A traveling system for mobile bodies includes a control device for controlling traveling operation of a first and a second mobile bodies based on detection information provided by a relative distance detecting device mounted on only one of the first and second mobile bodies for detecting a distance to the other of the first and second mobile bodies, a first distance detecting device for detecting a distance between the first mobile body and a first reference position, and a second distance detecting device for detecting a distance between the second mobile body and a second reference position.

Abstract: The object-detection device for vehicle provides a transmission-and-reception device; a reflection point calculation device; a segment setting device; a median point calculation device; and a relative speed calculation device, wherein the relative speed calculation device eliminates a calculation result of the relative speed in the car width direction, with respect to the reflection points calculated based on the electromagnetic waves which are irradiated to the most downward direction in the specified angle in the vertical direction, in case that the number of difference between the reflection points in the current processing and the reflection points in the previous processing is equal to or greater than a predetermined number.

Abstract: A visual sensor for generating an array of binarized feature signals based on a visual field is provided. The visual sensor comprises an array of photoreceptor circuits capable of generating photoreceptor signals based on the visual field, an array of feature detectors capable of generating feature signals based on the photoreceptor signals, and a reconfigurable binary generator array capable of generating binarized feature signals based on the feature signals.

Abstract: A flow velocity detector for detecting a flow velocity of a fluid flowing through a flow passage is provided, the flow velocity detector including a flow passage-forming section which defines the flow passage; a stress light-emitting section which is arranged at the flow passage-forming section to receive a stress having a magnitude depending on the flow velocity of the fluid and which emits a light of which amount corresponds to a change of the received stress; and a light-receiving sensor which receives the light emitted by the stress light-emitting section. The flow velocity of the fluid is detected based on an amount of the light received by the light-receiving sensor to generate a detection signal. Accordingly, the structure is simple and small-sized, and the flow velocity of the fluid can be detected at low cost.

Abstract: A method, operation position sensor device for an electronic musical, and musical instrument for detecting an operation position of an operation member in an electronic musical instrument. A determination is made of an amount of measured light resulting from the depression of the operation member has changed in excess of a predetermined difference value a number of times. A determination is made of a difference value of clock counts measured at a last two determinations that the measured light changed in excess of the predetermined difference value in response to determining that the amount of the measured light has changed in excess of the predetermined difference value the number of times. The difference value is converted to a key depression speed. A sound generation command is issued based on the key depression speed to a sound source.

Abstract: An optical encoder including a sensor module including a light emitting member, a light receiving member opposite to the light emitting member to receive the emitted light, and at least one boss extending in a first direction; a shade member located between the light emitting member and the light receiving member and having a shading pattern; a first support supporting the sensor module and including at least one recessed portion engaged with the boss, and a groove connected with the recessed portion and extending in a second direction, wherein the sensor module is attached to the first support by being moved in the second direction while the boss is guided by the groove, and wherein the recessed portion has a depth greater than the height of the boss, and a portion of the groove adjacent to the recessed portion has a depth less than the height of the boss.

Abstract: An apparatus for measuring a closing velocity of a vehicle door includes a housing, first and second sensors, and a processor. The first sensor is coupled to the housing, has a first detection field, and is configured to generate a first signal when the vehicle door passes through the first detection field. The second sensor is coupled to the housing, has a second detection field, and is configured to generate a second signal when the vehicle door passes through the second detection field. The processor is in operable communication with the first and second sensors and is configured to receive the first and second signals and measure a time period between the receiving of the first and second signals.

Abstract: A system and method uses light signals to detect and display the position of an airborne vehicle, such as a helicopter, during takeoff or landing or low speed, low altitude operation. A transmitter on the vehicle emits light signals while an optical receiver retrieves reflected light signals. Using light detection and ranging techniques, various parameters, such as altitude, ground speed and relative wind, are calculated based on the Doppler shift within the reflected light signals. The signals are transmitted in three different directions to facilitate the measurements of different Doppler shifts. The parameters are also displayed on a screen or other visual device within the vehicle.

Abstract: An apparatus has an optical member having a boundary surface on which light is incident, the optical member being adapted to transmit light entering the boundary surface from one side and to reflect light entering the boundary surface from the other side; a light source that emits light toward the optical member and irradiates light outgoing from the optical member onto a moving body; a camera that photographs via the optical member an image of light reflected from a reflection marker provided on a surface of the moving body; and a computation portion that computes movement information for the moving body based on the image of the light reflected by the reflection marker and photographed by the camera. An outgoing angle of the light outgoing from the boundary surface substantially coincides with an incoming angle at which the light reflected by the reflection marker enters the boundary surface.

Abstract: There is provided a system for forming an optical screen, including a continuous wave or pulsed laser transmitter for transmitting a beam of radiation at a predetermined wavelength and forming a planar or curved surface to be traversed by a moving object, at least one receiver including an array of detectors for receiving reflected or scattered beam radiation from the object and directing it towards the detectors for producing a signal, and a detection logic receiving the signal and determining parameters selected from the group of spatial position, velocity and direction of propulsion of the moving object. A method for detecting a moving object is also provided.

Abstract: A system for observing a field of view including a light transmitter and a light detector. A path is defined between the transmitter and the detector. The light transmitter generates substantially coherent light onto a transmit portion of a light path and the light detector is positioned in a receive portion of the light path defined by reflected light from some of the target locations. The system includes a component for configuring at least a portion of the light path such that a subset of the plurality of potential target points are included in the light path.

Abstract: A device for measuring air turbulence in the surroundings of an aircraft includes a measurement system having lidars which are mounted on the aircraft and which are intended to carry out, during a flight of the aircraft, twelve measurements of aerodynamic velocity in the environment surrounding the aircraft. The measurement system carries out the twelve measurements at four different measurement points, each time according to three predetermined axes. A central unit which, with the aid of the aerodynamic velocity measurements and of a first order predetermined mathematical model describing an aerodynamic velocity field as a function of twelve variables, determines an aerodynamic velocity field which exists in the environment of the aircraft and which is representative of the air turbulence.

Abstract: The present invention discloses a device for observing a flow state comprising a translucent duct. It further comprises an irradiation unit irradiating projection light, a condensing unit condensing the projection light along a length direction with respect to an axial core area of the translucent duct in which a fluid flows; and an image pickup unit for picking up images of scattered reflected light from the axial core area of the translucent duct at a plurality of times.

Abstract: A liquid droplet measurement apparatus has: a first laser light source emitting a laser light; a first optical device which makes, in terms of a beam cross-section of the laser light, a beam width in a direction perpendicular to a direction of ejection of a liquid droplet, greater than a beam width in the direction of ejection of the liquid droplet, and makes light intensity of the laser light fall within a prescribed range within a range where variation in a position of the liquid droplet occurs in the direction perpendicular to the direction of ejection of the liquid droplet, at a position where the laser light from the first laser light source is irradiated onto the liquid droplet ejected; a first light receiving device which receives the laser light that has been irradiated onto the liquid droplet by the first optical device and generates a determination signal; and a first liquid droplet characteristics calculation device which calculates at least one of a volume of the liquid droplet and a velocity of t

Abstract: Devices capable of capturing still and motion imagery are integrated with an accurate distance and speed measuring apparatus. By measuring the changing distance of the target over that time, a target's speed can be determined. At substantially the same time as the target's speed is determined, imagery of the target is captured in both a still and moving format. Using a queuing mechanism for both distance and imagery data along with time stamps associated with each, a target's image, both in motion and still, can be integrated with its speed. In situations in which a still image is unavailable, a target's speed can be associated with a portion of a continuous stream of motion imagery to a point where a positive identification can be captured with a still image.

Abstract: In this multi-beam optical range sensor, since the diffraction grating splits output light of the light-emitting element into a plurality of beams, a plurality of beams can be outputted from the diffraction grating even with one light-emitting element. Therefore, according to this multi-beam optical range sensor, the numbers of the light-emitting elements and the light-emission side lenses can be cut down, the space on the light emission side can be reduced, and the sensor can be downsized. Also according to this range sensor, there is no need for scanning a plurality of light-emitting elements and so the detection time can be shortened.

Abstract: Systems and methods for sensing air outside a moving aircraft are presented. In one embodiment, a system includes a laser for generating laser energy. The system also includes one or more transceivers for projecting the laser energy as laser radiation to the air. Subsequently, each transceiver receives laser energy as it is backscattered from the air. A computer processes signals from the transceivers to distinguish molecular scattered laser radiation from aerosol scattered laser radiation and determines one or more air parameters based on the scattered laser radiation. Such air parameters may include air speed, air pressure, air temperature and aircraft orientation angle, such as yaw, angle of attack and sideslip.

Abstract: One embodiment relates to a method of velocity prediction using a sensor array. Differential signals are obtained from the sensor array at multiple frame rates. A first velocity prediction is determined from the differential signals at a first frame rate, and a second velocity prediction is determined from the differential signals at a second frame rate. Another embodiment relates to an optical navigation apparatus which includes a sensor array, differential circuitry, driver circuitry, and a signal processing device. The driver circuitry is configured to drive the sensor array and differential circuitry so as to operate at multiple frame rates in an interleaved manner. The signal processing device is configured to compute a first velocity prediction from the differential signals at a first frame rate and to compute a second velocity prediction from the differential signals at a second frame rate. Other embodiments and features are also disclosed.

Abstract: A movable-body-speed-detecting apparatus includes a movable body capable of moving linearly and/or circularly, a plate fixed to the movable body, the plate having a predetermined length in a direction in which the movable body moves, and light emission/reception means arranged such that light output from a light-emitting element enters a light-receiving element. The plate has a window section that passes between the light-emitting element and the light-receiving element in accordance with movement of the movable body and that blocks or allows passage of light to the light-receiving element. The apparatus further comprises speed calculation means for calculating the speed of the movable body by converting the amount of light received by the light-receiving element into a signal and measuring the signal.

Abstract: A method and apparatus for calibrating a position of an image sensor, and a method of detecting the position of an image sensor are provided. The method of calibrating the position of an image sensor includes: obtaining first image information corresponding to a first position of the image sensor and obtaining second image information corresponding to a second position of the image sensor, calculating cross-correlation values between the obtained first image information and second image information; determining whether or not the calculated cross-correlation values are symmetrical; setting a driving power value of the image sensor for moving the image sensor the distance between the first position to the second position as a reference driving power value for moving the image sensor one-pixel distance, if it is determined that the cross-correlation values are not symmetrical; and calibrating the position of the image sensor by using the set driving power value.

Abstract: The invention relates to an optical measurement device intended for determining a relative velocity vector {right arrow over (v)} of a carrier, such as an aircraft, with respect to a reference medium MILREF. The device includes an optical signal system EMIREC, delivering an optical signal Sinc that follows a direction called the line of sight LDV and is concentrated in a focusing zone ZOF, and means for displacing the focusing zone ZOF in the reference medium MILREF.

Abstract: An optical encoder including a sensor module including a light emitting member, a light receiving member opposite to the light emitting member to receive the emitted light, and at least one boss extending in a first direction; a shade member located between the light emitting member and the light receiving member and having a shading pattern; a first support supporting the sensor module and including at least one recessed portion engaged with the boss, and a groove connected with the recessed portion and extending in a second direction, wherein the sensor module is attached to the first support by being moved in the second direction while the boss is guided by the groove, and wherein the recessed portion has a depth greater than the height of the boss, and a portion of the groove adjacent to the recessed portion has a depth less than the height of the boss.

Abstract: The invention provides an optical flow meter for measuring fluid flow through a pipe which obviates the need for the flow to be seeded with foreign particles. The meter comprises a fiber optic Sagnac interferometer with optical path crossing the flowing fluid. The interferometer measures velocity of the fluid by measuring the phase difference between the two beams propagating in the optical path in opposite directions. Light, which is deflected by the fluid, is collected by optical means at both sides of the optical path for calculation, the scintillating statistics and compensation for light intensity.

Abstract: An optical navigation device and a method thereof, wherein the optical navigation device comprises a pair of linear sensor arrays which are arranged non-parallel to each other for detecting light signal. Furthermore, an algorithm including correlation and vector analysis is processed by a computation unit to determine velocity and displacement according to present and previous light signal data sequences. Hence, the linear sensor arrays adapted to be the approach of navigation device can achieve the goal of reducing the computing data, increasing operation speed effectively and reducing hardware cost because of its fewer optically sensitive elements.

Abstract: The optical tracking device of this invention comprises a lens unit, a control circuitry communicatively coupled to the lens unit, and an imaging unit optically coupled to the lens unit. The lens unit comprises at least one Micromirror Array Lens, wherein the Micromirror Array Lens comprises a plurality of micromirrors and is configured to have a plurality of optical surface profiles by controlling rotations or translations of the micromirrors. The optical tracking device of the invention further comprises an image processing unit, communicatively coupled to the imaging unit, configured to process the image information from the imaging unit and generates a control signal for the control circuit to control the lens unit. The optical tracking device of the present invention provides capability of tracking a target moving in a high speed, providing three-dimensional image information of the object, and compensating the aberration of the optical tracking device.

Abstract: A method for estimating motion with at least one laser radar is disclosed. The method involves scanning a first range image at a first time, locating a plurality of object features in the first range image, scanning a second range image at a second time, receiving motion data for a time period between the first and second times, and locating the plurality of object features in the second range image based, at least in part, on the motion data to determine an orientation of the object. Based on the orientation of the object, the method estimates motion by comparing the location of the plurality of object features in the first scanned range image to the location of the plurality of object features in the second scanned range image.

Abstract: A single axis scanning PIV system, comprising a laser for generating a laser beam, optics for scanning the laser beam through particles in motion, an optical imager for capturing, images of the particles due to interaction between the laser beam and the particles, and a processor for implementing an algorithm that determines velocity information of the particles based on the images.

Abstract: The invention relates to a method for measuring a distance-related variable such as distance, speed or acceleration, or for levelling. An emitting device (1-6) comprising at least one microlaser (3) is used as an emitter, and the beam reflected off an object surface is received and evaluated for measurement. A beam is emitted and evaluated after being received, in a substantially simultaneous manner in at least two different wavelengths. Preferably, said method is carried out by means of a device whereby the microlaser (3) in the form of a passively pulsating microlaser (3) emits at least two different wavelengths. A receiver (15, 40) for the laser beam reflected off an object is arranged downstream from the evaluating device (41).

Abstract: A method of finding a temporal location of a reflected pulse in a system for remotely measuring characteristics of a target scene. The method includes steps of: (a) transmitting a pulse burst of two or more pulses toward the target scene; (b) capturing a copy of the pulse burst transmitted in step (a); (c) measuring an inter-pulse separation between at least two pulses in the pulse burst captured in step (b); (d) receiving a signal reflected from the target scene; (e) determining a temporal location of a first pulse in the signal received in step (d); and (f) determining a temporal location of a second pulse in the signal received in step (d) based on the inter-pulse separation measured in step (c).

Abstract: A method and apparatus for measuring particle motion using electromagnetic radiation uses beams of radiation modulated with a distinct frequency and/or phase. A particle traversing these beams scatters a portion of the radiation. Scattered radiation, which retains its modulation information, is then detected, and a cross-correlation technique is used to quantify the particle's motion, for example, particle velocity.

Abstract: A velocimetry apparatus and method comprising splitting incoming reflected laser light and directing the laser light into first and second arms, filtering the laser light with passband filters in the first and second arms, one having a positive passband slope and the other having a negative passband slope, and detecting the filtered laser light via light intensity detectors following the passband filters in the first and second arms.

Abstract: An image qualification method. A motion detection method. An optical navigation sensor. Image qualification, requiring only a single image frame to determine if an image frame is qualified, proceeds in real time. On the basis of the image qualification method, a motion detection method that prevents erroneous flickers is also provided for use in an optical navigation sensor.

Abstract: [PROBLEMS] A (a) (b) separation unit can confirms a separation state, a detection unit enhances a lighting efficiency and a light reception sensitivity, and a dispensing unit ensures the normal state of a specimen. [MEANS FOR SOLVING PROBLEMS] A specimen separation device characterized by comprising a container for storing a specimen, a nozzle for sucking and ejecting the specimen from the container, a nozzle operating means for moving the nozzle vertically and laterally, and a nozzle controlling means for controlling the suction force and ejection force of the nozzle.

Abstract: The present invention relates to a method and apparatus used to calculate at least one velocity component for a target within the region. The invention employs an energy source which is activated using an activation system in a cyclic pattern with a selected source frequency. A receiver is also employed in conjunction with a shielding system where this shielding system is configured to block the sensing of reflected energy from the target in a cyclic pattern with a selected receiver frequency. The invention operates through measuring a frequency change in the source frequency of the energy source signal when received by the receiver and determines a velocity component for a target based on a measured frequency change for a known direction of travel. The invention may also be extended to provide a two or three dimensional velocity vector through the addition of further energy sources.

Abstract: A method of sensing movement or proximity of objects by optical reflection is provided. The method includes the steps of transmitting a train of optical pulses towards a destination, sensing optical pulses reflected from the destination, and sensing and evaluating movement or proximity characteristics of objects at the destination with reference to variation in pulse width between transmitted and reflected optical pulses.

Abstract: An image velocity computing device having a camera, a microcomputer, and a camera control is provided. The camera has a controllable exposure time, and is capable of capturing a plurality of images of objects. The microcomputer is coupled to the camera and is configured to determine an image flow of an object of at least one pixel occurring in images captured by the camera, to determine an exposure time to achieve a predetermined image flow, and to compute an image velocity based on the exposure time of the camera. The camera control is configured to receive exposure time information from the microcomputer and to control the exposure time of the camera.

Abstract: The invention provides an optical flow meter for measuring fluid flow through a pipe which obviates the need for the flow to be seeded with foreign particles. The meter comprises a fiber optic Sagnac interferometer with optical path crossing the flowing fluid. The interferometer measures velocity of the fluid by measuring the phase difference between the two beams propagating in the optical path in opposite directions. Light, which is deflected by the fluid, is collected by optical means at both sides of the optical path for calculation, the scintillating statistics and compensation for light intensity.

Abstract: Systems, methods, and apparatus for monitoring rotation of a substrate during cleaning are disclosed. The invention may include a substrate cleaner adapted to support and clean a substrate; an optical source adapted to provide a light beam having a path within the substrate cleaner; and an optical sensor positioned along the path so as to receive the light beam from the optical source and adapted to detect an orientation feature on the substrate when the orientation feature traverses the path. The optical sensor includes an array of light detectors. Numerous additional aspects are disclosed.

Abstract: A technique for relative velocity determination between a surface and a velocity determination system involves capturing a set of outputs from a first photosensor array and then comparing subsequently captured sets of outputs from a second photosensor array to the set of outputs from the first photosensor array until a satisfactory match is found between the outputs. Once a satisfactory match is found, the elapsed time between the capture of the two sets of outputs represents the time to travel the known separation distance between the two photosensor arrays. Given the known distance of travel and the elapsed time to travel the distance, the relative velocity is a simple calculation of the distance traveled divided by the time to travel the distance.

Abstract: The invention relates to a Doppler frequency shift measuring device of the optical type comprising an optical signal channel delivering, through a polarization-splitting coupler, through a bidirectional signal port of the coupler, a signal light beam illuminating a reference medium, the coupler receiving, through said bidirectional port, a backscattered light beam returned by the reference medium; a reference channel providing a reference light beam for detection of the Doppler frequency shift, the frequency shift being determined by the frequency shift between the light signal illuminating the reference medium and the light beam returned by the reference medium. The reference light beam is applied to a reference port of the polarization-splitting coupler, said coupler delivering, at a port, a beat signal between the frequency of the reference light beam applied to the port and the frequency of the backscattered light beam applied to the port, possibly containing the Doppler shift.

Abstract: A monitoring system and associated method are provided to determine various parameters, such as the speed and/or angle of motion, of an object. The monitoring system includes a phototransmitter for illuminating the space through which the object will pass. The monitoring system also includes a plurality of photoreceivers spaced apart from one another with each photoreceiver including a plurality of receiver elements. The monitoring system further includes a controller to analyze output signals provided by the receiver elements and to detect the object in relation to a respective photoreceiver based upon differences between the output signals provided by the receiver elements of the respective photoreceiver. The controller is also configured to determine a parameter associated with the flight of the object, such as the speed and/or angle of motion of the object, based upon detection of the object in relation to each of a plurality of the photoreceivers.

Abstract: An optical navigation device and a method thereof, wherein the optical navigation device comprises a pair of linear sensor arrays which are arranged non-parallel to each other for detecting light signal. Furthermore, an algorithm including correlation and vector analysis is processed by a computation unit to determine velocity and displacement according to present and previous light signal data sequences. Hence, the linear sensor arrays adopted to be the approach of navigation device can achieve the goal of reducing the computing data, increasing operation speed effectively and reducing hardware cost because of its fewer optically sensitive elements.

Abstract: A method is provided for imaging targets using an unmanned air vehicle. The method comprises the steps of making a determination of cloud obscuration of a target, selecting an imaging sensor based on the cloud obscuration determination, and using the selected imaging sensor to produce an image of the target. An apparatus that performs the method is also provided.

Abstract: A method (200) and system (220) for range detection is provided. The system can include a sensing unit (110) for detecting a location and movement of a first object (401), and a processor (107) for providing a measure of the movement. The processor can convert the measure to a coordinate signal for moving a second object (124) in accordance with a location and movement of the first object. The system can include a pulse shaper (109) for producing a pulse shaped signal (167) and a phase detector (101) for identifying a movement from a reflected signal (166). A portion of the pulse shaped signal can be a frequency modulated region (312), a constant frequency region (316), or a chirp region (324). In one arrangement, the pulse shaper can be a cascade of all-pass filters (515) for providing phase dispersion.

Abstract: A method and apparatus for performing simultaneous multi-point measurements of multiple velocity components in a gas flow is described. Pulses of laser light are directed to a measurement region of unseeded gas to produce Rayleigh or Mie scattered light in a plurality of directions. The Rayleigh or Mie scattered light is collected from multiple directions and combined in a single collimated light beam. The Rayleigh or Mie scattered light is then mixed together with a reference laser light before it is passed through a single planar Fabry-Perot interferometer for spectral analysis. At the output of the interferometer, a high-sensitivity CCD camera images the interference fringe pattern. This pattern contains the spectral and spatial information from both the Rayleigh scattered light and the reference laser light. Interferogram processing software extracts and analyzes spectral profiles to determine the velocity components of the gas flow at multiple points in the measurement region.

Abstract: A relative movement sensor for measuring movement of an object (15) and the sensor relative to each other, the sensor comprising a plurality of lasers (3,5) for generating respective measuring beams and illuminating the object (15) therewith, and a plurality of respective photodiodes (4,6) for measuring changes in operation of each laser cavity caused by reflected measuring beam radiation re-entering the respective laser cavity and the optical wave in the laser cavity. The plurality of lasers (3,5) are operated in a time-multiplexed manner such that only a subset (i.e. one or more) of the lasers is operated at any one time, the remaining lasers being idle. This reduces peak power dissipation and prevents erroneous interference caused by measuring beam radiation from one laser entering the cavity of another laser.