Showing papers on "Laser Doppler vibrometer published in 1986"

Laser Doppler velocimeter using the self-mixing effect of a semiconductor laser diode.

Abstract: A laser Doppler velocimeter (LDV) using a semiconductor laser diode (LD) with its self-mixing effect has been developed. A Doppler signal, caused by mixing a returned wave with an originally existing wave inside the LD, is detected with a photodetector in the LD package; it is also picked up from the variation of the LD driving voltage. When the returned light is weak enough, it confirms that there is no change in the single-mode oscillation and its spectral width of the LD. A LDV of this type is compact enough for many applications.

Imaging by laser beam scanning

Abstract: A laser beam scanning system includes a laser for emitting a laser beam modulated with image information to be recorded and a deflecting device, such as polygon mirror, for deflecting the laser beam over a predetermined angle repetitively, so that the laser beam is scanned on a scanning surface, thereby an image is formed on the scanning surface. When a plurality of laser beams are used at the same time, the plurality of laser beams are arranged in an array inclined with respect to the scanning direction. In this case, a sync sensor generates a sync signal in response to a laser beam received in the first place. When a polygon mirror is so structured to have a reflecting surface which is defined by a curved surface having a predetermined radius of curvature, a fθ lens may be discarded. In this case, when a transparent layer is formed on this curved reflecting surface, no distortion in scanning speed is produced even without using any electrical correction. Besides, it is also preferable to control the intensity of laser beam so as to maintain the image density of a resultant image at constant.

Heterodyne laser instantaneous frequency measurement system

Abstract: A heterodyne laser instantaneous frequency measurement system is disclosed. The system utilizes heterodyning of a pulsed laser beam with a continuous wave laser beam to form a beat signal. The beat signal is processed by a controller or computer which determines both the average frequency of the laser pulse and any changes or chirp of the frequency during the pulse.

High speed fiberoptic laser module

Abstract: A small module contains means for converting an electrical signal to a correspondingly modulated light signal on an optical fiber. Frequency of the signal can range from D.C up to many gigahertz. A semiconductor laser diode is mounted on a high thermal conductivity substrate on a thermoelectric cooler for controlling laser temperature. The optical fiber output is soldered to the laser substrate with an end in alignment with the laser junction. A laser bias circuit is on a connection substrate adjacent to the laser substrate. A connection substrate also includes a deposited signal lead line connected to the bias circuit by an impedance matching means. Electrical signals from the pin of an external coaxial connector are coupled to the lead line. The laser bias circuit and signal lead line are electrically connected to the laser diode by wires between the connection substrate and the laser substrate. A photodiode in the module in the light path from the laser provides a control signal.

FM dye lasers

Abstract: We have investigated the detailed operation of a frequency modulated dye laser (FML). The FML consists of a standing wave Rh6G dye laser with an intracavity transverse ADP phase modulator which is driven at a frequency close to the cavity mode spacing. An ideal FML output consists of a laser beam which is constant in amplitude but sinusoidally varying in frequency. This provides a source of many laser modes which are equally spaced by the modulation frequency. Several dye laser configurations have been investigated. Measurements of the mode intensities, total power, amplitude modulation and rf beat amplitudes have been made as a function of the rf driving frequency of the phase modulator. The FM laser obtained has been frequency stabilised by locking it to a reference interferometer and also by frequency offset locking it to a single-frequency dye laser.

Laser scanner for bar code reader

Abstract: A laser scanner wherein an elliptical laser light beam is directed to the target (a bar code symbol) so as to increase the signal to noise ratio of the laser light received by the photodetector The use of laser light in the shape of an ellipse, instead of the prior spherical shaped laser light, where the long axis of the elliptical laser light is aligned with the bars of the code being read reduces the distortion of the optical signals received by the photodetector Thus the signal to noise ratio is maximized so as to enable the resolution of fine, dense bar codes

Semiconductor laser output control device

Abstract: A semiconductor laser output intensity control device is provided in a laser beam scanning system, such as a laser printer. A laser beam emitted from a semiconductor laser is modulated by image information and scanned across a photosensitive member for forming an image thereon. The present output intensity control device employs an up/down counter whose count determines the level of driving current to be applied to a laser driver which drives the semiconductor laser. The up/down counter changes its count either up or down depending on the magnitude of the output intensity of the laser beam as compared with a reference level. The present device includes a control circuit which prevents the power setting operation of the laser from taking place during a scanning time period in which the photosensitive member is scanned by the laser beam.

Focusing of multimode laser beams with variable beam parameters

Abstract: This paper deals with the focusing of multimode radiation. Two special types of resonator are presented: type 1 produces constant beam radius at varying internal thermal lensing and type 2 has, under some conditions, constant beam divergence. It will be shown that by suitable imaging, a focus of constant diameter and constant position can be realized, if the output beam of the laser is varying in diameter only. Variation of the output beam divergence can be compensated by a different optical system.

Method for mobile survey of road surface

Abstract: A road surface illuminated by sunlight is scanned with a laser beam at right angles to the direction of travel, the intensity of the laser beam being intensity modulated with a predetermined frequency; laser beams reflected from the road surface are received and optically filtered to filter out light having frequencies outside that of the laser beam The optically filtered laser beam strikes a plurality of beam position sensing elements from which respective electrical signals are derived The resulting electrical signals are then multiplexed and electrically band-pass filtered wherein the center frequency of the band-pass filtering coincides with the frequency at which the laser beam is intensity modulated

Laser beam profile measurement by a thermographic technique

Abstract: A thermal method to measure laser beam profiles has been developed. A laser beam is absorbed by a heat‐resisting film and transformed into heat. A profile of the temperature increment over the receiving film is radiometrically detected by a thermographic instrument. The method is demonstrated by one‐dimensional profile measurements of a pulsed YAG laser beam whose energy density is several J per cm2.

Fibre-optic vibration probe

Abstract: A practical all-fibre laser vibrometer is described. The design has been optimised for hand-held use and incorporates a frequency-scanned laser diode and a single-mode optical fibre coupler. The vibration information is extracted by a pseudoheterodyne technique.

Measured signal amplitude distributions for a coherent FM-cw CO2 laser radar.

Abstract: Measurements of signal amplitude distributions with a FM-cw CO2 laser radar have been made against various targets in both imaging and staring modes. Data show good agreement with theoretical distributions. From the measurements conclusions are drawn about the atmospheric- as well as target-induced effects. Beam wandering effects are shown to be of importance in the staring mode.

Laser doppler displacement measuring system and apparatus

Abstract: Apparatus for the precise measurement of the displacement of a moving cooperative target from a reference position, traveling, for example, over a distance of several meters, and with the measurement accuracy being better than a fraction of a millimeter. The apparatus includes a low-cost laser which generates a beam of a selected frequency. The laser beam is directed at the moving target and is reflected by the target. The apparatus also includes additional elements which measure the Doppler phase shift of the reflected laser beam so as to obtain a precise measurement of the displacement of the target with respect to the reference position.

Laser emitting apparatus and laser beam printer using same

Abstract: An information recording apparatus includes a temperature detector for detecting the temperature of a semiconductor laser and a condition setter for generating a signal corresponding to a laser beam wavelength at a predetermined temperature. The apparatus further includes a control system for controlling a laser output of the semiconductor laser in response to the temperature detection signal from the temperature detector and the condition signal set by the condition setter.

Intracavity Helium-Neon Laser Photothermal Deflection as a Sensitive Technique for Trace Gas Analysis

Abstract: A novel, compact, ultrasensitive, and inexpensive He-Ne laser intracavity photothermal deflection spectrometer has been developed. In this apparatus a gas sample is placed inside a cavity of the He-Ne laser, which serves as a probe laser. A CO2 excitation laser coaxially overlaps with the He-Ne laser beam inside the sample cell. The detection limit for ethanol vapor in air at 1 atm excited with 1.5 W of CO2 laser chopped at 13.3 Hz is estimated to be 2.5 ppb.

Laser doppler velocimeter with laser backscatter discriminator

Abstract: A laser doppler velocimeter with laser backscatter discrimination for determining the relative velocity between an optical platform and another target where a laser beam is generated and directed toward the target. A detector produces a doppler signal in response to the detection of the laser beam. Noise and backscatter signals with bandwidths and amplitudes outside selected thresholds are rejected, and the legitimate doppler signal from the target is enhanced.

Fibre-Optic Vibration Probe

Abstract: A practical all-fibre laser vibrometer is described. The design has been optimised for hand-held use and incorporates a frequency-scanned laser-diode and a single-mode optical-fibre coupler. The vibration information is extracted by a pseudo-heterodyne technique.

Uniform intensity per pixel when the linear speed of a laser beam varies along a scanline

Abstract: A modulated laser beam emitted from a semiconductor laser is deflected by a rotating light beam deflector to scan a desired surface. The frequency of an image scanning clock signal and the intensity of the laser beam from the semiconductor laser are varied according to a scanning rate at which the surface is scanned by the modulated laser beam.

Monitoring of noise and vibration for construction work

Abstract: PURPOSE:To improve the environmental preservation with a better monitoring of noise and vibration during work, by detecting noise and vibration with a noise microphone and a vibration pickup to give a warning when the detection values exceed the set values. CONSTITUTION:A noise microphone 1 is provided at the top of an aluminum pole 2 erected on the border of a working site and connected to an ordinary noise gauge 9. Then, a vibration pickup 5 is provided on a fixing rod 6 set on the ground of the site border and connected to a vibrometer 10 for public nuisance. Then, the noise gauge 9 and the vibrometer 10 are connected to a level processor 20, a record data logger 11, a level display 13, red and yellow rotary lamps 16a and 16b and an alarm 17 comprising a buzzer 17a and a chime 17b. Signals of noise and vibration measured with the noise gauge 9 and the vibrometer 10 are sent to the level processor 20 to be compared with the preset level. When the signals are above the level, the red rotary lamp 16a lights and the buzzer 17a sounds. This measure can improve the environmental preservation.

Internal laser interferometer

Abstract: An instrument of measuring motion of a vibratory system, such as an ultrasonic bonder, employs a laser (10) that receives within its lasing cavity light transmitted (24) to the object (26) to be monitored and retroreflected (24), so that oscillations within the laser cavity experience interference peaks corresponding to the phase relation between the outgoing and incoming laser beams (24). The interference peaks of the beam within the cavity are counted to provide an indication of motion of the reflecting object. Sensitivity is enhanced by choosing a front reflector (14) of the laser cavity to have a transmissivity at the frequency of interest that is selected to achieve maximum interference peak values. The laser cavity length is selected to cause the laser to have no more than two modes at the output frequency of interest, thereby avoiding beat frequencies that approach the frequency of vibration of the mechanical system of which motion is being observed.

Wide-range directional LDV employing modulated semiconductor laser source

Abstract: A laser Doppler velocimeter (LDV) based on a semiconductor laser is described. Information on the direction of flow is obtained by applying a single-sideband technique using direct modulation of the laser diode. A measuring range of 8.4 MHz is reached with this technique, where the nonideal FM properties of the semiconductor laser are dealt with by an equalisation of the modulation current.

Focus and tracking detection apparatus for optical head employing light guide means having different radii of curvature

Abstract: In an optical head, a laser beam L emitted from a semiconductor laser is collimated by a collimator lens and is incident on a beam splitter. The laser beam passing through the beam splitter is and a quarter wave plate converged by an objective lens onto an optical disk and reflected by the optical disk. The reflected laser beam passing through the objective lens and the quarter wave plate is returned to the beam splitter and is reflected from a polarizing surface of the splitter. The reflected laser beam is guided to a beam emerging surface of the prism, the surface being defined by a flat surface and a semicylindrical concave surface. The laser beam is separated at the surfaces and converged by a projection lens onto a photodetector.

Two-frequency laser interferometer

Abstract: The invention relates to a two-frequency laser interferometer with signal evaluation in accordance with the so-called heterodyne method. To be able to construct particularly small and rugged laser heads for such interferometers, two laser diodes which are operated at different operating points are used as lasing source. They are arranged optically crosswise to one another and their rays are reflected in on the same axis to one another via a polarisation beam divider.

Laser sensor with encoded laser output signal

Abstract: A transducer defined by a laser is set forth Strain, movement, velocity, temperature, pressure, and vibration coupled to the laser change the lasing frequency or form a Doppler shift The laser is thus installed at a specified location to couple a measured phenomenon and thereby enable transmission of the encoded variable in the laser beam A receiver located remote from the laser picks up the beam for data retrieval

Laser beam recording apparatus

Abstract: A laser beam recording apparatus having a parallel-plane plate, such as a dust proof glass plate or a light controlling filter, which is disposed across the optical path of the laser beam. The beam transmitting surfaces of the parallel-plane plate are so inclined that the angle of incidence of the laser beam thereon is not zero throughout the scanning movement of the laser beam.

A rapidly scanning three-velocity-component laser Doppler anemometer

Abstract: A directionally sensitive, three-velocity-component laser Doppler anemometer has been developed. It permits straight-line scans through three-dimensional flows to obtain space-time velocity information, and has a lower signal-averaging bias than point-wise measurements. A Ronchi ruling is employed to create a horizontal fringe pattern and a dual Bragg cell is used to produce sets of moving vertical fringes. It is also shown that a proposed three-beam scheme does not produce a fringe pattern moving in the on-axis direction that would measure the on-axis velocity components. The Doppler frequency is independent of the position of the receiving optics, and only one photomultiplier tube is needed to receive the signals for all three velocity components. Measurements made on a stationary solid object as well as in a dispersion of particles in water show that signals with low noise level and high fringe visibility are obtained.