Showing papers on "Laser Doppler vibrometer published in 1988"

Laser beam treatment device for an endoscope

Abstract: A laser beam irradiation apparatus comprising a laser generating device, a laser beam irradiation probe for applying a laser beam from the laser generating device to a region of an object of irradiation, an ultrasonic transmitter/receiver for emitting ultrasonic waves toward the region to which the laser beam is applied by the probe, receiving reflected waves from the irradiated region, and converting the reflected waves into an electrical signal, a measuring device for measuring the temperature of the irradiated region in accordance with the electrical signal from the ultrasonic transmitter/receiver, and an output adjuster for adjusting the output of the laser generating device in accordance with a temperature signal from the measuring device.

Small laser doppler-velocimeter based on the self-mixing effect in a diode-laser

Abstract: A very small and simple velocimeter is presented consisting of a diode laser with a gradient-index lens in front of it. The basis of the velocity measurement is the mixing that occurs when light, scattered back by the moving object into the laser cavity, interferes with light inside the laser. This mixing induces large fluctuations of the laser intensity with the Doppler frequency. These fluctuations can be detected either with a photodiode or by measuring the voltage across the diode laser. As an illustration of the performance of the velocimeter, velocity measurements of a rotating disk covered with white paper are described. The differences arising because of using a single-mode or a multilongitudinal mode laser were calculated and verified in experiments. The advantage of the use of a multimode laser is that differential measurements of the distance between laser and moving object are also possible.

Method and apparatus for stabilizing the frequency of a laser beam

Abstract: For stabilizing the frequency of a narrow-band Excimer laser beam the interference rings of a Fabry-Perot interferometer 16 are projected onto a solid-state image sensor 18 and by means of the solid-state image sensor an electrical signal is generated which is dependent on the frequency of the laser beam. The electrical signal is compared with a stored reference signal to derive an adjusting signal 32 for an optical reflection grating 38 with which the frequency of the laser beam 12 is regulated to a desired value. The absolute value of the frequency of the laser beam 12 is determined by means of the optogalvanic effect.

Synchronizing signal generating system for laser scanner

Abstract: A synchronizing signal generating system for a laser scanner comprises a source for emitting a first laser beam for scanning and a second laser beam for synchronization of scans by the first laser beam, a polygonal mirror for causing the first laser beam to scan a medium and for causing the second laser beam to scan a grating which has bright portions and dark portions alternately arranged along a scanning direction of the second laser beam, a converging optical system for converging the second laser beam transmitted through the grating, a light receiving system for receiving the second laser beam converged by the converting optical system and for generating a synchronizing signal, and a circuit for controlling the source responsive to the synchronizing signal so as to synchronize a scan timing of the first laser beam. The converging optical system comprises a plurality of lenses or concave mirrors provided for a length corresponding to a scan length of the second laser beam on the grating.

Laser and avalanche diodes for velocity measurement by laser Doppler anemometry

Abstract: The paper describes the possibilities of using semiconductor components for laser Doppler anemometers. This includes laser diodes D at the transmitting optics and PIN and avalanche diodes at the receiver. The advantages and disadvantages of various laser diode types are described, reference is made to problems such as focussing and wavelength stabilization and practical hints are given for the use of LDA. Extensive measurements of the attainable signal-to-noise ratios (SNR) of photomultipliers and of a number of photodiodes of different make have shown that some photodiode models are now superior to photomultipliers. Laser diodes should be used together with photodiodes to construct miniaturized laser Doppler anemometers, as such semiconductor LDA are much more efficient than conventional anemometers with gas lasers and photo-multipliers. Moreover, miniaturized LDA designs can now also be used for battery operation and field application.

Color video projecting apparatus using acousto-optical deflector

Abstract: Disclosed is a laser beam scanning system which includes a plurality of laser sources each of which produces a laser beam having a different wavelength. The laser beam component is intensity-modulated with a corresponding color video signal and deflected by an acousto-optical deflector to scan a medium in at least one direction to produce a color image thereon. Because of the color dispersion inherent to the deflector, the angle of deflection is dependent on the wavelength of the laser beam component. To compensate for the color dispersion, a signal processor is provided to adjust the intensity modulation for the corresponding laser beam component in such a manner that each of the laser beam components is intensity-modulated differently from the others in terms of scanning time to obtain substantially the same angle of deflection for all the beam components.

Laser beam depicting apparatus

Abstract: A laser beam depicting apparatus adapted to depict a raster image by modulating a laser beam by image data and raster-scanning the laser beam by the reflecting surfaces of a rotational polygonal mirror comprises a laser source for producing a laser beam by oscillating light components of plural wavelengths at the same time, a light modulator for modulating the laser beam without causing color dispersion, a light deflector for correcting any deviation in a direction orthogonal to the deflection of the laser beam caused by the tilting error of each reflecting surface of the rotational polygonal mirror without causing color dispersion, and an fθ lens having its chromatic aberration corrected for condensing the laser beam deflected by the rotational polygonal mirror in order to raster-scan an object to be depicted.

Measurement of head/disk spacing modulation using a two channel fiber optic laser Doppler vibrometer

Abstract: A two-channel laser Doppler vibrometer system is described for studying spacing modulation of the head/disk interface in a magnetic recording disk file. Three types of sliders, namely a standard two-rail slider, an experimental negative-pressure slider, and a cross-cut slider, are studied. In comparing the results from the single-channel and dual-channel laser Doppler systems, excellent agreement is observed for the resonant frequencies of the air bearing. The single-channel system, however, exhibits problems with offset in the velocity and displacement signals that are absent with the two-channel system. >

Doppler modulation and Zeeman modulation: laser frequency stabilization without direct frequency modulation.

Abstract: We discuss two methods (Zeeman modulation and Doppler modulation) for locking the frequency of a singlemode cw laser to an atomic absorption line. These methods do not require the laser frequency to be modulated directly. In the first scheme the absorption frequency of the atom is modulated via the Zeeman effect; in the second scheme the laser frequency is modulated indirectly via the Doppler effect in an atomic beam. We used the two methods successfully to lock two dye lasers to the transitions 6S((1/2)) ? 7S((1/2)) and 7S((1/2)) ? 15P(?) in atomic cesium.

Laser reproducing apparatus

Abstract: The present invention relates to a laser reproducing apparatus which reproduces recorded data recorded on a recording medium such as an optical disc, a magneto-optical disc or the like by the irradiation of a laser beam, in which the current value of a driving signal which drives a laser diode (12) is set near a value at which there is the least interference with the laser beam is by reflected-back light from the recording medium, and the irradiation by the laser beam from the laser diode (12) at the thus set current value is intermittently carried out at predetermined intervals. Also, the duration of lock pulse of this laser beam is selected to be a duration in which writing on the recording medium (11) cannot be carried out by the thus set current value. Thus, the influence exerted on the laser beam by the reflected-back light from the recording medium (11) is small so that the data can be reproduced satisfactorily. Also, the arrangement of the drive circuit for driving the laser diode (12) can be simplified.

Ring laser with improved beam quality

Abstract: A rod laser having a ring cavity configuration, and including a polarization rotator to compensate for birefringence of the laser's rod. Preferably, the rotator is a 90° crystal quartz rotator. In a preferred embodiment, the ring laser is a stable quasi-unidirectional, non-confocal solid state ring laser. A telescope, including at least two lenses with variable inter-lens spacing, is preferably positioned in the laser beam path as closely as possible to the laser rod. The spacing between the telescope lenses is preferably controlled by a servo mechanism. In a preferred embodiment, a power density detector is provided for producing a beam power signal, and a means (which may include a microprocessor) coupled to the power density detector generates a servo mechanism feedback control signal from the beam power signal. Since the system of the invention maintains a high quality output beam having low far-field beam divergence and small laser beam focal spot diameter, over a wide and varying range of output beam power, the output beam is particularly useful for such applications as high speed drilling, welding, and cutting.

Multiple-line laser Doppler velocimetry.

Abstract: A laser Doppler velocimetry diagnostic fitting high-strain rate motion of solids as in shock wave experiments by now requires a single-mode laser. We have worked out a new method of increasing by 1 order of magnitude the luminosity of such a diagnostic. We use a broadband pulsed laser coupled to a Fabry-Perot acting as a spectrum modulator and demodulator. This enables us to analyze over a wider range the behavior of poorly reflective materials subjected to shock loading. The principle and experimental results are presented.

Method of correcting laser output power

Abstract: There is disclosed a method of correcting the laser beam output power of an NC laser beam cutting machine composed of a computerized numerical control (CNC) apparatus and a laser beam cutting machine. When a laser is initially energized, a correcting coefficient is determined from a laser beam output power command value and an actual laser beam output power by a correcting means (11), and the actual laser beam output power is measured at each periodic interval of time by an output measuring device (33). The NC laser beam cutting machine is controlled by a command control means (13) to eliminate the difference between the laser beam output power command value and the actual laser beam output power. When the laser is initially energized, a long-term variation in the laser beam output power is corrected, and when an actual cutting operation is carried out, a short-term variation in the laser beam output power is corrected, so that the laser output power can be produced accurately.

A miniature, battery operated laser Doppler anemometer

Abstract: Describes a hand-held, lithium battery operated, 30 mW laser diode, backscatter LDA constructed in a tube of 30 mm diameter and 250 mm length. The tube also contains micro-optical beam collimation, a miniature Galilean telescope, miniature beamsplitter and prism, spatial filtering, solid state detector, electronic amplifier, bandpass filter, discriminator and either (1) telemetry to transmit Doppler signals to a remote signal processor or (2) integral frequency analysis and LCD display of single-component velocity. All components are mounted on micro-optical benching. The velocity range is up to a few metres per second; the system operates for a few hours before battery replacement is necessary.

Laser beam scanning type ophthalmological instrument

Abstract: A laser beam scanning type ophthalmological instrument has a first laser beam light source for emitting a first laser beam; a second laser beam light source for emitting a second laser beam of a different wavelength from that of the first laser beam; and a light receiving element for receiving a laser beam reflected by an eye fundus, and in which the eye fundus is scanned by the first and second laser beams in order to observe the eye fundus or in order that a view field, etc. can be inspected. The laser beam scanning type ophthalmological instrument is characterized in that the first and second laser beams emitted by the first and second laser beam light sources can independently be adjusted in light quantity.

Laser exposure apparatus

Abstract: A laser exposure system for use in scanning and recording images, the system comprising subdividing the laser beam from the laser source into several parallel traces of laser beams; modulating the laser beams individually in response to the image signals be means of a multi-channel optical modulator; directing the modulated laser beams through a first mirror and a second mirror so as to enable the laser beams from the second mirror to be in parallel with the reference plane with respect to the sub-scanning direction; varying the distance between the modulator and the first mirror; and adjusting the angles of the first and second mirrors to the reference plane so that a possible decline of the laser beams in the sub-scanning direction is compensated.

Three-dimensional Doppler anemometer using a holographic optical element.

Abstract: A new simple 3-D laser Doppler system has been developed for simultaneous measurement of the instantaneous velocity vector of a scattering particle. The system is based on the reference beam method. It uses a hologram to generate the reference beams. Only one laser operating in single mode is required as the light source. The system has been tested by measuring all the components of the Reynolds stress tensor in a round cold air jet. The results are presented.

Laser beam scanning apparatus

Abstract: A laser beam scanning apparatus deflects laser beams of different wavelengths to scan an object or medium in at least one direction using an acousto-optic deflector. The angle of scanning deflection is dependent on the frequency of the drive signal applied to the acousto-optic deflector and the wavelength of each laser beam, the deflection resulting in color dispersion of the laser beam. A pair of photosensors which are sensitive to the corresponding wavelengths of the laser beams produce start and stop signals during a scanning time period. In response to these signals, writing or reading clock signals are generated and their durations are adjusted to be substantially the same for each laser beam during the scanning time period.

Method and apparatus for laser exposure in an image scanning/recording apparatus

Abstract: A laser exposure apparatus of an image scanning recording apparatus comprises a single laser light source 2, a beamsplitter 3 for dividing a laser beam emitted from the single laser light source 2 into two laser beams, a modulator 7, 8 for modulating two laser beams in accordance with a recording signal, a half-wave retardation plate 9 for polarizing one of the beams in association with the other one of the beams so that the modulated laser beams constitute a pair of orthogonal polarization, a polarizing beamsplitter 10 for arranging two beams constituting a pair of orthogonal polarization with each other orthogonally in a line, and an optical system 11 for reducing the laser beams arranged in a line.

CO2 laser dynamics by optical modulation of inversion

Abstract: In this paper a method is proposed for studying laser dynamics, which relies on periodical inversion modulation in its active medium with the aid of external radiation. Through the example of a CO2 laser, the possibilities of this approach are shown in determining the most important dynamic parameters of a laser system, such as the frequency of natural relaxation vibrations, the resonance curve width, the inversion relaxation rate and the saturation parameter. The main advantage of this method is that it does not require the introduction of additional losses into the cavity, yet it permits investigation of the laser transfer characteristics over a wide range of frequencies. Such measurements are very important in making intracavity investigations. They also make it possible to predict the level of technical fluctuations and to carry out internal modulation and stabilization of the radiation power which is essential in developing laser systems for various practical applications.

Beam control device for a laser used in an optical memory system

Abstract: Method and device of beam control for stabilizing the laser beam output by controlling the driving current of laser beam source (1), by receiving output light from laser beam source (1) by a photo detector (14), converting it into an electric signal corresponding to the light intensity, and comparing this signal output with a specified reference level.

Method and apparatus for improving the measuring accuracy of a micrometer

Abstract: This invention provides apparatus and method to increase the direct measurement accuracy of a rotary encoder type of micrometer 10. To overcome a maximum measurement accuracy of 100 microinches there is provided a laser displacement meter which includes a laser head 24 which is coupled to a micrometer bed 12 by a pair of of clamps 26a and 26b and by a magnetic plate 28. Laser head 24 has an output display 30 associated therewith for indicating the magnitude of the measurement made by the laser head 24. Laser head 24 is operable for providing an output chirped laser beam 32 and for receiving a reflected output beam 34. A corner cube reflector 36 is mounted by an arm 38 to a headstock spindle 18. The reflected return beam is detected and processed by a phase demodulator and converted into pulses. The pulses are counted and converted to distance and displayed. Operating in accordance with the Doppler effect, movement of the reflector induces a frequency shift in the chirped laser beam, the frequency shift being a function of velocity of the moving reflector and, hence, the velocity and distance traveled by the spindle 18. This frequency shift is detected by the phase demodulator and is converted to a displacement.

Laser doppler anemometer using high-frequency laser pulses

Abstract: A laser Doppler anemometer with at least two laser beams pass to a region of a fluid flow containing particles. The scattered light is frequency shifted by the Doppler frequency resulting from the flow speed. The construction is very compact and permits a high signal-to-noise ratio for the measurement signals. The laser beams consist of high-frequency pulses, the frequency of the pulse sequence of which is a multiple of the Doppler frequency.

Method and apparatus for determining the sign of the direction of a particle stream

Abstract: In a method in which a heterodyne-laser-Doppler method is used for the demination of the sign of the direction of a particle stream, the beam from a laser source is directed by means of an optical arrangement used as an emitter optical system to a measuring volume in an interferometer device. A frequency difference between the emitted laser beam and the laser beam returning into the optical arrangement is measured through heterodyne reception by means of the same optical arrangement used as a receiving optical system; this returning laser beam is frequency-shifted because of scattering by particles moving with the same speed in the particle stream and because of the Doppler effect. In the method according to the invention, an additional Doppler shift with a definite sign then is alternately impressed on the laser beam in exactly defined areas of beam paths, the additional Doppler shift being preferably considerably smaller than the Doppler shift generated by the particle movement. The exact direction of the particle stream then is determined from the received scattered back laser beam by comparison of this scattered back laser beam with a laser source reference beam. The additional Doppler shift can be impressed on a reference beam or emitted beam split from the laser beam, on the laser beam scattered back by the measuring volume or on the emitted beam and signal beam flowing in opposite directions in the optical arrangement.

Fiber Optic Doppler Systems For Remote Sensing Of Fluid Flow.

Abstract: An experimental study of the use of lasers in measuring flows associated with compressional waves has been undertaken. A prototype differential laser Doppler system amenable to a variety of design modifications has been assembled and tested on single frequency wave fields in a water-filled standing wave tube. The use of polarization preserving fibers in the laser Doppler velocimeter (LDV) can lead to both (1) a very compact design for the optical measuring head, and (2), novel signal processing capabilities. The discussion is illustrated with experimental data obtained with a 1 watt argon-ion laser.

A microprocessor-controlled iodine-stabilised ion laser

Abstract: Microprocessor control of an iodine-stabilised ion laser is described. This control is achieved using an STD-bus based Z-80 processor and standard STD input/output cards to interface with the various laser transducers and detectors. Automatic control functions include laser wavelength selection and optimisation, laser current and intensity control, and high resolution frequency scanning with recognition of, and stabilisation to, selected saturated iodine features. Automatic switching between iodine-stabilised Kr+ ion laser wavelengths at 568 nm and 531 nm is specifically described.