Showing papers on "Laser Doppler vibrometer published in 1982"

An investigation into the origin of frequency sweeping in a hybrid TEA CO2 laser

Abstract: An analysis of the sources of the intrapulse frequency modulation in the hybrid TEA CO2 laser is presented. Two principal effects predominate: the falling frequency at the start of the pulse is shown to be due to plasma effects, while the increasing frequency during the remainder of the pulse arises from a laser induced refractive index perturbation. The significance of these results to the design of high stability pulsed lasers is discussed.

Laser surgical equipment

Abstract: In a laser surgical equipment consisting of a laser oscillator oscillating a laser output, an optical waveguide connected to the laser oscillator and transmitting the laser output and a hand piece connected to the optical waveguide and radiating the laser output to a diseased part to be radiated, the improvement comprising detection means for detecting the laser output from the hand piece, comparison means for comparing the output of the detection means with a predetermined value and control means for controlling the laser oscillator by the output of the comparison means and for setting the laser output of the hand piece to the predetermined value.

Laser apparatus utilizing marking laser for triggering operative laser

Abstract: A laser apparatus includes an operating laser oscillator for generating an operating laser beam for medical treatment and a marker laser oscillator for generating a visible laser beam (i.e., marker laser beam) in order to mark a portion of the body cavity to be treated. The marker laser beam is guided coaxial with the operating laser beam to become incident on a laser probe. The marker laser beam is intermittently shielded by a chopper. The shielded marker laser beam is reflected by a reflecting surface of the chopper and is guided to a photosensor. The operating laser oscillator is driven in response to an output signal from the photosensor.

Interaction of three coherent fields with Doppler broadened serial four-level systems: Application to four-level FIR lasers

Abstract: The semiclassical density matrix treatment is applied to serial four-level systems for the steady state. Phase and energy relaxations as well as Doppler effects and M degeneracy are accounted for. The calculations are restricted to parallel polarized fields, avoiding problems of quantum interference. The formalism is used to calculate the gain spectra of different four-level far-infrared (FIR) laser schemes: double resonance pumped laser, Raman laser, two-photon pumped laser, and hyper-Raman-laser.

Eye safe laser transmitter

Abstract: An apparatus for converting a high intensity spatially coherent laser beam into a source of spatially incoherent radiation that retains the temporal, amplitude and frequency characteristics, and also the polarization, of the spatially coherent laser beam A laser is oriented so that its coherent output beam falls on a transmissive optical lens which images the coherent beam onto the surface of a ground glass plate that has been etched with hydrofluoric acid to form a spatial diffuser The radiation that emerges from the diffuser has been converted into spatially incoherent radiation that retains some important characteristics of the coherent beam, namely polarization and temporal coherence The diffuser outputs a diverging beam of substantially incoherent radiation to a collimator that provides a collimated output beam that can be used in laser communicators, laser rangefinders and other laser field devices in an "eyesafe" mode

Miniature solid-state directional laser Doppler velocimeter

Abstract: A miniature laser Doppler velocimeter (LDV) using a single-mode solid-state semiconductor laser is described. Current-induced output frequency modulation of the laser output, combined with an unbalanced interferometer, is used to provide direction sensing.

Laser surgical apparatus

Abstract: In a laser surgical apparatus having a laser oscillator operable to oscillate to produce a laser beam, and an optical path connected to the laser oscillator for transmission of the laser beam, a hand piece at the fore end of the optical path is equipped with a vibrator element comprised of a piezoelectric transducer, and the vibrator element applies a vibration to the hand piece.

Laser doppler velocimeter for measuring torsional vibration

Abstract: The velocity and change in velocity of a rotating or otherwise moving surface is measured by a laser Doppler technique. In particular, a diffraction grating is formed on the moving surface either by machining processes or by affixing a ready-made grating thereto. The grating surface exhibits periodicity in one or more directions, either separately or simultaneously. The presence of the grating produces Bragg order diffraction reflections at specific angles relative to the surface. These Bragg order reflections contain information, in the form of Doppler shifts, concerning the motion of the surface and the body to which it is attached. This Bragg order Doppler shift information is readily analyzable using conventional signal processing apparatus and processes to produce the desired velocity and torsional vibration information.

Two-beam scanning optical system

Abstract: A two-beam scanning optical system comprising two laser beams each having a polarization characteristic, a first polarization beam splitter (3) for compounding the two laser beams into one laser beam, a rotary polygonal mirror (4) for scanning the compounded laser beam, a second polarization beam splitter (6) for separating the compounded laser beam into two laser beams, and a lens system (5) for focusing the separated laser beams onto a surface of a sensitive drum (8) of a laser printer and onto a surface of an original document (7) to be read, respectively, so that said two separated laser beams scan the respective surfaces of the sensitive drum and the original document.

Laser Doppler velocimetry: A status report

Abstract: Since the first experimental work in 1964, the measurement of velocity by means of the Doppler shift in scattered laser light has developed into an important tool in fluid mechanics research which often provides data unobtainable with other instruments. This paper reviews the fundamentals of laser Doppler velocimeter system design including optical requirements and signal processing considerations. Numerous applications are described to illustrate the present state of the art.

Device for modifying and uniforming the distribution of the intensity of a power laser beam

Abstract: A device for modifying and uniforming the distribution of the intensity of a power laser beam is provided wherein a rotatable support body includes three mirrors for reflecting an incident laser beam. The rotation of the mirrors with the support body effects a uniform distribution of the intensity of the incident laser beam resulting in a reflected laser beam having uniform distribution of intensity across its cross section. A modification section is included for modifying the amplitude of the reflected laser beam passing from the support body.

A vibration compensated high frequency heterodyne CO2 laser interferometer for plasma diagnostics

Abstract: A CO2 laser interferometer has been developed for electron density and density fluctuation measurements in the new and larger reversed field pinch plasmas. (Density range 2*1019 to 2*1021 electrons m-3 plasma minor radii 0.26 and 0.6 m.) The instrument incorporates an acousto-optic modulator to produce the 40 MHz intermediate frequency for heterodyne detection and uses a common path, visible HeNe laser interferometer, based on the same heterodyne technique, to monitor vibration of the optical components. The system has been demonstrated by measuring the rapid rise and decay of the electron density in a small Z-pinch plasma in the presence of induced vibration.

Improvements in or relating to laser light sources

Abstract: A light source comprises a first laser 10 and a second laser 11 which is arranged so that light from the first laser can be injected into the second. The bias to the lasers is controlled so that the first laser acts as an oscillator and the second laser as a modulator, the output from the modulator being a single longitudinal mode. A low frequency signal is applied to the first laser 10 and detected in the output of the second laser 11. A phase sensitive detector 18 is responsive to the sensed signal to provide a feedback signal for the second laser 11 such that the cavity modes of the two lasers are aligned automatically.

Method for measuring particle velocity using differential photodiode arrays

Abstract: A method for measuring the velocity of a scatterer in a moving fluid by examining the spatial structure of the optical field on the detector of a Laser Doppler Velocimeter (LDV). The optical field after scattering from the laser beam is a traveling wave of a shape dependent on the detector optics alone. A pair of differential linear arrays are used to find the direction of velocity of the traveling wave and hence that of the scatterer. Furthermore, this method eliminates the Doppler pedestal which requires high pass filter in most of the conventional methods.

Pulse compression LIDAR system - uses Doppler effect in reflected laser light to track moving target

Abstract: The system includes a laser generator (2) serving as a local oscillator to produce a first frequency modulated laser wave, and an average value FE, the wave being intended for transmission. A second unmodulated wave of frequency FL= FE - Fl is produced for superheterodyne reception, FL being the local frequency, and Fl the intermediate frequency. A photomixer (4) mixes the local wave with the received light signals, and produces a beat at the intermediate frequency which is affected by a Doppler derivative FD when a moving target is detected. By compression and demodulationthe distance and Doppler frequency due to the moving target may be determined.

Method for diagnosis of unbalance position by vibration of rotating machine

Abstract: PURPOSE:To determine the position of unbalance from the relation between the unbalance position owing to the unbalance of a rotator and its vibration characteristics. CONSTITUTION:Sahft vibrations are detected by the vibration pickup 6 of a bearing 5, and the output signal thereof is inputted to a vibrometer 7, by which it is converted to an electric signal proportional to vibration amplitudes. This signal is inputted to a multiplex data input device 8. The output signal of the device 8 is inputted via an A/D converter 9 to a control arithmetic device 10. The revolution signal from a revolution detector 13 is amplified and digitized by a tachometer 12, after which it is inputted to the devive 10. The device 10 determines the relation between the number of revolutions and vibration amplitudes by vibration signal and the rotating machine signal at the point of the time when said signal is taken in and further the vibration signal is analyzed by the device 10. By using the vibration value obtained as a result, the evaluation of the cause position for unbalance is executed and the result of the diagnosis is displayed in a display device 11.

Measuring head for a laser Doppler vibrometer

Abstract: In a laser Doppler vibrometer, a Bragg cell (3) immediately adjacent to the laser (2) is used both to obtain a primary beam (4) directed straight onto the object and to obtain a reference beam (5) which is frequency-shifted relative thereto; its control voltage is set such that the reference beam (5) and the radiation (13) back-scattered at the object have approximately the same intensity when superimposed. This renders mechanical adjustment of individual components of the vibrometer superfluous with regard to differing object properties. The beat frequency of the radiation produced by the superimposition is detected by means of photodiodes (14, 15) as a characteristic of the object vibration.

Method and apparatus for diagnosing vibration of rotary machine

Abstract: PURPOSE:To enable automatic diagnosis of the occurence of the thermal deformation of a rotor through the realization of a fact that the direction of time-dependent variation and the tendency of the amplitude variation of an unbalanced vibration vector within a fixed time are substantially constant CONSTITUTION:The vibrations of rotor bearings 41-46 detected by vibration detectors 51-56 are sent to a processing device 10 through a vibrometer 7, a data input device 8 and an A-D converter 9 The processing device 10 extracts the components of the vibrations, while the output of a pulse pickup 6 receives a reference signal which has been processed by a waveform converter 11 or a tachometer 12 for data processing The processed data is sent to a memory 14 and to a discriminator 15 The discriminator 15 decides if the vibrations are due to unbalance or not An operator 16 performs the operation of variation vectors Comparators 17 and 18 check the tendency of phase variation and the tendency of amplitude variation, respectively A discriminator 19 decides the thermal deformation and the result of decision is indicated in an indicator 21 through a controller 20 Thus automatic diagnosis of the thermal deformation is attained

Knocking detecting method and its apparatus of internal combustion engine

Abstract: PURPOSE:To detect knocking with high accuracy, by detecting the vibration of cooling water and the variation of pressure in a water chamber, which are caused through a partition wall by knocking in the combustion chamber. CONSTITUTION:In a knocking detection device installed to a water-cooling system internal combustion engine, when knocking occurs in a combustion chamber 2, cooling water in a water chamber 4 vibrates through its knocking cylinder 3, and its vibration is detected by a vibration-detecting part 14 of a vibrometer. As a result, a bimorph element 18 of the vibrometer resonates, and the output voltage of the bimorph pressure element 18 is outputted to a terminal 19. Since the vibrometer 13 is insulated in vibration from engine blocks 1, 7 and faces the water chamber 4, the vibration of the engine blocks 1, 7 having a lot of noises is not detected and the vibration of cooling water in the water chamber 4, which scarcely has a noise is detected, therefore, the SN-ratio is raised and the detecting accuracy of knocking becomes high.

Laser beam monitoring system

Abstract: Laser beam monitoring systems include laser-transparent plates set at an angle to the laser beam passing therethrough and light sensor for detecting light reflected from an object on which the laser beam impinges.

Vibration diagnosis of rotary machine

Abstract: PURPOSE:To improve reliability of a rotary machine by supervising axial vibration of the rotary machine and damping effectively the axial vibration when the vibration is big. CONSTITUTION:The signals detected by a vibration pick-up in the journal upper part of a bearing 5 are put into a vibrometer 7 to be converted into d digital quantity through an A/D converter 8, the digital signal is then delivered to a diagnosis device 9. In a data processing device 11 forming the core of the diagnosis device 9 the axial vibration data of an axial system are taken in to be registered in a memory device 12 for being processed according to the process instruction put in from a process instruction input device 14 to indicate in the indicator device 13. The content of the diagnosis consists in the execution of vibrarion diagnosis by combining those fundamental elements such as the balancing weight calculation for reducing axial vibrarion, vibrarion value calculation after adding a weight, synthesis of the vibration value and the quantity of the weight, an average of the vibrarion value and the weight quantity, extraction of a characteristic of the axial vibrarion and the comparison with a standard of judgement of vibration as the processing units.

Resonant Doppler velocimetry in supersonic nitrogen flow

Abstract: The development of the Resonant Doppler Velocimeter (RDV) is discussed It is a new nonintrusive laser technique for flow diagnosis The RDV technique is applied to supersonic nitrogen flow with sodium atoms as tracer particles The measurements are achieved by shining a tunable single frequency laser beam into the flow The resonant absorption spectrum of the seeded species is determined by observing the fluorescence signal intensity as a function of excitation wavelength By comparing the peak absorption wavelength with a reference frequency marker, the flow velocity along the excitation beam can be obtained through the Doppler shift relation By fitting the spectrum with a theoretical line profile, the static temperature and pressure of the flow an be determined

Oscillation monitoring device

Abstract: PURPOSE:To provide a monitoring system of high reliability by measuring the correlations among signals by using a changeover switch and a correlation analyzer with respect to the entire vibrometer output signals of the monitoring system and displaying abnormal output signals CONSTITUTION:Turbine rotors 1, 2 and a generator rotor 3 are coupled, and vibrometers A4-F9 are connected to respective bearing parts A correlation matrix former 13 and a display device 14 are connected to these Each two sets of signals are drawn out from the output signals of the respective vibrometers by means of a changeover switch 10, and the correlations thereof are measured with a correlation analyzer 11 If there is any correlation, they are turned off and if there are no correlations, they are turned on by a microswitch 12 If it is assumed that only the vibrometer C is abnormal, the line C and the row C are on and the rest are off as shown in the figure, thereby displaying the abnormality of the vibrometer C The monitoring system of high reliability is obtained

Diagnosis apparatus for vibration of rotary apparatus

Abstract: PURPOSE:To permit a vibration diagnosis at high accuracy, by providing a plurality of filters in the stage prior to the frequency analysis of the shaft vibration signal, and changing over said filters to each other according to the change in the number of revolutions or the change of the condition of a rotary apparatus when the analysis is performed. CONSTITUTION:The vibration of a rotating body 1 is detected by a shaft vibrometer 2 and amplified before being inputted to filters 11 and 12. On the other hand, by a pulse gear 9 directly connected to the shaft of the rotating body 1 and a revolution signal generator 10, the signal corresponding to the detected number of revolutions is inputted to a change-over signal generator 14. The change-over signal generator 14 generates a filter changing-over signal according to a prescribed set level so that the filter 11 is used at starting, however, the filter 12 is used when the number of revolutions has increased.

Vibration diagnostic device of rotary apparatus

Abstract: PURPOSE:To get rid of a decision error due to a fault of a diagnostic device itself, and to diagnose the vibration of a rotary apparatus with high accuracy, by deciding a fault by means of mutual comparison of overall values obtained from an axial vibration waveform. CONSTITUTION:The vibration of a rotary body 1B is detected by an axial vibrometer 3, a detection signal is A/D-converted at 5, and after that, is inputted to a Fourier analyzer 7, a spectrum signal corresponding to the rotational frequency is extracted and is supplied to a setting comparator 8. When a result of comparison is abnormal, a switch 15 is turned on, a detection output of an axial vibrometer 2 of a rotary body A is led into a detector 9, and an overall value is provided to a comparator 11. On the other hand, the converted 5 output is processed to a mean value 6, and the processed value is provided to the comparator 11. The comparator 11 outputs an abnormal decision normal signal 14 only when both the overall values have become coincident, drives a switch 16 and sents out the decision result of the comparator 8 to the outside.

Laser doppler vibrometer

Abstract: PURPOSE:To facilitate the regulation of the positions of a focal point and an irradiation by transmitting irradiating and reflected laser light by using optical fibers CONSTITUTION:An irradiating laser light is focused by a lens 11, inputted into optical fibers 12 and transmitted Light emitting from the tip of the fibers 12 is converged on the surface of an object to be measured by an objective lens 14 Since the focal length of the lens 14 can be reduced, adjustment for the position of focal point and that of irradiation can be easily performed The light reflected from the surface of the object to be measured is inputted into optical fibers 13 and transmitted Light radiated from the fibers 13 is led to a prism 17 by a lens 16, and made to interfer with the reference light with a shifted frequency When the fibers 12, 13 are selected adequately in length, optical path length to the object 15 to be measured can be made easily to be at an optimum value

Laser Doppler Method for Measuring Oscillating Flow in Prismatic Tanks

Abstract: THE flowfield inside a partially filled prismatic tank with a rectangular section which oscillates laterally has been analyzed using a laser Doppler velocimeter. The distribution of vertical velocity near the free surface, when the frequency of the acting force is equal to one of the natural frequencies of the liquid-tank system, shows that the maxima and the nodes are shifted toward the center of the tank in comparison with the positions computed using the linear theory. Considering the effective value of the horizontal velocity along a vertical line, it is possible to show a velocity out of phase at different points. This phenomenon is particularly noticeable for the vibration modes of higher order. Contents Experimental studies of the sloshing flow, which are needed essentially to determine the natural frequencies of the tankliquid system, have been carried out by flow visualization or by measuring the free surface levels, the accelerations, and the pressures.1 Few attempts have been made to analyze the velocity field instead. In fact, the particular characteristic that the velocity of the fluid motion oscillates near the zero value has made it difficult to analyze the fluid field experimentally. In the present paper good results are obtained using a laser Doppler velocimeter (LDV) to determine the velocity field inside the fluid in a tank laterally excited. The LDV method enables one to obtain very accurate velocity measurements with a good spatial resolution, without disturbing the field in any way. The tests have been carried out using a Plexiglas rectangular tank (30 X 15 cm) rigidly fixed to the oscillating table which is excited by a sinusoidal force of given amplitude and frequency supplied by an electromagnetic vibrator; the height of the liquid at rest was kept at h= 15 cm. The vibrator is controlled through an amplifier by a signal generator with a 0.01-Hz sensitivity in the low-frequency band (Fig. 1). The LDV is a one channel system and was used in the dual beam mode.2'3 The transparent walls of the tank permit the use of the forward-scattering method. The two beams are then led in the tank and allowed to cross at the point of interest. The LDV apparatus consists essentially of an-He-Ne laser of 5 mW power; an optical unit with a Bragg cell to shift the frequency, in order to measure negative velocities and those close to zero; a photomultiplie r; a series of filters, in order to reduce the noise-signal ratio; and a tracker, in order to measure the Doppler frequency. The output signal from either the accelerometer amplifier or the trackers are sent to an rms voltmeter which measures the effective value of acceleration and velocity. The vertical component of velocity is measured by the LDV at the point M which has been taken on the symmetry plane 2