Showing papers on "Laser Doppler vibrometer published in 1983"

Laser phase and frequency stabilization using an optical resonator

Abstract: We describe a new and highly effective optical frequency discriminator and laser stabilization system based on signals reflected from a stable Fabry-Perot reference interferometer. High sensitivity for detection of resonance information is achieved by optical heterodyne detection with sidebands produced by rf phase modulation. Physical, optical, and electronic aspects of this discriminator/laser frequency stabilization system are considered in detail. We show that a high-speed domain exists in which the system responds to the phase (rather than frequency) change of the laser; thus with suitable design the servo loop bandwidth is not limited by the cavity response time. We report diagnostic experiments in which a dye laser and gas laser were independently locked to one stable cavity. Because of the precautions employed, the observed sub-100 Hz beat line width shows that the lasers were this stable. Applications of this system of laser stabilization include precision laser spectroscopy and interferometric gravity-wave detectors.

Calibration of automated laser machining apparatus

Abstract: A computer controlled apparatus is disclosed for controlling a sequence of machine steps utilizing a laser beam whose power level is adjusted in accordance with its parameters as a function of a measurement of the power level of the generated laser beam. The laser apparatus includes a laser source or rod for emitting a laser beam and means in the illustrative form of a laser lens assembly for focusing and directing the laser beam onto the work piece. The laser source is associated with excitation means in the form of lamps for pulse driving or exciting the laser rod to emit a like sequence of laser pulses, whose parameters, e.g. pulse width and frequency, are selectively varied and controlled. The power level of the laser beam is calibrated by first measuring the power level of the laser beam as directed onto the laser piece, and then by using the measurement of laser power to calibrate or to adjust the degree of lamp excitation.

Body vibration and sound production in an insect (Atta sexdens) without specialized radiating structures

Abstract: 1. The leaf cutting antAtta sexdens stridulates using a file-and-scraper device (Markl 1968). The temporal and spectral characteristics of the cuticular vibration and airborne sound are fairly typical of the stridulatory sounds of insects that lack specialized radiating structures (Masters 1980). We used laser-Doppler vibrometry (LDV) to measure the velocity of different points on the ant's body during stridulation to determine what sorts of body vibration are produced by the impact of the scraper on the file, both in air and with mass-loading of the cuticle underwater, and how the vibration relates to this radiated sound. 2. The gaster, on which the file is located, appears to be the principal sound-radiating part of the ant. From theoretical considerations, we would expect four types of gaster vibration to be excited by the scraper impact: (I) dipole swinging of the entire gaster, (II) quadrupole distortion of the gaster shape due to volume flow of the gaster contents, (III) monopole pulsation of the gaster and (IV) bending waves travelling in the gaster shell. Each type of vibration has associated modal resonances whose frequencies are predicted in a semi-quantitative fashion from a simple mechanical model of the gaster. 3. Vibrometer measurement shows that each tooth strike typically excites low frequency (∼1 kHz) and high frequency (∼10 kHz) damped vibrations that can be detected at most points on the gaster. Broadband spectral energy can be detected up to about 30 to 40 kHz (in rare cases to ∼60 kHz). The low frequency resonance appears to be due to type I rather than type II vibration, and the high frequency resonance due to type III rather than type IV vibration. 4. Underwater, both low and high frequency resonances were still present, but their frequencies were reduced by about 15% and 35% respectively. We expect the decrease to be even greater when the ant is buried underground. 5. The rate at which the scraper strikes the teeth of the file is close to the ∼1 kHz modal frequency of the gaster, but in contrast to our expectation does not exactly match this frequency (Fig. 2). The reason for this discrepancy is not clear. 6. Below about 30 kHz there is fairly good correspondence between the energy spectra of the airborne sound recorded with a microphone and the gaster vibration recorded by LDV. Above this frequency the sound usually shows a complicated power spectrum that we can relate to the vibration of the body only in a qualitative fashion.

Scanning type laser system

Abstract: A laser system emits a laser beam from a laser oscillator (10) through a kaleidoscope (18) to make intensity distribution of the laser beam uniform. This laser system is a scanning type in which a plurality of kaleidoscopes are bundled together to form a kaleidoscope bundle (18). The laser beam from the laser oscillator (10) is scanned and is applied to the input ends of the respective kaleidoscopes of the kaleidoscope bundle (18) successively.

Non-Contact Ultrasonic Waveforms in Metals Using Laser Generation and Interferometric Detection

Abstract: A range of ultrasonic waveforms have been generated in an aluminum plate by a Q-switched Nd: YAG laser. Displacements on the far side of the plate were detected on-epicentrz by an interferometer with a resolution of 0.2 A and a bandwidth of 40 MHz. At optical power densities below the ablation threshold, the thermoelastic waveform was observed without signal averaging. At increased generating power densities t he waveform was seen to be modified. In all cases, good agreement was seen with predictions of wave propagation theory. Studies were also undertaken for generation at modified surfaces.

Diesel Engine Health: Laser Diagnostics

Abstract: This paper describes two simple laser instruments which the automotive engineer can use in vibrational studies of diesel engines. The first is a "normal surface velocity" instrument which the engineer can hand hold and simply "point" at the target surface for measurement. Field tests have shown it to be quick and easy to use with excellent accuracy and reliability. It is a particular time-saver in test cell use where the necessity for many accelerometer fittings is removed. The second is a laser torsional vibrometer which can measure the torsional oscillation of rotating machinery parts. This has shown itself to be superior to the more standard techniques of slotted discs and slip rings, etc. and provides advantages of higher frequency response, greater accuracy and non-contact measurement. Conclusions drawn herald a step forward in measurement techniques and demonstrate the great potential of laser technology in heavy engineering applications.

Alignment apparatus and method for interferometer spectrometers

Abstract: An interferometer spectrometer aligning apparatus and method are disclosed, in which the laser beam generator, which is in the instrument to provide data controlling clock signals, is also used to accomplish initial (and as needed) alignment of the instrument. The laser beam is directed through a target both on its way from the laser generator to the interferometer, and as it is reflected back from the interferometer, thereby validating the perpendicularity of the reflector to the axis of the interferometer. A semi-transparent mirror, i.e., a small beamsplitter, is used in the path of the laser beam ahead of the interferometer beamsplitter, thereby enabling portions of the laser beam to go into both the interferometer and the sample chamber. A second semi-transparent small mirror (beamsplitter) is also used in the path of the laser beam, for the purpose of providing two parallel laser beams both in the interferometer and in the sample chamber, the parallel beams being used for a plurality of optical checking and adjusting tasks.

A Simple Method for Single-Frequency Operation and Amplitude- and Frequency-Stabilization of an Internal-Mirror He–Ne Laser

Abstract: This paper describes a new and simple method for obtaining the amplitude- and frequency-stabilized single mode output of an internal-mirror He–Ne laser (λ=633 nm). The laser tube is cooled with a constant-speed fan and the electric current signal which is proportional to the total back beam intensity is detected with a silicon photodiode and is applied to an electric heater which controls the laser tube length change due to thermal contraction. Consequently, the laser amplitude and frequency are stabilized at the same time. A relative amplitude stability of ±0.16% and relative frequency stability of ±9×10-9 are obtained over a period of 10 minutes or longer.

System for optically recording information

Abstract: An optical information recording system in which predetermined information is recorded by a first laser light beam on a recording medium along a guiding groove previously formed in the recording medium. Second and third laser light beams are projected onto the recording medium at positions deviated from the center of the guiding groove and preceding and succeeding to the first laser beam. A pattern in which no mutual interference of information to be recorded by the first laser beam is present is detected from an information signal which modulates the intensity of the first laser light beam. A difference is determined between the quantity of light reflected upon illumination of the recorded pattern by the second laser beam chronographically succeeding to the first laser beam and the quantity of light reflected upon illumination by the third laser beam. The position of the first laser beam is controlled on the basis of the thus determined difference for effecting an information tracking operation with improved accuracy.

Laser beam modulating method and apparatus

Abstract: A laser beam modulating method is characterized in that the distribution of power density of the laser beam is changed by closing and opening a passage for the laser beam from a laser resonator. An apparatus for carrying out the method includes a modulator for opening and closing the passage for the laser beam from the laser resonator to a laser processing head assembly.

Simplified road surface status measuring apparatus

Abstract: PURPOSE: To enable to simply measure the road surface status by a construction wherein a vehicle capable of traveling includes a vibrometer, a recorder for recording an amplitude of the signal from the vibrometer a mileage meter for the vehicle, and a signal in conjunction with the mileage meter. CONSTITUTION: Every time when a self-propelled vehicle 1 or pulled vehicle 2 loaded with a vibrometer 3 travels over a certain distance, a signal 7 in conjunction with a trip meter 6 mounted to a distance measuring wheel 5 transmits a pulse signal. This pulse signal is sent to a recorder 4 to advance a chart thereof. Accordingly, the amplitude recorded on the chart due to unevenness of the road surface exhibits accumulation of amplitudes occurred through a certain section being traveled. The range of the amplitude can be easily read and analysis work of the road surface status is very simplified, thus permitting efficient survey by few examiners. COPYRIGHT: (C)1984,JPO&Japio

Vibration measuring device

Abstract: PURPOSE: To execute safely a monitoring even under a bad environment by constituting so that a non-contact vibrometer can be moved to an optional place by a moving device, and also a direction of the vibrometer can be adjusted by an angle adjusting mechanism. CONSTITUTION: An operator transmits through communication devices 14a, 14b a signal (a) for making a moving device 11 run along a prescribed cyclic path, by operating a control panel 16. When it is made to run up to a place to be checked, it is stopped. Subsequently, a signal (b) for controlling an angle adjusting mechanism 13 is supplied, a vibrometer 12 is directed to an object to be measured, and a measurement of vibration is executed. A detecting signal C of the vibrometer 12 is sent to the control panel 16 and used as a displaying and monitoring data. COPYRIGHT: (C)1985,JPO&Japio

Automatic balancer of rotary grinding stone

Abstract: PURPOSE:To enable to perform grinding efficiently by a method wherein the generation of unbalance due to the wear or the like of the rotating grinding wheel is automatically detected and the unbalance is automatically compensated by supplying fluid. CONSTITUTION:When vibration occurs in a center axis 1 or the like due to the partial wear or the like of the rotating grinding wheel, a vibrometer 12 detects the vibration and nearly exactly cyclic vibration signals are obtained from the detected vibration by means of a band-pass filter 13. Controlling signals are formed from said vibration signals by means of a phase compensator 14 and inputted to a pulse generator 15 in order to be converted to pulses to generate. Said pulse signals are applied to a supersonic generator 16, resulting in generating amplified vibration in a vibration horn so as to vibrate a ball valve 22 in order to jet fluid from a fluid injection nozzle 17. The nozzle 17 is installed opposite to a plurality of pockets 7 provided concentric to the grinding wheel 4. Time lag based upon the phase difference in rotation between said controlling signals and generated pulses is adjusted by said phase compensator 14.

Co2 laser device

Abstract: PURPOSE:To continuously measure the output value of a CO2 laser beam by measuring the output value of said beam indirectly from the output value calculated out from the amount of light of a He-Ne laser beam. CONSTITUTION:A photo detector 4 covered with a cover 5 with the front edge projected out is provided in the neighborhood of a lens 2, and then the amount of light of the He-Ne laser beam A a visible light which permeates through an optical fiber together with the CO2 laser beam is detected. In general, in a laser knife, etc., the light of an almost constant output of approx. 2mW is used as the guide light therefor. The degree of output attenuation of this beam due to permeation through the fiber becomes well proportional experimentally to that of the CO2 laser beam due to permeation through the fiber, thus having a great correlation, which can be therefore immediately calculated out from a conversion table.

Laser device and interferometer comprising such a laser device

Abstract: According to the invention, in a laser device the effective wave length of which is stabilized, the Fabry-Perot interferometer (15) which forms an effective wave length etalon is also used as a mode selector so that a simple, cheap multimode He-Ne laser can be used. Such a laser device can very readily be used in interferometers.

A Frequency Stabilization and Trigger Control Unit for Hybrid TEA-CO2 Lasers,

Abstract: : A simple, reliable technique is described for frequency stabilizing a CW-TEA hybrid laser for use as a transmitter in a laser radar system with heterodyne detection. In this technique, modulation is applied to the laser cavity, the output frequency of the laser is monitored when operating in the CW mode, and the TEA laser discharge is triggered when the desired output laser frequency is detected. Details are given of the electronics used to implement the technique, as well as those for controlling the pulse repetition rate and protecting the laser itself if arcs are generated in laser discharge. (Author)

"A Thermally Stabilized, Two Frequency Laser Measurement System For Industrial Use"

Abstract: Hewlett-Packard Company introduced a new laser system based upon a new HeNe laser tube in September 1982 The 5528A Laser Measurement System is finding wide spread use in industry for improving productivity in the numerically controlled machine shop, and is now being designed into machines as a basic positioning transducer The new laser tube design is simpler and less expensive than that previously built by HP using 2-frequency techniques

Effect of wall scattering on SNR in off-axis differential-type laser Doppler velocimetry

Abstract: Though various properties and applications of laser Doppler velocimetry have been extensively studied in the past decade, there is little discussion on the effect of light scattering from the surface of a cell on Doppler beat signals or on methods of reducing it. In this paper, the effect of light scattering from the surface of the cell is treated as a background noise and is studied theoretically and experimentally on the detecting process of Doppler beat signals in off-axis differential-type laser Doppler velocimetry. Laser Doppler velocimetry of an off-axis type is verified to be effective for measurement of the flow velocity in the vicinity of a scattering wall. The effect of the light scattered from the wall surface on the signal-to-noise ratio (SNR) of Doppler beat signals is discussed in detail. The minimum distance, which is close to the wall and at which good Doppler beat signals can be obtained, is defined and determined quantitatively. This minimum distance is found to be strongly affected by the off-axis angle of the detecting optical system.

Method for measuring relative movements by means of laser radiation in accordance with the Doppler radar principle

Abstract: In the so-called heterodyne method for measuring relative movements by means of laser radiation according to the Doppler radar principle, two laser beams having a constant frequency difference are needed. Utilising the interaction of transverse laser modes, laser beams having a constant frequency difference are generated and coupled out in part areas of a single laser.

Magnetic resonance of cesium atoms in the case of optical pumping by radiation from a single-mode injection laser

Abstract: An investigation was made of the influence of single-mode radiation from an injection laser on the magnetic resonance signal as a function of the laser radiation frequency. It was found that the amplitude, phase, and rate of decay of the free precession signal depended on the tuning of the laser radiation frequency within the Doppler profile of the line representing the hyperfine levels of the ground state of cesium.

Laser Probing of SAW Convolver Waveguide

Abstract: HE surface acoustic wave laser probe based on a superheterodyne principle [l] has demonstrated good linearity and sensitivity over a frequency range to 1 GHz. Its high spatial resolution has facilitated detailed measurements in convolver waveguides [2]. Recent laser probe measurements of waveguide attenuation will be reported here. In the next section the applied measurement technique will be described. Some typical results will then be presented and discussed, demonstrating that the setup has a very good reproducibility and a high accuracy. 11. MEASUREMENTS The laser probe setup which has been discussed in detail previously [l], is shown in a simplified diagram in Fig. l(a). A laser beam is focused by a lens on the propagating surface and reflected through the same lens towards a double photodiode. The focused spotsize on the surface is less than an acoustic wavelength. The tilting perturbation introduced on the laser beam by the surface wave is therefore sensed as a lateral movement by the photodiode. An electrooptic modulator amplitude modulates the laser beam at a frequency near the surface wave frequency. The beat frequency of these two frequencies is detected by the photodiode, thus facilitating a low frequency lock-in amplifier detection scheme. This setup has been applied as described below to obtain accurate measurements.

Method for information transmission

Abstract: In a method for information transmission by means of laser radiation which is modulated as a function of time, the laser beam is modulated on the basis of the interaction of transversal laser modes. By deliberately changing the parameters of the laser resonator as a function of time, this interaction of the transversal laser modes, and hence the laser beam modulation, are influenced as a function of time.