Showing papers on "Laser Doppler vibrometer published in 1987"
TL;DR: Sideband cooling of an ion in an rf (Paul) trap is reexamined including the effects of finite laser bandwidth and the energy of the rf micromotion and the implications for high-resolution, high-accuracy spectroscopy are investigated.
Abstract: The limitations to the achievement of low kinetic energies for laser cooling of single ions confined in electromagnetic traps are discussed. Sideband cooling of an ion in an rf (Paul) trap is reexamined including the effects of finite laser bandwidth and the energy of the rf micromotion. The micromotion is the oscillatory motion of the ion at the same frequency as the rf voltage applied to the trap electrodes. Sideband cooling of ions in a Penning trap is examined for the first time. In both cases, cooling to the zero-point energy of the ion in the trap should be possible and a method for verifying this condition is suggested. The implications for high-resolution, high-accuracy spectroscopy are investigated. Under certain conditions, the uncertainty in the second-order Doppler shift may be significantly less than 1 part in ${10}^{18}$. .AE
137 citations
NEC1
TL;DR: A simple and inexpensive method of directional discrimination of velocity based on the analysis of the Doppler signal's waveform obtained through a self-mixing type laser Dopplers velocimeter (LDV) is described.
Abstract: A simple and inexpensive method of directional discrimination of velocity based on the analysis of the Doppler signal's waveform obtained through a self-mixing type laser Doppler velocimeter (LDV) is described. The technique does not need the components commonly used to give the frequency offset required to yield directional information in LDV. The device is described, and experimental evidence is presented.
115 citations
Patent•
18 Aug 1987
TL;DR: In this paper, the position of the receiver is established in three dimensions by detecting the elevation of the laser reference plane and reflecting the laser energy back to the transmitter, where the reflected energy is employed to produce a signal indicative of the range of a receiver and its location with respect to a reference axis.
Abstract: A laser beam alignment system includes a transmitter which establishes a laser reference plane by continuously rotating a horizontal laser beam about the transmitter. A remotely located receiver senses the elevation of the laser reference plane and reflects a portion of the laser energy back to the transmitter where the reflected energy is employed to produce a signal indicative of the range of the receiver and its location with respect to a reference axis. The position of the receiver is thus established in three dimensions.
67 citations
Patent•
21 Sep 1987
TL;DR: A heterodyne laser spectroscopy system utilizes laser homodyne techniques for the purposes of laser isotope separation, vapor diagnostics, processing of precise laser frequency offsets from a reference frequency, and spectral analysis of a laser beam as discussed by the authors.
Abstract: A heterodyne laser spectroscopy system utilizes laser heterodyne techniques for purposes of laser isotope separation spectroscopy, vapor diagnostics, processing of precise laser frequency offsets from a reference frequency and the like, and provides spectral analysis of a laser beam.
58 citations
Patent•
IBM1
TL;DR: In this paper, a process and apparatus for producing a beam of coherent radiation at essentially 459 nm by mixing, in a nonlinear crystal consisting essentially of KTP, two laser beams, one at essentially 1064 nm and the other at essentially 808 nm.
Abstract: A process and apparatus are disclosed for producing a beam of coherent radiation at essentially 459 nm by mixing, in a nonlinear crystal consisting essentially of KTP, two laser beams, one at essentially 1064 nm and the other at essentially 808 nm. The 1064 nm radiation is derived from a Nd:YAG laser that consists of an input mirror, an output mirror and a Nd:YAG crystal, and contains also the KTP crystal. The Nd:YAG laser is pumped by an essentially 808 nm semiconductor diode laser beam, which passes through the input mirror and through the KTP crystal into the Nd:YAG laser crystal where it is absorbed. The 1064 nm radiation oscillating inside the Nd:YAG laser resonator is mixed either with the said 808 nm pump beam or with 808 nm radiation provided by a second semiconductor diode laser whose light is coupled with the 1064 nm beam using a beamsplitter. The essentially 459 nm beam passes through the output mirror to a utilization device.
54 citations
Patent•
17 Apr 1987
TL;DR: In this paper, a method for detecting the seismic discontinuity in acoustic impedance caused by an acoustically hard, reflective object buried a few feet below poroelastic soil using seismic activity induced through acoustic coupling with a remote sound source was proposed.
Abstract: A method for detecting the seismic discontinuity in acoustic impedance caused by an acoustically hard, reflective object buried a few feet below poroelastic soil using seismic activity induced through acoustic coupling with a remote sound source. The abrupt change in the soil impedance caused by the buried object causes sound to reflect between the object and the surface and increase the amplitude of the seismic vibrations induced by the incident acoustic energy. The change in the seismic displacement of the soil is on the order of angstroms which can be detected using remote optical test equipment such as a laser-doppler vibrometer (LDV) commonly used in nondestructive testing. A sound source emits sound at frequencies that induce significant seismic coupling with the poroelastic soil. Part of a beam of laser light of an LDV is scanned over the ground. The laser light is shifted in frequency from its source frequency by an amount intended to approximate the frequency of the anticipated seismic vibrations. The seismic vibrations of the soil frequency modulate the laser light to form upper and lower side bands. The amplitude of the side bands increases in the presence of an acoustically hard object due to the greater seismic vibrations over the acoustically reflecting surface. Laser light that is scattered back is combined with unshifted laser light in the photodetector of the LDV so as to eliminate the optical frequency effects of the laser and to cause the carrier frequency and side bands to emerge as distinct signals.
53 citations
TL;DR: The design of an optical element for laser beam line expansion which bears some resemblance to a prism with a small radius at its apex expands the laser beam in one direction only is described.
Abstract: The design of an optical element for laser beam line expansion is described. The element which bears some resemblance to a prism with a small radius at its apex expands the laser beam in one direction only. The technique for designing such a lens is given together with examples of lenses having different rates of divergence.
53 citations
TL;DR: Basic considerations of fibre optics and Rayleigh light scattering are applied to the field of laser Doppler blood flow meters and it has been found that it is important to ensure that the fields of view of the illuminating and detecting fibres do not overlap at the skin surface and that probe contact with theskin surface should be maintained.
Abstract: Laser Doppler flowmetry with optical-fibre beam transmission is a sensitive fast and convenient method of measuring tissue blood flow. However, its sensitivity can also be a problem because of movement artefacts. This study applies some basic considerations of fibre optics and Rayleigh light scattering to the field of laser Doppler blood flow meters. Practical suggestions are given by which movement arterfacts can be reduced by choice of optical fibres, attention to probe geometry, cladding the fibres to reduce their movements and in the method of application. Experiments which test the normalisation circuitry of laser Doppler instruments are described and the effects of movement artefacts on the interpretation of the pulsatile component of laser Doppler records are also discussed. Probe and fibre line movements cause high-frequency intensity fluctuations due to speckle movement. The intensity fluctuations produce an apparent Doppler shift much greater than the Doppler shift produced by the relative movements of probe and tissue. It has been found that it is important to ensure that the fields of view of the illuminating and detecting fibres do not overlap at the skin surface and that probe contact with the skin surface should be maintained.
42 citations
Patent•
31 Aug 1987
TL;DR: In this article, the wavelength of a laser beam was detected by utilizing an optogalvano effect based upon atoms or molecules in the plasma. And the result of detection was used for controlling the laser beam.
Abstract: A method and an apparatus for detecting the wavelength of a laser beam by utilizing an optogalvano effect based upon atoms or molecules in the plasma. Atoms or molecules in the plasma are irradiated with a laser beam. The impedance of the plasma at this moment is detected to determine whether the wavelength of the laser beam is in agreement with a predetermined absolute wavelength. The result of detection is used for controlling the wavelength of the laser beam.
38 citations
TL;DR: In this paper, a readback signal modulation (RSM) technique was used for measuring the dynamics of the head/disk interface in magnetic disk files using the modulation of a sinusoidal read-back signal that results from head/ disk spacing variation.
Abstract: -A new method is developed for measuring the dynamics of the head/disk interface in magnetic disk files. This method utilizes the modulation of a sinusoidal readback signal that results from head/ disk spacing variation. Measurements of slider dynamics using this readback signal modulation (RSM) technique are compared with measurements made with the laser-Doppler vibrometer (LDV) for transient slider motions that are introduced by several different means of slider disturbance. The RSM measurements are calibrated experimentally by use of the LDV together with the functional form provided by the Wallace equation, which expresses the dependence of the readback voltage on various recording parameters including the head/disk spacing. The RSM technique for head/disk spacing measurement variation has a resolution of 50 nm without correction, and this can be improved to 5 nm by removal of the systematic error that is associated with the recorded signal. A frequency range of 20 Hz to 100 kHz is achievable. Since the read/write head of the disk file is used as the measurement transducer without modification, and relatively simple and inexpensive additional instrumentation is required for the implementation of the RSM technique, it is expected that this method may become a useful tool in the research and development of magnetic disk files.
TL;DR: In this article, the mean optical frequency of a single-mode semiconductor laser used under modulation in a FSK heterodyne transmission system is achieved by a novel method that locks the laser to one of the resonance frequencies of a Fabry-Perot interferometer (FPI).
Abstract: The stabilization of the mean frequency of a single-mode semiconductor laser used under modulation in a FSK heterodyne transmission system is achieved by a novel method. The frequency stabilization scheme locks the laser to one of the resonance frequencies of a Fabry-Perot interferometer (FPI). The laser is weakly modulated at a frequency higher than any signal frequencies. Light reflected from the FPI is detected and synchronously demodulated for feedback and current control of the laser. A laser modulated by a pseudorandom sequence with a rate of 140 Mbit/s and an optical frequency deviation of 280 MHz is stabilized with this method against variations in operating temperature and bias current. The mean optical frequency is maintained within ± 10 MHz for hours. Analysis and experiments confirm that the laser frequency remains stable even when the laser linewidth changes under weak optical feedback.
Patent•
14 Apr 1987
TL;DR: In this article, a laser recording apparatus for printing multi-tone image data by driving a laser diode according to levels of an analog signal containing the image data is described, and the output of the diode is stopped or reduced in level for a certain time in each of periods at predetermined intervals, each period corresponding to each pixel in the printed image.
Abstract: A laser recording apparatus for printing multi-tone image data by driving a laser diode according to levels of an analog signal containing the image data thereby to modulate a laser beam output by the laser diode, and causing the modulated laser beam to scan a recording medium in transverse directions. The output of the laser diode is stopped or reduced in level for a certain time in each of periods at predetermined intervals, each period corresponding to each pixel in the printed image. This eliminates mode hopping noise and optical feedback induced intensity noise, and hardly gives rise to the problem of electromagnetic wave disturbance. By elongating or shortening the time for stopping or reducing the emission by the laser diode (which time is shorter than the period corresponding to one pixel), the image density may be adjusted without impairing the above advantage.
Patent•
21 Aug 1987
TL;DR: In this paper, an optical filter in the path of propagation of the laser beam from a laser light source to an image forming surface to form an image with the beam transmitted through the filter, and the transmittance of the filter based on the result obtained by detecting the intensity of the transmitted laser beam and comparing the detected value with a value of image density set by an operator.
Abstract: A laser beam control device related to the present invention includes an optical filter in the path of propagation of the laser beam from a laser light source to an image forming surface to form an image with the laser beam transmitted through the filter, and controls the transmittance of the filter based on the result obtained by detecting the intensity of the transmitted laser beam and comparing the detected value with a value of image density set by an operator.
TL;DR: In this article, a small differential laser Doppler velocimeter which uses a semiconductor laser and a small number of optical components is described, where the light from the laser diode is split into coherent beams by means of a diffraction grating.
Abstract: A small differential laser Doppler velocimeter which uses a semiconductor laser and a small number of optical components is described. In this device the light from the laser diode is split into coherent beams by means of a diffraction grating. The two first-order beams are crossed in a probe volume with a lens. In a test experiment the velocity of water containing 0.9 mu m polystyrene spheres was determined from the fluctuation of the scattered light. This velocity agreed with the velocity calculated from flux measurements.
Patent•
05 Jun 1987TL;DR: In this paper, an optical type head device consisting of a laser beam source, a light focussing means for converging the laser beam on a data storing surface of an optical-type data storing medium, a laser beacon detecting means which receives the laser beacon reflected by the optical type data stored medium and modulated by data held by the same, and converting the data into electric signals, a driving current supplying means for supplying a high frequency current to the laserbeam source.
Abstract: An optical type head device comprises a laser beam source for emitting a laser beam, a light focussing means for converging the laser beam on a data storing surface of an optical type data storing medium, a laser beam detecting means which receives the laser beam reflected by the optical type data storing medium and modulated by data held by the same, and converts the data into electric signals, a driving current supplying means for supplying a driving current to the laser beam source. The driving current supplying means comprises a high frequency current generator which supplys to the laser beam source a high frequency current having a waveform ranging from the lower part of the threshold value at which the laser beam source starts emission of the laser beam to the higher part of the thresheld value, and the frequency of the high frequency current is at least twice as high as the maximum frequency component of information which is contained in the data storing medium.
Patent•
28 Dec 1987
TL;DR: In this paper, an arrangement for position finding of a laser beam in a scattering medium with a laser transmitter and a laser receiver followed by an evaluation circuit is presented. But the evaluation circuit cannot differentiate in the incoming laser radiation the unscattered coherent content and the scattered content.
Abstract: An arrangement for position finding of a laser beam in a scattering medium with a laser transmitter and a laser receiver followed by an evaluation circuit. In order to be able to differentiate in the incoming laser radiation the unscattered coherent content and the scattered content, the laser transmitter is connected to a modulation circuit for intensity modulation of the transmitted laser beam with a characteristic modulation frequency (fL >1/Ts) with the pulse duration spread being Ts, which a brief laser pulse experiences upon being scattered in the medium. In addition, the receiver is connected to an electronic frequency filter tuned to the characteristic modulation frequency. Thereby, essentially only the unscattered coherent content of the laser beam is utilized for evaluation.
TL;DR: The principal noise of the LDOV is due to transit broadening rather than the most commonly suggested signal shot; the phase ambiguity noise is also shown as less serious for the dual-beam LDOVM as discussed by the authors.
Abstract: The principal noise of the Laser Doppler Velocimeter is shown to be due to transit broadening rather than the most commonly suggested signal shot; the phase ambiguity noise is also shown as less serious for the dual-beam Laser Doppler Velocimeter. On the basis of optical geometry and Fourier analysis of electric fields interacting with moving particles, the transit broadening noise has been calculated; some supporting experimental evidence is also discussed along with means for reducing this principal noise.
Book•
01 Jan 1987
Patent•
16 Oct 1987
TL;DR: In this article, the Stokes frequency shift of the waveguide material has been used to distinguish between the data-carrying and the pump-laser beam at the receiving end.
Abstract: At the receiving end or point at which a data or information carrying seed laser beam is to be received after traveling through a medium, a pump laser beam is propagated through the medium to the sending end of the medium at which point the now aberrated pump laser beam may be amplified if necessary and directed to and propagated through a waveguide composed of a suitable third order optically nonlinear medium. The data carrying seed laser beam is directed to and through the waveguide where it is phase conjugated and then through the medium in the direction opposite to that of the pump laser and arrives at the receiving end as an unaberrated laser beam. The data carrying laser beam and the pump laser beam have a frequency difference equal to the Stokes frequency shift of the waveguide material.
Patent•
22 Dec 1987
TL;DR: In this article, a laser beam recording method and apparatus are constituted for recording an image by obtaining a laserbeam whose optical intensity is modulated by controlling a drive current for a semiconductor laser on the basis of a light emission level instructing signal corresponding to an image signal, and scanning the laser beam on a photosensitive material.
Abstract: A laser beam recording method and apparatus are constituted for recording an image by obtaining a laser beam whose optical intensity is modulated by controlling a drive current for a semiconductor laser on the basis of a light emission level instructing signal corresponding to an image signal, and scanning the laser beam on a photosensitive material. The optical output is stabilized by detecting the optical intensity of the laser beam and feeding back a feedback signal corresponding to the detected optical intensity to the light emission level instructing signal. A filter circuit formed so that the gain gradually increases from near to a cutoff frequency of a circuit for the optical output stabilization toward a higher frequency side is disposed in a stage prior to the circuit for the optical output stabilization. Or, a bias current of a value smaller than the value of the drive current that produces the laser beam of the minimum optical intensity capable of exciting the photosensitive material is always fed to the semiconductor laser.
Patent•
30 Sep 1987TL;DR: In this article, the Doppler shift information is integrated with the absolute distance measurements made in the chirp mode to calculate the radial distance from the laser distance gauge to the target.
Abstract: A laser distance gauge measures the distance and shape of a target by alternately performing (a) a Doppler shift measurement during optical scanning of the target's surface and/or motion of the target and (b) a chirp measurement with a chirp frequency laser signal. To ascertain changes in radial distance from the gauge to the target, the Doppler shift information is integrated and the result is combined with absolute distance measurements made in the chirp mode. A single CW laser, which operates single frequency, serves for both types of measurement. A computer changes the gauge from Doppler mode to chirp mode when the Doppler shift reaches a predetermined amount. When a chirp measurement of absolute distance is completed it reverts to Doppler mode.
Patent•
05 Nov 1987
TL;DR: In this article, the measuring laser beam (35) is directed ahead of the power laser beam into the area of the seam and reflected by an optoelectronic measuring device (10).
Abstract: In this method, the measuring laser beam (35) - as viewed in the welding feed direction S - is directed ahead of the power laser beam (7) into the area of the seam (31) and - reflected - is received by an optoelectronic measuring device (10). In this arrangement, the measuring laser beam (35) can both be blocked out as a partial beam from the power laser beam (7) and also taken from a separate laser- beam source (37). For better recognition, the measuring laser beam (35) is preferably directed periodically across the seam (31).
Patent•
02 Oct 1987TL;DR: In this paper, a device for forming an image with a laser beam is described, which consists of a laser, means for on-off modulating a laser and means for converting a wavelength of the laser beam generated by the laser.
Abstract: A device for forming an image with a laser beam is disclosed. The device comprises a laser, means for on-off modulating a laser beam, means for converting a wavelength of the laser beam generated by the laser and means for scanning the laser beam. With means for converting a wavelength of the laser beam, the laser which generates a laser beam, the wavelength of which does not directly meet the requirements, may be adopted to form an image.
Patent•
28 Oct 1987
TL;DR: In this article, a two-dimensional scanner was proposed to enable the observation of the fundus without increase in noise of an amplifier and also to enable observation with the second laser beam even when Landort ring is found by the first laser beam.
Abstract: PURPOSE: To enable observation of the fundus without increase in noise of an amplifier and also to enable observation of the fundus with the second laser beam even when Landort ring is found by the first laser beam. CONSTITUTION: From the first and the second laser beam sources 1 and 5, visual laser beam and infrared laser beam are emitted. Infrared laser beam emitted from the source 5 enters into a two dimensional scanner 7 through a beam splitter 6 after reflected by a half mirror 4. This scanner 7 scans the fundus of a test eye H and reflected laser beam which has reflected in the fundus is received by a photodetector 9. Light receiving signals is input in a indicator 11 in accordance with the amount of light received to produce fundic image, which can be observed. Since a light modulating circuit 3 modulating signals during a certain period, the light modulating circuit 2 emits visual laser beam from the first laser beam source 1. In this way, reaction of a subject can be examined by giving stimulation of desired strength. COPYRIGHT: (C)1989,JPO&Japio
Patent•
14 Jan 1987
TL;DR: In this article, a dual-beam amplitude-modulated laser transmitter/receiver suitable for laser-radar applications is proposed, which is scalable to high powers because there is no active modulator element that the beam passes through.
Abstract: A dual-beam amplitude-modulated laser transmitter/receiver suitable for laser-radar applications is scalable to high powers because there is no active modulator element that the laser beam passes through. The transceiver comprises a laser source with two separate independent laser optical cavities. Each laser cavity is similar, but each operates at its own frequency. Signals from the two cavities are superimposed at a combining beam splitter to form two transmitter output beams with each combined beam intensity modulated at the laser difference frequency. The output consists of two beams separated in elevation and with equal beam powers from each laser cavity the intensity modulation is 100%. Each beam has its own homodyne detector and separate local oscillator. Thus, each beam path is considered to be a distinct homodyne transceiver. If the frequency of one of the laser sources is changed in time, an AM/FM/CW output suitable for absolute range measurements and fine doppler is generated. The laser transmitter does not require internal or external modulators such as acousto-optic or electro-optic cells. Thus, it is not limited by the modulator characteristics.
TL;DR: In this article, a vibration sensor with a platform mounted Bragg c frequency shifter and heterodyne detection system is presented, where the reference beam is modulated with the component of platform vibration normal to the sensing beam, such that a similar modulation of the sensing beacon is cancelled by the heterodyning process.
Abstract: The invention provides a vibration sensor with a platform mounted Bragg c frequency shifter and heterodyne detection system, wherein the reference beam is modulated with the component of platform vibration normal to the sensing beam, such that a similar modulation of the sensing beam is cancelled by the heterodyning process.
Patent•
11 Sep 1987
TL;DR: In this article, the authors measured the micro-vibration of an ultrasonic or elastic wave in a non-contact manner, by obtaining an AC electric signal containing the phase modulation proportional to the surface vibration of a body by using two laser beams different in beam frequency.
Abstract: PURPOSE:To measures the micro-vibration of an ultrasonic or elastic wave in a non-contact manner, by obtaining an AC electric signal containing the phase modulation proportional to the surface vibration of a body by using two laser beams different in beam frequency. CONSTITUTION:Two laser beams of beam frequencies f1, f2 are generated from a laser generator 1 and the surface 3 of a specimen is irradiated with one of them to obtain reflected beam. Next, the reflected beam and the other laser beam are superposed to be allowed to interfere with each other and converted to an electric signal by a beam detector 2. By this method, an AC electric signal of frequency f3(=¦f1-f2¦) containing phase modulation proportional to the surface vibration speed of the specimen is obtained (heterodyne interferometer A). Further, the AC electric signal of the frequency f3 is divided into two by a two-splitter 4 to apply arbitrary time difference between two AC electric signals and the phase difference of two AC electric signals is detected by a phase comparator 6 (signal converter B). Next, by providing a frequency multiplier 7 between the interferometer A and the converter B, more micro-vibration can be measured in a non-contact manner.
TL;DR: In this paper, a dual sinusoidal modulation scheme for a laser Doppler velocimeter (LDV) employing a semiconductor laser source is described. And a single-side-band DOP shift of 8.5 MHz with an image sideband suppression of 29dB is demonstrated.
Abstract: A dual sinusoidal modulation scheme introducing directional sensing of a laser Doppler velocimeter (LDV) employing a semiconductor laser source is described. With this technique using direct current modulation a single-sideband Doppler shift of 8.5 MHz with an image sideband suppression of 29dB is demonstrated.