Showing papers on "Laser Doppler vibrometer published in 1992"

Laser Doppler velocimeter based on the self-mixing effect in a fiber-coupled semiconductor laser: theory

Abstract: A laser Doppler velocimeter that consists of a semiconductor laser coupled to a fiber and that uses the self-mixing effect is presented. The velocimeter can be used for solids and fluids. A theoretical model is developed to describe the self-mixing signals as a function of the amount of feedback into the laser and the distance from the laser to the moving object. Good agreement is found between this theory and measurements.

Frequency response subtraction for simple measurement of intrinsic laser dynamic properties

Abstract: The authors describe a new technique for extracting the intrinsic laser-diode dynamic properties accurately. This simple technique eliminates the need for accurate microwave calibration of the test equipment and problems of microwave reflections, nonideal frequency response of laser mount, and detector. The effect of the parasitic components of the laser diode are also eliminated from the results so that measurements of important dynamic properties of the laser can be found up to high frequencies (10-20 GHz) on standard laser diodes. The techinque being used to measure variations of resonance peak and damping factor at different bias levels for a standard bulk active region 1.3 mu m laser diode is shown. >

Laser operations on a workpiece with uneven surface - where distances between workpiece and laser are measured during intervals between working pulses

Abstract: The method comprises (a) relative motion taking place between the workpiece and the first laser; (b) determining the distance between the first laser and the workpiece by an optical sensor between two laser pulses; (c) comparing the measured distance with a required value; (d) and setting the distance equal to the required value. The appts. includes means for producing horizontal relative motion betwee the workpiece and the first laser, an optical distance measuring sensor, a control system for distance adjustment, and means for phase coupling between the optical sensor and the first laser. Pref. a pulsed second laser and a position-sensitive photodetector are used for distance measurement, with the pulse frequencies of the first and second laser being the same. The lasers are synchronized with a phase shift by means of a lock-in circuit. The second laser is coupled into the beam path of the first laser by means of a mirror. The distance measurement is based on a triangulation procedure, or alternatively a cutting process is utilised. USE/ADVANTAGE - In laser cutting, boring and welding technologies, for example. It enables distances on irregular and steeply curved surfaces to be measured reliably and with a high degree of accuracy.

Zeeman laser interferometer errors for high-precision measurements.

Abstract: We present a theoretical analysis of the errors of a Zeeman laser interferometer due to the nonorthogonally elliptic polarizations of laser modes. The polarizations make the measured Doppler frequency-shift signal become a modulated and nonharmonic signal and make the phase shift unstable and nonrepeatable when the signal is measured by a phasemeter. If the orthogonality error between two major axes of the laser polarizations is 6 degrees , the relative errors of the phasemeter output will exceed 200% when the measured phase shift is changed from -16.2 degrees to +3.5 degrees . We also introduce a way to eliminate the errors.

Direct measurement of the temperature‐dependent piezoelectric coefficients of composite materials by laser Doppler vibrometry

Abstract: The longitudinal (d33) and transverse (d31) piezoelectric coefficients of a piezoelectric composite material (NTK PR‐306) are determined as functions of frequency and temperature by using laser Doppler vibrometry to measure the strain induced in the sample by an electric field. Measurements are performed over the temperature range from −50 °C to 50 °C and over a frequency range from 0.1–10 kHz. Some measurements were made at frequencies up to 100 kHz in order to demonstrate the ability of the technique at frequencies in the vicinity of an electromechanical resonance. The results show that the viscoelastic relaxation affects the piezoelectric response of the composite material primarily through the dielectric stiffness rather than the elastic stiffness. The d33 coefficient is observed to relax in a normal fashion near the glass transition of the polymer phase whereas the relaxation in the d31 coefficient varies over the entire measured range of temperature.

High resolution laser beam scanner and method for operation thereof

Abstract: A laser beam scanner in its preferred form has a laser source which emits a laser beam at a prism. The prism receives and deflects the laser beam toward a spherical lens, which receives the laser beam and converges it. A spherical reflector then redirects and focuses the converging laser beam to a laser scan spot along a scan line. The laser beam scanner may include one or multiple prisms, wherein individual prisms may be single or multi-faceted prisms. The laser beam scanner effectively eliminates across-scan error and generates a mathematically perfect scan line. The scanner has a high optical efficiency and a very short retrace time or blackout time. A method for laser scanning using a prism, spherical lens, and spherical reflector is also disclosed.

Three color laser

Abstract: A three color laser system employs a diode pumped Nd:YAG or Nd:YLF laser to provide a green output beam and to pump two Ti:S lasers. One Ti:S laser emits a tunable red beam, while the second emits a near infrared beam. The near infrared beam is frequency doubled by a NLO device to provide a tunable blue output beam. The beams may be directed to separate optical fibers or to a single fiber. A reversed Cassegrainian mirror arrangement is used to combine a plurality of beams for transmission in a single optical fiber.

Load/unload investigations on a rotary actuator disk drive

Abstract: Head-disk contacts in a disk file with a rotary actuator are examined during load/unload using laser Doppler vibrometry and acoustic emission techniques. A novel scheme that allows tracking of the slider with the laser beam of a laser Doppler vibrometer during load/unload is implemented. Head-disk contacts are found to occur as a function of the velocity of the slider along the inclined ramp prior to loading, and it is shown that a low vertical loading velocity is less likely to introduce head-disk contacts than a high loading velocity. For the swing-arm actuated drive investigated, head-disk contacts start to appear at loading velocities as low as 25 mm/s. A careful design of the tip of the ramp is of utmost importance in ramp loading mechanisms to reduce the effective vertical component of the slider as it comes off the tip of the ramp during loading. >

Pulsed solid state ring laser injection locking stabilizer

Abstract: An injection seeded, single frequency ring laser source is presented wherein stabilization and single frequency control is accomplished by measuring the intensity or power of the portion of the high power laser beam generated in the ring slave laser and which is directed to return to the seed laser. When the intensity of the return beam falls below a preset threshold level, the in-phase operation of the laser system has been established and high energy single frequency pulses are generated and emitted.

Fiber-optic Doppler velocimeter that incorporates active optical feedback from a diode laser.

Abstract: A fiber-optic Doppler velocimeter that incorporates the effect of self-mixing in a diode laser is described A theoretical model, based on self-mixing interference theory, is presented, and a simple experimental arrangement is constructed The results of the experimental research are found to be in good agreement with the theoretical analysis A Doppler velocity of as much as 3 m/s was measured directly, and a good linear relationship between the Doppler velocity and the Doppler-shifted frequency was obtained, which can be used to determine the speed of a moving object

Determination of laser beam parameters with the phase space beam analyser

Abstract: The properties of the phase space beam analyser (PSBA), first introduced by Nemes, were investigated theoretically and experimentally. This optical system enables one to measure far-field divergence and beam radius of a laser beam simultaneously. Experiments were performed with a pulsed Nd: YAG laser with stable and unstable resonators and with a HeNe laser in fundamental mode operation. The theoretical description was based on Fresnel integrals, which were solved numerically using a FFT algorithm. The results presented indicate that the PSBA provides a simple means to determine beam quality and to investigate the mode properties of optical resonators, if diffraction effects are properly compensated.

Laser vibrometer identification friend-or-foe (IFF) system

Abstract: A friend-or-foe (IFF) identification system (10) comprises a laser generator (12) for generating and transmitting a laser beam (B). A beam splitter (16) divides the laser beam into two beams. One of the beams (B1) is directed along a reference path (P). This beam is reflected back along the path by a mirror (24) positioned at the end of the path. The other laser beam (B2) is directed at an object (T) to be identified as a friend or foe. This second beam reflects off the object and the return, reflected beam is detected. The reflected beam includes a vibration signature of the object under investigation. The return beam and reference beam are processed together to correct the vibration signature of the object for arty distortions. This allows an accurate target signature to be obtained. Next, the target signature is compared against other signatures. The results of the comparison provide the IFF identification.

Distance measuring device utilizing semiconductor laser

Abstract: A laser distance measuring device includes a semiconductor source, such as a laser diode, that produces a laser beam, preferably in the visible range. A driver selectively drives the semiconductor source at a minimum of two different driving frequencies. A laser beam receiver has a detector that produces an output signal which varies with the intensity of the received laser beam, an amplifier that amplifies the output signal of the detector, and counter means for controllably counting the number of cycles in a clock signal. A beam director selectively directs the laser beam toward an object and receives the reflected laser beam from the object, and directs the laser beam toward the receiver without traveling to the object. A microprocessor controls the driver, the counter, and the beam director.

Use of laser scanning system on mobile underwater platforms

Abstract: An underwater laser-based synchronous scanning system which produces high quality images through turbid waters is described. A prototype system has been developed to demonstrate the operational feasibility of the synchronous line scan architecture. This prototype system incorporated an argon ion laser operating at 488 and 514.5 nm. Operational systems could incorporate a frequency doubled Nd:YAG solid-state laser operating at a wavelength of 532 nm. Both laser configurations operate at wavelengths attractive for use in underwater systems due to minimum light attenuation at these wavelengths. The operational platform results presented were performed on a research submarine and a towed body. >

Impedance analysis of acoustic vibration element using giant magnetorestrictive material

Abstract: Giant magnetoresistive material offers great magnetostriction over 1000 p.p.m., making it well-suited to acoustic transducers for acoustic ocean tomography systems. The acoustic vibration element using giant magnetostrictive material (AVEG) is a transducer is a drive unit developed for this purpose. The authors discuss the following three points through measurement of AVEG impedance: measurement of mechanical resonance frequency based on electrical impedance characteristics; calculation of equivalent circuit constraints based on analysis of motional impedance characteristics; and comparison between calculated and measured values for the displacement-current sensitivity of the vibrating terminal. Around the resonance frequency, the displacement-current sensitivity values measured with a laser Doppler vibrometer almost exactly matched the values calculated by using the equivalent circuit constants. This indicates that mechanical vibration can be estimated from the impedance characteristics. >

Method and apparatus for laser beam drift compensation

Abstract: A method and apparatus for laser beam drift compensation. A portion of the laser beam is split off and focused onto a photocell through a reticle. As the laser beam scans the reticle, the actual position of the laser beam is determined and compared with its anticipated position. Compensation is made for any deviation in the beam position in a closed-looped manner to provide accurate optical alignment of the laser beam to the workpiece.

Height measurement apparatus using laser light beam

Abstract: In a height measurement apparatus, a laser light beam is applied to a surface of a height-measurement object. A portion of the laser light beam is reflected at the surface of the object. An optical position sensor is exposed to the portion of the laser light beam which is reflected at the surface of the object. The optical position sensor generates a position signal depending on a point at which the reflected laser light beam meets the optical position sensor. The position signal represents a height of the surface of the object. A position of the laser light beam is vibrated relative to the surface of the object. The height represented by the position signal is temporally averaged into a mean height while the position of the laser light beam is vibrated relative to the surface of the object. The mean height is defined as a final measurement result.

Non-linear optical crystal vibration sensing device

Abstract: A non-linear optical crystal vibration sensing device (10) including a photorefractive crystal (26) and a laser (12) The laser (12 ) produces a coherent light beam (14) which is split by a beam splitter (18) into a first laser beam (20) and a second laser beam (22) After passing through the crystal (26) the first laser beam (20) is counter-propagated back upon itself by a retro-mirror (32), creating a third laser beam (30) The laser beams (20, 22, 30) are modulated, due to the mixing effect within the crystal (26) by vibration of the crystal (30) In the third laser beam (30), modulation is stable and such modulation is converted by a photodetector (34) into a usable electrical output, intensity modulated in accordance with vibration applied to the crystal (26)

Dual laser resonator and beam combiner

Abstract: Apparatus for providing beams of laser radiation at wavelengths of 1.44 μm and 1.064 μm on demand. Two Nd:YAG lasers are arranged in a side-by-side configuration and operated to provide laser output at wavelengths of 1.44 μm and 1.064 μm, respectively. In the preferred embodiment, a reflective spectral filter comprised of two reflectors reduces the amount of 1.064 μm radiation in the output beam from the 1.44 μm laser by a factor of 100 to 1000, but only reduces the amount of 1.44 μm radiation in the output beam from the laser by less than 2%. The apparatus also provides collinear addition of the output from the 1.064 μm laser. This collinear addition enables output radiation from both lasers to be coupled together into a single optical fiber. In fact, a user can choose to operate either laser separately or to operate both lasers simultaneously.

Laser diode assembly for laser scanner system

Abstract: A laser source arrangement is provided for use in a laser instrument of a kind used to transmit a scan pattern to a target which is spaced from the laser instrument and to detect light reflected from the target. The laser source arrangement preferably comprises a laser diode for producing a laser beam used to form the scan pattern. The laser diode is characterized by astigmatism which is subject to variation with the temperature of the case of the diode. The arrangement further includes drive apparatus for driving the laser diode in a pulsed mode having a duty cycle which reduces the astigmatism and substantially controls the temperature dependence of the astigmatism. Optics are also provided for statically correcting the astigmatism of the laser diode.

Ultrasonic joining equipment and quality monitoring method

Abstract: PURPOSE:To realize superior ultrasonic junction having constant junction quality wherein, when interposing objects like coating material and an oxide film which hinder the junction exist, or when material to be joined is insufficiently fixed, the junction progress state is monitored, and the junction condition is controlled in the optimum state. CONSTITUTION:The title equipment is provided with the following; a junction system constituted of an ultrasonic wave control equipment and a junction head, a vibration monitoring system constituted of a laser oscillator 8, a laser optical system and a vibrometer 7, and mechanism which feeds back monitored results to the junction condition. Thereby ultrasonic wave vibration change at the tool tip, or relative vibration change between a tool and a work and between one work and the other work can be accurately measured, so that the junction state can be accurately judged, and superior junction can always obtained by applying feedback to the junction condition.

Novel fiber-optic torsional vibrometers

Abstract: Two configurations for a fiber‐optic torsional vibrometer are described, which can be classified as (i) differential and (ii) reference. Common features of both techniques are noncontact measurement, immunity to nontorsional vibration, large dynamic range coupled with passive, miniature, remote sensor heads. Measurements of rotation speed and torsional jitter were made with a total illuminating laser power of 130 μW (reference mode) and 1.5 mW (differential mode). Rotation speeds in the range of 270–19 000 RPM were measured.

Laser beam optical scanning system

Abstract: A laser beam optical scanning system which has a laser source unit for emitting a laser beam which is a parallel pencil of rays, a first imaging system for imaging the laser beam emitted from the laser source unit on a reflective facet of a deflector, and a second imaging system for imaging the laser beam deflected by the deflector on a photosensitive drum. At least one of the first and the second imaging systems has a resin lens. The resin lens changes its power according to temperature so as to offset a change in light converging performance of the laser source unit.

Laser gun ammunition measurement equipment

Abstract: A laser gun ammunition measurement equipment is described for measuring the velocity of an object by measuring the Doppler frequency shift of a reflected laser beam A laser beam is projected onto a target area which is moving with respect to the inertial frame of the laser transmitter and the laser receiver The reflected laser energy is mixed with a local oscillator beam and the mixed beam is focused onto a radiation detector The Doppler frequency shift is measured, thus indicating the object's velocity A sacrificial mirror is employed so that internal projectile velocity measurements may be made on the projectile The laser beam permits measurement both external and internal to the barrel for large and small caliber weapons Additionally integration and differentiation means may be provided so that instantaneous position and acceleration data can also be generated for the projectile

Laser doppler type vibrometer

Abstract: PURPOSE: To provide the vibrometer strong against disturbance such as vibration or the fluctuation of air. CONSTITUTION: In the vibrometer, laser beam 2f having two wavelengths is outputted from a laser beam source 12 and inputted to a deflecting beam splitter 3 through the 1/2 wavelength plate 15 of a laser beam splitting means 13 to be split into beams 2c, 2d. One laser beam 2c is passed through a 1/4 wavelength plate 16b and an optical system 7 to irradiate a vibration object 8 and the scattered beam 2e from the vibration object 8 is directed to the deflecting beam splitter 3 through the optical system 7 and the 1/4 wavelength plate 16b. The other laser beam 2d is applied to a mirror 14 serving as a laser beam reflecting means through the 1/4 wavelength plate 16a and the laser beam 2d reflected from the mirror 4 is again directed to the deflecting beam splitter 3 through the 1/4 wavelength plate 16a. The beam 2d and the scattered beam 2e are allowed to interfere with each other by an analyser 17 to form an interference beat signal which is, in turn, made to enter a photodetector 9. COPYRIGHT: (C)1994,JPO&Japio

A Description of an Improved Homodyne Laser Interferometer

Abstract: First appearing on the commercial market in the mid 1980’s, diode-pumped, continuous-wave (cw) Nd:YAG lasers have more recently been used to obtain visible output, by the incorporation of frequency doubling optics in the laser cavity.The laser diode pumping of a Nd:YAG laser rod is selective and highly efficient, resulting in compact, high power, spatial mode lasers. Frequency-doubling processes are non-linear and lead to doubling TEM00 only of the high energy fundamental temporal mode, resulting in operation of the 532 nm laser in a single spatial and single longitudinal mode. The technology is rapidly advancing, and green lasers with energies of up to 1W could soon be available. The beam properties of the lasers described above are highly desirable in the field of interferometry, where such lasers are now in direct competition with the much larger Argon lasers, which have already been employed in high power interferometric systems. We describe here the performance of a modified Michelson interferometer [1–4], built to incorporate a 90 mW ADLAS 300 diode-pumped Nd:YAG laser. In previous versions of the Michelson interferometer, we have used HeNe lasers with a few milliwatts output, requiring mirror-quality surfaces on our samples. A 90 mW laser power enables us to make displacement measurements on metal surfaces with little or no preparation. The laser could also, of course, be used in other, more elaborate interferometer types, such as the confocal Fabry-Perot, which are better suited to industrial environments.

Laser beam control apparatus

Abstract: The laser beam control apparatus according to the invention having a photodiode for outputting a current consisting of high and low-frequency components in accordance with the amount of a laser beam emitted from a laser diode. The current output from the photodiode is separated into high and low-frequency components by a CR filter, and the separated low-frequency current is amplified by an amplifier. The current amplified by this amplifier is added to the high-frequency current separated by the CR filter. The resulting sum current is converted into a voltage by an amplifier, and the amount of the laser beam emitted from the laser diode is controlled in accordance with the voltage converted by this amplifier. With this operation, the laser beam output power of the laser diode can be stably controlled in a wide band.