Showing papers on "Laser Doppler vibrometer published in 1985"

Multiple laser beam scanner with beam intensity control

Abstract: A semiconductor laser beam scanning device includes a plurality of semiconductor lasers for emitting respective laser beams which are combined into a single laser beam to scan a desired surface. The amount of energy of the single laser beam is detected by a laser beam energy detector which applies a laser beam energy signal to a laser drive/control circuit. Alternatively, the laser beam energy signal is applied to a comparator which compares the laser beam energy signal with a reference signal and issues a difference signal to a control circuit connected to a laser drive circuit. The laser drive/control circuit or the control circuit is responsive to the applied signal for controllably energizing at least one of the semiconductor lasers to control the amount of energy of the laser beam emitted therefrom to thereby keep the amount of energy of the single laser beam at a constant level. The laser beam energy detector may be disposed adjacent to the surface to be scanned for detecting the amount of energy of the single laser beam in each scanning cycle, or may detect a laser beam divided from the single laser beam by a beam splitter disposed on a beam path for the single laser beam.

Heterodyne frequency measurements on N2O at 5.3 and 9.0 microns

Abstract: Heterodyne frequency measurements on the 01(1)1-00(0)0 band of N2O have been made with the use of a tunable-diode laser, CO laser transfer oscillator, and a CO2 laser frequency synthesizer. A beat frequency was measured between a CO laser and tunable-diode laser whose frequency was locked to the peak of N2O absorption features. The frequency of the CO laser was simultaneously determined by neasuring the beat frequency with respect to a reference synthesized from two CO2 lasers. New rovibrational constants are given for the 01(1)1 state of N2O, which are in excellent agreement with previous results, although the band center is 4 MHz higher than in the previous measurements. A table for the line frequencies and their absolute uncertainties is given for the N2O absorption lines in the wave-number region from 1830 to 1920 kaysers. Some additional frequency measurements near the lower-frequency end of the 02(0)0-00(0)0 band have also been made with respect to a C-12)(0-18)2 laser.

Chirp laser stabilization system

Abstract: A chirp laser system includes an intracavity electro-optical crystal which is modulated at a relatively high frequency, for example 250 kilohertz, to sweep the frequency of the transmitter laser above and below its nominal center frequency. One of the mirrors associated with the laser transmitter is adjustable to vary the length of the laser cavity and to thereby shift the frequency of the transmitter laser. When the frequency of the transmitter laser is shifted, the output amplitude of the laser changes to some extent. With the center frequency of the laser at a maximum gain point, the amplitude of the output signals during the positive and negative frequency excursions of the transmitter laser will be substantially symmetrical. However, if thermal or other effects cause the frequency of the laser to shift away from the maximum gain point, the output during positive and negative excursions will be asymmetrical, for example, with the gain dropping off during an upward frequency excursion, and perhaps increasing or not dropping off nearly as much during a low frequency excursion. A small part of the output from the transmitter laser is sampled, and the amplitude during positive and negative frequency shift excursions is compared, using a square wave derived from the chirp modulating driver. Where the detected signals for the positive and negative frequency excursions are substantially equal, no change in the position of the mirror is accomplished; however, when the excursions result in a difference in the amplitude of the detected signals, the position of the piezoelectrically adjustable mirror is shifted to restore the nominal center frequency of the laser to its maximum amplitude point on the gain curve.

Optical type information reproducing device

Abstract: An optical type information reproducing device for playing back a laser disc comprises a laser beam source for projecting laser beam on the laser disc, a pickup and signal processing circuit for receiving the laser beam reflected from or transmitted through the disc and performing photo-electric conversion and signal processings and outputting a reproduced signal, and a laser beam source control circuit responsive to the level of the laser beam received by the pickup and signal processing circuit for controlling the level of the laser beam. By detecting the level of the laser beam reflected from or transmitted through the disc and controlling the laser beam output in response to the detected value, the level of the reflected or transmitted laser beam is maintained at a constant value.

An experimental comparison of the head/disk interface dynamics in 51/4- and 8-inch disk drives

Abstract: A laser Doppler vibrometer is used to measure the head/disk interface dynamics in computer disk drives. The stability of the head under steady operating conditions is compared between a 5/14-inch and two different 8-inch "Winchester" drives. In the larger drives, high-frequency vibrations (between 5 and 10 kHz) are detected on the slider which are not present in the smaller drive. These vibrations have amplitudes on the order of magnitude of the head/disk spacing and are related to the rolling and pitching modes of the slider. The vibrations of the disk, suspension, and actuator arm are also investigated and correlated with the results obtained on the slider.

Frequency Jitter from Mechanical Vibrations in a Diode Laser Mounted on a Closed-Cycle Refrigerator

Abstract: Frequency jitter in a tunable diode laser output due to impact shocks produced by the closed-cycle refrigerator has been characterized as a function of the piston movement during different phases of the cycle. An analysis of the influence of the vibration-induced noise suggests a random (Gaussian) contribution to the laser spectrometer lineshape.

Method of, and apparatus for, generating a predetermined pattern using laser radiation

Abstract: A writing laser beam and a scanning laser beam are coaxially superposed for position determination and for correcting mechanical movements during the writing of lines of a desired pattern into a metalized three-dimensional integrated circuit. The coaxially superposed writing and scanning laser beams are directed, using a single beam splitter for the scanning laser beam, to a lens head and to a workpiece as well as to a turret for alternately employing one of a number of measuring or observing instruments. The individual members are precisely adjustable and during automatic evaluation of the thus determined values, correction of any error that may occur, can be directly obtained at the desired rate by such automatic evaluation. In order to properly arrange and shorten the radiation paths there is used a laser beam collimator which preferably is also provided with a writing laser beam detector. Furthermore, a scanning laser beam detector can be arranged to follow the beam splitter for the scanning laser beam. A very simple optical connection exists between the lens head and the turret, whereby the occurrence of errors due to vibrations is prevented. The inventive method and apparatus are particularly suited for the rapid and precise treatment of metalized three-dimensional integrated circuits or wafers.

Laser doppler interferometry on magnetic recording systems

Abstract: Laser Doppler interferometry is used to determine the six components of velocity of read/write heads in magnetic disk files. These measurements are made on production drives in which the only alteration is the installation of a window so that the laser beams can be directed onto any of the four corners of the slider. A laser Doppler vibrometer (LDV) is used to measure the out-of-plane velocity of the four corners from which we calculate the out-of-plane velocity of the geometric center as well as the pitch and roll of the slider. A laser Doppler anemometer (LDA) measures the in-plane velocity of the four corners, which gives the radial and tangential velocity of the geometric center and the yaw of the slider. We are also using the LDV for the measurement of disk runout and surface topography as well as suspension and actuator vibration. These measurements allow us to determine the natural frequencies of the slider bearing, the rotating disk, the actuator, and the suspension arm. In this paper we summarize some of the results we have obtained using this method on various 5-1/4" and 8" rigid disk drives that employ "Winchester" and "mini-Winchester" sliders together with stepper motor and servo controlled actuators of both the linear and swing arm designs.

Steerable doppler transducer probes

Abstract: An ultrasonic diagnostic probe is provided which performs simultaneous ultrasonic imaging and Doppler flow measurement. The Doppler transducer is mounted for rotation by a mechanical assembly, which permits the Doppler beam to be steered during imaging to the point in the body where a flow measurement is to be taken. As the Doppler transducer is rotated, a variable impedance device within the probe is adjusted in correspondence with the transducer rotation so as to provide an indication signal of the direction in which the Doppler beam is being directed.

Optical injection locking of laser diode arrays

Abstract: An apparatus for amplifying a laser beam through injection locking of a laser array by a single master laser is presented. The apparatus is comprised of a master laser which produces a beam that is shaped or focused onto a laser array facet which is further comprised of an array junction plane wherein the laser array is biased above threshold.

Laser radar utilizing pulse-tone waveform

Abstract: Pulse-tone laser radar utilizing an acousto-optic angular multiplexer and frequency shifter. The laser radar includes both a pulsed laser and a CW laser. A portion of the CW laser beam is utilized as a reference or local oscillator. An acousto-optic angular multiplexer passes the output of the pulsed laser when the acousto-optic multiplexer is in its off state and passes and frequency shifts the output of the CW laser when the acousto-optic multiplexer is in its on state. The acousto-optic angular multiplexer is operated to pass a pulse followed by a CW tail to generate the pulse-tone waveform. The return signal from a target is beat together with the local oscillator signal derived from the CW laser. The resulting beat signal includes both range and velocity information.

Semiconductor laser beam scanning device

Abstract: A semiconductor laser beam scanning device includes a plurality of semiconductor lasers (11, 12, 13, 14) for emitting respective primary laser beams (41, 42, 43, 44) which are combined into a single laser beam (45) to scan a desired surface (7). The power of the combined laser beam (45) is detected by a laser beam energy detector (52) which applies a laser beam energy signal (P) to a laser drive/control circuit (51). Alternatively, the laser beam energy signal (P) is applied to a comparator (46) which compares the laser beam energy signal with a reference signal (Sr) and issues a difference signal (H/L) to a control circuit (56) connected to a laser drive circuit (55). The laser drive/control circuit (51) for the control circuit (56) is responsive to the applied signal for controllably energizing at least one (14) of the semiconductor lasers to control the power of the laser beam (44) emitted therefrom thereby to keep the power of the combined laser beam (45) at a constant level. The laser beam energy detector (52) may be disposed adjacent to the surface (7) to be scanned for detecting the power of the combined laser beam in each scanning cycle, or may detect a laser beam (87a) divided from the combined laser beam (87) by a beam splitter (92) disposed on a beam path for the combined laser beam.

Projection lens scanning laser velocimeter system

Abstract: A laser Doppler velocimeter (LDV) system (10) has a laser (12), a waist position adjusting lens (13), and a beam splitter (15), which direct laser beams (14) parallel to optical axis (16) of negative lens (18). Negative lens (18) is fixed relative to afocal lens pair (24,26). A pair of planar mirrors (20, 22) intersect at right angles and respectively intersect optical axis (16) and optical axis (28) of the afocal lens pair. Mirrors (20, 22) are movable along optical axis (28) toward and away from afocal lens pair (24, 26) to focus laser beams (14) in focus area (30) while maintaining a constant beam waist, crossing angle and intersection with other laser beams to produce a constant sensitive volume as the focus is changed.

Frequency modulated laser radar

Abstract: An apparatus and a method for measuring the distance to an arbitrary target (52) includes a radiation source (62) producing a beam of coherent radiation the frequency of which is continuously varied. The beam is divided into a ranging beam and a reference beam. The'ranging beam is coupled to a ranging interferometer (70), which directs a portion of the ranging beam at the target (52). The ranging interferometer (70) produces a first signal indicative of the phase difference between a portion of the ranging beam directed at and scattered by the target and another portion of the ranging beam which has traveled over a path of fixed length. The reference beam is coupled to a reference interferometer (66). A portion of the reference beam is directed by the reference interferometer (66) along a reference path of a predetermined length X ref , and the phase difference between the portion of the reference beam directed along the reference path and another portion of the reference beam which has travelled over a path of a fixed length is measured. The phase difference between the two portions of the reference beam and the phase difference between the two portions of the ranging beam are processed to determine the distance of the target from the ranging interferometer (70). The number of fringes resulting from the wave interference produced in the ranging interferometer (70) and the number of fringes in the wave inferference pattern produced by the reference interferometer (66) are counted and used, together with the known

Apparatus for measuring the profile of a laser beam

Abstract: An apparatus for accurately measuring laser beam intensity profiles so as to permit adjusting the oscillation mode of the laser to achieve good workability of the beam. The beam from a CO2 laser generator is attenuated and applied to an infrared sensor which produces an electrical analog signal representing the beam intensity. The sensed signal is amplified and applied via an A/D converter and an interface to a computer. The computer controls a scanner which scans successive scanning lines of the laser beam profile across the sensor. The computer also produces a visual image of the laser beam intensity profile from the sensor signal. An operator veiwing such image can make an accurate and convenient measurement of the laser beam intensity profile, thereby providing a basis for quantitative analysis in quality inspection of workpieces subjected to the laser beam.

Experimental measurement of scattered surface waves using a laser–Doppler technique

Abstract: A laser–Doppler vibrometer was used to detect gated harmonic surface waves traveling along a steel block, together with their reflections from a rectangular plate attached to the block through a viscous couplant. A signal demodulator was designed to allow visualization of the waves on an oscilloscope, and computer data acquisition was performed. Using various plates and couplants, curves showing the reflected/incident power ratio as a function of the wavelength were obtained and compared with those obtained from a previous theoretical analysis. The correlation between the positions, number, and amplitudes of the resonances obtained from experiment and theory was analyzed, as was the influence of the couplant.

Method and apparatus for making a contact-free measurement of the actual position and of the profile of a coarse surface

Abstract: The invention is directed to a method and apparatus for the contact-free measurement of the actual position and/or of the profile of coarse surfaces. Laser light generated by a laser has at least two different wavelengths and is directed to the surface to be measured. A beam splitter is placed between the surface to be measured and the laser to split the laser light into a reference beam and a measuring beam. The reference beam is reflected on a reference plane surface. A speckle pattern is formed in the interferogram plane of the reflected light. From the speckle pattern, a bright laser speckle is selected for all wavelengths by means of a measuring diaphragm having a diameter less than that of a laser speckle. Behind the measuring diaphragm, the two wavelenths are separated from each other and the phase difference between the signals of the different wavelengths is measured. The phase difference is transformed into a signal proportional to the distance between the measuring point and the reference surface and is displayed. The reference light beam can be shifted in frequency with respect to the measuring beam by means of a heterodyne device.

Device for varying laser output

Abstract: A device for varying laser output including a source for generating a laser beam, at least one parallel flat plate having a transmissive characteristic for the laser beam and so arranged that the laser beam enters with the optical axis thereof at a Brewster's angle, a mechanism for rotating the plate about the optical axis, and a laser absorbing body for absorbing the laser beam reflected from the plate.

Simple laboratory demonstration of the Doppler shift of laser light

Abstract: The edge of a smoothly rotating turntable was used as a reflecting surface in a Michelson interferometer configuration to demonstrate the Doppler effect on laser light. Attached to the edge of the turntable was reflective tape which greatly enhanced the backscattered light. Spectrum analysis of the detected signal indicated that all of the signal and noise components were contained in a frequency range of about 15% of the central Doppler frequency. As a quantitative test of the method, the wavelength of the laser source, known to be 633 nm, was measured to be (612±43) nm using an oscilloscope as the output device and (634±12) nm using a spectrum analyzer for the output. All components that were used with the exception of the spectrum analyzer are commonly available items. The techniques described in this paper provide a quantitative demonstration of the Doppler effect of light and overcome the usual problems caused by motional instabilities associated with the moving mirror.

Method of and apparatus for correction of laser beam phase front aberrations

Abstract: In accordance with one embodiment of the present invention, a controlling laser beam at a first wavelength is introduced into an interferometer such that one half of it contains the aberrations of the laser beam to be controlled and the other half is and remains undistorted. The aforementioned two halves of the controlling laser beam are combined at the output of the interferometer and then, together with the laser beam to be controlled at a second wavelength is introduced collinearly into a gas cell or phase corrector. Upon combination or interference of the two halves of the controlling laser beam the phase-front aberrations are translated to intensity modulations across the cross section of the beam. Utilizing nonlinear dispersion in the gas cell in accordance with the invention, the intensity modulations across the controlling laser beam are transformed by nonlinear dispersion interaction into appropriate refractive index variations at the second wavelength which in turn causes corresponding phase changes across the phase front of the controlled laser beam. Adjustment of path length in the interferometer permits compensation of the aberrations in the controlled laser beam.

Simultaneous measurement of velocity and temperature by the use of a laser Doppler velocimeter

Abstract: A simple, new method of measuring velocity and temperature simultaneously without imparting any disturbances to the fluid is developed. The key idea is to use a certain liquid that undergoes thermochromism as a test fluid, the temperature of which can be observed directly by its color change or measured quantitatively by a suitable optical method. If a laser Doppler velocimeter is used, the temperature at the measuring point, in addition to the velocity, can be determined simultaneously and instantaneously by detecting the otherwise discarded intensity of the transmitted light of the laser beams. This method was applied to measurements of distributions of velocity and temperature of a plume in a Hele–Shaw cell. Results were in fairly good agreement with similarity laws derived theoretically in this paper.

Cleaved-coupled-cavity-laser-driven system for measuring small signals

Abstract: A laser-driven interferometric signal sensing system has a cleaved-coupled cavity laser with separate stabilization servo loops of different time constants for the modulator and laser sections thereof. The laser section is biased above lasing threshold, and its stabilization loop is operated at a frequency twice the frequency of laser section bias current modulation. A laser loop feedback error signal is a function of predetermined, environmental-type, parameter variations in the sensing location and is processed to be a function of the second derivative of interferometer output intensity with respect to laser section current. That error signal is applied to modify laser section bias current in a direction to zero out the feedback signal.