Showing papers on "Laser Doppler vibrometer published in 1970"

Laser Doppler detection systems for gas velocity measurement.

Abstract: The velocity of gas flow has been remotely measured using a technique which involves the coherent detection of scattered laser radiation from small particles suspended in the fluid utilizing the doppler effect. Suitable instrumentation for the study of wind tunnel type and atmospheric flows are described. Mainly for reasons of spatial resolution, a function of the laser wavelength, the wind tunnel system utilizes an argon laser operating at 0.5 micro. The relaxed spatial resolution requirement of atmospheric applications allows the use of a carbon dioxide laser, which has superior performance at a wavelength of 10.6 micro, a deduction made from signal-to-noise ratio considerations. Theoretical design considerations are given which consider Mie scattering predictions, two-phase flow effects, photomixing fundamentals, laser selection, spatial resolution, and spectral broadening effects. Preliminary experimental investigations using the instrumentation are detailed. The velocity profile of the flow field generated by a 1.27-cm diam subsonic jet was investigated, and the result compared favorably with a hot wire investigation conducted in the same jet. Measurements of wind velocity at a range of 50 m have also shown the considerable promise of the atmospheric system.

Electro-optical image-tracing systems, particularly for use with laser beams

Abstract: To provide for digital positioning, without inertia of moving parts, a laser beam is transmitted to a substrate which is to be exposed, etched, or the like, particularly when microcircuits are to be produced, by monitoring the displacement of the substrate, mechanically, in two mutually perpendicular directions and positioning the laser beam, as monitored, in at least one direction by controlling voltages applied to a deflector cell in the path of the laser beam, by digitally, selectively, energizing an electro optical crystal effective to rotate the polarized laser beam through a plane of 90*, followed by a doubly refracting crystal which deviates the path of the laser beam, depending on its direction of polarization with respect to the optical axis of the crystal, so that, by successive deflections, the beam, from the laser, can be positioned in predetermined locations on the substrate The entire arrangement is preferably computer controlled, so that data inserted into the computer will cause deflection of the laser beam in accordance with a predetermined program

Laser Doppler velocity measurement without directional ambiguity by using frequency shifted incident beams

Abstract: A simple laser Doppler heterodyning system has been developed where velocities in any set of orthogonal axes can be measured without the directional ambiguity of 180°. The method employs a two‐incident‐beam heterodyning system where the two incident beams used are of different frequencies. This is accomplished by using a rotating diffraction grating or by employing a Bragg cell. The Doppler signal from the moving scatterer is no longer an ``even'' function of velocity and the frequency bias can be adjusted depending on the maximum value of the velocity to be measured.

Simplified laser Doppler velocimeter optics

Abstract: A simple, efficient optical system for a laser Doppler velocimeter is described which requires almost no optical heterodyne alignment and which is stable and insensitive to stress and vibration.

Laser system for monitoring the motion of objects

Abstract: The motion of an object may be monitored by directing a laser beam at both 3.39 Mu and 0.6328 Mu from a helium-neon laser oscillator toward the object to be monitored in such manner that a portion of the laser beam is reflected by the object back into the laser, causing the laser to produce output laser energy at 0.6328 Mu which varies significantly in intensity in accordance with the motion of the object. The number of intensity maxima and minima is indicative of the distance moved, while the number of maxima and minima per unit time is indicative of the velocity of movement. The 0.6328 Mu output laser energy may be detected and processed electrically to obtain distance- and velocityindicating signals. A laser amplifier may be disposed in the path of the laser beam to extend the range of the system and/or enable monitoring of lower reflectivity objects.

Doppler shift laser velocimeter data processor

Abstract: An aPparatus for extracting doppler shift frequency information from signals which are produced by dual scatter laser velocimeter over the doppler frequency range of 1 to 300 MHz. The laser doppler velocimeter data which is translated and processed into a form compatible with digital computer inputs may be obtained for very short scan times.

A Radial-shear Interferometer for Use with a Laser Source

Abstract: An interferometer is described that combines the design simplicity of a laser interferometer and the insensitivity to vibration of a common-path instrument. It is used to test wave aberration in ‘single passage’.

Frequency stabilized laser

Abstract: Single frequency laser oscillation is realized by including within the laser cavity a resonant etalon, tuned to the desired laser frequency. This has the effect of suppressing all other modes while permitting the laser to oscillate at the desired single frequency. In addition, the etalon tuning is frequency modulated about the desired frequency, producing an amplitude modulation of the laser signal. The amplitude modulation thus produced is sensed by a phase detector which generates an error signal whenever the laser frequency tends to deviate from the mean, etalon frequency. The error signal is used, in turn, to retune the laser cavity. It is an advantage of the present arrangement that spurious frequency modulation of the laser frequency, introduced by the stabilization system, is substantially less than that produced by comparable prior art stabilization circuits. Furthermore, such modulation can be conveniently reduced, or eliminated, by the addition of a dummy etalon driven in antiphase to the active etalon.

New Velocity Measuring Technique Using Dual-Scatter Laser Doppler Shift

Abstract: : Conventional laser Doppler velocimeters (LDV) detect velocity by heterodyning scattered, Doppler shifted radiation with unscattered, reference radiation A new dual-scatter LDV technique is described which simultaneously illuminates a moving scatterer from two different directions and heterodynes the two superimposed radiations simultaneously scattered in a common direction Significant advantages are derived from the fact that the Doppler difference frequency thus obtained is independent of the scattered direction, permitting unusually large quantities of scattering radiation to be collected without adversely affecting the signal frequency dispersion; these advantages include enhanced signal-to-noise performance and a capability to measure fluid flows with unusually high velocity and/or low seed density System performance, experimental verifications, and typical system designs are presented

Device for controlling the frequency of a laser beam

Abstract: A system for stabilizing the frequency of a laser having the resonator reflectors mounted on the ends of a gas discharge tube by controlling the temperature of the tube in response to an optical output signal from the laser.

Resolution of sidebands in a semiconductor laser frequency modulated by ultrasonic waves

Abstract: Frequency modulatlon or a semiconductor laser via ultrasonic waves is achieved at a modulating frequency \omega_{m} - 150 MHz for CW operation at 4.2°K. Individual sidebands are resolved whose variation with pressure agree well with theory, indicating that little distortion is present. A modulation index of 6 is achieved corresponding to a frequency deviation of 900 MHz and an acoustic pressure of 3 atmospheres. Under pulsed operation at 4.2°K and 77°K frequency modulation is observed as a blurring of the laser frequency.

High‐resolution laser doppler velocity measurement of bidirectional pulsatile fluid flow

Abstract: A laser Doppler heterodyning system has been developed for localized measurement of the magnitude and direction of time‐varying fluid flow velocity. Directional sensitivity is achieved by shifting the frequency of the reference laser beam by an acoustical diffraction cell. A Doppler frequency shift proportional to fluid flow velocity is obtained by heterodyning the scattered laser light with a frequency‐shifted reference laser beam. Experimental results for time‐varying flow velocity in perturbed flow sections are presented.

Phase lock of a far-infrared laser to an absolute frequency standard

Abstract: The 890-GHz line of a HCN laser has been phase-locked to a frequency standard The technique, which is applicable to any laser frequency that can be reached by mixing with known frequencies, will allow frequency measurements of lasers to at least parts in 109

Phase-locked far infrared laser

Abstract: A technique for stabilizing a gas laser to a frequency standard, and more particularly to the use of a phase lock loop in which the laser and its power supply are disposed, with the output of the laser being arranged to be compared with a multiplied frequency standard. In this invention the laser output is mixed with the multiplied frequency standard in a mixer, with the beat frequency from the mixer being compared to a radio frequency reference in a phase detector. The output of the phase detector is sent to a current controller which varies the laser power supply current, thus selectively changing the frequency of the laser. If the laser fluctuates in phase, a control signal brings the beat frequency signal back in phase with the reference input to the phase detector. As a result, a hydrogen cyanide laser phase locked in accordance with this invention has produced an output signal whose beat is less than 50 Hz wide, with a long term stability of less than 10 Hz.

Development testing and application of a three-dimensional laser Doppler velocimeter for the measurement of gas flows

Abstract: Three-dimensional laser Doppler velocimeter for measuring local mean and fluctuating gas velocities

Laser Doppler Measurement of Water Velocity.

Abstract: : The feasibility of measuring ship's speed by the doppler shift in light scattered from a laser beam is investigated. Theoretical aspects of the Doppler effect and optical processing are discussed. The significant design parameters are enumerated and the effects of each analyzed. Problems encountered while testing a bread-board model of a laser water speed sensor reveal certain design criteria and aid in a model design review. It is concluded that with lasers available today the laser log concept is feasible, but difficult and expensive to implement. Optical heterodyning of the source and scattered laser beams results in a signal, readily amenable to electronic processing, but often hidden in noise. It is also concluded that the characteristics of a laser doppler speed-sensing system make it far more valuable as a laboratory tool for studying small-scale flow phenomena and turbulence. (Author)

Optical FM System for Measuring Mechanical Shock

Abstract: A technique is described for calibrating shock accelerometers by measuring the Doppler shift in light frequency produced by the change in velocity of a target. The system employs a quadrature laser interferometer and a single-side-band carrier insertion circuit to distinguish between positive and negative velocities. Key words: Accelerometer; calibration; Doppler; interferometer; laser; shock measuring; single-side-band.

Laser Frequency Stabilization Techniques & Its Applications

Abstract: A review of progress in laser stabilization techniques and laser frequency measurement is given. Methods for relating laser frequencies to the time standard and methods for absolute laser frequency stabilization are described . Experimental information on reproducibility and noise characteristics is reported. Application to frequency and wavelength standards is discussed.