Laser Doppler vibrometer

About: Laser Doppler vibrometer is a research topic. Over the lifetime, 6319 publications have been published within this topic receiving 76068 citations.

Differential Doppler Heterodyning Technique

Abstract: Measuring velocity without disturbing the moving object is possible by use of the laser doppler heterodyning technique. Theoretical considerations on the doppler shift show that the antenna property of the photodetector can solve an apparent conflict between two different ways of calculating the detected doppler frequency. We found that the doppler frequency for this particular setup is independent of the direction of detection. Investigations of the signal-to-noise ratio (SNR) show that the maximum SNR—considering the optical setup—is obtained by measuring the frequency difference between two doppler-shifted beams rather than by measuring the shift of a single beam by comparing it with a reference beam. Measurements seem to be in agreement with the theoretical consideration.

Laser vibrometry meets laser speckle

Abstract: This paper begins with a review of the fundamental mechanism by which speckle noise is generated in Laser Vibrometry before describing a new numerical simulation of speckle behavior for prediction of noise level in a real measurement. The simulation data provides real insight into the phase and amplitude modulation of the Doppler signal as a result of speckle changes. The paper also includes experimental data looking at the influence of speckle noise in measurements on rotors with a selection of surface treatments and in scanning and tracking configurations.

Synchronizing signal generating system for laser scanner

Abstract: A synchronizing signal generating system for a laser scanner comprises a source for emitting a first laser beam for scanning and a second laser beam for synchronization of scans by the first laser beam, a polygonal mirror for causing the first laser beam to scan a medium and for causing the second laser beam to scan a grating which has bright portions and dark portions alternately arranged along a scanning direction of the second laser beam, a converging optical system for converging the second laser beam transmitted through the grating, a light receiving system for receiving the second laser beam converged by the converting optical system and for generating a synchronizing signal, and a circuit for controlling the source responsive to the synchronizing signal so as to synchronize a scan timing of the first laser beam. The converging optical system comprises a plurality of lenses or concave mirrors provided for a length corresponding to a scan length of the second laser beam on the grating.

Laser alignment servo method and apparatus

Abstract: A servo alignment method and apparatus for maintaining laser beam alignment. An operating parameter of the laser (such as output beam power) is measured, and error signals are generated from the measured operating parameter signal for controlling the laser beam alignment. In one class of embodiments, modulation signals are supplied to an intra-cavity component of a laser system to modulate the beam path. The beam path may be modulated by reciprocating a laser resonator mirror about a mirror axis or two substantially orthogonal mirror axes. In the latter case, the mirror may be vibrated about the axes either alternately (first about one axis and then about the other) or simultaneously. In embodiments in which an intra-cavity component is modulated, the laser operating parameter is measured during such modulation, the measured operating parameter signal is demodulated (preferably by multiplication in a mixer with a selected frequency component of the modulation signal currently being asserted, and error signals are generated from the demodulated signal for controlling the laser beam alignment.

Detection of shear wave in ultrasonic range by using a laser Doppler vibrometer

Abstract: A laser Doppler vibrometer is used to measure shear waves propagating through solids in the ultrasonic frequency range. The laser Doppler vibrometer detects translational motion of small spherical lenses mounted on a solid surface. Stacking of wave-form signals increases the signal-to-noise ratio. Wave motion on a solid surface can be obtained from the surface vibrations measured at different incident angles of a laser beam. The observed longitudinal and shear wave amplitudes from a thickness-dilation-mode transducer agreed fairly well with the calculated amplitudes modeled by a piston force source.