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.

A Scanning Spherical Mirror Interferometer for Spectral Analysis of Laser Radiation

Abstract: The results of a theoretical and experimental investigation of a scanning spherical mirror interferometer designed specifically for analysis of laser radiation are given. It is shown that the high degree of spatial coherence and monochromaticity of laser radiation makes it possible to excite individual interferometer modes selectively. A theory of single-mode excitation is presented, and a specific example treated. The mechanical construction of the instrument and the dynamics of the scanning system are described. The capability of the instrument for observation of laser mode separation, amplitudes, and frequency shifts is illustrated by specific experiments. It is shown that the instrument can easily be used in both the visible and infrared. Results of simultaneous observation of beats between laser modes with an rf spectrum analyzer and of the laser optical field with the scanning interferometer are given, and it is shown that the combined system, in certain cases, will permit determination of the relative phases of the laser modes. Experiments illustrating the use of the scanning interferometer for observation of mode competition and the effects of magnetic fields on laser output are recounted, as is also the operation of an active scanning interferometer with which resolving powers of 2.5 × 109 and finesses of 1040 were obtained. Effects of coupling between laser and interferometer are shown, and a polarization isolator for decoupling is described.

Acoustic chaos and sonic infrared imaging

Abstract: We describe a quasichaotic mechanism for the generation of complex vibrations from the application of a 450 ms, 40 kHz excitation coupled nonlinearly to a sample under inspection by means of sonic infrared (SIR) imaging. Monitoring the sample vibration by means of a laser vibrometer, we find that the vibration switches from the fundamental and harmonics to several series of frequencies that are rational fractions of the fundamental driving frequency. The transition to this quasichaotic behavior is important in obtaining high-quality SIR images.

Self-induced thermal distortion in the near field for a laser beam in a moving medium

Abstract: A theoretical model is developed that predicts the steady-state self-induced thermal distortion of a laser beam in an absorbing medium flowing transverse to the direction of propagation A general perturbation solution is obtained that is appropriate when the thermal distortion effects are small A computer iteration of this solution is performed to obtain results that are applicable over an increased range of distortion conditions The effects of diffraction are neglected, and therefore the solution is limited to the near-field range of the laser beam or to a range where a caustic or infinite intensity is predicted as a result of the self-focusing associated with the thermal distortion effects of the flow The thermal distortion of an initially Gaussian collimated laser beam causes a shift of the beam into the direction of the flow and, at the outset of the thermal effects, a decrease in the peak intensity As the thermal distortion becomes more severe, the self-induced effects cause an increase in the peak intensity, ie, a focusing to occur Experimental results are presented for the thermal distortion of a CW CO 2 laser beam propagating in CS 2 that moves transverse to the propagation direction The data verify the predicted beam deflection and the defocusing as well as focusing effects of the self-induced thermal distortion

Lamb wave Structural Health Monitoring Using a Hybrid PZT-Laser Vibrometer Approach

Abstract: Lamb waves are dispersive and multi-modal, which makes the interpretation of Lamb wave signals very difficult in either the time or frequency domain. In the this article, we present our studies on Lamb wave propagation characterization and crack detection using a hybrid lead zirconate titanate (PZT)-laser vibrometer system and frequency–wave number analysis. A scanning laser Doppler vibrometer is used to acquiring high-resolution time–space Lamb wavefield excited by a PZT actuator. The recorded wavefield is then transformed to frequency–wave number domain by two-dimensional Fourier transform. Wave spectrum in the frequency–wave number domain shows clear distinction among Lamb wave modes being present. These concepts are illustrated through several experimental tests. However, the space information is lost during this transformation. A short-space two-dimensional Fourier transform is then adopted to obtain the frequency–wave number spectra at various spatial locations, resulting in the space–frequency–wave...

A Low-Cost Optical Sensor for Noncontact Vibration Measurements

Abstract: This paper presents a new noncontact method to measure vibrations by using a low-cost optical approach that is able to provide a submicrometer resolution. The transducer exploits a simple optical setup based on an intensity-detection scheme that is implemented with plastic optical fibers, whereas innovative non demanding spectral data processing allows compensation of the vibrating surface reflectivity and the gains of the measurement chain. The performance of the proposed system has been assessed, through comparison with other techniques, by performing several measurement tests that use targets vibrating at frequencies from a few hertz up to several tens of kilohertz and with different values of reflectivity.