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.

Laser relaxation-oscillation frequency imaging

Abstract: We describe a new imaging technique based on modification of laser relaxation frequency induced by coherent optical feedback from an external target. A direct comparison (both theoretical and experimental) is made with laser feedback interferometry techniques, in which there is a modification of the laser’s steady state. We show that, for a laser with a cavity damping rate γc higher than the population damping rate, γ1, the modification of the laser relaxation frequency can be several orders of magnitude more sensitive than the perturbation of the laser’s output power. Application of this technique to imaging is reported.

Experimental validation of the topological sensitivity approach to elastic-wave imaging

Abstract: In this study the method of topological sensitivity (TS) for solving inverse scattering problems, previously supported by a broad set of numerical simulations, is put to test experimentally with the focus on 2D obstacle reconstruction in a thin aluminum plate via elastic waves. To this end, the in-plane measurements of transient elastodynamic waveforms along the edges of the plate are effected in a non-contact fashion by a 3D laser Doppler vibrometer. Using an elastodynamic (time-domain) finite element model as a computational platform, the TS reconstruction maps are obtained and analyzed under varying experimental conditions. The results show significant agreement between the defect geometry and its reconstruction, thus demonstrating the utility of the TS approach as an efficient and robust solution tool for this class of inverse problems. For completeness, the experimental investigation includes a set of parametric studies geared toward exposing the effect of key problem parameters on the quality of obstacle reconstruction such as the (dominant) excitation frequency, the source aperture, and the duration of the temporal record. On the analytical front, it is shown that the use of a suitable temporal windowing function in specifying the L2 cost functional (that underpins the TS formulation) is essential from both theoretical and computational points of view.

Comparative study of autodyne and heterodyne laser interferometry for imaging.

Abstract: For given laser output power, object under investigation, and photodiode noise level, we have theoretically compared the signal-to-noise ratios of a heterodyne scanning imager based on a Michelson interferometer and of an autodyne setup based on the laser optical feedback imaging (LOFI) technique. In both cases, the image is obtained point by point. In the heterodyne configuration, the beating between the reference beam and the signal beam is realized outside the laser cavity (i.e., directly on the detector), while in the autodyne configuration, the wave beating takes place inside the laser cavity and therefore is indirectly detected. In the autodyne configuration, where the laser relaxation oscillations play a leading role, we have compared one-dimensional scans obtained by numerical simulations with different lasers' dynamical parameters. Finally, we have determined the best laser for LOFI applications and the experimental conditions for which the LOFI detection setup (autodyne interferometer) is competitive compared to a heterodyne interferometer.

Three-dimensional image capturing device and its laser emitting device

Abstract: A three-dimensional image capturing device comprises a plurality of laser devices, and an imaging device, such as a CCD, having a plurality of photo-diodes. Each of the laser devices radiates a pulse modulated laser beam so as to detect distance information or data relating to a topography of a measurement subject. The laser beam is radiated onto the measurement subject and a reflected light beam is sensed by the CCD. Signal charge corresponding to a distance from the image capturing device to the measurement subject is accumulated in each of the photo-diodes, and thus the above distance information is sensed. Each laser beam, respectively radiated from each of the laser devices, shares illuminating area at the distance of the measurement subject, so that radiant energy of each laser beam can be reduced by sharing a single distance measurement operation among the plurality of laser devices.

A simple laser system for atom interferometry

Abstract: We present here a simple laser system for a laser-cooled atom interferometer, where all functions (laser cooling, interferometry and detection) are realized using only two extended cavity laser diodes, amplified by a common tapered amplifier. One laser is locked by frequency modulation transfer spectroscopy, the other being phase locked with an offset frequency determined by an field-programmable gate array-controlled direct digital synthesizer, which allows for efficient and versatile tuning of the laser frequency. Raman lasers are obtained with a double pass acoustooptic modulator. We demonstrate a gravimeter using this laser system, with performances close to the state of the art.