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.

Active vibration control of a smart beam through piezoelectric actuation and laser vibrometer sensing: simulation, design and experimental implementation

Abstract: A velocity feedback control system is evaluated in the active control of vibrations of a smart beam with a pair of surface mounted piezoelectric ceramic patches, and finite element (FE) model results are validated against measured ones. To this end, a three-layered smart beam FE model is utilized, where a partial layerwise theory and a fully coupled electro-mechanical theory are considered for the formulation of the displacement field and electric potential, respectively. Regarding the test rig, it consists of a cantilever smart aluminum beam with two piezoelectric patches mounted close to the clamped end. One of the piezoelectric patches is utilized to excite the beam while the other is utilized as an actuator in the feedback control loop. The control voltage applied to the actuator is proportional to the transverse velocity at the free end, which is measured by a laser vibrometer. First, the quasi-static actuation capacity of the piezoelectric patches is evaluated. Next, the free and forced velocity responses to an initial displacement field and harmonic excitation are analyzed. The capacity to predict instabilities and the accuracy of the FE model are demonstrated and the applicability and functionality of the velocity feedback vibration control system are discussed.

Monolithic microchip laser with intracavity beam combining and sum frequency or difference frequency mixing

Abstract: A method for producing low-noise laser output at various wavelengths and/or in various operation modes in a monolithic microchip laser comprises schemes of generating two fundamental beams in separate cavities, precise intracavity beam combination based on the walk-off effect in birefringent crystal, and wavelength conversion in nonlinear optical crystals. The fundamental beams are produced from light sources selected upon the desired wavelengths, polarizations, and other features related to the laser output. Low-noise laser devices operated in SLM or with spectra of flat-top or desired bandwidths are constructed according to the method. High-volume fabrication is feasible. Apparatus of compact size and efficient frequency conversion is demonstrated with various configurations including those for generating low-noise 491 nm laser, as a replacement of Argon ion laser.

Accurate determination of dispersion curves of guided waves in plates by applying the matrix pencil method to laser vibrometer measurement data

Abstract: Accurate knowledge of the dispersion relations of guided waves in plates is important for the efficient use of Lamb wave-based damage-detection methods. In this paper, we introduce a method which aims at automatically extracting the dispersion curves from laser vibrometer measurement data in an easy and robust manner. This method works by Fourier transforming the measurement data into the wavenumber domain and then applying the matrix pencil method by Hua and Sarkar to extract the wavenumber-dependent frequencies. As an additional result, we are able to experimentally detect backward propagating waves in aluminium plates.

Laser beam scanner apparatus

Abstract: In a laser beam scanner apparatus for scanning the surface of a photosensitive drum (1) or a document to be read by deflecting a laser beam emitted from a laser diode (LD) with a deflector (50), there is provided a drive current control circuit (100) for controlling the magnitude of drive current of said laser diode on the basis of a beam deflection angle of said deflector.

Reduction of the Influence of Laser Beam Directional Dithering in a Laser Triangulation Displacement Probe.

Abstract: Directional dithering of a laser beam potentially limits the detection accuracy of a laser triangulation displacement probe. A theoretical analysis indicates that the measurement accuracy will linearly decrease as the laser dithering angle increases. To suppress laser dithering, a scheme for reduction of the influence of laser beam directional dithering in a laser triangulation displacement probe, which consists of a collimated red laser, a laser beam pointing control setup, a receiver lens, and a charge-coupled device, is proposed in this paper. The laser beam pointing control setup is inserted into the source laser beam and the measured object and can separate the source laser beam into two symmetrical laser beams. Hence, at the angle at which the source laser beam dithers, the positional averages of the two laser spots are equal and opposite. Moreover, a virtual linear function method is used to maintain a stable average of the positions of the two spots on the imaging side. Experimental results indicate that with laser beam pointing control, the estimated standard deviation of the fitting error decreases from 0.3531 mm to 0.0100 mm , the repeatability accuracy can be lowered from ±7 mm to ±5 μ m , and the nonlinear error can be reduced from ±6 % FS (full scale) to ±0.16 % FS.