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.

Device and method for biological tissue stimulation by high intensity laser therapy

Abstract: A method for laser anti-inflammatory treatment of painful symptomatologies and for tissue regeneration includes generating a pulsed laser beam with laser at a wavelength between 0.75 and 2.5 micrometers. The laser energy is conveyed to a hand unit where the laser beam is preferably defocused. The operator then applies the defocused laser beam the skin of a patient in need of treatment. The average power density per pulse of the defocused laser beam on the skin being 8 W/cm2 per pulse or more.

Laser beam generator

Abstract: A laser beam generator (13) includes first and second mirrors (14R, 16R), a laser light source (11), a laser medium (15), a non-linear optical crystal element (16) and a birefringent element (14). The laser light source generates a pumping light beam. The laser medium (15), arranged between the first and second mirrors (14R, 16R) is irradiated with the pumping light beam via one of the mirrors (14R) to generate a fundamental laser beam based on the pumping light beam. The non-linear optical crystal element (16) is arranged between the first and second mirrors to generate a second harmonic laser beam under the type II phase matching as the fundamental laser beam from the laser medium (15) is passed through it in resonant oscillation. The birefringent element (14) has its one surface at a pumping light beam inlet side coated with a high reflectance coating (14R) and has its opposite surface parallel to it with a nonreflective coating (14T). The birefringent element (14) is set so that its optical axis is inclined at a predetermined azimuth angle with respect to the crystal axis of the non-linear optical crystal element (16). The surface of the birefringent element (14) coated with a high reflectance coating (14R) constitutes one of the first or second mirrors.

Feasibility of Using Lateral Mode Coupling Method for a Large Scale Ultrasound Phased Array for Noninvasive Transcranial Therapy

Abstract: A hemispherical-focused, ultrasound phased array was designed and fabricated using 1372 cylindrical piezoelectric transducers that utilize lateral coupling for noninvasive transcranial therapy. The cylindrical transducers allowed the electrical impedance to be reduced by at least an order of magnitude, such that effective operation could be achieved without electronic matching circuits. In addition, the transducer elements generated the maximum acoustic average surface intensity of 27 W/cm2. The array, driven at the low (306-kHz) or high frequency (840-kHz), achieved excellent focusing through an ex vivo human skull and an adequate beam steering range for clinical brain treatments. It could electronically steer the ultrasound beam over cylindrical volumes of 100-mm in diameter and 60-mm in height at 306 kHz, and 30-mm in diameter and 30-mm in height at 840 kHz. A scanning laser vibrometer was used to investigate the radial and length mode vibrations of the element. The maximum pressure amplitudes through the skull at the geometric focus were predicted to be 5.5 MPa at 306 kHz and 3.7 MPa at 840 kHz for RF power of 1 W on each element. This is the first study demonstrating the feasibility of using cylindrical transducer elements and lateral coupling in construction of ultrasound phased arrays.

Imaging of Barely Visible Impact Damage on a Complex Composite Stiffened Panel Using a Nonlinear Ultrasound Stimulated Thermography Approach

Abstract: Thermosonics, also known as ultrasonic stimulated thermography, is a rapid non-destructive evaluation technique that uses an infrared camera to visualise material defects by detecting the frictional heating at crack surfaces when a part under inspection is vibrated These vibrations are usually produced by an ultrasonic horn being pressed against the surface of the test sample, which result in uncontrolled generations of frequency components and excitation amplitude This makes thermosonics highly non-reproducible and unreliable This paper presents a novel thermographic method, here named as nonlinear ultrasound stimulated thermography, for the detection and imaging of real material defects such as impact damage on a complex composite stiffener panel This technique combines nonlinear ultrasonic techniques with thermography A nonlinear ultrasonic approach was used as signature for a reliable frequency-selective excitation of material defects, while an infrared camera was employed to reveal the damage location and severity A nonlinear narrow sweep excitation method was employed to efficiently excite the local resonance frequencies of the damaged region in order to give rise to the highest nonlinear harmonic response in the material leading to a high heat generation at the crack surface The experimental tests were carried out with a laser vibrometer in order to better understand the interaction of elastic waves with nonlinear scattering An ad-hoc nonlinear thermal-structural finite element and crack model was developed to study the heat generation caused by the movement of the crack surfaces when elastic waves with a particular frequency impinges on the crack interphase with good agreement with the experimental results The proposed new method allows to detect single and multiple barely visible impact damage in a quick, reliable and reproducible manner and overcomes the main limitations of classical thermosonics

Broadband optical detection of transient motion from a scattering surface

Abstract: A method and apparatus for optically detecting transient motion from a scattering surface A laser beam having a predetermined frequency is directed onto such a surface to thereby scatter the laser beam and produce a scattered laser beam defining an optical wavefront and having an optical spectrum with a central peak at the laser frequency and a sideband on either side of the central peak The laser beam scattered by the surface is caused to interfere with a reference beam derived from the scattered laser beam and having an optical wavefront substantially matching the wavefront of the scattered beam and an optical spectrum with a single peak at the laser frequency and no sidebands, to obtain an optical signal which is detected and converted into an electrical signal representative of the transient motion The optical detection technique according to the invention has a broad frequency bandwidth and a large etendue providing greater sensitivity of detection, and is particularly useful for detecting small surface deformations of a material or workpiece subjected to ultrasonic energy