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.

Gas-coupled laser acoustic detection as a non-contact line detector for photoacoustic and ultrasound imaging

Abstract: Conventional contacting transducers for ultrasonic wave detection are highly sensitive and tuned for real-time imaging with fixed array geometries. However, optical detection provides an alternative to contacting transducers when a small sensor footprint, a large frequency bandwidth, or non-contacting detection is required. Typical optical detection relies on a Doppler-shifted reflection of light from the target, but gas coupled-laser acoustic detection (GCLAD) provides an alternative optical detection method for photoacoustic (PA) and ultrasound imaging that does not involve surface reflectivity. Instead, GCLAD is a line-detector that measures the deflection of an optical beam propagating parallel to the sample, as the refractive index of the air near the sample is affected by particle displacement on the sample surface. We describe the underlying principles of GCLAD and derive a formula for quantifying the surface displacement from a remote GCLAD measurement. We discuss a design for removing the location-dependent displacement bias along the probe beam and a method for measuring the attenuation coefficient of the surrounding air. GCLAD results are used to quantify the surface displacement in a laser-ultrasound experiment, which shows 94% agreement to line-integrated data from a commercial laser vibrometer point detector. Finally, we demonstrate the feasibility of PA imaging of an artery-sized absorber using a detector 5.8 cm from a phantom surface.

Closed-loop phase-shifting interferometry with a laser diode.

Abstract: A closed-loop phase-shifting Fizeau-type interferometer at ?=633 nm was constructed with the direct frequency modulation of laser diodes. The interferometer is servo controlled fully in the phase domain where optical phases are detected by a two-frequency optical heterodyne method. Stepwise phase shifting was accomplished with good stabilization against external disturbances (vibration, air flow, etc.)??and laser frequency fluctuations.

A vibration-insensitive optical cavity and absolute determination of its ultrahigh stability.

Abstract: We use the three-cornered-hat method to evaluate the absolute frequency stabilities of three different ultrastable reference cavities, one of which has a vibration-insensitive design that does not even require vibration isolation An Nd:YAG laser and a diode laser are implemented as light sources We observe approximately 1 Hz beat note linewidths between all three cavities The measurement demonstrates that the vibration-insensitive cavity has a good frequency stability over the entire measurement time from 100 ms to 200 s An absolute, correlation-removed Allan deviation of 14 x 10(-15) at s of this cavity is obtained, giving a frequency uncertainty of only 044 Hz

System and method for high-speed laser detection of ultrasound

Abstract: A laser light amplification system that amplifies a laser beam emitted from a source as low-amplification seed laser light signal. The low-amplification seed laser light signal is amplified by stimulating emissions of the population inversion provided by a pumping diode to generate an amplified laser light signal. Amplified laser light signal is directed to an object undergoing laser ultrasound testing. Amplified laser light is scattered by the sound energy wave about the object. Scattered laser light is collected by an interferometer and used to detect and characterize acoustic energy. The present invention provides higher pulse rates, improved pointing stability, and optionally variable pulse rates for a variety of uses, including for non-destructive laser ultrasonic testing of materials.