Non-contact ultrasonic inspection by Gas-Coupled Laser Acoustic Detection (GCLAD)

Gas-Coupled Laser Acoustic Detection (GCLAD) is an ultrasonic, non-contact detection technique that has been recently proven to be applicable to the inspection of mechanical components. GCLAD response raises as the intersection length between the probe laser beam and the acoustic wavefront propagating in the air increases; such feature differentiates the GCLAD device from other optical detection instruments, making it a line detection system rather than a point detector. During the inspection of structures mainly extending in two dimensions, the capability to evidence presence of defects in whichever point over a line would enable moving the emitter and the detector along a single direction: this translates in the possibility to decrease the overall required time for interrogation of components compared to point detectors, as well as generating simpler automated monitoring layouts. Based on this assumption, the present study highlights the possibility of employing the GCLAD device as a line inspection tool. To this end, preliminary concepts are provided allowing maximization of the GCLAD response for the non-destructive testing of components which predominantly extend in two dimensions. Afterwards, the GCLAD device is employed in pulse-echo mode for the detection of artificial defects machined on a 12 mm-thick steel plate: the GCLAD probe laser beam is inclined to be perpendicular to the propagation direction of the airborne ultrasound, generated by surface acoustic waves (SAWs) in the solid which are first reflected by the defect flanks and subsequently refracted in the air. Numerical results are provided highlighting the SAW reflection patterns, originated by 3 mm deep surface and subsurface defects, that the GCLAD should interpret. The subsequent experimental campaign highlights that the GCLAD device can identify echoes associated with surface and subsurface defects, located in eight different positions on the plate. B-scan of the component ultimately demonstrates the GCLAD performance in accomplishing the inspection task.

An estimate of size of copper nanoparticles levitating over the melt surface using the measurements of spectral reflectance

A strong decrease in normal reflectance of a probe laser beam of 660 nm wavelength reflected from the surface of copper sample just after the beginning of the sample melting in a rarefied argon atmosphere has been observed recently by the authors. A similar time dependence of the reflectance is obtained in the laboratory experiments of the present paper at the wavelengths of 532 nm. The additional spectral measurements enable the authors to estimate the size of condensed nanoparticles levitating over the copper melt.

Non-Contact Ultrasonic Inspection by Gas-Coupled Laser Acoustic Detection (GCLAD)

Gas-Coupled Laser Acoustic Detection (GCLAD) is an ultrasonic, non-contact detection technique that has been recently proven to be applicable to the inspection of mechanical components. GCLAD response raises as the intersection length between the probe laser beam and the acoustic wavefront propagating in the air increases; such feature differentiates the GCLAD device from other optical detection instruments, making it a line detection system rather than a point detector. During the inspection of structures mainly extending in two dimensions, the capability to evidence presence of defects in whichever point over a line would enable moving the emitter and the detector along a single direction: this translates in the possibility to decrease the overall required time for interrogation of components compared to point detectors, as well as generating simpler automated monitoring layouts. Based on this assumption, the present study highlights the possibility of employing the GCLAD device as a line inspection tool. To this end, preliminary concepts are provided allowing maximization of the GCLAD response for the non-destructive testing of components which predominantly extend in two dimensions. Afterwards, the GCLAD device is employed in pulse-echo mode for the detection of artificial defects machined on a 12 mm-thick steel plate: the GCLAD probe laser beam is inclined to be perpendicular to the propagation direction of the airborne ultrasound, generated by surface acoustic waves (SAWs) in the solid which are first reflected by the defect flanks and subsequently refracted in the air. Numerical results are provided highlighting the SAW reflection patterns, originated by 3 mm deep surface and subsurface defects, that the GCLAD should interpret. The subsequent experimental campaign highlights that the GCLAD device can identify echoes associated with surface and subsurface defects, located in eight different positions on the plate. B-scan of the component ultimately demonstrates the GCLAD performance in accomplishing the inspection task.

Determine Dispersion Coefficient of 85Rb Atom in the Y–Configuration

In this work, we derive analytical expression for the dispersion coefficient of 85Rb atom for a weak probe laser beam induced by a strong coupling laser beams. Our results show possible ways to control dispersion coefficient by frequency detuning and of the coupling lasers. The results show that a Y-configuration appears two transparent window of the dispersion coefficient for the probe laser beam. The depth and width or position of these windows can be altered by changing the intensity or frequency detuning of the coupling laser fields. Keywords: Electromagnetically induced transparency, dispersion coefficient.