High-spatial-resolution sub-surface imaging using a laser-based acoustic microscopy technique

Abstract

Scanning acoustic microscopy techniques operating at frequencies in the gigahertz range are suitable for the elastic characterization and interior imaging of solid media with micrometer-scale spatial resolution. Acoustic wave propagation at these frequencies is strongly limited by energy losses, particularly from attenuation in the coupling media used to transmit ultrasound to a specimen, leading to a decrease in the depth in a specimen that can be interrogated. In this work, a laser-based acoustic microscopy technique is presented that uses a pulsed laser source for the generation of broadband acoustic waves and an optical interferometer for detection. The use of a 900-ps microchip pulsed laser facilitates the generation of acoustic waves with frequencies extending up to 1 GHz which allows for the resolution of micrometer-scale features in a specimen. Furthermore, the combination of optical generation and detection approaches eliminates the use of an ultrasonic coupling medium, and allows for elastic characterization and interior imaging at penetration depths on the order of several hundred micrometers. Experimental results illustrating the use of the laser-based acoustic microscopy technique for imaging micrometer-scale subsurface geometrical features in a 70-μm-thick single-crystal silicon wafer with a (100) orientation are presented.

Chemically Specific Imaging Through Stimulated Raman Photoexcitation and Ultrasound Detection: Minireview

“…While hyper-sound (GHz and higher) waves do not reach the detector owing to their significant absorption by the tissue, detectors with the broadband frequency response extending beyond 50MHz would greatly benefit the detection of those signals. [57] While GHz ultrasound detection is possible, [58] those transducers are based on a resonator, which also serves as a filter for a selective band of ultrasound frequencies. [59] Alternatively, one can improve the detection system by using optical spectroscopy based on ultrasensitive detection by means of microring resonators, [60] interferometers, [61] photonic crystal structures [62] or surface plasmon resonance sensors.…”

Methods for Detection of Subsurface Damage: A Review

“…Both surface and subsurface defects can be detected at a high efficiency. However, SAM provides lateral resolution in the order of tens of microns [94][95][96][97][98], which is not applicable to the ultra-precision manufacturing. Generally, the signal acquired by SAM is combined with strong spurious signals which come from the surface waves and elastic waves in acoustic elements [96], making it difficult to distinguish the SSD information.…”

Design and Fabrication of Air-Based 1-3 Piezoelectric Composite Transducer for Air-Coupled Ultrasonic Applications

“…The nondestructive inspection modes can be broadly divided into contact methods and noncontact methods. At present, the methods of noncontact ultrasonic testing are mainly aircoupled ultrasonic testing [3], laser ultrasonic testing [4], and electromagnetic ultrasonic testing [5].…”