Picosecond Ultrasonics at the Nanoscale
Recent advances in plasmonics have enabled unprecedented control of light matter interaction, making it possible to concentrate optical energy at the nanoscale. In this project, we explore plasmonic nanofocusing approaches to confine light at the apex of a scanning probe microscope tip . We use the confined light to create a near-field ultrafast optical probe for time-resolved detection of elastic waves with picosecond temporal resolution and nanoscale local spatial resolution. We also explore the nanofocusing approach to create near-field optical probes arrays using two dimensional arrays of metallic dimmers to enable parallel multi-point detection. This project advances the state-of-the art in optical imaging and laser based ultrasonic instrumentation and provides a tool for fundamental studies of nanoscale phonon transport, phonon and photon interaction, elastic wave propagation in nanostructures, and the dynamics of ultrafast nanomechanical resonators. This project has future applications in areas such as, nanomechanical signal processing, nondestructive materials characterization, and biophotonic sensing.
Tunable Phononic Crystals and Metamaterials
Laser-Ultrasonic Sensing of Additive Manufacturing Processes
Additive manufacturing (AM) technologies have advanced rapidly over the last three decades to the point where they have the potential to fundamentally change the way that complex parts will be designed and fabricated in the future. In-situ sensor technologies that can be integrated with AM techniques are needed for monitoring process conditions such as local temperature distribution, melt pool size, product structural integrity (porosity, microstructure, and defect state), part shape precision, surface conditions, and depth dependent material properties. The objective of this project is to explore laser generated elastic waves in the ultrasonic frequency range for in-situ process quality control of metal additive manufacturing process. The project will provide the measurement science needed to enable a fast, reliable, and cost-effective ultrasonic methodology for real-time assessment of additive manufacturing product quality, process condition monitoring, and control of defects during component fabrication.
Pulsed lasers have been exploited in different contexts to generate controlled mechanical deformation in materials at extreme pressures or stresses in the tens to thousands of MPa range and strain rates of up to 108 1/s. We are interested in understanding the role of inertia, elastic wave propagation, and rate dependent effects on the spontaneous delamination and blister deformation of thin films. Through these studies, we hope to exploit dynamic blister deformation of thin films as actuators in applications ranging from ballistic testing of protective materials using accelerated micro-particle projectiles, needle-less drug delivery using coated nano-particles, and manufacturing of complex surface patterns in flexible electronic structures.
Mechanics of the Bicycle Wheel