Optically excited nanoscale ultrasonic transducers.

In order to work at higher ultrasonic frequencies, for instance, to increase the resolution, it is necessary to fabricate smaller and higher frequency transducers. This paper presents an ultrasonic transducer capable of being made at a very small size and operated at GHz frequencies. The transducers are activated and read optically using pulsed lasers and without physical contact between the instrumentation and the transducer. This removes some of the practical impediments of traditional piezoelectric architectures (such as wiring) and allows the devices to be placed immediately on or within samples, reducing the significant effect of attenuation which is very strong at frequencies above 1 GHz. The transducers presented in this paper exploit simultaneous optical and mechanical resonances to couple the optical input into ultrasonic waves and vice versa. This paper discusses the mechanical and optical design of the devices at a modest scale (a few µm) and explores the scaling of the transducers toward the sub-micron scale. Results are presented that show how the transducers response changes depending on its local environment and how the resonant frequency shifts when the transducer is loaded by a printed protein sample.

A plasmonic SAW transducer.

In this work, an acoustic-optical transducer that is based on the utilization of plasmons is proposed to optically detect SAW of wavelength (<400 nm) smaller than the optical wavelength (800 nm). Although grating based coupling of plasmons is well known, it has not been applied in the detection of ultrasound. In this work, designs utilizing this operating principle are proposed which can achieve higher changes in reflectivity than those achievable by traditional methods, thus overcoming the traditional difficulties in the detection of very high frequency (10 GHz range) SAWs. The proposed device can be fabricated on surfaces at low cost and be used to detect remotely.