arXiv subjects

K. G. Scheuer

Publications and source records attributed to K. G. Scheuer.

4 recordsLinked to original sources

arXiv2024

Coupling the thermal acoustic modes of a bubble to an optomechanical sensor

We report experimental observations of the volume acoustic modes of air bubbles in water, including both the fundamental Minnaert breathing mode and a family of higher-order modes extending into the megahertz frequency range. Bubbles were placed on or near optomechanical sensors having a noise floor substantially determined by ambient medium fluctuations, and which are thus able to detect thermal motions of proximate objects. Bubble motions could be coupled to the sensor through both air (i.e., with the sensor inside the bubble) and water, verifying that sound is radiated by the high-order modes. We also present evidence for elastic-Purcell-effect modifications of the sensor's vibrational spectrum when encapsulated by a bubble, in the form of cavity-modified linewidths and line shifts.

physics.flu-dyn↗

arXiv2024

Air-coupled ultrasound using broadband shock waves from piezoelectric spark igniters

We used an optomechanical sensor to study the ultrasound generated by manually operated piezoelectric spark igniters. These low-energy sparks produce short-duration acoustic shock-wave pulses, with sub-microsecond rise times and frequency content extending well beyond 2 MHz in air. The same source-receiver combination was then used to demonstrate broadband characterization of solid (polymer and glass) plates in a simple setup, where single spark events yielded high-SNR data without the need for critical alignment. This setup also enabled us to estimate pressure excursions approaching 105 Pa at millimeter-scale distances from the spark. The results are in large part made possible by the small size, wide bandwidth, and high sensitivity of the optomechanical sensor, and might be of interest for air-coupled ultrasound applications in non-destructive testing.

physics.app-ph↗

arXiv2022

Accounting for objective lens autofluorescence in quantum emitter measurements

The rise of interest in the study of quantum emitters has recently prompted many research groups to construct their own confocal epifluorescence microscopy/spectroscopy instruments. The low light levels typically involved in quantum emitter measurements makes it critically important to account for any potential sources of background fluorescence by components used within such setups. In this report, we show that emission originating from various microscope objectives can possess elusive sharp linewidths that could potentially be mistaken for quantum emission. Impurities present in many glasses overlap in wavelength with single photon emission from several candidate emitter systems of current interest. A careful consideration of this system noise could be critical to exploratory work of the optical properties of materials such as transition metal dichalcogenides and hexagonal boron nitride.

physics.optics↗

arXiv2022

Ultrasound sensing at thermomechanical limits with optomechanical buckled-dome microcavities

We describe the use of monolithic, buckled-dome cavities as ultrasound sensors. Patterned delamination within a compressively stressed thin film stack produces high-finesse plano-concave optical resonators with sealed and empty cavity regions. The buckled mirror also functions as a flexible membrane, highly responsive to changes in external pressure. Owing to their efficient opto-acousto-mechanical coupling, thermal-displacement-noise limited sensitivity is achieved at low optical interrogation powers and for modest optical (Q ~ 10^3) and mechanical (Q ~ 10^2) quality factors. We predict and verify broadband (up to ~ 5 MHz), air-coupled ultrasound detection with noise-equivalent pressure (NEP) as low as ~ 30-100 $μ$Pa/Hz^1/2. This corresponds to an ultrasonic force sensitivity ~ 2 x 10^-13 N/Hz^1/2 and enables the detection of MHz-range signals propagated over distances as large as ~ 20 cm in air. In water, thermal-noise-limited sensitivity is demonstrated over a wide frequency range (up to ~ 30 MHz), with NEP as low as ~ 100-800 $μ$Pa/Hz^1/2. These cavities exhibit a nearly omnidirectional response, while being ~ 3-4 orders of magnitude more sensitive than piezoelectric devices of similar size. Easily realized as large arrays and naturally suited to direct coupling by free-space beams or optical fibers, they offer significant practical advantages over competing optical devices, and thus could be of interest for several emerging applications in medical and industrial ultrasound imaging.

physics.ins-det↗