RESUMEN
We describe a system for interrogating the acoustic properties of sub-nanoliter liquid samples within an open microfluidics platform. Sessile droplets were deposited onto integrated optomechanical sensors, which possess ambient-medium-noise-limited sensitivity and can thus passively sense the thermally driven acoustic spectrum of the droplets. The droplet acoustic breathing modes manifest as resonant features in the thermomechanical noise spectrum of the sensor, in some cases hybridized with the sensor's own vibrational modes. Excellent agreement is found between experimental observations and theoretical predictions, over the entire â¼0-40 MHz operating range of our sensors. As an application example, we used the technique to monitor the temporal evolution of evaporating droplets. With suitable control over droplet size and morphology, this technique has the potential for precision acoustic sensing of small-volume biological and chemical samples.
RESUMEN
In this observational study, we embed few-layer hexagonal boron nitride (hBN) inside a planar Fabry-Perot cavity fabricated using a pulsed DC magnetron sputtering system and show that the hBN retains its inherent visible range, defect-based luminescent properties following relatively energetic deposition processing. The observed surface-normal emission enhancement factor of â¼40 is in good agreement with theoretical predictions. We also found that embedded hBN subjected to a rapid thermal annealing treatment exhibits a cracking effect where the edges of the material glow distinctly brighter than adjacent regions. Our results might inform future efforts involving monolithic integration of hBN active layers.
RESUMEN
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 â¼ 103) and mechanical (Q â¼ 102) quality factors. We predict and verify broadband (up to â¼ 5 MHz), air-coupled ultrasound detection with noise-equivalent pressure (NEP) as low as â¼ 30-100 µPa/Hz1/2. This corresponds to an ultrasonic force sensitivity â¼ 2 × 10-13 N/Hz1/2 and enables the detection of MHz-range signals propagated over distances as large as â¼ 20 cm in air. In water, thermal-noise-limited sensitivity is demonstrated over a wide frequency range (up to â¼ 30 MHz), with NEP as low as â¼ 100-800 µPa/Hz1/2. These cavities exhibit a nearly omnidirectional response, while being â¼ 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.
RESUMEN
We present a hexagonal boron nitride (hBN) polymer-assisted transfer technique and discuss subtleties about the process. We then demonstrate localized emission from strained regions of the film draped over features on a prepatterned substrate. Notably, we provide insight into the brightness distribution of these emitters and show that the brightest emission is clearly localized to the underlyin-g substrate features rather than unintentional wrinkles present in the hBN film. Our results aide in the current discussion surrounding scalability of single photon emitter arrays.
RESUMEN
We describe a ball lens assembly, which functions as a broadly tunable bandpass filter and polarizer with imaging capabilities. The physical basis is resonant tunneling of light through an air gap between two half-ball lenses symmetrically coated by few-layer (Si/SiO2 or Ta2O5/SiO2) admittance matching stacks. Tuning is achieved by simultaneous adjustments of the incident angle and the air gap thickness. Individual filters with operational ranges spanning visible (â¼400-700nm) and near-infrared (â¼1000-1800nm) wavelengths were assembled using 10 mm diameter lenses. We show that these filters, configured as a stand-alone scanning spectrometer, can provide a resolving power â¼100 and f-number â¼2.5 for a fiber-compatible input aperture <15µm in diameter. We also demonstrate that, with supplementary optics, the tunable ball filter might be used to implement a compact hyperspectral imaging system.