Halo (optical phenomenon) | EPFL Graph Search

A halo () is an optical phenomenon produced by light (typically from the Sun or Moon) interacting with ice crystals suspended in the atmosphere. Halos can have many forms, ranging from colored or white rings to arcs and spots in the sky. Many of these appear near the Sun or Moon, but others occur elsewhere or even in the opposite part of the sky. Among the best known halo types are the circular halo (properly called the 22° halo), light pillars, and sun dogs, but many others occur; some are fairly common while others are extremely rare. The ice crystals responsible for halos are typically suspended in cirrus or cirrostratus clouds in the upper troposphere (), but in cold weather they can also float near the ground, in which case they are referred to as diamond dust. The particular shape and orientation of the crystals are responsible for the type of halo observed. Light is reflected and refracted by the ice crystals and may split into colors because of dispersion. The crystals be

Label-free plasmonic biosensors for real-time live cell analysis

Xiaokang Li

For decades, the understanding of life has been focused on its most fundamental building blocks: molecules. Deciphering the dynamic activities of protein molecules in human cells is of vital significance for fundamental and clinical studies. The minuscule scale of protein molecules poses a great challenge for precise quantification. Labeling the molecules of interest with fluorescent and enzymatic tags has thus become an effective strategy to indicate their existence. However, the addition of extrinsic fluorescent tags has shown a number of evident side effects interfering with protein functions and cell biology. The extra steps caused by molecular labeling also increase the complexity of the entire assay and decrease the temporal resolution of the measurement from hours to days. These drawbacks of traditional strategies inevitably hinder the real-time monitoring of cellular activities with minimum interval or external interference. This doctoral thesis focuses on the engineering and demonstration of novel label-free biosensing platforms for real-time cell studies: (1) the secretion of protein molecules from live cells, and (2) the characterization of cellular interactions. For the first topic, a biosensor using plasmonic nanohole arrays as the core sensing elements has been designed. These nanohole arrays consist of a thin gold film perforated with periodic nanoholes. They enable extraordinary optical transmission (EOT), an optical phenomenon that has shown promising capabilities for biochemical detection. This thesis demonstrates, for the first time the application of these structures for real-time monitoring of protein secretions from live cells. On the one hand, the secretion of VEGF (a type of growth factor) from live cancer cells has been monitored in real-time at the temporal resolution of seconds without any additional sample treatment. On the other hand, the integration with the advanced microfluidic system has enabled the biosensor to measure secretion events at the single-cell level by solving a number of technical issues (e.g., low analyte abundance, liquid evaporation). In particular, the real-time production of IL-2 (a cytokine) from single lymphoma cells were monitored for hours, which shows the exceptional versatility of this optofluidic nanobiosensor. For the second topic, a multiparametric surface plasmon resonance (SPR) biosensor has been exploited to investigate interactions between T-cell receptors (TCR) and peptide-major histocompatibility complexes (pMHC). This type of interaction plays a central role in T cell-mediated immunity. Notably, intact human T cells - rather than purified recombinant TCR proteins - were directly used as analytes. A biomimicking lipid membrane was created on the sensor surface to present pMHC molecules, enabling the capture of T cells in vitro. Therefore, the affinity (e.g., binding kinetics) between different types of T cells and membrane-bound pMHC molecules can be readily measured in a label-free manner. The results presented in this thesis rely on a wide range of engineering technologies (imaging, microfluidics, and micro-/nano-manufacturing) and knowledge of biology, chemistry, and optics. The proposed methods using label-free plasmonic biosensors represent a promising strategy to overcome the challenges related to current biochemical analyses. We anticipate that plasmonic biosensors will boost new biodetection methodologies for biomedical research.

EPFL2019

Single crystal diamond micro-disk resonators by focused ion beam milling

Teodoro Graziosi, Sichen Mi, Niels Quack

We report on single crystal diamond micro-disk resonators fabricated in bulk chemical vapor deposition diamond plates (3 mm x 3 mm x 0.15 mm) using a combination of deep reactive ion etching and Focused Ion Beam (FIB) milling. The resulting structures are micro-disks of few mu m in diameter and less than 1 mu m thick, supported by a square or diamond section pillar resulting from the multi-directional milling. Thin aluminum and chromium layers are used to ground the substrate, limit the ion implantation, and prevent edge rounding and roughening. FIB damage is then removed by a combination of hydrofluoric acid etching, oxygen plasma cleaning, and annealing at 500 degrees C for 4 h in air. We experimentally characterize the optical behavior of the devices by probing the transmission of a tapered fiber evanescently coupled to the micro-disk, revealing multiple resonances with a quality factor up to 5700 in the S- and C-band. (c) 2018 Author(s).

AMER INST PHYSICS2018

Quantum-coherent coupling of a mechanical oscillator to an optical cavity mode

Tobias Kippenberg, Albert Schliesser, Stefan Alexander Weis

Optical laser fields have been widely used to achieve quantum control over the motional and internal degrees of freedom of atoms and ions(1,2), molecules and atomic gases. A route to controlling the quantum states of macroscopic mechanical oscillators in a similar fashion is to exploit the parametric coupling between optical and mechanical degrees of freedom through radiation pressure in suitably engineered optical cavities(3-6). If the optomechanical coupling is 'quantum coherent'-that is, if the coherent coupling rate exceeds both the optical and the mechanical decoherence rate-quantum states are transferred from the optical field to the mechanical oscillator and vice versa. This transfer allows control of the mechanical oscillator state using the wide range of available quantum optical techniques. So far, however, quantum-coherent coupling of micromechanical oscillators has only been achieved using microwave fields at millikelvin temperatures(7,8). Optical experiments have not attained this regime owing to the large mechanical decoherence rates(9) and the difficulty of overcoming optical dissipation(10). Here we achieve quantum-coherent coupling between optical photons and a micromechanical oscillator. Simultaneously, coupling to the cold photon bath cools the mechanical oscillator to an average occupancy of 1.7 +/- 0.1 motional quanta. Excitation with weak classical light pulses reveals the exchange of energy between the optical light field and the micromechanical oscillator in the time domain at the level of less than one quantum on average. This optomechanical system establishes an efficient quantum interface between mechanical oscillators and optical photons, which can provide decoherence-free transport of quantum states through optical fibres. Our results offer a route towards the use of mechanical oscillators as quantum transducers or in microwave-to-optical quantum links(11-15).