77 research outputs found
Projecting light beams with 3D waveguide arrays
Free-space light beams with complex intensity patterns, or non-trivial phase structure, are demanded in diverse fields, ranging from classical and quantum optical communications, to manipulation and imaging of microparticles and cells. Static or dynamic spatial light modulators, acting on the phase or intensity of an incoming light wave, are the conventional choices to produce beams with such non-trivial characteristics. However, interfacing these devices with optical fibers or integrated optical circuits often requires difficult alignment or cumbersome optical setups. Here we explore theoretically and with numerical simulations the potentialities of directly using the output of engineered three-dimensional waveguide arrays, illuminated with linearly polarized light, to project light beams with peculiar structures. We investigate through a collection of illustrative configurations the far field distribution, showing the possibility to achieve orbital angular momentum, or to produce elaborate intensity or phase patterns with several singularity points. We also simulate the propagation of the projected beam, showing the possibility to concentrate light. We note that these devices should be at reach of current technology, thus perspectives are open for the generation of complex free-space optical beams from integrated waveguide circuits
Selective plane illumination microscopy on a chip
Selective plane illumination microscopy can image biological samples at a high spatiotemporal resolution. Complex sample preparation and system alignment normally limit the throughput of the method. Using femtosecond laser micromachining, we created an integrated optofluidic device that allows obtaining continuous flow imaging, three-dimensional reconstruction and high-throughput analysis of large multicellular spheroids at a subcellular resolution
Conical emission, pulse splitting and X-wave parametric amplification in nonlinear dynamics of ultrashort light pulses
The precise observation of the angle-frequency spectrum of light filaments in
water reveals a scenario incompatible with current models of conical emission
(CE). Its description in terms of linear X-wave modes leads us to understand
filamentation dynamics requiring a phase- and group-matched, Kerr-driven
four-wave-mixing process that involves two highly localized pumps and two
X-waves. CE and temporal splitting arise naturally as two manifestations of
this process
Anisotropy parameters for two-color photoionization phases in randomly oriented molecules: theory and experiment in methane and deuteromethane
We present a combined theoretical and experimental work investigating the
angle-resolved phases of the photoionization process driven by a two-color
field consisting of an attosecond pulse train and an infrared pulse in an
ensemble of randomly oriented molecules. We derive a general form for the
two-color photoelectron (and time-delay) angular distribution valid also in the
case of chiral molecules and when relative polarizations of the photons
contributing to the attosecond photoelectron interferometer differ. We show a
comparison between the experimental data and the theoretical predictions in an
ensemble of methane and deuteromethane molecules, discussing the effect of
nuclear dynamics on the photoionization phases. Finally, we demonstrate that
the oscillating component and the phase of the two-color signal can be fitted
using complex asymmetry parameters, in perfect analogy with the atomic case
Structured-light-sheet imaging in an integrated optofluidic platform
: Heterogeneity investigation at the single-cell level reveals morphological and phenotypic characteristics in cell populations. In clinical research, heterogeneity has important implications in the correct detection and interpretation of prognostic markers and in the analysis of patient-derived material. Among single-cell analysis, imaging flow cytometry allows combining information retrieved by single cell images with the throughput of fluidic platforms. Nevertheless, these techniques might fail in a comprehensive heterogeneity evaluation because of limited image resolution and bidimensional analysis. Light sheet fluorescence microscopy opened new ways to study in 3D the complexity of cellular functionality in samples ranging from single-cells to micro-tissues, with remarkably fast acquisition and low photo-toxicity. In addition, structured illumination microscopy has been applied to single-cell studies enhancing the resolution of imaging beyond the conventional diffraction limit. The combination of these techniques in a microfluidic environment, which permits automatic sample delivery and translation, would allow exhaustive investigation of cellular heterogeneity with high throughput image acquisition at high resolution. Here we propose an integrated optofluidic platform capable of performing structured light sheet imaging flow cytometry (SLS-IFC). The system encompasses a multicolor directional coupler equipped with a thermo-optic phase shifter, cylindrical lenses and a microfluidic network to generate and shift a patterned light sheet within a microchannel. The absence of moving parts allows a stable alignment and an automated fluorescence signal acquisition during the sample flow. The platform enables 3D imaging of an entire cell in about 1 s with a resolution enhancement capable of revealing sub-cellular features and sub-diffraction limit details
Far-field spectral characterization of conical emission and filamentation in Kerr media
By use of an imaging spectrometer we map the far-field ()
spectra of 200 fs optical pulses that have undergone beam collapse and
filamentation in a Kerr medium. By studying the evolution of the spectra with
increasing input power and using a model based on stationary linear asymptotic
wave modes, we are able to trace a consistent model of optical beam collapse
high-lighting the interplay between conical emission, multiple pulse splitting
and other effects such as spatial chirp.Comment: 8 pages, 9 figure
Localization of light and second-order nonlinearity enhancement in weakly disordered one-dimensional photonic crystals
We show how one-dimensional photonic crystal structures which suffer from a weak random disorder in the layer lengths may give rise to strong localization of light. Using the transfer matrix method we numerically study the effects of this localization in media with a second-order nonlinearity. Localization has a deep impact on the second-harmonic generation efficiency and may give rise to very strong enhancement in correspondence to the localized wavelengths
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