Advancing the path to imaging in freely moving mice via multimode-multicore fiber based holographic endoscopy.

Significance: Hair-thin multimode optical fiber-based holographic endoscopes have gained considerable interest in modern neuroscience for their ability to achieve cellular and even subcellular resolution during deep brain imaging. However, the application of multimode fibers in freely moving animals presents a persistent challenge as it is difficult to maintain optimal imaging performance while the fiber undergoes deformations.

Aim: We propose a fiber solution for challenging applications with the capability of deep brain high spatial resolution imaging and neuronal activity monitoring in anesthetized as well as awake behaving mice.

Field electron emission from tungsten micro-tips coated with various thicknesses of polystyrene nanolayers: Characteristics & analysis.

This paper studies and analyses the characteristics of cold field electron emission from uncoated polycrystalline tungsten tips before and after being coated with an insulating polystyrene layer of different thicknesses. The process of testing the samples has been carried out under high vacuum conditions (10 mbar). Uncoated tungsten tips were prepared using the electrochemical etching process.

Optically Transportable Optofluidic Microlasers with Liquid Crystal Cavities Tuned by the Electric Field.

Liquid crystal microdroplets with readily adjustable optical properties have attracted considerable attention for building reconfigurable optofluidic microsystems for sensing, imaging, and light routing applications. In this quest, development of active optical microcavities serving as versatile integrated sources of coherent light and ultra-sensitive environmental sensors has played a prominent role. Here, we study transportable optofluidic microlasers reversibly tunable by an external electric field, which are based on fluorophore-doped emulsion droplets of radial nematic liquid crystals manipulated by optical tweezers in microfluidic chips with embedded liquid electrodes.

Memory effect assisted imaging through multimode optical fibres.

When light propagates through opaque material, the spatial information it holds becomes scrambled, but not necessarily lost. Two classes of techniques have emerged to recover this information: methods relying on optical memory effects, and transmission matrix (TM) approaches. Here we develop a general framework describing the nature of memory effects in structures of arbitrary geometry.

Compressively sampling the optical transmission matrix of a multimode fibre.

The measurement of the optical transmission matrix (TM) of an opaque material is an advanced form of space-variant aberration correction. Beyond imaging, TM-based methods are emerging in a range of fields, including optical communications, micro-manipulation, and computing. In many cases, the TM is very sensitive to perturbations in the configuration of the scattering medium it represents.

Robustness of Light-Transport Processes to Bending Deformations in Graded-Index Multimode Waveguides.

Light transport through a multimode optical waveguide undergoes changes when subjected to bending deformations. We show that optical waveguides with a perfectly parabolic refractive index profile are almost immune to bending, conserving the structure of propagation-invariant modes. Moreover, we show that changes to the transmission matrix of parabolic-index fibers due to bending can be expressed with only two free parameters, regardless of how complex a particular deformation is.

Thermally induced micro-motion by inflection in optical potential.

Recent technological progress in a precise control of optically trapped objects allows much broader ventures to unexplored territory of thermal motion in non-linear potentials. In this work, we exploit an experimental set-up of holographic optical tweezers to experimentally investigate Brownian motion of a micro-particle near the inflection point of the cubic optical potential. We present two complementary views on the non-linear Brownian motion.

Omnidirectional Transport in Fully Reconfigurable Two Dimensional Optical Ratchets.

A fully reconfigurable two-dimensional (2D) rocking ratchet system created with holographic optical micromanipulation is presented. We can generate optical potentials with the geometry of any Bravais lattice in 2D and introduce a spatial asymmetry with arbitrary orientation. Nontrivial directed transport of Brownian particles along different directions is demonstrated numerically and experimentally, including on axis, perpendicular, and oblique with respect to an unbiased ac driving.

Thermally induced passage and current of particles in a highly unstable optical potential.

We discuss the statistics of first-passage times of a Brownian particle moving in a highly unstable nonlinear potential proportional to an odd power of position. We observe temperature-induced shortening of the mean first-passage time and its dependence on the power of nonlinearity. We propose a passage-time fraction as both a simple and experimentally detectable witness of the nonlinearity.