Parametric control of a diffractive axicon beam rider.

A laser beam rider is a large-scale optical structure designed so that it is attracted toward the optical axis, while also affording forward propulsion via radiation pressure along the beam path. Such structures form the basis of laser-driven light sails. Experimental measurements are described whereby a thin diffractive axicon film is shown to exhibit a natural restoring force when its axis is displaced from the optical axis. This effect is attributed to the optical momentum change of diffracted light. Whereas continuous illumination supports harmonic motion, modulated illumination is shown to support both parametric gain and parametric damping. The 12.7µm period photopolymer axicon grating was suspended in a vacuum torsion oscillator and irradiated with a 1.5 W near-infrared laser modulated at a period of 38 s.

Stable diffractive beam rider.

A passively stable laser-driven lightsail is described, which makes use of a spatially variant "bi-grating" sail with a mass (payload) attached to a boom (patent pending). A two-dimensional analytical model of the system, a linear stability analysis, and numerical solutions of the equations of motion are reported. The acceleration of the light sail along the beam path is found to depend on the grating parameters. We identify stability conditions that depend on the grating design, beam parameters, and boom length. The inclusion of damping is found to enhance the dynamic range of stability.

Experimental Verification of a Bigrating Beam Rider.

An optical beam rider making use of a light sail comprising two opposing diffraction gratings is experimentally demonstrated for the first time. We verify that the illuminated space-variant grating structure provides an optical restoring force, exhibiting stable oscillations when the bigrating is displaced from equilibrium. We further demonstrate parametric cooling by illuminating the sail with synchronized light pulses. This experiment enhances the technical feasibility of a laser-driven light sail based on diffractive radiation pressure.

Measurements of Radiation Pressure Owing to the Grating Momentum.

The radiation pressure force on a nearly single-order diffraction grating was measured for a transmission grating near the Littrow angles at wavelengths of 808 and 447 nm. The component of force parallel to the grating agreed well with our prediction, being proportional to the product of the grating order and the ratio of the wavelength and grating period. The normal component of force varied with the incident angle, vanishing near the Littrow angle as expected. The measurements verify a correspondence between the Fourier grating momentum and the mechanical momentum. This Letter provides opportunities for in-space fly-by-light sailcraft as well as terrestrial applications.

Effect of liquid ubiquinol supplementation on glucose, lipids and antioxidant capacity in type 2 diabetes patients: a double-blind, randomised, placebo-controlled trial.

Ubiquinone is a lipid antioxidant, and a novel liquid ubiquinol (a hydro-soluble, reduced form of coenzyme Q10) supplement was recently developed. The purpose of this study was to examine the levels of glucose, lipids and antioxidant capacity of type 2 diabetes patients after liquid ubiquinol supplementation. This study was designed as a randomised, double-blind, placebo-controlled trial. In all, fifty participants were randomly assigned to a placebo (n 25) or liquid ubiquinol (100 mg/d, n 25) group, and the intervention lasted for 12 weeks. Plasma coenzyme Q10, glucose homoeostasis parameters, lipid profiles, oxidative stress and antioxidative enzyme activities were measured during the study. After 12 weeks of supplementation, glyco Hb (HbA1c) value was significantly decreased in the liquid ubiquinol group (P=0·03), and subjects in the liquid ubiquinol group had significantly lower anti-glycaemic medication effect scores (MES) compared with those in the placebo group (P=0·03). The catalase (P<0·01) and glutathione peroxidase (P=0·03) activities were increased significantly after supplementation. Plasma coenzyme Q10 was correlated with the insulin level (P=0·05), homoeostatic model assessment-insulin resistance (P=0·07), quantitative insulin sensitivity check index (P=0·03) and the anti-hyperglycaemic agents' MES (P=0·03) after supplementation. Lipid profiles did not change after supplementation; however, the subjects in the placebo group had a significantly lower level of HDL-cholesterol after 12 weeks of intervention. In conclusion, oral intake of 100 mg/d liquid ubiquinol might benefit type 2 diabetes patients by increasing antioxidant enzyme activity levels, reducing HbA1c levels and maintaining HDL-cholesterol levels.

Crawling wave optical coherence elastography.

Elastography is a technique that measures and maps the local elastic property of biological tissues. Aiming for detection of micron-scale inclusions, various optical elastography, especially optical coherence elastography (OCE), techniques have been investigated over the past decade. The challenges of current optical elastography methods include the decrease in elastographic resolution as compared with its parent imaging resolution, the detection sensitivity and accuracy, and the cost of the overall system. Here we report for the first time, we believe, on an elastography technique-crawling wave optical coherence elastography (CRW-OCE)-which significantly lowers the requirements on the imaging speed and opens the path to high-resolution and high-sensitivity OCE at relatively low cost. Methods of crawling wave excitation, data acquisition, and crawling wave tracking are presented.

Assessing microstructures of the cornea with Gabor-domain optical coherence microscopy: pathway for corneal physiology and diseases.

Gabor-domain optical coherence microscopy (GD-OCM) was applied ex vivo in the investigation of corneal cells and their surrounding microstructures with particular attention to the corneal endothelium. Experiments using fresh pig eyeballs, excised human corneal buttons from patients with Fuchs' endothelial dystrophy (FED), and healthy donor corneas were conducted. Results show in a large field of view (1 mm×1 mm) high definition images of the different cell types and their surrounding microstructures through the full corneal thickness at both the central and peripheral locations of porcine corneas. Particularly, an image of the endothelial cells lining the bottom of the cornea is highlighted. As compared to healthy human corneas, the corneas of individuals with FED show characteristic microstructural alterations of the Descemet's membrane and increased size and number of keratocytes. The GD-OCM-based imaging system developed may constitute a novel tool for corneal imaging and disease diagnosis. Also, importantly, it may provide insights into the mechanism of corneal physiology and pathology, particularly in diseases of the corneal endothelium.