Periodic arrangements of micro- and nano-holes with controllable period, diameter and depth at the surface of materials are of high interest for a large range of applications. Here we present a laser-based approach using micro-Bessel beams with adjustable length to machine arrays of holes with subwavelength diameters and depths reaching several micrometers at the surface of fused silica. Suitability and limitations of the technique are investigated, including the challenge of avoiding crosstalk effects. The performance level shows the potential of the direct-laser-processing method towards the realization of integrated devices, as a flexible and cost-effective alternative technique to current multistep nanofabrication methods.
Arrays of nanoholes or nanochannels constitute the building block of integrated devices that open attractive applications like 2D photonic crystals, 2D metamaterials or nanostructured surfaces. Here we present a laser-based technique that enables to generate short-length micro-Bessel beams (irrespective of their core diameter) that we further use to machine depth-controlled holes with a cylindrical depth profile. We illustrate the potential of this method by fabricating square arrays of subwavelength-diameter holes with several-micrometers depth by direct laser ablation at the surface of fused silica.
Modulation transfer function (MTF) is an important parameter for image quality evaluation of on-orbit optical image systems. Various methods have been proposed to determine the MTF of an imaging system which are based on images containing point, pulse and edge features. In this paper, the edge of the moon can be used as a high contrast target to measure on-orbit MTF of image systems based on knife-edge methods. The proposed method is an extension of the ISO 12233 Slanted-edge Spatial Frequency Response test, except that the shape of the edge is a circular arc instead of a straight line. In order to get more accurate edge locations and then obtain a more authentic edge spread function (ESF), we choose circular fitting method based on least square to fit lunar edge in sub-pixel edge detection process. At last, simulation results show that the MTF value at Nyquist frequency calculated using our lunar edge method is reliable and accurate with error less than 2% comparing with theoretical MTF value.
Multicore structures based on increased index waveguiding traces are fabricated by ultrafast laser photo inscription in bulk optical glass. A parametric study of the geometry of structure, number of traces and index contrast is discussed with respect to guided modes characteristics. Multicore waveguide present optical designs allowing large mode area light guiding by ultrafast laser photo inscription with coherent mode superposition in near infrared and mid-infrared in fused silica and Chalcogenide glass.
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