Micro-lensing

C. Wachter, et ah, Fibre-chip coupling with silicon micro-lenses, to appear in Proc. SPIE 5728 (2005). 

Gravitahonal (micro) lensing is now recognised as a way of revealing otherwise hidden matter. It is universally used to estimate the distribution and quantity of dark matter on a variety of distance scales. The study of dark matter in the halo of our own Galaxy is not the least significant amongst these. 

Abstract These notes present the physics of gravitational lensing in various cosmological contexts. The equations and approximations that are commonly used to describe the displacement field or the amplification effects are presented. Several observational applications are discussed. They range from micro-lensing effects to cosmic shear detection that is a weak lensing effect induced by the large-scale structure of the Universe. The scientific perspectives of this latter application are presented in some details. 

Lu, Y., Yin, Y, and Xia, Y, A self-assembly approach to the fabrication of patterned, two-dimensional arrays of micro lenses of organic polymers, Adv. Mater, 13, 34, 2001. 

Fig. 8 Tunable micro-lenses, (a) Hydrogel-based micro-lens according to (Kim et al. 2004), (b) Liquid lens controlled by a hydrogel ring according to (Dong et al. 2007)...

Figure 4-15 Electron micrograph showing spherical protrusion In perspective. The optical micro lenses produced according to the procedure in Fig. 4-14 measure 400 pm in diameter and approximately 20 pm in height.

In the previous chapters, the optical axes of the tunable microlenses discussed were perpendicular to their substrates. However, in-plane micro-lenses utilizing the curvature formed by the interfaces between two immiscible liquids or between air and liquid can be introduced to observe objects in microfluidic channels. Their optical axes are parallel to the substrate of microlenses—a distinctly different system from what we have seen previously. 

The facile cleavage of Si-Si bonds by UV radiation is also made use of in the application of polysilanes as photoresists. This application has been weU studied [107-110]. The technology covers a wide range from the structuring of metal films to the fabrication of micro lenses. 

Ultrasonic devices have been extensively used to process sol-gel precursor solutions, e.g. precursor dispersion in liquid solution. Besides, several works report on the fabrication of calibrated powders from ultrasonically sprayed sol-gel precursors (process D, according to classification by Vigui6 and Spitz). The sol-gel fabrication of micro-lenses from a drop-on-demand ultrasonic nozzle (ink-jet type) was also studied in details (Biehl, 1998 Danzebrink, 1999, 2001). However, in this latter case, no aerosol was formed. When considering the use of an ultrasonically generated aerosol, it appears that very few works... 

The current status of exoplanet characterization shows a surprisingly diverse set of giant planets. For a subset of these, some properties have been measured or inferred using radial velocity (RV) measurements, micro-lensing, transits, and astrometry. These observations have yielded measurements of planetary mass, orbital elements, planetary radii and during the last few years, physical and chemical characteristics of the upper atmosphere of some of the transiting planets. Specifically, observations of transits, that provide a radius estimate for the planet, combined with RV information, that provide a mass estimate for the planet, have provided estimates of the density of... 

Other specific applications are presented in the book published by L.C.Klein [KLE 94] like micro lenses, composite layers (organic-inorganic) etc., as well as optical applications of massif sol-gel materials. 

Micro-lenses are widely used in electro-optical and information transmitting systems [111 - 117]. To create lenses of this type, diffusion of a monomer is performed to a forepolymeric plane support through a mask. Therewith, the refractive index gradient is formed in both radial and axial directions. The mask shape is determined by the difference of the support refractive index - a sequence of disks is used as mask, around which diffusion of the monomer proceeds. 

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