Imaging Nanostructures with Aspherical Microlenses

Additive manu­facturing is a technique in which the final three-dimen­sional object is produced by succes­sively adding new layers of building material to those that have already been deposited. Recently, the commer­cially available 3D printers have been experien­cing rapid development and so do the 3D-printers materials, including transparent media of high optical quality. These advance­ments open up new possi­bilities in many fields of science and techno­logy including biology, medicine, meta­materials studies, robotics and micro-optics. Researchers from the Faculty of Physics, University of Warsaw, Poland, have designed tiny lenses that can easily be manu­factured by laser 3D printing technique on top of various materials, including fragile novel 2D graphene-like materials.

Scanning electron microscope image of 3D-printed aspherical microlenses. Thanks to short printing time, it is possible to produce hundreds of such microlenses on one sample. (Source: A. Bogucki et al., U. Warsaw)

The presented lenses increase the extrac­tion of light emitted from semi­conductor samples and reshape its outgoing part into an ultranarrow beam. Thanks to this property, there is no longer a need for including a bulky micro­scope objective in the experimental setup when performing optical measure­ments of single nanometer-sized light emitters like quantum dots, which up to now could not be avoided. A typical micro­scope objective used in such a study has roughly a handbreadth size, weights up to one pound and must be placed at a distance of about one-tenth of a few milli­meters from the analysed sample. These impose significant limi­tations on many types of modern experiments, like measurements in pulsed high magnetic fields, at cryogenic tempera­tures or in microwave cavities, which on the other hand can easily be lifted by the presented lenses.

High speed of the 3D-printing technique makes it very easy to produce hundreds of micro­lenses on one sample. Arranging them into regular arrays provides a convenient coor­dinate system, which accu­rately specifies the location of a chosen nano­object and allows for its multiple measure­ments in different laboratories all over the world. The invaluable oppor­tunity of coming back to the same light emitter allows for much more time-efficient research and hypothesis testing. Speci­fically, one can entirely focus on designing and performing a new experiment on the nanoobject studied before, instead of carrying out a time-consuming inves­tigation of thousands of other nano­objects before even­tually finding an analogue to the previous one.

The shape of the proposed micro­lenses can easily be adapted to the 2.5D micro­fabrication technique. The objects satisfying its prere­quisites can be produced over large-scale surfaces by pressing a patterned stamp against the layer of material they are supposed to be made of. The 2.5D fabri­cation protocol is especially attrac­tive from the viewpoint of potential applications of the micro­lenses, as can be readily up-scaled which is an important factor in possible future industrial use. (Source: CAS)

Reference: A. Bogucki et al.: Ultra-long-working-distance spectroscopy of single nanostructures with aspherical solid immersion microlenses, Light: Sci. Appl. 9, 48 (2020); DOI: 10.1038/s41377-020-0284-1

Link: Solid State Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland

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