Design and experimental test of diffractive superresolution elements

Far-field super-focusing by a feedback-based wavefront shaping method

Abbe diffraction limit has always been an important subject in conventional far-field focusing and imaging systems, where the resolution of an image is usually limited to 0.5λ/NA. Recently, the studies of the optical super-oscillation lens (SOL) enable us to break the limitation in both theory and practice successfully. Here a genetic algorithm was introduced to design the SOL phase more controllably and precisely obtain much better focusing such as the focal spot with 0.105λ/NA (or 79.0% minification) in the simulation and 65.5% minification in the experimental demonstration. This technique is of great significance in advanced optical lithography or biology microscopy, because it promises non-invasive unlabelled imaging from the far field.

Design of diffractive optical elements for subdiffraction spot arrays with high light efficiency

Spot arrays beyond the diffraction limit are required in many optical applications, and the shaping of a light beam into subdiffraction spot arrays can be implemented by diffractive optical elements (DOEs). However, the low light efficiency of spot arrays is undesired in many applications. In this paper, a modified Gerchberg-Saxton algorithm is presented for generating DOEs to realize subdiffraction spot arrays with higher light efficiency. In the simulation, the spot size is reduced to approximately 70%-90% of the diffraction-limited spot, and the corresponding light efficiency is within the range of 20% to 50%. The experimental results are also shown to demonstrate the effectiveness of the proposed algorithm.

Superresolved femtosecond laser nanosurgery of cells

We report on femtosecond nanosurgery of fluorescently labeled structures in cells with a spatially superresolved laser beam. The focal spot width is reduced using phase filtering applied with a programmable phase modulator. A comprehensive statistical analysis of the resulting cuts demonstrates an achievable average resolution enhancement of 30 %.

Hybrid refractive-diffractive-gradient-index superresolving focusing device

The focusing properties and resolving power of a device consisting of a tapered gradient-index (GRIN) lens with spherical input and output faces are investigated through the use of the ABCD formalism to achieve minimization of the Airy radius for the device. Diffractive elements, such as zone plates, can, with an appropriate choice of their parameters, increase the resolution of an imaging system compared with a conventional lens. We demonstrate that by combining both elements a hybrid refractive-diffractive-GRIN device can be designed that exhibits improved superresolution characteristics.