Bessel beam generator based on annular Dammann gratings

Abstract

A bessel beam generator based on an annular Dammann gratings is sequentially formed by the annular Dammam gratings sharing the same optical axis, a first lens, an amplitude type spatial filter, a second lens and a focusing objective lens. The first lens and the second lens are a confocal lens group, each annular Dammam grating is first-ordered and multi-cycle and has the two-value phase difference of pi, and the amplitude type spatial filter is located on a confocal plane of the first lens and the second lens. Diffraction-free light beams with micron dimension or submicron dimension crosswise facula and 10-102 wavelength of axial focal depth can be generated in a focusing backfield of the focusing objective lens. Switch efficiency is as high as 80%. By means of a spatial filtering mode, quality of generated bessel beams is further improved. The micron or submicron diffraction-free bessel beam can be widely used in the fields of optical micro-machining, optical storage, large focus depth imaging, laser grain capture and quickening, a self-focusing servo-system and the like.

Description

technical field [0001] The invention relates to a non-diffraction Bessel beam, in particular to a Bessel beam generator based on an annular Damman grating. It can generate Bessel beams with micron-scale focusing spot and ultra-long focal depth at the same time, and has important application value in optical processing, optical storage, optical capture, imaging with large depth of field and self-focusing servo system. Background technique [0002] It is well known that the lateral size of the focal spot of the general laser beam focusing field is inversely proportional to the numerical aperture of the focusing lens. In order to obtain a highly focused spot or micron or even submicron resolving power, a high numerical aperture objective lens must be used. On the other hand, the depth of focus of the focused light field is inversely proportional to the square of the numerical aperture of the focusing lens. That is to say, when we use the method of increasing the numerical ape...

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Problems solved by technology

However, the extension of this depth of focus can only reach 2 to 4 times the original depth of focus.

Moreover, this solution often leads to a sharp increase in the sidelobe of the transverse focal spot. For some practical applications, the influence of the sidelobe is also a key factor, such as optical storage technology

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