Combined cone lens for generating long-distance diffraction-free Bessel beam

Abstract

The invention discloses a combined cone lens for generating a long-distance diffraction-free Bessel beam. The combined cone lens has a structure formed by tightly gluing two conical surfaces of a positive-axis pyramid and a negative-axis pyramid. Base angles of the conical surfaces of the positive-axis pyramid and the negative-axis pyramid are equal, and a refractive index of the positive-axis pyramid is slightly more than that of the negative-axis pyramid. In the invention, the positive-axis pyramid and the negative-axis pyramid can be manufactured by using two kinds of common optical glass having slightly-different refractive indexes and combined, and the long-distance diffraction-free Bessel beam can be obtained by a combined single element, so the problems that the conventional pyramid cone has a small cone angle and is difficult to process are solved. The combined cone lens for generating the long-distance diffraction-free Bessel beam has the advantages of easiness of element processing, simple structure, high conversion efficiency and high light damage threshold and provides a new simple and effective way to acquire the long-distance diffraction-free Bessel beam. Moreover, a diffraction-free distance of the diffraction-free Bessel beam can be adjusted by adjusting the radius of an incident beam and a difference value between the refractive indexes of the positive-axis pyramid and the negative-axis pyramid. The combined cone lens for generating the long-distance diffraction-free Bessel beam has a great practical value in the fields of high-precision collimation, large-scale linear measurement, equipment manufacturing industry and laser communication.

Description

technical field [0001] The invention relates to a combined axicon lens capable of generating long-distance non-diffraction Bessel beams, which can be used for long-distance high-precision collimation, large-scale linear measurement, space laser communication systems, and atmospheric laser communication systems. There are important applications in industry and laser communication. Background technique [0002] Compared with ordinary beams, Gaussian laser beams have the advantages of good directionality and energy concentration, and are often used as straight line benchmarks in engineering applications to measure straightness, coaxiality, flatness, parallelism, etc. However, due to the disturbance of atmospheric turbulence, it has been difficult to improve the measurement accuracy when using Gaussian beams for large-scale, long-distance collimated measurements. J. Durnin of the University of Rochester in the United States first proposed the concept of non-diffracting Bessel b...

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Problems solved by technology

[0003] At present, there are many kinds of optical components that generate Bessel beams: such as optical holograms, lens axicons, Bessel-Gaussian resonators and axicons, etc.; among them, the anti-damage threshold of optical holograms is relatively low, which limits the Bessel beam. The intensity of the Bessel beam; when the lens axicon produces a Bessel beam, the center needs to be blocked, the energy utilization rate is not high, and the quality of the Bessel beam produced is not high; the Bessel-Gauss resonator can directly generate the Bessel beam , but the obtained Bessel beam has a relatively short non-diffraction distance due to the limitation of the length of the resonator, and a long-distance non-diffraction distance is often required in long-distance collimation measurement and communication systems; due to its high damage threshold and high energy, the axicon The characteristics of utilization rate and simple structure have become the most commonly used optical elements to obtain Bessel beams, and the non-diffraction distance of non-diffraction Bessel beams can be expressed as That is, when the beam radius a is fixed, the non-diffraction distance is approximately inversely proportional to the base angle γ of the axicon surface and the difference n-1 between the axicon and the vacuum refractive index, so it is necessary to obtain a long-distance non-diffraction Bessel beam , First, you can choose an axicon with a small base angle of the cone surface, but it is very difficult to process a small base angle of the cone surface. At present, it can be processed to a minimum of 0.5° on the market, and the price is high.

Another solution is to use a material with a lower refractive index to process the axicon, but the range of refractive index of commonly used optical glass materials is not large, and materials with a smaller refractive index are rare and expensive

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