CN103760673A - Optical system for generating approximate diffraction-free zero-order Mathieu beam - Google Patents

Abstract

The invention discloses an optical system for generating an approximately non-diffraction zero-order Mathieu beam, which includes an optical platform, on which a laser is placed, and a cylindrical lens, a short focal length lens, a long focal length lens and an axis are sequentially placed along the optical path of the laser Pyramid; wherein, the short focal length lens is placed near the focal point of the cylindrical lens, and the focal point of the short focal length lens coincides with the focal point of the long focal length lens. An approximately non-diffraction zero-order Mathieu beam can be produced by the optical system of the invention, and a simple and effective new way is provided for obtaining the zero-order Mathieu beam. The beam can be used in laser material processing, collimation measurement, optical wireless communication and other fields.

Description

An optical system that produces approximately non-diffraction zero-order Mathieu beam

technical field

The invention relates to the field of optics, in particular to an optical system that generates an approximately non-diffraction zero-order Mathieu beam. the

Background technique

The concept of the non-diffraction beam was proposed by Durnin in the United States in 1987, and it has received a lot of attention because its light intensity distribution in the propagation direction does not change with the propagation distance. The non-diffracting beam is a set of special solutions to the space free scalar wave equation. The well-known Bessel beams (Bessel beams) are a set of solutions of the wave equation in the cylindrical coordinate system. If the wave is solved in the elliptic cylindrical coordinate Equation, you can get another set of solutions, which is Mathieu beams (Mathieu beam). Like non-diffraction Bessel beams, Mathieu beams can also be used in optical measurement, optical plate making, medical imaging, nonlinear optics and optical wireless communication. the

At present, there are many methods to generate zero-order Mathieu beams: such as computer holography, annular slit lens method, laser cavity method, etc. However, the computer holography method needs to use a computer and a spatial light modulator, which is costly and complex. The laser resonator method is difficult to debug the laser cavity and the equipment cost is high. Although the annular slit lens method is simple, the aperture of the light is small and the light energy The utilization rate is low, so it is not conducive to the practical application of Mahtieu beams. the

Contents of the invention

The object of the present invention is to provide an optical system that can produce approximately non-diffraction Mathieu beam quickly, simply and efficiently. the

In order to achieve the above object, the present invention adopts the following technical solutions:

It includes an optical platform on which a laser is placed, and a cylindrical lens, a short focal length lens, a long focal length lens and an axicon are sequentially placed along the laser light path of the laser; wherein, the short focal length lens is placed near the focal point of the cylindrical lens, and the short focal length lens The focal point coincides with the focal point of the long focal length lens. the

The above-mentioned laser is a He-Ne laser. the

The above-mentioned cylindrical lens is a convex cylindrical lens. the

The short focal length lens and the long focal length lens form a collimating beam expander system, and the magnification of the collimating beam expander system can be adjusted by selecting different lens focal lengths. the

The above-mentioned axicon is a conventional refractive axicon. the

After adopting the above scheme, when the laser beam emitted by the laser is first transformed into an elliptical Gaussian beam through a cylindrical lens, then collimated and expanded by a collimator beam expander system, then focused by an axicon, and finally within a certain distance behind the axicon An approximately non-diffracting Mathieu beam is formed. The structure of the optical system is very simple, and the axicon has the advantages of high optical damage threshold and large clear aperture, so using the axicon to generate Mathieu beam is simpler and less costly than the computer holography method and resonant cavity method, and more efficient than the annular slit lens method high. Therefore, the present invention provides a simple and efficient new way to obtain approximately non-diffraction Mathieu beam. In practical applications, especially in the fields of laser material processing and biomedicine, it has special significance. the

Description of drawings

Fig. 1 is the composition schematic diagram of optical system of the present invention;

Fig. 2 is the optical path schematic diagram of optical system of the present invention;

Fig. 3 is a computer simulated light spot diagram of the optical system of the present invention. the

Fig. 4 is an experimental light spot diagram of the optical system of the present invention. the

Detailed ways

In order to further explain the technical solution of the system of the present invention, the system of the present invention will be described in detail below through specific examples. the

A kind of optical system that produces approximate non-diffraction Mathieu beam of the present invention, as shown in Figure 1, comprises optical platform 1 and supports and is positioned on the laser device 2 on optical platform 1 with fixed support 7 respectively, cylindrical lens 3, short focal length lens 4 , long focal length lens 5 and axicon 6. The laser 2 is arranged on the optical platform 1 through the fixed bracket 7, and the cylindrical lens 3, the short focal length lens 4, the long focal length lens 5, the axicon 6, and the microscope and CCD camera system 8 are placed in sequence along the laser light path of the laser 2. the

Laser 2 adopts He-Ne laser. the

The cylindrical lens 3 is a convex cylindrical lens. the

The short focal length lens 4 is near the focal point of the cylindrical lens 3 , and it is not required that the focal points of the short focal length lens 4 and the cylindrical lens 3 coincide strictly. the

The focal point of the short focal length lens 4 coincides with the focal point of the long focal length lens 5, and a collimating beam expander system is formed by the short focal length lens 4 and the long focal length lens 5, and the magnification of the collimating beam expander system can be selected by selecting different lens focal lengths as required to adjust. the

The axicon 6 adopts a traditional refracting axicon. The axicon 6 is placed behind the long focal length lens 5 along the optical path, and the distance is not limited. the

The microscope and the CCD camera system 8 are integrated, and are used to photograph the distribution of light spots at different propagation distances. the

When working, as shown in Figure 2, first the He-Ne laser 2 is turned on, and the laser beam is transformed into an elliptical Gaussian beam through a cylindrical lens 3, and then collimated and expanded by a short focal length lens 4 and a long focal length lens 5, and then in the axicon 6 A long and narrow elliptical spot is formed on , and an approximate non-diffraction Mathieu beam is formed within a certain distance behind the axicon 6. The maximum non-diffraction propagation distance can be approximately calculated by the formula Z _max ≈a[(n-1)γ], where a is the major axis radius of the elliptical light spot incident on the axicon 6 , n is the refractive index of the axicon 6 , and γ is the base angle of the axicon 6 .

As an embodiment, we select the focal length f=300mm of the convex cylindrical lens 3, the focal length f=15mm of the short focal length lens 4, the focal length f=190mm of the long focal length lens 5, the base angle γ=0.5 ° of the axicon 6, and the refractive index n =1.458, during the experiment, the optical path system was built according to the optical path in Figure 2, and a microscope and a CCD camera 8 were used to shoot at a certain distance behind the axicon 6, and the shooting results are shown in Figure 4. In order to verify the consistency between the experiment and the theory, according to the Fresnel diffraction integral theory, we choose the base angle γ=0.5° of the axicon 6, the refractive index n=1.458, and the length of the spot of the elliptical Gaussian beam incident on the axicon 6 Axle radius ω _x = 5mm, short axis radius ω _y = 1.5mm as parameters, numerical simulation calculation is carried out to obtain the light intensity distribution diagram of the zero-order approximate non-diffraction mathieu beam at different propagation distances after the axicon 6, as shown in Figure 3 Show. It is experimentally measured that the major axis radius of the elliptical spot incident on the axicon 6 is 5 mm, and the maximum non-diffraction distance calculated by using the formula Z _max ≈ a[(n-1)γ] is about 625 mm, and the maximum non-diffraction distance measured by the experiment is Diffraction distance is 610mm, the experiment basically agrees with the theory.

Therefore, this optical system provides a simple and effective method for obtaining approximately non-diffraction Mathieu beam. In practical applications, especially for laser material processing, biomedicine and other fields, it has special significance. the

The above-mentioned embodiments and drawings do not limit the product form and style of the system of the present invention, and any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the system of the present invention. the

Claims (5)

1. an optical system that produces an approximate non-diffraction zero-order Mathieu beam, is characterized in that: comprise an optical platform, a laser is placed on the optical platform, and a cylindrical lens, a short-focus lens, and a long-focus lens are placed successively along the laser light path of the laser and an axicon; where the short focal length lens is placed near the focal point of the cylindrical lens, and the focal point of the short focal length lens coincides with the focal point of the long focal length lens. 2. a kind of optical system that produces approximate non-diffraction zero-order Mathieu beam as claimed in claim 1, is characterized in that: above-mentioned laser is He-Ne laser. 3. a kind of optical system that produces approximate non-diffraction zero-order Mathieu beam as claimed in claim 1, is characterized in that: above-mentioned cylindrical lens is convex cylindrical lens. 4. a kind of optical system that produces approximate non-diffraction zero-order Mathieu beam as claimed in claim 1, is characterized in that: above-mentioned short focal length lens and above-mentioned long focal length lens form a collimating beam expanding system, this collimating beam expanding system The magnification can be adjusted by selecting different lens focal lengths. 5. A kind of optical system producing approximate non-diffraction zero-order Mathieu beam as claimed in claim 1, characterized in that: above-mentioned axicon is a traditional refracting axicon.

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