CN112147730A - Single-focus spiral zone plate - Google Patents

Single-focus spiral zone plate Download PDF

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CN112147730A
CN112147730A CN202011196740.9A CN202011196740A CN112147730A CN 112147730 A CN112147730 A CN 112147730A CN 202011196740 A CN202011196740 A CN 202011196740A CN 112147730 A CN112147730 A CN 112147730A
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zone plate
spiral
spiral zone
focus
elements
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CN112147730B (en
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臧华平
刘晓旻
王萌光
苗壮磊
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Zhengzhou University
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    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1876—Diffractive Fresnel lenses; Zone plates; Kinoforms

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Abstract

The invention discloses a single-focus spiral zone plate, which comprises a transparent substrate, wherein a light-tight metal layer is arranged on the transparent substrate and consists of randomly distributed spiral elements; the randomly distributed helical elements are obtained by the following method: dividing each period of the conventional spiral zone plate into N parts, each part being a spiral element, the spiral elements being arranged on the inner and outer diameters r of the conventional spiral zone plateiAnd roAnd a large number of elements are randomly distributed along the radial direction to form a single-focus spiral zone plate which tends to have a cosine transmittance function and can generate optical vortex with only one-order diffraction focus. The invention overcomes the defect that the common spiral zone plate has multi-stage focus, only has one-stage diffraction focus, and can improve the imaging contrast when being used for the edge enhanced imaging of the spiral zone plate.

Description

Single-focus spiral zone plate
Technical Field
The invention belongs to the technical field of diffraction optics, and particularly relates to a single-focus spiral zone plate.
Background
Optical vortices were first noted and studied since the 30 s of the 19 th century. Then Airy finds a peculiar helical spot in its focal plane after the beam has passed through the lens. The vortex beam has zero central light intensity on the axis, and is therefore called a hollow beam. Moreover, the physical properties of the vortex light beams are unique, the light intensity of the light beams is distributed annularly in the process of propagation, the wavefront structure is spiral, and the expression of the light field contains phase factors:
Figure BDA0002754244400000011
where p is the topological charge of the vortex beam. The dark nucleus in the central area has a small size, and the particles are controlled without heating damage effect. In addition, optical vortices also carry orbital angular momentum during forward propagation. Optical vortices have been widely studied and applied in optical manipulation, optical information transmission, and biomedicine.
The spiral zone plate is a simple and effective way to generate optical vortices, which combines the focusing properties of fresnel zone plates with radial hilbert transform, and can generate optical vortices at the focal point. At the same time, it also, like fresnel zone plates, inevitably leads to the presence of higher order diffraction. In 2017, Shexiqing et al proposed to use a two-parameter modulation window function to modulate the transmittance function (Single-focus helical zone panels, Optics Letters, Yonghao Liang, Enliang Wang, Yilei Hua, ChangqingXie and Tianchun Ye) of a spiral zone plate, thereby playing a role in suppressing the high-order diffraction of the spiral zone plate. However, the method of modulating the transmittance function of the spiral zone plate by the window function inevitably reduces the light transmission amount of the spiral zone plate, and reduces the diffraction efficiency of the spiral zone plate.
In the present invention, we propose to use a large number of spiral elements randomly distributed along the radial direction to form a single focus spiral zone plate that tends to have a cosine transmittance function. The single-focus spiral zone plate has the capability of inhibiting the high-order diffraction of the spiral zone plate under the condition of keeping the diffraction efficiency basically unchanged.
Disclosure of Invention
The invention aims to provide a single-focus spiral zone plate, which aims to generate optical vortex with only a first-order focus with high diffraction efficiency.
In order to achieve the purpose, the invention adopts the technical scheme that:
a single-focus spiral zone plate comprises a transparent substrate, wherein a light-tight metal layer is arranged on the transparent substrate and consists of randomly distributed spiral elements; randomly distributed helical elements pass throughThe method comprises the following steps: dividing each period of the conventional spiral zone plate into N parts, each part being a spiral element, the spiral elements being arranged on the inner and outer diameters r of the conventional spiral zone plateiAnd roA large number of elements are randomly distributed along the radial direction to form a single-focus spiral zone plate which tends to have a cosine transmittance function and can generate an optical vortex with only one-order diffraction focus;
the transmittance function of the conventional spiral zone plate is
Figure BDA0002754244400000021
The outer diameter of the wave band is as follows:
Figure BDA0002754244400000022
the inner diameter is:
Figure BDA0002754244400000023
wherein, the external diameter and the internal diameter of printing opacity wave band are respectively:
Figure BDA0002754244400000024
the width of the transmission band can be expressed as
Figure BDA0002754244400000025
The period of the spiral zone plate is M, wherein: p is topological charge, p is 1,2,3, …, and λ is the wavelength of incident light wave; f is the focal length of the spiral zone plate;
Figure BDA0002754244400000026
is the azimuth angle.
The transmission function of a monofocal spiral zone plate is expressed as:
Figure BDA0002754244400000027
wherein n represents the nth period of the monofocal spiral zone plate,
Figure BDA0002754244400000028
Figure BDA0002754244400000029
n is the number of primitives per cycle,
Figure BDA00027542444000000210
wherein rand represents a random number between 0 and 1.
The single-focus spiral zone plate is suitable for various electromagnetic wave bands of microwave, infrared light, visible light, ultraviolet light and X rays.
The light-tight metal layer is one of metal tantalum, chromium, gold, aluminum, copper, nickel and niobium.
The transparent substrate is one of silicon dioxide, silicon carbide, silicon nitride and polyimide.
The zone plate of the present invention may be transferred to a counter zone plate or may be replicated to a replica zone plate.
The single focus spiral zone plate of the invention has the following advantages:
1) the design and the manufacture are simple, and the corresponding design can be completed only by providing parameters such as focal length, wavelength and the like;
2) the processing difficulty is equivalent to that of a common spiral zone plate, and the method is suitable for processing technologies such as electron beam etching and the like;
3) compared with the common spiral zone plate, the single-focus spiral zone plate can inhibit high-order diffraction;
4) is easy to be practically popularized and used, in particular to the wave band from vacuum ultraviolet to soft X-ray.
Drawings
Fig. 1 is a schematic structural diagram of a monofocal spiral zone plate with a topological charge p-1 in an (x, y) coordinate system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a local primitive distribution of a single focus spiral zone plate according to an embodiment of the present invention;
FIG. 3 is a comparison graph of axial intensity distributions of a monofocal spiral zone plate and a conventional spiral zone plate under the same parameters according to an embodiment of the present invention;
FIG. 4 is a comparison graph of focal position spots of a single-focus spiral zone plate and a common spiral zone plate under the same parameters according to an embodiment of the present invention;
fig. 5 is a schematic flow chart illustrating a manufacturing process of a single-focus spiral zone plate according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The application of the principles of the present invention will be further described with reference to the accompanying drawings and specific embodiments.
Please refer to fig. 1-5:
the embodiment discloses a single-focus spiral zone plate which comprises a transparent substrate, wherein a light-tight metal layer is arranged on the transparent substrate and consists of randomly distributed spiral elements; the randomly distributed helical elements are obtained by the following method: dividing each period of the conventional spiral zone plate into N parts, each part being a spiral element, the spiral elements being arranged on the inner and outer diameters r of the conventional spiral zone plateiAnd roA large number of elements are randomly distributed along the radial direction to form a single-focus spiral zone plate which tends to have a cosine transmittance function and can generate an optical vortex with only one-order diffraction focus;
the transmittance function of a conventional spiral zone plate is
Figure BDA0002754244400000031
The outer diameter of the wave band is as follows:
Figure BDA0002754244400000032
the inner diameter is:
Figure BDA0002754244400000033
wherein, the external diameter and the internal diameter of printing opacity wave band are respectively:
Figure BDA0002754244400000034
the width of the transmission band can be expressed as
Figure BDA0002754244400000035
The period of the spiral zone plate is M, wherein: p is topological charge, p is 1,2,3, …, and λ is the wavelength of incident light wave; f is the focal length of the spiral zone plate;
Figure BDA0002754244400000036
is the azimuth angle.
Fig. 1 is a schematic structural view of a 50-cycle, p-1, monofocal spiral fractal zone plate of the present invention, in which the white filled spiral structure is a light-transmitting portion, and the black area is a light-opaque portion; FIG. 2 is a diagram of the distribution of local primitives according to the present invention.
In this embodiment, the opaque metal layer is gold metal, the transparent substrate is silicon carbide, in other embodiments, the opaque metal layer may also be one of tantalum, chromium, aluminum, copper, nickel, and niobium, and the transparent substrate may also be one of silicon dioxide, silicon carbide, silicon nitride, and polyimide.
The zone plate of the present invention may be transferred to a counter zone plate or may be replicated to a replica zone plate.
The transmission function of a monofocal spiral zone plate is expressed as:
Figure BDA0002754244400000041
where N is the number of primitives per cycle,
Figure BDA0002754244400000042
wherein rand represents a random number between 0 and 1. The total period is taken as M being 50, N being 100, and the topological charge p being 1.
To better illustrate the effect of the invention in suppressing higher order diffraction, a computer simulation of the diffraction characteristics of the invention is performed below, while comparing the results with a spiral zone plate of the same parameters; the parameters of the single focus spiral zone plate are: p is 1, M is 50, λ is 632.8nm, f is 200 mm; the parameters of a common spiral zone plate are also: p is 1, M is 50, λ is 632.8nm, and f is 200 mm.
Fig. 3(a) and (b) show the axial intensity distribution diagrams of the monofocal spiral zone plate and the ordinary spiral zone plate of the present invention under the above parameters, respectively, and fig. 4 shows the intensity distribution comparison diagram of the vortices generated by the monofocal spiral zone plate and the ordinary spiral zone plate of the present invention under the above parameters at the corresponding peaks along the optical axis, where data1 is the axial light intensity distribution of the monofocal spiral zone plate and data2 is the axial light intensity distribution of the ordinary spiral zone plate, and it can be clearly seen that the monofocal spiral zone plate suppresses the high order diffraction well.
In this embodiment, only the example of the diffraction characteristics of the visible light band is given, and the single-focus spiral zone plate of the present invention is still applicable to other bands, such as X-ray, ultraviolet light, and infrared light, and only the corresponding parameters need to be modified in this example.
The above detailed description of the structure and focusing characteristics of the monofocal spiral zone plate of the present invention, and for better understanding of the aspects and effects of the present invention, the following detailed description of the manufacturing method of the specific embodiment of the present invention:
as shown in fig. 5, the specific steps are as follows:
a) determining the periodicity M, the topological charge p, the target wavelength lambda, the required focal length f and the like of the zone plate according to the actual application requirements, and generating an L-Edit format graphic file of the zone plate by using a computer:
plating a layer of opaque material (gold film) on a transparent substrate, then coating a layer of photoresist, and opening holes on the transparent substrate to form a hollow self-supporting gold film;
b) b, utilizing numerical control focusing electron beam lithography equipment, controlling by an LEDIT file generated in the step a, carrying out electron beam exposure on the film generated in the step b by using the zone plate layout structure shown in the figure 1, and then developing by using a developing solution and a fixing solution to obtain a zone plate photoresist graph;
c) carrying out chemical corrosion on the gold film in the development area for a proper time by using an etching solution to form a through hole in the development area;
d) removing the photoresist to obtain a single-stage spiral wave zone plate suitable for the required wavelength; fig. 5 is a process flow chart corresponding to steps a, b, c, and d.
The spiral ring belt is convenient to design and manufacture, and only a generation formula of the spiral ring belt needs to be designed according to requirements; the processing difficulty is equivalent to that of a common spiral zone plate, and the method is suitable for processing technologies such as electron beam etching and the like; compared with a spiral zone plate with the same numerical aperture, a series of strip-shaped hollow structures are generated on the optical axis, and the axial focal depth is effectively lengthened; is easy to be practically popularized and applied, in particular to the wave band from vacuum ultraviolet to soft X-ray.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (5)

1. A single focus spiral zone plate is characterized by comprising a transparent substrate, wherein a light-tight metal layer is arranged on the transparent substrate and consists of randomly distributed spiral elements; the randomly distributed helical elements are obtained by the following method: dividing each period of the conventional spiral zone plate into N parts, each part being a spiral element, the spiral elements being arranged on the inner and outer diameters r of the conventional spiral zone plateiAnd roA large number of elements are randomly distributed along the radial direction to form a single-focus spiral zone plate which tends to have a cosine transmittance function and can generate an optical vortex with only one-order diffraction focus;
the transmittance function of the conventional spiral zone plate is
Figure FDA0002754244390000011
The outer diameter of the wave band is as follows:
Figure FDA0002754244390000012
the inner diameter is:
Figure FDA0002754244390000013
wherein the light is transmittedThe outer and inner diameters of the wave bands are respectively:
Figure FDA0002754244390000014
the width of the transmission band can be expressed as
Figure FDA0002754244390000015
The period of the spiral zone plate is M, wherein: p is topological charge, p is 1,2,3, …, and λ is the wavelength of incident light wave; f is the focal length of the spiral zone plate;
Figure FDA0002754244390000016
is the azimuth angle.
2. A monofocal spiral zone plate according to claim 1, wherein the transmission function of the monofocal spiral zone plate is expressed as:
Figure FDA0002754244390000017
wherein n represents the nth period of the monofocal spiral zone plate,
Figure FDA0002754244390000018
Figure FDA0002754244390000019
n is the number of primitives per cycle,
Figure FDA00027542443900000110
wherein rand represents a random number between 0 and 1.
3. A single focus spiral zone plate according to claim 1, wherein said single focus spiral zone plate is adapted for use in microwave, infrared, visible, ultraviolet, X-ray electromagnetic bands.
4. A monofocal helical zone plate according to claim 1, wherein the opaque metal layer is one of the metals tantalum, chromium, gold, aluminum, copper, nickel and niobium.
5. A single focal spiral zone plate as claimed in claim 1, wherein said transparent substrate is one of silicon dioxide, silicon carbide, silicon nitride and polyimide.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114217454A (en) * 2022-02-22 2022-03-22 华中科技大学 Design and implementation method of spatial frequency spectrum modulation device based on diffraction optical element
CN116931146A (en) * 2023-07-28 2023-10-24 长江大学 Method for constructing spiral cone-shaped zone plate and spiral cone-shaped zone plate manufactured by same

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114217454A (en) * 2022-02-22 2022-03-22 华中科技大学 Design and implementation method of spatial frequency spectrum modulation device based on diffraction optical element
CN114217454B (en) * 2022-02-22 2022-06-10 华中科技大学 Design and implementation method of spatial frequency spectrum modulation device based on diffraction optical element
CN116931146A (en) * 2023-07-28 2023-10-24 长江大学 Method for constructing spiral cone-shaped zone plate and spiral cone-shaped zone plate manufactured by same
CN116931146B (en) * 2023-07-28 2024-01-26 长江大学 Method for constructing spiral cone-shaped zone plate and spiral cone-shaped zone plate manufactured by using same

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