CN110275232A - A Zoom Imaging Method Based on Greek Ladder Photon Sieve - Google Patents

Abstract

A zoom imaging method based on the Greek ladder photon sieve, the main device of the zoom imaging is the Greek ladder photon sieve, and the Greek ladder photon sieve is a diffractive optical element capable of realizing three-dimensional array imaging. The invention can realize discretized zooming of a fixed system from x-rays to terahertz wave bands under a coherent light field, can realize off-axis imaging by designing a photon sieve, and increases the degree of freedom of optical path design. Such devices will likely have applications in zoom systems, intraocular lenses, x-ray microscopy, terahertz imaging, and optical trapping.

Description

A Zoom Imaging Method Based on Greek Ladder Photon Sieve

technical field

The invention relates to diffraction imaging of coherent light field, in particular to a method capable of realizing zoom imaging of coherent light field.

Background technique

Zoom plays an important role in many optical systems such as cameras, mobile phones, endoscope systems, microscopic imaging, cell sorting, optical capture and manipulation of particles, ophthalmic optics and target aiming, but traditional zoom systems are mostly used in the visible light band , in the x-ray and extreme ultraviolet bands, due to the strong absorption of materials, the refraction system cannot achieve focused imaging. As a diffractive optical element, the Fresnel zone plate can realize the focused imaging of X-rays and extreme ultraviolet bands. On the basis of zone plates, L.Kipp [L.Kipp, M. Skibowski, R. Johnson, R. Berndt, R. Adelung, S. Harm, and R. Seemann, Sharper images by focusing soft X-rays in 2001 with photon sieves, Nature414, 184-188(2001)] firstly proposed the concept of photon sieve, photon sieve can achieve higher resolution than zone plate, but both zone plate and photon sieve have only one main focus. In 2015, we introduced the ancient Greek ladder sequence into the nanostructure, resulting in a three-dimensional array diffraction imaging device capable of achieving equal intensity distribution[Zhang J.Three-dimensional array diffraction-limited foci from Greek ladders to generalized Fibonacci sequences[J] .Opt.Express, 2015,23(23):30308-30317].

We apply this device to the optical zoom technology, which can realize the discretized zoom under the fixed optical path system from soft x-ray to terahertz band under coherent conditions. This new type of zoom imaging technology can be applied to zoom systems and imaging in coherent light source x-ray and extreme ultraviolet bands, such as biological cell imaging, x-ray microscopy and array imaging. In addition, zoom technology also has important application value in research fields such as terahertz imaging and intraocular lens.

Contents of the invention

The technical problem to be solved by the present invention is to provide a zoom imaging method based on the Greek ladder photon sieve to realize zoom imaging in the coherent light field from x-rays to terahertz bands. The zoom imaging method can realize the discretized zoom of a fixed system without moving the imaging device. In addition, off-axis imaging can also be realized, which improves the freedom of optical path design.

Technical scheme of the present invention is as follows:

A zoom imaging method based on a Greek ladder photon sieve, which is characterized in that the zoom optical path is composed of a Greek ladder photon sieve, and zooming can be realized without changing the parameters of the optical system; the Greek ladder photon sieve can produce a three-dimensional array Focal points, the number of array focal points generated is represented by m×n×p, where m×n represents the number of images on the same plane, and p represents the number of image planes. The sequence of Greek ladders satisfies the following recurrence relation:

The zoom optical path includes a He-Ne laser, a spatial pinhole filter, a lens, an imaging object, a Greek ladder photon sieve, a photocoupler detector CCD and a data processing terminal;

Further, the He-Ne laser generates 632.8nm laser light, which is placed at the forefront of the zoom optical path;

Further, the spatial pinhole filter is placed behind the He-Ne laser to generate a point light source and improve the beam quality;

Further, the lens cooperates with the spatial pinhole filter to generate uniformly distributed parallel light;

Further, the imaging object is used as the input object of the zoom optical path, illuminated by the parallel light generated by the lens and the spatial pinhole filter, and the imaging result can be obtained at certain discrete object distances;

Further, the Greek ladder photon sieve is placed at a distance behind the imaging object for zoom imaging of the zoom optical path;

Further, the photocoupler detector CCD is placed behind the Greek ladder photon sieve, and the position of the photocoupler detector CCD is adjusted to be placed on the image plane for detecting the image generated by the zoom optical path to obtain imaging with different focal lengths;

Further, the data processing terminal is used for recording and displaying the detection results of the photocoupler detector CCD;

Compared with prior art, the beneficial effect of the present invention is:

The invention can realize zooming without changing the parameters of the optical system, and the zoom device is an amplitude diffraction element, which can realize focusing and imaging from soft x-rays to terahertz bands under coherent conditions. In addition, this type of zoom device can produce three-dimensional array focusing and imaging with equal intensity distribution, and realize off-axis imaging. In this way, detection or processing elements can be added to the optical path without affecting the subsequent optical path imaging, which improves the degree of freedom of design. It can be applied to zoom systems and imaging in coherent light source x-ray and extreme ultraviolet bands.

Description of drawings

Fig. 1 is the principle schematic diagram of zoom imaging optical path of the present invention;

Fig. 2 is the structural representation of 1 * 1 * 2 device of Greek ladder photon sieve of the present invention;

Fig. 3 is the 1 × 1 × 2 zoom input diagram of the Greek ladder photon sieve of the present invention, wherein (a) object distance is -290.8mm, (b) object distance is -868.8mm, (c) object distance is -231.7mm, ( d) The object distance is -493.0mm, (e) the object distance is -188.2mm, (f) the object distance is -330.6;

Fig. 4 is the zoom imaging result figure of Greek ladder photon sieve 1 * 1 * 2 of the present invention;

Fig. 5 is a 2×2×2 zoom input image of the Greek ladder photon sieve of the present invention, wherein (a) the object distance is -373.8mm, and (b) the object distance is -804.4mm;

Fig. 6 is the zoom imaging result figure of Greek ladder photon sieve 2 * 2 * 2 of the present invention;

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

Example 1

As shown in Figure 1 and Figure 2, the present invention provides a zoom imaging method based on the Greek ladder photon sieve, which is realized by the diffraction lens-Greek ladder photon sieve, and can produce three-dimensional images with equal intensity distribution under monochromatic parallel wave illumination. The array focal point realizes discrete zooming from x-ray to terahertz band under fixed system.

The Greek ladder photon sieve can produce a diffraction-limited three-dimensional array focus m×n×p, where m×n represents the number of images on the same plane, and p represents the number of image planes. Taking the design of a 1×1×2 Greek ladder photon sieve as an example, the design process is described in detail, and the design results are shown in Figure 2. Regarding the Greek Ladder, it can be described as:

1 3 7 19 41...

1 2 5 12 29... (2)

The nth number of the first row of ladders is defined as G _n , the nth number of the second row of ladders is defined as F _n , and the ratio of G _n to F _n is asymptotically Carry out encoding mapping on the Greek ladder, encode the sequence of the Greek ladder into a sequence, project the sequence under the square root curve, and the corresponding 0 and 1 are opaque and transparent rings respectively, to obtain the Greek ladder bars, and enclose the bars into rings to get the Greek The ladder annulus, the transparent area on the annulus is replaced with a small hole to obtain the Greek ladder photon sieve, and the Greek ladder photon sieve with bifocals on the axis is constructed. The optical structure is shown in Figure 1. The structure has 99 bright rings and 140 a dark ring. The incident wavelength of the laser is 632.8nm, the two focal points of the on-axis bifocals appear at 128.014mm and 181.093mm respectively, and the expected value of the optical focal length ratio is equal to Close to the limit ratio of the sequence. The ratio of the diameter of the photon sieve hole to the width of the corresponding zone plate ring is called the hole-ring ratio. The hole-ring ratio is related to the light intensity of the two focal planes. In order to obtain the equal light intensity of the two focal planes, the overlap of the sieve holes should be considered In this case, the hole-to-ring ratio is set to 1.16 to obtain the focal point of equal intensity distribution. The full width at half maximum (FWHM) corresponding to the light field distribution on the two focal planes is 8.74um and 12.36um respectively, and the ratio of the full width of the focal spot is 12.36/8.74=1.4142, which is close to the expected value of the optical focal length ratio. In summary, we have obtained a diffraction-limited three-dimensional array imaging device that can achieve equal intensity and different resolution.

The schematic diagram of the zoom optical path is shown in Figure 1. The zoom optical path includes a He-Ne laser 1, a spatial pinhole filter, a lens, an input object 2 and an input object 3, a Greek ladder photon sieve 4, a photocoupler detector CCD5 and data Process Terminal 6. Use USAF1951 resolution boards of different sizes as the input objects of the zoom optical path;

Further, the He-Ne laser 1 generates 632.8nm laser light, which is placed at the forefront of the zoom optical path, as the light source of the zoom optical path, through a spatial pinhole filter with a pinhole diameter of 10 μm and a lens with a focal length of 175 mm to generate parallel light , that is, the point light source is placed on the front focal plane of the lens, then the parallel light with uniform distribution is generated behind the lens;

Further, the input object of the zoom imaging optical path is the U.S. Air Force resolution plate USAF1951 of different sizes, illuminated with parallel light generated by a lens and a spatial pinhole filter, and obtain corresponding zoom imaging results at different object distances;

Further, the Greek ladder photon sieve 4 is placed at a distance behind the U.S. Air Force resolution USAF1951 (2) and (3), imaging on the same image plane without changing the parameters of the optical system, and realizing the discretization of the fixed system zoom. Taking 1×1×2 Greek ladder photon sieve as an example, the focal lengths are 128.014mm and 181.093mm respectively, and f ₁₁ and f ₁₂ represent the corresponding short focus and long focus respectively. When the object distance is 290.8mm and 868.8mm, the zoom results of the same size can be obtained when the image distance is 228.6mm through short focus and telephoto focus imaging respectively. When the imaging receiving device of the zoom system is placed at other image distances, it can also zoom corresponding to objects at two object distances. The goal is to make full use of the receiving size of the imaging receiver, that is, when the size of the zoom image plane is equal to 2.694mm, the discretized object distance zoom is realized for the corresponding imaging object. As shown in Table 1 below, it is zooming at different object distances;

Table 1: Zoom imaging at different object distances

Further, the resolution corresponding to the photocoupler detector CCD5 is 5.5 μm×5.5 μm, and the pixel points are 3296×2472. Place the photocoupler detector CCD5 behind the Greek ladder photon sieve, adjust the position of the photocoupler detector CCD5 and place it on the image plane to detect the image generated by the zoom imaging optical path, and the data processing terminal 6 displays the final imaging result. The corresponding input objects are shown in Figure 3. When the light spot detection coupler CCD5 is placed at 228.6mm, the zoom of the input object 3(a) and the input object 3(b) with the object distance of -290.8mm and -868.8mm can be realized. Figure 3(c) and 3(d) zoom to obtain an image with an image distance of 286mm, and Figure 3(e) and 3(f) zoom to obtain an image with an image distance of 400mm. The zoom imaging results are shown in Figure 4. Thus, at different object distances, different focal lengths can be zoomed, and the imaging law conforms to the Gaussian formula of traditional lens imaging:

Among them, S _i represents different object distances, fi _represents different focal lengths, and S' represents image distance.

Example 2

In the Greek ladder photon sieve m×n×p, m, n, and p can all be greater than 1, and the Greek ladder photon sieve can be used for off-axis aggregation and imaging. Repeating Example 1, the off-axis zooming result can be obtained. Taking the 0-1 level of the U.S. Air Force resolution board USAF1951 as the input, Figure 5(a) and Figure 5(b) contain the number and position of each plane that can be imaged off-axis, and the input can be for each any of the planes. When the object distance is -373.8mm and -804.4mm respectively, the imaging result of the same size is obtained at the image distance of 453mm. The imaging result is shown in Figure 6, and the off-axis zoom imaging of input objects with different object distances is realized.

Coaxial or off-axis zoom imaging under different object distances in the same optical path is realized by using the Greek ladder photon sieve. At the same time, the zoom range can be increased by designing the number of focal points of the zoom imaging element. The off-axis zoom imaging optical path can not affect the subsequent optical path after optical detection or optical processing components are added to the optical path, which improves the degree of freedom in design.

The content not described in the present invention is common knowledge of those skilled in the art.

The specific implementation examples described above have further described in detail the purpose, technical solutions and beneficial effects of the present invention. It should be understood that what is described above is only a specific implementation example of the present invention, and is not intended to limit the present invention. Any modification, equivalent replacement or improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (7)

1. A zoom imaging method based on Greek ladder photon sieve, the method comprises the following steps: (1) design can produce the Greek ladder photon sieve device of the diffraction-limited three-dimensional array of equal intensity distribution; (2) build zoom imaging optical path; 2. the zoom imaging method based on Greek ladder photon sieve according to claim 1, is characterized in that: the design of described Greek ladder photon sieve comprises the steps: Greek ladder sequence is expressed as Map the sequence code to the annulus of the Fresnel zone plate, encode it into aperiodic transparent and opaque annulus according to the sequence, and then replace the transparent annulus with a large number of randomly distributed sieve holes to obtain a device capable of producing three-dimensional array imaging ; 3. the zoom imaging method based on the Greek ladder photon sieve according to claim 1, is characterized in that: the zoom imaging optical route He-Ne laser (1) is used as illumination light source, places space successively along this He-Ne laser output light direction A pinhole filter, a lens, an input object (2), an input object (3), a Greek ladder photon sieve (4) and a photoelectric coupling detector (5) are constructed into a zoom imaging optical path, and the photoelectric coupling detector (5 ) is connected with the data processing terminal (6); 4. The zoom imaging method based on the Greek ladder photon sieve according to claim 1 or 2, characterized in that: the He-Ne laser produces 632.8nm laser light, which is placed at the forefront of the zoom optical path, and the spatial pinhole The filter and the lens work together to produce parallel light with uniform beams; The input object is the U.S. Air Force resolution plate USAF1951 of different sizes located at different object distances, and the input object is illuminated by parallel light generated by a lens and a spatial pinhole filter; The Greek ladder photon sieve is placed at a certain distance behind the U.S. Air Force resolution board USAF1951 for zoom imaging of the zoom optical path; The photoelectric coupling detector CCD is placed behind the Greek ladder photon sieve, and the position of the photoelectric coupling detector CCD is adjusted to be placed on the image plane for detecting and collecting images generated by the zoom optical path; The data processing terminal is connected to a photocoupler detector CCD for recording and displaying imaging results. 5. The zoom imaging method based on the Greek ladder photon sieve according to claim 1 or 2, characterized in that, the Greek ladder photon sieve is a diffractive optical element, which can realize the transformation from x-ray to solar radiation under the relevant light field. Focusing and imaging in the Hertzian band. 6. According to claim 1 or 2, the three-dimensional array focal point can be produced based on the Greek ladder photon sieve, and the number of the array focal point produced is represented by m * n * p, wherein m * n represents the number of imaging on the same plane, p Indicates the number of image planes; it is characterized in that the Greek ladder photon sieve m, n, and p can all be greater than or equal to 2 to realize off-axis zoom imaging. 7. The zoom imaging method based on the Greek ladder photon sieve according to claim 1 or 2, wherein the zoom imaging optical path is applied to zoom systems, ophthalmology, particle capture, biological cell imaging, x-ray microscopy , terahertz imaging and intraocular lens research.