An ultrashort wavelength evanescent wave generator and its optical frequency-shifted super-resolution imaging device

Abstract

An evanescent wave generator with an ultra-short wavelength and its optical frequency-shifted super-resolution imaging device. The evanescent wave generator includes a substrate and a micro-nano structure. The device includes: a planar light source for generating non-polarized monochromatic visible light with a planar wavefront, an evanescent wave generator for generating an ultra-short wavelength evanescent wave with a full wave vector direction, an imaging sample for scattering the generated ultra-short wavelength evanescent wave into a propagating wave, a microscope objective lens and a tube lens for receiving the propagating wave, and a CCD for imaging. When the incident light perpendicularly irradiates the evanescent wave generator, the evanescent wave generated on its surface can be used as an illumination light source. After the sample is illuminated by the evanescent wave, its scattered light is received by the microscope objective lens in the far field, forming a super-resolution image with a shifted spatial frequency, further improving the imaging resolution of the system, and solving the problems of multi-directional imaging and multi-frame image post-processing in the optical frequency-shifted super-resolution imaging technology. It has the characteristics of simple structure, convenient operation and cost saving.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical imaging, and particularly relates to an ultrashort wavelength evanescent wave generator and an optical frequency-shifted super-resolution imaging device thereof. Background Art

[0002] Due to the existence of the diffraction limit, it is very difficult for the imaging resolution of an optical microscope to break through the limitation of half wavelength. For example, when illuminated with visible light with a wavelength of 400 nm, the imaging resolution limit is about 200 nm. Among many super-resolution imaging technologies, fluorescence microscopy uses the control of fluorescent molecules to achieve nanoscale imaging resolution, which has greatly promoted the development and progress in the fields of biology, medicine, etc. However, in the non-fluorescent field, the means of optical super-resolution microscopy imaging are relatively limited, and it is also very difficult to achieve an imaging resolution below 50 nm.

[0003] In non-fluorescent super-resolution imaging technologies, optical frequency-shifted imaging technology is a very promising imaging means. Its ultimate imaging resolution depends on the wavelength of the evanescent wave of near-field illumination. Therefore, as long as an evanescent wave with a short enough wavelength can be generated, its imaging resolution can be further improved. However, when using the prism total reflection technology to generate an evanescent wave, its shortest wavelength depends on the refractive index of the prism (Chinese Patent Publication No.: CN103048272A). In nature, it is very difficult to find a material with a refractive index greater than 2.5 in the visible light band. Therefore, the ultimate imaging resolution of this scheme is limited by optical materials. Another method of generating an evanescent wave is to use the evanescent wave generated on the surface of sub-wavelength micro-nano structures, such as a sub-wavelength grating structure (Chinese Patent Publication No.: CN103353675A). The wave vector direction of the evanescent wave generated on its surface is perpendicular to the grating groove direction, that is, an evanescent wave in a single direction. In addition, when performing optical frequency-shifted super-resolution imaging, its resolution has direction differences, that is, it has the characteristics of super-resolution imaging in the direction of the evanescent wave vector, while in the direction perpendicular to the evanescent wave vector, the imaging resolution is not improved. Therefore, in the existing optical frequency-shifted super-resolution imaging technology based on prism total reflection, the generated evanescent wave has a single wave vector direction, that is, only one specific direction can achieve super-resolution imaging. To achieve omnidirectional super-resolution imaging, usually the direction of the sample needs to be rotated to obtain super-resolution imaging images in each direction, and finally, image post-processing technology is used to synthesize the super-resolution images in all directions to obtain an omnidirectional super-resolution image. The cumbersome image post-processing in this scheme limits its application in dynamic high-speed imaging. Summary of the Invention

[0004] To overcome the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide an ultrashort-wavelength evanescent wave generator and its optical frequency-shifted super-resolution imaging device. The ultrashort-wavelength evanescent wave generator can generate ultrashort-wavelength evanescent waves by using a special micro-nano structure, and adopts a rotationally symmetric structure to realize evanescent waves with vector directions in all directions. When this evanescent wave generator is used in an optical frequency-shifted super-resolution imaging system, the imaging resolution of the system can be further improved, and the multi-directional imaging and image post-processing in the original technology can be simplified, greatly improving the imaging efficiency of this technology.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] An ultrashort-wavelength evanescent wave generator includes a substrate 1 and a micro-nano structure on its surface. The micro-nano structure is a sub-wavelength micro-nano structure composed of a group of equally spaced concentric rings 2.

[0007] Both the substrate 1 and the micro-nano structure are made of transparent dielectric materials.

[0008] The interval period between adjacent rings 2 in the micro-nano structure is less than the wavelength of the incident light.

[0009] The etching depth of the micro-nano structure is on the order of hundreds of nanometers.

[0010] The sub-wavelength concentric structure of the ring 2 can be etched on the surface of the substrate by any one of photolithography, ion beam etching, laser direct writing, or nanoimprinting.

[0011] An optical frequency-shifted super-resolution imaging device composed of the above-mentioned ultrashort-wavelength evanescent wave generator is arranged in sequence including:

[0012] A plane light source 3 for generating non-polarized monochromatic visible light with a plane wavefront;

[0013] An evanescent wave generator for generating ultrashort-wavelength evanescent waves with all wave vector directions;

[0014] An imaging sample 4 for scattering the generated ultrashort-wavelength evanescent waves into propagating waves;

[0015] A microscope objective 5 and a tube lens 6 for receiving the propagating waves;

[0016] A CCD 7 for imaging.

[0017] Compared with the existing technology, the present invention has the following beneficial effects:

[0018] An ultrashort wavelength evanescent wave generator, which includes a substrate 1 and a micro-nano structure. The micro-nano structure on the substrate surface consists of a sub-wavelength micro-nano structure formed by a group of equally spaced concentric rings 2, and can generate evanescent waves with shorter wavelengths and wave vectors in all directions. An optical frequency-shifted super-resolution imaging device using an ultrashort wavelength evanescent wave generator is arranged in sequence including: a planar light source 3, an evanescent wave generator, an imaging sample 4, a microscope objective 5, a tube lens 6, and a CCD 7. Applying the ultrashort wavelength evanescent wave generator to the optical frequency-shifted super-resolution imaging system can further improve the imaging resolution of the system, simplify the process of frequency-shifted super-resolution imaging, without rotating the sample for multi-directional imaging, nor the post-processing operation of multiple frames of images, and can greatly improve the imaging efficiency, with the characteristics of simple structure, convenient operation, and cost savings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. is a schematic structural diagram of an ultrashort wavelength evanescent wave generator in the present invention.

[0020] Figure 2 FIG. is a schematic diagram of the principle of generating ultrashort wavelength evanescent waves in the present invention.

[0021] Figure 3 FIG. is a schematic structural diagram of an optical frequency-shifted super-resolution imaging device using an ultrashort wavelength evanescent wave generator in the present invention. [[ID= / / 15]]

[0022] Figure 4 FIG. is the spatial spectrum that can be obtained during single imaging of the optical frequency-shifted super-resolution imaging device in the present invention.

[0023] Wherein: 1. Substrate; 2. Concentric rings; 3. Planar light source; 4. Imaging sample; 5. Microscope objective; 6. Tube lens; 7. Imaging CCD. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] In order to make the technical problems, technical solutions, and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the present invention. The detailed description is as follows.

[0025] Refer to Figure 1 , an ultrashort wavelength evanescent wave generator, includes a substrate 1 and a micro-nano structure. The micro-nano structure on the substrate 1 surface consists of a sub-wavelength micro-nano structure formed by a group of equally spaced concentric rings 2. The interval between two adjacent concentric rings 2 is its spatial period. The size of the period can be determined according to the required evanescent wave wavelength, and the wavelength of the generated evanescent wave can be shortened by reducing its spatial period. This structure has rotational symmetry along the incident light direction and is periodically distributed in any direction in space.

[0026] The substrate 1 is made of transparent quartz or glass material. The material of the micro-nano structure is the same as that of the substrate 1 and can be obtained by etching on the surface of the substrate 1 using a focused ion beam etching machine, an electron beam lithography machine, laser direct writing, or nanoimprinting.

[0027] In the prior art, using the total internal reflection of a prism to generate an evanescent wave is a common solution. The shortest wavelength of the generated evanescent wave is determined by the refractive index of the prism, and the refractive index of the prism is limited by the optical material, making it difficult to further shorten the wavelength of the evanescent wave. Therefore, the present invention takes a different approach, using a micro-nano structure to generate an evanescent wave and further shortening the wavelength of the evanescent wave by reducing the period of the micro-nano structure. When a plane wave irradiates the surface with a micro-nano structure, its wavefront will be modulated by the micro-nano structure, forming a wavefront with the morphology of the micro-nano structure. The wave vector direction of the evanescent wave is consistent with the period repetition direction of the micro-nano structure. That is, when the micro-nano structure is a one-dimensional grating, the wave vector direction of the generated evanescent wave is consistent with the grating vector. To generate evanescent wave vectors in any direction, the present invention uses a micro-nano structure composed of concentric rings 2, and its rotational symmetry ensures that it is a one-dimensional grating structure in any direction. Therefore, evanescent waves with wave vectors in any direction can be generated simultaneously. The above are the two most important characteristics of the ultra-short wavelength evanescent wave generator of the present invention.

[0028] Refer to Figure 2 , when a plane wave irradiates the surface with a micro-nano structure, its wavefront will be modulated by the micro-nano structure, forming a wavefront with the morphology of the micro-nano structure. When the period of the micro-nano structure is less than the incident wavelength, that is, when the spatial frequency of the micro-nano structure is higher than the spatial frequency of the incident light wave, the light field generated during transmission or reflection on the surface of the micro-nano structure includes a propagating wave that can propagate to a distance and an evanescent wave confined to the surface, and the wavelength of the evanescent wave depends on the period of the micro-nano structure. Therefore, by fabricating a micro-nano structure with a smaller period, a shorter wavelength of the evanescent wave can be obtained. In the present invention, the wavelength of the evanescent wave depends on the period of the micro-nano structure, rather than the refractive index of the material. Therefore, an evanescent wave with a shorter wavelength can be obtained through more precise micro-nano processing technology. For example, to obtain an evanescent wave with a wavelength of 100 nm, the period of the surface micro-nano structure needs to be 100 nm.

[0029] Refer to Figure 3, An optical frequency-shifted super-resolution imaging device based on an ultrashort-wavelength evanescent wave generator, which is arranged in sequence including: a planar light source 3, the evanescent wave generator, an imaging sample 4, a microscope objective 5, a tube lens 6, and a CCD 7. Among them, the planar light source 3 is a non-polarized monochromatic visible light with a planar wavefront; the evanescent wave generator is used to generate an ultrashort-wavelength evanescent wave with a full wave vector direction; the generated evanescent wave is used to illuminate the imaging sample 4 located above the evanescent wave generator; after being scattered by the imaging sample 4, the evanescent wave on the surface is converted into a propagating wave; the propagating wave is received by the microscope objective 5 and the tube lens 6 and imaged on the surface of the CCD 7; the CCD 7 can record the light field intensity information reaching the image plane. According to the principle of frequency-shifted super-resolution imaging, the CCD 7 image plane will receive the magnified image of the sample, and its spatial spectrum is converted from high frequency to low frequency and can be received by the microscope objective 5.

[0030] Applying the evanescent wave generator to an optical frequency-shifted super-resolution imaging system can generate an ultrashort-wavelength evanescent wave for illuminating the sample 4 to be imaged, thereby improving the imaging resolution of the imaging device; in addition, since the generated evanescent wave has wave vectors in all directions, the imaging device has the same imaging resolution for the spatial structures in all directions during imaging. Therefore, there is no need for multi-directional and multiple imaging, and no image post-processing, thus greatly improving the imaging efficiency.

[0031] Refer to Figure 4 for the imaging spatial spectrum distribution of the optical frequency-shifted super-resolution imaging device based on the ultrashort-wavelength evanescent wave generator of the present invention. The innermost circle is the spatial spectrum range that the microscope objective 5 can image when illuminated by ordinary far-field light, and this spectrum range is determined by the numerical aperture of the microscope objective 5. The ring formed by the two outer circles corresponds to the imaging spatial spectrum range of the optical frequency-shifted super-resolution imaging device of the present invention. The difference between the outer and inner radii of the ring is the spectrum range of the microscope objective 5 itself, that is, the diameter size of the innermost circle. The inner diameter of the ring depends on the wavelength of the illuminating evanescent wave. The shorter the wavelength of the evanescent wave, the larger the inner diameter of the ring, that is, the higher the spatial frequency that can be imaged. It can be seen that by using the evanescent wave generator designed in the present invention, since an evanescent wave with a shorter wavelength can be generated, a higher imaging resolution, that is, a higher spatial spectrum, can be obtained. In addition, since the evanescent wave generated by the evanescent wave generator designed in the present invention has an omnidirectional wave vector, a frequency-shifting phenomenon occurs in all directions, that is, a circular imaging spectrum can be generated, such as Figure 4 the range of the ring formed by the two solid outer circles in

[0032] An ultrashort-wavelength evanescent wave generator and its optical frequency-shifted super-resolution imaging device, which utilize micro-nano structures and can generate an ultrashort-wavelength evanescent wave with an omnidirectional wave vector. It can be applied to optical frequency-shifted super-resolution imaging technology to improve its imaging resolution, simplify the imaging process, and improve the imaging efficiency of this technology; it can also be applied to other evanescent wave application fields such as optical sensing and optical measurement.

[0033] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. An ultra-short wavelength evanescent wave generator, characterized in that, It includes a substrate (1) and the micro-nano structure on its surface, and the micro-nano structure is a sub-wavelength micro-nano structure composed of a group of equally spaced concentric rings (2); the interval period between adjacent rings (2) in the micro-nano structure is less than the wavelength of the incident light.

2. The evanescent wave generator with an ultrashort wavelength according to claim 1, characterized in that, Both the substrate (1) and the micro-nano structure are made of transparent dielectric materials.

3. A super-short wavelength evanescent wave generator according to claim 1, characterized in that The etching depth of the micro-nano structure is on the order of hundreds of nanometers.

4. A super-short wavelength evanescent wave generator according to claim 1, characterized in that The sub-wavelength concentric structure of the ring (2) can be etched on the surface of the substrate by any one of photolithography, ion beam etching, laser direct writing or nanoimprinting.

5. An optical frequency-shifted super-resolution imaging device, characterized in that, The sequential arrangement includes: A plane light source (3) for generating non-polarized monochromatic visible light with a planar wavefront; A sub-wavelength evanescent wave generator as described in any one of claims 1 to 4 for generating an evanescent wave with an ultrashort wavelength having a full wave vector direction; An imaging sample (4) for scattering the generated sub-wavelength evanescent wave into a propagating wave; A microscope objective lens (5) and a tube lens (6) for receiving the propagating wave; A CCD (7) for imaging.

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