A mid-infrared super-resolution lensless imaging system

Abstract

The present invention relates to the technical field of imaging systems and provides a mid-infrared super-resolution lensless imaging system, comprising: a light source emission system; a first spectrometer for splitting the pulsed laser output by the light source emission system into a first pulsed laser transmitted along a first path and a second pulsed laser transmitted along a second path; a mid-infrared light generation system for converting the first pulsed laser into mid-infrared light, which then continues to transmit along the first path to illuminate the imaging object; and an optical parametric amplification imaging system, comprising a mid-infrared crystal and a camera, wherein the mid-infrared crystal is used to couple the mid-infrared illumination signal light and the second pulsed laser. The present invention does not require a mid-infrared imaging lens and can synthesize super-resolution images by utilizing the spatial and spectral correlations between multiple images. This overcomes the limitations of conventional methods in the mid-infrared band, which are limited by mid-infrared components such as lenses, resulting in insufficient resolution and sensitivity, while achieving high-resolution and large-field-of-view imaging.

Description

Technical Field

[0001] The present invention belongs to the technical field of imaging systems, and in particular relates to a mid-infrared super-resolution lensless imaging system. Background Art

[0002] Due to its unique spectral characteristics, mid-infrared imaging has important applications in a wide range of fields, including optical property diagnosis, defect detection, and thermal analysis of materials such as semiconductors and ceramics, detection and analysis of biological tissue cells and human blood glucose, and atmospheric pollution monitoring. However, compared to visible-to-near-infrared imaging, mid-infrared imaging quality is inferior. Its spatial resolution, imaging sensitivity, and signal-to-noise ratio are no longer sufficient for many target objects. This is primarily due to the lagging development of mid-infrared light sources, optoelectronic devices, detection methods, and diagnostic technologies. On the one hand, the equipment and components required for imaging are expensive, often several or even dozens of times more expensive than those in the visible-to-near-infrared region. On the other hand, the performance of the detectors, mid-infrared light sources, and imaging lenses required for imaging is insufficient. These factors have severely restricted the development of mid-infrared imaging.

[0003] In recent years, extensive research has been conducted internationally to overcome the shortcomings of mid-infrared imaging, such as inadequate spatial resolution. Near-field scanning techniques, such as optical microscopy or atomic potential microscopy, can achieve mid-infrared imaging with submicron spatial resolution. Mid-infrared photoacoustic or photothermal imaging using visible light probes can surpass the diffraction limit, even reaching submicron resolution. However, all of these techniques must be implemented using two-dimensional scanning lenses, and some require additional lock-in amplification, which is very time-consuming. Mid-infrared imaging based on non-degenerate two-photon absorption (IGA) can replace silicon-based cameras with IGA cameras due to the high two-photon absorption efficiency of IGA, enabling high-speed, real-time mid-infrared imaging. However, the use of IGA cameras comes at a certain cost in imaging sensitivity and spatial resolution. However, these traditional mid-infrared imaging systems suffer from a fixed resolution-field-of-view product, preventing them from simultaneously achieving high resolution and a large field of view. Summary of the Invention

[0004] An embodiment of the present invention provides a mid-infrared super-resolution lensless imaging system, aiming to solve at least one technical problem among the above-mentioned background technologies.

[0005] The embodiment of the present invention is implemented as follows: a mid-infrared super-resolution lensless imaging system, the system comprising:

[0006] A light source emission system for outputting pulsed laser;

[0007] A first beam splitter is provided on the light output path of the light source emitting system, and is used to split the pulsed laser output by the light source emitting system into a first pulsed laser transmitted along a first path and a second pulsed laser transmitted along a second path;

[0008] a mid-infrared light generating system, disposed on the first path, for converting the first pulsed laser into mid-infrared light, wherein the mid-infrared light continues to travel along the first path to illuminate the imaging object, thereby forming mid-infrared illumination signal light carrying object information;

[0009] An optical parametric amplification imaging system includes a mid-infrared crystal and a camera. The mid-infrared crystal is arranged at the intersection of the first path and the second path, and is used to couple the mid-infrared illumination signal light and the second pulse laser transmitted along the second path to generate visible light that can be imaged by the camera.

[0010] Preferably, the mid-infrared light generating system comprises:

[0011] a second optical splitter, wherein the first path includes a first branch and a second branch, and the second optical splitter is used to split the first path of pulsed laser light into two paths that are transmitted along the first branch and the second branch respectively;

[0012] A supercontinuum generating device, provided on the first branch, for converting the first pulse laser transmitted along the first branch into a near-infrared supercontinuum;

[0013] An optical parametric amplifier crystal is provided at the intersection of the ends of the first branch and the second branch, and is used to couple the near-infrared supercontinuum spectrum and the first pulse laser transmitted along the second branch to generate mid-infrared light.

[0014] Preferably, the supercontinuum generating device includes a lens, a Kerr medium and at least one first reflector. The first pulse laser passes through the lens and is focused on the Kerr medium to generate the near-infrared supercontinuum. The first reflector is used to guide the first pulse laser to transmit along the first branch.

[0015] Preferably, the second branch is provided with a first delay device and at least one second reflector.

[0016] Preferably, the angle of the optical parametric amplification crystal is adjustable to form tunable mid-infrared light.

[0017] Preferably, the optical parametric amplification crystal is a β-BBO crystal with a cutting angle of 21.5°, a thickness of 3 mm, and a type I phase matching mode.

[0018] Preferably, a second delay device and at least one third reflector are provided on the second path, and at least one fourth reflector is provided on the first path.

[0019] Preferably, the angle of the mid-infrared crystal is adjustable so as to be able to acquire multiple frames of low-resolution visible light images of different wavelengths in a sequence from low frequency to high frequency.

[0020] Preferably, the mid-infrared crystal is a β-BBO crystal with a cutting angle of 23.8° and a thickness of 1 mm.

[0021] Preferably, the light source emission system is an ultrashort pulse laser system with a wavelength of 800 nm.

[0022] Compared with the existing technology, a first spectrometer is set to split the pulsed laser into two paths, one of which is converted into mid-infrared light by a mid-infrared light generation system to illuminate the imaging object, forming a mid-infrared illumination signal light carrying object information. The mid-infrared illumination signal light will be coupled with the other pulsed laser through a mid-infrared crystal, and thus converted into a visible light band for detection and recording without the need for a mid-infrared imaging lens. By acquiring multiple frames of low-resolution images of visible light, super-resolution images can be synthesized by utilizing the spatial and spectral correlations between multiple images, overcoming the limitations of traditional optical imaging methods in the mid-infrared band, such as insufficient resolution and sensitivity caused by mid-infrared devices such as lenses, while achieving high-resolution and large-field-of-view imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of a mid-infrared super-resolution lensless imaging system according to one embodiment of the present invention;

[0024] Figure 2 FIG. 1 is a schematic structural diagram of a mid-infrared light generating system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, 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 are not intended to limit the present invention.

[0026] Example 1

[0027] See also Figure 1 , which shows a mid-infrared super-resolution lensless imaging system according to a first embodiment of the present invention, comprising:

[0028] A light source emission system 10, configured to output pulsed laser light;

[0029] The first beam splitter 20 is provided on the light output path of the light source emitting system 10 and is used to split the pulsed laser output by the light source emitting system 10 into a first pulsed laser transmitted along the first path 100 and a second pulsed laser transmitted along the second path 200;

[0030] The mid-infrared light generating system 30 is provided on the first path 100 and is used to convert the first pulsed laser into mid-infrared light. The mid-infrared light is then transmitted along the first path 100 to illuminate the imaging object 300, forming a mid-infrared illumination signal light that carries object information.

[0031] The optical parametric amplification imaging system 40 includes a mid-infrared crystal 41 and a camera 42. The mid-infrared crystal 41 is arranged at the intersection of the first path 100 and the second path 200, and is used to couple the mid-infrared illumination signal light and the second pulse laser transmitted along the second path 200 to generate visible light that can be imaged by the camera 42, thereby completing the mid-infrared imaging of the imaging object 300.

[0032] That is, in this embodiment, the pulsed laser output by the light source emission system 10 is split into two paths by setting a first spectrometer 20. One path is converted into mid-infrared light by the mid-infrared light generation system 30 and then illuminates the imaging object 300, forming a mid-infrared illumination signal light carrying object information. The mid-infrared illumination signal light will be coupled with the other pulsed laser through the mid-infrared crystal 41, and thus converted into the visible light band for detection and recording.

[0033] Specifically, the second path 200 is provided with a second delay 201 and at least one third reflector 202. The second delay 201 is used to adjust the time synchronization of the optical parametric amplification, so that the light transmitted through the first path 100 and the second path 200 can simultaneously reach the mid-infrared crystal 41 for coupling. The second delay 201 can specifically be a precision displacement platform. After the second pulsed laser is transmitted along the second path 200, it forms delayed visible pump light. The third reflector 202 is used to guide the light along the set second path 200. The first path 100 is provided with at least one fourth reflector 101, which is used to guide the light along the set first path 100.

[0034] For specific implementation, please refer to Figure 2 , which is a schematic diagram of an optional specific implementation of the mid-infrared light generating system 30, the mid-infrared light generating system 30 may specifically include:

[0035] The second optical splitter 31, the first path 100 includes a first branch 10a and a second branch 10b, and the second optical splitter 31 is used to split the first pulse laser into two paths that are transmitted along the first branch 10a and the second branch 10b;

[0036] The supercontinuum generation device 32 is provided on the first branch 10a and is used to convert the first pulse laser transmitted along the first branch 10a into a near-infrared supercontinuum;

[0037] The optical parametric amplifier crystal 33 is arranged at the intersection of the first branch 10a and the second branch 10b, and is used to couple the near-infrared supercontinuum spectrum and the first pulse laser transmitted along the second branch 10b to generate mid-infrared light.

[0038] Specifically, the supercontinuum generation device 32 includes a lens 321, a Kerr medium 322, and at least one first reflector 323. After passing through the lens 321, the first pulsed laser is focused onto the Kerr medium 322, generating a near-infrared supercontinuum. The first reflector 323 is used to guide the first pulsed laser along the first branch 10a. The second branch 10b is provided with a first delay 102 and at least one second reflector 103. The first delay 102 is used to synchronize the optical parametric amplification (OPA) process, ensuring that the light transmitted from the first branch 10a and the second branch 10b simultaneously reaches the OPA crystal 33 for coupling. The first delay 102 can also be a precision displacement platform. After the first pulsed laser is transmitted along the first branch 10a, it forms delayed pump light. The angle of the OPA crystal 33 is adjustable to generate tunable mid-infrared light. This tunable mid-infrared light can be used as illumination and detection light for an object by tuning the angle of the OPA crystal 33.

[0039] In a specific implementation, the light source emission system 10 can be an ultrashort pulse laser system with a wavelength of 800nm, outputting 800nm ​​femtosecond pulsed laser light as the incident light. The first beam splitter 20 is specifically a dichroic mirror, and the second beam splitter 31 is specifically a beam splitter, which can be an 800nm ​​broadband beam splitter. The Kerr medium 322 is specifically a sapphire optical window. After passing through lens 321, the incident laser is focused on the sapphire optical window to generate a near-infrared supercontinuum from 900nm to 1.50μm. The optical parametric amplifier crystal 33 is a β-BBO crystal with a 21.5° cutting angle, a thickness of 3mm, and a type I phase-matched mode. The near-infrared supercontinuum is coupled with the 800nm ​​femtosecond pulsed laser light through the optical parametric amplifier crystal 33 to produce mid-infrared light. When the near-infrared supercontinuum spectrum is tuned from 1.09μm to 1.33μm, the generated mid-infrared light is correspondingly tuned from 3.0μm to 2.0μm and is used to illuminate mid-infrared objects.

[0040] It should be noted that when using optical parametric amplification technology to achieve lensless imaging, phase matching of the pump light and the signal light is involved. In optical parametric amplification technology, phase matching of the pump light and the signal light refers to maintaining a constant phase between the two so that their phase matching vectors match. By controlling the propagation of light under phase matching conditions, clear imaging of objects is achieved. Specifically, by utilizing the characteristics of parametric nonlinear crystals, when the pump light and the signal light pass through the nonlinear crystal, their phase matching conditions will lead to a nonlinear polarization effect. This effect will generate a new frequency light signal, called idler light. In lensless imaging, this idler light is the signal light used for imaging and reaches the imaging plane.

[0041] As a preferred implementation in this embodiment, in the imaging system, it is assumed that the signal with object information is E s (r,φ,ω s ), then the idler light E i (r,φ,ω i ) along the propagation distance z through the mid-infrared crystal can be described as:

[0042]

[0043]

[0044] Where, the subscript "s", "i" or "p" indicates the frequency of the light s 、ω i Or ω p The corresponding signal light, idler light or pump light with object information, and the superscript "'" indicates the complex conjugate. n and d eff are the refractive index and the effective nonlinear coefficient, respectively. c and β are used for the speed of light in vacuum and the non-collinearity angle between the signal and pump beams, Δ k is the phase mismatch. Therefore, the value of the idler light after passing through the mid-infrared crystal is:

[0045]

[0046] The subscript "S0" represents the input signal of the crystal, and "i1" represents the output idler light. i is the gain of the mid-infrared crystal. For a mid-infrared crystal with a thickness of l, under the paraxial approximation and slowly varying amplitude approximation, G i It can be expressed as:

[0047]

[0048] The parameters κ and r are

[0049] k 2 =k s k i ′=ωs ω s d eff 2 I P / (2ε0n s n i n p c 3 )

[0050] r=Δk / (2k)

[0051] where Ip is the pump intensity. Therefore, the idler image recorded in the post-imaging plane of the 4f imaging system can be described as:

[0052]

[0053] in is the normalized pump intensity. Therefore, after passing through the mid-infrared parametric amplifier, the object information carried by the signal light is transferred to the idler light, and the signal is amplified due to the gain of the parametric crystal. Therefore, this imaging system can amplify weak signals and can be used for lensless 321 imaging of weak illumination light.

[0054] As a preferred embodiment of this invention, the mid-infrared parametric crystal uses a 1mm-thick β-BBO crystal with a 23.8° cut angle. The wavelength of the idler light detected and recorded is primarily determined by the energy conservation requirements between it and the visible light pump and mid-infrared illumination probe light, corresponding to a range of 462-500nm. Therefore, the 2-3µm mid-infrared illumination probe light is converted into the visible light band for detection and recording. By adjusting the angle of the mid-infrared parametric crystal, an appropriate phase mismatch is introduced into the zero-frequency component information of the target object, enabling the mid-infrared parametric amplifier to achieve low-bandwidth amplification of the target object's specific spatial frequency components, thereby obtaining a visible light low-resolution image of that specific spatial frequency component. The angle of the mid-infrared parametric crystal is then further adjusted to change the specific spatial frequency component amplified by the mid-infrared parametric amplifier, generating multiple frames of visible light low-resolution images at different wavelengths, ranging from low frequency to high frequency. By integrating the correlation and complementary information between these multiple low-resolution frames, as well as the characteristics of the different wavelength spectra, an image synthesis algorithm is used to combine these multiple low-resolution frames into a single super-resolution image. Super-resolution imaging systems can fully utilize the advantages of each wavelength to obtain richer and more accurate image information.

[0055] For lensless imaging, it follows the principle of diffraction imaging and assumes that the detection light is a plane wave E1

[0056] E1=A*e (i*(kz-wt))

[0057] After reaching the object surface, it is multiplied by the object's complex amplitude coefficient (assuming it is q(x,y)) to obtain the light after passing through the object

[0058] w(x,y)=A*q(x,y)*e (i*(kz-wt))

[0059] Then the image is diffracted to the image plane and the light complex amplitude distribution function on the image plane is obtained.

[0060]

[0061] Where z is the distance from the object plane to the image plane, and λ is the wavelength of the light source. Therefore, the image quality of the image plane is related to the wavelength of the light source and the distance from the object plane to the image plane.

[0062] The resolution of lensless imaging is limited by the distance L between the object and the image detector, the image frame length d of the image detector, and the wavelength λ of the illumination light. Assuming that the resolution is represented by R, then

[0063]

[0064] Therefore, the frame size length d of the imaging CCD detector and the distance L between the object and the image plane detector satisfy the resolution limit formula and the maximum spatial resolution is taken.

[0065] In summary, the mid-infrared super-resolution lensless imaging system in this embodiment splits the pulsed laser into two paths by setting a first spectrometer. One path is converted into mid-infrared light by the mid-infrared light generation system and then illuminates the imaging object 300, forming a mid-infrared illumination signal light carrying object information. The mid-infrared illumination signal light will be coupled with the other pulsed laser through a mid-infrared crystal, and thus converted into a visible light band for detection and recording without the need for a mid-infrared imaging lens. By acquiring multiple frames of low-resolution images of visible light, the spatial and spectral correlations between the multiple images can be used to synthesize a super-resolution image, thereby overcoming the limitations of traditional optical imaging methods in the mid-infrared band, such as insufficient resolution and sensitivity caused by mid-infrared devices such as lenses, while achieving high-resolution and large-field-of-view imaging.

[0066] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A mid-infrared super-resolution lensless imaging system, characterized in that: For realizing lens-less imaging, that is, without any optical lens between the object and the camera, the system comprises: A light source emission system for outputting pulsed laser; A first beam splitter is provided on the light output path of the light source emitting system, and is used to split the pulsed laser output by the light source emitting system into a first pulsed laser transmitted along a first path and a second pulsed laser transmitted along a second path; a mid-infrared light generating system, disposed on the first path, for converting the first pulsed laser into mid-infrared light, wherein the mid-infrared light continues to travel along the first path to illuminate the imaging object, thereby forming mid-infrared illumination signal light carrying object information; An optical parametric amplification imaging system, comprising a mid-infrared crystal and a camera, wherein the mid-infrared crystal is disposed at the intersection of the first path and the second path, and is used to couple the mid-infrared illumination signal light with the second pulsed laser transmitted along the second path to generate visible light capable of being imaged by the camera; The mid-infrared light generation system comprises: a second optical splitter, wherein the first path includes a first branch and a second branch, and the second optical splitter is used to split the first path of pulsed laser light into two paths that are transmitted along the first branch and the second branch respectively; A supercontinuum generating device, provided on the first branch, for converting the first pulse laser transmitted along the first branch into a near-infrared supercontinuum; an optical parametric amplifier crystal, disposed at the intersection of the first branch and the second branch, for coupling the near-infrared supercontinuum with the first pulse laser transmitted along the second branch to generate mid-infrared light; In which, the angle of the optical parametric amplifier crystal is adjustable to form tunable mid-infrared light, and the angle of the mid-infrared crystal is adjustable to obtain multiple frames of low-resolution visible light images of different wavelengths in a low-frequency to high-frequency sequence. Specifically, by adjusting the angle of the mid-infrared crystal, a phase mismatch is introduced into the zero-frequency component information of the target object, so that the mid-infrared crystal can achieve low-bandwidth amplification of the specific spatial frequency component of the target object, that is, obtain a low-resolution visible light image of the specific spatial frequency component, and then adjust the angle of the mid-infrared crystal to change the specific spatial frequency component amplified by the mid-infrared crystal, and obtain multiple frames of low-resolution visible light images of different wavelengths in a low-frequency to high-frequency sequence.

2. The mid-infrared super-resolution lensless imaging system according to claim 1, characterized in that: The supercontinuum spectrum generating device includes a lens, a Kerr medium and at least one first reflector. The first pulse laser passes through the lens and is focused on the Kerr medium to generate the near-infrared band supercontinuum spectrum.

3. The mid-infrared super-resolution lensless imaging system according to claim 1, characterized in that: The second branch is provided with a first delay device and at least one second reflecting mirror.

4. The mid-infrared super-resolution lensless imaging system according to claim 1, characterized in that: A second retarder and at least one third reflector are provided on the second path, and at least one fourth reflector is provided on the first path.

5. The mid-infrared super-resolution lensless imaging system according to claim 1, characterized in that: The light source emission system is specifically an ultrashort pulse laser system.

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