Rangefinder, photoacoustic probe and photoacoustic imaging apparatus for photoacoustic imaging

Abstract

The application discloses a grating sensor for photoacoustic imaging, a photoacoustic probe and a photoacoustic imaging device, and the grating structure is processed by adopting a three-dimensional photoetching process, the design of the external solid structure and the internal periodic structure is combined, the external solid structure and the multiple cavity regions form a significant refractive index difference, and therefore the resonance effect of the grating is enhanced. In the ultrasonic detection process, the periodic resonance effect caused by the refractive index difference of the grating structure can efficiently convert the ultrasonic wave pressure into a light signal and further convert the light signal into an electric signal for photoacoustic imaging. Compared with the conventional ultrasonic sensor, the application provides higher sensitivity and a wider bandwidth, can realize clearer and more accurate imaging effect in high-resolution imaging, and effectively avoids the phenomenon that the ultrasonic sensor in the prior art has poor imaging effect in high-resolution imaging. In addition, the two-photon processing and ultraviolet light curing are adopted to form a significant refractive index difference, and therefore the acoustic spectrum detection capability of photoacoustic endoscopic imaging is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photoacoustic imaging, in particular to a grating sensor for photoacoustic imaging, a photoacoustic probe and a photoacoustic imaging device. BACKGROUND

[0002] Photoacoustic imaging (PAI) as a new biomedical imaging technology combines the high resolution of optical imaging and the high penetration of ultrasound imaging in deep biological tissues, and has developed rapidly in recent years. The basic principle of photoacoustic imaging is that when biological tissue is irradiated by pulsed laser, the absorber in the tissue absorbs the laser energy and expands instantaneously, generating an ultrasonic signal. By receiving these signals with an ultrasonic sensor and combining signal processing and image reconstruction techniques, an image of the light absorption distribution in the tissue can be generated. This makes photoacoustic imaging have broad application prospects in disease detection, tissue analysis and molecular imaging. In photoacoustic imaging, the performance of the ultrasonic detector plays a key role in imaging quality.

[0003] Traditional ultrasonic transducers are mainly based on piezoelectric materials and work by converting pressure signals into electrical signals through the piezoelectric effect. However, with the development of technology, piezoelectric micro-machined ultrasonic transducers (PMUT) as a new type of transducer based on piezoelectric materials have been widely studied. PMUT is prepared using micro-nano manufacturing technology and has the characteristics of high compatibility with integrated circuit technology, small size, light weight, low power consumption, high integration and flexible design. Its basic structure includes a vibrating membrane and upper and lower electrodes. Although PMUT has significant advantages, due to its small size and narrow working bandwidth, it is difficult to obtain multi-scale information, which limits its application performance in high-resolution imaging.

[0004] In order to solve the shortcomings of PMUT in bandwidth and sensitivity, attention has gradually been shifted to ultrasonic sensors based on optical technology. For example, phase-shifted fiber Bragg grating (FBG) is a high-resolution fiber optic sensor that has great potential in static and dynamic strain measurement due to its narrow-band spectral characteristics and excellent dynamic strain detection capabilities. However, there are certain limitations in the practical application of phase-shifted FBG, such as the need for high-performance, narrow-linewidth tunable lasers, which significantly increases the system cost; at the same time, its performance is easily affected by environmental factors (such as temperature, humidity), resulting in a decrease in sensitivity and stability.

[0005] To overcome these limitations, further exploration of ultrasonic sensors based on waveguide technology has been made. Previous studies have shown that ultrasonic detectors based on polymer Bragg grating (BGW) can be prepared by electron beam lithography and DUV lithography. However, such BGW structures still have the problem of low resolution. In view of this problem, Goraus et al. designed a polymer SR-BG waveguide through 3D laser lithography technology, and improved the system resolution by using high-order reflection modes. The main feature of the SR-BG structure is that the width of the waveguide changes periodically along the propagation direction, and by arranging the SR-BG pattern on the high column waveguide, fiber direct coupling is realized. This design shows good construction prospects in on-chip optical devices and tunable sensor applications. However, such polymer gratings usually rely on low refractive index difference periodic modulation, and long gratings are needed to achieve high sensitivity, which makes it difficult to miniaturize and detect with high sensitivity.

[0006] In summary, the ultrasonic sensor in the related art has the technical problem of poor imaging effect when applied to high-resolution imaging due to the reasons of narrow working bandwidth, low refractive index difference, low resolution, and low sensitivity. SUMMARY

[0007] The main purpose of the present application is to provide a grating sensor for photoacoustic imaging, a photoacoustic probe and a photoacoustic imaging device, which aims to at least solve the technical problem of poor imaging effect of the ultrasonic sensor in the related art when applied to high-resolution imaging.

[0008] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows:

[0009] In a first aspect of the present application, a grating sensor for photoacoustic imaging is provided, which includes at least one grating structure processed by a three-dimensional lithography process; the grating structure includes an external solid structure and an internal periodic structure, the internal periodic structure is provided with a plurality of cavity regions arranged linearly according to a predetermined period, and the external solid structure and the plurality of cavity regions form a refractive index difference; wherein when the grating sensor is used for ultrasonic detection, the internal periodic structure and the external solid structure generate a resonance effect based on the refractive index difference, so as to convert the light signal caused by the ultrasonic wave pressure into an electrical signal for photoacoustic imaging.

[0010] On the basis of the first aspect, the three-dimensional lithography process comprises a two-photon polymerization process and a curing process; the internal periodic structure is formed by irradiating a target irradiation area of liquid photosensitive resin material with femtosecond laser pulses used in the two-photon polymerization process, so that the target irradiation area initiates a molecular polymerization reaction; the plurality of cavity regions in the internal periodic structure are formed based on non-target irradiation areas in the photosensitive resin material; and the external solid structure is formed by curing the remaining liquid photosensitive resin material in the plurality of cavity regions and the surface layer of the internal periodic structure through the curing process; wherein the two-photon polymerization process is used to form the internal periodic structure with a first refractive index, and the curing process is used to form the external solid structure with a second refractive index, and the refractive index difference is the difference between the first refractive index and the second refractive index.

[0011] On the basis of the first aspect, the curing process comprises an ultraviolet light curing process; the non-target irradiation area is provided with a solid filler formed by irradiating the remaining liquid photosensitive resin material with ultraviolet light used in the ultraviolet light curing process to trigger the remaining liquid photosensitive resin material to cure; and the external solid structure is formed by curing the remaining liquid photosensitive resin material in the plurality of cavity regions and the surface layer of the internal periodic structure with ultraviolet light used in the ultraviolet light curing process.

[0012] On the basis of the first aspect, the photosensitive resin material comprises photoresist or polydimethylsiloxane.

[0013] On the basis of the first aspect, the surface of the external solid structure forms a plurality of solid regions arranged linearly, the plurality of solid regions and the plurality of cavity regions are arranged in a staggered manner in the length direction of the grating structure, and one solid region and one cavity region in an adjacent relationship form one resonance region; wherein the refractive index difference formed by the solid region and the cavity region in each resonance region is equal.

[0014] On the basis of the first aspect, the grating parameters of the grating structure comprise: a waveguide width of 1.4-1.6 μm, a corrugation depth of 140-150 nm, a period size of 500-600 nm, and a period number of 90-110; wherein the grating parameters are determined by simulating the simulated grating structure in the FDTD simulation process.

[0015] On the basis of the first aspect, in the FDTD simulation process, the grating parameters match the resonance frequency of excitation light of a target wavelength, and satisfy narrow resonance at the resonance frequency; wherein the target wavelength is 1500-1600 nm.

[0016] On the basis of the first aspect, when the internal periodic structure is processed by the two-photon polymerization process, the femtosecond laser pulses are focused by an oil objective lens to be focused on the photosensitive resin material on the glass sheet, and irradiated from top to bottom according to a preset processing path in a galvanometer processing mode; wherein the processing path is determined by a three-dimensional model file, the three-dimensional model file is determined based on the simulated grating structure, and the three-dimensional model file includes geometric features of the external solid structure and the internal periodic structure.

[0017] In a second aspect of the present application, a photoacoustic probe is provided, comprising a probe main body and a grating sensor for photoacoustic imaging as described in the first aspect, and the grating sensor is integrated in the probe main body.

[0018] In a third aspect of the present application, a photoacoustic imaging device is provided, comprising a photoacoustic imaging processor and a photoacoustic probe as described in the second aspect, and an output end of the photoacoustic probe is electrically connected to the photoacoustic imaging processor.

[0019] The grating sensor for photoacoustic imaging, the photoacoustic probe and the photoacoustic imaging device of the present application process the grating structure by using a three-dimensional lithography process, and combine the design of the external solid structure and the internal periodic structure, so that the external solid structure and the plurality of cavity regions form a significant refractive index difference, thereby enhancing the resonance effect of the grating. In the process of ultrasonic detection, the periodic resonance effect caused by the refractive index difference of the grating structure can efficiently convert the ultrasonic wave pressure into a light signal and further convert it into an electrical signal for photoacoustic imaging. Compared with the conventional ultrasonic sensor, the present application provides higher sensitivity and wider bandwidth, and can realize clearer and more accurate imaging effect in high-resolution imaging, effectively avoiding the phenomenon that the ultrasonic sensor in the prior art has poor imaging effect in high-resolution imaging. In addition, two large refractive index differences are formed by using two-photon processing and ultraviolet curing to realize miniaturization and high-sensitivity detection, thereby improving the acoustic spectrum detection capability of photoacoustic endoscopic imaging. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.

[0021] Figure 1 A three-dimensional schematic diagram of the grating sensor provided by the embodiments of the present application;

[0022] Figure 2 An internal structure schematic diagram of the grating sensor provided by the embodiments of the present application;

[0023] Figure 3 A perspective view of a grating sensor in an embodiment of the present application.

[0024] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0025] It should be understood that the specific embodiments described herein merely exemplify the application and do not limit the application.

[0026] It should be noted that related terms such as "first", "second", etc. can be used to describe various components, but these terms do not limit the components. These terms are only used to distinguish one component from another component. For example, without departing from the scope of the present application, a first component can be referred to as a second component, and a second component can be similarly referred to as a first component. The term "and / or" refers to a combination of any one or more of the related terms and the described terms.

[0027] Please refer to Figure 1 , Figure 2 and Figure 3 The embodiment of the present application provides a grating sensor for photoacoustic imaging, which comprises at least one grating structure 1 processed by a three-dimensional photoetching process.

[0028] Specifically, the grating structure 1 comprises an external solid structure 10 and an internal periodic structure 20 in an inner-outer two-layer structure, the internal periodic structure 20 is provided with a plurality of cavity regions 201 arranged linearly according to a preset period, and the external solid structure 10 and the plurality of cavity regions 201 form a refractive index difference.

[0029] The numerical value of the refractive index difference is generally greater than or equal to 0.01, which can significantly enhance the resonance effect. When the grating sensor is used for ultrasonic detection, the internal periodic structure 20 and the external solid structure 10 generate a periodic resonance effect based on the refractive index difference, so as to convert the light signal caused by the ultrasonic wave pressure into an electrical signal for photoacoustic imaging.

[0030] Therefore, the grating sensor for photoacoustic imaging has the grating structure processed by the three-dimensional photoetching process, combines the design of the external solid structure and the internal periodic structure, and makes the external solid structure form a significant refractive index difference with the plurality of cavity regions, so that the resonance effect of the grating is enhanced. In the ultrasonic detection process, the periodic resonance effect caused by the refractive index difference of the grating structure can efficiently convert the ultrasonic wave pressure into a light signal and further convert the light signal into an electrical signal for photoacoustic imaging. Compared with the conventional ultrasonic sensor, the grating sensor for photoacoustic imaging provided by the application has higher sensitivity and wider bandwidth, can realize clearer and more accurate imaging effect in high-resolution imaging, and effectively avoids the phenomenon that the ultrasonic sensor in the prior art has poor imaging effect in high-resolution imaging.

[0031] In the optional implementation of the embodiment, the three-dimensional photoetching process includes a two-photon polymerization process and a curing process, and the internal periodic structure and the external solid structure are respectively formed by the two-photon polymerization process and the curing process.

[0032] In the first stage of processing, the two-photon polymerization process is used to form the internal periodic structure. Specifically, the internal periodic structure can be formed by irradiating a target irradiation area of a liquid photosensitive resin material (for example, photoresist) with a femtosecond laser pulse used in the two-photon polymerization process, so that the target irradiation area initiates a molecular polymerization reaction, and the plurality of cavity regions in the internal periodic structure are formed based on a non-target irradiation area of the photosensitive resin material.

[0033] In the second stage of processing, the curing process is used to form the external solid structure. Specifically, after the internal periodic structure is processed by the two-photon polymerization process, the plurality of cavity regions (for example, cuboid cavities) are still filled with uncured liquid photoresist after the structure processing is completed, and the internal periodic structure is in a coexistence state of solid and liquid. The internal periodic structure in the coexistence state is processed by the curing process, that is, the remaining liquid photosensitive resin material in the plurality of cavity regions and the surface layer of the internal periodic structure are cured (in this way, the refractive index of the internal periodic region of the structure changes, and a high refractive index difference is formed between the outside and the inside), and finally the external solid structure is formed on the basis of the internal periodic structure.

[0034] It can be seen that, by combining the two-photon polymerization process, the curing process (ultraviolet curing process) and the photoresist, the internal periodic structure forms a first refractive index (1.52-1.53), and the external solid structure forms a second refractive index (1.53-1.54), that is, the ultraviolet curing (external) refractive index can reach 1.53-1.54, the two-photon polymerization reaches 1.52-1.53, and the refractive index difference (the difference between the first refractive index and the second refractive index) reaches 0.01 or more. Further, the high refractive index difference formed can effectively enhance the optical resonance effect and improve the conversion efficiency of the photoacoustic signal, thereby achieving higher sensitivity and clearer imaging effect in photoacoustic imaging.

[0035] In an optional embodiment of the present embodiment, the curing process includes an ultraviolet curing process. In the second phase of processing, the remaining liquid photo-sensitive resin material in the plurality of cavity regions is irradiated by ultraviolet light of the ultraviolet curing process to trigger the remaining liquid photo-sensitive resin material (photoresist) to undergo a curing reaction for curing, and the surface layer of the internal periodic structure is irradiated by ultraviolet light to undergo a curing reaction for curing, forming the external solid structure.

[0036] Specifically, by using the ultraviolet curing process, the curing reaction of the remaining liquid photo-sensitive resin material can be quickly triggered to ensure the integrity and uniformity of the external solid structure, and the surface layer of the internal periodic structure is strengthened. The refractive index of the internal periodic region of the structure changes, and a high refractive index difference is formed between the outside and the inside. This innovative structure realizes the organic combination of external and internal periodic refractive index modulation through two-photon polymerization technology and ultraviolet curing, further improves the stability, sensitivity and photoacoustic signal conversion efficiency of the grating sensor, and meets the needs of high-resolution photoacoustic imaging.

[0037] It should be noted that the photo-sensitive resin material includes photoresist or polydimethylsiloxane, or a material with a small Young's modulus.

[0038] In an optional embodiment of the present embodiment, the surface of the external solid structure 10 forms a plurality of solid regions 101 arranged in a linear arrangement, and the plurality of solid regions 101 and the plurality of cavity regions 201 are arranged in an interlaced arrangement in the length direction of the grating structure 1, and one solid region 101 and one corresponding cavity region 201 form a resonance region in an adjacent relationship.

[0039] Specifically, each resonant region is composed of a solid region 101 and its corresponding cavity region 201, and the optical resonance effect is generated by the refractive index difference between the two. Moreover, the refractive index difference between the solid region and the cavity region in each resonant region is equal, indicating that the optical properties and resonant frequency of each resonant region are uniform, thereby ensuring the consistency and efficiency of the response of the photoacoustic sensor, effectively enhancing the optical resonance effect of the grating structure, improving the sensitivity and conversion efficiency of the sensor to ultrasonic pressure changes, and achieving higher resolution and more accurate photoacoustic imaging.

[0040] In an optional embodiment of the present embodiment, the grating parameters of the grating structure with the optimal sensitivity include: a waveguide width of 1.4-1.6 μm, a corrugation depth of 140-150 nm, a period size of 500-600 nm, and a period number of 90-110; wherein the grating parameters are determined by simulating the simulated grating structure in the FDTD (Finite-Difference Time-Domain) simulation process.

[0041] In the FDTD simulation process, the MODE Solutions module of the Lumerical software is used to simulate and optimize the selected grating parameters multiple times, i.e., to continuously optimize the waveguide width, the internal waveguide depth, and the grating period and grating length, until the parameter combination resonates to the resonant frequency of the target wavelength (e.g., 1500-1600 nm) excitation light, while also satisfying narrow resonance at the resonant frequency, so as to obtain a high Q value (Quality Factor) to ensure that the grating structure can achieve high sensitivity and wide bandwidth performance in photoacoustic imaging.

[0042] It should be noted that according to the simulation results, the Q value can reach the order of 105. The structure is successfully processed on the chip using a two-photon three-dimensional lithography machine, and experimental tests show that the on-chip single-two-photon grating for photoacoustic endoscopic imaging has high sensitivity and small volume, which is conducive to the next step of biological tissue imaging, and further serves as a photoacoustic endoscope.

[0043] In an optional implementation of the present embodiment, after the simulation process is completed, a three-dimensional model is established based on the simulated grating structure determined in the simulation process by using a three-dimensional tool such as SolidWorks, and a corresponding three-dimensional model file (which can be an STP format file) is exported. In this way, after the three-dimensional model file is obtained, the processing method of the structure to be processed can be programmed, such as whether to process the frame, the processing direction, and the like. That is, the internal periodic structure and the external solid structure can be processed based on the three-dimensional model file using a two-photon polymerization process: first, drop the photoresist on one side of the glass substrate, and after the glass sheet is fixed, focus the femtosecond laser pulses of the laser device (wavelength 780 nm, maximum power 50 mW, repetition frequency 80 MHz) through the oil objective lens (magnification can be 63 times) to focus on the photosensitive resin material (photoresist, IP-Dip, Nanoscribe GmbH) on the glass sheet, and then determine the processing steps through the software of Nanoscribe, and use the galvanometer processing method to irradiate according to the preset processing path from top to bottom, at a scanning speed of 100000c and a laser energy setting of 40, and finally solidify by ultraviolet light, control the distance between the ultraviolet light and the sample and the irradiation time to achieve different intensities of solidification (generally, the distance is 1-2 cm, and the irradiation time is about 1 min), so that a complete single-two-photon grating is processed, that is, the internal and external two-layer structures are completed.

[0044] It should be noted that the photoresist is a high refractive index material. Since the photoresist can only be polymerized when the intensity of the focused voxel is higher than the threshold intensity, the writing speed and laser power are optimized to obtain high resolution. The faster the speed, the shorter the processing time. The laser energy needs to be reasonably controlled. If it is too large, the structure will be broken down due to overexposure, and the naked eye will see a kind of burning feeling. If it is too small, the structure may not be visible on the sheet after development.

[0045] In an optional implementation of the present embodiment, the processed grating structure can be detected by ultrasonic detection. The sample can be placed in a protective sleeve in advance to protect the fiber core from breaking, and then the protective sleeve is placed in a funnel filled with pure water, and an ultrasonic transducer is placed at the bottom of the funnel in full contact with the water, so as to generate ultrasonic sound penetration, and two optical fibers are connected to the two ends of the sample, and the transmitted optical signal is detected by a PD and recorded by an oscilloscope. If the signal does not meet the expected requirement, the following two aspects can be adjusted: 1. change the structure parameters and reprocess; 2. adjust the processing method, such as changing the laser energy and scanning speed, so as to detect the ability of the probe to detect ultrasonic signals. In addition, after verifying the detection ability of the grating, it needs to be encapsulated with a low refractive index ultraviolet curing glue such as NOA1315 for subsequent use in photoacoustic endoscopic imaging.

[0046] The embodiment of the present application also provides a photoacoustic probe, comprising a probe main body and the grating sensor for photoacoustic imaging in the above embodiment, and the grating sensor is integrated in the probe main body.

[0047] The embodiment of the present application also provides a photoacoustic imaging device, comprising a photoacoustic imaging processor and the photoacoustic probe in the above embodiment, and an output end of the photoacoustic probe is electrically connected with the photoacoustic imaging processor.

[0048] The grating sensor for photoacoustic imaging, the photoacoustic probe and the photoacoustic imaging device of the present application can enhance the resonance effect of the grating by adopting a three-dimensional photoetching process to process the grating structure, combining the design of the external solid structure and the internal periodic structure, so that the external solid structure and the plurality of cavity regions form a significant refractive index difference, thereby enhancing the resonance effect of the grating. In the process of ultrasonic detection, the periodic resonance effect caused by the refractive index difference of the grating structure can efficiently convert the ultrasonic wave pressure into a light signal and further convert it into an electrical signal for photoacoustic imaging. Compared with the conventional ultrasonic sensor, the present application provides higher sensitivity and wider bandwidth, and can realize clearer and more accurate imaging effect in high-resolution imaging, effectively avoiding the poor imaging effect of the ultrasonic sensor in high-resolution imaging in the prior art. In addition, two large refractive index differences are formed by adopting two-photon processing and ultraviolet curing to realize miniaturization, high-sensitivity detection, thereby improving the acoustic spectrum detection capability of photoacoustic endoscopic imaging.

[0049] In addition, the present application directly processes the waveguide on the chip to realize a single-two-photon grating structure, which not only has smaller volume, is convenient to process, is cheaper, has good repeatability, has a very high Q value, can replace the conventional piezoelectric ultrasonic transducer, and has 1-2 orders of magnitude improvement in sensitivity compared with the conventional piezoelectric ultrasonic transducer. It is also 1-2 orders of magnitude higher than the Q value of some optical resonators. In addition, the grating structure of the present application is controllable, can be designed according to different needs, and the structure processed has excellent performance in theory.

[0050] In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0051] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent flow transformation made by using the content of the specification and drawings of the present application, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A grating sensor for photoacoustic imaging, characterized by, The grating sensor comprises at least one grating structure processed by a three-dimensional photoetching process; The grating structure comprises an external solid structure and an internal periodic structure, the internal periodic structure is provided with a plurality of cavity regions arranged linearly according to a preset period, and the external solid structure and the plurality of cavity regions form a refractive index difference; In the ultrasonic detection of the grating sensor, the internal periodic structure and the external solid structure generate a resonance effect based on the refractive index difference to convert an optical signal caused by ultrasonic wave pressure into an electrical signal for photoacoustic imaging.

2. The optical raster sensor for photoacoustic imaging of claim 1, wherein, The three-dimensional photoetching process comprises a two-photon polymerization process and a curing process; The internal periodic structure is formed by irradiating a target irradiation region of a liquid photosensitive resin material with femtosecond laser pulses used in the two-photon polymerization process to cause a molecular polymerization reaction in the target irradiation region; The plurality of cavity regions in the internal periodic structure are formed based on non-target irradiation regions in the photosensitive resin material; The external solid structure is formed by curing the remaining liquid photosensitive resin material in the plurality of cavity regions and a surface layer of the internal periodic structure through the curing process; The two-photon polymerization process is used to form a first refractive index of the internal periodic structure, the curing process is used to form a second refractive index of the external solid structure, and the refractive index difference is a difference between the first refractive index and the second refractive index.

3. The optical raster sensor for photoacoustic imaging of claim 2, wherein, The curing process comprises an ultraviolet light curing process; The non-target irradiation region is provided with a solid filler formed by irradiating the remaining liquid photosensitive resin material with ultraviolet light used in the ultraviolet light curing process to trigger the remaining liquid photosensitive resin material to cure; The external solid structure is formed by curing the remaining liquid photosensitive resin material in the plurality of cavity regions and a surface layer of the internal periodic structure with ultraviolet light used in the ultraviolet light curing process.

4. The optical raster sensor for photoacoustic imaging of claim 3, wherein, The photosensitive resin material comprises photoresist or polydimethylsiloxane.

5. The optical raster sensor for photoacoustic imaging of claim 3, wherein, A surface of the external solid structure forms a plurality of solid regions arranged linearly, the plurality of solid regions and the plurality of cavity regions are arranged alternately in a length direction of the grating structure, and one of the solid regions and one of the cavity regions adjacent to each other form one resonance region; The refractive index difference formed by the solid region and the cavity region in each resonance region is equal.

6. The optical raster sensor for photoacoustic imaging of claim 2, wherein, Grating parameters of the grating structure include a waveguide width of 1.4-1.6 μm, a corrugation depth of 140-150 nm, a period size of 500-600 nm, and a period number of 90-110; The grating parameters are determined by simulating a simulated grating structure in an FDTD simulation process.

7. The optical-raster sensor for photoacoustic imaging of claim 6, wherein, In the FDTD simulation process, the grating parameters match a resonance frequency of excitation light of a target wavelength and satisfy a narrow resonance at the resonance frequency; The target wavelength is 1500-1600 nm.

8. The optical raster sensor for photoacoustic imaging of claim 6, wherein, When the internal periodic structure is processed by the two-photon polymerization process, the femtosecond laser pulse is focused by an oil immersion objective to irradiate the photosensitive resin material on the glass sheet from top to bottom according to a preset processing path in a galvanometer processing mode; The processing path is determined by a three-dimensional model file, the three-dimensional model file is determined based on the simulated grating structure, and the three-dimensional model file includes geometric characteristics of the external solid structure and the internal periodic structure.

9. A photoacoustic probe, characterized by The grating sensor for photoacoustic imaging as claimed in any one of claims 1 to 8 is integrated in the probe body.

10. A photoacoustic imaging apparatus, characterized by, The photoacoustic probe as claimed in claim 9 is electrically connected to the photoacoustic imaging processor.

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