Optical fiber nanoindenter and testing method

Abstract

The present invention relates to the field of biomaterial technology, and in particular to an optical fiber nanoindenter and a testing method. The optical fiber nanoindenter comprises: a laser light source, an optical fiber micro-force probe and an optical fiber grating demodulator optically connected in sequence; the laser light source is used to emit an optical signal and transmit the optical signal to the optical fiber micro-force probe; the optical fiber micro-force probe is used to perform step indentation on a test sample in the optical signal to obtain an interference signal, and transmit the interference signal to the optical fiber grating demodulator; the optical fiber grating demodulator is used to collect and analyze spectral information according to the interference signal to obtain a resonant wavelength; the optical fiber nanoindenter also includes a mobile platform, the optical fiber micro-force probe is clamped on the mobile platform, and the mobile platform is used to install a glass slide with a test sample placed thereon. The optical fiber nanoindenter provided by the present invention is a nanoindenter with a simple system and an optical demodulation method, which expands the scope of application of the nanoindenter.

Description

Technical Field

[0001] The invention relates to the technical field of biomaterials, and in particular to an optical fiber nanoindenter and a testing method. Background Art

[0002] In recent years, with the development of materials science, various micro-nanoscale materials have been widely used in aerospace, biomedicine, petrochemical and other fields. Nanoindenters are widely used in the testing and morphology characterization of micro-nanoscale mechanical properties of material surfaces with their extremely high load and displacement resolution. Nanoindentation technology is an advanced material mechanical properties testing method suitable for micro-nanoscale thin films and coating materials. This technology uses a micrometer-sized probe tip to press into the sample and record the load-displacement curve during this period to analyze the microscopic mechanical behavior of the material.

[0003] However, the existing nanoindenter system is complex and uses electrical demodulation, which is not suitable for testing samples in liquids, greatly limiting the application of nanoindenters in the characterization of biomaterials.

[0004] Therefore, the prior art has defects and needs to be improved and developed. Summary of the invention

[0005] The technical problem to be solved by the present invention is that, in view of the above-mentioned defects of the prior art, a fiber optic nanoindenter and a testing method are provided, aiming to solve the problems that the nanoindenter in the prior art has a complex system and adopts an electrical demodulation method which is not suitable for testing samples in liquids, thus greatly limiting the application of the nanoindenter in the characterization of biomaterials.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] The first aspect of the present application provides a fiber optic nanoindenter, wherein the fiber optic nanoindenter includes: a laser light source, a fiber optic micro-force probe, and a fiber optic Bragg grating demodulator optically connected in sequence; the laser light source is used to emit a light signal, and transmit the light signal to the fiber optic micro-force probe; the fiber optic micro-force probe is used to perform step indentation on a test sample in the light signal to obtain an interference signal, and transmit the interference signal to the fiber optic Bragg grating demodulator; the fiber optic Bragg grating demodulator is used to collect and analyze spectral information according to the interference signal to obtain a resonant wavelength; the fiber optic nanoindenter also includes a moving platform, the fiber optic micro-force probe is clamped on the moving platform, and the moving platform is used to mount a glass slide with a test sample placed thereon.

[0008] In one embodiment of the present application, the optical fiber micro-force probe is prepared by using femtosecond laser two-photon polymerization technology, and a reflective light shielding layer is also provided on the optical fiber micro-force probe.

[0009] In one embodiment of the present application, the optical fiber micro-force probe comprises:

[0010] Optical fiber cladding;

[0011] an optical fiber core, wherein the optical fiber core is embedded in the optical fiber cladding;

[0012] A cantilever beam, wherein the cantilever beam is arranged at the end surface of the optical fiber cladding and is arranged opposite to the optical fiber core to form a Fabry-Perot interferometer cavity;

[0013] a probe tip, the probe tip being disposed on the cantilever beam;

[0014] Wherein, the reflected light shielding layer is mounted on a side of the cantilever beam away from the optical fiber core.

[0015] In one embodiment of the present application, the mobile platform includes:

[0016] Stage base;

[0017] A three-axis probe coarse displacement stage, arranged on the stage base;

[0018] A single-axis probe micro-displacement stage is arranged on the three-axis probe coarse displacement stage, and the single-axis probe micro-displacement stage is used for displacement on the Z axis;

[0019] An optical fiber clamp is arranged on the single-axis probe micro-displacement platform;

[0020] A two-axis hollow coarse translation stage, arranged on the stage base;

[0021] and a three-axis hollow micro-displacement stage, which is arranged on the two-axis hollow coarse displacement stage, and the three-axis hollow micro-displacement stage is used to install a glass slide on which a test sample is placed;

[0022] Wherein, the optical fiber micro-force probe is clamped on the optical fiber clamp.

[0023] In one embodiment of the present application, the two-axis hollow coarse displacement stage and the three-axis hollow micro displacement stage are both provided with hollow transparent grooves; the fiber optic nanoindenter also includes: an inverted optical microscope and a linear array camera connected to each other; the inverted optical microscope is accommodated in the stage base and the transparent groove; the inverted optical microscope is used to focus the test sample on the three-axis hollow micro displacement stage, and the linear array camera is used to obtain a sample image based on the reflected light of the test sample by the inverted optical microscope.

[0024] The second aspect of the present application provides a testing method based on the optical fiber nanoindenter as described above, and the testing method includes:

[0025] Using a mobile platform to control the optical fiber micro-force probe to move to a test point of a test sample, and controlling the optical fiber micro-force probe to perform nanoindentation on the test point;

[0026] When the optical fiber micro-force probe receives the optical signal emitted by the laser light source, it steps a preset step distance at each test point to obtain an interference signal, and transmits the interference signal to the optical fiber Bragg grating demodulator;

[0027] When the fiber Bragg grating demodulator collects and analyzes spectral information according to the interference signal to obtain the resonant wavelength, the displacement depth of the fiber optic micro-force probe at the test point is recorded, and a first corresponding relationship between the displacement depth corresponding to the test point and the resonant wavelength is generated.

[0028] In one embodiment of the present application, when the fiber Bragg grating demodulator collects the current spectrum according to the interference signal and analyzes the resonant wavelength, after recording the indentation depth of the fiber micro-force probe at the test point and generating the first corresponding relationship between the displacement depth corresponding to the test point and the resonant wavelength, it also includes:

[0029] After completing the preset number of steps, the optical fiber micro-force probe is controlled to return to a position at a preset distance from the sample;

[0030] The three-axis hollow micro-displacement stage of the mobile platform is controlled to move in a plane to replace the test points until the tests of all the test points are completed.

[0031] In one embodiment of the present application, the testing method further includes:

[0032] Based on a pre-calibrated second correspondence between the resonant wavelength and the external force, converting the first correspondence into a third correspondence between the indentation depth and the external force;

[0033] The tip radius of the optical fiber micro-force probe and the Poisson's constant of the test sample are obtained, and the Young's modulus of the test sample at the test point is obtained based on the Hertz fitting model, the tip radius and the Poisson's constant.

[0034] In one embodiment of the present application, the testing method further includes:

[0035] The current state of the optical fiber micro-force probe is determined based on the spectral information collected by the optical fiber Bragg grating demodulator, and the mobile platform is controlled according to the current state.

[0036] A third aspect of the present application provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and the computer program can be executed to implement the steps of the test method as described above.

[0037] The present invention discloses a fiber optic nanoindenter and a testing method, wherein the fiber optic nanoindenter comprises: a laser light source, a fiber optic micro-force probe and a fiber optic Bragg grating demodulator optically connected in sequence; the laser light source is used to emit a light signal and transmit the light signal to the fiber optic micro-force probe; the fiber optic micro-force probe is used to perform step indentation on a test sample in the light signal to obtain an interference signal and transmit the interference signal to the fiber optic Bragg grating demodulator; the fiber optic Bragg grating demodulator is used to collect and analyze spectral information according to the interference signal to obtain a resonant wavelength; the fiber optic nanoindenter also comprises a mobile platform, the fiber optic micro-force probe is clamped on the mobile platform, and the mobile platform is used to install a glass slide on which a test sample is placed. The present invention utilizes a fiber optic micro-force probe to replace a complex and large spatial optical path, greatly compresses the volume of the system, and collects and demodulates a spectrum through a fiber optic Bragg grating demodulator to track the drift of a specific resonant wavelength, and then obtains the mechanical information of the sample after data processing. Therefore, the fiber optic nanoindenter provided by the present invention is a nanoindenter with a simple system and an optical demodulation method, which expands the scope of application of the nanoindenter. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural block diagram of a preferred embodiment of a fiber optic nanoindenter in the present invention.

[0039] Figure 2 It is a stereoscopic diagram of the optical fiber micro-force probe of the present invention.

[0040] Figure 3 It is a front view of the optical fiber micro-force probe of the present invention.

[0041] Figure 4 It is a structural schematic diagram of the mobile platform in the present invention.

[0042] Figure 5 It is a schematic diagram of the working principle of the inverted optical microscope in the present invention.

[0043] Figure 6 It is a schematic diagram of the first corresponding relationship in the present invention.

[0044] Figure 7 It is a logic block diagram of the test steps in the present invention.

[0045] Figure 8 It is the interface of the lattice mechanical imaging results of testing the polydimethylsiloxane material in the present invention.

[0046] Fig. 9 This is the Young's modulus data result of testing the polydimethylsiloxane material in the present invention.

[0047] Fig.10 It is the presentation interface of the result data stored after measurement in the present invention.

[0048] Description of reference numerals:

[0049] 100. Laser light source; 200. Fiber optic micro-force probe; 210. Reflection light shielding layer; 220. Fiber optic cladding; 230. Fiber optic core; 240. Cantilever beam; 250. Probe tip; 300. Fiber Bragg grating demodulator; 400. Mobile platform; 410. Stage base; 420. Three-axis probe coarse displacement stage; 430. Single-axis probe micro displacement stage; 440. Fiber optic clamp; 450. Two-axis hollow coarse displacement stage; 460. Three-axis hollow micro displacement stage; 500. Inverted optical microscope; 600. Linear array camera. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present invention clearer and more specific, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] Existing nanoindenters are limited by their large demodulation systems, complex operating procedures, and low detection throughput. In addition, traditional nanoindenters generally use electrical demodulation and are not suitable for testing samples in liquids, which greatly limits the application of nanoindenters in the characterization of biomaterials.

[0052] Optical fiber is a bendable optical fiber. The optical fiber nanomechanical probe formed by it has the advantages of stable performance, compact size, high sensitivity and multi-point simultaneous multiplexed measurement. Most importantly, optical fiber can replace complex and large spatial optical paths, greatly compressing the volume of the system.

[0053] like Figure 1 As shown, the present invention provides a fiber optic nanoindenter, which includes: a laser light source 100, a fiber optic micro-force probe 200 and a fiber optic Bragg grating demodulator 300 optically connected in sequence. The laser light source 100 is used to emit a light signal, and transmit the light signal to the fiber optic micro-force probe 200; the fiber optic micro-force probe 200 is used to perform step indentation on a test sample in the light signal to obtain an interference signal, and transmit the interference signal to the fiber optic Bragg grating demodulator 300; the fiber optic Bragg grating demodulator 300 is used to collect and analyze spectral information according to the interference signal to obtain a resonant wavelength. The fiber optic nanoindenter also includes a moving platform 400, on which the fiber optic micro-force probe 200 is clamped, and the moving platform 400 is used to install a glass slide on which a test sample is placed.

[0054] Specifically, the fiber optic micro-force probe 200 is mainly used to perform step indentation on the test sample and collect relevant optical signals. Light is emitted from the laser light source 100, and after interference by the cantilever beam 240 of the fiber optic micro-force probe 200, the interference signal is transmitted back to the fiber optic Bragg grating demodulator 300 through the coupler, and the fiber optic Bragg grating demodulator 300 can collect the current spectrum with high precision.

[0055] The embodiment of the present application utilizes an optical fiber micro-force probe 200 to replace the complex and bulky spatial optical path, greatly compressing the volume of the system, and collects and demodulates the spectrum through a fiber grating demodulator 300 to track the drift of a specific resonant wavelength, and then obtains the mechanical information of the sample after data processing. Therefore, it is a nanoindenter with a simple system and an optical demodulation method, which expands the scope of application of the nanoindenter.

[0056] In the embodiment of the present application, the optical fiber micro-force probe 200 is prepared by using femtosecond laser two-photon polymerization technology, and a reflective light shielding layer 210 is also provided on the optical fiber micro-force probe 200 .

[0057] Specifically, the optical fiber micro-force probe 200 is obtained by three-dimensional processing using femtosecond laser two-photon polymerization technology, which has the advantage of high precision. The size of the optical fiber micro-force probe 200 is in the order of hundreds of microns, and the size of the probe tip 250 is also only in the order of microns, which realizes the high-precision and small point spacing measurement of the probe. During the test, the optical fiber micro-force probe 200 was found to be interfered by the interference signal of the FP cavity formed between the optical fiber end face and the sample, and the existence of this interference will seriously affect the demodulation process. Therefore, the optical fiber micro-force probe 200 used in the embodiment of the present application is provided with a layer of reflected light shielding layer 210, and a layer of internally hollowed square cone is printed above the cantilever beam 240 part directly opposite to the optical fiber core 230, thereby forming a reflected light shielding layer 210, destroying the spatial flatness between the optical fiber end face and the sample, so as to achieve the destruction of the FP interference, thereby minimizing the influence of this part of the interference. Experimental results show that as long as the printing quality is guaranteed, the reflected light shielding layer 210 can improve the accuracy of the sample automated dot matrix measurement.

[0058] In the embodiments of the present application, Figure 2 and Figure 3 As shown, the optical fiber micro-force probe 200 includes:

[0059] Optical fiber cladding 220;

[0060] An optical fiber core 230, wherein the optical fiber core 230 is embedded in the optical fiber cladding 220;

[0061] A cantilever beam 240, wherein the cantilever beam 240 is disposed on an end surface of the optical fiber cladding 220 and is disposed opposite to the optical fiber core 230 to form a Fabry-Perot interferometer cavity;

[0062] A probe tip 250, wherein the probe tip 250 is disposed on the cantilever beam 240;

[0063] The reflective light shielding layer 210 is mounted on a side of the cantilever beam 240 away from the optical fiber core 230 .

[0064] Specifically, the Fabry-Perot interferometer cavity is the FP interferometer cavity. The optical fiber micro-force probe 200 can simultaneously sense micro-force and micro-displacement. The end face of the optical fiber core 230, the lower surface of the cantilever beam 240 and the upper surface of the cantilever beam 240 resonate to form the reflection spectrum of the optical fiber micro-force probe 200; the end face of the optical fiber core 230 and the lower surface of the cantilever beam 240 form an air micro-cavity; the lower surface of the cantilever beam 240 and the upper surface of the cantilever beam 240 form a polymer micro-cavity; the end face of the optical fiber core 230 and the upper surface of the cantilever beam 240 form a hybrid micro-cavity. The probe tip 250 and the reflected light shielding layer 210 are the probe part of the optical fiber micro-force probe 200. By setting up the reflected light shielding layer 210 above the cantilever beam 240, a probe part that is more suitable for automated measurement is formed.

[0065] In the embodiment of the present application, the probe tip 250 and the reflected light shielding layer 210 are simultaneously arranged on the end face of the optical fiber core 230, and the FP interference formed by the cantilever beam 240 and the end face of the optical fiber core 230 is collected and demodulated by the fiber grating demodulator 300. In the embodiment of the present application, the deflection and force magnitude of the probe tip 250 are obtained by tracking the drift of a specific resonant wavelength, combining the mechanical elastic coefficient of the cantilever beam 240, and demodulating at the same time, so that the mechanical information of the sample can be obtained through data processing, and after the mechanical information is processed, the Young's modulus and other information of the test sample can be obtained according to the needs.

[0066] In the embodiments of the present application, Figure 4 As shown, the mobile platform 400 includes:

[0067] Stage base 410;

[0068] A three-axis probe coarse displacement stage 420, which is disposed on the stage base 410;

[0069] A single-axis probe micro-displacement stage 430 is disposed on the three-axis probe coarse displacement stage 420, and the single-axis probe micro-displacement stage 430 is used for displacement on the Z axis;

[0070] The optical fiber clamp 440 is arranged on the single-axis probe micro-displacement stage 430;

[0071] A two-axis hollow coarse translation stage 450, disposed on the stage base 410;

[0072] and a three-axis hollow micro-displacement stage 460, which is disposed on the two-axis hollow coarse displacement stage 450, and the three-axis hollow micro-displacement stage 460 is used to install a glass slide on which a test sample is placed;

[0073] The optical fiber micro-force probe 200 is clamped on the optical fiber clamp 440 .

[0074] Specifically, the mobile platform 400 includes a micro-displacement stage and a coarse displacement stage. The micro-displacement stage 400 includes a single-axis probe micro-displacement stage 430 and a three-axis hollow micro-displacement stage 460. The single-axis probe micro-displacement stage 430 can drive the optical fiber micro-force probe 200 to move up and down in the Z axis, thereby satisfying the step displacement of the optical fiber micro-force probe 200 for the sample. The three-axis hollow micro-displacement stage 460 can drive the sample to move in three dimensions, so that the probe can scan the sample in two dimensions, and its hollow design can also achieve compatibility with the inverted optical microscope 500. The coarse displacement stage includes a three-axis probe coarse displacement stage 420 and a two-axis hollow coarse displacement stage 450. The three-axis probe coarse displacement stage 420 and the two-axis hollow coarse displacement stage 450 can roughly find the test area of ​​the test sample with the help of the inverted optical microscope 500 to perform a nanoindentation test.

[0075] The embodiment of the present application realizes automatic stepping of the probe by using the mobile platform 400, thereby improving the testing efficiency of the optical fiber nanoindenter.

[0076] In the embodiments of the present application, Figure 4 As shown, the two-axis hollow coarse displacement stage 450 and the three-axis hollow micro displacement stage 460 are both provided with hollow transparent grooves; the fiber optic nanoindenter also includes: an inverted optical microscope 500 and a linear array camera 600 connected to each other; the inverted optical microscope 500 is accommodated in the stage base 410 and the transparent groove; the inverted optical microscope 500 is used to focus the test sample on the three-axis hollow micro displacement stage 460, and the linear array camera 600 is used to obtain a sample image based on the reflected light of the test sample by the inverted optical microscope 500.

[0077] Specifically, in order to enhance the integration of the measurement system, the fiber Bragg grating demodulator 300 and the light source used in the present invention are modular devices, and the inverted optical microscope 500 used for observation is also constructed using scattered devices to save the space occupied by them as much as possible.

[0078] like Figure 5As shown, the working principle of the inverted optical microscope 500 is as follows: after the light from the white light source is emitted, it passes through the reflector and the semi-transparent mirror, and is focused by the objective lens onto the sample on the stage, and its reflected light then passes through the semi-transparent mirror and enters the linear array camera 600, and the sample image of the test sample is collected by the program, so as to achieve the purpose of observing the sample. Among them, the stage is the two-axis hollow coarse displacement stage 450 and the three-axis hollow micro displacement stage 460.

[0079] The embodiment of the present application also provides a testing method based on the optical fiber nanoindenter as described above, the testing method comprising:

[0080] Step S100, using a mobile platform to control the optical fiber micro-force probe to move to a test point of a test sample, and controlling the optical fiber micro-force probe to perform nanoindentation on the test point;

[0081] Step S200: When the optical fiber micro-force probe receives the optical signal emitted by the laser light source, it steps a preset step distance at the test point each time to obtain an interference signal, and transmits the interference signal to the fiber Bragg grating demodulator;

[0082] Step S300: When the fiber Bragg grating demodulator collects and analyzes spectral information according to the interference signal to obtain the resonant wavelength, the displacement depth of the fiber micro-force probe at the test point is recorded, and a first corresponding relationship between the displacement depth corresponding to the test point and the resonant wavelength is generated.

[0083] Specifically, the embodiment of the present application realizes multi-point measurement of the same sample by linking a fiber Bragg grating demodulator, a mobile platform and an inverted optical microscope. After completing the dot matrix measurement, the displacement depth and resonant wavelength of each point will be recorded. The displacement depth refers to the displacement of the probe driven downward by the mobile platform. The preset step distance is the unit distance of the step, and the displacement depth is obtained based on the product of the preset step distance and the current step frequency, thereby obtaining the relationship between the displacement depth and the resonant wavelength of each point, that is, the first corresponding relationship, such as Figure 6 shown.

[0084] The embodiment of the present application records the first corresponding relationship between the displacement depth corresponding to the test point and the resonant wavelength, thereby achieving the characterization of the mechanical properties of the test sample.

[0085] In the embodiment of the present application, when the fiber Bragg grating demodulator collects the current spectrum according to the interference signal and analyzes the resonant wavelength, after recording the indentation depth of the optical fiber micro-force probe at the test point and generating the first corresponding relationship between the displacement depth corresponding to the test point and the resonant wavelength, it also includes:

[0086] After completing the preset number of steps, the optical fiber micro-force probe is controlled to return to a position at a preset distance from the sample;

[0087] The three-axis hollow micro-displacement stage of the mobile platform is controlled to move in a plane to replace the test points until the tests of all the test points are completed.

[0088] Specifically, when testing the test sample, the test sample is placed on a glass slide and mounted in the center of a three-axis hollow micro-displacement stage. The test sample is observed using an inverted optical microscope of the system, and the probe tip is adjusted to a preset distance above the test sample, which can be tens of microns. After the preparation is completed, the probe tip of the fiber optic micro-force probe can automatically find the sample surface and perform nanoindentation on the test point of the sample using a designed program for automatically finding the sample surface. Every time the fiber optic micro-force probe steps a set step distance on the sample surface, the FP resonance wavelength of the selected order at that point will be recorded. After completing the set number of steps, the fiber optic micro-force probe will retreat and move away from the sample surface by a few microns. After retreating, it takes a few seconds for the probe to return to its original state. After the program determines that the probe has returned to its original state, the sample will be moved in a plane through the three-axis hollow micro-displacement stage to complete the point change operation, and the single-point measurement operation will be repeated to complete the test of all test points according to the pre-set dot matrix measurement parameters, including the number of points measured on the sample surface and the distance between the measurement points.

[0089] like Figure 7 As shown, the test steps specifically include:

[0090] Step S1, saving the original spectrum;

[0091] Step S2, probe stepping;

[0092] Step S3, recording the resonant wavelength;

[0093] Step S4, determine whether the mutual correlation coefficient is less than a threshold; if so, execute step S5; if not, return to step S2;

[0094] Step S5, probe stepping;

[0095] Step S6, recording the resonant wavelength;

[0096] Step S7, determine whether the step reaches a predetermined distance; if so, execute step S8; if not, return to step S5;

[0097] Step S8, the probe is withdrawn;

[0098] Step S9, probe recovery;

[0099] Step S10, sample displacement;

[0100] Step S11, determine whether the number of test points reaches a predetermined number; if so, end; if not, return to step S2.

[0101] The mutual correlation coefficient in step S4 refers to judging whether the probe has touched the surface by using whether the mutual correlation coefficient is less than a threshold value when the probe automatically searches for the surface.

[0102] The embodiment of the present application achieves characterization of the mechanical properties of the test sample by automatically measuring the first corresponding relationship between the displacement depths corresponding to a number of test points and the resonant wavelength.

[0103] In an embodiment of the present application, the testing method further includes:

[0104] Based on a pre-calibrated second correspondence between the resonant wavelength and the external force, converting the first correspondence into a third correspondence between the indentation depth and the external force;

[0105] The tip radius of the optical fiber micro-force probe and the Poisson's constant of the test sample are obtained, and the Young's modulus of the test sample at the test point is obtained based on the Hertz fitting model, the tip radius and the Poisson's constant.

[0106] Specifically, since the probe tip is made of polymer, it is very sensitive to the environment, so the mechanical properties of the probe tip will change in different environments. Therefore, in order to improve the measurement accuracy, the probe tip will be pre-calibrated before each sample measurement. The probe tip is first vertically fixed on the uniaxial micro-displacement stage by a fiber optic clamp and pressed onto a glass slide on a three-axis hollow micro-displacement stage. Since the hardness of the glass slide is very high, its stepping distance can be approximated to the deflection of the probe. The resonant wavelength is recorded while stepping, and combined with the calibrated probe elastic coefficient, the linear relationship between the resonant wavelength and the external force can be obtained. Specifically, during calibration, the displacement depth of the pressed glass slide and the measured resonant wavelength are recorded to obtain the corresponding relationship between the calibrated displacement depth and the resonant wavelength, and then the formula is used. , where For external force, is the elastic coefficient of the probe, is the displacement depth, and the external force corresponding to each displacement depth is obtained, and then the linear relationship between the resonant wavelength and the external force is constructed, that is, the second corresponding relationship.

[0107] Based on the calibration obtained resonant wavelength-external force correspondence, that is, the second correspondence between resonant wavelength and external force, the indentation depth-resonant wavelength relationship can be converted into the indentation depth-external force relationship, that is, the third correspondence. Specifically, the indentation depth is the depth of the probe after displacement and pressing into the sample. This is because after the probe is pressed into the test sample, the probe itself changes, so there will be two different data, displacement depth and indentation depth. When performing the conversion, use the formula , where For external force, is the current resonant wavelength; is the initial resonance wavelength, i.e., the resonance wavelength of the spectrum before the test sample is indented; is the slope of the relationship between the external force and the resonant wavelength, that is, the second corresponding relationship obtained by calibration. After obtaining the external force, the formula is used , where is the indentation depth, is the displacement depth, For external force, is the elastic coefficient of the probe; then the indentation depth is obtained, and the third corresponding relationship between the indentation depth and the external force is obtained.

[0108] After obtaining the third corresponding relationship between the indentation depth and the external force, the Hertz fitting model can be used to fit and calculate the Young's modulus of the sample at the test point in combination with the known probe tip radius and the Poisson constant of the sample, thus realizing the characterization of the mechanical properties of the soft material. Specifically, the formula of the Hertz fitting model is: , where For external force, is the Young's modulus of the test sample, is the Poisson constant of the test sample, is the tip radius of the probe tip, is the indentation depth. In addition, other mechanical properties can also be tested with the help of this relationship.

[0109] The embodiments of the present application can realize low-cost and high-efficiency nanoindentation testing, and are particularly suitable for in vivo and in vitro mechanical property testing or scanning imaging of biological materials such as biological cells, bacteria, cartilage and tissues in the fields of biomaterials, tissue engineering and biomedicine.

[0110] In an embodiment of the present application, the testing method further includes:

[0111] The current state of the optical fiber micro-force probe is determined based on the spectral information collected by the optical fiber Bragg grating demodulator, and the mobile platform is controlled according to the current state.

[0112] Specifically, the system determines the current state of the fiber optic micro-force probe through the spectral signal collected by the fiber optic Bragg grating demodulator, and controls the micro-displacement stage according to the current state, thereby avoiding damage to the probe and accurately completing operations such as searching for surfaces and indentations.

[0113] A fiber optic nanoindenter can achieve a high degree of integration, and can observe biological tissues and small samples while conducting nanoindentation experiments. In addition, it can perform customized dot matrix measurements on the surface of a sample to better study the mechanical properties of the sample.

[0114] The fiber optic cantilever micro-force probe can achieve high-precision and fast dot-matrix mechanical imaging. The test results of a piece of polydimethylsiloxane (PDMS) material are as follows: Figure 8 As shown, Figure 8 The distance between the horizontal and vertical coordinates refers to the distance from the starting measurement point. The corresponding data is as follows: Fig. 9 As shown. Among them, Fig. 9 The probe K value in is the probe elastic coefficient. The determination coefficient refers to the degree of conformity of the data to the fitting function. The closer it is to 1, the higher the degree of conformity between the predicted value and the actual observed value. The data of each test point will be stored and presented separately. The third corresponding relationship is as follows Fig.10 shown.

[0115] An embodiment of the present application further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and the computer program can be executed to implement the steps of the testing method as described above.

[0116] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0117] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, "N" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0118] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or N executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present application includes additional implementations, in which the order shown or discussed may not be followed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0119] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can read instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or N wirings (electronic devices), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically by optically scanning the paper or other medium and then editing, interpreting or otherwise processing in a suitable manner if necessary and then storing it in a computer memory.

[0120] It should be understood that the various parts of the present application can be implemented by hardware, software, firmware or a combination thereof. In the above embodiment, the N steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. If implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0121] A person skilled in the art may understand that all or part of the steps in the above-mentioned embodiment method may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0122] In addition, each functional unit in each embodiment of the present application may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0123] The storage medium mentioned above may be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present application.

[0124] The present invention provides a fiber optic nanoindenter and a testing method, wherein the fiber optic nanoindenter comprises: a laser light source, a fiber optic micro-force probe and a fiber optic Bragg grating demodulator optically connected in sequence; the laser light source is used to emit a light signal and transmit the light signal to the fiber optic micro-force probe; the fiber optic micro-force probe is used to perform step indentation on a test sample in the light signal to obtain an interference signal, and transmit the interference signal to the fiber optic Bragg grating demodulator; the fiber optic Bragg grating demodulator is used to collect and analyze spectral information according to the interference signal to obtain a resonant wavelength; the fiber optic nanoindenter also includes a mobile platform, the fiber optic micro-force probe is clamped on the mobile platform, and the mobile platform is used to install a glass slide on which the test sample is placed. The present invention uses a fiber optic micro-force probe to replace a complex and large spatial optical path, greatly compresses the volume of the system, and collects and demodulates the spectrum through a fiber optic Bragg grating demodulator to track the drift of a specific resonant wavelength, and then obtains the mechanical information of the sample after data processing. Therefore, the fiber optic nanoindenter provided by the present invention is a nanoindenter with a simple system and an optical demodulation method, which expands the scope of application of the nanoindenter.

[0125] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A fiber optic nanoindenter, characterized in that: The fiber optic nanoindenter includes: a laser light source, a fiber optic micro-force probe and a fiber optic Bragg grating demodulator optically connected in sequence; the laser light source is used to emit a light signal and transmit the light signal to the fiber optic micro-force probe; the fiber optic micro-force probe is used to perform step indentation on the test sample in the light signal to obtain an interference signal, and transmit the interference signal to the fiber optic Bragg grating demodulator; the fiber optic Bragg grating demodulator is used to collect and analyze spectral information according to the interference signal to obtain a resonant wavelength; the fiber optic nanoindenter also includes a moving platform, the fiber optic micro-force probe is clamped on the moving platform, and the moving platform is used to install a glass slide on which the test sample is placed; The optical fiber micro-force probe is prepared by using femtosecond laser two-photon polymerization technology, and a reflection light shielding layer is also provided on the optical fiber micro-force probe; The optical fiber micro-force probe comprises: Optical fiber cladding; an optical fiber core, wherein the optical fiber core is embedded in the optical fiber cladding; A cantilever beam, wherein the cantilever beam is arranged on the end surface of the optical fiber cladding and is arranged opposite to the optical fiber core to form a Fabry-Perot interferometer cavity; a probe tip, the probe tip being arranged on the cantilever beam; Wherein, the reflected light shielding layer is mounted on a side of the cantilever beam away from the optical fiber core; The reflected light shielding layer is used to destroy the spatial flatness between the optical fiber end face and the test sample, and to destroy the interference of the Fabry-Perot interference cavity formed between the optical fiber end face and the test sample.

2. The optical fiber nanoindenter according to claim 1, characterized in that: The mobile platform comprises: Stage base; A three-axis probe coarse displacement stage, arranged on the stage base; A single-axis probe micro-displacement stage is arranged on the three-axis probe coarse displacement stage, and the single-axis probe micro-displacement stage is used for displacement on the Z axis; An optical fiber clamp is arranged on the single-axis probe micro-displacement platform; A two-axis hollow coarse translation stage, arranged on the stage base; and a three-axis hollow micro-displacement stage, which is arranged on the two-axis hollow coarse displacement stage, and the three-axis hollow micro-displacement stage is used to install a glass slide on which a test sample is placed; Wherein, the optical fiber micro-force probe is clamped on the optical fiber clamp.

3. The optical fiber nanoindenter according to claim 2, characterized in that: The two-axis hollow coarse displacement stage and the three-axis hollow micro displacement stage are both provided with hollow transparent grooves; The fiber optic nanoindenter also includes: an inverted optical microscope and a linear array camera connected to each other; the inverted optical microscope is accommodated in the stage base and the transparent groove; the inverted optical microscope is used to focus the test sample on the three-axis hollow micro-displacement stage, and the linear array camera is used to obtain a sample image based on the reflected light of the test sample from the inverted optical microscope.

4. A testing method based on the optical fiber nanoindenter according to any one of claims 2 to 3, characterized in that: The test method includes: Using a mobile platform to control the optical fiber micro-force probe to move to a test point of a test sample, and controlling the optical fiber micro-force probe to perform nanoindentation on the test point; When the optical fiber micro-force probe receives the optical signal emitted by the laser light source, it steps a preset step distance at each test point to obtain an interference signal, and transmits the interference signal to the optical fiber Bragg grating demodulator; When the fiber Bragg grating demodulator collects and analyzes spectral information according to the interference signal to obtain the resonant wavelength, the displacement depth of the optical fiber micro-force probe at the test point is recorded, and a first corresponding relationship between the displacement depth corresponding to the test point and the resonant wavelength is generated; When the fiber Bragg grating demodulator collects the current spectrum according to the interference signal and analyzes and obtains the resonant wavelength, after recording the displacement depth of the optical fiber micro-force probe at the test point and generating a first corresponding relationship between the displacement depth corresponding to the test point and the resonant wavelength, the method further includes: After completing the preset number of steps, the optical fiber micro-force probe is controlled to return to a position at a preset distance from the sample; Control the three-axis hollow micro-displacement stage of the mobile platform to move in a plane to change the test points until the test of all the test points is completed; The test method also includes: Based on a pre-calibrated second correspondence between the resonant wavelength and the external force, converting the first correspondence into a third correspondence between the indentation depth and the external force; The tip radius of the optical fiber micro-force probe and the Poisson's constant of the test sample are obtained, and the Young's modulus of the test sample at the test point is obtained based on the Hertz fitting model, the tip radius and the Poisson's constant.

5. The testing method according to claim 4, characterized in that: The test method also includes: The current state of the optical fiber micro-force probe is determined based on the spectral information collected by the optical fiber Bragg grating demodulator, and the mobile platform is controlled according to the current state.

6. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and the computer program can be executed to implement the steps of the testing method according to any one of claims 4 to 5.

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