Method and device for laser processing of biological hard tissues based on optical frequency comb

Abstract

The application discloses a biological hard tissue laser processing method and device based on an optical frequency comb. The method is characterized in that the method is designed by integrating laser measurement and processing, and combines femtosecond optical frequency comb technology. The method can realize real-time measurement and analysis of spectral power and time-frequency domain information generated when a laser irradiates a biological hard tissue without increasing the complexity of an optical path and a monitoring system. The method is based on characteristic spectral types, intensity and power ratio and time-frequency domain characteristic analysis of optical signals such as reflected light of the optical frequency comb, excited plasma and thermal radiation, and obtains state and absolute distance information. The method realizes positioning, size measurement, rapid focusing and state monitoring integration based on characteristic spectrum and double-color optical comb spectrum interference measurement synchronous measurement. The method can be applied to precise processing and surgical treatment of biological hard tissues such as bones and teeth, and is related to the fields of biological product processing and biological medical treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser processing, in particular to a biological hard tissue laser processing method and device based on an optical frequency comb. BACKGROUND

[0002] With the development of an aging society, changes in modern lifestyles, and the pursuit of higher quality of life, the demand for surgical diagnosis and treatment involving the processing of biological hard tissues such as bones and teeth is increasing. Taking dental diseases as an example, the World Health Organization reports that dental caries is one of the three major non-communicable diseases with the highest prevalence in humans, and nearly 90% of adults suffer from dental hard tissue diseases such as dental caries. The grinding, drilling, and cutting of biological hard tissues are the most commonly used surgical procedures in surgical treatment and are widely used in the preparation and filling of dental hard tissues, skull incision, laminectomy, footplate fenestration, joint replacement, and fracture treatment. Compared with mechanical processing and other surgical treatment methods, laser processing provides a non-mechanical damage high-precision biological hard tissue processing method due to its non-contact processing, high precision, high repeatability, and ease of integration, and has become an important research direction in this field.

[0003] To minimize, inhibit, and eliminate the risk of laser processing damage, research on positioning and monitoring techniques that match the characteristics of laser processing technology is an important part of promoting the widespread application of biological hard tissue laser processing. For biological hard tissue laser processing, there have been reports of using various types of light signals related to the processing state induced during laser processing to achieve biological hard tissue processing positioning, online monitoring, and real-time feedback. For example, plasma spectrum-based differentiation of bone tissue and spinal cord, integrated laser processing positioning, monitoring, and processing based on the characteristic spectral power ratio of second harmonic, plasma, and thermal radiation light signals, and bone thermal damage assessment based on the relative intensity changes of Ca and Na element characteristic spectral lines of normal bone tissue and bone carbonized tissue. The positioning and monitoring methods based on the measurement of light signals excited during laser processing provide a new idea for positioning and monitoring that matches the characteristics of laser processing, and are different from optical positioning during mechanical processing. Through integrated design of the laser processing and measurement light paths, it is expected to further overcome the errors caused by shielding and scattering.

[0004] On the other hand, optical frequency comb ranging positioning is a highly precise ranging positioning method that can be traced. By locking the initial frequency and repetition frequency of a femtosecond pulse laser to a high-stability clock and measuring the distance through spectral interference, nanometer-level precision can be achieved in the meter range. Like the above-mentioned measurement methods and devices based on excited light signals, it also uses a spectrometer for spectral measurement and analysis, but gives absolute distance information from the analysis and processing of frequency domain information.

[0005] Laser processing provides a high-precision biological hard tissue processing method without mechanical damage due to non-contact processing, high precision, high repeatability and easy integration. However, when facing biological hard tissue processing, how to monitor the absolute position, size and state of processing in real time, accurately control the laser processing parameters, and minimize and eliminate the risk of thermal and mechanical damage is a key to push laser processing into the field of biological product processing and biological medical treatment. SUMMARY

[0006] The biological hard tissue laser processing method based on optical frequency comb provided by the application can at least solve one of the above technical problems.

[0007] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0008] A biological hard tissue laser processing method based on optical frequency comb, comprising the following steps:

[0009] Step one, pretreating the biological hard tissue before processing;

[0010] Step two, measuring the optical comb spectrum interference distance measurement information to calibrate the sample processing position and set the focal length of the processing system;

[0011] Step three, starting processing according to the predetermined parameters, monitoring the characteristic spectral types and power meter power ratios of the plasma and thermal radiation light signals to monitor the focal length and damage state of the processing light path while monitoring the position and size combined with the optical comb spectrum interference absolute distance measurement;

[0012] Step four, feeding back the control of the laser processing system according to the monitoring information of the position, size and state, continuously performing positioning, monitoring and processing operations, and completing accurate and non-invasive processing.

[0013] As can be seen from the above technical solutions, the biological hard tissue laser accurate and minimally invasive processing application requirements are matched, the biological hard tissue laser processing method based on optical frequency comb of the application proposes an integrated design method of laser measurement and processing, combines femtosecond optical frequency comb technology, measures and analyzes the spectral power and time-frequency domain information generated when laser irradiates biological hard tissue in real time without increasing the complexity of the optical path and monitoring system, and obtains absolute position and state information based on the characteristic spectral power ratio and time-frequency domain feature analysis of the optical frequency comb reflected light and the excited plasma and thermal radiation light signals. The positioning, size measurement, rapid focusing and state monitoring integration based on the characteristic spectral power ratio and dual-color optical comb spectrum interference measurement are realized. The method can be applied to accurate processing and surgical treatment of bone and tooth biological hard tissues, and is related to the fields of biological product processing and biological medical treatment.

[0014] The present application is aimed at the application demand of precise processing of biological hard tissue, by introducing optical frequency comb, using the synchronous measurement and analysis of two dimensions of spectral power and time-frequency domain, realizing real-time focusing and damage monitoring based on spectral characteristic power proportion, at the same time, based on optical comb spectral interference absolute ranging for precise positioning and position size monitoring, a two-dimensional spectral measurement positioning and monitoring integrated method and device suitable for biological hard tissue laser processing is proposed, which effectively improves the accuracy and safety technology of existing biological hard tissue laser processing, and can control the absolute length and position size through optical frequency comb. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The present application is aimed at the application demand of precise processing of biological hard tissue, by introducing optical frequency comb, using the synchronous measurement and analysis of two dimensions of spectral power and time-frequency domain, realizing real-time focusing and damage monitoring based on spectral characteristic power proportion, at the same time, based on optical comb spectral interference absolute ranging for precise positioning and position size monitoring, a two-dimensional spectral measurement positioning and monitoring integrated method and device suitable for biological hard tissue laser processing is proposed, which effectively improves the accuracy and safety technology of existing biological hard tissue laser processing, and can control the absolute length and position size through optical frequency comb.

[0016] Figure 2 The present application is aimed at the application demand of precise processing of biological hard tissue, by introducing optical frequency comb, using the synchronous measurement and analysis of two dimensions of spectral power and time-frequency domain, realizing real-time focusing and damage monitoring based on spectral characteristic power proportion, at the same time, based on optical comb spectral interference absolute ranging for precise positioning and position size monitoring, a two-dimensional spectral measurement positioning and monitoring integrated method and device suitable for biological hard tissue laser processing is proposed, which effectively improves the accuracy and safety technology of existing biological hard tissue laser processing, and can control the absolute length and position size through optical frequency comb.

[0017] Figure 3 The bone processing sample diagram, specifically the bone processing original sample surface, irregular shape carbonized sample without accurate control of processing shape and damage state, circular carbonized sample without accurate control of damage state, shallow pit processing sample and round hole sample without damage. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments.

[0019] In order to monitor the position size and state information of laser processing, it is proposed that Figure 1 The research scheme shown integrates laser processing and optical comb measurement system, through integrated design of processing and measurement optical path, and uses the spectrum analyzer to measure the laser processing excitation light signal and the reflection signal of the sample irradiated by the optical comb, to obtain the type, intensity and proportion information of the characteristic spectrum and the spectral interference absolute distance measurement information, to simultaneously feedback control the laser processing information from two dimensions.

[0020] The corresponding design is as follows Figure 2The illustrated light comb ranging and laser processing integrated system includes a laser light source, two optical filters, three beam splitters, two mirrors, a coupling system, a beam expanding and collimating system, a cooling device, a data processing system, and a spectrometer. The laser light source includes an optical frequency comb and a processing light source. The processing light source output light passes through the collimating and expanding system, is adjusted by the mirror, and is combined with the optical frequency comb output light at the beam splitter. One path is used as reference light, and the other path is used as object light and radiated to the biological hard tissue surface. The diffuse reflection light generated by the laser acting on the biological hard tissue surface is received by the coupling system and then processed. The coupling system is composed of a telescope system and a coupling mirror. The large-aperture telescope receives most of the diffuse reflection light and emits it. A coupling device is arranged at the emission port to converge the light and transmit it into the filter. After filtering out other optical signals, the light is combined with the reference light at the beam splitter. After passing through the optical filter, the spectrometer is used to measure the interference spectrum between the two signals in real time, and the data processing system is entered. According to the real-time signal measurement and analysis, the cooling device is added. By real-time measurement and analysis of the change of the light signal, the type, intensity, and proportion information of the characteristic spectrum and the spectral interference absolute distance measurement information are obtained. The laser processing information is feedback controlled from two dimensions at the same time until the processing is completed.

[0021] The specific implementation steps are as follows:

[0022] Step one: before processing, the biological hard tissue such as bone and tooth is pretreated by cleaning and the like.

[0023] Step two: the optical frequency comb passes through the beam splitter. One path is used as reference light. The other path is combined with the output light of the processing light source. The coupling system receives the diffuse reflection light generated by acting on the biological hard tissue. The two lights are recombined after passing through the beam splitter. The interference spectrum between the two signals is measured in real time by the spectrometer after passing through the filter. The distance is obtained by converting the phase correlation information. The bone sample to be processed position calibration and processing system focal length setting are realized.

[0024] The principle of the measurement technology in the ranging application adopts a Michelson interferometer ranging light path. First, the ultra-short laser pulses emitted by the femtosecond optical frequency comb are energy-split. One path is used as a measurement light path, and the other path is used as a reference light path. The two lasers are reflected by the reference mirror and the target mirror respectively and then recombined at the beam splitter. The target distance is the optical path difference between the two paths, L=L2-L1. From the frequency domain, each comb tooth of the frequency comb interferes with each other. The frequency comb after recombination contains self-interference information of all comb teeth. Because the frequencies of each comb tooth are different, the grating spectrometer can observe the interference fringes with light and dark intervals in the optical frequency domain by receiving the interference signal. The interval between the fringes carries the distance information of the target to be measured.

[0025] For spectrally resolved absolute distance measurement, the intensity of the spectral interference fringes received by the spectrometer as a function of the optical frequency can be expressed as

[0026] g(v) = s(v) [1 + cos φ(v)] (1)

[0027] where s(v) is the comb tooth power spectral function of the femtosecond optical frequency comb, and the distance dependent interference phase term can be expressed as

[0028] φ(v) = 2πva (2)

[0029] where a represents the optical path delay, written as the following equation

[0030] a = 2n(v)L / c (3)

[0031] where n(v) is the refractive index; c is the speed of light in vacuum.

[0032] Fourier transforming equation (1) can transform the spectrum to the pseudo-time domain, obtaining

[0033]

[0034] S(τ) is the Fourier transform of s(v). Since the power spectral density function g(v) is a real function, its Fourier transform is symmetric about τ = 0, and there are three peaks at -a, 0, a. At this time, the peak value at a can be extracted separately by using a bandpass filter function, and inverse Fourier transform is performed, obtaining

[0035]

[0036] Its phase term can be easily obtained from the trigonometric function

[0037]

[0038] Every 2π radian, the phase term φ(v) will appear to be deconvoluted, so the real absolute phase of φ(v) is obtained by deconvolution expansion of φ(v), and its slope corresponds to the distance L to be measured, expressed as

[0039]

[0040] N = n + (dn / dv). Here, n is the group refractive index of air, and v is a function of the center wavelength of the laser light source. The distance L can be expressed as

[0041]

[0042] Absolute distance L without ambiguity NARThe light frequency resolution p of the spectrometer determines. According to the Nyquist sampling frequency, in order to prevent aliasing, the value of a is not allowed to exceed 1 / 2p. Therefore, the unambiguous distance of the optical spectrum interferometric distance measurement is L NAR = (4Np).

[0043] Step three, start processing according to the predetermined parameters, combine the optical comb spectrum interference absolute distance measurement to monitor the position size, and monitor the characteristic spectral type and power ratio of the plasma and thermal radiation and other light signals to monitor the focal length and damage state of the processing light path;

[0044] Step four, feedback control the laser processing system according to the monitoring information of position, size and state, continuously carry out positioning, monitoring and processing operation, and complete accurate and non-invasive processing.

[0045] The following is an example:

[0046] The embodiment of the application discloses a kind of biological hard tissue laser processing method and device based on optical frequency comb, with typical biological hard tissue sample pig stick femtosecond laser processing as an example, specifically including the following steps:

[0047] Step one, take pig stick middle section to remove attachment, and adopt distilled water to flush to remove blood dirt and obtain Figure 3 As shown in the bone original sample surface.

[0048] Step two, according to Figure 2 As shown in the processing device, by measuring optical comb spectrum interference distance measurement information, sample processing position calibration and processing system focal length setting

[0049] Step three, preset laser power 2W, laser repetition frequency 100kHz, beam scanning speed 1000mm / s, set scanning shape as circle, scanning interval 30 μm, while monitoring spectral information in processing.

[0050] Step four, feedback optimization laser power, laser repetition frequency, beam scanning speed, cooling parameters, etc., carry out vinegar processing until end, Figure 3 As shown in the figure, the damage and non-damage sample obtained by processing.

[0051] As described above, the embodiment of the application aims at the application demand of biological hard tissue accurate processing, by introducing optical frequency comb, using spectral power and time-frequency domain two-dimensional synchronous measurement and analysis, realizing real-time focusing based on spectral characteristic power ratio and damage monitoring, based on optical comb spectrum interference absolute distance measurement for accurate positioning and position size monitoring, a kind of two-dimensional spectral measurement positioning and monitoring integrated method and device suitable for biological hard tissue laser processing are proposed, effectively improve the accuracy and safety technology of existing biological hard tissue laser processing, and absolute length and position size can be controlled by optical frequency comb.

[0052] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those ordinarily skilled in the art should understand: the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A laser processing method for biological hard tissue based on optical frequency comb, characterized in that, Includes the following steps, Step 1: Pre-treat the biological hard tissue before processing; Step two: By measuring the optical comb spectral interferometry ranging information, the sample processing position is calibrated and the focal length of the processing system is set; Step 3: Start processing according to the predetermined parameters. While monitoring the position size by combining the absolute distance measurement of optical comb spectral interferometry, monitor the characteristic spectral types, intensities, and power meter power ratios of plasma and thermal radiation optical signals to monitor the focal length and damage status of the processing optical path. Step four: Based on the monitoring information of position, size and status, control the laser processing system to continuously perform positioning, monitoring and processing operations to complete precise and non-invasive processing; Step two specifically includes, After passing through a beam splitter, one path serves as a reference light, while the other path merges with the output light from the processing light source. A coupling system is used to receive the diffuse reflection light generated on the biological hard tissue. The two beams are then re-combined after passing through the beam splitter, filtered, and then the interference spectrum between the two signals is measured in real time by a spectrometer. This spectrum is converted into phase-related information to obtain the distance, thus enabling the calibration of the processing position of the biological hard tissue sample and the setting of the focal length of the processing system.

2. The method for laser processing of biological hard tissue based on optical frequency comb according to claim 1, characterized in that: Step two involves calibrating the sample processing position and setting the focal length of the processing system by measuring the optical comb's spectral interferometry ranging information. Specifically, this includes: First, the ultrashort laser pulses emitted by the femtosecond optical frequency comb are split into two beams: one for measurement and the other for reference. The two laser beams are then reflected by the reference mirror and the target mirror, respectively, before being recombined by the beam splitter. The target distance is the optical path difference between the two beams. ; For absolute distance measurements with spectral resolution, the relationship between the intensity of the spectral interference fringes received by the spectrometer and the optical frequency is expressed as follows: （1） in, Let be the power spectral function of the femtosecond optical frequency comb, and let the distance-dependent interference phase term be expressed as: （2） in, The optical path delay is expressed by the following formula: （3） in, c is the refractive index; c is the speed of light in a vacuum. Performing a Fourier transform on equation (1) to transform the spectrum to the pseudo-time domain yields the following result: （4） S(τ) is the Fourier transform of s(v); since the power spectral density function g(v) is a real function, its Fourier transform is symmetric about τ=0, showing three peaks at their respective positions. α, 0, α, at this point, the peak at α is extracted separately using a bandpass filter function, and then an inverse Fourier transform is performed to obtain... （5） Its phase term can be easily obtained from trigonometric functions. Phase term every 2π radians This will cause folds to appear, therefore, The reverse fold unfolds to obtain The true absolute phase of the distance being measured corresponds to the slope of the slope of the distance being measured. L , represented as , n Let be the group refractive index of air. v It is a function of the center wavelength of the laser source; distance L Represented as Unambiguous distance in absolute ranging L NAR Optical frequency resolution from spectrometer p The decision is based on the Nyquist sampling frequency; to prevent aliasing, The value of is not allowed to exceed 1 / 2p; therefore, the unambiguous distance in spectral interferometric ranging is . .

3. The method for laser processing of biological hard tissue based on optical frequency comb according to claim 1, characterized in that: In step four, the feedback control laser processing system includes feedback optimization of laser power, laser repetition frequency, beam scanning speed, and cooling parameters.

4. A laser processing apparatus for biological hard tissue based on an optical frequency comb, used to implement the laser processing method for biological hard tissue based on an optical frequency comb as described in any one of claims 1-3, characterized in that: It includes a laser source, two optical filters, three beam splitters, two mirrors, a coupling system, a beam expander and collimator system, a cooling device, a data processing system, and a spectrometer. The laser source includes an optical frequency comb and a processing light source. The light emitted from the processing light source passes through a collimation and beam expansion system. After the light path direction is adjusted by a reflector, it merges with the light emitted from the optical frequency comb at the beam splitter. One path serves as a reference light, and the other path serves as the object light, radiating onto the surface of biological hard tissue. Most of the diffuse reflection light generated by the laser acting on the surface of biological hard tissue is received and processed by the coupling system. The coupling system consists of a telescope system and a coupling mirror. After receiving most of the diffuse reflection light, the large-aperture telescope emits the light. A coupling device is added at the emission port to focus the light and transmit it into a filter. After filtering out other light signals, the light is combined with the reference light at the beam splitter. After passing through the optical filter, the interference spectrum between the two signals is measured in real time by a spectrometer and then enters the data processing system. Based on real-time signal measurement and analysis, a cooling device is added. By measuring and analyzing changes in optical signals in real time, information on the type, intensity, and proportion of characteristic spectra, as well as the absolute distance measurement information of spectral interference, is obtained. The laser processing information is simultaneously fed back and controlled from two dimensions until the processing is completed.

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