A method for generating a high-stability supercontinuum light source based on solid thin films

Abstract

The invention discloses a method for generating a high-stability supercontinuum light source based on a solid slice, which is as follows: S1: placing at least one solid slice on a two-dimensional or multi-dimensional micro-displacement platform; S2: after an ultrashort laser pulse converges and enters a certain irradiation area on the front surface of the solid slice, a nonlinear optical effect is generated during the propagation process in the solid slice to achieve spectrum broadening; S3: an optical power probe is simultaneously used to sample and detect the ultrashort laser pulse after the action on the solid slice, so as to achieve real-time measurement and recording of the power of the sampled beam; S4: based on the detected power value, the variation amplitude of the real-time power relative to the initial power is calculated, thereby obtaining a quantitative evaluation of the aging condition of the solid slice; S5: a main control system issues a control instruction to control the micro-displacement platform to move according to a pre-set motion mode, so as to achieve continuous updating of the irradiation area of ​​the solid slice, thereby achieving an ultrashort pulse light source for generating a high-stability supercontinuum.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrashort laser pulses, and more specifically, to a method for generating a high-stability supercontinuum light source based on a solid slice. Background Art

[0002] For the field of ultrashort laser pulses, achieving shorter pulse time widths has always been the focus and difficulty of the field's development. From the time-bandwidth product relationship of the Fourier transform limiting pulse, it can be seen that to obtain a shorter pulse time width, a wider spectral bandwidth is necessary to support it. Usually, under the premise of maintaining high coherence of different spectral components, the spectral bandwidth of the laser pulse is significantly widened through certain technical methods, and then the dispersion compensation of the pulse is performed through certain technical methods, which can achieve significant compression of the time width of the ultrashort laser pulse. In other words, how to expand the spectral bandwidth of the ultrashort pulse as coherently as possible is the core technical problem of enabling ultrashort pulses to obtain narrower time widths. Generally speaking, since the gain bandwidth of the laser gain medium is relatively fixed, the limiting pulse width of ultrashort laser pulses based on a specific laser gain medium is also basically the same. But in fact, in order to obtain a significant amplification of the energy of ultrashort laser pulses, it is often necessary to sacrifice the time width of the pulse. For example, in chirped pulse amplification technology, when chirped ultrashort laser pulses are amplified by high-intensity pumping in laser crystals, significant gain bandwidth narrowing will occur, which in turn causes the limit width of high-energy ultrashort pulses output by ultrashort laser amplifiers to be significantly greater than the limit width of low-energy ultrashort pulses output by ultrashort laser oscillators. For example, the limit pulse width of titanium (Ti) sapphire ultrashort pulse oscillators can be less than 10fs, while the limit pulse width of titanium sapphire ultrashort pulse amplifiers is generally greater than 20fs. In addition, ytterbium (Yb)-doped crystals have a much narrower gain bandwidth than titanium sapphire crystals, making it difficult for ultrashort laser pulses based on ytterbium-doped crystals to obtain pulse widths below 100fs. Therefore, whether for titanium sapphire ultrashort pulse lasers or ytterbium-doped ultrashort pulse lasers, these two mainstream ultrashort pulse lasers need to further perform significant coherent broadening of the pulse spectrum bandwidth outside the laser resonator, and then perform time domain compression to obtain extremely narrow pulse time widths that are even close to a single cycle.

[0003] At present, the spectral broadening of ultrashort pulses is mainly based on the third-order nonlinear effects induced by strong ultrashort pulses in transparent media, especially the induced optical Kerr effect (such as self-phase modulation and cross-phase modulation) to cause pulse spectral broadening. Typically, the transmission of strong ultrashort pulses in transparent solid media can achieve significant broadening of the ultrashort pulse spectrum, thereby forming a supercontinuum output. For example, in the 1980s, researchers used bulk fused quartz to achieve significant spectral broadening of ultrashort pulses, compressing the pulse time width from 100fs to 20fs. However, although there have been related studies followed up for a long time, this technology has not been widely used, especially in commercial applications.

[0004] On the one hand, this is because transparent solid media have a high third-order nonlinear coefficient and a low self-focusing threshold. When performing spectrum broadening on high-energy ultrashort pulses, it is easy to induce self-focusing to form a multi-filament transmission state, which ultimately leads to the disorder of the laser transverse mode and optical damage to the transparent medium. Therefore, when using transparent solid media for ultrashort pulse spectrum broadening, it is necessary to control the laser spot size incident on the medium surface according to the energy of the laser pulse, and select a suitable medium thickness so that the influence of self-focusing is not enough to destroy the transmission mode characteristics of the light beam. In other words, there is a strong competitive relationship between wide spectrum broadening and good output mode. It is very difficult to balance the relationship between the two to obtain a good spectrum broadening effect - this requires careful experimental exploration based on the characteristics of each sample (even each sample) to obtain suitable laser radiation conditions. For non-professional researchers, this technology does not have practical application conditions.

[0005] On the other hand, a more serious problem is that long-term high-energy ultrashort pulse radiation can cause significant material aging in transparent solid media: strong laser radiation can greatly enhance the absorption of laser light in the dielectric material due to the increase of defects, and also cause the appearance of transverse mode instability phenomena such as filamentation and fission. As the radiation time increases, these phenomena will form positive feedback (incubation effect) and become more and more significant, resulting in a significant reduction in pulse spectrum broadening, deterioration of beam mode, and significant reduction in energy. Accompanied by the incubation effect, permanent optical damage gradually appears inside the medium, and even severe ablation damage may eventually occur on the surface due to heat accumulation. This material aging phenomenon caused by strong laser radiation intensifies as the pulse radiation power density approaches the material laser damage threshold, that is, as the pulse energy increases, the faster the transparent solid medium ages, the faster permanent optical damage will appear. However, the spectral broadening of the pulse is significantly positively correlated with the radiation power density of the pulse. In order to pursue a wider spectral broadening, the radiation power density will inevitably approach the material damage threshold. Therefore, for conventional spectral broadening technology based on transparent solid media, the high performance of spectral broadening and the long-term high stability of its output cannot be achieved at the same time: to obtain excellent spectral broadening characteristics, it is necessary to sacrifice the service life of the material. This is the most important obstacle to the promotion and application of this technology, especially commercial applications.

[0006] Due to the above-mentioned problems of the ultrashort pulse spectrum broadening technology based on bulk solid media, this technology has not shown a clear application prospect, and therefore has not received much attention in the field for a long time. In recent years, an ultrashort pulse spectrum broadening technology based on solid thin slices (thin slice groups) has rekindled researchers' enthusiasm for solid medium spectrum broadening technology. Different from the method based on bulk solid media, this method based on solid thin slice groups uses multiple wide-bandgap transparent dielectric thin slices (such as fused silica thin slices) with a thickness of about 0.1 mm and are placed at a certain distance near the focal point of the ultrashort pulse to realize the strong-field nonlinear optical effect between the ultrashort pulse and the solid thin slice group, thereby achieving spectrum broadening. Unlike bulk solids, solid thin slices can separate the spectral broadening process from the self-focusing filamentation (including multifilamentation) process, so that the interaction between ultrashort pulses and thin slices only induces significant spectral broadening without causing self-focusing filamentation and multifilamentation: spectral broadening mainly comes from the self-phase and cross-phase modulation caused by the optical Kerr effect in the time domain. Under the condition of sufficiently high radiation power density, ultrashort pulses incident on dielectric thin slices can directly produce strong self-phase and cross-phase modulation without going through the self-focusing process to induce significant spectral broadening; while self-focusing comes from the spatial distribution of the medium refractive index change caused by the optical Kerr effect in the air domain, which requires the accumulation of a certain action distance to produce significant effects. Therefore, when the thickness of the thin slice is small enough, the ultrashort pulse passing through the thin slice can produce significant spectral broadening without producing significant self-focusing and filamentation effects. In addition to avoiding the problems caused by the self-focusing effect, the spectral broadening technology of solid thin slice groups also provides a richer and more flexible adjustment dimension than bulk transparent media. For example, when a single solid sheet is not sufficient to produce sufficient spectral broadening, a cumulative spectral broadening effect can be produced by placing multiple solid sheets at specific intervals near the laser focus as needed, ultimately forming a broadband supercontinuum spectrum, which can obtain ultrashort pulse output of the order of periods after time domain compression.

[0007] The above-mentioned significant advantages of solid thin slice (thin slice group) spectrum broadening technology have aroused widespread interest among researchers in related fields. In recent years, the development of more related research and the presentation of results have promoted the understanding of the interaction characteristics between ultrashort pulses and solid thin slices, while also revealing some shortcomings of this technology. Among them, the most notable is that although the solid thin slice technology has achieved the separation of spectrum broadening and filamentation process, the thin slice solid medium and the bulk solid medium are essentially the same matrix material, so the two have similar aging characteristics under the same strong ultrashort pulse radiation, that is, the above-mentioned aging problems that the bulk solid medium system needs to face will also be encountered in the thin slice solid medium system, which is an important technical problem that the solid medium thin slice spectrum broadening technology cannot avoid. In fact, compared with the bulk solid, the ultrashort pulse transmission through the solid thin slice corresponds to a shorter nonlinear action distance, so when using solid thin slices for spectrum broadening, a higher pulse radiation power density needs to be applied to obtain significant spectrum broadening. Therefore, to obtain a similar spectrum broadening effect, the thin slice medium needs to withstand stronger radiation than the bulk solid medium, and will age faster during the radiation process. For the ultrashort laser pulse spectrum broadening technology based on solid thin films, the continuous and rapid aging characteristics of the material under high radiation power density will have a significant adverse effect on the stability of its output supercontinuum spectrum, such as causing the supercontinuum output power to continue to decrease, the spectrum broadening width to continue to narrow, and the fundamental transverse mode characteristics of the output beam to gradually deteriorate.

[0008] In short, the continuous and rapid aging characteristics of dielectric materials under strong ultrashort pulse radiation are an unavoidable inherent technical difficulty for the actual long-term stable industrial application of solid thin film (thin film group) spectral broadening technology. It is a direct technical bottleneck hindering the commercial application of this technology and urgently needs new technologies to achieve breakthroughs. Summary of the invention

[0009] In order to solve the problem of material aging caused by strong laser radiation in the above existing solid thin film supercontinuum technology, the present invention provides a method for generating a high-stability supercontinuum light source based on a solid thin film.

[0010] In order to achieve the above-mentioned purpose of the present invention, the technical scheme adopted is as follows:

[0011] A method for generating a high-stability supercontinuum light source based on a solid sheet, wherein the method steps are as follows:

[0012] S1: placing at least one solid sheet on a two-dimensional or multi-dimensional micro-displacement platform;

[0013] S2: After the ultrashort laser pulse is focused and incident on a certain irradiated area on the front surface of the solid slice, nonlinear optical effects are generated during the propagation process in the solid slice, thus achieving spectrum broadening;

[0014] S3: At the same time, an optical power sensor is used to sample and detect the ultrashort laser pulses after interacting with the solid slice, so as to achieve real-time measurement and recording of the sampling beam power;

[0015] S4: Based on the detected power value, calculating the change amplitude of the real-time power relative to the initial power, thereby obtaining a quantitative evaluation of the aging of the solid sheet;

[0016] S5: The main control system sends out control instructions to control the micro-displacement platform to move according to a pre-set motion mode, thereby realizing continuous updating of the irradiation area of ​​the solid slice, thereby realizing an ultrashort pulse light source that produces a high-stability supercontinuum spectrum.

[0017] The beneficial effects of the present invention are as follows:

[0018] In the process of ultrashort pulse irradiation of solid thin slices to produce supercontinuum, long-term high-intensity ultrashort laser pulse irradiation will cause significant aging of solid thin slice dielectrics: strong light irradiation induces the random generation of lattice defects in the material and the non-uniform change of the refractive index, which leads to significant enhancement of the material's absorption of lasers and also easily leads to the appearance of laser filamentation. As the irradiation time of strong lasers increases, these phenomena become more and more significant due to the incubation effect, which in turn causes permanent optical damage inside or on the surface of the solid thin slice medium, and even leads to severe ablation damage on the surface of the medium due to the heat accumulation caused by absorption. The continuous aging of transparent dielectric materials caused by the above-mentioned strong light irradiation will significantly reduce the spectral broadening of the supercontinuum generated by ultrashort pulse irradiation of solid thin slices, deteriorate the beam transverse mode mode, and significantly reduce the pulse energy, thereby greatly hindering the long-term and highly stable operation of the supercontinuum light source based on solid thin slice technology. The method of the present invention aims at the above-mentioned technical difficulties of the solid thin slice supercontinuum source, and obtains a quantitative evaluation of the aging of the solid thin slice by real-time monitoring of the variation of the beam power in the process of ultrashort laser pulse irradiation of the solid thin slice to generate the supercontinuum, and controls the solid thin slice to move according to a pre-set motion mode based on the evaluation, so as to realize the continuous updating of the irradiation area of ​​the solid thin slice during the long-term irradiation of the strong laser, thereby effectively avoiding the continuous accumulation of the aging process of the dielectric material in the irradiation area in time and space, and creating suitable material and physical conditions for the long-term stable output of the supercontinuum. That is, the present invention realizes the continuous updating of the irradiation area of ​​the thin slice by real-time and quantitative evaluation of the aging of the solid thin slice irradiated by the strong ultrashort laser pulse, and introduces the automatic control technology to realize the continuous updating of the irradiation area of ​​the thin slice, which effectively avoids the serious aging of the dielectric material in the irradiation area, thereby greatly reducing the influence of the material aging phenomenon on the power stability, spectral broadening degree, and transverse mode characteristics in the process of supercontinuum generation, and finally realizes the long-term high-stability output of the supercontinuum light source based on the solid thin slice technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1It is a flowchart of the method for generating a high-stability supercontinuum light source based on a solid slice according to the present invention.

[0020] Figure 2 The present invention provides a light path principle diagram of the method for generating a high-stability supercontinuum light source.

[0021] Figure 3 This is another optical path principle diagram of the method for generating a high-stability supercontinuum light source described in the present invention.

[0022] Figure 4 There are three pre-set motion modes for updating the ultrashort pulse irradiation area on solid thin sheets.

[0023] Figure 5 It is a motion trajectory for updating the ultrashort pulse irradiation area on a square solid sheet.

[0024] Figure 6 It is another motion trajectory for updating the ultrashort pulse irradiation area on a square solid sheet.

[0025] Figure 7 It is another motion trajectory for updating the ultrashort pulse irradiation area on a square solid sheet.

[0026] Figure 8 It is a motion trajectory for updating the ultrashort pulse irradiation area on a circular solid sheet.

[0027] Fig. 9 It is another motion trajectory for updating the ultrashort pulse irradiation area on a circular solid sheet.

[0028] In the figure, 1-femtosecond laser; 2-continuous attenuation plate; 3-variable aperture; 4-plano-convex lens; 5-solid thin film; 6-optical power sensor; 7-main control system; 8-micro-displacement platform; 9-beam splitter. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1

[0031] For the technology of generating supercontinuum based on irradiating solid thin slices (thin slice groups) with ultrashort laser pulses, the continuous aging characteristics of dielectric materials under high laser irradiation intensity will have a significant adverse effect on the stability of its supercontinuum output, such as causing the output power to continue to decrease, the spectrum broadening to become narrower, and the transverse mode characteristics of the output beam to continue to deteriorate. In other words, the inevitable aging of dielectric materials caused by strong laser irradiation is an important reason that hinders the long-term stable industrial application of this supercontinuum generation technology. The present invention focuses on this inherent problem of solid thin slice supercontinuum technology and proposes a method for generating a high-stability supercontinuum light source based on a solid thin slice, such as Figure 1 As shown, the details are as follows:

[0032] S1: placing at least one solid sheet on a two-dimensional or multi-dimensional micro-displacement platform;

[0033] S2: After the ultrashort laser pulse is focused and incident on a certain irradiated area on the front surface of the solid slice, nonlinear optical effects are generated during the propagation process in the solid slice, thus achieving spectrum broadening;

[0034] S3: At the same time, an optical power sensor is used to sample and detect the ultrashort laser pulses after interacting with the solid slice, so as to achieve real-time measurement and recording of the sampling beam power;

[0035] S4: Based on the detected power value, calculating the change amplitude of the real-time power relative to the initial power, thereby obtaining a quantitative evaluation of the aging of the solid sheet;

[0036] S5: The main control system sends out control instructions to control the micro-displacement platform to move according to a pre-set motion mode, thereby realizing continuous updating of the irradiation area of ​​the solid slice, thereby realizing an ultrashort pulse light source that produces a high-stability supercontinuum spectrum.

[0037] In a specific embodiment, Figure 2As shown, the ultrashort laser pulse output by the femtosecond laser 1 is converged sequentially through a continuous attenuation plate 2 for controlling the single pulse energy of the ultrashort laser pulse, a variable aperture 3 for controlling the diameter of the incident ultrashort laser pulse beam, and a plano-convex lens 4 for focusing, and then incident on a certain irradiation area on the front surface of the solid thin slice 5. The irradiation light intensity generated by the ultrashort laser pulse on the surface of the solid thin slice 5 can cause the incident ultrashort laser pulse to produce a significant nonlinear optical effect with the solid thin slice 5, and at the same time, the aging time constant of the solid thin slice 5 can be in the "hour" time scale. In this embodiment, the ultrashort laser pulse output by the femtosecond laser 1 is converged by the plano-convex lens 4 and irradiated on the front surface of the solid thin slice 5. The irradiation light intensity generated can cause the incident ultrashort laser pulse to produce a significant nonlinear optical effect with the solid thin slice. Specifically, the femtosecond laser 1 used in this embodiment has a central wavelength of 800nm, a pulse width of 50fs, a repetition frequency of 1KHz, and a beam diameter of 8.5mm (1 / e 2 width), and the polarization is linear polarization in the horizontal direction. The solid thin sheet 5 used is a quartz glass thin sheet with optically polished front and back surfaces, with a thickness of 0.1 mm and a square light-transmitting surface size of 10 mm×10 mm. Among them, the ultrashort laser pulse output by the femtosecond laser can be controlled by a single pulse energy through a continuous attenuation sheet 2, and the transverse mode of the beam with Gaussian distribution can be further controlled in diameter by a variable aperture 3 placed in the center of the laser beam, and the subsequent converging operation should be achieved by selecting a plano-convex lens 4 with a suitable focal length according to the irradiation conditions generated by the supercontinuum spectrum. In general, the beam diameter of the focused spot of a collimated beam is proportional to the focal length of the converging lens and inversely proportional to the diameter of the incident beam. Therefore, by adjusting the continuous attenuation plate 2 to control the energy of the incident ultrashort pulse, adjusting the variable aperture 3 to control the diameter of the incident ultrashort pulse beam, and selecting plano-convex lenses 4 with different focal lengths, the instantaneous light intensity irradiated on the solid thin slice 5 can be flexibly controlled, thereby obtaining suitable conditions for ultrashort laser pulses to irradiate the solid thin slice to produce a supercontinuum spectrum: the converged ultrashort laser pulses can produce strong nonlinear optical effects with the solid thin slice to significantly broaden its own spectrum, and at the same time, the irradiation intensity will not cause rapid laser-induced destruction of the solid thin slice (although the dielectric material will still undergo cumulative structural changes or even ablation destruction under long-term irradiation of laser of this intensity).

[0038] For example, in a typical irradiation parameter setting, the variable aperture 3 is fully opened, that is, the femtosecond laser Gaussian beam is not affected by the variable aperture 3, and the focal length of the plano-convex lens 4 is selected to be 2.0m, and the diameter of the waist of the convergent Gaussian beam is about 0.24mm. Under this convergence condition, typically, when the laser irradiation power is 370mW, although the ultrashort laser pulse propagates in the air without self-focusing filamentation, and the ultrashort laser pulse irradiation of the solid thin film 5 can produce significant spectrum broadening, the irradiated area of ​​the solid thin film 5 will rapidly undergo ablation damage on a time scale close to 1 minute (if the time interval from initial irradiation to ablation damage is defined as the aging time constant, the aging time constant is close to 1 minute at this time). However, by adjusting the continuous attenuation plate 2 to reduce the laser irradiation power to 250mW, the solid thin film 5 will not undergo ablation damage under laser irradiation for more than 1 hour (the aging time constant is greater than 1 hour), and only the laser transmittance will decrease due to cumulative structural changes, that is, the output power of the supercontinuum spectrum will decrease. Moreover, under this convergence condition, when the irradiation power is 250mW, the spectrum width of the supercontinuum generated by ultrashort laser pulse irradiation of solid thin slices is close to saturation. Therefore, this irradiation condition can be used as a suitable condition for ultrashort laser pulse irradiation of solid thin slices to generate supercontinuum.

[0039] For another example, in another typical irradiation parameter setting, the variable aperture 3 is adjusted to a 2 mm aperture, and the focal length of the plano-convex lens 4 is selected to be 0.10 m. At this time, the diameter of the Airy disk formed by the convergence of the flat-top beam is about 0.10 mm. Under this convergence condition, typically, when the laser irradiation power is 68 mW, the ultrashort laser pulse irradiation of the solid thin film 5 can produce significant spectrum broadening, but the irradiated area of ​​the solid thin film 5 will quickly undergo ablation damage on a time scale close to 1 minute (the aging time constant is close to 1 minute). However, by adjusting the continuous attenuation plate 2 to reduce the laser irradiation power to 46 mW, the solid thin film 5 will not undergo ablation damage (the aging time constant is greater than 1 hour) under laser irradiation for more than 1 hour, and only the transmittance will decrease due to the cumulative structural change, that is, the output power of the supercontinuum spectrum will decrease. Moreover, under this convergence condition, when the irradiation power is 46 mW, the spectrum width broadening of the supercontinuum spectrum generated by the ultrashort laser pulse irradiation of the quartz thin film is also close to saturation. Therefore, this irradiation condition can also be used as a suitable condition for producing supercontinuum spectrum by irradiating solid thin slices with ultrashort laser pulses.

[0040] In a specific embodiment, in step S1, a solid sheet 5 is placed on a two-dimensional micro-displacement platform 8 to achieve the purpose of the system continuously and automatically updating the laser irradiation area during the long-term irradiation of the sheet by the strong laser. In this embodiment, the displacement range of the two-dimensional micro-displacement platform 8 or the multi-dimensional micro-displacement platform should be able to cover the entire light-transmitting surface of the solid sheet 5, and the displacement path of the two-dimensional or multi-dimensional micro-displacement platform can be pre-set and stored in the main control system, so that the solid sheet 5 can be scanned and irradiated with ultra-short laser pulses according to the set path. On the other hand, since the sampling detection of the ultra-short laser pulse after the solid sheet is acted on in this embodiment is achieved by directly detecting the power of the reflected laser beam after the solid sheet 5 is acted on, the surface normal of the solid sheet 5 needs to form a non-0 degree angle with the transmission direction of the incident ultra-short laser pulse, so that the reflected ultra-short laser pulse beam is spatially separated from the incident ultra-short laser pulse beam, and then the detection of the reflected ultra-short laser pulse beam can be achieved. In fact, the laser irradiation condition of the solid sheet 5 is generally set to the Brewster angle to minimize the reflection loss of the solid sheet 5. Taking into account the requirements of sampling power and the above-mentioned anti-reflection requirements, the angle between the surface normal of the solid sheet 5 and the transmission direction of the incident light in this embodiment is set to be close to the Brewster angle, rather than the Brewster angle, so as to retain the appropriate reflected light power for sampling and monitoring. Under this laser incident angle setting, in order to ensure that the spatial position of the laser irradiated sheet in the beam propagation direction remains unchanged when the solid sheet 5 is updated to the new irradiation area (so that the laser irradiation light intensity remains consistent after the solid sheet 5 updates the irradiation area), the two mutually perpendicular displacement axis directions of the micro-displacement platform with a two-dimensional translation function should be set to be within the light-transmitting surface of the solid sheet 5, and in this embodiment, they are respectively along the horizontal direction (horizontal axis) and the vertical direction (vertical axis or y-axis) to match the laser polarization condition along the horizontal direction. For the solid sheet 5 with a square light-transmitting surface in this embodiment, when it is placed on the micro-displacement platform, the ideal placement scheme that meets the above requirements is to make the two mutually perpendicular side directions of the solid sheet 5 respectively along the two mutually perpendicular displacement directions of the micro-displacement platform, so that the subsequent irradiation area update operation can fully utilize the light-transmitting area of ​​the solid sheet 5. Then, the operation of adjusting the laser incident angle of the solid slice 5 is achieved by directly rotating the micro-displacement platform along the y-axis.

[0041] The two-dimensional micro-displacement platform in this embodiment can also be expanded to a three-dimensional micro-displacement platform. For a three-dimensional micro-displacement platform, typically, the directions of its three mutually perpendicular displacement axes can be set to be respectively along the incident light transmission direction (z-axis), and along the horizontal direction (x-axis) and vertical direction (y-axis) in the plane perpendicular to the incident light transmission direction. Under the condition of having three-dimensional motion capability, the micro-displacement platform can ensure that when the solid thin slice 5 placed arbitrarily on the micro-displacement platform updates the irradiation area, the spatial position of the laser irradiated thin slice in the direction of light beam propagation remains unchanged through one-axis, two-axis or three-axis motion, without considering the above-mentioned special direction association requirements between the two when the two-dimensional micro-displacement platform places the solid thin slice, so the solid thin slice has greater adjustment flexibility. For example, the operation of adjusting the laser incident angle of the solid thin slice 5 placed on the three-dimensional micro-displacement platform 8 can be achieved by keeping the micro-displacement platform fixed and rotating the solid thin slice along the y-axis.

[0042] One solid sheet 5 in this embodiment can also be expanded into a solid sheet group, that is, in addition to placing one solid sheet 5 near the focal point of the ultrashort laser pulse, two or more solid sheets can also be placed at a certain interval near the focal point of the ultrashort laser pulse to achieve two-level or multi-level spectrum broadening of the ultrashort laser pulse irradiated solid sheets, thereby greatly improving the spectrum broadening capability of the solid sheet spectrum broadening technology. For this solid sheet group, there are two typical forms of micro-displacement platform settings: one is that all solid sheets are placed on the same micro-displacement platform, that is, all solid sheets update the radiation area position at the same time; the other is that each solid sheet is placed on a micro-displacement platform, so that the aging of each sheet can be monitored separately, and the irradiation area of ​​each solid sheet can be updated separately.

[0043] In a specific embodiment, in step S2, the high-energy ultrashort laser pulse generates spectrum broadening due to nonlinear optical effects during propagation in the solid thin slice 5, forming a supercontinuum spectrum ultrashort pulse output. Specifically, after the ultrashort laser pulse is incident on a certain irradiation area on the front surface of the solid thin slice 5, it will propagate in the solid thin slice medium. As described above, by adjusting the continuous attenuation plate 2 and the variable aperture 3, and selecting the plano-convex lens 4 with different focal lengths, the instantaneous light intensity irradiated on the solid thin slice 5 can be controlled to be in a suitable irradiation condition window for the ultrashort laser pulse to interact with the solid thin slice to produce a supercontinuum spectrum, such as the two typical irradiation parameter settings listed above. Under these irradiation conditions, since the laser irradiation intensity is in a physical action intensity window where third-order nonlinear optical effects such as self-phase modulation, cross-phase modulation, four-wave mixing, and stimulated Raman scattering occur significantly, the incident ultrashort laser pulse will produce the above-mentioned third-order nonlinear optical effects with the solid thin slice medium during propagation in the solid thin slice, resulting in significant spectrum broadening, and forming a supercontinuum spectrum ultrashort pulse output after passing through the solid thin slice.

[0044] In this embodiment, the above two typical irradiation parameter settings can be used to expand the spectral bandwidth (full width at half maximum) of the ultrashort laser pulse from 30nm to 60nm after the incident ultrashort laser pulse initially interacts with a solid thin sheet, and the pulse energy utilization rate can be close to 95%. However, under the condition that the irradiation area is fixed, as the irradiation time increases, the above spectral bandwidth expansion amplitude and pulse energy utilization rate of the output supercontinuum ultrashort pulse will gradually decrease. When the solid thin sheet is moved to update the irradiation area, the spectral bandwidth expansion amplitude and pulse energy utilization rate of the output supercontinuum ultrashort pulse will return to the initial value.

[0045] In a specific embodiment, in step S3, the reflected light beam generated by the converged high-energy ultrashort laser pulse on the front and rear surfaces of the solid slice 5 is collected by the optical power probe 6, and transmitted to the main control system 7 after photoelectric conversion, so as to realize the real-time measurement, recording and monitoring of the power of the reflected laser beam. In this embodiment, it is necessary to sample and detect the high-energy ultrashort laser pulse after the solid slice 5, so as to realize the real-time measurement and monitoring of the power of the sampled ultrashort laser pulse beam. In fact, the ultrashort laser pulse irradiating the solid slice will generate reflection on the front and rear surfaces of the solid slice, and the reflected light beam can be used as a sampling beam to monitor the change of the laser power after the solid slice 5. That is, the sampling detection of this embodiment is realized by detecting the ultrashort laser pulse beam reflected after the solid slice 5.

[0046] It should be noted that the reflected light beam detected in this embodiment includes the reflected light from the front surface and the back surface of the solid sheet 5. The reflected light from the front surface reflects the reflection generated during the interaction between the incident ultrashort laser pulse and the front surface of the solid sheet, while the reflected light from the back surface reflects the reflection generated during the interaction between the supercontinuum ultrashort pulse after spectrum broadening and the back surface of the solid sheet. Both of them will have a decrease in reflectivity due to aging or damage on the surface and inside of the solid sheet. In the process of power monitoring of the reflected light beam, the optical power probe 6 with a sufficiently large detection area completely collects the reflected light from the front and back surfaces to ensure the stability of the measured power data during long-term detection and reduce the influence of beam jitter on data accuracy.

[0047] In this embodiment, the angle between the surface normal of the solid sheet 5 and the transmission direction of the incident light is set to 45 degrees, which is close to but not equal to the Brewster angle (56 degrees) of quartz glass, so as to ensure that under the above-mentioned typical irradiation parameter setting conditions, suitable reflected light power can be retained for the probe 6 to achieve stable low-noise detection.

[0048] For example, under the conditions of the above-mentioned laser incident angle and the first irradiation parameter setting, the reflected light beam power value generated by the incident laser with a power value of 250mW irradiating the solid thin film 5 is approximately 85μW; under the conditions of the above-mentioned laser incident angle and the second irradiation parameter setting, the reflected light beam power value generated by the incident laser with a power value of 46mW irradiating the solid thin film 5 is approximately 16μW: these two reflected light beam power values ​​can ensure that the optical power probe 6 used in this embodiment is in a high-sensitivity and low-noise detection range.

[0049] In the detection setting of this embodiment, a silicon photoelectric power sensor with an effective detection area of ​​10mm×10mm is used to realize the complete collection of the reflected light beam. In addition, since the reflected light beam is emitted by a converging light beam close to the beam waist, it has a divergent characteristic. The silicon photoelectric sensor should be placed at a suitable distance from the solid thin slice to avoid the detection signal from having nonlinear or even saturated characteristics due to the ultrashort pulse instantaneous irradiation intensity on the probe surface being too high, or the beam divergence being too large to achieve complete collection. In addition, to avoid the probe from having nonlinear or even saturated characteristics due to the instantaneous irradiation intensity being too high, before the reflected ultrashort laser pulse enters the probe, the reflected ultrashort laser pulse can be attenuated by a neutral filter before entering the probe.

[0050] For example, corresponding to the first irradiation parameter setting, the silicon photoelectric probe 6 is placed centered relative to the reflected light beam at a distance of 50 cm from the irradiation point of the solid thin film 5, and a suitable neutral filter is arranged in front of the probe to attenuate the incident ultrashort laser pulse (placing the filter close to the probe can also reduce the influence of ambient light) to avoid nonlinear characteristics of the signal detected by the probe.

[0051] The probe 6 converts the collected optical signal into an electrical signal and transmits it to the main control system 7, which then records and presents the real-time collected power data, thereby achieving real-time measurement, recording and monitoring of the reflected ultrashort laser pulse beam power.

[0052] In a specific embodiment, in step S4, the main control system 7 further calculates the real-time change amplitude of the detected real-time power relative to the initial power based on the detected power value of the reflected laser beam, and obtains a real-time, quantitative evaluation of the aging of the solid thin film 5 irradiated by the ultrashort laser pulse. Generally speaking, as the irradiation time of the strong ultrashort laser pulse increases, the irradiated area of ​​the solid thin film will gradually age, resulting in a gradual increase in the material's absorption of the irradiated laser. This gradual increase in the absorption of the irradiated laser is fed back to the reflected light beam, causing the power of the detected reflected light beam to gradually decrease, and the decrease amplitude of the reflected light is positively correlated with the increase amplitude of the absorption of the irradiated light. Therefore, by detecting the real-time decrease amplitude of the reflected light, the aging of the solid thin film can be evaluated in real time and quantitatively.

[0053] Theoretically, the aging rate of solid thin films is directly related to the irradiation laser intensity and shows significant nonlinear evolution characteristics: as the irradiation laser intensity gradually increases and approaches the single-pulse damage threshold, the aging rate of solid thin films will become faster and faster. The time interval from initial irradiation to ablation damage, that is, the aging time constant (Δt d ) will become shorter and shorter. In fact, when the aging rate of the solid sheet is in a relatively fast range (such as Δt d On the time scale of "minutes", the aging process of solid sheets will become more random (such as Δt d The uncertainty will increase), which is not conducive to the stable output of the supercontinuum spectrum and the closed-loop feedback control of the system. Therefore, in order to avoid the excessive aging of the solid sheet during the supercontinuum generation process and cause various adverse effects, in practical applications, the laser irradiation intensity should be controlled to make the solid sheet aging speed in a relatively slow range. For example, the laser power selection corresponding to the typical irradiation parameter settings in the above two examples can make the solid sheet in the slow aging range, and its Δt d On an "hour" time scale.

[0054] In a specific embodiment, in step S5, based on the evaluation of the aging condition of the solid thin slice, the main control system 7 issues an instruction to control the movement of the micro-displacement platform, so that the micro-displacement platform 8 moves according to a preset mode, thereby achieving continuous updating of the irradiation area of ​​the thin slice during the long-term irradiation of the solid thin slice 5 by the strong laser.

[0055] In this embodiment, based on the evaluation of the aging of the solid sheet, this embodiment can adopt one of the following preset solid sheet motion control modes to achieve continuous position update of the solid sheet irradiation area, such as Figure 4 As shown in the preset motion mode 1 in the figure: the main control system monitors the decrease in the sampling beam power. When the decrease in the beam power is greater than a preset first threshold, the main control system controls the micro-displacement platform to move along a preset path with an update motion spacing greater than the irradiation spot diameter.

[0056] Specifically, the solid slice can be evenly divided into several radiation areas according to the size of the solid slice, the diameter of the irradiation spot of the ultrashort laser pulse, and the incident angle formed by the incident ultrashort laser pulse and the solid slice; by setting a first threshold of the beam power drop amplitude as a trigger condition for the movement of the solid slice, when the beam power drop amplitude is greater than the preset first threshold, the main control system controls the micro-displacement platform to perform corresponding movement, so that the radiation area of ​​the ultrashort laser pulse is switched from the current radiation area to the adjacent radiation area, thereby realizing the spatial fixed-point and time-discrete update of the irradiation area of ​​the solid slice.

[0057] In the solid sheet motion control mode described in this embodiment, when the real-time decrease in the detection laser power is greater than a preset first threshold, the main control system 7 will issue an instruction to control the movement of the micro-displacement platform 8, so that the solid sheet irradiation area is updated by the micro-displacement platform moving a preset distance along a preset path. Specifically, the setting of the first threshold needs to focus on two factors.

[0058] First, the first threshold should not be set too small, because the beam power of the incident ultrashort pulse laser is not absolutely stable, and it will inevitably have certain random or systematic fluctuations over time, and this intrinsic beam power noise may cause false triggering of the threshold condition. Among them, for the case of random noise, the measured power value statistically presents a normal distribution with a specific average power and power standard deviation. According to the characteristics of the normal distribution, the probability of 1 times the standard deviation is 68.26895%, the probability of 2 times the standard deviation is 95.44997%, the probability of 3 times the standard deviation is 99.73002%, the probability of 4 times the standard deviation is 99.99367%, and the probability of 5 times the standard deviation is 99.99994%. Considering the detection time with a time scale of "hours" and the number of sampling detections in the thousands, it can be seen from the above data that when the first threshold is set to be equal to or greater than 4 times the standard deviation of the incident beam power, a lower probability of false triggering of the laser power can be obtained; and when the first threshold is set to be equal to or greater than 5 times the standard deviation of the incident beam power, it can be ensured that the reason for triggering the first threshold of the power is almost always caused by the aging of the solid sheet, rather than the power noise of the laser. Therefore, in order to avoid false triggering of the first threshold condition as much as possible, the first threshold described in this embodiment is set to be equal to or greater than 5 times the standard deviation of the ultrashort pulse laser power.

[0059] Specifically, when the first threshold is set to 5 times the standard deviation of the ultrashort pulse laser power, considering a single measurement, the probability of random noise triggering the first threshold condition is only 0.00006%, which is less than one in a million. Considering 1,000 measurements, the probability of random noise triggering the first threshold condition is also only 0.06%, which is less than one in a thousand. That is, for the ultrashort laser pulse light source with a power root mean square error <0.5% (RMSE, 24 hours of continuous measurement) used in this embodiment, when the first threshold is set to a power drop of 2.5%, which is approximately equal to 5 times the standard deviation of the laser power, the probability of the laser power noise triggering the first threshold condition is almost negligible.

[0060] In addition, in order to further reduce the input laser power noise, especially the influence of long-term systematic fluctuations of laser power caused by environmental changes on the stability of power measurement, and thus further reduce the probability of false triggering of the first threshold condition, the input laser beam power before interacting with the solid sheet can be sampled and detected in real time. I (t), by measuring the laser sampling power W after the probe 6 in real time R (t) and the initial input laser sampling power W before action I (0) and the real-time input laser sampling power W I The corrected laser sampling power after the effect is obtained by multiplying the ratio of (t): W Rr (t) = W R (t)·W I (0) / W I (t), the laser power noise is cancelled and the influence of the input laser power noise on the measured power after the action is significantly reduced, so that the real-time measured power after the action can more truly reflect the degree of aging of the solid sheet.

[0061] On the other hand, by increasing the sampling integration time when the probe 6 is used to detect the laser power, the influence of short-term random noise of the laser power can be effectively reduced, and more stable laser power data can be obtained.

[0062] Secondly, under the condition that the threshold setting lower limit requirement is met, the threshold should be set in an interval near the lower limit, such as an interval of 1.0 to 1.5 times the lower limit, so as to avoid the threshold being too large, resulting in the characteristics (power and spectrum broadening) of the supercontinuum output by the system before the irradiation area is updated. For the high-stability supercontinuum light source technology of automatically updating the irradiation area of ​​the solid sheet in the embodiment, the stability of the long-term output of the supercontinuum is determined by the set threshold. For example, if the threshold set above is that the beam power decreases by more than 2.5%, the maximum decrease in the power curve of the long-term output of the supercontinuum will be anchored at 2.5%, and it will show a characteristic of approximately periodic appearance, reflecting the periodic fluctuations of the curve caused by systematic reasons. That is, the larger the threshold setting, the greater the periodic fluctuations, and the more the supercontinuum light source deviates from the high-stability working characteristics; the smaller the threshold setting, the smaller the periodic fluctuations, and the supercontinuum light source can obtain a smaller systematic deviation, achieving better high-stability working characteristics.

[0063] Therefore, taking into account the above two factors of threshold setting, in this embodiment, the first threshold is directly set to the threshold lower limit required for almost completely avoiding noise false triggering, that is, the threshold is 5 times the standard deviation of the ultrashort pulse laser power.

[0064] In this embodiment, a pre-set threshold is stored in the main control system. When the main control system monitors that the decrease in the power of the detection beam is greater than the threshold, the main control system 7 will issue an instruction to control the movement of the micro-displacement platform 8. The instruction contains the displacement movement instruction of one, two or three displacement axes in the two-dimensional or three-dimensional micro-displacement platform, specifically involving the movement direction (forward or reverse) and movement distance of each displacement axis that needs to move. Based on the light-transmitting area of ​​the solid sheet, the irradiation spot diameter, and the incident angle of the ultrashort laser pulse, the movement path of the solid sheet can be reasonably planned in advance so that the light-transmitting area of ​​the solid sheet can be effectively utilized; the pre-planned movement path is stored in the main control system to realize the update of the ultrashort laser pulse irradiation area of ​​the solid sheet according to the set path. Generally speaking, the distribution of laser irradiation points in the solid sheet can be set in the form of a rectangular dot matrix to facilitate scanning path planning.

[0065] Specifically, according to the irradiation spot size determined by the above two typical irradiation parameter settings and the laser incident angle, the appropriate horizontal and vertical intervals between the center points of two adjacent irradiation areas can be obtained, so that the light-transmitting area of ​​the solid sheet can be fully utilized, and the rear irradiation area will not be affected by the aging of the front adjacent irradiation area. After determining the horizontal and vertical intervals between the center points of adjacent irradiation areas, the movement path of the solid sheet irradiation area during long-term irradiation can be set according to the size of the solid sheet and the laser incident angle, as well as the movement parameters of each micro-displacement axis when each irradiation area is updated.

[0066] For example, for the 10mm×10mm quartz glass used in this embodiment, when the irradiation spot diameter is 0.10mm and the incident angle is 45 degrees, it can be set to start irradiation at a point close to the upper left corner of the solid slice (such as a point 0.24mm and 0.20mm away from the left and upper edges respectively), and then first update the irradiation point at an interval of 0.28mm on the slice surface in the horizontal direction (corresponding to the setting of the above-mentioned two-dimensional platform, the horizontal displacement axis moves 0.28mm; corresponding to the setting of the above-mentioned three-dimensional platform, the x and z displacement axes move 0.20mm respectively). After scanning 35 irradiation points in the horizontal direction, the irradiation point reaches the upper right corner of the solid slice. At this time, the update of the next irradiation point needs to be completed by moving downward in the vertical direction on the slice surface at an interval of 0.20mm (corresponding to the setting of the above-mentioned two-dimensional or three-dimensional platform, the y displacement axis moves 0.20mm). Then, the update operation of the second row of irradiation points can be similar to the first row, moving in the opposite direction until it approaches the left edge of the solid slice. At this time, the irradiation point update operation will return to the first row by moving downward in the vertical direction at an interval of 0.20 mm. By repeating the above scanning operation, the light-transmitting area of ​​the entire solid sheet will be effectively utilized, and 35×49=1715 irradiation points can be obtained in the end. The schematic diagram of the movement path of the irradiation area of ​​the above solid sheet is shown in Figure 5As shown, it is pre-set and stored in the main control system. In fact, if the movement direction or initial position of the solid sheet irradiation area is changed, different movement paths with the same technical effect for this embodiment can be obtained, such as Figure 6 , 7 As shown, there are many possibilities for the motion path, which will not be listed here one by one.

[0067] In this embodiment, after the main control system 7 issues an instruction to control the movement of the micro-displacement platform 8, the micro-displacement platform will move a specific distance according to the above-mentioned pre-set path, so that the irradiation area of ​​the solid sheet is updated. For the solid sheet, if the average use time of each irradiation point is controlled to be greater than 1 hour, the total use time of this solid sheet will exceed 1715 hours, that is, the long-term high-stability output time of this supercontinuum light source can exceed 1715 hours, which is much longer than the solid sheet supercontinuum spectrum light source of this type without closed-loop control of irradiation area update and single-point irradiation. In fact, if the irradiation and movement parameters are kept unchanged, but the size of the solid sheet is expanded to 30mm×30mm, that is, the effective surface area becomes 9 times the original, then the total use time of the corresponding sheet will exceed 1715×9=15435 hours, that is, at this time, the long-term high-stability output time of the supercontinuum light source can exceed 15435 hours, which can meet the service life requirements of the entire operation cycle of general light source equipment. That is, the solid thin-film supercontinuum light source generated by the method described in this embodiment does not require replacement of the supercontinuum spectrum generating medium during its entire operating life cycle, thereby significantly reducing its operating and maintenance costs.

[0068] Generally, under the conditions of the determined irradiation parameter settings, the average use time of each irradiation point is determined by the laser irradiation power (determining the aging speed of the solid sheet, that is, the rate of decrease of the sampled power after the action) and the power decrease threshold (determining the ultimate aging degree of the solid sheet, that is, the ultimate decrease amplitude of the sampled power after the action). Therefore, when the power decrease threshold is set to a fixed value, such as when it is equal to 5 times the standard deviation of the ultrashort pulse laser power, the average use time of the irradiation point is only determined by the laser irradiation power. For the above two typical irradiation parameter settings of this embodiment, the laser irradiation power is set in the power range that makes the pulse spectrum broadening close to saturation. In fact, in this laser irradiation power range, the change of the laser irradiation power will cause a significant change in the aging speed (aging time constant) of the solid sheet, that is, the average use time of the irradiation point will change significantly, but the change of the pulse spectrum broadening is not significant. Therefore, this embodiment can obtain the average use time of the irradiation point that meets the above requirements by appropriately adjusting the laser irradiation power in the above laser irradiation power range, while also taking into account the requirements of pulse spectrum broadening.

[0069] The displacement motion mode of the two-dimensional or three-dimensional micro-displacement platform described in this embodiment is not limited to the above-mentioned translation motion mode, but also includes a rotation motion mode, or a combination of the two displacement motion modes of translation and rotation. For example, a two-dimensional micro-displacement stage composed of a one-dimensional translation stage and a one-dimensional rotation stage can also realize continuous position update of the irradiation area of ​​the solid sheet through the combined motion of the two displacement dimensions. In particular, when the solid sheet has a circular light-transmitting surface instead of the above-mentioned square light-transmitting surface, the two-dimensional micro-displacement stage composed of a one-dimensional translation stage and a one-dimensional rotation stage can fully utilize the irradiation area of ​​the circular light-transmitting surface of the solid sheet by setting a suitable two-dimensional motion scheme so that the irradiation spot forms a spiral scanning line on the disc, such as Figure 8 , 9 That is, for a circular solid sheet, compared with a pure translational two-dimensional displacement mode, this two-dimensional displacement mode of a combination of rotation and translation is a displacement motion mode that is more compatible with the sheet.

[0070] In addition, the material of the solid sheet described in this embodiment is not limited to quartz glass, but also includes various other transparent solid media that can be applied to supercontinuum generation, such as various common wide bandgap crystals or amorphous materials. The thickness of the solid sheet described in this embodiment is not limited to 0.10 mm, and its thickness can be flexibly adjusted according to actual application requirements. The number of solid sheets described in this embodiment is not limited to 1, and the number of solid sheets can be flexibly set according to actual application requirements.

[0071] Example 2

[0072] In this embodiment, in step S3, unlike the sampling detection of the ultrashort laser pulse reflected after interacting with the solid sheet in embodiment 1, the ultrashort laser pulse transmitted through the solid sheet after interacting with the solid sheet is split and sampled for detection. Figure 3 Specifically, when the ultrashort laser pulse passing through the solid sheet is further split for sampling and detection, a beam splitter 9 for beam splitting is arranged behind the solid sheet 5 to divide the emitted ultrashort laser pulse into two parts, one of which is output as a supercontinuum ultrashort pulse, and the other is a sampling beam, which is collected by an optical power probe and transmitted to the main control system after photoelectric conversion, so as to realize real-time measurement and monitoring of the power of the ultrashort laser pulse sampling beam, and then obtain the aging condition of the solid sheet.

[0073] Embodiment 1 uses the reflected light beam power of the high-energy ultrashort laser pulse after interacting with the solid sheet for real-time detection and monitoring. Compared with Embodiment 2, Embodiment 1 can directly use the reflected light beam of the solid sheet itself to realize real-time monitoring of the high-energy ultrashort laser pulse beam power after interacting with the solid sheet, without adding additional optical elements (Embodiment 2 needs to add an additional beam splitter 9 in the optical path), which is more concise and efficient in terms of optical path design; at the same time, Embodiment 1 uses the reflected light beam of the solid sheet for sampling, detection and monitoring, which will not affect the characteristics of the output supercontinuum (output power and spectral chirp characteristics), and effectively avoids the inevitable influence of Embodiment 2 on the ultrashort pulse characteristics of the output supercontinuum caused by inserting optical elements in the output optical path, and has higher practicality. Therefore, Embodiment 1 using the ultrashort laser pulse reflected after interacting with the solid sheet for sampling and detection is a better choice.

[0074] Example 3

[0075] Based on Example 1 or Example 2, for the preset solid sheet motion control mode adopted in step S5 of Example 1, this embodiment provides another preset solid sheet motion control mode, such as Figure 4 Specifically, the main control system controls the quasi-continuous motion of the micro-displacement platform, so that the ultrashort laser pulse scans the solid thin slice quasi-continuously according to the preset scanning path, thereby realizing the continuous updating of the irradiation area of ​​the thin slice during the long-term irradiation of the solid thin slice by the strong laser, thereby realizing the high-stability output of supercontinuum ultrashort pulses.

[0076] The main control system 7 described in this embodiment quasi-continuously issues instructions for controlling the movement of the micro-displacement platform 8 at a time interval much smaller than the aging time constant, so that the micro-displacement platform 8 moves quasi-continuously along a preset path at a specific movement interval significantly smaller than the irradiation spot diameter, so that the irradiation area of ​​the solid sheet is updated in a nearly continuous scanning manner in space and time. During the platform movement process, based on the monitoring of the decrease in the real-time sampling power, the average movement speed of the platform (average movement speed = update movement interval / update time interval) will be subject to the closed-loop optimization feedback control of the main control system 7, so that the decrease in the real-time sampling power of the solid sheet relative to the initial sampling power during the long-term irradiation process is stable and close to 0 or a smaller preset value, thereby improving the long-term stability of the supercontinuum spectrum ultra-short pulse output. Specifically, the average movement speed can be controlled by controlling the update movement interval alone, or the update time interval alone, or by controlling the update movement interval and the update time interval at the same time.

[0077] Since the preset solid sheet motion control mode described in Example 1 has the irradiation area update triggered by the power drop threshold, it has the characteristics of fixed point in space and discrete in time, which will cause the power curve of the supercontinuum output to show periodic jumps determined by the threshold drop amplitude. In addition, since the threshold should be set to be greater than the standard deviation of multiple incident laser power, this periodic fluctuation that determines the working stability of the supercontinuum light source will cause the stability of the output supercontinuum to be significantly lower than the stability of the incident laser.

[0078] In contrast, the preset solid sheet motion control mode described in this embodiment is not triggered by a threshold condition in the irradiation area update, so the problem of power periodic jump caused by the existence of the threshold in Example 1 will be well solved in this embodiment. It can be seen that the irradiation area update mode of this embodiment can bring higher stability performance to the output supercontinuum. In fact, since the movement speed of the micro-displacement platform in this embodiment will be subject to the closed-loop optimization feedback control of the main control system 7, it can make the monitored power drop less than the second threshold, which can also make the output of the supercontinuum obtain a very high stability.

[0079] In the preset solid sheet motion control mode of the present embodiment, the initial average motion speed is obtained based on the detection and evaluation of the solid sheet aging condition. Specifically, through steps S3 and S4, the data of the change of the solid sheet fixed-point irradiation power over time can be measured to obtain a quantitative evaluation of the solid sheet aging speed, such as obtaining a quantitative aging time constant, and then setting a suitable initial average motion speed (suitable irradiation update motion spacing and irradiation update time interval) based on the evaluation. Generally speaking, the set initial average motion speed should at least meet the time interval of the aging time constant, and the motion spacing of the irradiation area should be greater than the laser irradiation spot diameter, so as to avoid excessive aging accumulation of the irradiation area during the near-continuous scanning process, and even ablation damage. For example, corresponding to the average use time of 1 hour for each irradiation point in Example 1 (the aging time constant is greater than 1 hour), when the value of the initial average movement speed is set in this embodiment to satisfy the quasi-continuous movement of the micro-displacement platform in the horizontal direction by 0.28 mm in 1 hour, that is, the initial average movement speed in the horizontal direction is set to 0.28 mm / hour, in terms of irradiation effect, this embodiment and Example 1 can obtain similar solid sheet aging characteristics, so the initial average movement speed set in this way can effectively avoid serious aging of the solid sheet.

[0080] In fact, the quasi-continuous scanning irradiation method adopted in this embodiment (the front and rear irradiation spot areas overlap significantly) can make more full use of the area covered by the scanning path than the interval fixed-point irradiation method adopted in Example 1 (the front and rear irradiation spot areas avoid overlapping), thereby obtaining a larger effective irradiation area. Therefore, if the two solid sheet motion control modes use the same average motion speed, the material of this embodiment will show weaker aging characteristics. That is, this embodiment has more advantages in making full use of the sheet surface area and slowing down material aging.

[0081] It is worth noting that in this embodiment, the solid sheet adopts a quasi-continuous motion mode rather than a true continuous motion mode. Specifically, the main control system 7 issues an instruction to control the movement of the micro-displacement platform 8 at an update time interval that is much smaller than the aging time constant, so that the micro-displacement platform 8 moves at an update motion interval that is much smaller than the irradiation spot diameter. Since the update motion interval is set to be much smaller than the irradiation spot diameter and the update time interval is set to be much smaller than the aging time constant, this motion can be regarded as a quasi-continuous motion from the perspective of the spatial scale of the irradiation spot or the time scale of the aging time constant.

[0082] Although the motion patterns of Example 1 and this embodiment are essentially discrete motions in time and space, the relationship between the time interval for updating the irradiated area and the aging time constant, and the relationship between the motion interval for updating the irradiated area and the irradiation spot diameter determine that they have significantly different motion pattern characteristics and irradiation effects, which ultimately bring significant differences in the impact on the stability of the supercontinuum output. For example, in Example 1, the time interval for updating the position of the irradiated area is determined by the threshold trigger condition, and its typical value is 1 hour, while the corresponding horizontal motion interval of 0.28 mm is twice the irradiation spot diameter (under the condition of 45-degree oblique incidence of the irradiation laser), so this motion pattern is a typical discrete motion in time and space, and the resulting mutation of the irradiated area update will bring about significant periodic fluctuations in the ultrashort pulse output curve of the supercontinuum. The initial time interval and initial movement spacing (which jointly determine the initial average movement speed) of the irradiated area position update in this embodiment are determined by the movement parameters set by the main control system 7 (the parameters are obtained by evaluating the aging of the solid sheet in steps S3 and S4): Typically, when the update time interval is set to 45 seconds and the initial movement spacing is set to 0.0035 mm, this embodiment can not only obtain the average movement speed (0.28 mm / hour) consistent with that in Example 1, but also obtain an approximately quasi-continuous movement mode. Because the time interval (45 seconds) is much smaller than the aging time constant (greater than 1 hour), and the movement spacing (0.0035 mm) is also much smaller than the irradiation spot diameter (0.10 mm). This quasi-continuous movement mode in this embodiment enables the material aging characteristics of the irradiated area to extend evenly and slowly along the movement path, avoiding the sudden change of material characteristics during the irradiated area update process in Example 1, and is therefore more conducive to obtaining a long-term high-stability output of the supercontinuum spectrum.

[0083] In this embodiment, the solid sheet adopts a quasi-continuous motion mode rather than a continuous motion mode, which is beneficial to reducing the operating load of the micro-displacement platform and the control system on the one hand, and is also beneficial to the real-time processing of the feedback signal and the timing stability of the closed-loop control process in the closed-loop control process on the other hand. First, for the micro-displacement platform based on the stepper motor used in this embodiment, compared with long-term continuous operation, periodic intermittent operation is more conducive to the long-term stable operation of the platform stepper motor. For example, for the above-mentioned quasi-continuous motion with a 45-second time interval and a 0.0035mm motion spacing, the stepper motor micro-displacement platform in this embodiment can continuously run 7 steps in 1 second with a step amount of 0.0005mm to achieve a 0.0035mm motion spacing. That is, in the 45-second irradiation area update time interval, the micro-displacement platform is in a running state only for less than 1 second, and the micro-displacement platform is in a stationary state for more than 44 seconds, so the heating problem caused by the long-term continuous operation of the platform stepper motor can be significantly reduced, and its working stability and life can be improved. On the other hand, since the control module of the micro-displacement platform is in standby state most of the time, the operating load of the system control program in the quasi-continuous motion mode is also low, which makes it easy to realize real-time processing of feedback signals by the control program during closed-loop control and ensure the timing stability of the closed-loop control process.

[0084] The average motion speed parameter in this embodiment is an important parameter that determines the output power of the supercontinuum source and the stability of the spectrum broadening. In theory, if the average motion speed of the solid sheet is too slow, the laser irradiation flux received by each unit area is too high, which will cause excessive aging of the material and affect the output quality and stability of the supercontinuum; if the average motion speed of the solid sheet is too fast, the irradiation area is updated too quickly, which will cause the solid sheet to be scanned in the entire area in a short time and need to be replaced, shortening its service life. As described above, the initial average motion speed in this embodiment is obtained by detecting and evaluating the aging of the solid sheet and the data of the fixed-point irradiation power changing with time. This detection and evaluation can ensure that the initial average motion speed is in a relatively suitable range, providing a parameter basis for the initial operation of the system. Then, during the quasi-continuous motion of the micro-displacement platform, based on the monitoring of the power drop amplitude, the average motion speed of the platform will be further controlled by the closed-loop optimization feedback of the main control system 7, so that the power drop amplitude of the solid sheet during long-term irradiation is stable and close to 0 or a smaller preset value. If the power drop gradually increases or maintains a large value, it means that the material aging is aggravated or more serious, that is, the irradiation area is updated too slowly, so the main control system 7 will increase the average movement speed of the displacement platform (under the condition of keeping the update time interval unchanged, by increasing the update movement interval, or under the condition of keeping the update movement interval unchanged, by reducing the time interval) to speed up the update of the solid sheet irradiation area, so that the power drop is reduced to close to 0 or a smaller preset value. Through this closed-loop optimization feedback control, the supercontinuum source based on the solid sheet can obtain a long-term stable output, and its stability can be close to the level of the input ultrashort pulse laser.

[0085] Furthermore, if the initial average motion speed is directly set so that the aging degree (power drop amplitude) of the solid thin slice during the near-continuous scanning process is in a slight range, for example, the drop amplitude of the real-time laser power compared to the initial laser power is less than 1 times the standard deviation of the ultrashort pulse laser power, then the influence of the thin slice aging on the power stability and spectrum broadening characteristics of the output supercontinuum spectrum ultrashort pulse is almost negligible, and the noise of the output supercontinuum spectrum ultrashort pulse is mainly determined by the noise of the input ultrashort pulse, so the stability close to the input ultrashort laser pulse and the spectrum broadening close to the thin slice under the initial irradiation can be obtained. In fact, under such near-continuous scanning and weak irradiation aging conditions, it is not necessary to implement the above-mentioned closed-loop optimization feedback control to obtain a supercontinuum spectrum ultrashort pulse output with high stability.

[0086] Under the same laser irradiation parameter settings, the motion path of this embodiment can be implemented completely according to the motion path of Example 1. Therefore, under the same average motion speed conditions, for the two motion modes, the solid sheet of the same area has the same service life. That is, for this embodiment, a 30mm×30mm solid sheet can also obtain a service life of more than 15435 hours, which can achieve the system's full operating life cycle without replacement of the supercontinuum generation material.

[0087] Example 4

[0088] For the preset solid sheet motion control mode adopted in step S5 of embodiment 1 or embodiment 3, this embodiment provides another preset solid sheet motion control mode, such as Figure 4 Specifically, the main control system controls the micro-displacement platform to move continuously along a preset path, so that the ultrashort laser pulse continuously scans the solid thin slice according to the preset scanning path, thereby realizing the continuous updating of the irradiation area of ​​the thin slice during the long-term irradiation of the solid thin slice by the strong laser, thereby realizing the high-stability output of supercontinuum ultrashort pulses.

[0089] In Example 3, in step S5, the solid sheet adopts a quasi-continuous motion mode rather than a true continuous motion mode. As described in Example 3, this motion mode is consistent with the motion characteristics of the displacement platform based on the stepper motor in Example 3 (even if the stepper motor runs continuously, its motion nature is still discrete), and is also conducive to the implementation of closed-loop optimization feedback control. In fact, if a micro-displacement platform with continuous displacement capability is used, such as a micro-displacement platform based on technologies such as linear motors, voice coil motors, and piezoelectric actuators, the solid sheet placed on the micro-displacement platform can achieve true continuous motion, thereby achieving continuous scanning and irradiation of the solid sheet by ultrashort laser pulses in space and time. In this embodiment, by replacing the micro-displacement platform based on the stepper motor in Example 3 with a micro-displacement platform based on the linear motor, the main control system 7 can control the micro-displacement platform 8 to move continuously along a preset path, so that the ultrashort laser pulse continuously scans the solid sheet along the preset scanning path, and realizes the continuous update of the sheet irradiation area, thereby achieving the high stability output of the supercontinuum spectrum ultrashort pulse.

[0090] In this embodiment, in step S5, the solid sheet maintains a constant speed during long-term continuous motion and performs continuous uniform motion along a preset path. That is, the sheet does not adjust the motion speed through closed-loop optimization feedback control during long-term motion. Compared with Embodiment 1 and Embodiment 3, the motion control mode of the solid sheet in this embodiment is simpler, and its motion characteristics are completely determined by the motion parameters initially set, and do not rely on feedback control. Therefore, this embodiment significantly reduces the equipment and technical requirements of the control module in the main control system.

[0091] On the other hand, since closed-loop feedback control is not implemented during the long-term irradiation of ultrashort pulses, the aging degree of the solid sheet in this embodiment during the long-term irradiation process is completely determined by the motion parameters of the micro-displacement platform under the condition that the irradiation parameters are set consistently. Therefore, it is particularly important to obtain appropriate motion parameters of the micro-displacement platform for this embodiment. Similar to Example 3, the movement speed of the solid sheet in this embodiment is obtained based on the detection and evaluation of the aging of the solid sheet: through steps S3 and S4, the data of the change of the fixed-point irradiation power of the solid sheet over time can be measured, and a quantitative evaluation of the aging speed of the solid sheet can be obtained, such as obtaining a quantitative aging time constant, and then setting a suitable movement speed based on the evaluation. Generally speaking, the set movement speed should at least meet the time interval of the aging time constant, and the movement spacing of the irradiated area should be greater than the diameter of the laser irradiation spot to avoid excessive accumulation of aging in the irradiated area during continuous scanning, or even ablation damage. For example, according to the evaluation of the aging of the solid slice in Example 1 and Example 3, the movement speed of the micro-displacement platform is set to 0.28 mm / hour in this embodiment (consistent with the average movement speed of Example 1 and Example 3). When the irradiation parameter setting and the movement path are consistent with Example 3, this embodiment can effectively avoid the serious aging of the solid slice, and obtain the irradiation aging characteristics of the solid slice and the ultra-short pulse output characteristics of the supercontinuum spectrum similar to those of Example 3. In fact, the continuous motion mode adopted in this embodiment can completely avoid the irradiation characteristic jump (even if the jump amplitude is very small) that still exists in the quasi-continuous motion mode of Example 3 when the irradiation area is updated, so theoretically, the tiny system noise of the supercontinuum spectrum output power brought by the above-mentioned quasi-continuous motion mode can be eliminated.

[0092] In this embodiment, the movement speed is further increased on the basis of the above movement speed, so that the aging degree (power drop range) of the solid thin slice during the continuous scanning process can be in a milder range. For example, similar to the weak irradiation aging in Example 3, a higher movement speed is set so that the drop range of the real-time laser power compared to the initial laser power is less than 1 times the standard deviation of the ultrashort pulse laser power. At this time, the influence of the thin slice aging on the output supercontinuum spectrum ultrashort pulse power stability and spectrum broadening characteristics is almost negligible, and the noise of the output supercontinuum spectrum ultrashort pulse is mainly determined by the noise of the input ultrashort pulse. Therefore, the stability close to the input ultrashort laser pulse and the spectrum broadening close to the thin slice under initial irradiation can be obtained. It is worth noting that increasing the movement speed of the solid thin slice requires sacrificing the service life of the solid thin slice. Therefore, in practical applications, the pros and cons of both aspects can be weighed to set a suitable movement speed, and while meeting the technical requirements of the supercontinuum spectrum output power stability and spectrum broadening characteristics, suitable application economy and service life can also be obtained.

[0093] Under the same laser irradiation parameter settings, the motion path of this embodiment can also be implemented completely according to the motion path of Example 1. Therefore, under the condition of having a similar motion speed as that of Example 1 and Example 3, this embodiment can also obtain a service life of more than 10,000 hours by using a 30mm×30mm solid sheet, realizing the system's full operating life cycle without replacement of the supercontinuum generation material.

[0094] Obviously, the above embodiments of the present invention are only examples for clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for generating a high-stability supercontinuum light source based on a solid sheet, characterized in that: The steps of the method are as follows: S1: placing at least one solid sheet on a two-dimensional or multi-dimensional micro-displacement platform; S2: After the ultrashort laser pulse is focused and incident on a certain irradiated area on the front surface of the solid slice, nonlinear optical effects are generated during the propagation process in the solid slice, thus achieving spectrum broadening; S3: At the same time, an optical power sensor is used to sample and detect the ultrashort laser pulses after interacting with the solid slice, so as to achieve real-time measurement and recording of the sampling beam power; S4: Based on the detected power value, calculating the change amplitude of the real-time power relative to the initial power, thereby obtaining a quantitative evaluation of the aging of the solid sheet; S5: The main control system issues a control command to control the micro-displacement platform to move according to a pre-set motion mode, thereby continuously updating the irradiation area of ​​the solid sheet, thereby realizing an ultrashort pulse light source that generates a high-stability supercontinuum spectrum; The ultrashort laser pulse is converged by passing through an attenuation plate for controlling the energy of a single ultrashort laser pulse, an aperture for controlling the diameter of an incident ultrashort laser pulse beam, and a converging mirror for focusing the beam, and then is incident on a certain irradiation area on the front surface of the solid thin slice; The irradiation intensity generated by the ultrashort laser pulse on the surface of the solid slice causes the incident ultrashort laser pulse to produce a significant nonlinear optical effect with the solid slice, and at the same time makes the aging time constant of the solid slice in the "hour" time scale; The aging time constant is the length of time from the start of irradiation to the occurrence of ablation damage of the solid slice under fixed-point irradiation conditions; The displacement motion mode of the two-dimensional or multi-dimensional micro-displacement platform is a translation motion mode, a rotation motion mode, or a combination of translation and rotation motion modes; The displacement range of the two-dimensional or multi-dimensional micro-displacement platform should be able to cover the entire light-transmitting surface of the solid slice; The displacement path of the two-dimensional or multi-dimensional micro-displacement platform is preset and stored in the main control system, so as to realize the update of the ultrashort laser pulse irradiation area of ​​the solid slice according to the set path; The displacement path is planned based on the light-through area of ​​the solid slice, the diameter of the irradiated light spot, and the incident angle of the ultrashort laser pulse, so that the light-through area of ​​the solid slice is effectively utilized.

2. The method for generating a high-stability supercontinuum light source based on a solid sheet according to claim 1, characterized in that: Step S3, sampling and detecting the ultrashort laser pulse after interacting with the solid sheet, is achieved by detecting the ultrashort laser pulse beam reflected after interacting with the solid sheet; The reflected ultrashort laser pulse beam includes an ultrashort laser pulse beam reflected by the front surface of the solid sheet and an ultrashort laser pulse beam reflected by the back surface; The surface normal of the solid sheet forms a non-0 degree angle with the transmission direction of the incident ultrashort laser pulse beam, so that the reflected ultrashort laser pulse beam and the incident ultrashort laser pulse beam are spatially separated, thereby realizing the detection of the reflected ultrashort laser pulse beam.

3. The method for generating a high-stability supercontinuum light source based on a solid sheet according to claim 1, characterized in that: Step S3, sampling and detecting the ultrashort laser pulse after interacting with the solid sheet, is achieved by performing beam splitting sampling and detection on the ultrashort laser pulse that passes through the solid sheet after interacting with the solid sheet; The beam splitting sampling detection is specifically achieved by arranging a beam splitter for beam splitting behind the solid sheet to divide the ultrashort laser pulse passing through the solid sheet into two parts, one of which is output as a supercontinuum ultrashort pulse, and the other is detected as a sampling beam through an optical power probe.

4. The method for generating a high-stability supercontinuum light source based on a solid sheet according to claim 1, characterized in that: Step S5, the pre-set motion mode is: the main control system monitors the decrease in the sampling beam power, and when the decrease in the beam power is greater than a pre-set first threshold, the main control system controls the micro-displacement platform to move along a pre-set path with an update motion spacing greater than the irradiation spot diameter.

5. The method for generating a high-stability supercontinuum light source based on a solid sheet according to claim 1, characterized in that: Step S5, the pre-set motion mode is: the main control system sends an instruction to control the motion of the micro-displacement platform at an update time interval less than the aging time constant, so that the micro-displacement platform moves along a pre-set path at an update motion interval less than the irradiation spot diameter.

6. The method for generating a high-stability supercontinuum light source based on a solid sheet according to claim 1, characterized in that: Step S5, the pre-set motion mode is: the main control system controls the micro-displacement platform to perform continuous uniform motion along a pre-set path at a constant motion speed, that is, to achieve continuous motion in space and time; The movement speed is obtained based on the detection and evaluation of the aging condition of the solid thin film, and its value should at least meet the time interval of the aging time constant. The movement spacing of the irradiated area is larger than the irradiation spot diameter to avoid excessive accumulation of aging in the irradiated area during continuous scanning and cause ablation damage.

7. The method for generating a high-stability supercontinuum light source based on a solid sheet according to claim 4, characterized in that: In order to effectively avoid false triggering of the first threshold condition due to laser power noise, the first threshold is set to be equal to or greater than N times the standard deviation of the ultrashort laser pulse power; In order to further reduce the probability of false triggering of the first threshold condition due to laser power noise, real-time beam splitting sampling detection is performed on the input laser beam before it interacts with the solid slice, and laser power noise cancellation is achieved by multiplying the real-time measured power after the interaction with the ratio of the initial input power before the interaction to the real-time input power.

8. The method for generating a high-stability supercontinuum light source based on a solid sheet according to claim 5, characterized in that: Based on the monitoring of the decrease in real-time sampling power, the average movement speed of the micro-displacement platform is regulated by the closed-loop optimization feedback of the main control system, so that the decrease in the real-time sampling power of the solid sheet relative to the initial sampling power during the long-term irradiation process is less than the second threshold value; The average movement speed=update movement pitch / update time interval, so the average movement speed is regulated by regulating the update movement pitch alone, or regulating the update time interval alone, or regulating the update movement pitch and the update time interval simultaneously.

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