Optical lens curved surface polishing method based on femtosecond laser

Abstract

The invention relates to an optical lens curved surface polishing method based on femtosecond laser, which is applied to the technical field of optical lens precision machining. The optical lens curved surface polishing method comprises the following core steps: establishing hard synchronous trigger connection of femtosecond laser and coaxial white light OCT (Optical Coherence Tomography); after the laser pulse, the OCT is delayed and triggered to collect three-dimensional data, and meanwhile, coaxial micro-airflow purging is carried out to resist interference; carrying out qualification judgment on the machining depth, the surface roughness and the subsurface damage by adopting a multi-parameter end point model of a weighted voting mechanism; and if not, dynamically adjusting a 3D galvanometer scanning parameter and a femtosecond laser parameter according to the deviation and the material removal rate, and executing predictive thermal management based on OCT reflectivity monitoring. Through closed loop of anti-interference monitoring, multi-parameter intelligent judgment, dynamic self-adaptive execution and thermal management, the four problems of monitoring interference, single quality criterion, efficiency and precision imbalance and thermal management lag in the prior art are solved, and high-precision, high-efficiency and high-yield polishing of the curved surface of the high-end optical lens is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical lens precision processing technology, and particularly relates to an optical lens curved surface polishing method based on femtosecond laser, BACKGROUND

[0002] In a large numerical aperture lithography machine system and a high-precision optical imaging system, in order to eliminate aberration and ensure imaging quality, the application of special surface (such as aspheric surface and free curved surface) optical lens is indispensable, and the processing quality of the lens directly depends on the real-time controllable high-precision polishing technology. At present, the main lens polishing and polishing technology is mainly divided into two categories, and both have significant defects.

[0003] 1. Limitations of mechanical polishing technology: mechanical polishing removes surface material through cutting and plastic deformation, needs to be matched with various abrasives, and needs to rely on artificial repeated polishing and surface shape detection for free surface type curved surface lenses - for example, when processing a diameter of 200mm sapphire aspheric surface lens, at least 5 rounds of polishing + 3 rounds of detection are needed, the single processing period is more than 48 hours, the production efficiency is low (daily production capacity ≤2 pieces), the product yield is less than 75%, and the mass production demand cannot be met; at the same time, the abrasives wear will cause poor processing consistency, and the surface type precision is difficult to break through 1.2λ (λ=632.8nm), which cannot meet the requirement of the lithography machine on the lens surface type precision ≤0.8λ.

[0004] 2. Defects of non-mechanical polishing technology: although non-mechanical polishing (such as electrochemical polishing, plasma polishing, liquid jet polishing, etc.) has improved in the automation level, there are two major problems: one is high cost (the cost of a single plasma polishing device is more than 5 million yuan, and the replacement period of consumables is short, and the single replacement cost is more than 100,000 yuan); the second is that harmful chemicals such as hydrofluoric acid and nitric acid are needed, and about 20L of fluorine-containing wastewater is generated for every 100 pieces of lenses processed, which causes irreversible pollution to the environment, and does not meet the current green manufacturing industry trend.

[0005] 3. Defects of existing femtosecond laser polishing technology: as a "cold processing" means, femtosecond laser has the advantages of wide material adaptability and small thermal influence zone (≤1.5μm), but the existing technology still faces four major technical bottlenecks in realizing batch and high consistency processing of arbitrary surface type optical lenses:

[0006] Monitoring interference problem: the plasma (duration about 3-8μs) and material debris generated in the processing process seriously interfere with the detection signal of the coaxial OCT, resulting in a detection signal-to-noise ratio of only 10:1, a depth detection error of ≥0.5μm, and the subsequent closed-loop control loses the reliable data basis;

[0007] Single problem of quality determination: the prior art only uses "processing depth" as the end point determination basis, which cannot evaluate the surface roughness (Ra is usually greater than or equal to 1.8 nm) and subsurface damage (such as 915 nm characteristic phase change peak of quartz mirror) online, resulting in hidden scrap of "geometric size meets the standard but optical performance is unqualified", and low yield;

[0008] Efficiency and accuracy imbalance problem: the material removal rate of different regions on the complex curved surface is significantly different, and fixed processing parameters (such as scan line spacing 50μm, laser energy 5μJ) cannot simultaneously meet the high accuracy requirement of steep section and the high efficiency requirement of plane section, and the overall processing efficiency is low (less than or equal to 15mm² / min);

[0009] Thermal management lag problem: although femtosecond laser is a cold processing, under the requirements of high repetition frequency and high efficiency, thermal accumulation effect will still cause local micro deformation (protrusion greater than or equal to 0.3μm) of the lens, and the traditional thermal management is mostly post-compensation, which has a lag response and seriously affects the consistency of the full aperture surface.

[0010] In order to solve the above problems, the present application proposes an intelligent polishing method of "femtosecond laser-3D galvanometer-coaxial OCT" cooperation, which realizes high-precision, high-efficiency and high-consistency processing of high-end optical lenses through hard synchronization trigger, multi-parameter determination, dynamic execution and thermal management. SUMMARY

[0011] The purpose of the present application is to overcome the defects of the prior art, solve the four industry bottlenecks of "monitoring interference problem, quality determination single problem, efficiency and accuracy imbalance problem, thermal management lag problem", and realize high-precision, high-efficiency and high-yield polishing of high-end optical lenses with arbitrary surface type and various materials.

[0012] In order to achieve the above purpose, the present application provides a method for polishing the curved surface of an optical lens based on femtosecond laser, which relies on a system (see Figure 2 ):

[0013] Femtosecond laser: pulse width 100-300fs, output power 1-5W, pulse energy 1-10μJ, repetition frequency 100kHz-2MHz adjustable;

[0014] Programmable delay circuit: model AD9516, trigger signal delay precision ±0.1μs, CLK_IN pin connected to the pulse synchronization signal of femtosecond laser, DELAY_OUT pin outputs trigger signal to OCT detection unit, realizes hard synchronization;

[0015] Coaxial white light OCT detection unit: axial resolution less than or equal to 5μm, lateral resolution less than or equal to 10μm, field of view range 100×100mm, sampling frequency greater than or equal to 1kHz, wavelength range 800-1000nm, resolution 1nm;

[0016] 3D galvanometer: scanning range ≥ 300 × 300 mm, positioning accuracy ± 5 μm, maximum scanning speed 1000 mm / s, supporting spiral, grating and other scanning paths;

[0017] Coaxial micro air flow nozzle: material 316L stainless steel, angle with laser light path 30° ± 5°, inner diameter 0.5-1 mm;

[0018] Inert gas supply unit: provides nitrogen / argon, purity ≥ 99.99%, pressure regulation range 0.1-0.5 MPa, flow rate controlled by mass flow controller;

[0019] Industrial control computer: CPU Intel i7-13700K, memory 32 GB, running multi-parameter end point model algorithm, linked with 3D galvanometer and OCT detection unit through RS485 communication protocol (response time ≤ 1 ms);

[0020] Processing platform: vacuum adsorption type, repeat positioning accuracy ± 2 μm, used for fixing the lens to be processed.

[0021] The optical lens curved surface polishing method based on femtosecond laser provided by the application is based on the logic chain of "anti-interference monitoring-multi-parameter judgment-dynamic execution-mode adaptation", and specifically includes the following steps (see Figure 1 ) :

[0022] Step S1: system startup and hard synchronization establishment

[0023] Fix the optical lens substrate to be polished (such as a sapphire aspherical lens with a diameter of 200 mm and a curvature R=50 mm) on the processing platform, start the coaxial white light OCT detection unit, femtosecond laser and 3D galvanometer; configure the programmable delay circuit AD9516 through the industrial control computer, establish the hard synchronization trigger connection of the femtosecond laser pulse signal and the OCT detection unit - output 1 pulse synchronization signal (frequency 100 kHz-2 MHz) from the femtosecond laser to the CLK_IN pin of AD9516, and after delay calculation, AD9516 outputs a trigger signal from the DELAY_OUT pin to the acquisition control module of OCT, with a delay accuracy of ± 0.1 μs, to ensure the precise timing matching of "laser pulse output-delay-OCT acquisition".

[0024] Step S2: anti-interference three-dimensional data acquisition

[0025] Through a hard-synchronization trigger connection, a 5-10μs delay is made after the femtosecond laser pulse output (avoiding the peak period of plasma interference; experimental verification shows that the OCT signal-to-noise ratio is ≥32:1 with a 5μs delay and ≥35:1 with an 8μs delay), triggering the coaxial white light OCT detection unit to acquire three-dimensional data (including depth data, intensity data, and spectral data) of the area to be processed on the lens. Simultaneously, the industrial control computer outputs control signals to the coaxial micro-airflow nozzle, spraying nitrogen gas (purity ≥99.99%) supplied by the inert gas supply unit at a flow rate of 0.3-0.8L / min, instantly dispersing debris with a particle size ≤1μm in the area to be processed. Experimental data shows that this operation can reduce the detection error caused by debris obstruction from 0.6μm to below 0.1μm.

[0026] The acquired 3D data is preprocessed for denoising using denoising algorithms (including but not limited to wavelet denoising, Gaussian denoising, and median denoising). This invention preferably uses a wavelet denoising algorithm of "db4 wavelet basis + 3-level decomposition + soft thresholding". Specifically, the original intensity data is decomposed into 3 levels of high-frequency coefficients and 1 level of low-frequency coefficients. The high-frequency coefficients are truncated using a soft threshold of "threshold = 0.1 × max (absolute value of high-frequency coefficient)". The signal-to-noise ratio of the reconstructed data is ≥35:1, and the depth data accuracy reaches ±0.1μm.

[0027] Step S3: Multi-parameter quality assessment

[0028] The preprocessed 3D data is input into a preset multi-parameter endpoint model, and the processing area is judged according to the following logic to determine whether it meets the preset processing target (see...). Figure 3 ):

[0029] Processing depth determination: Compare the OCT depth data with the target depth (e.g., target depth 50μm, allowable error ≤ ±0.3μm). If the target depth is met, 1 point is awarded for the depth item; otherwise, 0 points are awarded.

[0030] Surface roughness determination: Surface roughness Ra is inverted through the standard deviation of intensity data. The calculation logic is as follows: take 100 consecutive intensity sample values. Calculate the mean According to the formula Calculate Ra. If Ra ≤ 1 nm, the roughness item gets 1 point; otherwise, it gets 0 points.

[0031] Subsurface damage assessment: Analyze the spectral data. If no material phase transition characteristic peaks (such as the 915nm characteristic peak of quartz and the 850nm characteristic peak of sapphire) are found, or if the intensity of the characteristic peaks is ≤5% of the baseline, then the damage item will receive 1 point; otherwise, it will receive 0 points.

[0032] Weighted voting calculation: weighted score = depth item score x 0.4 + roughness item score x 0.3 + damage item score x 0.3, if weighted score ≥ 0.9 (i.e. at least two items score 1 and total score ≥ 0.9), determine as processing qualified, execute step S5; otherwise determine as reprocessing, output deviation data (such as "depth deviation -0.4 μm, Ra = 1.2 nm"), execute step S4. The output signal of the multi-parameter endpoint model is directly transmitted to the control unit of the 3D galvanometer through the RS485 communication protocol, realizing closed-loop control of algorithm decision and hardware execution, and avoiding parameter adjustment lag.

[0033] Step S4: dynamic parameter adjustment and thermal management According to the deviation data and the real-time calculated material removal rate, the parameters of the 3D galvanometer and the femtosecond laser are dynamically adjusted, and the thermal management is executed at the same time:

[0034] Material removal rate calculation: according to the formula , where Δd is the difference value of depth data collected by adjacent two times (such as the first collection depth 49.5 μm, the second 49.8 μm, Δd = 0.3 μm), Δt is the time interval of two times of collection (such as Δt = 0.6 s), then R = 0.5 μm / s;

[0035] Galvanometer parameter adjustment: if the material removal rate < 0.5 μm / s (such as the steep section of the curved surface, R = 0.3 μm / s), set the scanning path of the 3D galvanometer as a spiral scanning (the pitch matches the line spacing), and reduce the scanning line spacing from the initial value 50 μm to 20-30 μm, and increase the scanning circle number from 1 to 2-3 circles (experimental verification: when the line spacing is 25 μm, the removal rate is increased to 0.6 μm / s, and the depth deviation is ≤ ± 0.2 μm);

[0036] Laser parameter adjustment: if Ra > 1 nm (such as Ra = 1.2 nm), increase the repetition frequency of the femtosecond laser from the initial value 1 MHz to 2 MHz, and reduce the pulse energy from the initial value 5 μJ to 2 μJ (finishing stage parameters), realize finishing machining through "high frequency and low energy", and experiments show that this adjustment can reduce Ra to below 0.8 nm;

[0037] Thermal management step: the rate of reflectivity change of the edge of the processing area is monitored in real time by OCT (sampled every 10 ms), if the rate is ≥3% / ms (predicting thermal accumulation), immediately adjust the 3D galvanometer scanning sequence, preferentially process the cold area with a distance of ≥5 mm from the current area, and the cooling time of the cold area is ≥20 ms (experimental verification: after cooling for 20 ms, the area temperature decreases from 50℃ to 25℃, and the thermal deformation protrusion decreases from 0.3μm to 0.1μm); if the local thermal deformation protrusion detected by OCT is ≥0.2μm, reduce the femtosecond laser energy to below the preset thermal damage safety threshold, and the preset thermal damage safety threshold is 80% of the laser damage threshold of the substrate material of the lens to be processed, for example, the laser damage threshold of a quartz lens is 5μJ / μm², the laser damage threshold of a sapphire lens is 8μJ / μm², and the laser damage threshold of an infrared glass lens is 7μJ / μm². Step S5: cycle processing and end control 3D galvanometer moves to the next area to be processed, and steps S2-S4 are repeated until the polishing of the entire lens surface is completed.

[0038] 3. Processing mode adaptation

[0039] Before step S1, the preset processing mode can be selected according to the processing requirements (see Figure 4 ), and the mode parameters and effects are as follows:

[0040] Quality priority mode: the Ra threshold in step S3 is adjusted to ≤0.8nm, and the reflectivity change rate monitoring threshold in step S4 is adjusted to ≥2% / ms; the laser parameters are 2-4μJ / 1.5-2MHz, the 3D galvanometer scanning speed is 300-500mm / s, and the line spacing is 20-30μm; suitable for lithography machine aspherical lenses, finished product Ra≤0.8nm, surface accuracy ≤0.5λ;

[0041] Efficiency priority mode: the depth error threshold in step S3 is adjusted to ≤±0.5μm, and the reflectivity change rate monitoring threshold in step S4 is adjusted to ≥5% / ms; the laser parameters are 4-8μJ / 0.5-1MHz (coarse processing stage), the 3D galvanometer scanning speed is 600-1000mm / s, and the line spacing is 40-60μm; suitable for infrared detection lenses (slightly lower precision requirements), processing efficiency reaches 22mm² / min, which is 1.2 times that of the standard mode;

[0042] Standard mode: the parameters are as described in steps S1-S5, balancing accuracy and efficiency, suitable for most general optical lenses, finished product surface accuracy 0.6λ, qualified rate 95%, efficiency 18mm² / min.

[0043] Compared with the prior art, the present application has the following beneficial effects:

[0044] 1. Strong anti-interference ability, solve the problem of monitoring interference: through "hard synchronization delay (5-10 μs) + coaxial micro air flow to remove debris", the signal-to-noise ratio of OCT detection is improved from 10:1 to 35:1, and the depth detection error is ≤±0.1 μm, providing a reliable data source for closed-loop control.

[0045] 2. Comprehensive quality judgment, solve the problem of single quality judgment: multi-parameter end point model covers "depth-roughness-subsurface damage", the finished product rejection rate is reduced from 25% to less than 5%, meeting the requirements of high-end lenses for full-dimensional quality.

[0046] 3. Balance efficiency and precision, solve the problem of imbalance between efficiency and precision: dynamic parameter adjustment makes the processing efficiency increase from 15 mm² / min to 22 mm² / min (efficiency priority mode), and the surface precision increases from 1.2λ to 0.6λ, breaking the bottleneck of "efficiency and precision cannot be achieved simultaneously".

[0047] 4. Active thermal management, solve the problem of thermal management lag: predictive thermal management based on OCT reflectivity change rate + thermal deformation compensation, thermal influence area is reduced from 1.5 μm to 0.6 μm, ensuring the surface consistency of large-format lenses.

[0048] 5. Wide material adaptability, green and environmentally friendly: compatible with quartz, sapphire, infrared glass and other materials, lens diameter covers 50-500 mm; no harmful chemicals, only inert gas is used, no waste water and slag discharge, and no abrasive tool wear, reducing consumable cost by more than 30%. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is the method flowchart of the optical lens curved surface polishing method based on femtosecond laser of the present application.

[0050] Figure 2 is the structure block diagram of the system relied on by the optical lens curved surface polishing method based on femtosecond laser of the present application.

[0051] Figure 3 is the multi-parameter end point judgment logic flowchart in the present application.

[0052] Figure 4 is the processing mode and self-adaptive control flowchart in the present application. DETAILED DESCRIPTION

[0053] In order to make the technical scheme of the present application clearer, the following will be described in detail in combination with 4 specific examples and 1 comparative example, all examples are based on the above-mentioned system architecture and steps, only the parameters are adjusted to adapt to different scenes, and the technical progress of the present application is verified.

[0054] Example 1: standard mode processing sapphire aspherical lens

[0055] Processing object: sapphire aspherical lens, diameter 200 mm, curvature R = 50 mm, target depth 50 μm, laser damage threshold 8 μJ / μm² (thermal damage safety threshold 6.4 μJ / μm²).

[0056] System parameters:

[0057] Femtosecond laser: pulse width 200 fs, initial parameters 5 μJ / 1 MHz;

[0058] 3D galvanometer: scanning path is a spiral line (pitch 50 μm), initial scanning line spacing 50 μm, scanning speed 600 mm / s;

[0059] OCT detection: delay time 8 μs, micro-airflow nozzle flow rate 0.5 L / min (nitrogen, purity 99.999%), wavelet denoising (db4 base, 3 layers of decomposition);

[0060] Multi-parameter threshold: depth error ≤ ±0.3 μm, Ra ≤ 1 nm, spectral characteristic peak ≤ 5% baseline;

[0061] Thermal management: reflectivity change rate threshold ≥ 3% / ms, cold zone cooling time ≥ 20 ms.

[0062] Processing process and effect:

[0063] Step S2: the depth data collected by OCT after preprocessing, precision ±0.1 μm, signal-to-noise ratio 36:1;

[0064] Step S3: the first determination result is "depth 49.7 μm (score 1), Ra = 1.1 nm (score 0), no damage peak (score 1)", weighted score = 1 × 0.4 + 0 × 0.3 + 1 × 0.3 = 0.7 < 0.9, determine reprocessing;

[0065] Step S4: calculate the removal rate R = 0.3 μm / 0.6 s = 0.5 μm / s (no need to adjust the galvanometer), adjust the femtosecond laser parameters to 2 μJ / 2 MHz, and re-scan 1 circle; the second determination Ra = 0.9 nm (score 1), weighted score = 1.0, determine qualified; finished product effect: processing period 12 hours, surface accuracy 0.6λ (λ = 632.8 nm), Ra = 0.9 nm, thermal affected zone 0.6 μm, qualified rate 95%.

[0066] Example 2: quality priority mode processing quartz aspherical lens

[0067] Processing object: quartz aspherical lens (for lithography machine), diameter 100 mm, curvature R = 30 mm, target depth 30 μm, laser damage threshold 5 μJ / μm² (thermal damage safety threshold 4 μJ / μm²).

[0068] System parameters:

[0069] Femtosecond laser parameters: 2-4 μJ / 1.5-2 MHz;

[0070] 3D galvanometer: scanning path is a spiral line (pitch 20 μm), scanning speed 300 mm / s, line spacing 20 μm;

[0071] OCT detection: delay time 5 μs, micro-airflow nozzle flow rate 0.3 L / min (argon, purity 99.999%);

[0072] Multi-parameter threshold: Ra≤0.8 nm, spectral characteristic peak≤3% baseline;

[0073] Thermal management: reflectivity change rate threshold≥2% / ms.

[0074] Finished product effect: processing cycle 10 hours, surface accuracy 0.5λ, Ra=0.7 nm, subsurface damage-free peak (915 nm characteristic peak intensity≤2% baseline), completely meets the requirements of photolithography machine lenses, and the qualified rate is 98%.

[0075] Example 3: Efficiency priority mode processing of infrared glass freeform lens

[0076] Processing object: infrared glass freeform lens, diameter 300 mm, target depth 60 μm, laser damage threshold 7 μJ / μm² (thermal damage safety threshold 5.6 μJ / μm²).

[0077] System parameters:

[0078] Femtosecond laser parameters: rough machining 4-8 μJ / 0.5-1 MHz, finishing 2 μJ / 2 MHz (only when Ra is out of tolerance);

[0079] 3D galvanometer: scanning path is a spiral line (pitch 50 μm), scanning speed 800 mm / s, line spacing 50 μm;

[0080] OCT detection: delay time 10 μs, micro-airflow nozzle flow rate 0.8 L / min (nitrogen, purity 99.99%);

[0081] Multi-parameter threshold: depth error≤±0.5 μm, Ra≤1.2 nm;

[0082] Thermal management: reflectivity change rate threshold≥5% / ms.

[0083] Processing process and effect:

[0084] Processing area calculation: the effective processing area (material removal area) of the freeform lens is about 19800 mm² (converted from the target depth of 60 μm material removal volume);

[0085] Efficiency calculation: processing period 15 hours = 900 minutes, processing efficiency = 19800 mm² ÷ 900 min = 22 mm² / min (efficiency index in line with efficiency priority mode);

[0086] Finished product effect: surface accuracy 0.8λ, Ra = 1.1 nm, pass rate 92%, meeting the requirements of infrared detection system.

[0087] Example 4: 500 mm diameter infrared glass lens fitting verification

[0088] Processing object: 500 mm diameter infrared glass lens, curved surface type is spherical (curvature R = 200 mm), target depth 80 μm, laser damage threshold 7 μJ / μm² (thermal damage safety threshold 5.6 μJ / μm²).

[0089] System parameter fitting:

[0090] 3D galvanometer: adopt "sub-regional spiral scanning" (each region diameter 100 mm, matched with OCT detection field of view (100 x 100 mm), avoid detection accuracy decline caused by too large field of view; 5 mm overlap between regions, prevent processing fault at region connection);

[0091] Micro air flow nozzle: flow rate is increased to 0.8 L / min, ensure complete removal of debris during large aperture lens processing;

[0092] Femtosecond laser: set the repetition frequency to 1 MHz, pulse energy 6 μJ (balance processing efficiency and heat accumulation);

[0093] Heat management: cooling time in cold zone is extended to 25 ms, adapt to the heat diffusion characteristics of large aperture lens.

[0094] Finished product effect: processing period 30 hours, surface accuracy 0.9λ, Ra = 1.3 nm, pass rate 88%, prove that the method can be adapted to lens processing of 50-500 mm full range diameter.

[0095] Comparative example: processing effect without enhancement scheme

[0096] Using the baseline system without the "anti-interference monitoring + multi-parameter judgment + dynamic thermal management" function of the application (only femtosecond laser + 3D galvanometer + ordinary OCT, no delay trigger, micro-blowing and multi-parameter model), the same sapphire aspherical lens as in Example 1 is processed, and the results are as follows: the OCT signal-to-noise ratio is only 10:1, and the depth detection error is ≥0.5 μm; only through depth judgment end point, the finished product Ra=1.8 nm, and the subsurface 915 nm characteristic peak intensity reaches 12% of the baseline (damage exists); without thermal management, the thermal influence zone is 1.5 μm, and the surface accuracy is 1.2λ; the processing cycle is 24 hours, and the qualified rate is 75%. It can be seen that the application has achieved significant improvement in precision, efficiency and qualified rate, and the technical progress is clear.

[0097] Supplementary notes:

[0098] Method for measuring laser damage threshold: pretreat the sample of the material to be processed (such as quartz, sapphire) (cleaning, drying), place the sample in the femtosecond laser light path, gradually increase the laser energy density (step size 0.5 μJ / μm²), and detect the spectral data of the sample through the coaxial white light OCT; when the material phase change characteristic peak (such as quartz 915 nm, sapphire 850 nm) appears in the spectrum, record the energy density at this time as the laser damage threshold of the material; the thermal damage safety threshold is 80% of the laser damage threshold, to ensure that no new damage is generated during the re-scan.

[0099] Determination of wavelet denoising threshold: for the original intensity signal collected by OCT, the denoising effect of different thresholds (0.05, 0.1, 0.15, 0.2×max(high frequency coefficient absolute value)) is verified through experiments: when the threshold is 0.1, the signal-to-noise ratio of the denoised signal is ≥35:1, the depth detection error is ≤±0.1 μm, and no effective signal (such as surface roughness related intensity fluctuation) is lost, and the threshold is the optimal choice, which takes into account the denoising effect and signal integrity.

[0100] Parameter adjustability: all parameters in the application (such as delay time 5-10 μs, air flow 0.3-0.8 L / min) have been verified by experiments, and the expected effect can be achieved within the adjustment range, which is not a unique fixed value - for example, the debris removal rate is 92% at a micro-air flow nozzle flow rate of 0.2 L / min, and 98% at 1 L / min, both of which can meet the detection requirements, proving the flexibility and universality of the parameters.

[0101] Hardware compatibility: in addition to the programmable delay circuit AD9516, CDCE6214 (delay accuracy ±0.2 μs, meeting the requirements) can also be selected; the 3D galvanometer can be selected as ScanLab hurrySCAN 30 (scanning range 300×300 mm, positioning accuracy ±5 μm), which does not affect the implementation of the scheme.

[0102] Algorithm reproducibility: the "db4 base + 3 layer decomposition" of wavelet denoising and the "weighted voting" of multiple parameters are all general algorithm frameworks in the industry, and those skilled in the art can realize them through MATLAB wavelet toolbox and Python numpy library, without algorithm barriers.

[0103] Compatibility of denoising algorithm: in addition to the wavelet denoising adopted in the embodiment, those skilled in the art can select equivalent denoising algorithms such as Gaussian filtering and median filtering according to actual needs, as long as the preprocessing effect of signal-to-noise ratio ≥ 35:1 can be realized, which falls within the protection scope of the present application.

Claims

1. A method for optical lens surfacing based on femtosecond laser, characterized in that, The method comprises the following steps: S1: fixing the optical lens substrate to be polished on a processing platform, starting a coaxial white light OCT detection unit, a femtosecond laser and a 3D galvanometer, and establishing a hard synchronization trigger connection of the femtosecond laser pulse signal and the coaxial white light OCT detection unit through a programmable delay circuit; S2: through the hard synchronization trigger connection, triggering the coaxial white light OCT detection unit to collect three-dimensional data of the lens area to be processed 5-10 μs after the femtosecond laser pulse output, and controlling a coaxial micro-airflow nozzle at an angle of 30°±5° with the laser light path to spray inert gas at a flow rate of 0.3-0.8 L / min to blow away the debris of the area to be processed; the three-dimensional data comprises depth data, intensity data and spectral data; S3: inputting the three-dimensional data into a preset multi-parameter end point model to determine whether the area to be processed meets the preset processing target: the preset processing target comprises that the error of the processing depth and the target depth is ≤±0.3 μm, the surface roughness Ra based on the inversion of the intensity data is ≤1 nm, and there is no material phase transition characteristic peak or the characteristic peak intensity is ≤5% of the baseline in the spectral data; if all the three items are met, it is determined that the processing is qualified, and step S5 is performed; if at least one item is not met, it is determined that the processing is to be supplemented, deviation data is output, and step S4 is performed; S4: dynamically adjusting the scanning parameters of the 3D galvanometer and the processing parameters of the femtosecond laser according to the deviation data and the real-time calculated material removal rate: if the material removal rate is <0.5 μm / s, the scanning line spacing of the 3D galvanometer is reduced to 20-30 μm, and the number of scanning circles is increased; if the surface roughness Ra based on the inversion of the intensity data is >1 nm, the repetition frequency of the femtosecond laser is increased to 2 MHz, and the pulse energy thereof is reduced to 2 μJ; at the same time, a heat management step is performed: through the coaxial white light OCT detection unit, the reflectivity change rate of the edge of the processing area is monitored in real time, if the reflectivity change rate is ≥3% / ms, the scanning sequence of the 3D galvanometer is adjusted, and the cold area with a distance of ≥5 mm from the current area is preferentially processed; if the coaxial white light OCT detection unit detects that the local thermal deformation protrusion is ≥0.2 μm, the energy of the femtosecond laser is reduced to below the preset heat damage safety threshold of the material of the lens substrate to be processed, and the protrusion area is supplemented; S5: controlling the 3D galvanometer to move to the next area to be processed, and repeating steps S2-S4 until the polishing of the entire lens surface is completed; In step S4, the preset heat damage safety threshold is 80% of the laser damage threshold of the material of the lens substrate to be processed.

2. The method of claim 1, wherein the femtosecond laser-based optical lens surfacing method is characterized by, In step S1, the programmable delay circuit trigger signal delay accuracy of the hard synchronization trigger connection is ±0.1 μs.

3. The method of claim 1, wherein the femtosecond laser based optical lens surface polishing method is characterized by, In step S2, the inert gas is nitrogen or argon with a purity of ≥99.99%.

4. The method of claim 1, wherein the femtosecond laser-based optical lens surfacing method is characterized by, In step S2, the axial resolution of the coaxial white light OCT detection unit is ≤5 μm, the lateral resolution is ≤10 μm, and the sampling frequency is ≥1 kHz; the three-dimensional data collected is preprocessed through a denoising algorithm, and the signal-to-noise ratio of the preprocessed signal is ≥35:

1.

5. The method of claim 1, wherein the femtosecond laser based optical lens surface polishing method is characterized by, The output signal of the multi-parameter end-point model is directly transmitted to the control unit of the 3D galvanometer, and the control unit adjusts the scanning path parameters of the 3D galvanometer in real time according to the qualified or reprocessing signal, so as to realize closed-loop control of algorithm decision and hardware execution; and the multi-parameter end-point model adopts a weighted voting mechanism for judgment: 1 point is given when a single index meets the preset processing target, and 0 point is given when it does not meet the preset processing target, and the weighted score = processing depth error score × 0.4 + surface roughness score × 0.3 + spectral characteristic peak intensity score × 0.3, only when the weighted score ≥ 0.9, it is determined that the processing is qualified.

6. The method of claim 1, wherein the femtosecond laser-based optical lens surfacing method is characterized by, In step S4, the material removal rate is calculated by the formula where Δd is the difference between the depth data of two adjacent acquisitions, Δt is the time interval between the two acquisitions in units of μm / s; and the initial value of the scan line spacing of the 3D galvanometer is 50 μm, the initial value of the repetition frequency of the femtosecond laser is 1 MHz, and the initial value of the pulse energy is 5 μJ.

7. The method of claim 1, wherein the femtosecond laser based optical lens surface polishing method is characterized by, In step S4, when adjusting the scanning sequence of the 3D galvanometer, the cooling time of the cold region is ≥ 20 ms, and after cooling is completed, the original processing area is returned to continue polishing.

8. The method of claim 1, wherein the femtosecond laser-based optical lens surfacing method is characterized by, Before step S1, a pretreatment step is further included: selecting a preset processing mode according to the processing requirement, the processing mode including a quality priority mode, an efficiency priority mode and a standard mode; if the quality priority mode is selected, the threshold value of the surface roughness Ra in step S3 is adjusted to ≤ 0.8 nm, and the monitoring threshold value of the reflectivity change rate in step S4 is adjusted to ≥ 2% / ms; if the efficiency priority mode is selected, the threshold value of the processing depth error in step S3 is adjusted to ≤ ± 0.5 μm, and the monitoring threshold value of the reflectivity change rate in step S4 is adjusted to ≥ 5% / ms.

9. The method of claim 8, wherein the femtosecond laser-based optical lens surfacing method is characterized by, When the efficiency priority mode is selected, the pulse energy of the femtosecond laser in step S4 is adjusted to 4-8 μJ, the repetition frequency is adjusted to 0.5-1 MHz, and the scanning speed of the 3D galvanometer is adjusted to 600-1000 mm / s.

10. The method of claim 1, wherein the method is a femtosecond laser based optical lens surfacing method. The material of the optical lens substrate includes quartz, sapphire or infrared glass, the lens surface type includes spherical surface, aspherical surface or free-form surface, and the lens diameter ranges from 50 to 500 mm.

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