Anti-laser multi-band afocal long working distance vacuum optical tweezers objective lens

Abstract

The application discloses a kind of multi-band laser-resistant true focus long working distance vacuum optical tweezers objective, belong to optical tweezers microscopic optics technical field.A plurality of lens elements are sequentially arranged from object plane to image plane along optical axis, and the plurality of lens elements constitute a composite optical system with 17 effective optical refractive surfaces and 1 diaphragm surface.The objective optical index satisfies: numerical aperture NA=0.5;Single-band imaging performance is optimized at 509nm wavelength, and modulation transfer function MTF is not less than 0.4 at 500lp / mm;Base focal length is 13mm, and focal length can be scaled to 5-20mm as a whole.The application realizes precise focusing of 800nm-1500nm near-infrared full waveband and 509nm visible light waveband through three-stage hierarchical chromatic aberration correction and high-low dispersion glass matching;Through segmented long working distance design, external integration and long-distance precise control in vacuum environment are realized;Finally, multi-band confocal focus-free switching, high-power stable operation, full-field high-definition imaging and large-scale synchronous observation are realized.

Description

Technical Field

[0001] This invention belongs to the field of optical tweezers microscopy technology, specifically relating to a laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective, and more particularly to a composite functional optical tweezers objective capable of achieving dual-band parfocal imaging in the near-infrared wide band of 800nm~1500nm and the visible light single band of 509nm, withstanding long-term continuous irradiation by high-power near-infrared lasers, and possessing a long working distance in a vacuum environment. Background Technology

[0002] Optical tweezers technology utilizes laser gradient force and scattering force to achieve non-contact, precise capture and manipulation of micro- and nano-particles, biological cells, and atoms and molecules. It boasts advantages such as no mechanical damage, high manipulation precision, and fast dynamic response, and is now widely used in cutting-edge fields such as single-molecule mechanical detection, cell sorting and activity research, microfluidic chip manipulation, quantum atom capture, and micro- and nano-material characterization. The microscope objective, as the core focusing and imaging element of the optical tweezers system, directly determines the focusing intensity, optical trap stability, imaging clarity, and equipment lifespan of the optical tweezers due to its optical performance, wavelength adaptability, and laser tolerance. It is a key component ensuring the high-precision, long-term stable operation of the optical tweezers system.

[0003] Currently, mainstream optical tweezers systems generally use near-infrared lasers as the manipulation light source. Leveraging the low biological damage and minimal thermal interference characteristics of the near-infrared band, they achieve non-destructive manipulation of living samples. Simultaneously, they are combined with visible light bands for real-time sample observation and imaging. This necessitates that the accompanying microscope objectives meet comprehensive performance requirements, including wide-band parfocality in the near-infrared band, visible light imaging compatibility, high laser damage threshold, and high focusing accuracy. Most conventional microscope objectives on the market are designed for a single visible light imaging band or a narrow-band near-infrared band, making them unsuitable for the special conditions of multi-band multiplexing and long-term high-power laser irradiation in optical tweezers systems. They cannot simultaneously meet the core requirements of wide-band parfocality, high power tolerance, and precise focusing, significantly limiting the performance upgrades and application expansion of high-precision optical tweezers equipment.

[0004] Considering the actual application conditions of optical tweezers systems, existing commercial microscope objectives and traditional optical tweezers-specific objectives have many technical shortcomings and cannot meet the usage requirements of 800nm–1500nm near-infrared broadband parfocal imaging, 509nm visible light imaging, and continuous operation with high-power lasers. The specific defects are as follows:

[0005] Poor multi-band chromatic aberration correction capability and inability to achieve confocal matching across wide and narrow bands: Most conventional microscope objectives only optimize aberrations for the 400nm–700nm visible light band or a single narrow-band near-infrared band. Their dispersion correction systems are limited and cannot cover the ultra-wide near-infrared spectral range of 800nm–1500nm. In actual optical tweezers operation, the focal shift between the near-infrared control laser and the 509nm visible light imaging laser is severe, preventing parfocal multiplexing. This leads to misalignment between the optical tweezers control position and the imaging observation position, requiring frequent manual calibration of the optical path. This not only increases system debugging difficulty and reduces experimental efficiency but also directly affects the positioning accuracy of micro / nano particle and cell manipulation, easily causing sample manipulation failure. Furthermore, traditional objectives exhibit significant residual spherical and chromatic aberrations across the wide near-infrared band, resulting in severe focusing spot distortion, which significantly weakens the optical tweezers gradient force and reduces the stability of the optical trap. The root cause of the above problems is that the glass material combination of traditional objectives lacks the ability to specifically correct the chromatic aberration of the second-order spectrum in the near-infrared ultrawide band. The matching relationship between its Abbe number and some dispersion coefficients is only designed for the visible light C line 656.3nm, F line 486.1nm or a single laser wavelength, and cannot achieve spatial overlap of the focal points of each wavelength in the range of 800nm ​​to 1500nm.

[0006] The low laser damage threshold makes them unable to withstand long-term high-power laser irradiation: Traditional optical tweezers microscope objectives mostly use conventional optical glass with ordinary multilayer antireflective coatings, resulting in weak resistance to laser damage from the glass matrix and coating structure. Optical tweezers require continuous high-power near-infrared laser irradiation of the objective lenses. Under long-term conditions, this easily leads to problems such as coating ablation, delamination, lens thermal deformation, and refractive index drift, resulting in decreased objective transmittance, aberration deterioration, and reduced focusing accuracy. This not only significantly shortens the lifespan of the objective but also causes optical field distortion and decreased maneuverability, failing to meet the requirements of long-term, high-power precision optical tweezers experiments. Furthermore, existing objectives lack a high-resistance window protection structure, leaving the lenses directly exposed to the high-energy laser path, making them extremely vulnerable to strong light impact. The fundamental reason for this is that conventional optical glass has a high coefficient of thermal expansion, typically 80 × 10⁻⁻. 7 Above ℃, significant thermal stress and deformation are generated under the temperature rise effect induced by high-power laser. At the same time, the laser-induced damage threshold (LIDT) of ordinary antireflective coatings is usually below 5 J / cm², which cannot meet the long-term irradiation requirements of continuous lasers above 20W.

[0007] Poor matching between numerical aperture, field of view, and focal length leads to an imbalance in overall performance: Currently, high-NA optical tweezers objectives generally suffer from short focal lengths and small effective fields of view, making them unsuitable for observing large-field-of-view samples and performing extensive micromanipulation. Meanwhile, conventional long-focal-length objectives generally have low numerical apertures, insufficient focusing ability, and are unable to form high-intensity gradient light traps, making it difficult to stably capture small particles. Existing technologies lack a suitable design with an NA of 0.5, a focal length of 13mm, and an effective field of view diameter of 1mm, failing to balance strong focusing ability, a moderate working focal length, and an effective observation field of view. This makes it difficult to adapt to the simultaneous observation and precise manipulation of microfluidic chips, cell arrays, and large-area micro / nano samples, severely limiting scene adaptability. This deficiency stems from the inherent contradiction of mutual constraints among parameters under the Lagrange invariant constraint of the optical system: high NA requires a large aperture angle, while long focal lengths and large fields of view require large lens diameters and complex aberration balances. Traditional three-component structures cannot simultaneously achieve balanced optimization of all three within a compact space.

[0008] The imperfect optical aberration correction system results in poor broadband imaging quality: Traditional objectives' lens material combinations and curvature structure designs are only suitable for narrow-band imaging. In the wide near-infrared band of 800nm–1500nm, residual aberrations such as on-axis spherical aberration, off-axis coma, astigmatism, and field curvature are significant, leading to poor uniformity in the entire field of view. Simultaneously, conventional glass materials have insufficient dispersion matching, resulting in incomplete chromatic aberration correction over the broadband band. This causes the optical tweezers focusing spot to become diffuse and the imaging resolution to decrease, failing to simultaneously meet the dual requirements of high-precision optical field focusing and high-definition microscopic imaging, severely restricting the application of optical tweezers systems in precision scientific research. In particular, off-axis aberrations are exacerbated at the edges of large fields of view; the MTF value of traditional objectives at the edge field of view typically drops below 0.3 at 100 lp / mm, failing to meet the requirement of clear imaging across the entire field of view within a 1mm field diameter.

[0009] Lack of adaptability to vacuum environments and difficulties in integrating long working distances: Optical tweezers systems often need to operate within vacuum chambers in cutting-edge research such as quantum atom trapping and cold atom physics, requiring objectives with the ability to penetrate vacuum-tight windows with long working distances. However, existing objectives generally have short working distances (usually less than 2 mm), which cannot penetrate 6.35 mm thick vacuum window glass and form effective focusing (greater than 17 mm) within a vacuum chamber, severely limiting the application expansion of optical tweezers systems in extreme vacuum environments.

[0010] Insufficient versatility and integration: Existing dedicated optical tweezers objectives are mostly customized narrowband designs with limited spectral compatibility, unable to support near-infrared broadband manipulation and visible light single-band imaging, resulting in low equipment reusability. Furthermore, the structural parameters of most objectives are not standardized, making it difficult to adapt to mainstream optical tweezers microscope optical path systems. Integration and modification are challenging and costly, hindering the widespread adoption and large-scale application of the equipment. Summary of the Invention

[0011] The purpose of this invention is to provide a laser-resistant, multi-band parfocal, long-working-distance vacuum optical tweezers objective. This aims to improve upon the comprehensive technical deficiencies of existing optical tweezers microscope objectives, which generally suffer from poor multi-band chromatic aberration correction capabilities, low laser damage threshold, imbalance between numerical aperture and field-of-view focal length, incomplete broadband aberration correction, lack of long working distance in vacuum, and insufficient general integration. These shortcomings prevent them from meeting the application requirements of multi-band parfocal control in the 800nm–1500nm near-infrared broadband spectrum and 509nm visible light imaging, long-term tolerance to high-power lasers, and long working distances in vacuum environments.

[0012] This invention is implemented as follows:

[0013] This invention provides a laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective, comprising multiple lens elements arranged sequentially along the optical axis from the object plane to the image plane, the multiple lens elements constituting a composite optical system with 17 effective optical refractive surfaces and 1 aperture.

[0014] The objective lens optical specifications meet the following requirements: numerical aperture (NA) = 0.5; effective circular field of view diameter of 1 mm; parfocal focusing within the wavelength range of 800 nm to 1500 nm with a focal point offset not exceeding 1 μm; optimized single-band imaging performance at 509 nm wavelength, with a modulation transfer function (MTF) of not less than 0.4 at 500 lp / mm; circular field of view with a diameter of 1 mm; capable of withstanding continuous wave high-power near-infrared laser irradiation at a wavelength of 1064 nm and a power of not less than 20 W, with no optical surface damage or thermal image quality degradation after 1 hour of continuous operation; reference focal length of 13 mm, with the focal length adjustable and optimized to 5-20 mm; long working distance including a 3.5 mm air gap, a 6.35 mm fused silica window thickness, and a 17 mm vacuum section.

[0015] In one embodiment of the invention, the optical materials used for the plurality of lens elements include: H-LAK4L, H-ZF72A, H-ZPK7, H-LAF50B, H-ZF88GT, H-ZPK5, and fused silica SILICA. At least one lens element uses H-ZPK7 optical glass, and the H-ZPK7 element is located at the rear of the optical system and serves as part of the final focusing group to improve the system's tolerance to high-power near-infrared lasers.

[0016] In one embodiment of the present invention, the optical system structure and material parameters are as follows: arranged coaxially from the object side to the image side along the optical path: front convergence correction lens group L1: including the 1st to 4th refractive surfaces, corresponding to 2 lenses; middle broadband chromatic aberration correction lens group L2: including the 5th to 12th refractive surfaces, corresponding to 4 lenses and 2 sets of cemented doublets; aperture stop: located at the 8th optical surface; rear aberration balancing lens group L3: including the 13th to 17th refractive surfaces, corresponding to 3 lenses; and a high-power quartz protective window.

[0017] In one embodiment of the invention, the lens element closest to the image plane is made of fused silica SILICA to enhance transmittance and imaging contrast at a wavelength of 509 nm.

[0018] In one embodiment of the present invention, the aperture is disposed at the eighth optical surface position, and the aperture net diameter is 14.40 mm, which is used to limit the incident light beam and suppress stray light.

[0019] In one embodiment of the present invention, all optical surfaces are coated with a broadband antireflection film, the antireflection film having a single-sided reflectivity of less than 0.5% in the 800nm ​​to 1500nm wavelength band and a reflectivity of less than 0.1% at a wavelength of 509nm.

[0020] In one embodiment of the present invention, the total effective focal length of the optical system is 5 to 20 mm, and the working distance is greater than 3.5 mm + 6.35 mm / silica + 17 mm / vacuum, which has a very high working distance and is compatible with standard microscope mechanical interfaces.

[0021] In one embodiment of the present invention, the wavefront aberration RMS value of the optical system in the 800-1500nm band within a 1mm field of view is less than λ / 10, with 1064nm as the reference wavelength.

[0022] In one embodiment of the present invention, the objective lens is used to perform the following functions simultaneously:

[0023] Optical tweezers manipulation was performed in the near-infrared band of 800–1500 nm.

[0024] High-resolution fluorescence or bright-field imaging was performed at 509 nm in the visible light band.

[0025] It achieves two-band confocal focus, allowing switching of operating modes without the need for refocusing.

[0026] In one embodiment of the present invention, the optical system includes at least one set of cemented doublet lenses or separate positive and negative lens pairs for correcting chromatic aberration and spherical aberration, ensuring wide-band parfocal performance.

[0027] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention utilizes multiple combinations of optical glasses with different Abbe numbers and partial dispersion coefficients to specifically optimize the second-order spectral chromatic aberration and residual aberration in the ultra-wide near-infrared band of 800nm ​​to 1500nm. This achieves full-range parfocality in the near-infrared band with a focal position shift ≤1μm, while simultaneously precisely matching the 509nm visible light single-band imaging focal point. It completely overcomes the shortcomings of traditional objectives, such as poor confocal consistency across wide and narrow bands and misalignment between the control laser and the imaging laser focal points. It eliminates the need for frequent manual calibration of the optical path, significantly simplifies the optical tweezers system debugging process, and significantly improves the manipulation and positioning accuracy of micro / nano particles and biological cells, as well as the stability of the optical trap confinement. When switching at any wavelength within the 800nm ​​to 1500nm range, the objective focal drift is controlled within 1μm, which is at least an order of magnitude better than similar products.

[0028] This invention incorporates a fused silica (SILICA) protective window at the very end of the objective lens. The silica material possesses an ultra-high laser damage threshold >20 J / cm²@1064 nm and an extremely low coefficient of thermal expansion of 5.5 × 10⁻⁻⁻⁴. 7 With its excellent wide-spectrum light transmission and temperature range of / ℃, it can directly withstand long-term continuous irradiation by high-power near-infrared lasers, effectively protecting the front-end precision lenses and optical coatings, and avoiding problems such as film ablation, lens thermal deformation, refractive index drift, and aberration deterioration. Meanwhile, the rear lens group uses low-expansion, highly uniform optical glass to further suppress thermal distortion caused by high-energy laser irradiation, enabling the objective lens to withstand long-term, high-load, high-power laser operation conditions (1064nm, ≥20W continuous wave, 1 hour without damage). The equipment durability and operational stability are significantly superior to traditional objectives.

[0029] This invention employs a hierarchical correction structure consisting of a front-group primary correction, a middle-group core chromatic aberration correction, and a rear-group residual aberration balancing. Through global optimization of multi-surface curvature, lens thickness, and air gap, it can comprehensively correct system spherical aberration, coma, astigmatism, field curvature, and broadband chromatic aberration. Within a full effective field of view with a diameter of 1 mm, the beam wavefront distortion is extremely low (RMS < λ / 10 @ 1064 nm), resulting in good imaging uniformity, high resolution (MTF @ 500 lp / mm ≥ 0.4), and no significant blurring of the focused spot. This not only meets the requirements for high-definition microscopic imaging in the 509 nm visible light band but also forms a high-intensity, high-stability gradient optical trap in the 800 nm–1500 nm near-infrared band, ensuring high-precision micro-manipulation performance of the optical tweezers.

[0030] This invention precisely matches the optimal parameter combination of a numerical aperture (NA) of 0.5, a system focal length of 13mm, and a field of view diameter of 1mm, overcoming the technical pain point of parameter imbalance in traditional objectives. The high numerical aperture of 0.5 provides sufficient laser gradient force, ensuring stable capture and manipulation of micro- and nano-particles and tiny cells; the moderate 13mm focal length avoids the problems of insufficient working distance of short focal length objectives and weak focusing ability of long focal length objectives; the large effective field of view of 1mm diameter can meet the needs of large-scale observation and synchronous manipulation of microfluidic chips, cell arrays, and large-area micro- and nano-samples, significantly improving overall adaptability. The design concept of simultaneous optimization of these three parameters breaks through the performance bottleneck of mutual constraints among traditional objective parameters.

[0031] This invention, through a specialized design of a "3.5mm air gap + 6.35mm quartz window + 17mm vacuum cavity" for the working distance, achieves for the first time in an optical tweezers objective the ability to focus at a distance through a thick vacuum window. It can be directly integrated outside the vacuum cavity to perform optical tweezers manipulation and imaging observation of internal samples without placing the objective in a vacuum environment, which greatly reduces the complexity and maintenance cost of the vacuum optical tweezers system and provides key optical support for cutting-edge research such as quantum atom capture, cold atom physics, and ultra-high vacuum micromanipulation.

[0032] This invention features a compact optical structure and standardized parameters, allowing for direct compatibility with mainstream commercial and self-developed optical tweezer systems without requiring significant modifications to existing optical tweezers microscopy paths. It simultaneously supports near-infrared broadband laser manipulation and visible light single-band imaging in dual working modes, offering high equipment reusability. This effectively solves the problems of traditional objectives such as single-band operation, high customization requirements, high integration costs, and poor versatility, demonstrating significant value for engineering promotion and widespread adoption.

[0033] This invention significantly reduces system temperature drift and optical residual error through complementary correction of high and low dispersion glass, gentle curved surface structure design and selection of low expansion optical materials. Under long-term operation of high-power laser, there is no obvious image quality attenuation and optical field distortion. It can realize long-term, uninterrupted, high-precision and stable operation of optical tweezers system, meeting the precision experimental needs of cutting-edge fields such as biological research, micro-nano manufacturing, and quantum optics. Attached Figure Description

[0034] Figure 1 This is a table showing the lens material properties and radius of curvature parameters of the optical system of the microscope objectives in this embodiment of the invention;

[0035] Figure 2 This is a schematic diagram of the optical path structure of the microscope objective in an embodiment of the present invention;

[0036] Figure 3 This is a modulation transfer function (MTF) plot of the microscope objective in an embodiment of the present invention;

[0037] Figure 4This is a physical fabrication diagram of the microscope objective lens in an embodiment of the present invention;

[0038] Figure 5 This is a real-world resolution image of the microscope objective lens in an embodiment of the present invention;

[0039] Figure 6 This is a real-world image of a 500nm micropore star pattern taken with a microscope objective in an embodiment of the present invention.

[0040] Explanation of reference numerals in the attached diagram: L1 - Front convergence correction lens group; L2 - Middle broadband chromatic aberration correction lens group; L3 - Rear aberration balancing lens group. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0043] The present invention provides a laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective, comprising multiple lens elements arranged sequentially from the object plane to the image plane along the optical axis, the multiple lens elements constituting a composite optical system with 17 effective optical refractive surfaces and 1 aperture plane.

[0044] Optical system structure and material parameters: arranged coaxially from the object side to the image side along the optical path: front convergence correction lens group L1: containing the 1st to 4th refractive surfaces, corresponding to 2 lenses; middle broadband chromatic aberration correction lens group L2: containing the 5th to 12th refractive surfaces, corresponding to 4 lenses and 2 sets of cemented doublets; aperture stop: located at the 8th optical surface; rear aberration balancing lens group L3: containing the 13th to 17th refractive surfaces, corresponding to 3 lenses; and a high-power quartz protective window.

[0045] For details regarding the specific optical glass material properties, radius of curvature, implementation methods, and parameters, please refer to the appendix of the instruction manual. Figure 1 The table shows the lens material properties and radius of curvature parameters of the optical system.

[0046] The objective lens optical specifications meet the following requirements: numerical aperture (NA) = 0.5; effective circular field of view diameter of 1 mm; parfocal focusing within the wavelength range of 800 nm to 1500 nm with a focal point offset not exceeding 1 μm; optimized single-band imaging performance at 509 nm wavelength, with a modulation transfer function (MTF) of not less than 0.4 at 500 lp / mm; circular field of view with a diameter of 1 mm; capable of withstanding continuous wave high-power near-infrared laser irradiation at a wavelength of 1064 nm and a power of not less than 20 W, with no optical surface damage or thermal image quality degradation after 1 hour of continuous operation; reference focal length of 13 mm, with the focal length adjustable and optimized to 5-20 mm; long working distance including a 3.5 mm air gap, a 6.35 mm fused silica window thickness, and a 17 mm vacuum section.

[0047] The optical path structure is as shown in the instruction manual. Figure 2 As shown in the figure, the spatial arrangement of each lens group and the beam convergence path can be clearly seen. After the beam is initially converged by the front group, the middle group completes the broadband chromatic aberration correction. After the aperture is limited by the aperture stop, the rear group performs the final aberration balance. Finally, the beam exits through the quartz window onto the sample surface.

[0048] The optical materials used in multiple lens elements include: H-LAK4L, H-ZF72A, H-ZPK7, H-LAF50B, H-ZF88GT, H-ZPK5, and fused silica SILICA. At least one lens element utilizes H-ZPK7 optical glass. The H-ZPK7 element is located at the rear of the optical system and serves as part of the final focusing assembly to enhance the system's tolerance to high-power near-infrared lasers. H-ZPK7 glass has an extremely low temperature coefficient of refractive index: dn / dt approximately 2.5 × 10⁻⁻⁻⁻⁴. 6 / ℃ and high uniformity: refractive index uniformity is better than 5×10⁻ 6 This is to improve the system's tolerance to high-power near-infrared lasers and reduce thermally induced focusing drift.

[0049] The lens element closest to the image plane is made of fused silica SILICA, which has excellent transmittance of >99.5% and extremely high resistance to laser damage at a wavelength of 509nm. It is used to enhance transmittance and imaging contrast at a wavelength of 509nm, while also serving as a protective window that directly withstands high-power laser irradiation.

[0050] The aperture stop is located at the 8th optical plane, with a net aperture of 14.40 mm, used to limit the incident beam and suppress stray light. This aperture value corresponds to the entrance pupil diameter requirement of NA=0.5. Calculated with a system focal length of 13 mm and an object-side refractive index of 1.0, the entrance pupil diameter is 13 mm. Considering the lens group compression ratio, the actual aperture stop diameter is set at 14.40 mm, with appropriate edge margins to ensure full aperture light transmission.

[0051] Coating and optical performance parameters: All optical surfaces are coated with a broadband antireflection film. The single-sided reflectance of the antireflection film is less than 0.5% in the 800nm ​​to 1500nm wavelength band, and less than 0.1% at a wavelength of 509nm. The antireflection film adopts a multilayer dielectric film system design and is prepared by electron beam evaporation or ion-assisted deposition processes. The film materials are alternately selected from high refractive index materials, such as Ta2O5 or HfO2, and low refractive index materials, such as SiO2. The total number of film layers is optimized and determined according to the center wavelength to ensure extremely low residual reflectance in both the near-infrared broadband and 509nm bands.

[0052] Instruction manual attached Figure 3 The MTF curve of this invention shown demonstrates optimized single-band imaging performance at a wavelength of 509 nm, with the modulation transfer function (MTF) not lower than 0.4 at 500 lp / mm. The MTF curves maintain good consistency across the entire field of view at heights of 0 mm, 0.25 mm, 0.35 mm, and 0.5 mm, indicating effective control of off-axis aberrations and excellent uniformity in the entire field of view imaging.

[0053] Within a 1mm field of view, the wavefront aberration RMS value of the optical system in the 800–1500nm band is less than λ / 10. With 1064nm as the reference wavelength, this indicates that the system has achieved diffraction-limited imaging quality, and the focused spot is close to the ideal Airy disk distribution.

[0054] The objective lens achieves parfocality within the wavelength range of 800nm ​​to 1500nm, with a focal position offset of no more than 1μm. This performance was verified through multi-wavelength ray tracing simulations, showing that the standard deviation of the focal position is less than 0.3μm and the maximum deviation does not exceed 1μm across nine characteristic wavelengths: 800nm, 900nm, 1000nm, 1064nm, 1100nm, 1200nm, 1300nm, 1400nm, and 1500nm.

[0055] High-power laser resistance: The objective lens can withstand continuous-wave high-power near-infrared laser irradiation with a wavelength of 1064nm and a power of not less than 20W, without optical surface damage or thermal image quality degradation after one hour of continuous operation. This performance is verified through the following tests:

[0056] The objective lens was mounted on a standard microscope platform. A 20W continuous-wave 1064nm laser, after beam expansion and collimation, was perpendicularly incident on the objective lens and focused onto the sample surface. After continuous irradiation for 1 hour, the following indicators were measured: 1. Damage morphology of the optical surface, including no film ablation, peeling, and cracks, was observed using a dark-field microscope; 2. Transmittance attenuation was less than 0.5%; 3. The deviation of the MTF curve from the initial value was less than 3%; 4. Focal point position drift was less than 1μm. All indicators met the requirements.

[0057] The optical system has a total effective focal length of 5–20 mm and a working distance greater than 3.5 mm + 6.35 mm / silica + 17 mm / vacuum, providing a very high working distance and is compatible with standard microscope mechanical interfaces.

[0058] Working distance and mechanical interface: In this embodiment, the total effective focal length of the optical system is 13mm, and the working distance is 3.5mm "air gap" + 6.35mm "quartz window thickness" + 17mm "vacuum cavity depth", for a total equivalent working distance of 26.85mm, of which the 17mm vacuum section is the effective sample manipulation space. This optical path structure can be further optimized and adjusted to a focal length range of 5-20mm, all within the scope of protection of this patent.

[0059] The objective lens is compatible with standard microscope mechanical interfaces, including RMS threaded interfaces "20.32mm×0.706mm" or M25×0.75 standard objective lens threads, and can be directly mounted on mainstream brand microscope turntables or custom optical tweezers system interface boards.

[0060] Within a 1mm field of view, the wavefront aberration RMS value of the optical system in the 800–1500nm band is less than λ / 10, with 1064nm as the reference wavelength.

[0061] Multi-band confocal working mode: The objective lens is used to perform the following functions simultaneously:

[0062] Optical tweezers manipulation is performed in the near-infrared band of 800–1500 nm. The specific working wavelength can be selected according to experimental requirements. All wavelengths can form a stable optical trap without the need for refocusing.

[0063] High-resolution fluorescence or bright-field imaging is performed at 509 nm in the visible light band. 509 nm corresponds to the excitation or emission peak wavelength of many commonly used fluorescent dyes, such as GFP and FITC, which is suitable for fluorescence observation of biological samples.

[0064] It achieves two-band confocal focusing, allowing switching of operating modes without refocusing, with a switching response time of less than 1 second, which greatly improves experimental efficiency.

[0065] Chromatic aberration correction structure: The optical system includes at least one set of cemented doublets or separate positive and negative lens pairs to correct chromatic aberration and spherical aberration, ensuring wide-band parfocal performance. Specifically, the two cemented doublets in the intermediate broadband chromatic aberration correction lens group are paired combinations of H-ZPK7 / H-LAF50B and H-ZF88GT / H-ZPK7, respectively. Achromatic aberration is achieved by utilizing the Abbe number difference Δν > 30 between the positive and negative lenses, and further, secondary spectral correction at the apochromatic level is achieved by utilizing the partial dispersion difference ΔPg,F > 0.02.

[0066] Vacuum Integration Application: The objective lens, with its rear working distance design featuring a 3.5mm air gap, a 6.35mm quartz window, and a 17mm vacuum chamber, can be directly mounted on the external observation window flange of the vacuum chamber. The quartz window, as part of the vacuum sealing interface, enables near-infrared optical tweezers manipulation and visible light imaging observation of the internal sample without compromising the vacuum level. Vacuum Compatibility: Applicable vacuum level better than 1×10⁻ 6 Pa, applicable temperature range 10℃~40℃.

[0067] Instruction manual attached Figure 4 To the instruction manual Figure 6 The images shown are, respectively, a physical fabrication diagram, a real-shot resolution diagram, and a real-shot 500nm micropore star point diagram of the objective lens of this invention.

[0068] Instruction manual attached Figure 4 The actual machining diagram shows that the objective lens has a compact overall structure, high surface finish, excellent machining precision, and good coaxiality of each lens group.

[0069] Instruction manual attached Figure 5 The actual resolution image shows that the objective lens can clearly image the standard resolution test target under 509nm illumination. Each line pair can still be distinguished at the limit resolution. The measured limit resolution is better than 500lp / mm, which is in high agreement with the MTF simulation results.

[0070] Instruction manual attached Figure 6 The real-world image of the star pattern of the 500nm micro-aperture shows that the objective lens, under 1064nm laser illumination, produces a round and symmetrical star pattern with concentrated energy. There is no obvious star pattern deformation caused by coma, astigmatism, or chromatic aberration, indicating that the system has good wavefront aberration control and the focused spot is close to the diffraction limit.

[0071] In summary: The working principle of this laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective is as follows:

[0072] By highly focusing a high-power near-infrared laser beam through a microscope objective, an extremely strong optical field gradient is formed near the focal point. Microparticles in this optical field are simultaneously subjected to a gradient force pointing towards the center of the focal point and a scattering force along the direction of light propagation. When the two forces reach a dynamic equilibrium, the particles are stably bound in the optical potential trap formed by the focal point, achieving non-contact precision capture and manipulation. By setting a numerical aperture of NA=0.5, sufficient gradient force is ensured to form a high-intensity optical trap while also taking into account the working distance and field of view requirements, ensuring stable binding and high-precision manipulation of microparticles, biological cells, and atoms and molecules.

[0073] By employing a three-stage dispersion correction strategy of "preliminary correction in the front group, core correction in the middle group, and residual balancing in the rear group," the front group converging correction lens group uses a combination of positive and negative lenses made of low-dispersion lanthanide glass H-LAK4L and high-dispersion flint glass H-ZF72A to initially offset the system's primary axial chromatic aberration and marginal spherical aberration. The middle broadband chromatic aberration correction lens group consists of two sets of cemented doublets composed of various special dispersive optical materials such as H-ZPK7, H-LAF50B, and H-ZF88GT. This strategy utilizes different glass Abbe numbers and partial dispersion coefficients... The system accurately compensates for secondary spectral chromatic aberration in the ultra-wide near-infrared band of 800nm ​​to 1500nm, and the rear aberration balancing lens group performs final equalization compensation for residual aberrations at the front end, achieving apochromatic broadband correction. Ultimately, it achieves a focal spatial position overlap accuracy of better than 1μm between any wavelength in the 800nm ​​to 1500nm near-infrared band and the 509nm visible light band, allowing free switching between optical tweezers manipulation and imaging observation modes without refocusing, completely eliminating manipulation and imaging position misalignment defects caused by focal shift.

[0074] By synergistically enhancing the system's resistance to laser damage through both optical material selection and structural protection design, the rear lens group is constructed using low-expansion, highly homogeneous optical glasses such as H-ZPK5 and H-ZPK7, taking advantage of their extremely low refractive index temperature coefficient dn / dt of approximately 2.5 × 10⁻ 6 / ℃ To suppress thermally induced focusing drift and localized thermal distortion caused by high-power lasers, a fused silica SILICA protective window is added at the very end of the system at the structural level. This utilizes the extremely high laser-induced damage threshold of quartz material (>20 J / cm²) and its extremely low coefficient of thermal expansion (approximately 5.5 × 10⁻). 7 With a temperature range of / ℃ and excellent broadband transmittance of >99%@800~1500nm, the window directly withstands long-term continuous irradiation by high-power lasers while isolating external dust and moisture pollution. Ultimately, it achieves high tolerance performance with no optical surface damage, no film ablation, and no thermal image quality degradation after one hour of continuous irradiation with a 1064nm wavelength and ≥20W continuous wave laser, significantly improving the lifespan and optical stability of the objective lens under long-term high-load conditions.

[0075] By specifically optimizing the spatial allocation of the working distance behind the objective lens, a 3.5mm air gap ensures a safe distance between the objective lens tip and the vacuum window. A 6.35mm thick fused silica window simultaneously serves as both a high-power laser protection and a vacuum-sealed interface. A 17mm vacuum section provides ample space for sample manipulation and imaging, allowing the objective lens to be directly mounted on the external observation window flange of the vacuum chamber. The laser and imaging beams sequentially penetrate the aforementioned three paths to form a high-quality focused spot on the sample surface within the vacuum chamber. Ultimately, an equivalent working distance of 26.85mm is achieved without compromising vacuum levels, exceeding 1×10⁻⁻⁴ mm. 6Under the premise of Pa, it can realize near-infrared optical tweezers manipulation and visible light synchronous imaging observation of samples in vacuum chamber, which meets the application requirements of extreme vacuum environments such as quantum atom capture and cold atom physics.

[0076] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective, characterized in that, It includes multiple lens elements arranged sequentially along the optical axis from the object plane to the image plane. These multiple lens elements constitute a composite optical system with 17 effective optical refractive surfaces and 1 aperture stop. The objective lens optical specifications meet the following requirements: numerical aperture NA = 0.5; effective circular field of view diameter 1 mm; Achieve parfocal focus within the wavelength range of 800nm ​​to 1500nm, with a focal position offset of no more than 1μm; Single-band imaging performance was optimized at a wavelength of 509nm, with the modulation transfer function (MTF) not less than 0.4 at 500lp / mm; the field of view was circular with a diameter of 1mm. It can withstand continuous high-power near-infrared laser irradiation with a laser wavelength of 1064nm and a power of not less than 20W. It can work continuously for 1 hour without optical surface damage or thermal image quality degradation. The base focal length is 13mm, and the focal length can be scaled and optimized to 5-20mm. The long working distance includes a 3.5mm air gap, a 6.35mm fused silica window thickness, and a 17mm vacuum section.

2. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective according to claim 1, characterized in that, The optical materials used in the various lens elements include: H-LAK4L, H-ZF72A, H-ZPK7, H-LAF50B, H-ZF88GT, H-ZPK5, and fused silica SILICA. At least one lens element uses H-ZPK7 optical glass, which is located at the rear of the optical system and serves as part of the final focusing group to enhance the system's tolerance to high-power near-infrared lasers.

3. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective according to claim 1, characterized in that, Optical system structure and material parameters: arranged coaxially from the object side to the image side along the optical path: front convergence correction lens group L1: containing the 1st to 4th refractive surfaces, corresponding to 2 lenses; middle broadband chromatic aberration correction lens group L2: containing the 5th to 12th refractive surfaces, corresponding to 4 lenses and 2 sets of cemented doublets; aperture stop: located at the 8th optical surface; rear aberration balancing lens group L3: containing the 13th to 17th refractive surfaces, corresponding to 3 lenses; and a high-power quartz protective window.

4. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective according to claim 1, characterized in that, The lens element closest to the image plane is made of fused silica SILICA to enhance transmittance and imaging contrast at a wavelength of 509 nm.

5. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective according to claim 1, characterized in that, The aperture is located at the 8th optical surface, with a net aperture diameter of 14.40 mm, and is used to limit the incident beam and suppress stray light.

6. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective according to claim 1, characterized in that, All optical surfaces are coated with a broadband antireflection coating. The antireflection coating has a single-sided reflectance of less than 0.5% in the 800nm ​​to 1500nm wavelength range and a reflectance of less than 0.1% at a wavelength of 509nm.

7. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective according to claim 1, characterized in that, The optical system has a total effective focal length of 5–20 mm and a working distance greater than 3.5 mm + 6.35 mm / silica + 17 mm / vacuum, providing a very high working distance and is compatible with standard microscope mechanical interfaces.

8. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective according to claim 1, characterized in that, Within a 1mm field of view, the wavefront aberration RMS value of the optical system in the 800–1500nm band is less than λ / 10, with 1064nm as the reference wavelength.

9. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective according to claim 1, characterized in that, Objective lenses are used to perform the following functions simultaneously: Optical tweezers manipulation was performed in the near-infrared band of 800–1500 nm. High-resolution fluorescence or bright-field imaging was performed at 509 nm in the visible light band. It achieves two-band confocal focus, allowing switching of operating modes without the need for refocusing.

10. A laser-resistant multi-band parfocal long working distance vacuum optical tweezers objective according to claim 1, characterized in that, The optical system includes at least one set of cemented doublets or separate positive and negative lens pairs to correct chromatic aberration and spherical aberration, ensuring wide-band parfocal performance.

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