Optical lens for femtosecond laser focusing scanning

Abstract

The application discloses an optical lens for femtosecond laser converging scanning, which is based on a femtosecond laser with a wavelength of 1030 nm. The optical lens is arranged along an optical axis from a material side to an imaging surface and sequentially comprises a first lens with a negative focal length, a second lens with a positive focal length, a third lens with a positive focal length, a fourth lens with a negative focal length and a fifth lens with a positive focal length. The material side of the first lens is a concave surface, and the image side is a plane. The material side of the second lens is a plane, and the image side is a convex surface. The material side of the third lens is a convex surface, and the image side is a plane. The material side of the fourth lens is a plane, and the image side is a concave surface. The material side and the image side of the fifth lens are both convex surfaces. The focused light spot generated by the optical lens is equivalent to the theoretical diffraction limit range, and the light spot will not produce a significant dispersion state due to the inclined incident light. Meanwhile, the wavefront aberration is less than one wavelength, which can improve the uniformity of the laser beam energy and reduce the influence of laser internal interference.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to an optical lens for femtosecond laser focusing scanning. BACKGROUND

[0002] In the femtosecond laser myopia correction surgery, the action point of the laser focusing spot is required to be as small as possible to reduce the depth of field range of the spot and improve the precision of the laser surgery. At present, the laser surgery equipment used in the femtosecond laser myopia correction surgery mainly uses near-infrared laser as the main action light source. The wavelength range of the infrared light is limited by the diffraction limit of the optical principle, which tends to cause the action point of the energy of the spot to be large, thereby reducing the energy density. The existing optical lens acting on the infrared light has very good central parallel beam focusing capability, but it will produce serious coma and field curvature for the light with a certain tilt angle, which has a certain error for the application of the spot in the plane scanning. In the lens group acting on the plane scanning, although it has a wide plane scanning range and will not produce serious aberration for the light with a large tilt angle, the focusing spot is large and the depth of field is too long, which is difficult to meet the precise action requirement in the application of ophthalmic surgery. SUMMARY

[0003] The present application provides an optical lens for femtosecond laser focusing scanning.

[0004] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] An optical lens for femtosecond laser focusing scanning, based on a femtosecond laser with a wavelength of 1030nm, the scanning range is a circular range with a diameter of 1mm, the optical lens is composed of five lenses arranged along the optical axis from the object side to the imaging surface, and sequentially includes a first lens with negative focal power, the object side surface of which is a concave surface, and the image side surface of which is a plane; a second lens with positive focal power, the object side surface of which is a plane, and the image side surface of which is a convex surface; a third lens with positive focal power, the object side surface of which is a convex surface, and the image side surface of which is a plane; a fourth lens with negative focal power, the object side surface of which is a plane, and the image side surface of which is a concave surface; and a fifth lens with positive focal power, the object side surface and the image side surface of which are both convex surfaces.

[0006] Preferably, the total length of the optical lens is 372mm, the effective focal length is 36mm, the f number is 1.82, the entrance pupil diameter is 20mm, the field of view angle is -0.78°~+0.78°, and the maximum radius in the beam propagation process is 50mm.

[0007] Preferably, the convex surface of the third lens is an even aspheric surface.

[0008] Preferably, the distance between the first lens and the second lens is 185mm.

[0009] Preferably, the fourth lens is movable between the third lens and the fifth lens.

[0010] Preferably, the fifth lens is composed of a biconvex lens made of high dispersive material and a meniscus lens made of low dispersive material.

[0011] Compared with the prior art, the present application has the following beneficial effects:

[0012] The focusing light spot generated by the optical lens disclosed by the present application is equivalent to the theoretical diffraction limit range, and the light spot will not produce obvious dispersion state due to the oblique incident light, and the wavefront aberration is less than one wavelength, which can improve the uniformity of laser beam energy and reduce the influence of laser internal interference. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The optical path design layout of the present application is shown in the figure;

[0014] Figure 2 The optical dispersion spot diagram of the optical path design of the present application is shown in the figure;

[0015] Figure 3 The modulation transfer function (MTF) diagram of the optical path design of the present application is shown in the figure;

[0016] Figure 4 The circle-in energy fraction diagram of the optical path design of the present application is shown in the figure.

[0017] The figure shows: 1, first lens; 2, second lens; 3, third lens; 4, fourth lens; 5, fifth lens; 6, window mirror. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present application more clear and obvious, the present application will be further described in detail below in combination with examples and figures, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and do not limit the present application.

[0019] As Figure 1The optical lens for femtosecond laser convergent scanning shown in the application can make the scanning range a circular range with a diameter of 1 mm by using the existing mechanical structure such as a galvanometer which can deflect a light beam based on a femtosecond laser with a wavelength of 1030 nm. Specifically, the optical lens is composed of five lenses, which include, in the direction of the optical axis from the object side to the imaging surface, a first lens 1 with negative focal power, the object side of which is a concave surface and the image side of which is a plane, a second lens 2 with positive focal power, the object side of which is a plane and the image side of which is a convex surface, a third lens 3 with positive focal power, the object side of which is a convex surface and the image side of which is a plane, a fourth lens 4 with negative focal power, the object side of which is a plane and the image side of which is a concave surface, and a fifth lens 5 with positive focal power, the object side of which is a convex surface and the image side of which is a convex surface.

[0020] The light beam formed after the laser in the embodiment passes through the diaphragm is diverged by the first lens 1, then converges into parallel light to achieve the effect of beam expansion by the second lens 2, thereby achieving the purpose of improving the entrance pupil diameter; the light beam converging into parallel light passes through the third lens 3 to increase the focal power of the whole optical lens, thereby improving the convergent ability of the optical lens and reducing the effective focal length; then passes through the fourth lens 4 and the fifth lens 5 in turn to eliminate the influence of stray light and reduce the overall chromatic aberration, and then passes through the window mirror 6 to transmit light rays to achieve convergent scanning within a certain range at a certain depth of the cornea of the human eye, wherein the window mirror 6 is a biological interface protection type window mirror, which is preferably made of colorless transparent borosilicate glass material. Specifically, the fifth lens 5 is composed of a biconvex lens made of high dispersion material and a concave-convex lens made of low dispersion material, which are bonded together, and the mutual compensation of the high dispersion material and the low dispersion material makes the convergent ability of different wavelengths tend to be similar, thereby reducing the overall chromatic aberration and improving the versatility of the whole optical lens in different near-infrared wave bands; the fourth lens 4 can move between the third lens 3 and the fifth lens 5, which functions to eliminate unnecessary stray light by a small diaphragm range, and improves the processing ability of the coma and the scanning range of the optical lens by the central convergent effect of the two positive focal power lenses through the negative focal power of the fourth lens 4; the convex surface of the third lens 3 is an even aspheric surface, which improves the focal power of the whole optical lens by using the even aspheric surface of the third lens 3, thereby improving the convergent ability of the optical lens and reducing the effective focal length.

[0021] In the implementation, since the size of the lens is limited, in order to avoid the problem of energy loss of more light beams due to the too small lens, the light beams with different convergence and divergence angles are required to have a certain space to adjust the light beam width size passing through the lens, and therefore the fourth lens 4 is designed to be movable between the third lens 3 and the fifth lens 4. Specifically, the position of the fourth lens 4 is adjusted to adjust the distance between the fourth lens 4 and the third lens 3 and the fourth lens 4, and the distance between the third lens 3 and the fourth lens 4 and the distance between the fourth lens 4 and the fifth lens 5 have a complementary length relationship, that is, the overall optical length is constant. This arrangement facilitates the elimination of the effects of spherical aberration, coma, chromatic aberration, and field curvature in the simulation process.

[0022] In some embodiments, if the optical lens needs to achieve a smaller light spot, the ratio of the effective focal length to the diameter of the optical lens can be compared. The larger the ratio, the smaller the side light spot.

[0023] Embodiments

[0024] The total length of the optical lens is 372 mm, the effective focal length is 36 mm, the f number is 1.82, the entrance pupil diameter is 20 mm, the field of view angle is -0.78° to +0.78°, and the maximum radius in the light beam propagation process is 50 mm. Due to the divergence of the first lens 1, the longer the distance between the first lens 1 and the second lens 2, the higher the magnification of the beam expander composed of the first lens 1 and the second lens 2. The shorter the distance, the higher the magnification. For a certain magnification target light beam width, there is a certain lens distance requirement. Specifically, the data parameters of each lens of the optical lens in the embodiment are shown in Table 1:

[0025]

[0026] Table 1

[0027] In Table 1, the thickness corresponding to the object plane of each lens is the central thickness of the lens, and the thickness corresponding to the image plane is the distance between the lens and the next lens. Among them, the object plane of the third lens 3 is an even aspheric surface, which can effectively solve the problem of spherical aberration caused by wide beam convergence. The curve expression of this surface is:

[0028]

[0029] In the formula, C is the conic coefficient; X is the independent variable of the formula, Z represents the dependent variable of the even aspheric surface; K is e -7 ; B n is the nth order constant, and n is an even number; in this embodiment, n is 4, 6, and 8, respectively. The specific data is shown in Table 2:

[0030] Cone coefficient C 4th order term constant B4 6th order term constant B6 8th order term constant B8 -0.952 2.425e -7 ]]> 1.252e -11 ]]> 5.210e -16 ]]>

[0031] Table 2

[0032] In this embodiment, referring to the optical diffraction spot diagram shown in Figure 2 the diffraction limit size of the spot reflected by the data in the figure is 2.31um, when the beam is not incident at an angle, the image height is also at the center, the effective energy spot radius size is 1.068um, the geometric radius size is 3.675um, each figure shows the image height and the effective energy spot radius size and the geometric radius size of each point when incident at different angles. The maximum tilt angle is 0.78°, the lower height is 0.5mm, and the effective energy spot radius size is 1.49um.

[0033] Referring to the modulation transfer function MTF diagram shown in Figure 3 The figure is a MTF value data graph, and the spatial frequency resolution is 200 line pairs per millimeter. It can be concluded that when the spatial frequency reaches 200 line pairs per millimeter, the lens resolution reaches 200 line pairs per millimeter, and lines with a pitch of 5um can be distinguished.

[0034] Referring to the figure shown in Figure 4 The effective energy of the laser within a 1.5um radius range centered on each spot centroid reaches 60%, and the effective energy of the laser within a 2.5um radius range centered on each spot centroid reaches 80%.

[0035] In summary, the optical lens disclosed in this embodiment produces a focused spot that is comparable to the theoretical diffraction limit range. Specifically, the spot diameter is 5um, and the spot can be scanned within a circular range of 1mm in diameter, and the spot does not produce significant diffusion due to oblique incidence of light. And also can make the infrared laser center wavelength of ± 5um wavelength range without obvious dispersion and aberration. The laser energy at the center of the spot reaches 80% of the total laser energy, which can realize the full application of laser energy and improve the precision of cutting operation. The wavefront aberration is less than one wavelength, which can improve the uniformity of laser beam energy and reduce the influence of laser interference.

[0036] Of course, the present application can have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes and modifications should all belong to the protection scope of the claims attached to the present application.

Claims

1. An optical lens for femtosecond laser focusing scanning, based on a femtosecond laser with a wavelength of 1030 nm, characterized in that The scanning range is a circular range with a diameter of 1mm, the optical lens is composed of five lenses arranged along the optical axis from the object side to the imaging surface, and sequentially comprises: a first lens (1) with negative focal power, the object side surface of which is a concave surface, and the image side surface of which is a plane; a second lens (2) with positive focal power, the object side surface of which is a plane, and the image side surface of which is a convex surface; a third lens (3) with positive focal power, the object side surface of which is a convex surface, and the image side surface of which is a plane; a fourth lens (4) with negative focal power, the object side surface of which is a plane, and the image side surface of which is a concave surface; a fifth lens (5) with positive focal power, the object side surface and the image side surface of which are both convex surfaces, the fifth lens (5) being composed of a convex lens made of a high-dispersion material and a concave-convex mirror made of a low-dispersion material.

2. The optical lens for femtosecond laser focus scanning according to claim 1, wherein, The total length of the optical lens is 372mm, the effective focal length is 36mm, the f number is 1.82, the entrance pupil diameter is 20mm, the field of view angle is -0.78°~+0.78°, and the maximum radius in the process of beam propagation is 50mm.

3. The optical lens for femtosecond laser focus scanning according to claim 2, wherein, The convex surface of the third lens (3) is an even aspheric surface.

4. The optical lens for femtosecond laser focus scanning according to claim 2, wherein, The interval between the first lens (1) and the second lens (2) is 185mm.

5. The optical lens for femtosecond laser focus scanning according to claim 4, wherein, The fourth lens (4) is movable between the third lens (3) and the fifth lens (5).

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