CN101414052A - Galileo type multiple-wave length magnification changeable laser bundle-enlarging collimation system - Google Patents

Abstract

The invention discloses a Galilean multi-wavelength variable magnification laser beam expansion and collimation system. The system consists of a variable magnification group plano-convex single lens, a fixed group plano-concave single quadratic aspheric lens and a compensation group plano-convex quadratic aspheric lens. composition. The system can perform 2-12 times continuous variable magnification beam expansion for any laser wavelength between 250-2300nm with an outgoing divergence angle within 5mrad. The system has no real convergence point and can be used in the field of strong lasers. When designing, the image quality of the system obtained by adding an ideal lens after the compensation mirror shows that the wave difference PV value of the central field of view of any wavelength laser in the entire band is better than λ/50, and the PV value of the 0.7 field of view is basically better than The PV values of λ/10 and 1 field of view are better than λ/4, and the beam expansion collimation effect is excellent. The system structure is simple, easy to process and adjust, and easy to use.

Description

Galileo type multi-wavelength variable magnification laser beam expander collimation system

technical field

The present invention relates to optical elements and optical system design technology, in particular to a Galilean multi-wavelength variable magnification laser beam expansion and collimation system, which is suitable for lasers with real-time adjustable beam expansion magnification for multi-wavelengths and no real convergence point The design of the expanded beam collimation system.

Background technique

When a Gaussian beam propagates through free space and transforms through an aberration-free lens, it will always maintain a Gaussian distribution except that the contour scale factor changes.

In the collimation region of the Gaussian beam, the spot size changes slowly, and the spot size increases linearly with the distance away from the beam waist. The smaller the beam waist, the larger the divergence angle of the beam, and the larger the beam waist, the smaller the divergence angle of the beam. Although the beam emitted by the laser has excellent directivity, there is still a certain amount of lateral divergence angle. In actual use, the laser beam expander is used to improve its directivity, that is, to compress its divergence angle, which is the beam expansion and collimation of the laser beam.

Refractive laser beam expander system has no central obstruction, and can be divided into two types: Keplerian type with middle real convergence point and Galilean type without real convergence point. The Galileo beam expander system has no real convergence point and will not cause problems such as air ionization. It can be used in the field of strong lasers. The tube length is short and the axial aberration is well corrected. However, it is difficult to correct off-axis aberration, and it is even more difficult for the requirements of large divergence angle and high beam expansion ratio of the original laser. At this time, the aberration is often balanced by complicating the system structure and increasing the number of lenses. In strong laser applications, if there are multiple requirements for the divergence angle of the beam emitted by the laser or beam expansion and collimation requirements for multiple lasers (different exit divergence angles), if only a beam expander with a fixed magnification is used, then Multiple sets of beam expander systems are required. At this time, in order to avoid frequently switching between different fixed magnification beam expanders, it is very necessary to develop a magnification-adjustable laser beam expander with a relatively large zoom range and good collimation performance. At the same time, in order to simplify the structure of the beam expander optical system, a secondary aspheric lens that is easy to process and inspect is used.

Contents of the invention

The purpose of the present invention is to design a laser beam expander optical system with variable beam expansion ratio suitable for multi-wavelength work, so as to solve the problem of frequently switching and using different fixed ratio beam expanders existing in current fixed ratio laser beam expanders.

The variable magnification beam expander optical system of the present invention is shown in FIG. 1 , and the optical system is composed of a variable magnification group 1 , a fixed group 2 and a compensation group 3 . Zoom group 1 is a plano-convex spherical lens, fixed group 2 is a plano-convex quadratic aspheric lens, compensation group 3 is a plano-convex quadratic aspheric lens, compensation group 3 is a plano-convex quadratic aspheric lens and zoom The zoom groups composed of magnification group 1 and fixed group 2 are aberration-free.

The surface shape of the quadratic aspheric lens can be expressed as

$\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; cr</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}$

In the above formula, z is the sagittal height of the aspheric surface in the direction of the optical axis, c is the radius of curvature of the apex of the aspheric surface, k is the quadratic aspheric surface constant, and r is the radial distance of the aspherical surface.

The laser beam emitted by the laser is emitted in parallel after passing through the variable magnification group 1, the fixed group 2, and the compensation group 3. The aperture is enlarged and the divergence angle is reduced.

The magnification adjustment method of the variable magnification laser beam expander system of the present invention is: the fixed group 1 does not move, and the interval d12 between the variable magnification group 1 and the fixed group 2 is adjusted. At this time, the position of the image plane will change, and then the fixed group 2 and the compensation group are adjusted. The interval d23 of 3 restores the position of the image plane to infinity, and realizes beam expansion and collimation of the laser beam. Each specific interval d12 between zoom group 1 and fixed group 2 corresponds to an interval d23 between fixed group 2 and compensation group 3. When the interval d12 between zoom group 1 and fixed group 2 changes continuously, the corresponding fixed group 2 The distance d23 from the compensation group 3 also needs to be changed, so that the continuous change of the beam expansion ratio M can be realized.

The variable magnification laser beam expander system of the present invention can work in multiple wavelengths. Since the optical material has different refractive indices for lasers of different wavelengths, for the same beam expansion ratio, each time a laser wavelength is changed, after determining the interval d12 between the variable power group and the fixed group, adjust the interval d23 between the fixed group and the compensation group. The position of the image plane is restored to infinity, and the beam expansion of the wavelength and the magnification is realized. To expand the laser beam at the same magnification with adjacent wavelengths, you only need to fine-tune the interval d12 between the zoom group and the fixed group, and then adjust the interval d23 between the fixed group and the compensation group. When the optical material of the lens is quartz glass, the beam expander system of the present invention can work at any single wavelength within the wavelength of 250nm-2300nm.

The advantages of the present invention are:

1. There is no real convergence point in the system, which can be used for collimation and beam expansion of strong lasers;

2. The structure of the system is simple, consisting of only 2 plano-convex lenses and 1 plano-concave lens, and the processing tolerance is loose;

3. The plano-convex aspheric lens alone eliminates aberrations and is easy to process;

4. The fixed group does not move, adjust the position of the zoom group, and then adjust the position of the compensation group to ensure that the image plane is always at infinity, which can realize continuous zoom beam expansion with excellent performance of 2-12 times;

5. When zooming, the adjustment distance is small, and the focusing mechanism is simple and easy to implement;

6. Adjusting the positions of the zoom group and the compensation group can be applied to beam expansion and collimation of various laser wavelengths.

Description of drawings

Fig. 1 is a schematic diagram of the optical structure of the present invention,

In the figure: 1 is the zoom group;

2 is a fixed group;

3 is the compensation group;

R11 is the radius of curvature of the front surface of the zoom group 1 lens;

R12 is the radius of curvature of the rear surface of the zoom group 1 lens;

R21 is the radius of curvature of the front surface center of the fixed group 2 lens;

R22 is the radius of curvature of the rear surface of the fixed group 2 lens;

R31 is the radius of curvature of the front surface of the compensation group 3 lens;

R32 is the radius of curvature of the rear surface center of the zoom lens;

d1 is the central thickness of the zoom group 1 lens;

d12 is the air gap between the zoom group 1 lens and the fixed group 2 lens;

d2 is the central thickness of the fixed group 2 lens;

d23 is the air gap between the fixed group 2 lens and the compensation group 3 lens;

d3 is the central thickness of the compensation group 3 lens.

Detailed ways

Give a preferred embodiment of the present invention according to Fig. 1 below and set forth in detail:

The parameters of the incident laser beam: diameter 3mm, divergence angle 5mrad, any single wavelength within the wavelength 250-2300nm. (Due to the different optical materials of the lens, the wavelength range of the expandable collimation is also different)

The parameters of the outgoing laser beam are required: the beam expansion magnification is M (2≤M≤12), the aperture is 3M, and the divergence angle is 5/M.

Taking the 623.8nm laser wavelength as an example, the specific design parameters of the beam expander optical system are shown in Table 1:

Table 1 Data of variable magnification beam expander optical system

The distance between d12 and d23 is adjustable. When the variable magnification M is continuously changed between 2 and 12, for the laser wavelength of 0.6328nm, the value range of d12 is 42.50mm-3.50mm, and the value range of d23 is 177.85mm-195.84mm.

Add an ideal lens after the system to evaluate the design quality of the beam expander system. Taking the points of variable magnification M=2, 4, 6, 8, 10, and 12 as examples, see Table 2 for the wave aberration of each field of view. When the system continuously zooms between 2-12 times, the PV value of the central field of view is better than λ/50, the PV value of the 0.7 field of view is basically better than λ/20, and the PV value of the 1 field of view is better than λ/10 , excellent beam collimation effect.

Table 2 Image quality of each field of view with different beam expansion magnifications

For a single wavelength, during the zooming process, the zooming group moves linearly, while the compensation group moves approximately in a parabolic curve.

By changing the air interval d12 between the variable magnification group 1 and the fixed group 2, and the air interval d23 between the fixed group 2 and the compensation group 3, beam expansion and collimation of any single wavelength laser beam within the wavelength of 250-2300nm can be performed. For simplicity, select the wavelength λ=250, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300nm , select the points of beam expansion ratio M=2, 4, 7, 10, 12. For the wave aberration PV values of 0 field of view, 0.7 field of view (±3.5mrad), and 1.0 field of view (±5.0mrad) corresponding to each wavelength and beam expansion ratio, see Table 3. The wave aberration of each field of view under various conditions PV values are much smaller than λ/4. See Table 4 for the values of d12 and d23 when zooming and expanding the beam with a single wavelength or changing the laser wavelength.

For the 250-2300nm wavelength range, 2-12 times continuous beam expansion, the air gap d12 between the variable magnification group lens and the fixed group lens ranges from 45.0mm to 3.1mm, and the air gap d23 between the fixed group lens and the compensation group lens takes The value range is 159.6mm-206.8mm. The optical length of the system is less than 250mm.

Claims (5)

1. A Galilean multi-wavelength variable magnification laser beam expander collimation system, which has a spherical lens and two aspheric lenses, is characterized in that: The laser beam is refracted by a variable power group (1) composed of a plano-convex spherical lens, and then passes through a fixed group (2) composed of a plano-concave aspheric lens and a compensation group (3) composed of a plano-convex aspheric lens. Parallel emission, expanded aperture, smaller divergence angle; The beam expansion ratio of the system is adjusted by adjusting the distance d12 between the zoom group (1) and the fixed group (2) and the distance d23 between the fixed group (2) and the compensation group (3); The working wavelength of the system is changed by changing the distance d12 between the variable magnification group (1) and the fixed group (2) and the distance d23 between the fixed group (2) and the compensation group (3). 2. A kind of Galileo type multi-wavelength variable magnification laser beam expander collimation system according to claim 1, characterized in that: said fixed group (2) is a quadric surface aspherical lens. 3. A kind of Galileo type multi-wavelength variable magnification laser beam expander collimation system according to claim 1, characterized in that: said compensation group (3) is a quadratic aspheric lens with aberration elimination. 4. A Galileo-type multi-wavelength variable magnification laser beam expander collimation system according to claim 1, characterized in that: the adjustment range of the beam expander magnification of the system is 2-12 times. 5. A kind of Galileo type multi-wavelength variable magnification laser beam expansion and collimation system according to claim 1, characterized in that: when the optical system adopts the Q1 quartz glass lens of Schott Company, the operating wavelength range of the system It is 250nm-2300nm.

Images