Variable density optical filter with elliptically distributed transmissivity

Abstract

The invention belongs to the technical field of optical thin films, and particularly relates to a variable-density optical filter with elliptically distributed transmissivity, which comprises a transparent optical glass substrate and a metal film, the optical density distribution meets the formula: # imgabs0 # OD (r) = 0; when x2 + (ycos theta) 2 is greater than or equal to R2; wherein R is the short radius of the maximum concentric ellipse, theta is the included angle between the cross section of the light beam and the inclined plane, and f (r) is the variation trend of the optical density of the optical filter along the minor semi-axis (X-axis) direction. The method is ideal in homogenization effect, high in universality, adjustable in parameter and accurate in optical density distribution.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical films, and in particular relates to a variable density filter with a light density in the form of concentric elliptical distribution and a transmittance elliptical distribution that gradually becomes shallower from the inside to the outside, which is suitable for homogenizing elliptical light beams or oblique incident light beams. Background Art

[0002] Normally, we regard the intensity of a laser beam as a circular Gaussian distribution. To obtain a beam with uniform intensity distribution, a radially graded density filter can be placed in the optical path. The optical density of the radially graded density filter is distributed in concentric circles, becoming increasingly shallower with the radius, with a large attenuation at the center and a small attenuation at the edges, thus achieving a sharpening and flattening effect. However, in reality, the laser beam is more or less elliptical in distribution, and when a circular beam is incident at an oblique angle, it will also become an ellipse. Therefore, we can regard any beam as a circular beam incident at a certain angle. At this time, the light intensity of the oblique incidence and the vertical incidence has the following mapping relationship:

[0003] I′(x′,y′)=I(x,y)·cosθ

[0004] Where I is the light intensity and θ is the tilt angle.

[0005] Traditional radial gradient density filters homogenize circular Gaussian beams by distributing the optical density in concentric circles. However, in practical applications, laser beams often exhibit an elliptical distribution due to light source characteristics or oblique incidence, significantly reducing the homogenization effect of traditional filters. Existing technologies fail to effectively address the homogenization requirements for elliptical beams or oblique incidence, and present the following problems:

[0006] (1) Beam distortion: oblique incidence leads to asymmetric light intensity distribution, which cannot be compensated by traditional circular filters;

[0007] (2) Poor homogenization effect: When a circular filter is used on an elliptical beam, the edge light intensity is not sufficiently sharpened;

[0008] (3) Poor versatility: Existing filters are only applicable to beams of vertical incidence or specific ellipticity. Summary of the Invention

[0009] The present invention aims to overcome the deficiencies of the prior art and provide a variable density filter with an ideal homogenization effect, strong versatility, adjustable parameters, and a transmittance elliptical distribution with precise light density distribution.

[0010] To solve the above-mentioned technical problems, the present invention is achieved as follows:

[0011] A variable density filter with an elliptical transmittance distribution, comprising:

[0012] Transparent optical glass substrate;

[0013] A metal film plated on the substrate, wherein the thickness of the metal film is distributed in a concentric ellipse, and the optical density gradually decreases from the inside to the outside along the short semi-axis direction;

[0014] The optical density distribution satisfies the formula:

[0015]

[0016] OD(r)=0when x 2 +(y cosθ) 2 ≥R 2 hour;

[0017] Where R is the minor radius of the largest concentric ellipse, θ is the angle between the beam cross section and the inclined plane, and f(r) is the trend of change in the optical density of the filter along the minor semi-axis (X-axis).

[0018] Furthermore, the metal film is a nickel-chromium alloy film.

[0019] Furthermore, the optical density function f(r) is selected from one of the following forms:

[0020]

[0021]

[0022] Where A is the maximum optical density at the center of the variable density filter.

[0023] Furthermore, the thickness of the metal film is plated by a physical vapor deposition process.

[0024] Furthermore, the filter is suitable for homogenizing a light beam with an angle θ of the inclined surface ranging from 0° to 60°.

[0025] The present invention has an ideal homogenization effect, strong versatility, adjustable parameters, and precise optical density distribution. Compared with the prior art, the present invention has the following characteristics:

[0026] 1. Concentric elliptical light density distribution: through the elliptical gradient design of the metal film thickness, it matches the light intensity attenuation requirements of elliptical beams or oblique incidence;

[0027] 2. Parameter adjustability: Adapt to different application scenarios by adjusting the ratio of the major and minor axes of the ellipse (determined by the angle θ of the inclined plane) and the optical density function f(r);

[0028] 3. High-precision coating process: PVD technology is used to achieve nanometer-level thickness control to ensure accurate light density distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be described in detail below through specific examples. These examples are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art. As mentioned throughout the specification and claims, "including" or "comprising" is an open-ended term and is interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

[0030] Figure 1 This is a schematic diagram of the appearance of the product of the present invention.

[0031] Figure 2 It is the changing trend of the variable density sheet of the present invention along the short axis direction.

[0032] Figure 3 It is the changing trend of the variable density sheet of the present invention along the long axis direction.

[0033] Figure 4 Schematic diagram of the optical path when a circular light beam is incident at an angle. DETAILED DESCRIPTION

[0034] Preparation steps of variable density filter with transmittance elliptical distribution:

[0035] (1) Select transparent optical glass as the substrate;

[0036] (2) coating a metal (nickel-chromium alloy) film on a substrate with a thickness distributed in a concentric elliptical pattern;

[0037] (3) By coating a gradient film, the optical density distribution conforms to the following formula:

[0038]

[0039] OD(r)=0when x 2 +(y cosθ) 2 ≥R 2 Time (outside the largest ellipse).

[0040] Where R is the minor radius of the largest concentric ellipse, θ is the angle between the beam cross section and the inclined plane, and f(r) is the trend of change in the optical density of the filter along the minor semi-axis (X-axis).

[0041] f(r) is typically one of the following functions:

[0042]

[0043] Where A is the optical density of the center point, that is, the maximum optical density of the variable density film.

[0044] 1. Material selection: The substrate is made of fused quartz glass (refractive index 1.46), the metal film is nickel-chromium alloy (Ni:Cr=80:20), and the thickness range is 50-500nm.

[0045] 2. Coating process:

[0046] An elliptically distributed mask is designed on the substrate surface and a film is deposited by magnetron sputtering. The film thickness is monitored in real time during the coating process with an accuracy of ±1nm.

[0047] 3. Optical density verification:

[0048] Use a spectrophotometer to measure the filter transmittance and verify that it meets (Example parameters: R = 10, θ = 45°);

[0049] When R=10,θ=45°, When , the optical density of any point within the largest concentric ellipse of the variable density film can be expressed as:

[0050]

[0051] It can be further simplified to:

[0052] (When x 2 +0.5y 2 <100 hours)

[0053] The variation trend of the density-varying slice along the minor axis direction can be found in Figure 2 The trend of the change in density along the long axis is shown in Figure 3 shown.

[0054] Example 1: For a light beam with an angle θ of 30°, filter parameters (R=15) are designed, and the optical density function f(r)=2(1-r 2 / R 2 ).

[0055] The content of the present invention is not limited to the embodiments listed. Any equivalent transformation of the technical solution of the present invention made by ordinary technicians in this field after reading the description of the present invention is covered by the claims of the present invention.

Claims

1. A variable density filter with an elliptical transmittance distribution, characterized in that: include: Transparent optical glass substrate; A metal film plated on the substrate, wherein the thickness of the metal film is distributed in a concentric ellipse, and the optical density gradually decreases from the inside to the outside along the short semi-axis direction; The optical density distribution satisfies the formula: OD(r)=0 when x 2 +(y cosθ) 2 ≥R 2 hour; Where R is the minor radius of the largest concentric ellipse, θ is the angle between the beam cross section and the inclined plane, and f(r) is the trend of change in the optical density of the filter along the minor semi-axis (X-axis).

2. The variable density filter with elliptical transmittance distribution according to claim 1, characterized in that: The metal film is a nickel-chromium alloy film.

3. The variable density filter with elliptical transmittance distribution according to claim 2, characterized in that: The optical density function f(r) is selected from one of the following forms: Where A is the maximum optical density at the center of the variable density filter.

4. The variable density filter with elliptical transmittance distribution according to claim 3, characterized in that: The thickness of the metal film is made by physical vapor deposition process, and the coating accuracy is controlled within ±5nm.

5. The variable density filter with elliptical transmittance distribution according to claim 4, characterized in that: The filter is suitable for homogenizing a light beam with an included angle θ of the inclined surface ranging from 0° to 60°.

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