CN104923463A - Potassium dihydrogen phosphate (KDP) optical surface planarization method - Google Patents

Abstract

The invention relates to a KDP optical surface flattening method. At present, the ultra-precision processing method of KDP crystal will leave polishing liquid on the surface of KDP crystal, and produce small-scale ripples on the surface of KDP crystal, which will affect the optical surface quality of KDP crystal. In the present invention, the KH ₂ PO ₄ optical crystal material after single-point diamond turning and polishing is used as the processing object, and a layer of polymer film is coated on the optical surface of the KH ₂ PO ₄ optical crystal material by the method of spin coating, and then After the vacuum heat treatment, a polymer layer with low surface roughness is formed on the surface of the KH ₂ PO ₄ optical crystal material, and the upper surface of the polymer layer is a planarized surface. The invention forms a layer of polymer film with good mechanical properties, stable properties and low surface roughness on the surface of KDP, the process is simple, the requirements for equipment are low, the cost is low, and a better planarization effect can be obtained on the optical surface of KDP, and The application prospect is considerable.

Description

KDP Optical Surface Planarization Method

technical field

    The invention belongs to the technical field of optical component surface flattening, and in particular relates to a KDP optical surface flattening method.

Background technique

KDP crystal is the abbreviation of potassium dihydrogen phosphate (KH ₂ PO ₄ ) crystal. KDP crystal is a very good nonlinear optical crystal material, which has the characteristics of large nonlinear optical coefficient, wide light transmission band, excellent optical uniformity and high laser damage threshold, etc., and has been widely used It is used in high-tech fields such as laser frequency doubling devices, parametric oscillation, electro-optic modulation, piezoelectric transducers and fast optical switches. In laser inertial confinement fusion, KDP crystals are used in optical frequency doubling converters and electro-optic switches. However, KDP crystals are prone to deliquescence, high brittleness, sensitivity to temperature changes, and low hardness, which are not conducive to the processing of KDP crystals. Therefore, the polishing of KDP crystals, especially large-sized KDP crystals with high optical quality, is very difficult. At present, the ultra-precision processing methods of KDP crystal mainly include single-point diamond turning technology, magnetorheological polishing technology, ion beam etching and polishing technology, etc., but magnetorheological polishing technology will leave polishing fluid on the surface of KDP crystal, which cannot be removed. The single-point diamond turning technology will produce small-scale ripples on the surface of the KDP crystal, which will affect the optical surface quality of the KDP crystal. Direct etching and polishing of KDP crystal surface by ion beam is inefficient and cannot guarantee the surface quality.

Contents of the invention

The purpose of the present invention is to provide a KDP optical surface planarization method, which can form a polymer film with low roughness and no surface defects on the KDP surface, and use it in the ion beam etching and polishing technology.

The technical scheme adopted in the present invention is:

KDP optical surface planarization method is characterized in that:

Include the following steps:

Taking the KH ₂ PO ₄ optical crystal material after single-point diamond turning and polishing as the processing object, a layer of polymer film is coated on the optical surface of the KH ₂ PO ₄ optical crystal material by the method of spin coating, and then vacuum heat treatment Finally, a polymer layer with low surface roughness is formed on the surface of the KH ₂ PO ₄ optical crystal material, and the upper surface of the polymer layer is a planarized surface.

The coating glue of described polymer film selects BCB-1500 glue for use;

The conditions of spin coating are: low speed 500r/min~600r/min, time 18s, high speed 4000r/min~5000r/min, time 50s~60s;

The conditions of vacuum heat treatment are: temperature 50°C~100°C, time 4h~38h, heating time 30min~1h.

The coating glue of described polymer film selects BCB-700 glue for use;

The conditions of spin coating are: low speed 500r/min~600r/min, time 18s, high speed 2500r/min~3000r/min, time 50s~60s;

The conditions of vacuum heat treatment are: temperature 50°C~100°C, time 4h~38h, heating time 30min~1h.

The coating glue of described polymer film selects the dilution glue of BCB-700 for use, and the volume ratio of glue and diluent n-butyl acetate is 2:1;

The conditions of spin coating are: low speed 500r/min~600r/min, time 18s, high speed 2000r/min~3000r/min, time 50s~60s;

The conditions of vacuum heat treatment are: temperature 50°C~100°C, time 4h~38h, heating time 30min~1h.

The present invention has the following advantages:

In the present invention, the KDP after single-point diamond turning and polishing is used as the processing object, and a layer of polymer film is coated on the optical surface of the KDP by the method of spin coating, and a layer of polymer film with good mechanical properties and properties is formed on the surface of the KDP after vacuum heat treatment. Stable polymer film with low surface roughness, simple process, low equipment requirements, low cost, good planarization effect on KDP optical surface, and promising application prospect.

Description of drawings

Fig. 1 is after single-point diamond pre-polishing described in example 1, the optical surface roughness detection result of KDP crystal sample 1 before planarization, and the detection instrument used is Talysurf CCI-2000 non-contact surface profilometer, measuring range It is 0.18×0.18mm.

in:

a shows the roughness measurement results of the KDP surface after Gaussian filtering;

Figure b is the 3D topography of the measurement points on the KDP surface.

Fig. 2 is the optical surface roughness test result of the KDP crystal sample 1 after planarization.

in:

a shows the roughness measurement results of the KDP surface after Gaussian filtering;

Figure b is the 3D topography of the measurement points on the KDP surface.

Fig. 3 is the test result of the optical surface roughness of the KDP crystal sample 2 before planarization after single-point diamond pre-polishing described in Example 2, and the testing instrument used is a Talysurf CCI-2000 non-contact surface profiler.

in:

a shows the roughness measurement results of the KDP surface after Gaussian filtering;

Figure b is the 3D topography of the measurement points on the KDP surface.

Fig. 4 is the optical surface roughness detection result of the KDP crystal sample 2 after planarization.

in:

a shows the roughness measurement results of the KDP surface after Gaussian filtering;

Figure b is the 3D topography of the measurement points on the KDP surface.

Fig. 5 is the test result of the optical surface roughness of the KDP crystal sample 3 before planarization after the single-point diamond pre-polishing described in Example 3, and the testing instrument used is a Talysurf CCI-2000 non-contact surface profiler.

in:

a shows the roughness measurement results of the KDP surface after Gaussian filtering;

Figure b is the 3D topography of the measurement points on the KDP surface.

FIG. 6 is the optical surface roughness detection result of the KDP crystal sample 3 after planarization.

in:

a shows the roughness measurement results of the KDP surface after Gaussian filtering;

Figure b is the 3D topography of the measurement points on the KDP surface.

Fig. 7 is the test result of optical surface roughness of KDP crystal sample 4 before planarization after single-point diamond pre-polishing described in Example 4, and the testing instrument used is Talysurf CCI-2000 non-contact surface profiler.

in:

a shows the roughness measurement results of the KDP surface after Gaussian filtering;

Figure b is the 3D topography of the measurement points on the KDP surface.

FIG. 8 is the test result of the optical surface roughness of the KDP crystal sample 4 after planarization.

in:

a shows the roughness measurement results of the KDP surface after Gaussian filtering;

Figure b is the 3D topography of the measurement points on the KDP surface.

Detailed ways

The present invention will be described in detail below in combination with specific embodiments.

The KDP optical surface planarization method involved in the present invention, in order to solve the problem that the single-point diamond turning KDP crystal surface will produce small-scale ripples and the surface quality cannot be guaranteed by direct etching and polishing of the KDP crystal surface with ion beams, the single-point diamond turning On the basis of the KDP crystal, a polymer film is coated on the surface of the KDP crystal to cover the small-scale ripples on the surface, and a polymer film with low roughness and no surface defects is formed on the surface of the KDP, which is used in the ion beam Etching and polishing technology specifically includes the following steps:

Taking the KH ₂ PO ₄ optical crystal material after single-point diamond turning and polishing as the processing object (the surface roughness of the polished KH ₂ PO ₄ optical crystal material is about 2nm), the method of spin coating is used on KH ₂ PO ₄ The optical surface of the optical crystal material is coated with a layer of polymer film, and after vacuum heat treatment, a polymer layer with good mechanical properties, stable properties and low surface roughness is formed on the surface of the KH ₂ PO ₄ optical crystal material. The polymer layer The upper surface is a planarized surface.

(1) When the coating glue of the polymer film is BCB-1500 glue:

The conditions of spin coating are: low speed 500r/min~600r/min, time 18s, high speed 4000r/min~5000r/min, time 50s~60s;

The conditions of vacuum heat treatment are: temperature 50°C~100°C, time 4h~38h, heating time 30min~1h.

(2) When the coating glue of the polymer film is BCB-700 glue:

The conditions of spin coating are: low speed 500r/min~600r/min, time 18s, high speed 2500r/min~3000r/min, time 50s~60s;

The conditions of vacuum heat treatment are: temperature 50°C~100°C, time 4h~38h, heating time 30min~1h.

(3) The coating glue of the polymer film is BCB-700 thinner glue, and the volume ratio of the glue to the diluent n-butyl acetate is 2:1:

The conditions of spin coating are: low speed 500r/min~600r/min, time 18s, high speed 2000r/min~3000r/min, time 50s~60s;

The conditions of vacuum heat treatment are: temperature 50°C~100°C, time 4h~38h, heating time 30min~1h.

The polymer layer formed by the above method can effectively cover the small-scale ripples on the KDP surface, and the surface roughness of the polymer film is about 1.2nm, and the surface effect can be transferred to the KDP crystal surface by ion beam etching, so that the KDP Crystals are ultra-precision polished. The proposal of this technical solution is beneficial to the polishing of KDP crystal based on ion beam etching, and makes up for the technical defects of single-point diamond turning polishing and direct ion beam etching polishing of KDP crystal. Coating polymers on the surface of ultra-smooth optical elements can reduce their surface roughness, because the coated polymers have liquid fluidity, and an initial film is formed on the surface of the element by spin coating. Due to the fluidity of the liquid, the formed The initial film can effectively improve the surface morphology of components that still have defects on the surface, and can form a stable dielectric film layer with good electrical and mechanical properties after curing. After repeated experiments, the planarization technology of the present invention can effectively improve the surface quality of the optical surface of the KDP crystal, without changing the chemical composition and crystal structure of the KDP crystal, and without affecting the optical properties of the original crystal.

Example 1:

The method includes the following steps: firstly, the class II KDP crystal sample 1 with a size of 50×50×10 mm ² is turned by single-point diamond turning, and then the sample 1 after single-point diamond turning is used as the processing object, and the BCB -1500 flattening glue is applied on the surface of sample 1 for flattening. The main process parameters of flattening are controlled as follows: low speed 600r/min, time 18s, high speed 5000r/min, time 60s, vacuum heat treatment temperature 80℃, time 4h , Heating time 1h. The surface roughness of sample 2 was measured with a white light interferometer, and the scanning range was 0.18×0.18 mm. The roughness measurement results of sample 1 before and after planarization are shown in Figure 1 and Figure 2, from Figure 1 It can be seen from Figure 2 that the root mean square surface roughness Sq of sample 1 after single-point diamond turning is 2.2592 nm, and the root mean square roughness Sq of sample 1 after planarization is 1.2759 nm. After the planarization in this embodiment, the roughness value of the KDP crystal surface is reduced, and the surface roughness is improved.

Example 2:

It includes the following steps: first, turn the type II KDP crystal sample 2 with a size of 50×50×10 mm ² by single-point diamond turning, and then take the sample 2 after single-point diamond turning as the processing object, and use BCB -1500 flattening glue is applied on the surface of sample 2 for flattening. The main process parameters of flattening are controlled as follows: low speed 600r/min, time 18s, high speed 5000r/min, time 60s, vacuum heat treatment temperature 80℃, time 4h , Heating time 1h. The surface roughness of sample 2 was measured with a white light interferometer, and the scanning range was 0.18×0.18mm. The roughness measurement results of sample 2 before and after planarization are shown in Fig. 3 and Fig. 4. It can be seen from Fig. 4 that the root mean square surface roughness Sq of sample 2 after single-point diamond turning is 2.1014 nm, and the root mean square roughness Sq of sample 2 after planarization is 1.3291 nm. After the planarization in this embodiment, the roughness value of the KDP crystal surface is reduced, and the surface roughness is improved.

Example 3:

The method includes the following steps: firstly use single-point diamond turning to class II KDP crystal sample 3 with a size of 50×50×10 mm ² , and then take the sample 3 after single-point diamond turning as the processing object, and use BCB-700 to dilute The flattening glue is applied on the surface of the sample 3 for flattening. The main process parameters of the flattening are controlled as follows: low speed 600r/min, time 18s, high speed 3000r/min, time 60s, vacuum heat treatment temperature 80°C, time 4h, Heating time 1h. The surface roughness of sample 3 was measured with a white light interferometer, and the scanning range was 0.18×0.18 mm. The roughness measurement results of sample 3 before and after planarization are shown in Figure 5 and Figure 6, from Figure 5 It can be seen from Fig. 6 that the root mean square Sq of the surface roughness of the sample 3 after single-point diamond turning is 2.0266 nm, and the root mean square Sq of the surface roughness of the sample 3 after planarization is 1.3118 nm. After the planarization in this embodiment, the roughness value of the KDP crystal surface is reduced, and the surface roughness is improved.

Example 4:

It includes the following steps: firstly use single-point diamond turning to class II KDP crystal sample 4 with a size of 50×50×10 mm ² , and then take the sample 4 after single-point diamond turning as the processing object, and use BCB-700 to dilute The flattening glue is applied on the surface of the sample 4 for flattening. The main process parameters of the flattening are controlled as follows: low speed 600r/min, time 18s, high speed 3000r/min, time 60s, vacuum heat treatment temperature 80°C, time 4h, Heating time 1h. The surface roughness of the sample 4 was measured with a white light interferometer, and the scanning range was 0.18×0.18mm. The roughness measurement results of the sample 4 before and after planarization are shown in Figure 7 and Figure 8, from Figure 7 It can be seen from FIG. 8 that the surface roughness root mean square Sq of sample 4 after single-point diamond turning is 2.233 nm, and the surface roughness root mean square Sq of sample 4 after planarization is 1.2976 nm. After the planarization in this embodiment, the roughness value of the KDP crystal surface is reduced, and the surface roughness is improved.

The content of the present invention is not limited to the examples listed, and any equivalent transformation of the technical solution of the present invention adopted by those of ordinary skill in the art by reading the description of the present invention is covered by the claims of the present invention.

Claims (4)

1. KDP optical surface planarization method, is characterized in that: Include the following steps: Taking the KH ₂ PO ₄ optical crystal material after single-point diamond turning and polishing as the processing object, a layer of polymer film is coated on the optical surface of the KH ₂ PO ₄ optical crystal material by the method of spin coating, and then vacuum heat treatment Finally, a polymer layer with low surface roughness is formed on the surface of the KH ₂ PO ₄ optical crystal material, and the upper surface of the polymer layer is a planarized surface. 2. KDP optical surface flattening method according to claim 1, is characterized in that: The coating glue of described polymer film selects BCB-1500 glue for use; The conditions of spin coating are: low speed 500r/min~600r/min, time 18s, high speed 4000r/min~5000r/min, time 50s~60s; The conditions of vacuum heat treatment are: temperature 50°C~100°C, time 4h~38h, heating time 30min~1h. 3. KDP optical surface flattening method according to claim 1, is characterized in that: The coating glue of described polymer film selects BCB-700 glue for use; The conditions of spin coating are: low speed 500r/min~600r/min, time 18s, high speed 2500r/min~3000r/min, time 50s~60s; The conditions of vacuum heat treatment are: temperature 50°C~100°C, time 4h~38h, heating time 30min~1h. 4. KDP optical surface flattening method according to claim 1, is characterized in that: The coating glue of described polymer film selects the dilution glue of BCB-700 for use, and the volume ratio of glue and diluent n-butyl acetate is 2:1; The conditions of spin coating are: low speed 500r/min~600r/min, time 18s, high speed 2000r/min~3000r/min, time 50s~60s; The conditions of vacuum heat treatment are: temperature 50°C~100°C, time 4h~38h, heating time 30min~1h.