99.999% SPHERICAL REFLECTOR Processing Flow

Processing flow of 99.999% SPHERICAL REFLECTOR (Ultra-high Reflectivity Spherical Reflector) (Technical Description)

UltraOpto 99.999% SPHERICAL REFLECTOR (ultra-high reflectivity Spherical reflector) with 99.999% ultra-high reflectivity, precise spherical curvature and excellent environmental stability It is widely used in high-end scenarios such as deep ultraviolet lithography, excimer laser systems, aerospace optical equipment, and high-precision spectral analysis. The core of the processing lies in nano-scale spherical precision control and deposition of ultra-high reflectivity film systems, which requires standardized full-process process control, combined with precision equipment and professional technology to ensure that every indicator meets strict standards, the following is the detailed processing flow.

1. Prerequisites for processing Core: Selection and pre-treatment of high-purity substrates

The optical uniformity and thermal stability of the substrate directly determine the upper limit of accuracy of the spherical reflector. Customized selection and stress-free pretreatment are required for the target band:

Precise substrate selection

UV to near-infrared band (193nm-2.1μm) : Use UV-grade high-purity fused silica with purity ≥99.999%, hydroxyl content ≤10ppm, coefficient of thermal expansion ≤0.55×10⁻⁶/ ° C to avoid spherical curvature drift caused by temperature fluctuations.

Mid-infrared band (2-16μm) : 

Use single crystal silicon or germanium with high thermal conductivity and low infrared absorption, suitable for laser high-power scenarios.

The substrate should be free of defects such as bubbles, streaks, inclusions, etc., and the optical uniformity Δn≤2×10⁻⁶ should be strictly verified by the laser interferometer.

No stress  pretreatment process

Low-temperature precision cutting: Use diamond wire saws to cut the base material blanks with dimensional tolerances controlled within ±0.1mm and thickness deviations ≤±0.05mm to reduce cutting stress.

Annealing stress release: Place the base material in an annealing furnace, heat it up to 850 ° C at a rate of 50 ° C /h, hold it for 6 hours, then cool it down to room temperature at a rate of 30 ° C /h to completely eliminate internal stress.

Third-level super-clean cleaning: neutral cleaning agent ultrasonic cleaning → plasma activation cleaning → high-purity nitrogen air drying to ensure surface particle size ≤0.1μm, sent to Class 10 clean room for standby.

2. Core processing procedures: Spherical surface forming and ultra-smooth polishing

Spherical curvature accuracy and surface roughness are the basis for achieving ultra-high reflectivity, and nanoscale precision control is required through the "integrated grinding and polishing" process:

Custom spherical molds

According to the designed parameters of spherical radius of curvature (R) and diameter (D), the die core is made of tungsten steel using CAD modeling + CNC precision machining, with the die curvature accuracy ≤±0.05μm and surface roughness Ra≤0.01μm.

Spherical forming process

Hot pressing (for large diameters) : 

The base material and the mold are placed together in a vacuum furnace (vacuum ≥10⁻⁵Pa), heated to the softening temperature of fused silica (about 1200 ° C), apply a uniform pressure of 8MPa, and cool slowly after 2 hours. The curvature is monitored in real time by a laser displacement sensor, with the deviation controlled within ±0.1μm.

CNC grinding (for small diameters) : 

A five-axis CNC grinding machine is used for precise grinding at a feed rate of 0.001mm/r to initially form a spherical profile with a curvature accuracy of ±0.5μm.

Ultra-smooth polishing (core precision process)

Rough polishing: 

Use a polyurethane polishing pad + cerium oxide polishing liquid (particle size 0.5μm) to remove the grinding damage layer, reduce the surface roughness to Ra≤0.1μm, and correct the curvature accuracy to ±0.2μm.

Fine polishing: 

In a clean environment with constant temperature (20±0.1 ° C) and constant humidity (40± 5%RH), use a soft asphalt polishing pad + colloidal silica polishing liquid (particle size 0.05μm), with polishing pressure controlled at 0.2MPa and rotational speed 40r/min.

Real-time accuracy detection: 

The entire process is monitored using a phase shift interferometer until the spherical surface shape accuracy reaches λ/[email protected], the surface roughness Ra≤0.01μm, and the surface quality meets the 40-20 (scratch/pitting) standard.

Edge chamfering treatment

Use diamond chamfering wheels for 0.3mm×45° precise chamfering to remove sharp edges, avoid edge scattering and chipping risk, and improve product impact resistance.

3. Key process: Deposition of 99.999% ultra-high reflectivity film system

The realization of ultra-high reflectivity relies on the precise design and deposition of multilayer dielectric film systems, which is a core technical link in the processing flow:

Customized film system design

Using TFCalc optical simulation software, design multilayer film systems with alternating stacking of high/low refractive index materials (such as TiO₂/SiO₂), 50-100 layers, with each layer optical thickness precisely matched to λ/4, achieving 99.999% reflectance in the target band through reciprocal interference of light.

Simulate the effect of film thickness deviation on reflectance, preset coating compensation parameters to ensure film thickness deviation ≤±0.2nm.

Ultra-high vacuum coating process

The polished substrate is fed into the coating chamber, vacuumed to ≥10⁻⁷Pa, and a low-temperature cold trap is used to remove residual water vapor and impurities to ensure a clean coating environment.

Ion beam-assisted deposition (IAD) technology was adopted, with target materials of purity ≥99.999% selected. The deposition rate was controlled at 0.15nm/s. The film thickness was monitored in real time by a crystal controller and an ellipsometer to ensure that the global film thickness uniformity was ≤±1%.

Annealing stabilization treatment of the film system

After the coating is completed, the reflector is placed in the annealing furnace and heated to 180 ° C at a rate of 20 ° C /h for 5 hours, then cooled slowly to release the stress of the film layer, enhance the adhesion of the film layer (≥5B grade, ISO 15184 standard), and prevent the film layer from peeling off.

4. Quality control throughout the entire process and inspection of finished products

Implement dual control of process spot checks and full finished product checks to ensure that each mirror meets the 99.999% reflectance standard:

Core indicator testing

Reflectance detection: Using a laser reflectometer, accurately measure the reflectance of the target band to ensure values ≥99.999%, spherical reflectance uniformity ≤±0.0005%.

Geometric accuracy measurement: 

Spherical curvature radius, aperture, thickness measured with a coordinate measuring machine, tolerance ≤±0.05mm; Recheck the surface shape accuracy with an interferometer to ensure compliance.

Environmental reliability testing:

Sampling for high and low temperature cycling (-40 ° C to 85 ° C, 500 times), wet heat test (85% RH, 500 hours), and anti-laser damage test, with reflectance attenuation ≤±0.0002% after testing

Handling and archiving of nonconforming products

Isolate and analyze non-conforming products (such as non-compliant reflectivity, surface defects, etc.), re-grind, polish and recoat those that can be reworked, and directly scrap those that cannot be reworked.

Qualified products should be accompanied by test reports (including reflectance curves and surface shape spectra), and production and test data should be archived and preserved for at least 3 years to achieve quality traceability.

5. UltraOpto processing advantages

Precision controllable: 

Spherical surface shape accuracy up to λ/20, film thickness deviation ≤±0.2nm, reflectance stable at 99.999%, meeting the demanding requirements of high-end optical systems.

Material assurance: 

The purity of both the base and target materials is ≥99.999%,preventing impurities from affecting reflectance and stability from the source.

Full-process  quality control: 

100% random inspection of key processes, full inspection of finished products to ensure batch consistency.

Customized adaptation:

Spherical curvature, aperture, and target band can be customized as needed  to adapt to different application scenarios.

Processing cycle reference (batch size 100 pieces, standard specification)