As a core material in optical components, the surface treatment process of sapphire lenses exerts a direct influence on the light transmittance, wear resistance and service life of sapphire products. The following is a detailed description of the surface treatment process flow of sapphire lenses from raw materials to finished products.

1. Cutting and rough grinding

Sapphire crystal ingots are initially cut into sheet-like slabs at a thickness close to the target value by means of diamond wire saws. In the preliminary grinding stage, diamond abrasives with a particle size of 20-40μm are utilized, and the thickness tolerance is managed within ±0.05mm on a double-sided grinding machine. It is imperative that coolant is utilized throughout this process in order to reduce the temperature and avert the risk of local overheating, which could result in damage to the crystal structure.

2. Precise finish

A stepped anti-friction process was adopted, with 15 μm, 9 μm and 3 μm diamond grinding discs utilized in sequence for a total of three grinding operations. Following each process, the residual abrasives must be removed using an ultrasonic cleaning apparatus. The cleaning parameters are as follows: a frequency of 40kHz, pure water as the medium, and a duration of 3 minutes. It is imperative to emphasize that the grinding pressure must be meticulously regulated within the range of 0.1 to 0.15MPa. Excessive pressure has been demonstrated to cause the depth of subsurface cracks to exceed 2μm.

3. Polished finish

(1) Chemico-mechanical polishing

Preliminary polishing was carried out using silica alkaline polishing solution (pH9.5-10.5) in combination with polyurethane polishing pads under the rotating speed of 60rpm and the pressure of 7kPa . At this stage, over 90% of surface defects can be eliminated, achieving a roughness of Ra≤0.5nm.

(2) Ion beam shaping

The nanoscale trimming process was conducted in a vacuum environment utilizing Ar+ ion beams, with the incident angle set at 30°-45° and the energy density maintained at 1.5-2.0eV/atom. This step can effectively repair the lattice damage layer and further reduce the surface roughness to Ra≤0.2nm.

4. Coating technology

(1) Pretreatment

Plasma cleaning: Under a vacuum of 10^-3Pa, oxygen plasma treatment is carried out for 10 minutes.

Ion sputtering cleaning: Bombard the surface with 200eV argon ions for 3 minutes.

(2) Multi-layer coating

Layer 1: Deposit a 30nm thick layer of SiO2 as a transition layer

Layer 2: Alternately deposit 20 groups of HfO2/SiO2 nanofilms, with each group having a thickness of λ/4 (λ=550nm)

Outer layer: 5nm magnesium fluoride anti-reflection coating. 

5. Quality test

(1) Optical detection

When using an interferometer to detect the surface shape accuracy, the PV value should be less than λ/10. The spectrophotometer measures the transmittance, and the average transmittance in the visible light wavelength is required to be ≥99.2%.

(2) Mechanical property test

The Mohs hardness tester verified that the surface hardness reached the standard of grade 9. The wear resistance test was conducted on the friction testing machine. After 1000 cycles under a 500g load, the haze change should be less than 1%.

(3) Environment test

It is tested at a high-temperature and high-humidity of 85℃/85%RH for 240 hours. It is also subjected to cycles of temperature ranging from -40°C to +80°C, repeated 20 times.

6. Special treatment technology

(1) Anti-fingerprint coating

Perfluoropolyether (PFPE) material is used to form a monomolecular layer with 5-8nm thick through vacuum evaporation, with a contact angle of over 115°.

(2) Laser microstructure

The use of femtosecond lasers to process micron-sized flow diversion grooves in the edge area, with a groove width of 20 μm, a depth of 15 μm, and a spacing of 50 μm, has been shown to enhance the anti-fog performance by 30%. 

Sapphire lenses are utilized in Class 100 clean environments throughout the entire process. Each procedure following particle detection is designed to guarantee that the surface contaminant density remains below 5 particles per square centimetre. The intelligent production line has achieved real-time closed-loop control of process parameters and continuously optimizes processing parameters through big data analysis.