Fabrication of continuous phase plates with small structures based on recursive frequency filtered ion beam figuring

Area of Science:

• Optical Engineering
• Nanofabrication
• Surface Metrology

Background:

• Continuous phase plates (CPPs) require high-precision fabrication due to large surface gradients and high spatial frequencies.
• Traditional fabrication methods struggle with the fine structures and complex surface topographies of advanced CPPs.

Purpose of the Study:

• To propose and validate an optimized ion beam figuring (IBF) technology for fabricating CPPs with challenging characteristics.
• To enhance fabrication speed and surface quality for microstructures with small spatial periods.

Main Methods:

• Development of a multi-pass IBF approach utilizing frequency filtering and variable ion beam sizes.
• Detailed discussion on the selection principles for ion beam sizes and dwell times to optimize corrective capabilities.
• Comparison of the filtering method against traditional non-filtering IBF techniques.

Main Results:

• Successful imprinting of complex microstructures with spatial periods as small as 0.7 mm.
• Achieved surface peak-to-valley (PV) values below 200 nm and surface gradients up to 1.8 μm/cm.
• Fabricated surfaces met design specifications within 10 nm root-mean-square (RMS) error.

Conclusions:

• The proposed multi-pass IBF method with frequency filtering offers a faster and more effective solution for CPP fabrication.
• This optimized technique demonstrates superior performance in achieving high precision for complex micro-optical components.