Feedback-controlled laser fabrication of micromirror substrates

Area of Science:

• Materials Science
• Optical Engineering
• Laser Physics

Background:

• Micromirror fabrication is crucial for optical systems.
• Previous methods using longer laser pulses resulted in significant size dispersion.
• Achieving high precision and uniformity in micro-optics fabrication remains a challenge.

Purpose of the Study:

• To develop a method for fabricating high-quality concave micromirror templates.
• To improve the precision and reduce size dispersion in micromirror arrays.
• To investigate the feasibility of using short CO2 laser pulses for microfabrication.

Main Methods:

• Utilized short (40-200 μs), high-energy (≳100 μJ) single focused carbon dioxide (CO2) laser pulses.
• Ablated concave features with diameters of ≈20-100 μm on silica and fluoride glass.
• Implemented a fast feedback control loop (≈20 kHz bandwidth) based on sample-emitted light for real-time process monitoring and adjustment.

Main Results:

• Fabricated high-quality concave micromirror templates with sub-nanometer surface microroughness (RMS < 0.2 nm).
• Achieved an RMS size dispersion of less than 5% in fabricated arrays and on optical fiber tips.
• Demonstrated that the ablation process occurs on a timescale shorter than the laser pulse duration.

Conclusions:

• Short, high-energy CO2 laser pulses enable precise fabrication of high-quality concave micromirrors.
• The implemented fast feedback control loop significantly enhances uniformity and reduces size dispersion.
• This technique offers a substantial improvement for micro-optics fabrication compared to previous methods.