Ultrahigh Transmittance Biomimetic Fused Quartz Windows Enabled by Frequency-Doubling Femtosecond Laser Processing

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Fabricating antireflective subwavelength structures (ASS) on fused silica (SiO2) with femtosecond lasers is challenging due to parameter complexity and precision demands.
• Hole-type microstructures show superior potential for enhancing infrared window transmittance compared to other ASS designs.

Purpose of the Study:

• To investigate and optimize the fabrication of hole-type ASS on fused silica using femtosecond laser processing.
• To evaluate the impact of laser wavelength on ASS performance and durability for ultrahigh-transmittance applications.

Main Methods:

• Analysis of two representative ASS types to identify hole-type microstructures for infrared applications.
• Development of a dual-pulse femtosecond laser setup (1030 nm) and subsequent modification to 515 nm using a frequency-doubling crystal for finer microstructure fabrication.
• Characterization of ASS performance, including transmittance (up to 99% at 2.5 μm), water contact angle, surface roughness, and abrasion resistance.

Main Results:

• Hole-type microstructures fabricated with a 515 nm femtosecond laser achieved 99% transmittance at 2.5 μm.
• ASS produced at 515 nm demonstrated superior antireflective performance compared to other wavelengths.
• The fabricated ASS exhibited excellent stability and durability, maintaining high transmittance after abrasion testing and under various conditions.

Conclusions:

• Femtosecond laser processing at 515 nm is an effective method for fabricating high-performance antireflective subwavelength structures on fused silica.
• The developed hole-type ASS offer ultrahigh transmittance and robust durability for infrared window applications.
• This technique overcomes previous fabrication limitations, paving the way for advanced optical coatings.