Broadband terahertz antireflective microstructures on quartz crystal surface by CO₂ laser micro-processing.

Area of Science:

• Optics and Photonics
• Materials Science
• Terahertz Technology

Background:

• Anti-reflection (AR) coatings are crucial for terahertz (THz) systems but face manufacturing challenges with hard brittle materials.
• Existing methods like chemical etching and ultrafast laser processing are inefficient and yield low-quality subwavelength structures (SWS) at the hundred-micron scale.

Purpose of the Study:

• To investigate the direct ablation of broadband SWS on quartz crystal using precisely controlled CO2 laser pulses as an alternative to ultrafast lasers.
• To evaluate the anti-reflection properties and manufacturing efficiency of CO2 laser-ablated SWS for terahertz applications.

Main Methods:

• Directly ablated broadband subwavelength structures (SWS) on quartz crystal surfaces using precisely controlled CO2 laser pulses.
• Characterized the anti-reflection performance of SWS samples, including maximum transmittance, peak improvement, and optimal efficiency spectrum.
• Assessed the angular dependence of AR properties and demonstrated improved imaging quality using SWS-coated substrates.

Main Results:

• Achieved a two-orders-of-magnitude reduction in processing time compared to ultrafast laser methods.
• Demonstrated excellent AR properties with maximum transmittance of 97% at 0.71 THz and peak transmittance improvement of 13.5%.
• Observed an optimal efficiency spectrum from 0.28 to 1.21 THz with transmittance >90% and maintained performance up to ~40° incidence angles.

Conclusions:

• CO2 laser ablation offers an efficient and practical method for fabricating broadband SWS for anti-reflection in the terahertz band.
• This technique significantly enhances the transmission of optical components made from materials like quartz, alumina, and sapphire.
• The improved AR properties and imaging quality demonstrate the potential of this method for advancing terahertz system performance.