Femtosecond laser surface functionalization of glass

Sub-micrometric surface modification of glass

A femtosecond laser enables precise, ultra-shallow modification of both the front and back surfaces of glass without affecting its internal structure. By carefully selecting the processing parameters and operating close to the material damage threshold, it is possible to generate self-organized quasi-periodic surface patterns known as Laser-Induced Periodic Surface Structures (LIPSS). The geometry, period, and depth of these structures are determined by the laser processing parameters, allowing the surface properties to be tailored to the requirements of specific applications.

Figure 1. Surface of soda–lime glass modified using the Jasper X1 femtosecond laser.

Anti-reflective and anti-fogging properties of laser-processed glass

The presence of LIPSS imparts unique functional properties to the glass surface. First, the structures significantly reduce surface reflectance, producing an anti-reflective (AR) effect that increases optical transmission and improves visual clarity. Second, the modified surface becomes highly hydrophilic. The reduced effective surface energy causes condensed water droplets to spread into a thin, nearly transparent water film instead of forming discrete droplets that scatter light. As a result, the surface exhibits excellent anti-fog performance. 

Figure 2. Demonstration of the anti-fog effect on soda–lime glass locally modified using the Jasper X1 femtosecond laser.

Advantages of femtosecond laser processing comparing to conventional approaches

A key advantage of femtosecond laser surface functionalization for anti-reflective and anti-fog applications is its exceptional versatility. The process can be applied to virtually any type of glass. Our experience includes soda–lime glass, borosilicate glass (e.g., BK7), fused silica, and specialty glasses for electronic applications, including Corning® Gorilla® Glass and Corning® Eagle XG®. 

Another significant advantage is that the modification is performed directly on the glass surface without the need for additional functional coatings. The laser structuring process is carried out under ambient atmospheric conditions and does not require thin-film deposition, cleanroom facilities, or expensive protective-atmosphere equipment. Because the functional properties originate from the surface topography itself rather than from an applied coating, there is no risk of delamination or peeling during operation, unlike conventional anti-reflective or anti-fog coatings. 

Experimental studies have demonstrated that the modified surfaces retain their functional properties for at least six months, while long-term durability testing is still ongoing. In addition, the functional performance remains unchanged after repeated cleaning cycles, confirming the robustness of the laser-induced surface structures. 

Developed with industrial implementation in mind

The technology has been developed with industrial implementation in mind. The process can be readily integrated into existing manufacturing lines and fully automated. By combining the femtosecond laser with high-speed scanning systems, both small optical components and large-area glass panels with dimensions of several square meters can be processed efficiently. The current processing throughput reaches up to 200 cm²/min while maintaining excellent uniformity and high reproducibility of the generated surface structures across the entire processed area. 

Figure 3. Printed text viewed through a fused silica plate locally modified using the Jasper X1 femtosecond laser.

Enhances glass properties validated by quantitative reflectance and transmittance measurements.

Optical characterization in the visible (VIS) spectral range demonstrated a substantial decrease in specular reflectance for both BK7 and soda–lime glass following femtosecond laser surface texturing. The untreated glass exhibited a reflectance of approximately 8–10%, whereas laser-structured surfaces showed values as low as 1–2.5%. The anti-reflective effect was most pronounced in the near-ultraviolet and visible regions of the spectrum and gradually diminished toward the near-infrared. This wavelength-dependent behavior is attributed to the interplay between the characteristic dimensions of the laser-induced surface structures and the wavelength of the incident light, affecting both the effective refractive index gradient and light scattering. These results demonstrate that femtosecond laser texturing provides an effective and coating-free approach for fabricating broadband anti-reflective glass surfaces, with particularly high performance across the spectral range used in most optical and photonic systems.

Figure 4. Specular reflectance measurement for as-received and laser processed soda-lime and BK7 glass plates.