Ultrafast modification of oxide glass surface hardness

May 8, 2020

Locker, Sean, and S. K. Sundaram. “Ultrafast modification of oxide glass surface hardness.” Applied Physics B 125, no. 12 (2019): 225.

Abstract

Application of femtosecond lasers is widely utilized in micromachining transparent materials. We have successfully altered the surface hardness of various commercial silicate glasses using a high-intensity femtosecond pulse laser. The femtosecond laser generates pulse energy of 500 nJ with a central wavelength of 800 nm. Using a peak power of 2.2 W and a repetition rate of 5.1 MHz, we observed an 18–20% increase surface hardness in glasses with low-modifier content and 16.6% decrease in glasses with high-modifier content. All laser exposed glasses show no detectable induced-crystallization or surface ablation. X-ray photoelectron spectroscopy results of our samples confirmed that the laser irradiation had no detectable effect on surface chemistry. X-ray reflectometry data showed the change in hardness was attributed to a thin layer with modified density. Experimental results suggest the strengthening mechanism derives from local structural transformation of interatomic bond distances and angles.

“Soda-lime silicate (SLS), Borofoat (BF), and aluminoborosilicate (ABS) refractive indices were characterized using terahertz time domain spectroscopy (THz-TDS, TPS Spectra 3000, Teraview, UK). Terahertz radiation is produced by a mode-locked Ti:Sapphire laser with central wavelength of 800 nm, 80 MHz repetition rate and pulse width of 100 fs. The pulse is separated into a pump and probe beam; pump beam generates THz radiation and probe beam detects THz pulses using GaAs semiconductors. Samples were mounted on a holder with an optical aperture of 4.55 mm. Reference measurements were made with the empty sample holder in air. Broadband THz pulses are converted to a frequency regime through Fourier transformation. Measurements were performed by averaging 3000 scans with a resolution of 1.200 cm−1 and scan frequency of 30 Hz.”

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