Effect of ambient air pressure on debris redeposition during laser ablation of glass

Abstract

The effect of ambient air pressure on the redeposition of debris, ablated from the zinc borosilicate glass target using 6ns, 266nm laser pulses, has been studied for incident fluences of 3–18J∕cm2. Measurements were carried out in air at pressures ranging from 10–750Torr. Scanning electron microscopy and optical microscope observations of the target surface were made to analyze the morphology of the redeposited debris. It was found that for higher values of the laser fluence and ambient pressure, the target surface is extremely rough, with large pieces of molten glass and debris fragments deposited near and around the ablation site. The profile of the redeposited debris also shows signs of a strong shock-wave-cleaning effect and possibly a Rayleigh-Taylor instability at higher pressures. Contrary to this, under low-pressure environment the surface of the redeposited debris is cleaner and smoother, with minimal damage around the ablated crater. The measured radius of the debris field was found to be proportional to the inverse cube root of the ambient pressure, consistent with the stagnation distance of the expansion plume when energy balance with the displaced air is considered. In addition to this, the mass of the redeposited debris was estimated from the measured optical thickness of the film and compared to the ablated mass. In the range below 100Torr, both the mass of the redeposited debris and the percentage of the ablated mass which was redeposited were found to increase with the increasing fluence and the ambient air pressure.

Secondary shock wave in laser-material interaction

“…During propagation this internal shock front keeps a distribution width of several mean free paths ͑5 ns͒. Likewise, backward motion of the ablated particles was observed in several experiments by TOF spectroscopy or time resolved imaging, 4,7,8 providing considerable close agreement with our result.…”

“…Interesting theoretical study on gas dynamics of pulsed laser ablation by Han et al 6 was conducted on shock wave formation in helium ambient gas and reflection of the shock front on a silicon substrate. Recent measurements of the internal structure and expansion dynamics of laser aluminum plumes have been reported in the work of Harilal et al 7 Work by Singh et al 8 provided study on the effect of ambient pressure on the redeposition of debris and the plume backward motion. Time-of-flight ͑TOF͒ signal oscillations according to generation of the primary and secondary shock wave in the plume-background gas interaction were observed in the experimental work by Bulgakov et al, 9 and that exceptional feature has been covered empirically.…”

Recent Advances in Resonant Waveguide Gratings

“…Direct laser writing allows a sequential patterning while the exposition of excimer lasers or ultra‐fast lasers through a photomask allows parallel processing. Laser ablation may however suffer from the accumulation of redeposited debris particles around the ablation site . Using F 2 laser at 157 nm, submicrometer RWGs were realized with a grating depth in the 5–50 nm range .…”

Dynamics of the plume containing nanometric-sized particles ejected into the atmospheric air following laser-induced breakdown on the exit surface of a CaF2optical window

“…1 A number of reports have discussed the properties of the debris following long (ns) or short (fs) pulsed laser ablation in various materials including dielectrics, metals, and semiconductors. [2][3][4][5][6] One technologically important aspect of laser breakdown induced on the surface of materials (commonly referred to as laser ablation) is the production of a backward-deposited layer of the ablated material around the laser-irradiated region. This behavior has been attributed to confinement of the plasma formed near the surface.…”