Low-threshold ablation of dielectrics irradiated by picosecond soft x-ray laser pulses

Abstract

Ablation of LiF crystal by soft x-ray laser (XRL) pulses with wavelength λ=13.9 nm and duration TL=7 ps is studied experimentally and theoretically. It is found that a crater appears on a surface of LiF for XRL fluence, exceeding the ablation threshold Fa∼10.2 mJ/cm2 in one shot, or 5 mJ/cm2 in each of the three XRL shots. This is substantially below the ablation thresholds obtained with other lasers having longer pulse duration and/or longer wavelength. A mechanism of thermomechanical ablation in large bandgap dielectrics is proposed. The theory explains the low Fa via small attenuation depth, absence of light reflection, and electron heat conductivity.

The TARANIS laser: A multi-Terawatt system for laser-plasma investigations

“…This means that we could potentially generate a fluence of >50 mJ/cm 2 . This is well in excess of the ablation threshold found for LiF at similar wavelengths by Faenov et al (2009) and means that we have the latitude to investigate a variety of materials with differing ablation thresholds.…”

“…With the advent of new light sources such as the FLASH X-ray-ultraviolet free electron laser (Ackermann et al, 2007) and the potential for moving lithographic techniques for microchip production to the X-ray-ultraviolet regime (Newman, 1991), this has become a topic of current interest, with measurements of transmission of X-ray-ultraviolet beams through thin foils (Nagler et al, 2009) using the FLASH facility and ablation measurements of solids with similar X-ray lasers (Faenov et al, 2009) having been already made. The high photon energy (89 eV in the gold XRL case and 66 eV for molybdenum) means that mechanisms of ablation and damage might be expected to be quite different to the optical case.…”

Desorption/ablation of lithium fluoride induced by extreme ultraviolet laser radiation

“…[2,3] revealed very low ablation threshold (~0.01 J/cm 2 ) for LiF exposed to picosecond SXR laser pulses, reasoned out by the occurrence of spallative ablation [1]. The ablation threshold for LiF irradiated by UV excimer laser [11] (1 J/cm 2 ) is strongly affected by the value of l att , which is much higher compared to SXR/XUV spectral region meaning that laser energy is deposited into larger volumes.…”

“…Ablation threshold (symbols) for various pulsed UV/XUV/SXR laser systems with different wavelengths (specifi ed above the symbol) and pulse lengths (given in parentheses) correspond to values reported in Refs. [2][3][4] (for XUV/SXR) and in Ref. [11] (for UV).…”

“…Quantitative description of laser ablation phenomena is critically important for practical implementation of pulsed laser deposition (PLD) technique when utilizing radiation sources at this spectral range. The behavior of optical dielectrics upon SXR/XUV-laser irradiation is the subject of particular attention and lithium fl uoride (LiF) is often studied in this context as a reference large band-gap material [1][2][3][4]. Moreover, LiF is a feasible precursor of lithium atoms and ions for the purpose of tokamak diagnostics [5].…”