Low Ablation Threshold Research Articles

Generation of absorption waves by CO2 laser pulses at low power density

Optical breakdown generated by CO2 laser pulses in helium, argon, and xenon atmospheres has been investigated by fast plasma plume imaging and measurements of energy and temporal shape of the transmitted laser pulse. The role of preionization due to material evaporation has been examined by placing targets with low ablation threshold in the vicinity of the laser beam focus. Ambient gas pressure, laser pulse energy, and distance between target and laser beam focus have been varied in order to identify the physical mechanisms involved into the ignition and propagation of the laser-induced breakdown plasma. The understanding of the generation of absorption waves at low power density is useful for the design of plasma shutters with low threshold in the infrared spectral range.

VUV F 2 laser ablation of sodium chloride

We report an investigation of the ablation of NaCl crystals at the 157-nm wavelength of the F2 laser where there is very strong excitonic absorption. Probe-beam deflection and etch-rate measurements show that the interaction is characterised by a low ablation threshold (∼80 mJ cm-2) and a capability for controllable material removal at the nanometer level. Scanning electron microscopy of the exposed surfaces show this to be microscopically smooth but with fine cracks present. It is demonstrated that micron-scale features can be formed in NaCl using 157-nm laser ablation, a result attributed to the strongly localised optical and thermal nature of the interaction. The results are discussed within the framework of a thermal vaporisation model.

Ablation measurements on EML insulators using free-arcs

A new technique has been used to determine the ablation threshold and ablation rate of EML materials. Analysis of experimental data obtained by measuring free-arc velocity as a function of rail current in the presence of a background gas has been performed. A simulation of the free-arc motion has been developed using the graphical programming capabilities of LabVIEW. Nonablating theoretical data have been calculated from the free-arc model and have been used to identify the onset of ablation in the experimental data. Likewise, for the ablating case, the ablation coefficient can be extracted from the experimental data using system sensitivity and parameter identification methods. Ablation measurements were made on Lexan and mullite insulators. The ablation coefficients and ablation thresholds obtained indicate that Lexan ablates more significantly and has a lower ablation threshold than mullite, as expected.

Liquid-core light guides for near-infrared applications

The strong absorption of tissue water is responsible for the low ablation threshold for biological tissues at the Er:YAG and Er:YSGG laser wavelengths. These lasers are therefore considered to be promising tools for medical treatments. As the existing transmission systems are still unsatisfactory, three types of liquid-filled light guides are investigated here as alternatives to conventional near-IR fibers. In addition to mechanical advantages, the minimum attenuation is below 3 dB/m, and losses at bending radii down to 20 mm are negligible. The maximum output energy densities of 14.2 J/cm(2) (free-running Er:YAG) or power densities of 7 MW/cm(2) (Q-switched Er:YAG) are sufficient for soft-tissue ablation. When the liquid was circulated, much higher energy densities, exceeding the hard-tissue ablation threshold, were achieved. These properties make liquid-core light guides promising delivery systems for many near-IR applications, including medical ones.