At a wavelength of 193nm the photon energy is absorbed by most materials in a sub-micron-thick surface layer that ablates almost without thermal effect on the remaining material
The department of earth sciences at the Open University has installed the UP193HE, a second-generation 193nm laser ablation system from New Wave Research.
Installed in January 2003, the system is expected to unlock a new range of trace-element measurements.
Peter van Calsteren of the department comments, "Our Nu Instruments plasma ionisation mass spectrometer is an advanced, multi-collector research instrument and the sensitivity is such that it should be possible, in certain circumstances, to measure 234U/238U and 230Th /232Th for uranium-series dating in situ using our new UV excimer laser ablation system." Matrix independence, high spatial resolution and the ability to couple with UV transmissive materials without fracturing the sample are critical to laser ablation ICP-MS.
While laser ablation systems at 213nm and 266nm readily meet these requirements, new 193nm, excimer-based laser systems have since eclipsed these early systems on certain levels, particularly in geological and biological sampling. "Laser ablation adds more processes by which mass and element fractionation can take place, and it's essential to develop and calibrate sophisticated data reduction protocols," added van Calsteren.
"However, at a wavelength of 193nm the photon energy is absorbed by most materials in a sub-micron-thick surface layer that ablates almost without thermal effect on the remaining material.
The very high spatial resolution of this homogenised excimer system allows the study of incremental processes in the growth of individual minerals, or in the case of environmental archives such as stalagmites or shells, variations on an annual scale." The UP193HE laser ablation system incorporates an excimer laser that features high operating efficiency and a unique preionising technology.
This laser produces a flat beam, enabling the energy density to be more homogeneously spread across the profile of the laser beam.
The overall benefit is that cleaner, flatter craters are produced down to approximately 3-4µm in diameter, at energy densities up to 45J/cm2.
