David Hilton, Ph.D.

scripps institution of oceanography

New Developments

Our latest development involves coupling our new dual-wavelength laser probe to the MAP215 rare gas mass spectrometer.

The laser is designed to extract volatiles from inclusions, or trails of inclusions, contained in individual crystals and to melt samples (without use of a furnace which involves heating of a substantial mass of metal).

Our laser system is a Merchantek combined Nd-YAG/CO2 dual-laser package consisting of a quadrupled Nd-YAG laser (operating in the UV portion of the spectrum at 266 nm) as the ablating tool and a CO2 laser operating in the far IR (at 10.6 mm wavelength) for both ablation and general heating. Both lasers are mounted on a 2'x4' laser table and share beam focusing, sample viewing and positioning hardware. Two sample chambers are supplied with different windows: zinc sulfide (for IR radiation) and UV-grade quartz (for UV). The sample chambers are connected to the inlet line via standard stainless-steel flexible bellows.

The Nd-YAG laser (frequency-quadrupled into the UV and hence pulsed) has a number of advantages relevant to the types of studies we plan in the near future: (1) UV laser light is absorbed strongly by most silicates; (2) the shorter wavelength of UV light translates into much smaller spot sizes - of the order of 5 microns. Hence this laser possess significantly greater control for studies where spatial information on sites of gas release (e.g. small vesicles) is important; and (3) energy is delivered to the sample surface in a controlled (pulsed) manner. Power densities (when the beam is focused) are high enough to cause instantaneous ablation/vaporization and pulse lengths are of short enough duration to limit collateral damage. Continuous wave IR radiation from the CO2 laser can also be used for ablation studies but the larger wavelength translates into larger spot sizes (80-100 mm). By defocusing, the lower power densities of the CO2 laser can be used for general melting of samples.