Femtosecond lasers in fluid inclusion analysis: Three-dimensional imaging and determination of inclusion volume in quartz using second harmonic generation microscopy

Optical second harmonic generation microscopy was used to generate three-dimensional images of fluid inclusions in quartz. Because the exciting light was focused with a high numerical aperture microscope objective, phase-matching conditions in the quartz led to the generation of frequency doubled light only at the surfaces of the fluid inclusions and not in the bulk material, providing an axial resolution of approximately 1 μm. The volume of synthetic two-phase water inclusions was determined from second harmonic images. The bubble volume was measured using brightfield microscopy (the sample was heated to ensure a smaller bubble that could take on a spherical shape inside the inclusion). The bulk molar volume was then calculated from the vapor–liquid ratio. The values obtained for the bulk molar volume were found to be in good agreement with values calculated from measurements of the homogenization temperature.