Ruby fluorescence is used for pressure measurement. Measuring the position of the fluorescence lines of Ruby, allows to determine the pressure of the sample.
This is sensitive to the change of interatomic distances resulting from the application of external pressure. Photoexcitation of R-lines luminescence is usually provided by a laser source: the 514.5 nm or the 488 nm intense lines of the argon laser prove suitable for this application. The fluorescence spectrum is composed by the R1 and R2 lines occurring respectively at about 694.25 nm and 692.7 nm at room pressure, and shifts towards longer wavelengths when pressure increases.
Pressure measurement is performed through different calibrations of the R1 line shift, established in different ways depending upon pressure conditions and ranges. The linear calibration of the ruby shift, introduced by Piermarini et al., proves good up to 30 GPa for a quasi-hydrostatic environment. Mao and Bell extended the quasi hydrostatic calibration to 80 GPa and found a slight non linearity at high pressure. While – as for non-hydrostatic pressures – Bell et al. suggested a non-linear pressure calibration system ranging up to 180 GPa .
The LOTO-eng Infinitive Microscope is designed for collecting the fluorescence emission of a small ruby chip. It is placed inside the sample under pressure in the diamond anvil cell (DAC).
Photoexcitation is provided by a Laser source at 532nm. The intense line of the NdYag laser source is adjusted by a dedicated Fiber optic collimation system.
A long working distance microscope, objective 20X, ensures high fluorescence collection efficiency and good quality sample image. The fluorescence signal is sent through a dedicated optical fiber system to a compact spectrometer.
The side of the microscope has an optical entrance which allows, using the same microscope objective, to enlighten the sample for the visual observation. The light is carried to the microscope throw a fiber bundle from an external LED source.
Through a Digital camera linked to computer monitor it is possible to see the gasket and the ruby crystal. Also is possible to adjust the optic system over the ruby crystal by a X-Y-Z micropositioning system.