Pressure by Ruby Luminescence (PRL) systems are used on many beam lines (ID09A, ID27, ID28, ID24...) and in the high pressure laboratories for determining pressure in diamond anvil cell experiments. They consist of a monochromator with CCD-detector coupled to a microscope via an optical fibre and a green or blue-green (532-488 nm) Laser to excite the ruby luminescence (more information here). Typical excitation powers are a few mW. Sometimes, e. g. very high pressures (> 80 GPa), the luminescence signal can get very weak and more power is needed. Lasers are either bolted to the microscope, as shown in the attachment, or the beam is send to the microscope via an optical fibre. Microscopes are equipped with a Laser-shutter (Laser beam/light source beam switching box) which is only open during the pressure measurement (typical less then 1 sec). The microscopes are equipped with CCD-cameras for observation.

You can find all the characteristics here.