A liquid laser in which rare earth ions in solution are used as the laser active medium. An example is
KrF in liquid
Krlaser.
Source:
PAC, 1995, 67, 1913. 'Nomenclature, symbols, units, and their usage in spectrochemical analysis-XV. Laser-based molecular spectroscopy for chemical analysis - laser fundamentals (IUPAC Recommendations 1995)' on page 1921 (https://doi.org/10.1351/pac199567111913)