Temperature distribution measurement inside an Er:Yb:Lu2Si2O7 crystal under 1.55 μm laser operation

•Temperature measurement inside the laser crystal was performed based on the fluorescence intensity ratio technique.•Polarized up-conversion fluorescence spectra in 500–580 nm of an Er:Yb:Lu2Si2O7 crystal were measured at 300–680 K.•Temperature distribution inside an Er:Yb:Lu2Si2O7 crystal was measured in real time when a 1.55 μm laser was operating.•The experimental result was compared with the theoretical temperature distribution inside the crystal.