Pump modulation frequency resolved excited state absorption spectra in Tm3+ doped YLF

Abstract

Excited state absorption (ESA) in a 1% doped Tm:YLF crystal in the range from 1000 nm to 1300 nm is reported. In this spectral range, three ESA bands are expected: 3F4→3F2 (from 1040 nm to 1096 nm), 3F4→3F3 (from 1111 nm to 1169 nm), and 3H4→1G4 (from 1118 nm to 1240 nm). In a conventional continuous wave ESA setup only the first two bands are observed because the lifetime of the 3F4 level is much longer (15.6 ms) than the lifetime of the 3H4 level (1.56 ms). In order to observe the 3H4→1G4 ESA band, pump modulation dependent measurements were performed, where the modulation frequency of the pump selects the ESA signal to be measured.