INVESTIGATION OF 2.1-MU-M LASING PROPERTIES OF HO-TM-CR-YAG CRYSTALS UNDER FLASH-LAMP PUMPING AT VARIOUS OPERATING-CONDITIONS

Flash-lamp-pumped normal-mode and Q-switched 2.1-mum laser operations of Ho:Tm:Cr:YAG crystals have been evaluated under a wide variety of experimental conditions in order to determine an optimum lasing condition and to characterize the laser outputs. Q-switched laser-output energies equal to or in some cases more than the normal-mode laser energies were obtained in the form of a strong single spike by optimizing the opening time of a lithium niobate Q switch. The increase of the normal-mode laser slope efficiency was observed with the increase of the Tm concentration from 2.5 to 4.5 at. % at operating temperatures from 120 K to near room temperature. Laser transitions were observed only at 2.098 and 2.091 mum under various conditions. The 2.091-mum laser transition appeared to be dominant at high-temperature operations with low-reflective-output couplers and to have an energy-level assignment from 5313 cm-1 to 534 cm-1 or (and) from 5313 cm-1 to 536 cm-1.