Growth, spectroscopy and laser operation of Ho:KY(WO4)2

Abstract Monoclinic Ho:KY(WO 4 ) 2 crystals doped with up to 7.5 at.% Ho are grown by the Top Seeded Solution Growth-Slow Cooling method. The evolution of their unit cell parameters in dependence on the Ho doping and temperature is studied. The polarized low-temperature (6 K) optical absorption of the Ho 3+ ion is investigated in detail to determine the energy of the Stark sub-levels. Room-temperature absorption, stimulated-emission and gain cross-section spectra of Ho:KY(WO 4 ) 2 crystals are derived for polarizations parallel to the principal optical axes, E || N p , N m and N g . The maximum absorption cross-section for the 5 I 8 → 5 I 7 transition is 1.60×10 −20  cm 2 at 1961.0 nm and the maximum stimulated-emission cross-section for the 5 I 7 → 5 I 8 transition is 2.65×10 −20  cm 2 at 2056.3 nm (for E || N m ). The radiative lifetime of the upper laser level of the Ho 3+ ion ( 5 I 7 ) amounts to 4.8 ms. Continuous-wave Ho 3+ laser operation is achieved under in-band pumping by a Tm laser at 1946 nm. In the microchip configuration, the maximum output power reached 205 mW at 2105 nm with a slope efficiency as high as 85%.