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Upconversion fluorescence assisted visualization of femtosecond laser filaments in Er-doped chalcohalide 65GeS(2)-25Ga(2)S(3)-10CsCl glass

Blonskyi, Ivan
Kadan, Viktor
Shpotyuk, Oleh
Calvez, Laurent
Pavlov, Ihor
Pavlova, Svitlana
Dmytruk, Andriy
Rybak, Andriy
Korenyuk, Petro
Upconversion fluorescence of Er3+ ions (1 at. %) excited with femtosecond laser pulses of different repetition frequencies (seed laser 76 MHz, and laser amplifier 1 kHz) is studied in the Er-doped chalcohalide glass of 65GeS(2)-25Ga(2)S(3)-10CsCl composition. Strong weakening of fluorescence efficiency at 530 nm and 560 nm and photoinduced darkening are observed under 1 kHz excitation, which is most probably caused by free carriers generated by two-photon absorption. On the other hand, neither weakening nor photodarkening is observed under 76 MHz excitation, this being presumably due to concomitant thermal annealing. Taking an advantage of upconversion fluorescence, the femtosecond filamentation associated with positive changes in refractive index is recorded in the Er-doped 65GeS(2)-25Ga(2)S(3)-10CsCl glass, whereas exceeding the threshold of thermal melting is accompanied by an opposite decrease in the refractive index.