Two samples of Er-Yb doped phosphate glass were tested as a gain medium of longitudinally diode pumped
laser. One sample was a simple Er:Yb:glass rod (length 2.8 mm), second sample was composite rod consisting of
2.8mm long Er:Yb:glass and 6mm long YAG crystal. Diameter of both samples was 6 mm. Dopant concentration
for Er:Yb:glass was 0.75 × 1020 cm−3 Er and 1.7 × 1021 cm−3 Yb. The goal of the experiment was to investigate
an effect of the undoped YAG cap on the Er:Yb:glass laser operation. The active medium, fixed in cupreous
heatsink, was placed inside the 150mm long resonator consisted of a flat pumping mirror (HR @ 1.52−1.65 μm,
HT @ 0.97 μm) and curved output coupler (r = 150 mm, R = 97% @ 1.52−1.61 μm). For Er:Yb:glass pumping a
fiber coupled laser diode, operating in pulsed regime, was used. The pumping pulse width, energy, and wavelength
were 1 ms, 10 mJ, and 975 nm, respectively. The decrease of Er:Yb:glass laser output pulse energy with increasing
pumping repetition rate was observed for both samples. In case of simple Er:Yb:glass the energy dropped from
1.4mJ to 0.6mJ after pumping duty cycle increase from 0.5% to 6 %. In case of composite YAG/Er:Yb:glass active
medium the relative output energy decrease was only 20% for pumping duty cycle increase from 0.5% to 10%.
This result showed that the slope of the output energy decrease with increasing duty cycle was approximately
four times slower for composite active media in comparison with simple Er:Yb:glass.