Thin-rod active elements for amplification of femtosecond pulses

To study the possibility of amplifying the radiation of femtosecond fibre lasers in thin-rod active elements, amplifying modules based on thin rods made of broadband Yb : CaF₂ and Yb : Y₂O₃ materials are developed. It is shown that the gain in Yb : YAG and Yb : Y₂O₃ elements is limited because only part of the broadband signal is amplified, while amplification in Yb : CaF₂ elements occurs in a wider spectral range but is weak due to a small emission cross section. Amplification from submicrojuole to submillijoule level in the regenerative amplification regime is demonstrated. The new broadband Yb : CaF₂ and Yb : Y₂O₃ materials can amplify radiation with a considerably broader spectrum than Yb : YAG.