研究目的
To develop and fabricate a three-stage laser amplification system based on thin Yb : YAG rods with diode laser pumping, capable of raising the average power of a continuous train of femtosecond pulses to above 100 W.
研究成果
The developed femtosecond laser system based on thin rod Yb : YAG active elements achieved an output power above 110 W with an optical efficiency of 26 %. The system's total gain in the saturation regime was above 100, comparable with gain in regenerative amplifiers. Future work will focus on reducing the pulse repetition rate to 1 MHz to increase the pulse energy to 100 mJ at the same average power, requiring the employment of the chirped pulse amplification method for suppressing self-focusing in thin rods.
研究不足
The main drawback of the developed amplifying system is the employment of a large number of isolators for preventing self-excitation. The pulse duration was stretched to 580 fs due to the limited spectral band of the crystal gain in Yb : YAG.
1：Experimental Design and Method Selection:
The system comprises a femtosecond master oscillator based on an Yb : KGW crystal and three amplification units on thin rods from Yb : YAG crystals. The master oscillator generated a train of laser pulses of duration 80 fs at a pulse repetition rate of 80 MHz. The first two amplification stages operated by the double-pass scheme with a quarter-wave plate, and the third stage operated in a single-pass regime.
2：Sample Selection and Data Sources:
The active elements used were thin Yb : YAG rods with diameters varying from
3：8 to 3 mm and lengths from 30 to 40 mm, with ytterbium concentrations of 1 at. % and 2 at. %. List of Experimental Equipment and Materials:
The system included a femtosecond master oscillator, thin rod active elements, pump laser diode bars, lenses, mirrors, polarisers, a Faraday isolator, and a chirped mirror for dispersion compensation.
4：Experimental Procedures and Operational Workflow:
The MO laser beam was focused into the active elements to provide optimal overlapping with the pump beam. The amplified laser radiation passed through a thin film polariser and was collimated by a spherical lens. Dispersion spreading of pulses was compensated by using a chirped mirror.
5：Data Analysis Methods:
The output power, spectrum, and pulse duration were measured to evaluate the system's performance.
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