Diode-Pumped High-power Yb-Doped All-Solid-State Femtosecond Oscillator

The femtosecond laser with high output power is a hot topic in the field of lasers,and have widely applications in scientific research,nonlinear optical frequency conversion,medical and industrial processing.The diode-pumped all-solid-state femtosecond lasers have the advantages of small size,compact structure,long service and high output power.In recent years,with the rapid development of the high-power and high-brightness laser diode,it is very significance to develop the diode-pumped high-power all-solid-state ultrafast lasers.This thesis is mainly focus on the research of diode-pumped high-power Yb-doped all-solidstate femtosecond oscillator.The main contents and innovations of this paper are summarized as follows:1.The diode-pumped Yb:CGA femtosecond laser was demonstrated.Yb:CGA crystal was known as a good material in laser fields due to its good optical and thermal properties.By using a diode laser emitting at 980 nm as the pump source,we obtained both SESAM modelocked and Kerr-lens mode-locked Yb:CGA femtosecond oscillator.The SESAM modelocked Yb:CGA oscillator was obtained with 83 fs,366 m W and 104 fs,1.58 W.The Kerrlens mode-locked Yb:CGA oscillator was achieved with the help of an extra Kerr-medium.The pulse duration and the output power were 85 fs and 810 m W,respectively.This technique can eliminate the need of pump beam tight focusing in crystal and the use of highbrightness pump source,which is expected to achieve high-power femtosecond laser.2.A high-power SESAM mode-locked Yb:CGA oscillator was developed.A 4-mm thick Yb:CGA crystal was used as the gain medium.The crystal had antireflection coatings of 900-1100 nm on both surfaces.By optimizing the spot size on SESAM and precise dispersion compensation,a maximum output power of 5.34 W and a pulse duration of 117 fs was achieved.The repetition rate is 80 MHz,corresponding to the pulse energy of 66.7 n J and the peak power of 570 k W.Besides,a stable commercial 4.5 W SESAM mode-locked Yb:CGA femtosecond oscillator was designed with small size.3.The high-power SESAM mode-locked Yb:KGW oscillator was experimentally studied.The maximum output power of 5.35 W and pulse duration of 159 fs were obtained by optimizing the beam size on the SESAM and precise dispersion compensation,the repetition rate is 64 MHz,corresponding to the pulse energy of 83.6 n J and the peak power of 526 k W.4.We demonstrated a high-power Kerr-lens mode-locked Yb:KGW femtosecond oscillator.First,we investigated the Kerr-lens mode-locking operation by introducing a 2-mm thick fused silica or a 1-mm thick sapphire as the Kerr-medium,while the mode-locked laser was always operated with multi-pulses.Benefiting from the large nonlinearity of Yb:KGW crystal,we obtained a stable mode-locking pulses by optimizing the cavity structure.5.11 W,216 fs pulses were realized at a repetition rate of 64 MHz.The pulse energy and the peak power were 79.8 n J and 369 k W,respectively.This is the highest output power delivered from the diode-pumped Kerr-lens mode-locked Yb:KGW oscillator.