Nd,Y-codoped CaF₂ Ultrafast Laser

Near-infrared all solid-state ultrafast laser with good beam quality, high peak power, and short pulse width, which has great potentials in the applications of medical treatment, military, processing, scientific researches and so on, is one of the most popular laser researches for the advantages of high efficiency,compact structure, stable property. In the recent years, the emergency of Nd,Y-codoped Ca F2 disordered crystals operating in the near 1μm spectral region, is of great interest because of its excellent optical, mechanical and physical properties. First of all, With a higher thermal conductivity, Nd,Y:Ca F2 disordered crystals can be grown in large size with an excellent quality, and is suitable for direct laser diode pumping. Secondly, Nd,Y:Ca F2 disordered crystals have a long fluorescence lifetime and considerable emission cross section, which are beneficial to be the gain medium of Chirp Pulse Amplify(CPA) symstem. Finally, the most interesting property of Nd,Y:Ca F2 disordered crystal is that the bandwidth of its emission spectrum is 23.5 nm, which allows for short the femtosecond pulses generation even less than 100 fs. Therefore, Nd,Y:Ca F2 disordered crystals will be one of the most promising materials for generating femtosecond pulses. In this thesis, we focus on all solid-state modelocked laser based on Nd,Y:Ca F2. Main comments are summarized as follows:1. Experimental study on Nd,Y:Ca F2 disordered crystal pumped by continuous wave Ti:sapphire laser. Using the continuous wave Ti:sapphire laser as pumping source and a Nd,Y:Ca F2 disordered active crystal we obtained the stable continuous wave laser. Output coupler mirror with a 2.5% transmission was chosen to obtain the high output power. Under the pumping power of 1.1 W, a maximum continuous wave average output power of 210 m W was obtained, corresponding to a slop efficiency of 22%. Upon optimizing of the cavity characteristics, a commercial available semiconductor saturable absorber mirror for starting mode locking and a pair of SF6 prism for dispersion compensation were inserted into the cavity. Through carefully adjusting of the operating status of the laser, stable passively Q-switch mode-locked pulses were achieved with an output power of 100 m W and a 1.6% output coupler. We carried out theoretical analysis on the reason why continuous wave mode locking was not realized.2. Experimental study on Nd,Y:Ca F2 disordered crystal pumped by a laser diode with high power and high brightness. Using the laser diode as pumping source and a Nd,Y:Ca F2 disordered active crystal we obtained the stable continuous wave laser. A maximum output power of 410 m W was achieved with a 2.5% output coupler under the pump power of 5.2 W. In this case, the slope efficiency with respect to the pump power was 9.5 %. The continuous wave laser tunability was studied with a SF6 prism in the cavity arm containing the output coupler. The continuous tuning range extended from 1042 nm to 1076 nm for 2.5% output coupler under the pump power of 4.5 W. For femtosecond laser operation, we optimized the cavity design in order to obtain the shortest pulse duration. For this aim, an output coupler of 0.8% transmission was used in the cavity. Additionally, two GTI mirrors were inserted in the cavity arm containing the output coupler, In this case, pulses as short as 264 fs with a full width half maximum of 5.0 nm centered at 1063 nm were achieved directly from the oscillator. The average output power was up to 180 m W for an absorbed pump power of 2.5 W, with a repetition rate of 85 MHz. By inserting two SF6 prisms for dispersion compensation, pulse as short as 183 fs with a full width half maximum of 7.3 nm centered at 1065 nm was produced with the average maximum output power was 100 m W, with a repetition rate of 88 MHz. Cavity was designed at the edge of stable region with a pair of GTI mirrors inserted. Output mirror with a 0.8% transmission was chosen to make sure enough power density inside the cavity. Kerr-lens mode-locked running had been obtained by pushing the end mirror at a pump power of 5.2 W. Stable laser pulses of 357 fs with a repetition rate of 85 MHz was obtained. The average maximum output power was 210 m W and the central wavelength was 1063 nm.