All-solid-state Femtosecond Lasers At Near And Mid-infrared Wavelengths

Femtosecond lasers at near-infrared(NIR) and mid-infrared(MIR) wavelengths are widely applied in the fields of scientific research, military confrontation and medical treatment. Moreover, the solid-state laser has great advantages in stability and easily maintenance, therefore the study of femtosecond lasers at NIR and MIR region becomes one of the significant research focuses at home and abroad. This thesis focuses the research on the mode-locked NIR and MIR solid-state laser,the research contents can be divided into two parts, one is to study the ytterbium doped orthosilicate single crystal solid state lasers with the emission wavelength at about 1 ?m, including the continuous wave(CW) operation and semiconductor saturable absorption mirror(SESAM) mode-locking operation based on those three new-type silicate crystals of Yb:GSO, Yb:LSO and Yb:YSO; another is to study the chromium doped zinc chalcogenide solid-state lasers with the emission wavelength at about 2.3 ?m, including the CW and kerr-lens mode-locking(KLM) operations from Cr:Zn S laser, as well as the CW operation of Cr:Zn Se laser. The main contents and innovations of this paper are summarized as follows:1. Laser diode pump femtosecond mode-locking laser based on ytterbium-doped orthosilicate crystal is studied in this thesis. Firstly, the absorption rates of Yb:GSO, Yb:LSO and Yb:YSO at 976 nm pump laser are measured, on the basis of the obtained results, using a high brightness laser diode to pump the Yb:GSO crystal, the output power of CW operation close to 2 W at the absorbed power of 12.4 W with the central wavelength at 1057 nm is obtained. Then replacing the HR mirror with SESAM mirror and adjusting carefully all the laser cavity mirrors, the maximum laser output power of 700 m W and repetition frequency of 91 MHz mode-locked laser pulses are demonstrated with the full width at half maximum(FWHM) bandwidth of 3.4 nm. At the same time, single wavelength, dual-wavelengths and three wavelengths operations are obtained in the adjusting process of the experiment. For the case of Yb:LSO laser, with the two arms of the laser resonant cavity exchanging, the CW laser output power is 2.13 W at the pump power of 5.9 W, corresponding to an optical to optical conversion efficiency of 36%. The mode-locked laser are obtained by using SESAM, generating 553 m W output power with center wavelength at 1057 nm and the 4.2 nm FWHM bandwidth of the spectrum. The continuous mode-locked laser of 717 m W can be furtherly achieved by restoring the original cavity. Finally, the Yb:YSO crystal is characterized, at the pump power of 14.4 W, the power is 1.74, 2.01, 2.05 and 2.19 W at the output mirrors with transmittance of 0.8%, 1.5%, 2.5% and 10%, respectively.2. The study on the mid-infrared mode-locking laser is conducted in this thesis. A s-polarized narrow-linewidth laser at a central wavelength of 1645 nm is obtained by using a commercial Er:fiber laser pumping a non-planar ring Er:YAG oscillator firstly. Then the Cr:Zn S crystal is pumped by the narrow-linewidth laser, with a four mirrorcavity, the CW power of 105 m W is obtained when absorbing 1.7 W pump laser. Adjusting the laser close to the edge of the stable region, the kerr-lens mode locking(KLM) operation with the output power of 90 m W is obtained at 2333 nm, the spectrum has a FWHM bandwidth of 28.4 nm, corresponding to the theoretical limit pulse width of 200 fs, if a sech2 shape is assumed. Meanwhile, due to the polycrystalline characteristic of Cr:Zn S, which results on the random quasi-phase-matching, the second, third and fourth harmonics are obtained at the output wavelength of 1166 nm, 779 nm and 582 nm, respectively. By using the above structure, the maximum output power of 212 m W is obtained from the Cr:Zn Se laser, covering a tuning range of 2260-2534 nm. The mode-locking operation is further implemented.