Solid-state Femtosecond Mode-locked Lasers At Near-infrared And Mid-infrared Wavelength

Femtosecond lasers at near-infrared and mid-infrared wavelength have wide applications in industrial, military, medical and scientific fields. Solid-state lasers have advantages of good stability, compact structure and easy maintenance. Therefore, solid-state femtosecond mode-locked lasers operating at near-infrared and mid-infrared wavelength become the hot areas of laser-research, which drive us to focus on the study of these lasers. Nd,Y:Sr F2 crystal is a new femtosecond laser material applied as gain mediun for its high quantum efficiency and broad fluorescence emission spectrum.Yb:YAG ceramic and crystal are a kind of widely used laser materials because of their good performance in optics,machinery and thermotics. Cr:Zn S is the main laser crystal to realized sub-100 fs mode-locked laser at mid-infrared wavelength and known as the “mid-infrared Ti:Sapphire”. In this paper, we research on the ultrafast lasers based on the three laser materials and the related results are reported by the following aspects:1. Femtosecond mode-locked Nd,Y:Sr F2 lasers pumped by Ti:Sapphire laser were studied. Using 796 nm Ti:Sapphire continuous-wave(CW) laser as pumping source, efficient femtosecond mode-locked Nd,Y:Sr F2 laser with pulse duration of 332 fs and repetition frequency of 89.8 MHz was obtained. The average output power was 395 m W under 1 W pump power, corresponding to the optical-to-optical efficiency of 39.5%. Further, 97 fs mode-locked laser was realized by precisely managing the dispersion and choosing appropriate output coupler, with 102 m W average output power at pump power of 925 m W corresponding to the optical-to-optical efficiency of 11%. To the best of our knowledge, this is the first sub-100 fs mode-locked laser based on the Nd doped laser crystal. At the same time, Gain modulated chirped-pulse oscillator was observed in the experiment, which enriches the positive dispersion mode-locking theories. These results have been reported in Applied Physics Express 7 092704,CLEO(2014)and ASSL(2014).2. Laser diode(LD) pumped femtosecond mode-locked Yb:YAG lasers at long wavelength was introduced. Compared to the typical wavelength(1.03 μm) of Yb:YAG laser, 1.05 μm is defined as the long wavwlength of Yb:YAG laser in this paper. Mechanism of 1.05 μm Yb:YAG laser was theoretically analyzed by the theory of optimum gain medium length. Experimentally, by pumping the absorbed side-peak with 968 nm LD, femtosecond mode-locked lasers were achieved respectively on Yb:YAG crystal and Yb:YAG ceramic. Mode-locked laser of 1.2 W average output power based on Yb:YAG crystal was obtained under the incident pump power of 6.53 W, with the pulse duration of 417 fs and repetition rate of 77 MHz,centering at 1054 nm. Mode-locked laser of 1.6 W average output power based on Yb:YAG ceramic was obtained under the absorbed pump power of 3.63 W, with the pulse duration of 743 fs and repetition rate of 79 MHz, centering at 1049 nm. Improving the resonater and dispersion compensation, 469 fs pulse on ceramic was realized.3. Mid-infrared femtosecond mode-locked Cr:Zn S lasers were researched on. Cr:Zn S CW laser with 138 m W output power firstly pumped by 1.53 μm Er fiber laser was realized and obtained tunable wavelength of 2.23 μm to 2.62 μm with birefringent filter. Further pumping with 1.645 μm single frequency solid-state laser, the output power improved to 360 m W. Under the 1.645 μm pumping source, kerr lens mode-locked(KLM) laser was beening on the research. In the near future, we will realize the Cr:Zn S optical frequency comb as the design we had given.