Acoustooptic Q-switched Yb³⁺-doped All-fiber Laser Pumped By Diode-lasers

The all-fiber lasers have many merits, which include high efficiency, compact size and its portability. They are very attractive sources because of their wide applications in military affairs, industry, biomedicine, nonlinear frequency conversion, remote sensing and space communication, etc.This research makes a theoretical study of the characteristics of the CW fiber laser and the Q-switched fiber laser, and then offers a successful design of both the CW Yb³⁺-doped all-fiber laser and the Q-switched Yb³⁺-doped all-fiber laser. The main contents of this research are as follows.1. The comprehensive performance of the CW fiber laser with different pumping and output style is compared firstly from the perspective of the pump light and the signal light distribution. And the performance of the CW fiber laser with one-end pumping and one-end output style is studied mainly. The governing differential equations which describe the forward power and the backward power distribution inside the fiber core are solved. The quantitative relationship that the output power depends on the pump power, the fiber core diameter, the fiber length and the output reflectivity is worked out. So the general law about the output characteristics of the CW fiber laser is obtained. And the conclusions of this chapter are helpful to the design of the CW fiber laser.2. The operation of the CW Yb³⁺-doped all-fiber laser is realized. The cooling system used to control the temperature of the diode-laser is designed independently. During the experiment, the continous laser output of the Yb³⁺-doped all-fiber laser, whose wavelength is 1083nm, is achieved. The output power of 3.426W is obtained, and the optical to optical conversion efficiency reaches 28.5%.3. A novel method based on 'the relationship between the energy utility ratio and the initial particle inversion' to solve the final particle inversion remaining is advanced firstly. And this method simplified the numerical calculation procedure of the Q-switched fiber laser. According to the rate-equation theory of the Q-switched fiber laser, the general law that some important initial parameters such as pump power, fiber core diameter, fiber length, output transmittance and fiber inherent loss influence the pulse width and the pulse energy is worked out, with the methods to narrow the pulse width and to improve the pulse energy clarified. The analysis of this chapter is of important reference to designing the kindred Q-switched fiber lasers.4. The experimental study about the acoustooptic Q-switched Yb³⁺-doped all-fiber laser is developed firstly in China. On the base of the CW Yb³⁺-doped all-fiber laser, a pigtailed acoustooptic Q-switch is inserted between the totally reflected FBG and the combiner's signal port. During the experiment, the operation of the acoustooptic Q-switched Yb³⁺-doped all-fiber laser is realized. The 3μs pulse width and the 2.94mJ pulse energy are obtained at the repetition rate of 500Hz, and the repetition rate can be adjusted continuously between 10Hz and 100kHz.5. By firstly using the pigtailed acoustooptic Q-switch and the Stimulated Brillouin Scattering (SBS) effect of single-mode fiber simultaneously, the experimental study of the compoundly Q-switched Yb³⁺-doped all-fiber laser is accomplished, and a stable 150ns pulse width is obtained at the repetition rate of 50kHz.6. The Experimental study of the passively Q-switched Yb³⁺-doped all-fiber laser is developed. The operation of the passively Q-switched Yb³⁺-doped all-fiber laser is realized by adopting only the SBS effect of the single-mode fiber. And the narrow pulse width of 17ns is obtained at the repetition rate of 30MHz. Furthermore, by using the SBS effect of the multi-mode fiber, the 2μs pulse width is obtained at the repetition rate of about 50kHz.