Research On High Power Planar Waveguide Laser Amplification Technology

With the extensive application of laser technology, researchers have been seeking a breakthrough in high power and high energy. At the present time, high-energy solid-state laser is still faced with serious thermal effect, low efficiency and bulky volume. Planar waveguide structure is a transitional form of slab and fiber, thus combining the advantages of both. Planar waveguide is a promising gain medium to achieve high-power output, efficiency cooling, and high conversion efficiency, in addition, its extremely small size enables miniaturization and lightweight design of the laser system. Planar waveguide is one of the main developments of the high-energy solid-state lasers.The paper is based on the project "Research on increasing efficiency of high-energy solid-state lasers" from Laboratory of High-energy Laser Science and Technology, China Academy of Engineering Physics. This project is aiming at study on high efficiency and high brightness performance of the planar waveguide, based on the material and structural characteristics of solid-state lasers. The main contents include:1. The developments of planar waveguide lasers, including the development of the planar waveguide structures, spectral range and high-power planar waveguide lasers are introduced. It can be realized that compared with other high-power and high-energy solid-state lasers, planar waveguide lasers have better performance in the pump coupling and cooling.2. The waveguide theoretical basis and laser theoretical basis of planar waveguides are proposed. At first, based on the geometric optics and wave optics, the light transmission in the waveguide, as well as the effects of different waveguide structures on wave modes (TE modes and TM modes) are analyzed. And then, the laser rate equations and the gain coefficients are calculated and analyzed, which present a theoretical output power that can be achieved from the planar waveguide gain medium.3. The model of the thermal effects of end-pumped planar waveguide laser medium is established. According to the heat conduction theory, the temperature distribution and stress distribution are presented. It can be known that the different thickness of the core region and of the whole structure influence the pump power limits. The thicker the core region and the whole structure are, the lower power density waveguide medium can stand.4. The high-power planar waveguide laser amplification experimental designs are conducted, including the design of waveguide structure, the parameters of pump coupling and so on. The unit experiments and the overall program are produced:1) The waveguide characters experiment:The overall waveguide size of 1 mm×1 cm×6 cm and the core size of 100 ?m×1 cm×5 cm are proposed. The waveguide characters of ceramic, crystal and silica materials are compared. It can be found that the waveguide characters of crystal waveguide is little better than the same size of the ceramic waveguide.2) The efficient pump coupling system experiment:The effects of different incident angles on pump absorption efficiency have been verified.3) The seed oscillator system experiment:Taking into account the high energy density in the waveguide, an oscillator with repetition of 100 Hz and pulse width of 250 ?s is built to suppress amplified spontaneous emission (ASE) and parasitic oscillation (PO). The output energy of 233 mJ with beam quality M2 factors of 1.82 (x) and 1.65 (y) is achieved.4) The planar waveguide laser amplifier experiment:The laser amplifier experiment is launched in single-ended and double-ended pumping modes, quasi-continuous (QCW) and continuous (CW) working mechanism. When in the QCW (repetition frequency of 100 Hz, pulse width of 250 ?s), the maximum output energy of 327 mJ is received with the injected energy of 82.2 mJ, corresponding peak power of 1308 W and single-pass gain coefficient of G=4. The extraction efficiency of the system is about 56%; when in the QW, the maximum output power of 537 W is obtained with the injected power of 250 W and pump power of 940.6 W. The single-pass gain coefficient is G=2 and the optical-to-optical efficiency is about 30.5%. Finally, the spontaneous emission experiment gives a reasonable explanation for the ASE and PO, so a suppression method of waveguide end-chamfer is proposed.