Studies On Novel All-solid-state Lasers And Their Mode-locking Operations

The laser diode pumped all-solid-state laser is one of the spotlights in the laser research field, owing to its high efficiency, compact size, low cost and good beam quality. In particular, the all-solid-state laser based on ytterbium-doped gain media has attracted great attention recently because it can generate laser pulses of high power, large energy and ultrashort duration. In order to search for new all-solid-state lasers with low threshold, high efficiency, systematic experimental and theoretical laser studies have been carried out in this dissertation on various types of novel laser crystals including low threshold Yb:GSO lasers, high efficiency self-frequency-doubling (SFD) Yb:GdYAB lasers, self-Q-switched Yb,Na:CaF2 lasers, and their mode-locking studies. The studies provide guidance for new laser crystal growing, and are of theoretical and practical value for the development of a new generation of all-solid-state ultrafast lasers. In this dissertation, my work and innovations will be presented as follows:1. The rule that governs the intra-cavity laser spot distribution of LD pumped lasers is analyzed using ABCD transmission matrix. Based on that rule, a low threshold LD pumped Yb:GSO laser is developed for the first time to our knowledge. The theory of SESAM-based mode-locking lasers is analyzed, and both Q-switched and CW mode locking operations of all-solid-state Yb:GSO lasers are obtained using different cavity configurations and SESAMs with different modulation depths.2. Experimental and theoretical studies on SFD Yb:GdYAB lasers have been performed for the first time. An optical conversion efficiency of 67% and an infrared tunable spectrum of 67 nm are achieved, respectively. The critical parameters that determine SFD efficiency are analyzed in detail through the dynamic equation derived for SFD lasers. Based on the theoretical analysis, a conversion efficiency of 18.6% from LD to green light is achieved, which is the highest optical conversion efficiency from LD to SFD visible up to now.3. A SESAM mode locking Yb:GdYAB laser is built, with an ultrafast laser pulse output of 872 fs. Stable two wavelength (infrared and visible) operation of the mode-locked solid state Yb:GdYAB laser is also achieved for the first time. The dynamic equation for SESAM mode-locked lasers including SFD is derived. It is proved that appropriate self second harmonic generation in mode-locked lasers can suppress the tendency of Q-switched operation. 4. Laser and fluorescence experiments are carried out on a series of novel Yb,Na:CaF2 crystals. According to comparative experiments, it is proved that Na+ dopants can increase the fluorescence efficiency and lower the lasing threshold. A low threshold laser is realized in Yb³⁺, Na+ co-doped CaF2 crystals. Self-Q-switched mode-locking operation of the Yb,Na:CaF2 laser is observed. An appropriate co-doping concentration of Yb³⁺ ions and Na+ ions is found according to measured fluorescence, providing guidance for new laser crystal growing and research.