Experimental Research On LD Pumped Passively Continuous-wave Mode-locked Lasers With SESAM

Ultrafast lasers with ultrashort pulse duration, high pulse repetition rate, broadspectrum and high peak intensity are attracting growing interest because of numerousapplications in physics, biology, OCT, laser spectroscopy, high-capacitytelecommunication systems and nonlinear frequency conversion etc. Since theinvention of semiconductor saturable absorber mirrors (SESAM) in 1992, thepassively mode-locked lasers with SESAM have developed rapidly over the pastdecade because of their many virtues such as robust, inexpensive, compact etc. Inforeign countries and Taiwan, many researches have made on the SESAM and theSESAM laser, but there have only a few researches on it in mainland. This thesispresented modeling and experimental results on a LD pumping passivelymode-locked Nd: YVO4 laser with home made SESAM. We obtained continuouswave mode-locked (CWML) pulse trains with 5.3W average output power at theincident pump power of 17W. The main contents can be outlined as follows:1. Summarized several developed directions of mode-locked laser with SESAM ininternational and introduced the highest-level lasers achieved. The status ofmainland has also been introduced.2. Detailed introduced the characteristics of SESAM such as its naissance,macro-parameter, all kinds of structures, three manner of mode locking, how tosuppress the Q-switched mode-locking, thermal induced damage etc.3. Researched the thermal effects of LD end-pumped laser and side-pumped laser.Ray-tracing algorithm and finite difference method are used to simulate theabsorbed power and temperature distributions in crystal rod for differentside-pumping configurations. Simulation results show that there have importanceinfluences on the absorbed power and the temperature distributions at differentpumping configurations and parameters. The relation between the temperature inthe cross-section of the laser rod and the heat transfer coefficient is investigated.The former nonlinearly decreases with the increase of the latter, and thecoefficient has an optimal value.4. To the best of our knowledge, this is first time to deduce the second solution ofequivalent imaging mirror with the method of q parameter. This solution may besuperior to the well-known solution in some conditions. Using the Visual C++, aprogramm for laser cavity design is built. We can easily design a laser cavity by it.Introduced how to design a two-mirror linear cavity, three-mirror fold cavity, andfour-mirror Z-shape cavity. Revised the ordinary three mirror and reviewed asimple design method of Z-shape fold cavity.5. In two-mirror linear cavity, we obtained 8.32W CW output power at the incidentpump power of 16.42W. Experimentally investigated the three-mirror, four-mirrorand five-mirror fold cavity, analyzed the continuous background in mode-lockedpulse trains measured. At last, we obtained CWML pulse with 5.3W averageoutput power in five-mirror fold cavity. The corresponding incident pump powerwas 17W, optic-optic conversion efficiency 31.2% and slope efficiency 34.7%.Then, we preliminarily investigated the LD side-pumping Nd:YAG mode-lockedlaser.