Study On Active-passive Mode-locked Nd: YAG Pico-second Laser

Technology of mode-locked laser has about development in recentfour decades. Super-short pulse laser is obtained by means of differenttypes of mode-locked technology, that is, by active or passive means, tolocked a serial of longitudinal mode phase with same frequency intervalfrom lasers. Because the pulse width is narrow, mode-locked laser has highpower in pulse peaks. As a strong tool in the basic and applied science,super-short pulse plays an important role in several research fields. The keyfactor of mode-locked technology is to choose steady super-short pulsesequence by modulating the phase and intensity in intra or extra cavity. In order to improve the repetition of pure passive locked mode,severalmeans have been carried through. The active-passive mode-lockedYAG laser in my thesis bring pure passive mode-locked apparatus aboutsynchronous acoustic-optical modulation to resonance cavity, this design isthe simplest and highest efficiency ways of mode-locked technology. In myexperiment, the stability of laser was improve, mode-locked probability is100％,mode-locked threshold is decreased obviously ,the stability ofmode-locked laser pulse is changed obviously. And the change of intensityof the pulse at 10 Hz is about 5% Based on enhancing the stability of output and the mode-lockingprobability of an active-passive mode-locking laser, a lot of improvementsare made in theory and in experiment. Firstly, from the output mode ofgeneral lasers, we narrate the definition of mode-locked and the propertiesof mode-locking pulse in theory, and place emphasis on such as depictions: 第 61 页 共 63 页吉林大学硕士学位论文the theory of active and passive locked mode, the technologies by that wecan perform the active and passive locked mode. Based on above, wediscuss the output properties of an active-passive mode-locking Nd: YAGlaser, by the feature of acousto-optic standing wave modulator, changingmodulation window of acousto-optic standing wave modulator. Thistechnology will greatly improve the capability of active locked mode. Thestability of laser was improved. Experimentally, in order to mend thestability of the laser output, we renew and reconstruct the out-of-datedevices, mode-locked probability is 100％,mode-locked threshold isdecreased obviously ,the stability of mode-locked laser pulse is changedobviously. And the change of intensity of the pulse at 10 Hz is about 5%.By using the properties of the avalanche transistor, we make ourselves ahigh- voltage square wave generator for Pockel cell which can selectsingle pulse and a synchronized trigger circuit, these improvements forlaser will enhance the stability of the laser oscillatory output; we can obtainthe single pulse whose output is stable by single pulse selector, with onestage laser amplification, and two and third doubler finally wegain an active-passive mode-locking YAG laser with high stability andpower density. A single pulse laser output energy of the improved laser is7mJ at 1.06um wavelength,3.5mJ at 0.53um, and 0.7mJ at 0.3547um; therepetition frequency of the laser is 5pps,these properties of the improvedlaser can basically meet the applications in ultra fast spectrum. Otherwisewe analyze theoretically the cause of bringing on the jitter of laser outputpulse, and put forward a next project on improving the stability of the laseroutput. 第 62 页 共 63 页吉林大学硕士学位论文 Furthermore, the dynamical process about the photo-induced anisotropyof nonlinear materials was measured by using time-resolved instantaneousabsorption method for the improved laser.