The Optimization On The Modifications And Properties Of Novel Saturable Absorbers

In 1962,two years after laser's first appearance,the emergence of laser Q-switching technology led to the practical application of laser,which is a significant breakthrough in the history of laser.The basic principle of the Q-switching technology is to compress the laser energy into a very narrow pulse in order to increase the peak power of output laser.The development of Q-switching technology promotes the practical application of laser technology.Q-switching laser sources are widely used in the fields of laser ranging,laser radar,laser welding,laser medical treatment and laser weapons.The saturable absorber is an important part of Q-switched laser,which can directly affect the characteristics of output laser.Therefore,the study of saturable absorbers is very meaningful for the development of Q-switched lasers and their applications.In this thesis,we focused on three saturable absorbers with high interest in recent years:gold nanorods,graphite phase carbon nitride and molybdenum disulfide.Based on the current research situation of these three saturable absorbers,we analyzed their properties and proposed the methods to conquer their shortcomings.Then we constructed passively Q-switched lasers by using the improved material as a saturable absorber and investigated the characteristics of output lasers.The main contents of this thesis are as follows:?.The history of laser and solid state laser technology was summarized.The principle of Q-switching technology and the types of saturable absorbers were introduced.?.The properties and preparation method of gold nanorods were introduced.Then two kinds of gold nanorods,whose aspect ratios were 5 and 8 respectively,were prepared and their properties were characterized.A passively Q-switched laser emitting at 1.3 ?m was fabricated by using these two gold nanorods as saturable absorbers.We measured and analyzed the characteristics of the output laser.The results showed that compared with gold nanorods with aspect ratio of 5.gold nanorods with aspect ratio of 8 are more suitable to be the saturable absorber for passively Q-switched lasers emitting at 1.3 ?m.?.The structure and properties of graphite phase carbon nitride were analyzed,and a facile thermal modification method based on thermal oxidation etching was successfully developed as an effective way of overcoming the shortcomings of graphite phase carbon nitride.The method of preparing graphite phase carbon nitride and thermal oxidation etching were introduced and four different kinds of graphite phase carbon nitride samples were prepared.By comparing the properties of these four kinds of graphite phase carbon nitride samples.the changes of graphite phase carbon nitride after thermal oxidation etching were summarized.And the relationship between the thermal oxidation etching time and the properties of graphite phase carbon nitride was explored.The as-prepared four kinds of graphite phase carbon nitride samples were employed as the saturable absorbers for a passively Q-switched Nd:LLF laser emitting at 1.06 ?m,and the characteristics of the output laser were measured and analyzed.The experimental observations showed that the output properties of the Q-switched laser get improved by utilizing this kind of thermally modified graphite phase carbon nitride as saturable absorber and the degree of improvement is closely related to the duration of thermal oxidation etching treatment.?.Based on the properties of molybdenum diSsulfide and polypyrrole,a method of synthesizing molybdenum disulfide-polypyrrole composites to improve the properties of molybdenum disulfide as saturable absorber was proposed.The synthetic procedures of molybdenum disulfide-polypyrrole composites by in-situ chemical polymerization were described in detail.The properties of prepared molybdenum disulfide-polypyrrole composite sample and pure molybdenum disulfide sample were analyzed and compared.By employing the molybdenum disulfide-polypyrrole composite sample and pure molybdenum disulfide sample as saturable absorber,a diode-end-pumped passively Q-switched Nd:LLF laser at 1.06 ?m was demonstrated.After measuring the parameters of the output laser,we found that the proposed method of synthesizing molybdenum disulfide-polypyrrole composite material to improve the performance of molybdenum disulfide as saturable absorber is effective.It can make passively Q-switched laser show better output characteristics.