基于新型可饱和吸收体的被动调Q和被动锁模光纤激光器研究

发布时间：2018-06-06 22:52

本文选题：光纤激光器 + 被动调Q　；参考：《中国科学技术大学》2016年博士论文

【摘要】：光纤激光器具有光束质量好、效率高、结构紧凑、易于热管理等诸多优点,掀起了激光技术产业的革命。而脉冲光纤激光器因脉冲能量大、峰值功率高,在工业生产、科学研究、激光通信等领域拥有极其广泛的应用。目前,产生脉冲的主要方式是采用调Q技术和锁模技术,在这两种技术中,可饱和吸收体(SA)都起着至关重要的作用,由它构造的被动调Q和被动锁模激光器具有结构简单、体积小、价格低廉、环境稳定性高等优点。所以,我们可以说,脉冲激光器的发展在很大程度上决定于可饱和吸收材料的发展。传统的可饱和吸收体,如染料、半导体可饱和吸收镜等,面临着诸多缺陷,大大限制了脉冲激光器的发展。随着材料科学的进步,相继涌现出像碳纳米管(CNT)、石墨烯(Graphene)、过渡金属硫化物(TMDs)等各种新型纳米材料,它们的性能得到质的提升,价格也不断下降,脉冲激光器借此得到蓬勃发展。本论文主要针对新型纳米材料的可饱和吸收特性以及在脉冲光纤激光器中的应用展开研究,包括基于它们的被动调Q和被动锁模光纤激光器以及全光纤的被动调Q和被动锁模轴对称偏振光束(CVB)激光器。论文的最后,我们还对光纤激光器输出光场的匀滑技术进行了研究,以便应用在各种需要光滑平顶光束的场合。本论文的主要研究工作有：1、在实验上分别采用z扫描和双臂探测法研究了一种新型过渡金属硫化物—二硫化钨纳米片在1064nm和1550hm波段的超宽带可饱和吸收特性,并且验证了它的偏振无关特性和高损伤阈值,指出这是一种非常理想的可饱和吸收材料。2、利用二硫化钨州S2)和聚乙烯醇(PVA)制得的复合薄膜,我们分别搭建了基于二硫化钨的掺铒被动调Q光纤激光器和掺镱被动调Q光纤激光器。对于掺铒调Q激光器,当泵浦功率从279mW增加到609mW时,调Q脉冲重复频率从88.67kHz增加至157.29kHz,对应的脉宽从1.24岬减小到917ns,单脉冲能量最大达89.23nJ。在掺镱调Q激光器中,我们通过加入可调滤波器,实现了工作波长在1027-1065nm间连续可调,而调Q脉冲始终稳定存在。在固定工作波长1048.1nm的情况下,通过增大泵浦功率,调Q脉冲重复频率可以从60.2kHz增加到97.0kHz,最短脉冲宽度1.65μs。3、利用垂直蒸发法制备的厚度和浓度渐变的WS2-PVA薄膜,我们搭建了基于WS2的掺镱被动锁模光纤激光器。通过合理设计激光器结构和选择合适参数的SA,最终获得了0.55nm光谱宽度、20.66MHz重复频率、206ps脉宽的稳定耗散孤子脉冲。脉冲时间带宽积为30,带有非常大的啁啾,脉宽可在腔外得到进一步压缩。4、提出了一种全光纤被动调Q和被动锁模CVB激光器的方案,采用少模光纤光栅(FMFBG)作为横模选择元件,滤除基模,获得纯净的TM01(径向偏振光)和TE01(角向偏振光)模输出；同时分别采用WS2-PVA和CNT-PVA作为可饱和吸收体,利用它们的可饱和吸收特性和偏振无关特性,最终在保证调Q和锁模脉冲输出的同时,获得了高纯度的轴对称偏振光。相较于其它方案,该方案结构简单,轴对称偏振光方便获得,调Q状态和锁模状态不容易丢失。5、针对激光惯性约束核聚变和激光投影、激光显示中对靶面辐照均匀性的要求,我们设计了一种多束激光错位叠加和阵列透镜结合的束匀滑整形方案。通过理论分析和相关的数值模拟探讨了方案的可行性,并且详细研究了各个参数对靶面匀滑效果的影响。最后,我们还在实验上对方案进行了验证,最终得到不均匀度RMS低于4.6%的平顶光束。本论文的创新点：1、首次将WS2的应用扩展到1064nm波段,实现了波长和重复频率同时可调的掺镱调Q光纤激光器,保证波长在1027-1065nm间连续可调的同时,稳定调Q状态始终存在：另外,我们也实现了基于WS2的掺镱被动锁模光纤激光器,获得了20.66MHz重频、206ps脉宽的稳定耗散孤子脉冲。2、采用FMFBG作为横模选择元件,WS2作为调Q元件,搭建了全光纤被动调Q轴对称偏振光束激光器,重频在80KHz到120KHz间可调,最短脉宽958ns。通过调节腔内的偏振控制器,在调Q状态下获得了高模式纯度的径向偏振光和角向偏振光。3、采用FMFBG作为横模选择元件,CNT作为锁模元件,实现了全光纤被动锁模CVB激光器,最终在10.61MHz重频,22.73ps脉宽稳定锁模的同时,获得了模式纯度高达98.03%的径向偏振光。4、提出了一种多束激光错位叠加和阵列透镜结合的束匀滑整形方案。通过理论分析和相关的数值模拟探讨了方案的可行性,并在实验上进行了验证,该方案简单易行、适用性广,冗余度高。
[Abstract]:Fiber laser has many advantages, such as good beam quality, high efficiency, compact structure, easy to heat management and so on. It sets off the revolution of laser technology industry. The pulse fiber laser has a wide application in the fields of industrial production, scientific research and laser communication because of high pulse energy and high peak power. At present, the main mode of producing pulse is produced. Q technology and mode locking technology are used. In these two technologies, the saturable absorber (SA) plays a vital role. The passive Q and passive mode locked lasers have the advantages of simple structure, small size, low price and high environmental stability. So, we can say that the development of the pulse laser is to a great extent. Traditional saturable absorbers, such as dyestuffs, semiconductor saturable absorption mirrors, are faced with many defects, which greatly restrict the development of pulsed lasers. With the progress of material science, various new types of nanotubes such as carbon nanotubes (CNT), graphene (Graphene), transition metal sulfide (TMDs) and so on have been sprung up one after another. The properties of rice have been improved and their prices are decreasing, and the pulse laser is developing rapidly. This paper focuses on the saturated absorption characteristics of the new nanomaterials and their applications in pulsed fiber lasers, including their passive Q and passive mode locked fiber lasers and all light. The passive Q and passively mode-locked axisymmetric polarization beam (CVB) laser. Finally, we also study the smoothing technology of the output light field of the fiber laser, so as to apply the applications to various smooth flat topped beams. The main research work of this paper is as follows: 1, the experiment of Z scanning and double arm detection are used in the experiment. A new type of transition metal sulfide - two tungsten sulfide nanoscale in the 1064nm and 1550hm band is saturated and saturable absorption characteristics, and its polarization independent characteristics and high damage threshold are verified. It is pointed out that this is a very ideal saturated absorpable material.2, using two wolfram state S2) and polyvinyl alcohol (PVA) composite thin. We build an erbium doped passively Q fiber laser and a ytterbium passively Q fiber laser based on two tungsten sulfide. For erbium doped Q lasers, when the pump power is increased from 279mW to 609mW, the Q pulse repetition frequency is increased from 88.67kHz to 157.29kHz, and the corresponding pulse width is reduced from 1.24 to 917ns, and the energy of the single pulse is up to 89.2. 3nJ. in ytterbium doped Q laser, we achieve continuous adjustable wavelength between 1027-1065nm by adding tunable filter, and the Q pulse is always stable. In the case of fixed working wavelength 1048.1nm, by increasing the pump power, the Q pulse repetition frequency can be increased from 60.2kHz to 97.0kHz, and the shortest pulse width is 1.65 u s.3, Using the vertical evaporation method of thickness and concentration gradient WS2-PVA films, we build a WS2 based passive mode locked ytterbium doped fiber laser. By rationally designing the laser structure and selecting the appropriate parameters of the SA, the stable dissipative soliton pulse with the 0.55nm spectrum width, the 20.66MHz repetition rate, the 206ps pulse width and the pulse time band are finally obtained. The wide product is 30, with a very large chirp, and the pulse width can be further compressed out of the cavity to get further compression of.4. A scheme of all fiber passive Q and passive mode locked CVB lasers is proposed. A small mode fiber Bragg grating (FMFBG) is used as a transverse mode selection element to filter the base mode, and the pure TM01 (radial polarized light) and TE01 (angular polarized light) mode output is obtained. WS2-PVA and CNT-PVA are used as saturable absorber respectively. Using their saturated absorption characteristics and polarization independent characteristics, the axisymmetric polarized light with high purity is obtained at the same time, while the output of Q and mode locking pulse is guaranteed. Compared with other schemes, the scheme is simple and the axisymmetric polarized light is conveniently obtained, the Q state and the mode lock shape are adjusted. .5 is not easy to lose. In view of the requirement of laser inertial confinement fusion and laser projection and the uniformity of the target surface in the laser display, we design a beam smoothing and shaping scheme with the combination of multi beam dislocation superposition and array lens. The feasibility of the scheme is discussed through theoretical analysis and related numerical simulation, and the detailed study is made. The influence of each parameter on the target surface smoothing effect. Finally, we verify the scheme in the experiment, and finally get the flat topped beam with the inhomogeneity of RMS below 4.6%. The innovation of this thesis is: 1, the application of WS2 is extended to the 1064nm band for the first time, and the ytterbium doped Q fiber laser with simultaneous adjustable wavelength and repetition frequency is realized. While the wavelength is continuously adjustable between 1027-1065nm, the stable Q state has always existed. In addition, we also realized the ytterbium doped passively mode-locked fiber laser based on WS2, obtained the 20.66MHz heavy frequency, the 206ps pulse width of the stable dissipative soliton pulse.2, the FMFBG as the transverse mode selection element, WS2 as the Q component, the whole fiber passive Q axis was set up. A symmetrical polarization beam laser is adjustable between 80KHz and 120KHz, and the shortest pulse width 958ns. has high mode purity radial polarized light and angular polarized light.3 by adjusting the polarization controller of the cavity. FMFBG is used as a transverse mode selection element and CNT is used as a mode locking element to realize the all fiber passive mode locked CVB laser. At the end of the 10.61MHz heavy frequency and 22.73ps pulse width stabilizing lock mode, the radial polarized light.4 with the mode purity up to 98.03% is obtained. A beam smoothing and shaping scheme with the combination of multi beam dislocation superposition and the array lens is proposed. The feasibility of the square case is discussed through theoretical analysis and the related numerical simulation, and the experimental verification is carried out. The scheme is simple and easy to use, wide applicability and high redundancy.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN248

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