基于LCB晶体的355nm高功率皮秒紫外激光特性研究

Picosecond (ps) lasers at the wavelength of 355nm are extensively applied to micro-machining. Long time operation of traditional ultraviolet crystal will lead to unstable s ultraviolet laser because of deliquescence. In order to solve this difficult problem, in this proposal, we propose to adopt a novel La2CaB10O19 (LCB) with high damage threshold, high nonlinear coefficient and non-deliquescence. Through exploring a new cosolvent system of low viscosity and low volatility, we study the defect (such as growth stripes) formation mechanism during crystal growth, and test the relationship between different precision of temperature control and cooling rate and growth stripes. The process conditions of crystal growth and nucleation, growth rate of the crystal are matched with each other. The effect of different seed crystal orientations on the crystal quality and the impact of cosolvent ion on the crystal’s transmittance, the optimal process condition of LCB crystal growth which is suitable for ps laser with narrow pulse width and high peak power is obtained. The optical parameters of LCB crystal are accurately measured. Theoretical model of ps laser frequency transformation based on LCB is established. The impact of crystal matching orientation, temperature bandwidth, angle bandwidth and group-velocity mismatch on the sum frequency efficiency is revealed. Appling the above theory in the experiment, we can successively achieve high power (>10W) ultraviolet ps laser at the wavelength of 355nm based on the novel LCB. This research has significant innovation and practicality. It opens up a new scheme for the investigation of the novel LCB crystal and laser characteristic of high power ultraviolet ps laser with long-term stability.

355nm皮秒激光广泛应用于微加工领域，传统紫外和频晶体长时间运转会产生潮解使皮秒紫外激光不稳定。为解决这一难题，本项目采用损伤阈值高、不潮解的新型LCB晶体，前期研究中发现此晶体存在一些生长缺陷，本项目主要探索适合晶体生长的低粘度、低挥发度新助熔剂体系，深入研究晶体内部缺陷，尤其是生长条纹形成机理，试验不同控温精度和降温速率对生长条纹的影响，使晶体生长工艺条件与晶体成核、生长速度相互匹配，研究不同籽晶方向对晶体质量影响以及助熔剂离子对晶体透过率的影响，制备适合皮秒窄脉宽、高峰值功率的LCB晶体，准确测量其光学参数。建立基于LCB的皮秒激光频率变换理论，揭示晶体匹配方向、温度和角度带宽、尤其是皮秒激光群速度失配等对和频效率的影响，理论指导实验获得基于新型LCB晶体的355nm高功率皮秒紫外激光。具有显著的创新性和实用性，为基于新型LCB晶体长期稳定的高功率皮秒紫外激光特性研究开辟了新方案。

紫外超短脉冲激光在精细加工领域具有广泛应用，如柔性电路板制造，晶圆切割，心血管支架及太阳能电池制造等。紫外激光波长短，分辨率高，光子能量高，具有“冷加工”特性，另外，皮秒激光脉宽窄，加工中热影响区很小，因此，皮秒紫外激光加工精度高，广泛应用于石英玻璃、铟锡氧化物薄膜、存储器修复、精细打孔等领域。.项目开展了大能量高功率皮秒紫外脉冲激光技术的研究，通过研究窄脉冲宽度百皮秒激光种子源，多级串接侧面泵浦放大焦耳级大能量皮秒脉冲激光输出，研究放大过程中的空间滤波技术、相位共轭补偿技术和热退偏补偿技术获得高光束质量的大能量皮秒种子源，后续结合倍频技术和合频技术实现大能量皮秒紫外激光输出，355nm波段紫外皮秒脉冲能量为332mJ，266nm波段的紫外皮秒脉冲能量为205mJ该指标居国际先进水平，我国大能量皮秒紫外激光的研究提供了理论依据和技术支撑。