【作者】 张睿；

【导师】 张兆伟；

【作者基本信息】 华中科技大学 ， 光学工程， 2025， 博士

【摘要】 波长可调谐飞秒激光在强场物理、生物成像、超快光谱测量、激光加工与医疗等领域有着广泛的应用前景。基于白光种子源的飞秒光参量放大器（OPA）,为在可见光、近红外以及中红外波段产生波长可调谐的飞秒激光提供了一个重要的技术平台。针对飞秒OPA系统在获得高脉冲质量以及中红外波段输出等方面的困难,本论文主要研究如何控制飞秒OPA系统的光谱带宽,以及如何以较高的效率将飞秒OPA系统的输出波长拓展至中红外波段。本论文的主要研究成果如下:（1）提出通过控制白光啁啾来实现对OPA输出脉冲的光谱带宽的调控,从而获得高脉冲质量、接近变换极限的波长可调谐飞秒激光输出。深入分析了白光啁啾以及泵浦光啁啾对基于Ⅰ型相位匹配偏硼酸钡（β-Ba B₂O₄,BBO）晶体的绿光泵浦飞秒OPA输出脉冲特性的影响。数值仿真结果表明,通过增加白光啁啾,放大后无需色散补偿,OPA能够直接产生接近变化极限的光脉冲。搭建实验系统,获得了波长调谐范围为630～2600 nm的飞秒激光脉冲,在700 nm和1300 nm中心波长处测得的脉冲时间带宽积分别为0.88和0.33。（2）构建了多级OPA系统,将绿光泵浦的BBO-OPA作为预放大器,将基于砷酸钛氧钾（KTi OAs O₄,KTA）晶体的OPA作为最后一级放大器从而实现波长转换与功率放大,将OPA的输出波长调谐范围拓展至2.5～4.2μm中红外波段。利用绿光泵浦的BBO-OPA系统提供的1.36～1.76μm高脉冲质量飞秒脉冲作为KTA-OPA的种子光,获得了2.5～4.2μm波长可调谐、具有高脉冲质量的中红外飞秒激光输出,所测得的中红外飞秒激光脉冲的时间带宽积约为0.8。（3）构建了多级OPA系统,将绿光泵浦的BBO-OPA作为预放大器,将基于硒镓钡（Ba Ga₄Se₇,BGSe）晶体的OPA作为最后一级放大器从而实现波长转换与功率放大,解决了长波红外非线性晶体由于损伤阈值偏低所导致的低增益与低效率问题,在3.5～16μm都实现了较高的量子转换效率。为了在整个波段获得均匀的放大,需要选择较短的晶体长度以避免泵浦光和信号光之间发生时间走离。由于BGSe晶体的损伤阈值较低,较短的晶体长度无法产生足够的参量增益。绿光泵浦的飞秒BBO-OPA系统具有较高的参量增益,通过白光啁啾管理,能够提供波长覆盖1.09～1.47μm且具有较高脉冲质量的高能量飞秒脉冲作为BGSe-OPA的种子光,从而在BGSe-OPA增益较低的情况下也能实现高效率放大。实验中,BGSe-OPA系统在3.5～16μm波段都获得了高于24%的量子转换效率。综上,本文研究了通过白光啁啾管理实现对飞秒OPA输出脉冲的光谱带宽的调控,从而直接获得近变换极限的飞秒脉冲输出。在理论上深入分析了白光啁啾对飞秒OPA输出脉冲特性的影响,在实验上通过搭建BBO-OPA系统获得了具有较高转换效率和较高脉冲质量的波长可调谐飞秒激光脉冲。研究了将BBO-OPA系统作为预放大,将基于KTA晶体和BGSe晶体的OPA进行最后一级放大的多级级联技术方案,以较高的效率分别实现了覆盖2.5～4.2μm,3.5～17μm波长可调谐的中红外飞秒激光输出。更多还原

【Abstract】 Femtosecond optical pulses with tunable wavelength are essential for many applications including strong-field physics,multi-photon imaging,ultrafast spectroscopy,laser processing and laser medicine.Femtosecond optical parametric amplifiers（OPAs）based on broadband whitelight continuum（WLC）have been established as an important platform for generating femtosecond optical pulses in the visible,near-infrared and mid-infrared spectral regions.In order to solve the difficulties in obtaining high-pulse-quality femtosecond pulses from OPAs and building highly-efficient mid-infrared femtosecond OPAs,this thesis mainly studies how to control spectral bandwidth of femtosecond OPA,and how to efficiently extend the wavelength tuning range into mid-infrared region.The major research results are as follows:（1）We present that,by WLC seed chirp management,spectral bandwidth of OPA output pulse can be adjusted and controlled for efficiently generating femtosecond optical pulses with narrow band and small time-bandwidth product（TBP）.The influences of the chirp of the WLC seed and chirp of pump on the pulse characteristics of green-pumped femtosecond OPAs based on typeⅠphase-matchedβ-Ba B₂O₄（BBO）crystals are studied.By numerical simulations,we show that by manipulating the WLC seed pulses to be highly chirped,nearly transform-limited optical pulses can be directly obtained from OPAs,without dispersion-compensation elements after amplification.By experimental studies,we obtain femtosecond pulses tunable within630～2600 nm.TBP tested at central wavelength of 700 nm and 1300 nm are 0.88 and 0.33respectively.（2）We propose multi-stage cascaded OPA system,with green-pumped BBO-OPA used as the preamplifier and KTi OAs O₄（KTA）-OPA as final amplification stage,to efficiently extend wavelength into 2.5～4.2μm mid-infrared region.The green-pumped BBO-OPA preamplifier provides high-quality femtosecond pulses tunable from 1.36μm to 1.76μm as the seed source for the subsequent KTA-OPA.As a result,mid-infrared femtosecond optical pulses tunable within 2.5～4.2μm with high pulse quality and stability are obtained.The tested TBP is less than 0.8.（3）We propose multi-stage cascaded OPA system,with green-pumped BBO-OPA used as the preamplifier and Ba Ga₄Se₇（BGSe）-OPA as final amplification stage,to overcome low gain and low efficiency brought by low damage threshold of long-wave mid-infrared nonlinear crystal and fulfill high quantum efficiency for the whole 3.5～16μm region.In order to obtain uniform parametric amplification,short crystal length should be used to suppress pump-signal-walkoff,however low damage threshold results in a relatively low parametric gain for short BGSe crystal.The green-pumped BBO-OPA preamplifier,with high gain and chirp management,provides high-quality high-energy femtosecond pulses tunable from 1.09μm to1.47μm as the seed source for the subsequent BGSe-OPA.As a result,with a relatively low parametric gain for the final BGSe-OPA,a quantum conversion efficiency of higher than 24%is obtained for the full wavelength tuning range within 3.5～16μm.In conclusion,we firstly study how to adjust and control spectral bandwidth of OPA output pulses by WLC chirp management so as to directly obtain nearly transform-limited femtosecond optical pulses.The influence of the chirp of WLC seed on the pulse characteristics of femtosecond OPAs is analyzed in detail.By establishing BBO-OPA system,wavelength tunable femtosecond pulses with high efficiency and high pulse quality are achieved.We then research on multi-stage cascaded OPA system,with BBO-OPA system as the preamplifier and KTA-OPA or BGSe-OPA as final amplification stage,to efficiently obtain femtosecond pulses tunable from 2.5～4.2μm or 3.5～17μm respectively.更多还原