【作者】 杨康文；

【导师】 曾和平；

【作者基本信息】 华东师范大学 ， 光学， 2014， 博士

【摘要】 高精度宽谱带的光学频率梳是研究时频域可分辨精密光谱测量、相干反斯托克斯拉曼光谱成像、光梳精密测距等前沿科学领域的重要实验工具。光学频率梳向紫外、极紫外以及中红外、远红外的频率拓展,都离不开高功率高精度的光梳作为驱动源。本论文围绕着这一主题,以“光纤飞秒光梳高功率放大与控制”为主线,开展多波段光纤放大器性能优化和结构改进,多色超短脉冲精密时域同步,高功率多波长光学频率梳的产生,以及光梳相干合成中零频噪声抑制等方面的研究工作。论文针对飞秒脉冲级联式高功率光纤放大过程中的相位噪声问题,采用后向反馈的控制方案实现平均功率百瓦量级的超短脉冲载波包络相位及重复频率的精密锁定。同时,对于光梳相干合成中放大器引入的载波包络相位噪声,发展了基于声光移频器的前向反馈式补偿技术,有效抑制了梳齿的频率漂移,为基于相干合成和光谱组束实现高功率宽谱带的光学频率梳提供了实验基础。本论文的主要内容和创新点归纳如下：1.研制多个中心波长的超短脉冲光纤放大器,研究入射脉冲宽度,光纤掺杂浓度,放大器结构对脉冲时频域特性的影响。1)以掺镱新型陶瓷锁模激光器为种子源,采用大模场面积光子晶体光纤,实现中心波长1031nm,平均功率303W的超短脉冲。2)基于非线性偏振旋转锁模和全光纤级联放大技术,实现中心波长1064nm,平均功率20W的小型化全光纤皮秒激光器,并研究其长期工作的稳定性要求。3)采用偏振分离式放大结构,实现中心波长1560nm掺铒单模光纤的高效率低噪声放大,斜率效率提升16%,有效抑制1530nm处放大的自发辐射噪声。2.发展了高功率多波长超短脉冲的精密时域同步技术,为进一步探索宽谱带高功率的光学频率梳提供精确同步的多色飞秒脉冲。1)实现平均功率近百瓦量级的掺镱光纤激光与掺铒光纤激光、钛宝石飞秒激光的三波长超短脉冲精密时域同步,进一步发展光谱分割放大、交叉吸收调制的同步方法,获得同步抖动在飞秒量级的800nm,1030nm1550nm的超短脉冲。2)基于光学倍频,实现高功率超短脉冲的频率拓展,获得平均功率16.7W的515nm同步绿光输出,转换效率为33%。3.研制高功率近红外光学频率梳,获得了载波包络相位锁定精度在毫赫兹量级的超短脉冲,并通过非线性频率转换,拓展光梳的光谱范围。1)基于钛宝石飞秒振荡器和大模场面积光纤放大器,采用反馈控制振荡器泵浦功率的方法,获得了平均功率100W的高功率光梳脉冲,其载波包络零频线宽为2.25mHz。2)实验研究了自参考与交叉参考的f-2f测量方法对于精密锁定超短脉冲载波包络相位偏移频率的影响,对同一套系统,采用不同测量方法,锁定后的相位噪声分别为0.41rad和0.49rad,锁定后的线宽分别为1.86mHz和2.06mHz。3)基于非线性光学频率转换,实现光学频率梳的光谱拓展,获得平均功率12.8W的可见绿光和平均功率1.62W的紫外脉冲,近红外到紫外光的转换效率为3.85%。4.探索通过相干合成的方法提高光梳的平均功率,采用前向反馈方案,有效抑制光梳在光纤放大过程中载波包络相位相对漂移噪声,实验研究了两路光梳相干合成前后的时频域特性。1)基于Mach-Zendar干涉仪,研究高重复频率超短脉冲放大前后载波包络相位偏移频率的相对漂移,采用声光移频器前向反馈控制方法,相对漂移从自由运转的±15Hz降低到补偿后的±1.5Hz,相位噪声从0.23rad降低到0.14rad。2)基于主振荡-功率放大装置,以钛宝石光学频率梳为种子光源,实现两路平均功率10w的光纤放大器在光梳放大过程中,载波包络相位相对漂移噪声的主动补偿,实验研究了合成后脉冲宽度,光谱形状的变化,为探索脉冲相干合成实现高功率、多波长、高精度的光学频率梳提供新途径。更多还原

【Abstract】 Optical frequency combs with high average power and broadband spectral range provide significant experimental tools for precision spectroscopy, coherent anti-Stokes Raman scattering spectrum imaging, and high-accuracy long-distance measurement. Especially for the application of ultraviolet or mid-infrared frequency comb generation, high-power high accurate frequency comb is essential to acting as the driving source. To study the power scaling and precise control of frequency combs, my works are focused on the improvement of high-power fiber amplifiers, synchronization of multi-color femtosecond lasers, generation of cascade high-power multi-color fiber frequency comb, and suppression of carrier-envelope (CE) phase noise for coherent frequency comb combination. In this dissertation, we demonstrated a high-power low-noise broadband frequency comb stabilized by feedback control scheme. Meanwhile, an active feed-forward method was employed for compensating the relative carrier-envelope drifts of fiber optical amplifiers, paving a novel way to generate high-power, high-accuracy optical frequency combs by coherently combining a large number of fiber amplifiers seeded by the same comb oscillator.The works demonstrated in the dissertation include:high-power fiber amplifier improvement, multi-color laser synchronization,100-W frequency comb stabilization, and carrier-envelope phase noise compensation for comb combination. The details are summarized as follows:1. We optimized the temporal and spectral performance of high-power fiber amplifiers by changing the laser oscillator, the gain medium and the amplification structure. 1) Ultrashort pulses with an average power of303W at1031nm were produced by four-stage large-mode-area photonic crystal fiber amplifiers seeded by a diode-pumped Yb:YAG ceramic laser oscillator.2) A20-W all fiber picosecond laser at1064nm was built via nonlinear polarization rotation mode-locking and cascade all fiber amplifiers, electronic control and mechanical protection were integrated for practical use.3) We observed the16%increase of the slope efficiency and restraint of amplified spontaneous emission at1530nm in polarized separated erbium-doped single mode amplifier, which has the potential for ultra low noise frequency comb amplification.2. We achieved high-power synchronized multi-color ultrashort lasers by spectral fraction amplification and master-slave laser configuration, which could be used to generate ultra broadband optical frequency by spectral beam combination.1) Passive synchronization of three femtosecond mode-locked lasers at different central wavelengths was achieved. The timing jitter was7.7fs between800-nm Ti:sapphire and high-power1030-nm pulses, and56.5fs between1550-nm and1030-nm pulses, respectively.2) Synchronized frequency-doubled laser pulses at515nm with an average power of16.7W was obtained, corresponding to a nonlinear frequency conversion efficiency of33%.3. High-power infrared frequency comb was generated with carrier-envelope offset frequency locked to several millihertz via feedback scheme, which was incident on nonlinear crystal to obtain ultraviolet frequency comb.1) A frequency comb with100-W average power was achieved based on a Ti:sapphire femtosecond laser oscillator and large-mode-area fiber amplifiers, the line-width of locked offset frequency was2.25mHz.2) Experimental comparison between self-and cross-referenced f-2f measurements for carrier-envelope phase detection was implemented, the phase noise of locked beat signal were0.41and0.49rad, revealing a line-width of1.86and2.06mHz, respectively.3) By frequency quadrupling femtosecond pulse train from high-power large-mode-area fiber chirped-pulse amplifier at1030nm, we obtained ultraviolet pulse at258nm with an average power of1.62W, corresponding to an optical-to-optical efficiency of3.85%.4. Successful carrier-envelope drift noise suppression during comb amplification was achieved for demonstration of frequency comb combining with two amplifier branches.1) A Mach-Zender interferometer was used to characterize the relative CE drifts of an optical frequency comb before and after power scaling. The frequency noise of the relative CE drifts was well controlled in a variation range from±15Hz of free-running to approximately±1.5Hz via an active feed-forward compensation method, corresponding to an accumulated phase noise reduced from0.23rad to0.14rad.2) We controlled the CE drifts of two10-W Yb-doped fiber amplifiers to demonstrated coherent optical comb combination, opening up a way to scale the average power of optical frequency comb.更多还原