【作者】 刘斌；

【导师】 夏元钦；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2016， 硕士

【摘要】 光子回波技术广泛的用来研究各种物质的超快动力过程。伴随着飞秒激光以及掺钛蓝宝石锁模激光器的的出现,实验上能够获得脉冲宽度数个飞秒的激光脉冲,使得利用飞秒激光器研究溶剂超快动力学过程成为了可能。飞秒光子回波技术被认为是研究溶剂动力学过程非常有用的方法。这种方法可以测量几飞秒到几纳秒时间范围内的失相时间。光子回波采用共振激发的手段得到受激样品的振动动态信息。飞秒激光脉冲的频率宽度常常比电子激发态上的振动能级间隙要宽,所以利用飞秒光子回波能够同时将多个能级激励。通过光子回波信号的频谱可以得到电子激发态上的振动模式。理论上建立了光子回波多模布朗振动(Multimode Brownian Oscillator,简称MBO)模型的相关函数。模拟了时间响应函数的随入射频率的响应,结果表明相位重构光谱谱线沿着对角线方向被挤压。非相位重构光谱谱线沿着非对角线方向被挤压,沿对角方向的均匀加宽被抑制。通过建立的5种MBO型相关函数模拟了叶绿素A分子的光子回波光谱和峰移光谱。结果表明光子回波光谱和峰移光谱的变化规律和相关函数的变化规律相同。模拟了温度、脉冲宽度、脉冲类型、脉冲啁啾对光子回波光谱的影响。结果表明光子回波强度和温度之间是线性关系;和脉冲宽度之间是指数关系;和啁啾参量之间是对称关系。实验上利用飞秒光子回波光谱技术开展了叶绿素A分子和BBO晶体(β相偏硼酸钡,β-BaB2O4)的相干动力学研究。利用662nm激光脉冲为泵浦光,800nm的脉冲作为探测光,以浓度为5.6*10-5mol/L的叶绿素A甲醇溶液和BBO晶体为研究对象开展了双色三脉冲光子回波实验。拟合参数表明BBO晶体快速振动项比重较小,分子的慢速振动是主要的振动形式;BBO晶体的三维光子回波光谱表明入射飞秒脉冲激发了电子到单个激发态。通过叶绿素A分子的光子回波光谱得到不同延迟时间的衰减常数。拟合结果表明在初始时刻快速振动是分子的主要运动方式,慢速振动和静态微扰较弱,这是由叶绿素A分子在溶液中的布朗运动造成的。得到了叶绿素A分子瞬态光栅信号的快速衰减时间约为100fs,慢速衰减时间约为300fs。双色三脉冲光子回波实验结果表明MBO模型相关函数能够用于光子回波光谱分析。更多还原

【Abstract】 Photon echo technique is widely used for the study the ultrafast dynamical process in various substances. With the rise of femtosecond mode-locked and titanium sapphire laser, pulses with width of several femtoseconds can be experimentally obtained, which makes it possible to study the ultrafast solvent dynamics. Femtosecond photon echo technique, referred to as a useful method to the study of solvent dynamics, can measure dephasing time ranging from femtoseconds to nanoseconds, where dynamic information of vibration in the stimulated sample can be obtained via resonance excitation. Under many circumstances, the band width possesses a wider space than the vibrational level gap, so that a plurality of energy level can be simultaneously excited with the use of femtosecond photon echo. The vibrational modes in the electronically excited state can be obtained through its spectrum.Theoretically, the correlation function as model of photon echo Multimode Brownian Oscillator( MBO) is established and a simulation of time response function to incident frequency is operated, which shows that the spectral lines of the phase reconstruction are extruded along the diagonal direction and that lines of the non-phase reconstruction are extruded along the non-diagonal, and indicates that the homogeneous broadening is suppressed along the diagonal direction. The established correlation function for 5 MBO model simulates the spectrum of photon echo and peak shift of chlorophyll A molecule, and gives the result that both the variation of photon echo and peak shift spectrum, and variation of correlation function obey the same law. Simulation of temperature, pulse width, pulse type, pulse chirp influence on photon echo spectrum is conducted, which shows that the photon echo intensity has a linear relationship with temperature, an exponential relationship with pulse width and a symmetrical relationship with chirp parameter.Experimentally, the study of coherent dynamics of chlorophyll A molecule and BBO crystal(β phase Barium Boron Oxide, β-Ba B2O4) is carried out with femtosecond photon echo spectroscopy. The two-color three-pulse photon echo experiments apply the 622 nm pump light and the 800 nm probe light for the chlorophyll A methanol solution at a concentration of 5.6*10-5mol/L and the BBO crystal. The fitting parameter indicates that the rapid vibration term shares a small proportion while the slow is the main form. Three-dimensional photon echo spectrum of BBO crystal shows that the incident femtosecond pulse stimulates a single electron to the excited state. Through photon echo spectrum of chlorophyll A molecule, the decay constant for different delay time can be obtained. The fitting results shows that the rapid vibration is the main form for the initial time while the slow vibration and static perturbation is relatively weak, which is caused by the Brownian motion of chlorophyll A in solution. It can come to the conclusion that the rapid decay time of transient grating signal is about 100 fs in chloriphyll A, the slow decay time about 300 fs. The two-color three-pulse photon echo experiments show that the correlation function as MBO model can be applied for the analysis of photon echo spectroscopy.更多还原