We have defined and analytically derived a new parameter called “rescattering deflection parameter” ΓR to gauge the transition from strong field to ultra-strong field rescattering dynamics. We also have developed a 3D semiclassical relativistic rescattering model, including tunneling ionization and trajectory ensemble to quantify the laser-atom interaction at intense laser fields. Our analytical results for the rescattering deflection parameter and the numerical results obtained using the rescattering model are in very good agreement with each other. For 800 nm laser field, the ultra-strong field onset happens at 3 1016 W/cm2 and for longer wavelength radiation Lorentz force becomes significant even at lower intensities.;Ion yields from neon (Ne+ to Ne+8) and xenon (Xe+7 to Xe+12) at intensities from 10 14 W/cm2 to 1018 W/cm2 are reported along with the calculated ion yields from the rescattering model. For all the charge states measured here, the ADK model agrees very well with the measurement near saturation. Below saturation, the measurement clearly shows the characteristic “knee structure” (non-sequential ionization) in the measured ion yields from neon and xenon for charge states that saturate below an intensity of 3 1016 W/cm2 and also the presence of cross-shell ionization in xenon from L-shell to k-shell. The gradual decrease in the observed NSI yields below 3 1016 W/cm 2 is attributed to the decrease in the ionization cross section as one moves to higher charge states. Finally, for intensities beyond 3 10 16 W/cm2, the Lorentz deflection due to laser magnetic field becomes significant and start to suppresses the observed NSI yield by moving the returning electron wavepacket along the laser propagation direction. Below saturation, the model predicts the general trend in the non-sequential ionization, but the actual agreement is anywhere between 1% to 15%.;We have measured carbon fragmental (C+2 to C+5 ) ion yields from methane from both the linear and circular polarized laser fields from the onset of Coulomb regime (1014 W/cm 2) up to relativistic regime (1018 W/cm2). The linear polarization data clearly shows the presence of “knee structure” with all the charge states measured here and the knee structure is partially and completely suppressed for C+4 and C+5 respectively in circular polarized field. This result indicates C+2 and C+3 are produced through Coulomb explosion mechanism and the higher charge states C+4 and C+5 are increasingly produced through atomic-like tunneling and rescattering mechanism as one moves to ultra-strong laser fields. We have also measured photoelectron spectra from methane at intensities 8 1015 W/cm2 and 7 1018 W/cm2 in energies up to 0.6 MeV. The measured photoelectron spectra are in very good agreement with an atomic carbon ionization model at ultra-strong laser field. This result corroborates the results from carbon ion measurements that methane responses to ultra-strong laser field in atomic-like manner. The non-sequential ionization yield calculated for atomic carbon ionization is in good agreement with measured C+5 ion yield from methane, further corroborating our earlier results. This result can be generalized to larger molecules as the measured carbon ion yields from ethane, butane, and octane are nearly similar to the methane results.;The rescattering dynamics are expected to change significantly in a 400 nm laser field when compared to the same from 800 nm laser field. The returning photoelectron flux at the parent ion is enhanced in a 400 nm laser field. In that case, it is the kinetic energy of the returning photoelectron that determines whether the rescattering ionization is feasible or not. We have calculated the ion yields for neon (Ne+2 to Ne+8) and xenon (Xe+4 to Xe+12) from 400 nm laser field at intensities from 1014 W/cm2 to 10 18 W/cm2. Compared to the similar results from an 800 nm laser field, we observe suppression of non sequential ion yields up to ∼10 16 W/cm2 and enhancement beyond that. This suppression and enhancement in the ion yields are attributed to the return electron energy being smaller or higher than the ionization potential of the ion in question. (Abstract shortened by UMI.).
展开▼
机译：我们定义并分析得出了一个称为“散射偏转参数”ΓR的新参数，以测量从强场到超强场散射动力学的转变。我们还开发了3D半经典相对论散射模型，包括隧穿电离和轨迹系综，以量化在强激光场下的激光-原子相互作用。我们对散射偏转参数的分析结果与使用散射模型获得的数值结果彼此非常吻合。对于800 nm激光场，超强场开始发生在3 1016 W / cm2处，并且对于更长波长的辐射，即使在较低强度下，洛伦兹力也变得显着;氖（Ne +至Ne + 8）和氙（Xe +报告了从10 14 W / cm2到1018 W / cm2强度的7至Xe + 12）以及从散射模型计算出的离子产率。对于此处测量的所有电荷状态，ADK模型与接近饱和的测量非常吻合。在饱和以下，该测量清楚地显示出在电荷状态下饱和的强度低于3 1016 W / cm2且存在交叉壳的情况下，所测得的氖和氙离子产率中的特征性“膝结构”（非顺序电离）氙离子从L壳到k壳的电离。低于3 1016 W / cm 2时，观察到的NSI产量逐渐降低，是由于随着人们向更高的电荷态转变，电离截面的降低。最后，对于超过3 10 16 W / cm2的强度，由于激光磁场引起的洛伦兹挠度变得显着，并开始通过沿激光传播方向移动返回的电子波包来抑制观察到的NSI产量。在饱和以下时，该模型预测了非顺序电离的总体趋势，但实际一致性介于1％至15％之间;我们已经测量了两种甲烷中甲烷的碳碎片离子产率（C + 2至C + 5）线性和圆偏振激光场从库仑状态（1014 W / cm 2）开始到相对论状态（1018 W / cm2）。线性极化数据清楚地表明，此处测量的所有电荷状态都存在“膝结构”，并且在圆极化场中分别对C + 4和C + 5局部和完全抑制了膝结构。这一结果表明，随着库仑爆炸机理的产生，C + 2和C + 3产生，随着原子向超强激光场的迁移，越来越高的电荷态C + 4和C + 5通过类似原子的隧穿和散射机制产生。我们还测量了甲烷的光电子能谱，强度为8 1015 W / cm2和7 1018 W / cm2，能量高达0.6 MeV。在超强激光场下，测得的光电子光谱与原子碳电离模型非常吻合。该结果证实了碳离子测量的结果，即甲烷以原子样方式响应超强激光场。计算出的原子碳电离的非顺序电离产率与甲烷测得的C + 5离子产率非常吻合，进一步证实了我们先前的结果。该结果可以推广到更大的分子，因为从乙烷，丁烷和辛烷中测得的碳离子收率与甲烷的收率几乎相似。与400nm激光相比，预期在400 nm激光场中的重散射动力学将发生显着变化800 nm激光场。在400 nm的激光场中，母离子处返回的光电子通量得到了增强。在那种情况下，返回光电子的动能决定了再散射电离是否可行。我们已经从强度为1014 W / cm2到10 18 W / cm2的400 nm激光场计算了氖气（Ne + 2至Ne + 8）和氙气（Xe + 4至Xe + 12）的离子产率。与从800 nm激光场获得的类似结果相比，我们观察到抑制了高达10 16 W / cm2的非连续离子产量，并进一步提高了产量。离子产率的抑制和提高归因于返回电子能量小于或高于所讨论离子的电离电势。 （摘要由UMI缩短。）。
展开▼
