Kudryashov S I, Danilov P A, Kuzmin E V, Gulina Yu S, Rupasov A E, Krasin G K, Zubarev I G, Levchenko A O, Kovalev M S, Pakholchuk P P, Ostrikov S A, Ionin A A
Opt Lett. 2022 Jul 15;47(14):3487-3490. doi: 10.1364/OL.462693.
Microscale filamentation of 0.25 NA-focused, linearly and circularly polarized 1030 nm and 515 nm ultrashort laser pulses of variable pulse widths in fused silica, fluorite, and natural and synthetic diamonds demonstrates the Raman-Kerr effect in the form of critical pulse power magnitudes, proportional to squared wavelength and inversely proportional to laser pulse width of 0.3-10 ps. The first trend represents the common spectral relationship between the quantities, while the second indicates its time-integrated inertial contribution of Raman-active lattice polarization, appearing in transmission spectra via ultrafast optical-phonon Raman scattering. The optical-phonon contribution to the nonlinear polarization could come from laser field-induced spontaneous/stimulated Raman scattering and coherent optical phonons generated by electron-hole plasma with its clamped density in the nonlinear focus. Almost constant product value of the (sub)picosecond laser pulse widths and corresponding critical pulse powers for self-focusing and filamentation in the dielectrics ("critical pulse energy") apparently implies constant magnitude of the nonlinear polarization and other "clamped" filamentation parameters at the given wavelength.
在熔融石英、萤石以及天然和人造金刚石中，对脉宽可变的0.25数值孔径聚焦的、线偏振和圆偏振的1030纳米及515纳米超短激光脉冲进行微尺度丝状化实验，结果表明拉曼 - 克尔效应表现为临界脉冲功率大小，其与波长平方成正比，与0.3 - 10皮秒的激光脉冲宽度成反比。第一个趋势代表了这些量之间常见的光谱关系，而第二个趋势则表明了拉曼活性晶格极化的时间积分惯性贡献，它通过超快光学声子拉曼散射出现在透射光谱中。光学声子对非线性极化的贡献可能来自激光场诱导的自发/受激拉曼散射以及由非线性焦点处具有固定密度的电子 - 空穴等离子体产生的相干光学声子。对于电介质中的自聚焦和丝状化，（亚）皮秒激光脉冲宽度与相应临界脉冲功率的乘积值几乎恒定（“临界脉冲能量”），这显然意味着在给定波长下非线性极化和其他“固定”丝状化参数的大小恒定。
