Erokhin Alexander I, Bulychev Nikolay A, Parkevich Egor V, Medvedev Mikhail A, Smetanin Igor V
P. N. Lebedev Physical Institute of RAS, Leninskii prosp. 53, 119991 Moscow, Russia.
Moscow Aviation Institute, Volokolamskoe shosse 4, 125993 Moscow, Russia.
Nanomaterials (Basel). 2022 Jul 26;12(15):2567. doi: 10.3390/nano12152567.
Recent discoveries in nonlinear optical properties of nanoparticle colloids make actual the challenge to lower the energy threshold of phase conjugation and move it into the domain of shorter pulse widths. A novel effect of the stimulated Rayleigh-Mie scattering (SRMS) in two-photon absorbing nanocolloids is considered as a promising answer to this challenge. We report the results of experimental and theoretical study of the two-photon-assisted SRMS in Ag and ZnO nanocolloids in the nanosecond-to-picosecond pulse width domain. For 12 ns 0.527 μm laser pulses, the four-wave mixing SRMS scheme provides lasing and amplification of backscattered anti-Stokes signal in Ag nanocolloids in toluene at the threshold 0.2 mJ and the spectral shifts up to 150 MHz. For 100 ps 0.532 μm pulses, we observed for the first time efficient (over 50% in signal-to-pump ratio of pulse energies) SRMS backscattering of the anti-Stokes signal in Ag nanocolloids in toluene and predominantly Stokes signal in ZnO nanocolloids in water, with the spectral shifts up to 0.25 cm. We develop the first order-in-perturbation model of the four-wave mixing two-photon absorption-assisted SRMS process which shows that at nanosecond pulses, amplification is predominantly due to the thermal-induced coherent oscillations of polarization while the slow temperature wave acts also as a dynamic spatial grating which provides a self-induced optical cavity inside the interaction region. At a picosecond pulse width, according to our model, the spectral overlap between pump and signal pulses results in formation of only the dynamic spatial temperature grating, and we succeeded at recovering the linear growth of the spectral shift with the pump power near the threshold.
纳米颗粒胶体非线性光学性质的最新发现，使得降低相位共轭能量阈值并将其转移到更短脉冲宽度领域的挑战变得切实可行。双光子吸收纳米胶体中受激瑞利 - 米氏散射（SRMS）的一种新效应被认为是应对这一挑战的一个有前景的答案。我们报告了在纳秒到皮秒脉冲宽度范围内，对银和氧化锌纳米胶体中双光子辅助SRMS的实验和理论研究结果。对于12纳秒、0.527微米的激光脉冲，四波混频SRMS方案在甲苯中的银纳米胶体中，在阈值0.2毫焦时提供了反向散射反斯托克斯信号的激光发射和放大，光谱位移高达150兆赫。对于100皮秒、0.532微米的脉冲，我们首次在甲苯中的银纳米胶体中观察到了高效的（脉冲能量的信号与泵浦比超过50%）反斯托克斯信号的SRMS反向散射，在水中的氧化锌纳米胶体中观察到了主要是斯托克斯信号的反向散射，光谱位移高达0.25厘米。我们开发了四波混频双光子吸收辅助SRMS过程的一阶微扰模型，该模型表明，在纳秒脉冲时，放大主要是由于热诱导的极化相干振荡，而缓慢的温度波也作为一个动态空间光栅，在相互作用区域内提供了一个自诱导光学腔。在皮秒脉冲宽度下，根据我们的模型，泵浦脉冲和信号脉冲之间的光谱重叠仅导致动态空间温度光栅的形成，并且我们成功地恢复了在阈值附近光谱位移随泵浦功率的线性增长。
