用于受限光吸收的脉冲驱动集体超快相互作用
Burst-Driven Collective Ultrafast Interactions for Confined Optical Absorption
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中文总结 AI 辅助
本研究提出脉冲驱动集体超快相互作用机制，开发分析模型实现半导体纳米颗粒高效受限光吸收，可提升光子过程阶数，预期应用于非线性光声成像、荧光显微镜等领域。
中文摘要 AI 辅助
超快脉冲串（由紧密间隔的飞秒脉冲组成）可驱动单脉冲激发无法实现的光与物质相互作用，当脉冲间隔短于瞬态效应的弛豫时间时，前期脉冲产生的瞬态效应会非线性改变后续脉冲的相互作用。光激发领域长期存在一个权衡：多光子吸收可提供强空间受限性，但能量转移效率低；线性吸收效率高，但空间定位能力有限。本研究表明，超快脉冲串可通过多光子吸收在半导体纳米颗粒中集体建立自由载流子群体，这些自由载流子会以线性方式强吸收能量，且脉冲串结束后会迅速耗散。最终形成的吸收过程效率更高，且分别受多光子吸收和脉冲串持续时间的严格时空调控。研究开发了耦合载流子产生、俄歇复合与表面复合的分析模型，得到了载流子动力学的分段精确描述及集体能量沉积增强的直观标度关系。集体吸收的一个标志性特征是其对光强度的额外一次幂依赖，可将m光子过程的阶数有效提升至m+1，无需提高单个脉冲的强度。本研究以非线性光声成像为潜在应用场景，同时预期其可应用于非线性荧光显微镜等多种领域。
英文摘要
Ultrafast bursts, groups of closely spaced femtosecond pulses, can drive light-matter interactions that are not possible with single-pulse excitations. This occurs when earlier pulses create a transient effect that nonlinearly alters the interaction of later pulses, provided that the inter-pulse spacing is shorter than the relaxation time of the transient. A long-standing trade-off in optical excitation is between multiphoton absorption, which provides strong spatial confinement but low energy-transfer efficiency, and linear absorption, which is efficient but offers limited spatial localization. Here, we show that a burst of ultrafast pulses can collectively build up a population of free carriers in semiconductor nanoparticles via multiphoton absorption. The free carriers absorb linearly and strongly, and dissipate rapidly once the burst ends. The result is a more efficient absorption process that is strongly gated spatially and temporally by multiphoton absorption and burst duration, respectively. We develop an analytical model that couples carrier generation with Auger and surface recombination, yielding a piecewise-exact description of the carrier dynamics and an intuitive scaling relation for the collective energy-deposition enhancement. A signature consequence of collective absorption is its dependence on one extra power of the light intensity, effectively raising the order of an m-photon process to m+1 without requiring higher intensities for the individual pulses. While we focus on nonlinear photoacoustic imaging as a potential application, we anticipate diverse applications, including nonlinear fluorescence microscopy.
