难熔金属的宽带超快动力学：TiN和ZrN
Broadband Ultrafast Dynamics of Refractory Metals: TiN and ZrN
摘要：
过渡金属氮化物由于其合适的光学性质、难熔性质和大的激光损伤阈值，近年来在等离子体激元学、等离子体激元增强的光致发光、光热应用和非线性光学等领域受到关注。这项工作报告的比较研究薄膜的氮化钛，氮化锆，和金飞秒激发下的瞬态响应。宽带瞬态光学特性有助于裁定早期，有点不一致的报告热电子寿命的基础上单波长测量。这些泵浦探测实验表明，亚皮秒瞬态动力学仅在ε近零窗口的难熔金属。动力学主要由超快电子能量再分配引起的光致带间跃迁决定。在ε-近零窗口中的增强的反射调制使得在低泵浦能量密度下观察这些膜的超快光学响应成为可能。这些结果表明TiN和ZrN中的电子-声子耦合比Au中的大25-100倍。强的电子-声子耦合驱动亚皮秒光学响应，并且与Au相比促进更大的晶格加热，使得TiN和ZrN有希望用于光热应用。TiN和ZrN的光谱响应和动力学对泵浦能量密度和泵浦激发能只有微弱的敏感性。然而，在较高的泵浦光子能量和较高的注量下，响应的幅度要大得多，在ε接近零的窗口中，在TiN中达到15%的峰值观察值，在ZrN中达到50%的峰值观察值。
英文摘要：
Transition metal nitrides have recently gained attention in the fields of plasmonics, plasmon-enhanced photocatalysis, photothermal applications, and nonlinear optics because of their suitable optical properties, refractory nature, and large laser damage thresholds. This work reports comparative studies of the transient response of films of titanium nitride, zirconium nitride, and Au under femtosecond excitation. Broadband transient optical characterization helps to adjudicate earlier, somewhat inconsistent reports regarding hot electron lifetimes based upon single wavelength measurements. These pump-probe experiments show sub-picosecond transient dynamics only within the epsilon-near-zero window of the refractory metals. The dynamics are dominated by photoinduced interband transitions resulting from ultrafast electron energy redistribution. The enhanced reflection modulation in the epsilon-near-zero window makes it possible to observe the ultrafast optical response of these films at low pump fluences. These results indicate that electron-phonon coupling in TiN and ZrN is 25-100 times greater than in Au. Strong electron-phonon coupling drives the sub-picosecond optical response and facilitates greater lattice heating compared to Au, making TiN and ZrN promising for photothermal applications. The spectral response and dynamics of TiN and ZrN are only weakly sensitive to pump fluence and pump excitation energy. However, the magnitude of the response is much greater at higher pump photon energies and higher fluences, reaching peak observed values of 15 % in TiN and 50 % in ZrN in the epsilon-near-zero window.
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