使用腔增强频率梳探针的三重共振光谱学
Triple-Resonance Spectroscopy Using a Cavity-Enhanced Frequency Comb Probe
AI总结：
研究旨在解决高激发振动态红外热带跃迁测量难题，采用基于全光三重共振的非线性光谱方法，能高精度测量四个振动带间跃迁，为探索高激发分子态开辟新途径，提供完善分子模型所需光谱数据。
AI中文摘要：
准确且经实验验证的分子热带跃迁模型对于解释从系外行星大气到燃烧系统等环境中的高温光谱至关重要。然而，由于这些跃迁在室温下太弱而无法观测，在高温下光谱又会拥堵，导致高于10000 cm$^{-1}$的高激发振动态的红外热带跃迁的线分辨测量缺失。我们引入一种非线性光谱方法，基于全光三重共振（AOTR）方案，结合光学频率梳稳定、双种子连续波光参量振荡器的逐步中红外泵浦与腔增强光学频率梳的宽带高灵敏近红外探测，能在宽光谱范围内以亚多普勒分辨率和亚兆赫兹频率精度同时测量四个振动带之间高达12000 cm$^{-1}$的单个红外热带跃迁。作为原理验证，我们测量了甲烷高多重组（P）之间的跃迁。基于AOTR的光谱学为宽带探索高激发分子态开辟了新途径，提供了高精度光谱数据以完善分子模型和改进高温光谱预测。
英文摘要：
Accurate experimentally verified models of molecular hot-band transitions are essential for interpreting high-temperature spectra in environments ranging from exoplanetary atmospheres to combustion systems. However, line-resolved measurements of infrared hot-band transitions reaching highly excited vibrational states above 10000 cm$^{-1}$ are missing because these transitions are too weak to observe at room temperature and become spectrally congested at elevated temperatures. Here, we introduce a nonlinear spectroscopic approach that enables simultaneous measurement of individual infrared hot-band transitions between four vibrational bands up to 12000 cm$^{-1}$ over a broad spectral range with sub-Doppler resolution and sub-MHz frequency accuracy (10$^{-10}$ relative line position accuracy). The methods is based on an all-optical triple-resonance (AOTR) scheme that combines stepwise mid-infrared pumping using an optical-frequency-comb-stabilized, double-seeded continuous-wave optical parametric oscillator with broadband highly sensitive near-infrared probing using a cavity-enhanced optical frequency comb. As a proof of principle, we measure transitions between high polyads (P) of methane - groups of strongly interacting, near-degenerate vibrational energy states arising from couplings between the C-H stretching and bending modes. In a single probe spectrum, we simultaneously resolve sub-Doppler P4$\leftarrow$P0, P6$\leftarrow$P2 and P8$\leftarrow$P4 transitions, reaching the poorly understood polyad P8 near 12000 cm$^{-1}$ and providing the first set of 41 experimentally observed lines in the P8$\leftarrow$P4 spectral region.Comb-based AOTR spectroscopy opens a new route for broadband exploration of highly excited molecular states, delivering extensive high-accuracy spectroscopic data needed to refine molecular models and improve predictions of high-temperature spectra.
