## 3 Results
### Analysis of CARS-Selected Feature Bands  
The CARS-selected feature bands for AAs and TPs are shown in Table 2. For AAs, 19 bands were selected, including wavelengths such as 372 nm, 406 nm, 676 nm, 1415 nm, 1892 nm, and others. These bands are associated with the stretching and bending vibrations of N-H bonds, which are prominent in the molecular structure of AAs. For example, the 1415 nm band is close to the first overtone of the N-H stretching vibration at 1450-1470 nm, and the 1892 nm band is related to the combination of N-H stretching and H-N-H bending vibrations around 1900-1950 nm. However, these bands are also susceptible to interference from other components, such as moisture, proteins, and other organic compounds [27; 28].  
For TPs, the CARS-selected bands included 22 wavelengths, such as 354 nm, 645 nm, 1021 nm, 1428 nm, 2136 nm, and others. The 1428 nm band is close to the first overtone of O-H and C-H stretching vibrations at 1450-1460 nm, while the 1658 nm band may be attributed to the first overtone of C-H bonds in the aromatic ring and combination  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Quality** & **Modeling** & **FOD-** & **R2 (Train)** & **RMSE** & **R2 (Test)** & **RMSE** \\
**Indicator** & **Method** & **Order** & **R2 (Train)** & **(Train)** & **R2 (Test)** & **RMSE** (Test)** \\ \hline AA & CC+PLSR & 0.7 & 0.67 & 0.51 & 0.63 & 0.47 \\  & CARS+PLSR & 0.7 & 0.86 & 0.3 & 0.8 & 0.25 \\  & CC+PLSR & 0.1 & 0.48 & 3.21 & 0.39 & 4.57 \\  & CARS+PLSR & 0.1 & 0.7 & 2.79 & 0.42 & 3.96 \\ \hline \end{tabular}
\end{table}
Table 1: Inversion accuracy of AA and TP content in fresh tea leaves.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Quality** & **Modeling Method** & **Number of Bands** & **Characteristic Wavelengths (nm)** \\
**Indicator** & **Modeling Method** & **Number of Bands** & **Characteristic Wavelengths (nm)** \\ \hline AA & CARS+PLSR & 19 & 372, 406, 515, 553, 641, 643, 676, 1207, \\  & & 1415, 1892, 1893, 2103, 2413, 2430, \\  & & & 2443, 2456, 2465, 2470, 2496 \\  & & & 354, 362, 368, 418, 645, 1021, 1194, \\ TP & CARS+PLSR & 22 & 1428, 1541, 1651, 1658, 1678, 1685, 2136, 2273, 2430, 2449, 2458, 2476, \\  & & & 2483, 2488 \\ \hline \end{tabular}
\end{table}
Table 2: Characteristic bands for AA and TP content in fresh tea leaves.  
frequencies involving hydroxyl groups [29]. The 2136 nm band could be associated with the combination of C-H stretching and C=C stretching vibrations in the aromatic ring [30; 31].  
Overall, the selected characteristic bands for AAs and TPs are primarily influenced by the molecular structure of their functional groups and optical vibration modes, especially C-H, N-H, and conjugated systems. However, the exact locations of these bands may shift due to interference from other compounds. Assigning the selected bands to specific functional groups proved moderately challenging. While key peaks around 2284 nm (N-H) and 1661 nm (O-H) match known amino acid and polyphenol bonds, nearby C-H overtone features can overlap and cause ambiguity. Thus, some assignments may be confounded by signals from related compounds. These limitations underscore the need for targeted pure-compound spectra in the 350-2500 nm range to confirm and refine our attributions in future work.