利用太赫兹时域光谱技术研究了温度变化对正构烷烃（C11~C14）状态的影响。通过扫描不同温度下的样品得到了太赫兹时域谱。经数据处理后得到的频域谱、折射率谱、吸收系数谱均能反映正构烷烃状态的变化。温度下降至低于其凝点时，正构烷烃状态由液态变为固态晶体，导致频域谱中的有效频率区间变窄，频域面积减小。温度的降低会导致烷烃分子结晶，折射率增大，吸收系数与频率成线性关系。实验结果表明，太赫兹时域光谱技术可以应用于检测以正构烷烃为代表的非极性烃类物质。

The influences of temperature change on the states of n-alkanes (n-undecane(C11), n-dodecane(C12), n-tridecane(C13) and n-tetradecane(14)) were studied by using terahertz time-domain spectroscopy. The terahertz time-domain spectra were obtained by scanning the samples at different temperatures. The spectra of frequency-domain, refractive index and absorption coefficient obtained after data processing could reflect the state change of n-alkanes. When the temperature dropped below its freezing point, the states of n-alkanes were converted from liquid to solid crystals causing the effective frequency range in frequency-domain spectra to narrow and the area of frequency-domain to decrease. The decrease of temperature could result in the crystallization of alkane molecules, the increase of refractive index and the linear dependence of absorption coefficient on frequency. The experimental results showed that terahertz time-domain spectroscopy could be used to detect the non-polar hydrocarbons represented by normal alkanes.