**4.2 Bi2Te3 & Sb2Te3**

Temperature-dependent TRUS measurements are also performed in the nearinfrared region on micro flakes of bismuth telluride. At room temperature, many optically allowed transitions are detected in TIs. Additionally, it was discovered that the DR response below 100 K exhibits a noticeable transition that is connected to the surface state of bismuth telluride and antimony telluride. At 500 fs, **Figure 4** depicts the temperature-dependent DR signal, where two distinct NIR regimes are established. One is the bulk zone, while the other is the topological regime associated with surface states. The bulk regime exhibits a variety of optically allowed transitions between valence and conduction bands. Simultaneously, the surface regime denotes the shift from a surface to a more excited state [62].
