From the results of STM measurement to here, we have shown the chiral phases of the CDW in TiSe$_{2}$. In general, the tunnelling current can obtain information about one or two atomic layers. We employed optical ellipsometry to investigate more macroscopic property of the CDW system. Figure 3 (a) and (b) show the polarization dependence of the transient reflectivity vari- ation of 1T-TiSe$_{2}$ measured at 3 K and 1T-TaS$_{2}$ measured at 12 K, respectively. Figure 3 shows the clear 2-fold symmetry in TiSe$_{2}$. The transient variation in optical reflectance Δ R ( t ) was measured by changing the polarisation angle E$_{pol}$ of the incident probe laser pulse. In general, the peak intensity of transient signals corresponds to the number of elec- trons excited over the CDW gap [15, 16]. But in Fig. 3(a), the peak intensity behaved anisotropically. Surprisingly, when we plot the peak intensity as function of polarisation angle E$_{pol}$ (Fig. 3(c)), we observed 2-fold symmetry although 1T-TiSe$_{2}$ has a trigonal lat- tice structure. In contrast, this clear 2-fold property is not seen with 1T-TaS$_{2}$, which is the most common 2D CDW material with the same lattice structure (Fig. 3(b)(d)). Most two-dimensional CDWs do not exhibit an obvious 2-fold symmetry because three CDWs generate a triangular lattice that has 3-fold and 2-fold symmetry simultaneously. Thus, at least within the light penetration length, a special 2-fold structure was achieved in the CDW system. The macroscopic 2-fold property is consistent with the microscopic structure observed with STM. To understand these results, here let us consider the static charge distribution in real space. We propose a simple model of the CDW stacking. The CDW stacking is not con- ventional layer stacking with 2D CDW sheets [17–19] but CDW component stacking that makes internal structure in a CDW unit cell. Figure 4 shows the configuration of three CDW components. Charge concentration is indicated by the deeply coloured part. Each color corresponds the nesting vector illustrated in the inset of Fig. 4. In this model, the phase shifting of the density waves along the c -axis was permitted, so there is a nonzero relative phase difference between the three density waves. In a CDW unit cell, there are three density peaks at intervals of 2 c$_{0}$/ 3. Chirality is achieved by twisted stacking such as with cholesteric liquid crystals [20]. Thus, CDW component stacking results in helical stacking and helical axis parallel to the c -axis. Note that by putting three density peeks in 2 c$_{0}$ , there are two ways of CDW stacking, that is, when we permutate the sequence of two colored density waves (blue and green), the helix is inverted (Fig. 4(a)). A Charge 5