# Terahertz Emission Enhanced by a Laser Irradiating on a T-Type Target
## 3 Results  
Now, let us demonstrate the effect of THz emission enhancement in TTT. Firstly, the spatial distributions of the radiated electromagnetic fields (including the electric field \(E_{y}\) + magnetic field \(B_{z}\)) are shown in Figure 2 for both cases of SLT and DLT at different times \(t=90T_{0}\) and \(t=120T_{0}\). We could note that they were radiated by the forward fast electrons passing through the rear target-vacuum interfaces. Yet, the radiated electromagnetic field can be significantly enhanced under the action of TTT. Furthermore, from Figure 2b,d, the intensity of the radiated electromagnetic field was an order of magnitude higher in the case of TTT than that in the case of SLT. In addition, on the one hand, unlike that of the  
Figure 1: The features of the T-type target structure and the terahertz waves radiated behind the target by the coherent transition radiation (CTR) mechanism. Target I refers to the longitudinal target, while Target II stands for the transverse target. The electrons in Target I are pulled out and accelerated to very high energy, and they radiate terahertz waves after passing through Target II.  
SLT, when the THz emission was just generated behind the target, it produced two sets of radiation field distributions, as shown in Figure 2c. This indicates that they originated from two different electron sources. On the other hand, for the generated THz emission through the CTR in SLT, it emitted from the point sources around the laser irradiation spot at the rear side, and the strongest emission was along the target surfaces [22], as shown in Figure 2b. However, in TTT from Figure 2d, the radiated electromagnetic field along the rear surface exhibited a much weaker distribution in the center than at both wings, rather than traveling around the laser irradiation spot behind the target.  
In order to further quantitatively demonstrate the enhancement effect of the TTT on THz emission and whether it was in the THz band, both time-domain and frequency-domain spectra of the radiated electromagnetic field passing through the space point (\(146.67\lambda_{0}\), \(-20.0\lambda_{0}\)) at the (\(x\), \(y\)) plane for the SLT and TTT were, respectively, given, as shown in Figure 3. On the one hand, from the time-domain spectra of the radiated electromagnetic field in Figure 3a, the black line showed that the maximum in the case of the SLT was about 0.3 TV/m. However, the maximum value in the case of the TTT reached about 2.8 TV/m, which was greatly enhanced by an order of magnitude or so. On the other hand, from the frequency-domain spectra of the radiated electromagnetic field in Figure 3b, it showed that the generated THz emission was in the THz band. Furthermore, the maximum frequency of the generated THz wave reached 150 THz, which also proved that the THz wave generated by the interaction between the laser and plasma had the characteristics of wide bandwidth. Additionally, after integrating the spectrum curve, we also see that the power of the THz emission generated in the TTT was enhanced by about two orders of magnitude compared to that in the SLT. Therefore, the above results quantitatively prove that the TTT can significantly enhance the generation of THz emission.  
Figure 2: Two\(-\)dimensional spatial distributions of the radiated electromagnetic field in the case of SLT (**a**,**b**) and in the case of TTT (**c**,**d**) at different times \(t=90T_{0}\) and \(t=120T_{0}\).