Key Factors Controlling the Large Second Harmonic Generation in Nonlinear Optical Materials

Abstract

The second harmonic generation (SHG) responses of nonisostructural nonlinear optical (NLO) compounds, β

Second harmonic generation responses of KH2PO4: importance of K and breaking down of Kleinman symmetry

“…The Kleinman symmetry was not assumed throughout this work, because it is not rigorously correct in some cases. [22][23][24]38 The calculated results are given in Table 2.…”

“…These results provide a clear evidence that the presence of a static polarization is not essential for the SHG response. The result that d eff of P-KDP is greater than that of F-KDP can be simply understood by means of the quasi-linear relation 23,24 between d av and V/E g , where d av is the calculated average SHG coefficient or the effective SHG response d eff , V is the volume of the primitive unit cell, and E g is the experimental band gap. The calculated values of V/E g are 28.09, 25.4 A 3 eV À1 for P-KDP and F-KDP, which show the same order as their SHG responses ( Table 2).…”

“…25 Thus, in the case of P-KDP and F-KDP, the metal cations K + cations are expected to contribute strongly to the SHG responses, as found for those in KBe 2 BO 3 F 2 (KBBF). 24 Another inuential guideline was the belief that the SHG response of an NLO compound becomes stronger when its static (i.e., spontaneous) polarization is larger, which was rst noted by Jerphagnon 26 and has been invoked in explaining a number of NLO materials. [27][28][29] However, the SHG responses of certain NLO compounds do not depend explicitly on the static polarization.…”

“…[27][28][29] However, the SHG responses of certain NLO compounds do not depend explicitly on the static polarization. 24,30 For example, KBBF has a large SHG response although it has no static polarization. Thus, it is doubtful that Jerphagnon's observation is a reliable guideline.…”

“…However, it has been reported that the Kleinman symmetry is not rigorously correct in several cases. [22][23][24]38 Thus, it is of interest to probe the validity of the Kleinman symmetry, as well as the factors inuencing it, by studying the SHG responses of P-KDP and F-KDP.…”