Recently, researchers in Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS), have made new progress in the measurement of electro-optic (EO) coefficients of nonlinear materials. The researchers proposed a novel measurement method of the EO coefficient based on the χ⁽²⁾ nonlinear optical technology and measured  the linear EO coefficients of KDP, 23%-, 45%-, 68%-, 82%-, and 90%-DKDP precisely. The results were published in Optics Express on Jan. 18, 2021.

As excellent EO and nonlinear optical materials, the current studies and applications of the EO effect of KDP-family crystals are mainly focused on KDP and DKDP with high deuterium content. For the partially deuterated KDP crystals, their EO coefficients are sporadically reported, although they have crucial applications in many fields. Meanwhile, the existing EO coefficient measurement methods are mainly based on the linear optical effect, which requires the laser to strictly keep the stability of polarization in the whole measurement system.

In this study, the researchers presented a novel method utilizing the χ⁽²⁾ nonlinear optical technology. This measurement only depends on the nonlinear process in nonlinear materials, and other transfer processes will not affect it. Based on this method, the linear EO coefficients of a series of different deuterated KDP crystals were measured precisely, and a conclusion formula for determining the linear EO coefficients of DKDP crystals with different deuterium content was given. Moreover, the stability of output FHG energy can be greatly improved by using the EO properties of crystals, which provides important references for the deep ultraviolet laser generation and expanding the application of KDP-family crystals in the field of laser technology and nonlinear optics.

The work is supported by National Natural Science Foundation of China, Shanghai Sailing Program, “Strategic Priority Research Program” of Chinese Academy of Sciences, and Youth Innovation Promotion Association CAS.

Fig.1 (a) experiment setup for measuring the linear EO coefficient of K(H_1-xD_x)₂PO₄ crystals; (b) FHG characteristics of different deuterium content DKDP crystals based on the VTPM; (c) Linear EO coefficients of K(H_1-xD_x)₂PO₄ crystals. (Image by SIOM)