## 1 Introduction
[22] proposed a new high-resolution technique for measuring the hyperfine splitting of the excited state and developed a method to eliminate the error arising from nonlinear frequency scanning by employing an optical waveguide-type electro-optic phase modulator (EOPM) and a confocal Fabry-Perot cavity [23]. Using this technique, [PERSON] et al. [24] measured the hyperfine interaction constants of the \(4p^{6}5d\)\({}^{2}\)D\({}_{5/2}\) state of \({}^{85}\)Rb atoms. Recently, [PERSON] et al. [25] presented the measurement of the hyperfine structure of the Cs \(5p^{6}7s\)\({}^{2}\)S\({}_{1/2}\) excited state by using electromagnetically-induced transparency (EIT) spectroscopy with a Cs three-level cascade system. [PERSON] et al. [3] studied the electromagnetically induced grating diffraction controllability in a ladder-type (\(4p^{6}5s\)\({}^{2}\)S\({}_{1/2}\)-\(4p^{6}5p\)\({}^{2}\)P\({}_{3/2}\)-\(4p^{6}5d\)\({}^{2}\)D\({}_{5/2}\)) rubidium atomic system and the nonlinear dependence of the first-order diffraction efficiency on the coupling laser power. As for Cs \(5p^{6}7d\)\({}^{2}\)D\({}_{5/2}\) state, only a few studies showed a relevant measurement of its structure. [PERSON] et al. [26] determined the \(A\) value of the Cs \(5p^{6}7d\)\({}^{2}\)D\({}_{5/2}\) state from the optical double-resonance transition spectra. [PERSON] et al. [27] used the Cs \(5p^{6}6s\)\({}^{2}\)S\({}_{1/2}\)-\(5p^{6}7d\)\({}^{2}\)D\({}_{5/2}\) two-photon transition method by introducing an EOPM to determine the corresponding hyperfine splitting intervals and hyperfine interaction constants of the Cs \(5p^{6}7d\)\({}^{2}\)D\({}_{5/2}\) state. [PERSON] et al. [28] measured the absolute transition frequency and the hyperfine interaction constants of the Cs \(5p^{6}7d\)\({}^{2}\)D\({}_{5/2}\) states by using the frequency comb method in a two-photon excitation system. Recently, [PERSON] et al. [29] used a single laser with a wavelength of 767 nm driving the dipole forbidden transition \(5p^{6}6s\)\({}^{2}\)S\({}_{1/2}\)-\(5p^{6}7d\)\({}^{2}\)D\({}_{3/2}\), \(5/2\) in a thermal Cs vapor. The magnetic dipole coupling constant \(\mathbf{A}\) and the electric quadrupole coupling constant \(\mathbf{B}\) for the Cs 5\(p^{6}\)7\(d\)\({}^{2}\)\(D_{3/2,\,5/2}\) states were precisely determined by using the hyperfine splitting intervals. Due to the fact that its adjacent splitting intervals are less than \(\sim\)10 MHz, the main practical problem confronting us is how to improve the spectroscopic resolution and signal-to-noise ratio (SNR) of the Cs 5\(p^{6}\)7\(d\)\({}^{2}\)\(D_{5/2}\) state. Unlike previous experiments and theoretical studies, we employed ladder-type EIT spectroscopy to improve the spectroscopic resolution and SNR. We used a 698 nm coupling laser and 852 nm probe laser in opposite directions to realize the Cs cascade two-photon excitation in a Cs atomic vapor cell at room temperature. The effect of the 852 nm probe beam's linewidth and the optical intensity of the 852 nm probe beam and 698 nm coupling beam as a function of the spectroscopic SNR were investigated. After studying the effect of the spectroscopic scheme and the optimization of experimental parameters, the EIT-assisted double-resonance optical pumping (DROP) spectra with a higher SNR and better resolution were observed, and the hyperfine splitting intervals of the Cs 5\(p^{6}\)7\(d\)\({}^{2}\)\(D_{5/2}\) state were measured. The sideband of an optical waveguide-type EOPM was introduced as a frequency calibration to improve the accuracy of the frequency measurement.