Fig. 1. 780–795 nm DOT-MTS. (a) The modulation transfer process in 780–795 nm DOT-MTS and 780 nm MTS: the modulation of 780 nm pump light is transferred to the 780 and 795 nm probe light in a Rb87 cell. (b) The optical setup of the 780–795 nm DOT-MTS and 780 nm MTS includes a 780 nm ECDL (external-cavity diode laser), 795 nm ECDL, isolator, λ/2 (half-wave plate), PBS (polarization beam splitter), dichroic mirror M1 (780 nm transmission, 795 nm reflection), dichroic mirror M2 (780 nm reflection, 795 nm transmission), Rb87 cell, EOM (electro-optic modulator), PD1 (photodiode detector 1), PD2, and laser servo. (c) The energy levels of 780 nm MTS and 780–795 nm DOT-MTS: the blue line corresponds to the 795 nm probe light, and the red line corresponds to the 780 nm pump light and probe light.

Fig. 2. (a) 780 nm SAS and MTS: the green line represents the 780 nm SAS, showcasing three resonance peaks and three crossover peaks. The red line depicts the 780 nm MTS, with the 52S1/2 F=2→52P3/2 F=3 transition displaying the largest amplitude. (b) 795 nm SAS, 780–795 nm SAS, and 780–795 nm DOT-MTS: the blue line illustrates the 795 nm SAS, which includes two resonance peaks and one crossover peak. The green line represents the 780–795 nm SAS, featuring two resonance peaks and velocity transfer peaks. The red line shows the 780–795 nm DOT-MTS, with the 52S1/2 F=2→52P1/2 F=1 transition displaying the largest amplitude. (c) Signal gradient of 780 nm MTS and 780–795 nm DOT-MTS at various modulation frequencies.

Fig. 3. (a) Modulation transfer process for MTS and DOT-MTS and lineshape. (b) Comparison of lineshapes for 780 nm MTS and 780–795 nm DOT-MTS, resulting from theoretical calculations, including in-phase, mixed components, and quadrature phases. (c) Phase change of 780 nm MTS and 780–795 nm DOT-MTS observed experimentally, following a clockwise direction.

Fig. 4. Theoretical analysis examines the DOT-MTS of different transitions and saturation effects for the 780–795 nm DOT-MTS. (a) The relevant energy level diagram. (b), (c) The slope gradients of DOT-MTS between different transitions as a function of δ. The legend specifies wavelengths, with the first number denoting the pump beam’s wavelength, and the second number the probe beam’s wavelength. (d) The lineshape when considering saturation effects for the 780–795 nm DOT-MTS. (e) The slope gradient, considering saturation; the peak at a saturation parameter of approximately 15, selected as the experimental operating point. (f) The analysis features the DOT-MTS at the optimal saturation parameter, including experimental data and theoretical fitting.

Fig. 5. (a) Instability at different temperatures: the 1 s and 10 s instability of 780 nm laser and 795 nm laser as a function of varying temperatures. (b) Long-term instability at optimal temperature: the long-term instability of the 780 and 795 nm lasers at the optimal temperature of 40°C.