## 4 Results and Discussion
The result can be seen in Figure 3, where there is no fluctuation in intensity for modulation voltage (for the driver) up to 1.6 V. This value corresponds to stability in intensity and beam steering for modulation up to 30 MHz. Furthermore, our optical setup reduces the degradation of the efficiency and the circularity of the exit beam, as no complicated optical elements that are found in other noted studies are used. It is worth noting that the result of Figure 3 is based on an optimized optical setup, whereas many investigations on the beam property, such as beam waist, steering, and divergence, were recorded and the effect of these were all measured on the CPT peak. It was discussed in previous sections that the CPT is of \(\Lambda\)-type. This configuration is created when a small magnetic field (\(\approx\)450 mG) is applied collinearly to the direction of the beams. The applied magnetic field lifts the degeneracy; as a result, multiple \(\Lambda\) configurations form, as shown in Figure 4A. The ECDL was tuned to \({}^{87}Rb:|F=2,m_{F}=-1\rangle\rightarrow|F^{\prime}=1,m_{F}=0\rangle\), which means \(\omega_{0}\) is tuned to this transition. An appropriate voltage was selected for the 2 nd-AOM so that, at the exit of the 2 nd-AOM and in the interaction cell, \(\omega_{\pm}\) has a frequency that matches \({}^{87}Rb:|F=2,m_{F}=+1\rangle\rightarrow|F^{\prime}=1,m_{F}=0\rangle\); as a result, a \(\Lambda\)-type is created, as shown in Figure 4B. Application of a 1 V peak voltage with 0.05 V step triangular waveform to the 2 nd-AOM driver results in \(\omega_{\pm}\) being detuned around the \({}^{87}Rb:|F=2,m_{F}=+1\rangle\rightarrow|F^{\prime}=1\), \(m_{F}=0\rangle\) transition, and, at exact zero detuning, a CPT signal was obtained as shown in Figure 5. The CPT signal was found to have a full width half maximum (FWHM) of 168 Hz at an ambient temperature of 19 \({}^{\circ}\)C. The dispersion like signal of the resonance peak, which is the measured first derivative of the CPT signal, was found to have a slope of 63 Hz. This corresponds to a magnetic field of 9.0 nT for the above \(\Lambda\)-type CPT, (since the \(|F2\rangle\) state has 0.7 MHz shift per \(G\) as shown in Figure 4). This is the smallest shift in frequency and hence the magnetic field that can be detected for our present setup. Figure 4: In (**A**) multiple \(\Lambda\) configurations form when a magnetic field is applied to \({}^{87}Rb:F=2\to F^{\prime}=1\). The frequency shift responses to the applied magnetic field of the Zeeman sub-levels are 0.70 MHz/G and \(-0.23\) MHz/G for \(F=2\) and \(F^{\prime}=1\) energy levels, respectively. (**B**) is the \(\Lambda\) configuration where the CPT is based in this work; \(\omega_{0}\) is the unmodulated coupling beam, and \(\omega_{\pm}\) is the modulated probe beam. Figure 3: Intensity fluctuation as a result of applied periodical triangular waveform to the AOM driver. The initial green region indicates no or non-detectable fluctuation in intensity for scanning amplitude up to 1.6 V. This corresponds to intensity stability for modulation up to 30 MHz in the double pass setup. When scanning amplitude (i.e., the amplitude of the triangular waveform) is increased to above 1.6 V, small variation in intensity can be detected. Above 2.4 V, a clear fluctuation in intensity can be seen in the form of the color of the contour. It can be noted from the inset of Figure 5, there is a slight fluctuation in the CPT peaks. We have carried out no statistical calculations on the nature of this fluctuation due to the scope of this research, which was limited to an optimized optical setup using AOMs in the creation of a dark state magnetometer. It is the aim of future research to first increase the sensitivity of the magnetometer and also be able to record the absolute magnetic field strength, in which case such fluctuation as well as noise plays a crucial role. Previous studies related to properties and sensitivities of CPT resonances have reported a much narrower resonance linewidth as compared to our present result [16,17].