Fig. 1. Schematic diagram of the experimental setup.

Fig. 2. Wavefront distribution caused by manufacture defects of two cell side windows.

Fig. 3. Wavefront distributions associated with the vapor cell when the temperatures of the heater are (a) $60\,^{\circ }\text{C}$, (b) $80\,^{\circ }\text{C}$, (c) $100\,^{\circ }\text{C}$ and (d) $120\,^{\circ }\text{C}$, respectively.

Fig. 4. Wavefront distributions induced by the gas medium when the heater temperatures are (a) $60\,^{\circ }\text{C}$, (b) $80\,^{\circ }\text{C}$, (c) $100\,^{\circ }\text{C}$ and (d) $120\,^{\circ }\text{C}$, respectively.

Fig. 5. Temperature distributions at the cross-section of a vapor cell when the heater temperatures are (a) $60\,^{\circ }\text{C}$, (b) $80\,^{\circ }\text{C}$, (c) $100\,^{\circ }\text{C}$ and (d) $120\,^{\circ }\text{C}$, respectively.