The changes of (a) ω₁₂ (the blue line) and envelope peak (the red line) as frequency chirp time; (b) the phase change of the fine interference fringes, the red line and circular symbols, pink line and hexagonal symbols, brown line and diamond symbols represent I_4–3, while the black line and square symbols, blue line and triangle symbols, blue line and pentagonal symbols represent I_{1 – 2} when t = 0, 400, and 800 ms, respectively.