(a) Beat frequency signal diagram under different lasers’ power ratio (η = 1, η = 1.7, η = 5). The blue line with triangle symbol, red line with circle symbol, and black line with square symbol represent the beat fringes when the power intensity ratio is 1, 1.7, and 5 respectively; (b) The diagram of the signal’s amplitude decrease rate (the black dotted line) and measurement error (the blue solid line) as a function of the power ratio η between the two beams.