[求助]画图出现了问题，求大神们帮助

程序如下
k1 = 1.4*10^7*Sqrt[n1^2 - N^2]
k2 = 1.4*10^7*Sqrt[N^2 - n2^2 ]
k3 = 1.4*10^7*Sqrt[N^2 - n3^2]
r1 = ArcTan[k2/k1] + ArcTan[k3/k1]
g1 = ContourPlot[{k1*d*10^-9 - r1 == 0 , k1*d*10^-9 - r1 == Pi, k1*d*10^-9 - r1 == 2*Pi}, {d, 0, 50}, {N, 1.46, 1.55 }, PlotPoints -> 50]
运行结果如下：

希望获得大神帮助@eyofdu