I d ( q z ) = | T i T f F ( + Q z 1 ) + T i R f F ( − Q z 2 ) + R i T f F ( + Q z 2 ) + R i R f F ( − Q z 1 ) | 2 = T i 2 T f 2 | F ( + Q z 1 ) | 2 + T i 2 T f R f F ( + Q z 1 ) F ( − Q z 2 ) + T i R i T f R f F ( + Q z 1 ) F ( + Q z 2 ) + T i R i T f R f F ( + Q z 1 ) F ( − Q z 1 ) + T i 2 R f 2 | F ( − Q z 2 ) | 2 + T i 2 T f R f F ( + Q z 1 ) F ( − Q z 2 ) + T i R i T f R f F ( + Q z 2 ) F ( − Q z 2 ) + T i R i R f 2 F ( − Q z 1 ) F ( − Q z 2 ) + R i 2 T f 2 | F ( + Q z 2 ) | 2 + T i R i T f 2 F ( + Q z 1 ) F ( + Q z 2 ) + T i R i T f R f F ( + Q z 2 ) F ( − Q z 2 ) + R i 2 T f R f F ( − Q z 1 ) F ( + Q z 2 ) + R i 2 R f 2 | F ( − Q z 1 ) | 2 + T i R i T f R f F ( + Q z 1 ) F ( − Q z 1 ) + T i R i R f 2 F ( − Q z 1 ) F ( − Q z 2 ) + R i 2 T f R f F ( − Q z 1 ) F ( + Q z 2 ) {\displaystyle {\begin{aligned}I_{d}(q_{z})&=|T_{i}T_{f}F(+Q_{z1})+T_{i}R_{f}F(-Q_{z2})+R_{i}T_{f}F(+Q_{z2})+R_{i}R_{f}F(-Q_{z1})|^{2}\\&{\begin{aligned}=\,\,&T_{i}^{2}T_{f}^{2}|F(+Q_{z1})|^{2}&&+T_{i}^{2}T_{f}R_{f}F(+Q_{z1})F(-Q_{z2})\\&&&+T_{i}R_{i}T_{f}R_{f}F(+Q_{z1})F(+Q_{z2})+T_{i}R_{i}T_{f}R_{f}F(+Q_{z1})F(-Q_{z1})\\&+T_{i}^{2}R_{f}^{2}|F(-Q_{z2})|^{2}&&+T_{i}^{2}T_{f}R_{f}F(+Q_{z1})F(-Q_{z2})\\&&&+T_{i}R_{i}T_{f}R_{f}F(+Q_{z2})F(-Q_{z2})+T_{i}R_{i}R_{f}^{2}F(-Q_{z1})F(-Q_{z2})\\&+R_{i}^{2}T_{f}^{2}|F(+Q_{z2})|^{2}&&+T_{i}R_{i}T_{f}^{2}F(+Q_{z1})F(+Q_{z2})\\&&&+T_{i}R_{i}T_{f}R_{f}F(+Q_{z2})F(-Q_{z2})+R_{i}^{2}T_{f}R_{f}F(-Q_{z1})F(+Q_{z2})\\&+R_{i}^{2}R_{f}^{2}|F(-Q_{z1})|^{2}&&+T_{i}R_{i}T_{f}R_{f}F(+Q_{z1})F(-Q_{z1})\\&&&+T_{i}R_{i}R_{f}^{2}F(-Q_{z1})F(-Q_{z2})+R_{i}^{2}T_{f}R_{f}F(-Q_{z1})F(+Q_{z2})\\\end{aligned}}\\\end{aligned}}}