$${E_t=E_{t0} \exp\bigg[i\omega \bigg(t- \frac{ x \sin \gamma + z \cos \gamma}{v_2}\bigg) \bigg] = E_{t0} \exp \bigg[-\frac{i \omega z \cos\gamma}{v_2} \bigg] \exp \bigg[i\omega \bigg(t - \frac{x}{v_2/ \sin \gamma)}\bigg) \bigg]}$$