Four independent light waves are expressed as 

${\mathrm{y}}_1={\mathrm{a}}_1\mathrm{sin\omega t},{\mathrm{y}}_2={\mathrm{a}}_2\mathrm{sin\omega t},{\mathrm{y}}_3={\mathrm{a}}_3\mathrm{cos\omega t}$ and ${\mathrm{y}}_4={\mathrm{a}}_4\sin (\mathrm{\omega t}+\mathrm{\pi }/3)\text{. }$ The interference is possible between