According special relativity, the clock ticks slower on spaceship moving at relativistic speed because the light travels a longer diagonal distance with respect observer on ground. 

`
If light is a wave then how it gains the velocity of spaceship? such that it travels in a diagonal. 
`

`can light make an interference pattern in this scenario?`

[![enter image description here][1]][1]

[1]: https://i.sstatic.net/URB85.jpg