光が真空以外の培地に入ると、培地内の電子との相互作用のために遅くなります。

光の減速により、屈折と呼ばれている曲げが生じます。培地の光の速度は、媒体の屈折率によって与えられます。これは、真空中の光の速度の比率で、媒体の光速度と光速度です。

光が培地を出て、真空に再び入ると、真空中の光の速度であるCの元の速度に戻ります。光を加速するエネルギーはどこからも来ません。ライトは、媒体を出るとすぐに元の速度に戻ります。

元の波が培地を離れて真空に入るとすぐに、干渉は停止し、正味波はすぐにcの元の速度に戻ります
When light enters a medium other than a vacuum, it slows down due to its interaction with electrons in the medium. 

The slowing of light causes it to bend, which is known as refraction. The speed of light in a medium is given by the refractive index of the medium, which is the ratio of the speed of light in a vacuum to the speed of light in the medium. 

When light exits the medium and re-enters the vacuum, it speeds back up to its original speed of c, the speed of light in a vacuum. The energy that accelerates the light does not come from anywhere; the light simply returns to its original speed as soon as it exits the medium. 

As soon as the original wave leaves the medium and enters the vacuum, the interference stops, and the net wave immediately returns to its original speed of c