Why not use a laser and total internal reflection to measure the surface?

Light may be confined in the middle layer by total internal reflection.

Light is kept in the core by total internal reflection.

The polarization of the rainbow is caused by the internal reflection.

Total internal reflection can be observed while swimming, when one opens one's eyes just under the water's surface.

Another common example of total internal reflection is a critically cut diamond.

In those visions, there's no point at which residents stop to pray, visit a church, or have a moment of internal reflection.

The Commission is contributing to the internal reflection on all these issues.

In both cases internal reflection causes the light to be reflected back to where it originated.

Hence, the reflections occur through total internal reflection so very little light is lost.