The condition of half-wave loss is that half-wave will be lost when light enters dense medium from sparse medium. Top-down means that light enters the dense medium with large refractive index from the light sparse medium with small refractive index (n= 1.2), and the half-wave loss is λ/2; On the other hand, if the light enters the optical hydrophobic medium from the optical dense medium, there will be no half-wave loss, so from bottom to top, there will be no λ/2.

Supplementary formula of refractive index

1、n = c/v；

C refers to the speed of light in vacuum, and V refers to the speed of light in medium.

2、n = 1/sinC；

C refers to the critical angle of the medium.

Influence range of light refraction:

When light refracts into a medium from a vacuum, the ratio n between the sine of the incident angle and the sine of the refraction angle is called the refractive index of this medium. The refractive index of the medium is also equal to the ratio of the speed of light c in vacuum to the speed of light v in this medium.

Since the speed c of light in vacuum is greater than the speed v of light in any medium, the refractive index n of any medium is greater than 1. When light enters any medium from a vacuum, the incident angle is greater than the refraction angle.