LAUSR

Abstract Primary rainbow (Debye series, p = 2 ) of a common liquid droplet, i.e., water drop, has a smooth Airy rainbow structure, and the superimposed high frequency ripple structures are mostly generated by interference of refraction ( p = 2 ) and reflection ( p = 0 ). In this work, the primary rainbow ( p = 2 ) of a particle with high refractive index ( 1 . 547 n 2 ) is found to have ripples. This is because the primary rainbow transits from 2-rays rainbow to 3-rays rainbow. A third refraction light with a higher incident angle emerges at the same angle of the classical Airy rainbow, and its interference with the refractions around Descartes ray gives birth to the high frequency ripples. Characteristics of this refraction ripples, i.e., angular frequency, are investigated, and implications of this special ripple for particle measurement are also pointed out. This refraction ripple is not observed in other higher order rainbows.