Newton's Rings

Introduction

To download the associated FRED file: newtons-rings.frd

FRED allows for simulation of physical optics phenomena such as diffraction and interference. With this capability, components such as Gaussian laser beams and interferometers can be accurately modeled and incorporated into optical systems.

The FRED Model

Newton’s Rings form when reflections from a planer surface interfere with reflections from a spherical surface in contact. The interference pattern is based on increasing optical path difference from the point of contact outward. As spherical surface curvature increases, the amount of rings increases. A FRED model of Newton’s Rings is shown below:

Figure 1. Newton’s Rings. A slow (R=150 cm, D=1.25 cm) lens is placed in contact with a flat glass surface. Coherent, collimated “white” light (400-700 nm) shines from above. The uncoated glass surfaces partially reflect the light and interfere. White light fringes are visible near the point of contact. The fringes wash out as soon as optical path difference exceeds the coherence length of the light source.