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 planar 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. The number of rings is dependent on the radius of curvature of the surface being tested. A FRED model of Newton’s Rings is shown below:
The associated FRED file can be downloaded here: newtons-rings.frd
Figure 1. Newton’s Rings. A nearly planar surface (R=5000 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 contrast reduces as you move away from the center of the lens.