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
Interferometers can be used in metrology to measure surface quality of manufactured lenses and mirrors. A Fizeau interferometer is commonly used for such a measurement (Figure 1).
To modify the FRED file in Figure 1 for lens metrology, the reference flat becomes a reference sphere and the test flat becomes a plano-convex lens. The reference flat has a back radius of -70. Its curved surface is transmissive and its flat surface is uncoated. The test flat a front radius of 80. It is relocated to a Z shift of 54.25. The imaging lens has a Z-shift of 150 and the detector has a Z-shift of 10. The test lens is located in its nominal wavefront, and a slight axial displacement of this lens leads to interference fringes (Figure 2).
The associated FRED file can be downloaded from our knowledgebase.