Interferometer
Principle Interferometers are optical instruments used for measuring flatness Determining minute differences in length by direct reference to the wavelength of light.
Principle of interferometer
Fringes
Fringes a b c
Fringes A Here the error is indicated by the amount by which the fringes are out of parallelism with those on the base plate B If the work piece is concave or convex, fringe pattern will be as shown in Figure (b). C The surface is flat with slight rounding off at the corner
Optical flats Optical flats can be used to measure the flatness An optical reference flat of known quality A monochromatic light box Solvent and cleaning material
Typical setup of optical flat
Working
Fringe Pattern Air wedges Flatness error of zero Cylinder with flatness error of two fringes Contact method Convex Cylinder Concave Cylinder Convex Sphere Concave Sphere Convex Spheroid Concave Spheroid Saddle Highly Irregular
Air wedge Flatness error of zero (a) (a) (b) Cylinder with flatness error of two fringes (b)
Contact method Convex Cylinder Concave Cylinder
Saddle Highly Irregular
Interferometer
Principle Interferometers are optical instruments used for measuring flatness Determining minute differences in length by direct reference to the wavelength of light.
Principle of interferometer
Fringes
Fringes a b c
Fringes A Here the error is indicated by the amount by which the fringes are out of parallelism with those on the base plate B If the work piece is concave or convex, fringe pattern will be as shown in Figure (b). C The surface is flat with slight rounding off at the corner
Optical flats Optical flats can be used to measure the flatness An optical reference flat of known quality A monochromatic light box Solvent and cleaning material
Typical setup of optical flat
Working
Fringe Pattern Air wedges Flatness error of zero Cylinder with flatness error of two fringes Contact method Convex Cylinder Concave Cylinder Convex Sphere Concave Sphere Convex Spheroid Concave Spheroid Saddle Highly Irregular
Air wedge Flatness error of zero (a) (a) (b) Cylinder with flatness error of two fringes (b)
Contact method Convex Cylinder Concave Cylinder
Saddle Highly Irregular