The openness of following case has been allowed by our clients with exception of key parameters, which is only 90% of complete design process. I. Application For HeCd laser beam expander II. Requirements Applicable wavelength: 441.6 ± 15 nm Beam divergence angle: 1.0 mrad Magnification: 10 x Lens quantity: 3 pieces Lens facial type: all spherical Lens material: optical glass System total length: less than 90 mm Input largest diameter: 2 mm Output largest diameter: 20 mm Spatial filtering: 0.01 mm III. Features This non-coaxial optical system require spatial filtering, so inverted Kepler telescope is adopted. Optical input should consider divergence angle of light that laser beam itself release. When design, we take 1/4 of divergence angle of laser as the optimized FOV edge. Beam pattern is fundamental transverse mode. IV. Result