Design of Telephoto Superachromatic Focusing Objective Used for Measuring Laser Beam Divergence

When measuring the laser beam divergence in the range of 350–1600nm, the focal plane position of focusing objective for different wavelengths needs to recalibrate. The measuring procedures are cumbersome, and the measurement error is introduced easily in the measurement result. In this paper, to solve the above-mentioned problem and obtain long focal length focusing objective with short total measuring system length, the wide wavelength band telephoto superachromatic objective with less than 3/4 telephoto ratio is introduced. The longitudinal aberration curve of the objective shows that the spherical aberration curves of different wavelength almost intersect in one point at 0.707 apertures, and the focal shift curve of the objective shows that the maximum focal shift of the system is only 99.5μm.