Design of a Three-Element Apochromatic Lens to Correct Axial Chromatic Aberration at UVA Wavelength Band

Apochromat is usually designed for color correction in the range of the visible spectrum. But to correct the chromatic aberration of optical systems outside the visible spectrum, apochromatic lens in the same spectral band should be used. In this work, firstly, a three-element apochromatic lens in the UVA spectral region is pre-designed and optimized by spherical lenses with suitable glasses. The primary spherical aberration of this apochromat is almost zero and its tertiary spectrum has a small value of 2.558 microns.  Nevertheless, the spherical aberration of higher orders causes the RMS radius in the spot diagram to be several times larger than the Airy radius.  Then, by selecting aspheric surfaces and re-optimizing the system,  a spherical aberration-free apochromatic with a small tertiary spectrum is designed. In this last design, the RMS radius is smaller than the Airy radius, so almost all points are located inside the Airy disk. This lens can be used to correct chromatic aberration in UVA imaging spectrometers and cameras.