An optical alignment method includes providing an emitted radiation beam which includes a first peak wavelength and a second peak wavelength to a chromatic aberration enhancement component which increases a chromatic aberration of the emitted radiation beam, providing a first incident radiation beam having the first peak wavelength and a second incident radiation beam having the second peak wavelength which is shorter than the first peak wavelength to respective first and second alignment marks located at different vertical levels in a device under test, detecting reflected radiation from the first and second alignment marks, and using the detected reflected radiation for optical alignment of layers in the device under test.