Example

Laser exposure objective

Computer-generated holograms are deployed nowadays to test lenses, in the production or beamforming of lasers, in correcting objectives and in many other applications.

To produce the fine structures, a laser beam focused on light-sensitive material (photoresist) inscribes a high-resolution pattern.

Left: Illumination and photolithography process to create fine structures

Right: Spot diagram of the three calculated illumination objectives

Demands are high on the objectives that focus these lasers—for one thing, the beam’s energy most be focused on the smallest possible point; and for another, the focusing of the autofocus beam must also be extraordinarily good.

The mass of the objective is limited for the autofocus mechanism to function optimally.

Left: Beampath of one of the calculated objectives

Center: The chromatic focal shift diagram shows the focal deviation by wavelength

Right: The Seidel diagram shows which surfaces lead to which kinds of imaging errors

To achieve the result, we calculated three objectives for two different imagers. Here we outline the process of creating one of these objectives:

• Researching already-existing objectives with similar requirements
• An overview of possible lens arrangements was prepared
• With software specialized for optical calculations, arrangements were evaluated and optimized, then systematically tuned until we reached the optimal final result for this case
• By analyzing ghost reflection we determined that back-reflections from the lens surfaces would influence the function of the objective
• With tolerance analysis we checked whether the lenses and associated mountings could be manufactured economically using standard methods
• After these checks, component parts were built for an assembly. For this part and for centering tolerance the method with additional centering holders was chosen

Left: Cross section of the objective

Center: Exploded representation of the same objective

Right: Representation of the concept for the housing and centering adjustment