Optimization-free optical focal field engineering through reversing the radiation pattern from a uniform line source

Area of Science:

• Optics and Photonics
• Electromagnetism
• Nanotechnology

Background:

• Generating tailored optical focal fields is crucial for advanced applications.
• Existing methods often lack flexibility or require complex setups.

Purpose of the Study:

• To present a simple and flexible method for generating optical focal fields with prescribed characteristics.
• To demonstrate the creation of optical needles and double-focus fields.

Main Methods:

• Utilizing a 4Pi focusing system with two confocal high-NA objective lenses.
• Reversing the field pattern radiated from a uniform line source.
• Manipulating illumination distribution at the pupil plane.

Main Results:

• Successfully generated an arbitrary length optical needle with high longitudinal polarization purity and consistent transverse size (~0.36λ).
• Demonstrated coaxially double-focus fields with controlled spot size (~0.36λ transversal, ~λ axial) and separation.
• Showcased that the length of the optical needle and double-focus separation are determined by the line source length.

Conclusions:

• The presented method offers a simple and flexible approach for engineering optical focal fields.
• The generated fields, including optical needles and double-focus patterns, have potential applications in particle acceleration, optical microscopy, and optical trapping.