Sinusoidal-amplitude binary phase mask and its application in achieving an ultra-long optical needle

Area of Science:

• Optics
• Nanotechnology
• Materials Science

Background:

• Optical needles are crucial for applications requiring focused light, with sub-diffraction limits being a key research area.
• Existing methods for generating optical needles include diffractive lenses, reflective elements, and specialized objective lenses.
• Modulating both phase and amplitude of optical fields is essential for advanced optical needle generation.

Purpose of the Study:

• To propose and investigate novel designed phase and amplitude elements for generating ultra-long optical needles.
• To enhance the depth of focus of optical needles beyond current capabilities.
• To explore the potential of these elements in optical manipulation and utilization.

Main Methods:

• Development of a sinusoidal-amplitude binary phase mask (SA-BPM) to modulate incident vector optical fields (VOFs).
• Design of an upgraded Gaussian SA-BPM (GSA-BPM) incorporating a Gaussian function for amplitude modulation.
• Utilizing Richards-Wolf vector diffraction integral, exhaustive search, and genetic algorithms for parameter calculation and optimization.

Main Results:

• Successful generation of ultra-long optical needles using both SA-BPM and GSA-BPM.
• Achieved a 30%-70% improvement in the depth of focus compared to standard binary phase masks.
• Demonstrated simultaneous modulation of amplitude and phase distributions of VOFs.

Conclusions:

• SA-BPM and GSA-BPM are effective in creating ultra-long optical needles with extended focal depths.
• These novel optical elements offer significant advantages over conventional methods for optical needle generation.
• The proposed elements hold great potential for advanced applications in optical manipulation and precise light control.