Bessel terahertz imaging with enhanced contrast realized by silicon multi-phase diffractive optics

Area of Science:

• Optics and Photonics
• Terahertz (THz) Technology
• Imaging Systems

Background:

• Traditional terahertz (THz) imaging often relies on bulky optical components like parabolic mirrors.
• Achieving extended focal depth and high resolution in THz imaging presents significant challenges.
• Diffractive optical elements offer a potential solution for miniaturizing THz imaging systems.

Purpose of the Study:

• To demonstrate Bessel terahertz (THz) imaging using a novel diffractive optical element.
• To extend the focal depth and enhance the resolution of a compact THz imaging system.
• To evaluate the performance of a 4-level phase quantized Bessel zone plate (BZP) in THz imaging.

Main Methods:

• Development and implementation of a Bessel zone plate (BZP) using high-resistivity silicon fabricated by laser ablation.
• Utilizing a continuous wave (CW) THz imaging setup operating at 0.6 THz.
• Employing deconvolution algorithms to improve image resolution and contrast.

Main Results:

• Successfully demonstrated Bessel THz imaging with a focal depth extended up to 20 mm.
• Achieved minimal optical losses with the proposed Bessel zone plate (BZP) design.
• Enabled inspection of objects thicker than 10 mm with enhanced contrast and resolution up to 0.6 of the wavelength.

Conclusions:

• The developed Bessel zone plate (BZP) allows for a compact THz imaging system, eliminating the need for bulky parabolic mirrors.
• The system demonstrates effective inspection of thick objects with improved imaging performance.
• This approach offers a promising pathway for advanced THz imaging applications.