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The art of light engineering unveils a world of possibilities through the meticulous manipulation of photonic properties such as intensity, phase, and polarization. The precise control over these optical properties under various conditions finds application in fields spanning communication, light-matter interactions, laser direct writing, and imaging, enriching our technological landscape. In this study, we embark on a journey to establish a rational framework for the design and assembly of nonparaxial THz imaging systems. Our focus centers on a lensless photonic system composed solely of flat-silicon diffractive optics. These elements include the high-resistivity silicon-based nonparaxial Fresnel zone plate, the Fibonacci lens, the Bessel axicon, and the Airy zone plate, all meticulously crafted using laser ablation technology. A systematic exploration of these flat elements in various combinations sheds light on their strengths and weaknesses. Our endeavor extends to the practical application of these optical components, where they illuminate samples and capture the light scattered from these raster-scanned samples using single-pixel detectors. Through a comprehensive examination, we evaluate imaging systems across diverse metrics that include contrast, resolution, depth of field and focus. This multifaceted approach allows us to distill rational design principles for the optimal assembly of THz imaging setups. The findings of this research chart an exciting course toward the development of compact, user-friendly THz imaging systems where sensors and passive optical elements seamlessly integrate into a single chip. These innovations not only enhance capabilities in THz imaging but also pave the way for novel applications, ushering in a new encouraging era of advanced THz photonic technology., Comment: 26 pages

Bessel beams are known for their property of maintaining propagation-invariant transverse intensity distribution. The true Bessel beams has unlimited energy, however the experimental realization of limited energy Bessel-like beams provides almost diffraction-free beams over a certain distance. These beams are applicable to microfabrication, particle manipulation etc. where long and narrow intense beam is needed. A type of laser beams that maintains narrow intensity peak for long distances are often called optical needles. In this paper we propose a construction of an optical needle using a superposition of vector Bessel beams and for flexible engineering of axial intensity profile. We investigate both theoretically and experimentally generation of various optical beams of different axial profiles, lengths, beam widths etc. We use a spatial light modulator as a toy model of an optical element to shape the spatial spectrum of the beam. Moreover, we demonstrate distortions introduced into the optical needle by a planar interface between two dielectric media: spherical aberration and astigmatism due to the nonzero inclination angle and discuss ways to correct them.