Sub-wavelength terahertz beam profiling of a THz source via an all-optical knife-edge technique

Abstract

Terahertz technologies recently emerged as outstanding candidates for a variety of applications in such sectors as security, biomedical, pharmaceutical, aero spatial, etc. Imaging the terahertz field, however, still remains a challenge, particularly when sub-wavelength resolutions are involved. Here we demonstrate an all-optical technique for the terahertz near-field imaging directly at the source plane. A thin layer (<100 nm-thickness) of photo carriers is induced on the surface of the terahertz generation crystal, which acts as an all-optical, virtual blade for terahertz near-field imaging via a knife-edge technique. Remarkably, and in spite of the fact that the proposed approach does not require any mechanical probe, such as tips or apertures, we are able to demonstrate the imaging of a terahertz source with deeply sub-wavelength features (<30 μm) directly in its emission plane.

Time-Resolved Nonlinear Ghost Imaging

“…Therefore, nonlinear frequency conversion represents a suitable method to generate subwavelength THz patterns characterized by space–time separability, a critical requirement of computational imaging. Moreover, this approach allows us to generate THz patterns whose intensity scales as 1/ r 2 (as opposed to the well-known 1/ r 6 scaling of subwavelength apertures). − As a result, nonlinear frequency conversion of deeply subwavelength optical patterns allows generating THz structured light without compromising its spatial resolution, which is limited only by the “focusing power” of the fundamental beam (up to ). , Besides these conceptual challenges, optically induced transient photocarrier masks, which represent the most developed benchmark in the field of THz GI, require careful consideration of additional elements. For example, the masking effect induced by transient photocarriers is not restricted to the semiconductor surface in light of the relatively large skin depth at THz frequencies (e.g., several μm in photoexcited silicon).…”

“…44,45 Besides these conceptual challenges, optically induced transient photocarrier masks, which represent the most developed benchmark in the field of THz GI, require careful consideration of additional elements. For example, the masking effect induced by transient photocarriers is not restricted to the semiconductor surface in light of the relatively large skin depth at THz frequencies (e.g., several μm in photoexcited silicon 38 ).…”

Long-Focusing Device for Broadband THz Applications Based on a Tunable Reflective Biprism

“…The core structure is a Fresnel reflective biprism [37][38][39], generated by the modification of the profile of a gold-coated PDMS layer when heating radiation is focused onto a line. Due to the strong absorption of gold by radiations with wavelengths below ∼500 nm, PDMS expands, and thanks to its high dilatation coefficient, a two-pitch roof-like reflective structure is generated.…”

Rapid spontaneous Raman light sheet microscopy using cw-lasers and tunable filters

“…To characterize non-Gaussian beam profiles a direct differentiation of the measured KE traces is performed [16,17,22,23]. Here, we use this KE approach to retrieve the spontaneous Raman spectra from KE traces.…”