Exact Reconstruction of THz Sub-$\lambda$ Source Features in Knife-Edge Measurements

Peccianti, Marco; Clerici, Matteo; Pasquazi, Alessia; Caspani, Lucia; Ho, Sze Phing; Buccheri, Fabrizio; Ali, J.; Busacca, Alessandro; Ozaki, T.; Morandotti, Roberto

doi:10.1109/jstqe.2012.2209176

Cited by 21 publications

(19 citation statements)

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“…In particular, Optical Rectification (OR)16 combined with Electro-Optic Sampling (EOS) detection is still the configuration of choice in the few standard high energy pulsed THz system. For this reason, in this paper we present an analytical model able to simulate the full electromagnetic propagation which takes place in the THz-TDS set-up17, sketched in Fig. 1 ( refer to Methods ), based on OR and EOS and employing <110> ZnTe crystals.…”

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Wideband THz Time Domain Spectroscopy based on Optical Rectification and Electro-Optic Sampling

Tomasino

Parisi

Stivala

et al. 2013

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We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the following main aspects: (i) pump beam focusing into the generation crystal; (ii) phase-matching inside both the generation and detection crystals; (iii) chromatic dispersion and absorption inside the crystals; (iv) Fabry-Perot effect; (v) diffraction outside, i.e. along the propagation, (vi) focalization and overlapping between THz and probe beams, (vii) electro-optic sampling. In order to validate our model, we report on the comparison between the simulations and the experimental data obtained from the same set-up, showing their good agreement.G eneration and detection of THz electromagnetic waves (0.1-10 3 10 12 Hz) is not a novel topic 1-3 , but it has been arousing an ever-increasing interest only in the last decade. Recent studies demonstrated that many substances and particularly bio-polymers like proteins, amino and DNA possess specific global and sub-global modes in the THz band. Hence, particular consideration has been recently devoted to THz spectroscopy since it reveals information on the conformational stage of molecules and potentially enables their discrimination in various compounds. Indeed, THz pulses have been broadly used, ranging from spectroscopy and time-resolved pump-probe experiments to imaging applications 4,5 . Moreover, the negligible ionization power of the THz radiations compared to optical and X-rays technologies make them perfectly suitable for biological applications 6 . For the above-mentioned reasons, THz technology are penetrating in lots of areas, beyond fundamental Physics investigation, spanning from medical care and homeland security to cultural heritage conservation 7-13 . The most challenging technology development remains in the area of THz sources and detectors, since, in general, both wide band and high power are required at the same time. Thanks to the improvement of the pulsed laser technology, different types of stable THz sources have been developed so far, with peak power values ranging from kW to MW 14,15 . In particular, Optical Rectification (OR) 16 combined with Electro-Optic Sampling (EOS) detection is still the configuration of choice in the few standard high energy pulsed THz system. For this reason, in this paper we present an analytical model able to simulate the full electromagnetic propagation which takes place in the THz-TDS set-up 17 , sketched in Fig. 1 (refer to Methods), based on OR and EOS and employing ,110. ZnTe crystals. We will explain and justify the approach and the approximations which underlie the modelling of each stage and that allowed us to build a ...

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Wideband THz Time Domain Spectroscopy based on Optical Rectification and Electro-Optic Sampling

Tomasino

Parisi

Stivala

et al. 2013

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“…The THz pulse is detected by electro-optics sampling in a 3 mm-thick, <110>-cut ZnTe crystal at the Fourier plane using a parabolic mirror-based system. For the sub- λ characterization by the KE technique it is indeed essential to detect the central part of the spatial Fourier transform of the investigated field pattern 18 (note that this configuration differs from the standard setup in THz spectroscopic systems). The virtual blade on the output facet of the generation crystal is formed by UV femtosecond pulses ( λ = 400 nm, having a photon energy of 3.1 eV) that photo-excite the carriers into the conduction band of the ZnTe semiconductor in a sharp blade-shaped area projected by a telescope system (lenses L1 and L2 in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…3b where the THz power obtained by the integral of the squared field over time is plotted versus the blade position. Noteworthy, as the THz beam waist is significantly super- λ , the OKE does not introduce any significant changes in the field phase 18 (i.e. the waveform just scales as the beam is clipped by the edge).…”

Section: Resultsmentioning

confidence: 99%

“…A typical approach relies on a mechanical sub- λ probe, such as a tip or an aperture, able to sample the near-field of the THz field impinging on the sample. A possible alternative for the characterization of sub- λ THz features relies on the implementation of a knife-edge (KE) measurement of the field radiating from the surface of the sample under investigation 17 18 . The KE technique involves the partial clipping of a propagating field induced by a thin shield with a flat boundary, i.e.…”

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“…In particular, we recently highlighted that the reconstruction of sub- λ sources using KE techniques is in general characterized by severe image aberrations due to the non-separable space-time nature of the radiated non-paraxial field. Yet, exploiting the inherent field sensitivity of time-domain THz detection techniques, we demonstrated that the exact sub- λ reconstruction of the field profiles is indeed feasible 18 . For a proper sub- λ characterization via KE, a physical blade must be located and translated in close proximity (at a sub- λ ) distance from the sample, a quite unpractical constraint in many real-world scenarios.…”

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

Phing

Mazhorova

Shalaby

et al. 2015

Sci Rep

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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.

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Terahertz Thermometry: Combining Hyperspectral Imaging and Temperature Mapping at Terahertz Frequencies

Naccache

Mazhorova

Clerici

et al. 2017

Laser & Photonics Reviews

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The accurate and non‐invasive determination of multiple physical parameters, with well‐defined spatial resolution, is crucial for applications in manufacturing, chemistry, medicine and biology. Specifically, the ability to simultaneously measure both temperature and spectral signatures is still experimentally unavailable. To this end, we propose a mapping technique for biological systems, which exploits a linear correlation between terahertz wave reflectivity and temperature, and allows to spatially and spectrally resolve thermal distributions. This method is applied to a model biological system in two relevant cases where in one example, nanoplasmonic‐induced photothermal effects are imaged gaining new insights into collective heating phenomena. In the second example, we demonstrate a joint thermal‐hyperspectral imaging approach to chemically map the presence of a model drug formulation and simultaneously investigate its thermal stability in our biological system. This concept can be easily extended and widely applied to all materials that demonstrate a measurable change in their dielectric properties.

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Exact Reconstruction of THz Sub-$\lambda$ Source Features in Knife-Edge Measurements

Cited by 21 publications

References 32 publications

Wideband THz Time Domain Spectroscopy based on Optical Rectification and Electro-Optic Sampling

Wideband THz Time Domain Spectroscopy based on Optical Rectification and Electro-Optic Sampling

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

Terahertz Thermometry: Combining Hyperspectral Imaging and Temperature Mapping at Terahertz Frequencies

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