- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Terahertz and Visible Probing of Particles Suspended in Air
摘要： The attenuation of air suspended particles is measured with a terahertz time-domain spectrometer (THz-TDS). Simultaneously, the attenuation at a wavelength of 650 nm is probed with a laser diode. On the one hand, this dual measurement allows a direct assessment of the visibility evolution in the THz range compared to the visible range. On the other hand, this setup provides an estimation of the scattering strength and the density of particles. Using the Mie theory, the method is successfully applied to experimentally characterize the refractive index of sand grains and glass beads. The refractive indices of sand grains and glass beads, average over the acquisitions, are 1.67 and 2.54, respectively. The estimation of the scattering properties of sand grains are crucial to evaluate the performance of THz systems to image through brownout clouds that are created by helicopter rotors when landing in arid areas.
关键词： THz scattering,propagation,refractive index,THz time-domain spectroscopy
更新于2025-09-19 17:15:36
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - High-Power 0.33 mW Broadband THz Source Driven by an Ultrafast Yb-Based Thin-Disk Laser Oscillator
摘要： THz-time-domain spectroscopy (THz-TDS) is a well-established tool for characterizing material properties and investigating dynamics of complex molecular systems. As the broadband THz generation typically relies on sub-100-fs laser pulses, most systems are currently driven by Ti:sapphire lasers. In the last years there has been a strong effort to replace Ti:sapphire systems with power-scalable Yb-based directly diode-pumped solid-state lasers (DPSSLs). Ultrafast DPSSLs generate higher average power with lower complexity and better efficiency. However, their potential for high-power broadband THz operation has not yet been fully exploited. This study shows the high potential of TDL oscillator driven systems for high-power broadband THz generation. Thanks to the power scalability of the TDL technology we expect broadband THz sources operating at MHz repetition rates and several mW average power to be soon within reach.
关键词： THz-time-domain spectroscopy,thin-disk laser oscillator,broadband THz generation,Yb-based lasers
更新于2025-09-16 10:30:52
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Inhomogeneous Broadening of a Polaritonic Mode in the Ultrastrong Coupling Regime
摘要： Ultrastrong coupling (USC) regime has been an intriguing research topic in cavity quantum electrodynamics (QED) experiments due to its capability to modify the ground and the excited states of a coupled system[1-3]. We investigate the USC of Landau level (LL) transitions in a two dimensional electron gas to teraherz (THz) metasurfaces using THz time domain spectroscopy. Complementary THz split ring resonator (cSRR) arrays are used as metasurfaces[4]. A higher coupling rate can be achieved by reducing the capacitive gap of the resonator due to the increased vacuum ?eld ?uctuations. However, our results indicate that this reduction introduces an inhomogenous broadening of the upper polariton branch below a threshold gap width.
关键词： complementary split ring resonator,Ultrastrong coupling,Landau level transitions,THz time domain spectroscopy,THz metasurfaces
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - THz Time-Domain Reflection Spectroscopy of KTiOPO <sub/>4</sub>
摘要： Terahertz (THz) radiation has been of increasing interest in the last decades, for security, manufacturing, quality control, medical and security imaging applications. The field requires more efficient and affordable sources and nonlinear upconversion schemes point in this direction. KTiOPO, (KTP) is a well-established material for nonlinear optical applications in the visible and near-IR region thanks to its large transparency, high nonlinear coefficient and damage threshold. Its reasonably low absorption [1, 2] and strong polariton resonances [1] show promise for efficient IR to THz upconversion and Wu et al. [2] recently demonstrated its superiority to LiNbO3 and LiTaO3 in a back to back experiment. However, the complex refractive index needs to be measured before further power scaling is realistic. Terahertz time-domain spectroscopy (TTDS) allows for direct extraction of both the phase and amplitude of the THz electric field and grants the possibility of extracting the optical parameters n and α. In this work, we report on THz time-domain reflection spectroscopy of flux grown KTP from 0.5 to 7 THz at room temperature. The THz-TDS setup used air-filament plasma for generation of the THz radiation and the Pockel's effect in 300um thick GaP for detection. The a and b-axis of a KTP crystal were probed using an HDPE polarizer and rotation of the sample. The geometry of the setup is based on the work of Pashkin et al. [3], where the THz was focused onto the GaP crystal after the 25x15x0.5mm3 sample. Fig.1 shows the refractive index and the absorption coefficient from left to right, respectively. Blue and red color depict the two axes of the KTP crystal. Errors are estimated to: ?n < ±0.025 and ?α <±5 cm?1 (0.5?3THz), ?n < ±0.05 and ?α < ±25 cm?1 (3?5THz), ?n < ±0.1 and ?α < ±50 cm?1 (5?6THz), ?n < ± 0.25 and ?α < ±150 cm?1 (6?7THz). The accuracy in frequency was ≈ 90 GHz or 2 cm?1, limited by the scan time of 11ps. To the best of our knowledge, the convoluted frequency dependent nature of the refractive index has not been measured by direct time-resolved THz measurement before. Earlier spectroscopic studies of KTP have either lacked the possibility of directly extracting the complex refractive index [4] or been limited by absorption of the transmitted signal due to the strong resonances of KTP, limiting the bandwidth to about 2.5 THz [5]. In the regions where the bandwidth of this and older studies overlap, the measurements are similar, giving credibility to both measurements over the whole bandwidth. Besides, the measured resonances in Fig.1 can be related to IR active phonon modes, as seen in, e.g. [6]. This study will be of utmost importance when constructing new devices for optical to THz conversion. We also report a possible new phonon mode at 1.4 THz.
关键词： absorption coefficient,KTiOPO4,refractive index,THz time-domain spectroscopy,Terahertz
更新于2025-09-12 10:27:22
-
Characterization and Integration of Terahertz Technology within Microfluidic Platforms
摘要： In this work, the prospects of integrating terahertz (THz) time-domain spectroscopy (TDS) within polymer-based microfluidic platforms are investigated. The work considers platforms based upon the polar polymers polyethylene terephthalate (PET), polycarbonate (PC), polymethyl-methacrylate (PMMA), polydimethylsiloxane (PDMS), and the nonpolar polymers fluorinated ethylene propylene (FEP), polystyrene (PS), high-density polyethylene (HDPE), and ultra-high-molecular-weight polyethylene (UHMWPE). The THz absorption coefficients for these polymers are measured. Two microfluidic platforms are then designed, fabricated, and tested, with one being based upon PET, as a representative high-loss polar polymer, and one being based upon UHMWPE, as a representative low-loss nonpolar polymer. It is shown that the UHMWPE microfluidic platform yields reliable measurements of THz absorption coefficients up to a frequency of 1.75 THz, in contrast to the PET microfluidic platform, which functions only up to 1.38 THz. The distinction seen here is attributed to the differing levels of THz absorption and the manifestation of differing f for the systems. Such findings can play an important role in the future integration of THz technology and polymer-based microfluidic systems.
关键词： lab-on-a-chip,THz time-domain spectroscopy,microfluidics,polymer absorption
更新于2025-09-10 09:29:36
-
Hyperspectral Terahertz Tomography in Amplitude Contrast
摘要： Hyperspectral Terahertz Tomography in amplitude contrast is presented using a time-domain spectroscopy system in the spectral range 0.3 - 2.5 THz. The Fourier transformed signal data is used to reconstruct test objects’ cross-sections at multiple frequencies using standard filtered backprojection. The full hyperspectral set of images reconstructed at around 300 adjacent spectral points is used to trace the combined contribution of Beer-Lambert volume attenuation, Fresnel reflection losses and Rayleigh roughness scattering losses, which is in good overall agreement with the experimental results. The image quality for Styrofoam (refractive index around 1.02, attenuation coefficient < 1 mm-1) test objects is best in the range 0.8 - 2.0 THz depending on the porosity of the material.
关键词： THz,time-domain spectroscopy,hyperspectral imaging,Rayleigh roughness,hard-field tomography
更新于2025-09-09 09:28:46