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A polarization-resolved study of nanopatterned photoconductive antenna for enhanced Terahertz emission
摘要： Terahertz (THz) frequencies, despite having the potential for several important applications, have been relatively under-explored in the past owing to the unavailability of proper sources and detectors. The scenario has been changing over the last few decades due to the advent of convenient THz sources and detectors. THz photo-conductive antennas (PCA), due to their attractive features, such as cost-effectiveness, room temperature operation, is playing a key role in current and future research prospect in the field of THz spectroscopy, both as source and detectors. Complex PCA designs have been proposed and studied to boost the THz emission efficiencies. Elucidating the underlying physics in such devices requires a thorough investigation of a few physical parameters. This requires the integration of several experimental techniques under identical conditions. In this article, we show such a study, including a parametric variation of pump polarization, conducted on a PCA with nanopatterned active region which boosts the emitted THz radiation. Through the set of measurements, we unravel the subtle interplay of the various physical processes responsible for the emission of THz radiation from the device.
关键词： characterization setup,enhanced THz generation,Photo-conductive antenna,nano-pattern
更新于2025-09-23 15:22:29
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Terahertz generation in quantum-cascade lasers through down-conversion optical nonlinearity: Design and modeling
摘要： In this paper, we propose an electrically driven optically excited laser structure for terahertz (THz) generation in quantum cascade lasers (QCLs) through frequency down-conversion optical nonlinearity. In our distinct design, both the pump and THz radiations are generated simultaneously by optical and electronic intersubband transitions (ISTs) between the quantized states within the conduction band of the same active region of a QCL. The modeling of laser bandstructure is achieved using a self-consistent solution of Schrodinger-Poisson equations, and the detailed analysis of electronic transport of the proposed structure is performed using the density matrix approach and energy-density balance equation that self-consistently consider the optical, electrical and thermal interactions in the structure. Additionally, the waveguide loss for the THz optical mode is considered using the bulk Drude model. Using a stationary solution of the density matrix equations, an expression for the THz intensity gain is derived as a function of pump field intensity, carrier distributions and quantum coherence contributions. Using the presented model, we analyze the steady-state and transient characteristics of the device for two different heatsink temperatures, 220 and 300 K. Simulation results show that the proposed structure has a potential to generate room-temperature THz radiation in QCLs.
关键词： Quantum-cascade laser (QCL),terahertz (THz) generation,down-conversion optical nonlinearity,density-matrix formalism
更新于2025-09-23 15:21:01
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[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
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Numerical Study of CO Laser Down-Conversion into the THz Range With ZnGeP <sub/>2</sub> crystal
摘要： Difference frequency generation of rotational-vibrational lines of nonselective CO laser in ZnGeP2 crystal was numerically studied. It was shown that a great number of difference frequency lines can densely cover spectral range from 50 to 1000 (cid:2)m and even up to 5000 (cid:2)m. An influence of ZnGeP2 crystal absorption on THz generation was studied.
关键词： THz generation,CO laser,difference frequency generation,ZnGeP2 crystal
更新于2025-09-12 10:27:22
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[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) - Numerical Simulations of THz Generation with two-Color Mid-Infrared Laser Pulse and Relative Phase Control
摘要： The generation of terahertz (THz) radiation by two-color laser pulse induced gas plasma is an actively researched topic since its exploration [1]. It is a tabletop, powerful spectroscopic tool in the far-infrared spectral regime. The THz spectroscopy is capable to identify chemicals in a nondestructive way [2]. It is capable to generate THz radiation by remotely more than 100m from the laser system [3], the remote sensing of the THz radiation also possible [4]. By the combination of the former mentioned features, the THz spectroscopy is a powerful tool to identify drugs, poisons and explosives with remotely in a nondestructive way.
关键词： spectroscopy,relative phase control,gas plasma,two-color mid-infrared laser pulse,THz generation
更新于2025-09-12 10:27:22
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[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) - Theoretical Investigation of the Optimal Nonlinear Crystal Thickness for THz Generation from two-Color Laser Pulse Ionized Gas under Different Laser Pulse Parameters
摘要： The generation of terahertz (THz) radiation by two-color laser pulse induced gas plasma is an actively researched topic since its exploration. It is a tabletop, powerful spectroscopic tool in the far-infrared spectral regime. It is possible to generate THz radiation by remotely more than 100m from the laser system, the remote sensing of the THz radiation also possible. Furthermore, the THz spectroscopy is capable to identify chemicals in a nondestructive way. By the combination of the former mentioned features, the THz spectroscopy is a powerful tool to identify drugs, poisons and explosives with remotely in a nondestructive way. One of the drawbacks of the THz radiation generated from two-color laser pulse induced gas plasma is the low efficiency. In the last two decades many publications have been published about increasing the efficiency of this method. Spectrally shaped fundamental beam has been proved to be an effective way to control the generated THz field properties. Using a step phase plate is demonstrated to enhance the generated THz intensity with a factor of two. Combining the fundamental, the second harmonic and the third harmonic beams also increase the THz pulse generation efficiency. Increasing the fundamental laser pulse wavelength has proved to be improve the generation efficiency. In this publication, we examined the nonlinear crystal thickness effect on the THz generation from two-color laser pulse induced gas plasma. It was found the at a given fundamental pulse energy and pulse duration there is an optimal thickness for the nonlinear crystal, where the THz generation is the most effective as seen on Fig. 1. In case of a thinner crystal, than the optimal crystal thickness, the second harmonic generation effectivity decrease, which entails the THz generation effectivity also decrease. In case of thicker crystal, than the optimal crystal thickness, the material dispersion decreases both the fundamental and its second harmonic’s peak power, which entails the THz generation effectivity decrease. The optimal nonlinear crystal thickness was examined in the function of the fundamental laser pulse energy, pulse duration, central wavelength and the nonlinear crystal distance from the focal spot. It was found that all the former mentioned parameters have a great impact on the optimal nonlinear crystal thickness. In conclusion, choosing the proper crystal parameters considering the laser and the setup parameters are a crucial point of the THz generation from two-color laser pulse induced gas plasma.
关键词： optimal thickness,two-color laser pulse,gas plasma,nonlinear crystal thickness,THz generation
更新于2025-09-12 10:27:22
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[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) - Cherenkov Generation of Wideband Terahertz Radiation using a Sub-Micron LiNbO <sub/>3</sub> Slab Waveguide
摘要： Terahertz (THz) radiation is critical to the areas of security, medicine, communications, and consumer applications. THz generation is often achieved using lithium niobate, LiNbO3, since it has a high nonlinear coefficient in this regime (d33=180 pm/V [1]). Dramatic improvement to the generation efficiency has been achieved by incorporating this material into waveguiding configurations [2,3], since waveguides allow the pump pulse to remain confined over large distance (millimeters or longer). To date, waveguides investigated for THz generation utilize transverse core dimensions larger than a few microns. However, when the waveguide core is sub-wavelength with respect to the pump wavelengths, as well as the generated THz wavelengths, another benefit is observed: substantial broadening of the generated THz bandwidth. Here, we report on a sub-wavelength SiO2-LiNbO3-SiO2 slab waveguide that produces wideband THz radiation and emits it in the form of Cherenkov waves. The investigated LiNbO3 slab waveguide has transverse core dimensions of 720 nm × 4 mm and a length of 100 μm. This waveguide is excited using an electric field pulse having a duration of 50 fs and a central-wavelength of 780 nm. Figure 1(a) shows the generated THz electric field pulse, which has the short duration of <1 ps. The power spectrum of the generated THz pulse is shown in Fig. 1(b), having a central-frequency of 6.9 THz and a full-width half-maximum (FWHM) bandwidth of 2.1 THz. Notably, LiNbO3 has a strong phonon resonance at 7.6 THz [4]. However, since the generated THz radiation is emitted as Cherenkov waves, it exits the sub-wavelength LiNbO3 core after propagating a distance much less than a wavelength. This characteristic minimizes the high loss of the LiNbO3 phonon resonance, allowing for generation to occur directly at this phonon resonance. As such, the sub-wavelength nature of the LiNbO3 core allows for dramatic improvement to the THz radiation bandwidth. The data is Fig. 1 is obtained by performing finite-difference time-domain simulations. Experimental verification of this result is currently underway. In this experimental work, the LiNbO3 slab waveguide instead has a length of 1 cm and the excitation pulses will have energies ranging up to 200 nJ.
关键词： wideband THz generation,Terahertz radiation,LiNbO3,Cherenkov waves,sub-wavelength waveguide
更新于2025-09-12 10:27:22
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Comparison of the Features of Electron Transport and Subterahertz Generation in Diodes Based on 6-, 18-, 70-, and 120-Period GaAs/AlAs Superlattices
摘要： A comparison of the features of electron transport in diodes based on 6-, 18-, 30-, 70-, and 120-period GaAs/AlAs superlattices with a similar design is performed. However, the number of periods and diode areas are different. The values of the parasitic resistances of the near-contact diode regions are correlated, and the specific voltage drop across one superlattice period is determined for all special points in the current–voltage characteristics of the diodes. The mechanism of the appearance of stable current oscillations in diodes based on 6-, 18-, 30-, 70-, and 120-period GaAs/AlAs superlattices with a high doping level is investigated.
关键词： diodes,THz generation,electron transport,superlattices
更新于2025-09-11 14:15:04
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Control of THz field waveform emitted from air plasma by chirping two-color laser pulses
摘要： Few-cycle terahertz pulses can be effectively generated in air plasma by mixing an ultrashort laser pulse with its second harmonic. The temporal overlap between these two pulses is critical, which can degrade with the mismatch of group velocities. However, the overlap between the fundamental and second harmonic can be controlled by pre-stretching the temporally separated pulses. In this paper, we study the role of chirp and the relative phase between the fundamental and its second harmonic in the formation of the terahertz waveform. We demonstrate experimentally and explain within the context of transient photocurrent model, that the combination of chirping and relative phase shifting can provide a powerful tool to control the waveform of the terahertz pulse.
关键词： Dispersion,Plasma physics,Nonlinear optics,THz generation,Ultrashort pulses
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Exceptionally high THz energy densities generated from organic crystals pumped with mid-infrared pulses
摘要： Optical Parametric Chirped-Pulse Amplification (OPCPA) is an emerging laser technology, providing a flexibility in operating wavelengths and power upscaling. Here, we investigate THz generation in organic crystals (DAST) by optical rectification (OR) of intense Mid–Infrared (MIR) pulses. The broadband spectrum exceeds several octaves when pumped by 100 fs, 3.9 μm OPCPA pulses. We report on an extraordinarily high THz energy density of 3.1 mJ/cm2 and crystal damage threshold > 150 mJ/cm2.
关键词： optical rectification,OPCPA,mid-infrared pulses,THz generation,organic crystals
更新于2025-09-11 14:15:04