Polarization Gating Research Articles

A flexible beamline combining XUV attosecond pulses with few-femtosecond UV and near-infrared pulses for time-resolved experiments.

We describe a beamline where few-femtosecond ultraviolet (UV) pulses are generated and synchronized to few-cycle near-infrared (NIR) and extreme ultraviolet (XUV) attosecond pulses. The UV light is obtained via third-harmonic generation in argon or neon gas when focusing a phase-stabilized NIR driving field inside a glass cell that was designed to support high pressures for enhanced conversion efficiency. A recirculation system allows reducing the large gas consumption required for the nonlinear process. Isolated attosecond pulses are generated using the polarization gating technique, and the photon spectrometer employed to characterize the XUV radiation consists of a new design based on the combination of a spherical varied-line-space grating and a cylindrical mirror. This design allows for compactness while providing a long entrance arm for integrating different experimental chambers. The entire interferometer is built under vacuum to prevent both absorption of the XUV light and dispersion of the UV pulses, and it is actively stabilized to ensure an attosecond delay stability during experiments. This table-top source has been realized with the aim of investigating UV-induced electron dynamics in neutral states of bio-relevant molecules, but it also offers the possibility to implement a manifold of novel time-resolved experiments based on photo-ionization/excitation of gaseous and liquid targets by ultraviolet radiation. UV pump-XUV probe measurements in ethyl-iodide showcase the capabilities of the attosecond beamline.

Strong terahertz pulse induced Pockels and Kerr effect in crystalline quartz for ultrafast pulse switching

Ultrafast pulse switching is one of the key elements for ultrahigh speed communication technology. We study the terahertz (THz) induced birefringence response on the laser pulse through the quartz with different THz electric field strength. The magnitude of the observed Pockels signals scales linearly with the THz field amplitude, while the Kerr signals scale quadratically with the THz field amplitude. We demonstrate that the quartz is a good candidate for polarization modulation of 800 nm laser pulse, which has the advantages of low-cost, large bandgap, and negligible dispersion. Furthermore, our investigation finds application beyond ultrafast polarization switching, and the THz-induced polarization gating technique works as a tool for intense THz pulse detection.

Numerical investigations into the impact of substrate defects on a grooved GaN-based ultraviolet phototransistor with an AlGaN polarization gate

In this work, we propose defect-related models for a grooved GaN/AlxGa1−xN/GaN UV phototransistor with an AlGaN polarization gate. The AlGaN polarization gate is set under the absorptive layer. With the developed models, we find that without the AlGaN polarization gate, the donor-type traps increase the dark current. In contrast, the electron trapping effect by acceptor-type traps reduces the dark current. Moreover, the AlGaN polarization gate helps deplete the electrons under the grooved region, which makes the dark current further suppressed. We also investigate the influence of the Al composition and the polarization level for the AlGaN polarization gate on the carrier transport, the dark current, and the photocurrent. Meanwhile, we report that the grooved depth plays an important role in reducing the background channel electron concentration, and the channel under the grooved region can be effectively closed by the AlGaN polarization gate when the grooved depth is properly set.

The Generation of Circularly Polarized Isolated Attosecond Pulses with Tunable Helicity from CO Molecules in Polarization Gating Laser Fields

We theoretically demonstrate a scheme to generate circularly polarized (CP) isolated attosecond pulses (IAPs) with tunable helicity using a polarization gating laser field interacting with the CO molecule. The results show that a broadband CP supercontinuum is produced from the oriented CO molecule, which supports the generation of an IAP with an ellipticity of 0.98 and a duration of 90 as. Furthermore, the helicity of the generated harmonics and IAP can be effectively controlled by modulating the laser field and the orientation angle of the CO molecule. Our method will advance research on chiral-specific dynamics and magnetic circular dichroism on the attosecond timescale.

Performance analysis of dual material control gate cavity on source electrically doped TFET biosensor for biomedical applications

The fabrication complexity, low sensitivity, detection speed, and costs associated with nanoscale devices have been significant concerns in the development of label-free biosensors. To address these issues, we report a novel dual material control gate cavity on source electrically doped tunnel field-effect transistor (DM-CG-CS-ED-TFET) for label-free biosensors. In this regard, the n+ drain and p+ source regions within the proposed device are induced by applying polarity gate (PG) bias voltages of PG-1 = +1.2 V and PG-2 = −1.2 V, respectively, across the respective polarity gate electrodes. This approach not only overcomes doping control issues but also avoids thermal budget constraints and minimizes fabrication complexity when compared to conventional TFET. For biomolecule sensing in the device, a nanogap cavity is created within the gate dielectric by selectively etching a portion of the polarity gate dielectric layer towards the source side. The performance of the proposed biosensor device is evaluated based on the variations in carrier concentration profile, energy band diagram, electric field, transfer (IDS - VGS) characteristics, drain current (IDS) sensitivity, ON-state current (ION) sensitivity, switching ratio (ION/IOFF) and subthreshold swing (SS) sensitivity. The sensitivity of the device is also investigated based on nano-cavity dimensions, practical challenges such as various filling factors, and the step profile generated from the steric hindrance. Moreover, the effect of temperature on sensitivity has also been investigated. For this, various biomolecules including Streptavidin (k = 2.1), APTES (k = 3.57), ferrocytochrome c (k = 4.7), keratin (k = 8) and Gelatin (k = 12), have been investigated for their performance using Silvaco ATLAS device simulator. The simulation results demonstrate that the proposed biosensor is a viable option for biosensing applications in biomedical engineering.

A low-side-lobe folded transmitarray antenna based on metasurface with independent amplitude/phase control

In this paper, a low-side-lobe folded transmitarray antenna (LSLFTA) based on metasurface (MS) that can independently control amplitude and phase is proposed. An MS, composed of two vertically placed polarization gates, can realize the efficient reflection of y-polarized waves, efficient transmission of x-polarized waves, and independently control of phase and amplitude is designed for the top surface. A polarization conversion surface (PCS) using an open resonant ring that can efficiently achieve cross polarization conversion is presented. The feed antenna is placed on the center of the top surface to obtain an accurate electromagnetic amplitude distribution. To the best of our knowledge, our work is thus the first one to achieve low-side-lobe FTA. The LSLFTA operating at 14.5 GHz is fabricated and measured to verify the design. After adding amplitude modulation (Taylor distribution), the side lobe level (SLL) is 5.2 dB and 7.5 lower than that of only phase modulation in the yoz plane and xoz plane, respectively. The 3 dB gain bandwidth of the antenna is 19.4% (13.5∼16.4 GHz), and the maximum aperture efficiency is 25.8%. Our work is a promising candidate in the design of high-gain, low SLL, and low-profile antenna.

Enhancing reflected light filtration of photoelectronic detection system using polarization gating in scattering media

Photoelectronic technology has found extensive application due to its non-invasiveness, compact structure, and low cost. However, in semi-transparent media, the detection system based on reflection structure indiscriminately receives reflection light from different depths, resulting in the masking of target signals and a decrease in signal quality. To address this issue, selecting reflected light at different depths through polarization gates is an effective way. In this study, we analyzed a polarization gate-semi-infinite medium scattering model and investigated the impact of various factors on the reflected light filtering capability of the polarization gate, through Monte Carlo simulations and polystyrene microsphere scattering experiments. We found that the polarization gate can achieve a more effective control effect on the high polarization area on the reflective surface. Furthermore, the signal-to-noise ratio of the photoplethysmography sensor with an orthogonally polarized gate was improved from 0.72 to 2.36 dB. In other words, the polarization gate offers new insights into signal optimization through a structural design, which facilitates the development of wearable, low-power, and robust physiological signal measurement systems in the future.

Measurement of ultrashort laser pulses with a time-dependent polarization state using the d-scan technique

The dispersion scan (d-scan) technique is extended to measurement of the time-dependent polarization state of ultrashort laser pulses. In the simplest implementation for linearly polarized ultrashort pulses, the d-scan technique records the second harmonic generation spectrum as a function of a known spectral phase manipulation. By applying this method to two orthogonally polarized projections of an arbitrary polarized electric field and by measuring the spectrum at an intermediate angle, we can reconstruct the evolution over time of the polarization state. We demonstrate the method by measuring a polarization gate generated from 6fs pulses with a combination of waveplates. The measurements are compared to simulations, showing an excellent agreement.

Electrically Doped PNPN Tunnel Field-Effect Transistor Using Dual-Material Polarity Gate with Improved DC and Analog/RF Performance.

A new structure for PNPN tunnel field-effect transistors (TFETs) has been designed and simulated in this work. The proposed structure incorporates the polarity bias concept and the gate work function engineering to improve the DC and analog/RF figures of merit. The proposed device consists of a control gate (CG) and a polarity gate (PG), where the PG uses a dual-material gate (DMG) structure and is biased at -0.7 V to induce a P+ region in the source. The PNPN structure introduces a local minimum on the conduction band edge curve at the tunneling junction, which dramatically reduces the tunneling width. Furthermore, we show that incorporating the DMG architecture further enhances the drive current and improves the subthreshold slope (SS) characteristics by introducing an additional electric field peak. The numerical simulation reveals that the electrically doped PNPN TFET using DMG improves the DC and analog/RF performances in comparison to a conventional single-material gate (SMG) device.

Spin polarization gate device based on the chirality-induced spin selectivity and robust nonlocal spin polarization.

Nonlocal spin polarization phenomena are thoroughly investigated in the devices made of chiral metallic single crystals of CrNb3S6 and NbSi2 as well as of polycrystalline NbSi2. We demonstrate that simultaneous injection of charge currents in the opposite ends of the device with the nonlocal setup induces the switching behavior of spin polarization in a controllable manner. Such a nonlocal spin polarization appears regardless of the difference in the materials and device dimensions, implying that the current injection in the nonlocal configuration splits spin-dependent chemical potentials throughout the chiral crystal even though the current is injected into only a part of the crystal. We show that the proposed model of the spin dependent chemical potentials explains the experimental data successfully. The nonlocal double-injection device may offer significant potential to control the spin polarization to large areas because of the nature of long-range nonlocal spin polarization in chiral materials.

Single-shot decoherence polarization gated imaging through turbid media.

We propose a method for imaging through a turbid medium by using a single-shot decoherence polarization gate (DPG). The DPG is made up of a polarizer, an analyzer, and a weakly scattering medium. Contrary to intuition, we discover that the preferential utilization of sparsely scattered photons by introducing weakly scattering mediums can lead to better image quality. The experimental results show that the visibilities of the images acquired from the DPG imaging method are obviously improved. The contrast of the bar can be increased by 50% by the DPG imaging technique. Furthermore, we study the effect of the volume concentration of the weakly scattering medium on the speckle suppression and the enhancement of the visibilities of the images. The variances of the contrasts of the image show that there exists an optimum optical depth (∼0.8) of the weakly scattering medium for DPG imaging through a specific turbid medium.

Cascaded Logic Gates Based on High-Performance Ambipolar Dual-Gate WSe2 Thin Film Transistors.

Ambipolar dual-gate transistors based on low-dimensional materials, such as graphene, carbon nanotubes, black phosphorus, and certain transition metal dichalcogenides (TMDs), enable reconfigurable logic circuits with a suppressed off-state current. These circuits achieve the same logical output as complementary metal-oxide semiconductor (CMOS) with fewer transistors and offer greater flexibility in design. The primary challenge lies in the cascadability and power consumption of these logic gates with static CMOS-like connections. In this article, high-performance ambipolar dual-gate transistors based on tungsten diselenide (WSe2) are fabricated. A high on-off ratio of 108 and 106, a low off-state current of 100 to 300 fA, a negligible hysteresis, and an ideal subthreshold swing of 62 and 63 mV/dec are measured in the p- and n-type transport, respectively. We demonstrate cascadable and cascaded logic gates using ambipolar TMD transistors with minimal static power consumption, including inverters, XOR, NAND, NOR, and buffers made by cascaded inverters. A thorough study of both the control gate and the polarity gate behavior is conducted. The noise margin of the logic gates is measured and analyzed. The large noise margin enables the implementation of VT-drop circuits, a type of logic with reduced transistor number and simplified circuit design. Finally, the speed performance of the VT-drop and other circuits built by dual-gate devices is qualitatively analyzed. This work makes advancements in the field of ambipolar dual-gate TMD transistors, showing their potential for low-power, high-speed, and more flexible logic circuits.

Control of the electron dynamics in solid-state high harmonic generation on ultrafast time scales by a polarization-skewed laser pulse.

Since high-order harmonic generation (HHG) from atoms depends sensitively on the polarization of the driving laser field, the polarization gating (PG) technique was developed and applied successfully to generate isolated attosecond pulses from atomic gases. The situation is, however, different in solid-state systems as it has been demonstrated that due to collisions with neighboring atomic cores of the crystal lattice strong HHG can be generated even by elliptically- and circularly-polarized laser fields. Here we apply PG to solid-state systems and find that the conventional PG technique is inefficient for the generation of isolated ultrashort harmonic pulse bursts. In contrast, we demonstrate that a polarization-skewed laser pulse is able to confine the harmonic emission to a time window of less than one-tenth of the laser cycle. This method provides a novel way to control HHG and to generate isolated attosecond pulses in solids.

Generation of the isolated highly elliptically polarized attosecond pulse using the polarization gating technique: TDDFT approach.

This paper theoretically investigates the generation of isolated elliptically polarized attosecond pulses with a tunable ellipticity from the interaction of Cl2 molecule and a polarization-gating laser pulse. A three-dimensional calculation based on the time-dependent density functional theory is done. Two different methods are proposed for generating elliptically polarized single attosecond pulses. The first method is based on applying a single-color polarization gating laser and controlling the orientation angle of the Cl2 molecule with respect to the polarization direction of the laser at the gate window. An attosecond pulse with an ellipticity of 0.66 and a pulse duration of 275 as is achieved by tuning the molecule orientation angle to 40° in this method and superposing harmonics around the harmonic cutoff. The second method is based on irradiating an aligned Cl2 molecule with a two-color polarization gating laser. The ellipticity of the attosecond pulses obtained by this method can be controlled by adjusting the intensity ratio of the two colors. Employing an optimized intensity ratio and superposing harmonics around the harmonic cutoff would lead to the generation of an isolated, highly elliptically polarized attosecond pulse with an ellipticity of 0.92 and a pulse duration of 648 as.

Performance Assessment of a Junctionless Heterostructure Tunnel FET Biosensor Using Dual Material Gate

Biosensors based on tunnel FET for label-free detection in which a nanogap is introduced under gate electrode to electrically sense the characteristics of biomolecules, have been studied widely in recent years. In this paper, a new type of heterostructure junctionless tunnel FET biosensor with an embedded nanogap is proposed, in which the control gate consists of two parts, namely the tunnel gate and auxiliary gate, with different work functions; and the detection sensitivity of different biomolecules can be controlled and adjusted by the two gates. Further, a polar gate is introduced above the source region, and a P+ source is formed by the charge plasma concept by selecting appropriate work functions for the polar gate. The variation of sensitivity with different control gate and polar gate work functions is explored. Neutral and charged biomolecules are considered to simulate device-level gate effects, and the influence of different dielectric constants on sensitivity is also researched. The simulation results show that the switch ratio of the proposed biosensor can reach 109, the maximum current sensitivity is 6.91 × 102, and the maximum sensitivity of the average subthreshold swing (SS) is 0.62.

Modeling and Simulation Investigation of Ferroelectric-Based Electrostatic Doping for Tunnelling Field-Effect Transistor

In this paper, a novel ferroelectric-based electrostatic doping (Fe-ED) nanosheet tunneling field-effect transistor (TFET) is proposed and analyzed using technology computer-aided design (TCAD) Sentaurus simulation software. By inserting a ferroelectric film into the polarity gate, the electrons and holes are induced in an intrinsic silicon film to create the p-source and the n-drain regions, respectively. Device performance is largely independent of the chemical doping profile, potentially freeing it from issues related to abrupt junctions, dopant variability, and solid solubility. An improved ON-state current and ION/IOFF ratio have been demonstrated in a 3D-calibrated simulation, and the Fe-ED NSTFET's on-state current has increased significantly. According to our study, Fe-ED can be used in versatile reconfigurable nanoscale transistors as well as highly integrated circuits as an effective doping strategy.

Generation of micro-Joule level coherent quasi-continuum extreme ultraviolet radiation using multi-cycle intense laser-atom interactions

In the present work we report on the current progress of the recently constructed GW attosecond extreme ultraviolet (XUV) source developed at the Institute of Electronic Structure and Laser of the Foundation for Research and Technology-Hellas (I.E.S.L-FO.R.T.H.). By the implementation of a compact-collinear polarization gating arrangement, the generation of a broadband, coherent XUV quasi-continuum produced by the interaction of a many-cycle infrared field with a gas phase medium is achieved. The spectral width of the XUV emission generated in Xenon, is spanning in the range of 17–32 eV and can support isolated pulses of duration in the range from 0.4 fs to 1.3 fs and pulse energy in the 1 μJ level. Theoretical calculations, taking into account the experimental conditions of this work, are supporting the observations, offering also an insight regarding the temporal profile of the emitted radiation. Finally, the high intensity of the produced XUV pulses has been confirmed by investigating the two-XUV-photon double ionization process of Argon atoms. The demonstrated results inaugurate the capability of the beamline of producing intense coherent quasi-continuum XUV radiation, supporting isolated as pulses, that can be exploited in studies of non-linear XUV processes, attosecond pulse metrology and XUV-pump–XUV-probe experiments.

Study of Ion-Assisted E-Beam Evaporation Coating Process on Chirped Mirrors

A chirped mirror designed with 60 fs2 in group delay dispersion and reflectance large than 97.5% in the bandwidth between 700 and 900 nm by open-sourced thin film filter design software is presented. The chirped mirrors are then fabricated by an ion-assisted deposition coater. First, the optical constants of the thin films deposited by specific process parameters are calibrated by trial runs with single-layer samples measured by variable-angle spectroscopic ellipsometer; then factors are entered to compensate for the settings on film thickness. Afterward, the spectral phase of the coated mirrors is measured by polarization gating frequency-resolved optical gating whereas the reflectance is measured by photo-spectrometer. In conclusion, the measured results indicate a reasonable match with the design goals to show the effectiveness of the proposed method. It is noted that ion-assisted electron gun evaporation coating systems are applicable to the mass production of chirped mirrors employed for ultrafast lasers.

Epitaxial κ-Ga2O3/GaN heterostructure for high electron-mobility transistors

GaN power technology, especially AlGaN/GaN high electron-mobility transistors (HEMTs), has made significant progress in recent years. However, the performance of HEMTs is still limited due to a trade-off between on-resistance and off-state breakdown voltage (BV). Integrating a polar gate dielectric with GaN HEMTs can potentially improve both sheet resistance of the two-dimensional electron gas channel and the field distribution between gate and drain. In this regard, orthorhombic κ-Ga2O3 has attractive properties since it is predicted to be strongly polar and highly dielectric while it grows epitaxially on GaN. By successfully integrating crystalline κ-Ga2O3 on GaN HEMTs, the channel sheet resistance is reduced by 20% from a reference device with amorphous Al2O3 gate dielectric. As a result, the cut-off frequency increases from 4.8 to 9.1 GHz. The dielectric property of κ-Ga2O3 also improves BV from 354 to 380 V by reducing the peak electric field in the gate-drain region.

Controlling Drain Side Tunneling Barrier Width in Electrically Doped PNPN Tunnel FET

In this paper, we propose and investigate an electrically doped (ED) PNPN tunnel field effect transistor (FET), in which the drain side tunneling barrier width is effectively controlled to obtain a suppressed ambipolar current. We present that the proposed PNPN tunnel FETs can be realized without chemically doped junctions by applying the polarity bias concept to a doped N+/P- starting structure. Using numerical device simulations, we demonstrate how the tunneling barrier width on the drain side can be influenced by several design parameters, such as the gap length between the channel and the drain (Lgap), the working function of the polarity gate, and the dielectric material of the spacer. The simulation results show that an ED PNPN tunneling FET with an ED drain, which has been explored for the first time, exhibits a low ambipolar current of 5.87 × 10-16 A/µm at a gap length of 20 nm. The ambipolar current is reduced by six orders of magnitude compared to that which occurs with a conventional ED PNPN tunnel FET with a uniformly doped drain, while the average subthreshold slope and the ON state and OFF state currents remained nearly identical.