Polarization Gating Research Articles

Polarization gating using cross-polarized wave generation with multicycle lasers to produce isolated attosecond pulses in overdense media

A method to generate a polarization gate for multicycle laser pulses is presented. We study the performance of a pulse with time-dependent polarization to produce a single attosecond pulse after its interaction with an overdense plasma. The polarization gate is generated through the use of cross-polarized wave generation in a single BaF2 crystal combined with a dispersive medium. Numerical simulations demonstrate that using the polarization gate, the number of pulses in the attosecond train can be reduced. With this method a single attosecond pulse can be isolated by filtering the high harmonic orders in the reflected spectrum. The dependence of the ellipticity curve on the dispersion introduced is studied as well as its influence in the size of the polarization gate.

Design and Comparative Evaluation of a PCM-Based CAM (Content Addressable Memory) Cell

This paper presents the design of a content addressable memory (CAM) cell. This cell utilizes a phase change memory (PCM) as a storage element and an ambipolar transistor for data comparison; the operation of the ambipolar transistor is controlled by voltage at the polarity gate. A memory core consisting of a CMOS transistor and a PCM is employed (1T1P). For the search operation, the data in the 1T1P memory core are read and its values are established by using a differential sense amplifier. The proposed CAM cell is simulated and compared with other nonvolatile CAM cells by using emerging technologies (such as MTJ and memristor). The simulation results show that as the proposed CAM cell operates on a voltage basis, it offers significant advantages in terms of power delay product for the search operation and reduced circuit complexity (in terms of lower transistor and storage element counts) compared with other designs found in the technical literature.

Generation of isolated attosecond pulses with enhancement cavities—a theoretical study

The generation of extreme-ultraviolet (XUV) isolated attosecond pulses (IAPs) has enabled experimental access to the fastest phenomena in nature observed so far, namely the dynamics of electrons in atoms, molecules and solids. However, nowadays the highest repetition rates at which IAPs can be generated lies in the range. This represents a rather severe restriction for numerous experiments involving the detection of charged particles, where the desired number of generated particles per shot is limited by space charge effects to ideally one. Here, we present a theoretical study on the possibility of efficiently producing IAPs at multi- repetition rates via cavity-enhanced high-harmonic generation (HHG). To this end, we assume parameters of state-of-the-art Yb-based femtosecond laser technology to evaluate several time-gating methods which could generate IAPs in enhancement cavities. We identify polarization gating and a new method, employing non-collinear optical gating in a tailored transverse cavity mode, as suitable candidates and analyze these via extensive numerical modeling. The latter, which we dub transverse mode gating (TMG) promises the highest efficiency and robustness. Assuming 0.7 , 5-cycle pulses from the seeding laser and a state-of-the-art enhancement cavity, we show that TMG bares the potential to generate IAPs with photon energies around and a photon flux of at least at repetition rates of and higher. This result reveals a roadmap towards a dramatic decrease in measurement time (and, equivalently, an increase in the signal-to-noise ratio) in photoelectron spectroscopy and microscopy. In particular, it paves the way to combining attosecond streaking with photoelectron emission microscopy, affording, for the first time, the spatially and temporally resolved observation of plasmonic fields in nanostructures. Furthermore, it promises the generation of frequency combs with an unprecedented bandwidth for XUV precision spectroscopy.

Extreme nonlinear terahertz electro-optics in diamond for ultrafast pulse switching

Polarization switching of picosecond laser pulses is a fundamental concept in signal processing [C. Chen and G. Liu, Annu. Rev. Mater. Sci. 16, 203 (1986); V. R. Almeida et al., Nature 431, 1081 (2004); and A. A. P. Pohl et al., Photonics Sens. 3, 1 (2013)]. Conventional switching devices rely on the electro-optical Pockels effect and work at radio frequencies. The ensuing gating time of several nanoseconds is a bottleneck for faster switches which is set by the performance of state-of-the-art high-voltage electronics. Here we show that by substituting the electric field of several kV/cm provided by modern electronics by the MV/cm field of a single-cycle THz laser pulse, the electro-optical gating process can be driven orders of magnitude faster, at THz frequencies. In this context, we introduce diamond as an exceptional electro-optical material and demonstrate a pulse gating time as fast as 100 fs using sub-cycle THz-induced Kerr nonlinearity. We show that THz-induced switching in the insulator diamond is fully governed by the THz pulse shape. The presented THz-based electro-optical approach overcomes the bandwidth and switching speed limits of conventional MHz/GHz electronics and establishes the ultrafast electro-optical gating technology for the first time in the THz frequency range. We finally show that the presented THz polarization gating technique is applicable for advanced beam diagnostics. As a first example, we demonstrate tomographic reconstruction of a THz pulse in three dimensions.

Attosecond pulse generation isolated with an asymmetric polarization gating

High harmonics generated using the polarization gating technique are simulated under the strong-field approximation for the cases of equal and unequal ratios between the amplitudes of the two counter-rotating pulses. The effect of the field asymmetry is observed on the high harmonic yield and cut-off in the frequency domain and on the attosecond pulse duration and satellite peak contrast in the time domain. The case where the strong pulse comes later is more favourable in terms of generating a higher cut-off and a shorter pulse duration. It is predicted that thin metal filters can reduce the impact of satellite pulses while simultaneously reducing the pulse duration.

Design and Analysis of Polarity Controlled Electrically Doped Tunnel FET With Bandgap Engineering for Analog/RF Applications

In this paper, we investigate a polarity controlled electrically doped tunnel FET (ED-TFET) based on the bandgap engineering for analog/RF applications. The proposed device exhibits a heavily doped n-type Si-channel with two distinctive gate: 1) control gate (CG) and 2) polarity gate (PG). First, the work function of 4.72 eV is considered for CG and PG to convert the layer beneath CG and PG of intrinsic type. Further, a bias of −1.2 V is applied at PG terminal to induce a p+ region, so that, it follows the similar trend as like a n+-i-p+ gated structure of conventional TFET. To improve the ON-state current of the proposed device, we investigate an interfacing of III–V with IV group material for heterojunction. It shows higher ON-state current in the order of $10^{-4}$ A/ $\mu \text{m}$ , ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio (in the order of $10^{12}$ ) at ${V}_{\sf DS} = 0.7$ V. Further, its higher transconductance ${g} _{m}\approx 1.02$ mS and different RF performance parameters in the range of terahertz, enables its potential for analog/RF applications. However, linearity parameters are analyzed to give the assurance of the device for high-frequency applications. Moreover, a nonquasi-static RF model is adopted to analyze the behavior of the proposed ED-TFET in high frequency region. Based on this, the small-signal parameters were extracted and verified upto 500 GHz. The modeled result shows excellentmatching with the Y-parameters upto 500 GHz.

Effect of Gate Width on High Harmonic Generation from Polarization Gating Pulse with Longer Pulse Duration

Effect of Gate Width on High Harmonic Generation from Polarization Gating Pulse with Longer Pulse Duration

A Continuous Compact DC Model for Dual-Independent-Gate FinFETs

Multiple-independent-gate (MIG) silicon FinFETs were recently shown capable of enabling: 1) device-level polarity control; 2) dynamic threshold modulation; and 3) subthreshold slope tuning down to ultra-steep-slope operation. These operation mechanisms can unlock a myriad of opportunities in digital as well as analog design. Here we discuss a continuous compact direct-current (dc) model, capable of describing the current–voltage characteristics of a class of MIG FinFETS, namely dual-independent-gate (DIG) FinFETs, over all its biasing design space. This model captures some of the unique features of DIG FinFETs including the dependence of its super-steep subthreshold swing on drain bias and polarity gate bias. An excellent agreement is shown between the model and measured experimental current–voltage characteristics in these devices. Moreover, the predictive nature of the model is evaluated by foreseeing the perspectives of DIG FinFETs as efficient RF detectors at very high frequencies.

Interferometric near-infrared spectroscopy directly quantifies optical field dynamics in turbid media.

Sensing and imaging methods based on the dynamic scattering of coherent light (including laser speckle, laser Doppler, diffuse correlation spectroscopy, dynamic light scattering, and diffusing wave spectroscopy) quantify scatterer motion using light intensity fluctuations. The underlying optical field autocorrelation, rather than being measured directly, is typically inferred from the intensity autocorrelation through the Siegert relationship, assuming that the scattered field obeys Gaussian statistics. Here, we demonstrate interferometric near-infrared spectroscopy for measuring the time-of-flight (TOF) resolved field and intensity autocorrelations in turbid media. We find that the Siegert relationship breaks down for short TOFs due to static paths whose optical field does not decorrelate over experimental time scales. We also show that eliminating such paths by polarization gating restores the validity of the Siegert relationship. The unique capability of measuring optical field autocorrelations, as demonstrated here, enables the study of non-Gaussian and non-ergodic light scattering processes. Moreover, direct measurements of field autocorrelations are more efficient than indirect measurements based on intensity autocorrelations. Thus, optical field measurements may improve the quantiffcation of scatterer dynamics with coherent light.

Analysis of electrostatic doped Schottky barrier carbon nanotube FET for low power applications

This paper presents the analysis of electrostatic doped Schottky barrier carbon nanotube FET (ED-SBCNTFET) for low power applications. Electrostatic doping is introduced in intrinsic CNT as a channel material which reduces the process complexity; moreover dynamic configuration provides symmetric transfer characteristics for n-type and p-type for ED-SBCNTFET. Simulation results demonstrate that ED-SBCNTFET is better than conventional CNTFET in terms of IOFF and subthreshold swing (SS) which makes it suitable for low power applications. Simulations are performed and sensitivity analysis is carried out for CNT diameter, effective oxide thickness (EOT), high-k dielectric and polarity gate bias. It is observed that CNTs are most sensitive to diameter, since CNT with diameter 0.85 nm exhibits ION/IOFF ratio of ~109 and SS of 60.8 mv/dec whereas diameter of 0.55 nm results into ION/IOFF ratio of ~1011 with SS of 58.5 mv/dec. Optimized parameters are proposed for low power applications in terms of IOFF and SS. ED-SBCNTFET has been analysed for various process parameters and it has been demonstrated to be less sensitive to process variations.

A new approach for design and investigation of junction-less tunnel FET using electrically doped mechanism

For the first time, a distinctive approach based on electrically doped concept is used for the formation of novel double gate tunnel field effect transistor (TFET). For this, the initially heavily doped n+ substrate is converted into n+-i-n+-i (Drain-Channel-Source) by the selection of appropriate work functions of control gate (CG) and polarity gate (PG) as 4.7 eV. Further, the formation of p+ region for source is performed by applying −1.2 V at PG. Hence, the structure behave like a n+-i-n+-p+ gated TFET, whereas, the control gate is used to modulate the effective tunneling barrier width. The physical realization of delta doped n+ layer near to source region is a challenging task for improving the device performance in terms of ON current and subthreshold slope. So, the proposed work will provide a better platform for fabrication of n+-i-n+-p+ TFET with low cost and suppressed random dopant fluctuation (RDF) effects. ATLAS TCAD device simulator is used to carry out the simulation work.

Circuit Compatible Model for Electrostatic Doped Schottky Barrier CNTFET

This paper proposes a circuit compatible model for electrostatic doped Schottky barrier carbon nanotube field effect transistor (ED-SBCNTFET). The proposed model is an extension of the Schottky barrier carbon nanotube field effect transistor (SBCNTFET) to ED-SBCNTFET by adding polarity gates, which are used to create electrostatic doping. In ED-SBCNTFET, electrostatic doping is responsible for a fermi level shift of source and drain regions. A mathematical relation has been developed between fermi level shift and polarity gate bias. Both current–voltage (I–V) and capacitance–voltage (C–V) characteristics have been efficiently modeled. The results are compared with the reported semi-classical model and simulations from NanoTCAD ViDES for validation. The proposed model is much faster than numerical models as it denies self consistent equations. Finally, circuit application is demonstrated by simulating inverter using the proposed model in HSPICE.

Polarization-assisted amplitude gating as a route to tunable, high-contrast attosecond pulses

Attosecond spectroscopy is a powerful technique for probing electron dynamics in fundamental systems. However, extending this method to cover a wide range of element-specific, core-hole transitions requires the availability of broadly tunable attosecond pulses. In this Letter, we present a new method for generating high-flux, high-contrast single attosecond pulses tunable across the range of 50–120 eV. The method is referred to as a Polarization ASSisted Amplitude GatE (PASSAGE) and uses a few-cycle driving pulse along with a partial polarization gate to extend the bandwidth of high harmonic emission in the temporally isolated, cut-off portion of the spectrum. The simplicity of this technique will help pave the way for implementing attosecond core–hole spectroscopy to probe more complex reactions and bring attosecond science into a multidisciplinary setting.

Polarization gating of high harmonic generation in the water window

We implement the polarization gating (PG) technique with a two-cycle, 1.7 μm driving field to generate an attosecond supercontinuum extending to the water window spectral region. The ellipticity dependence of the high harmonic yield over a photon energy range much broader than previous work is measured and compared with a semi-classical model. When PG is applied, the carrier-envelope phase (CEP) is swept to study its influence on the continuum generation. PG with one-cycle (5.7 fs) and two-cycle (11.3 fs) delay are tested, and both give continuous spectra spanning from 50 to 450 eV under certain CEP values, strongly indicating the generation of isolated attosecond pulses in the water window region.

Solid-state harmonics beyond the atomic limit.

Strong-field laser excitation of solids can produce extremely nonlinear electronic and optical behaviour. As recently demonstrated, this includes the generation of high harmonics extending into the vacuum-ultraviolet and extreme-ultraviolet regions of the electromagnetic spectrum. High harmonic generation is shown to occur fundamentally differently in solids and in dilute atomic gases. How the microscopic mechanisms in the solid and the gas differ remains a topic of intense debate. Here we report a direct comparison of high harmonic generation in the solid and gas phases of argon and krypton. Owing to the weak van der Waals interaction, rare (noble)-gas solids are a near-ideal medium in which to study the role of high density and periodicity in the generation process. We find that the high harmonic generation spectra from the rare-gas solids exhibit multiple plateaus extending well beyond the atomic limit of the corresponding gas-phase harmonics measured under similar conditions. The appearance of multiple plateaus indicates strong interband couplings involving multiple single-particle bands. We also compare the dependence of the solid and gas harmonic yield on laser ellipticity and find that they are similar, suggesting the importance of electron-hole recollision in these solids. This implies that gas-phase methods such as polarization gating for attosecond pulse generation and orbital tomography could be realized in solids.

Generation of three-photon polarization-entangled decoherence-free states

We present a generation proposal of three-photon polarization-entangled decoherence-free states, which are immune to the collective decoherence. Based on weak cross-Kerr nonlinearities, the polarization and spacial entanglement gates are realized, and thus three-photon polarization-entangled decoherence-free states can be produced. According to the outcomes of Homodyne measurement performed in the spacial entanglement gate, one Swap gate is inserted into two paths of the photon 1 to swap its spacial modes, by means of classical feed forward. In addition, in the process for realizing two entanglement gates, unitary transformation operations are performed on the appropriate photons conditioned on the different phase shifts occurred on the coherent states, aiming to obtain the same state under two scenarios of the different path compositions of photons. At the output ports of the circuit, three-photon polarization-entangled decoherence-free states which can be utilized to represent two logical qubits, |0〉L and |1〉L are achieved. Apart from Kerr media, only simple linear optical elements and the classical feed forward techniques are necessary in this proposal, facilitating its practical implementation.

Ultrafast single-shot measurement of optical Kerr effect based on supercontinuum pulse.

We present an ultrafast single-shot measurement method for the optical Kerr effect based on a polarization gating technique. The advantages of this single-shot technique are demonstrated via a 26-ps chirped supercontinuum pulse used to measure the optical Kerr effect for three transparent organic liquids. The single-shot measurement results agree well with those of the time-resolved optical Kerr gate method, as regards both time and intensity. This method facilitates real-time observation of ultrafast optical Kerr responses of samples and simultaneous high-time-resolution data acquisition at ∼260 fs. We demonstrate that the single-shot measurement method is potentially a powerful tool for investigating the optical Kerr effects of unstable samples, and for application to high-power laser systems.

Improved polarization gating scheme on attosecond source generation

ABSTRACTAn improved polarization gating scheme on attosecond X-ray pulse generation from high-order harmonic generation has been investigated. It is found that by properly adding a linearly polarized pulse to the circularly polarized pulse, the harmonic spectrum is remarkably enhanced and controlled, leading to an efficient generation of the ultra-broadband supercontinuum covered by the spectrum range from ultraviolet to X-ray. Classical and the quantum time–frequency analyses have been shown to explain the harmonic emission process. Moreover, from analyzing the harmonic phases, we see that the phases of the generated harmonics are almost linear, which is beneficial to the attosecond pulse generation. As a result, a series of phase-steady and wavelength-tunable sub-50 as X-ray pulses can be obtained.

DC characteristics and analog/RF performance of novel polarity control GaAs-Ge based tunnel field effect transistor

In this paper, for the first time, DC characteristics and analog/RF performance of polarity control GaAs-Ge hetero TFET (GaAs-Ge H-TFET) structure have been analysed, using electrically doped dynamically configurable concept. For this, we have considered a hetero structure with two distinctive gates (Control gate and Polarity gate). Polarity gate induces p+ region at the source side and n+ region at the drain side, instead of relying on the abrupt doping profile at the junctions. Therefore, the fabrication process of the proposed device avoids ion-implantation, photo masking and complicated thermal budget. Hence, it shows high immunity against process variations, doping control issues and random dopant fluctuations (RDF). In order to optimize the device performance, interfacing of III–V groups materials with IV group semiconductor is done for hetero-junction. The introduction of hetero-junction and band gap engineering offer higher ION/IOFF ratio (5.1 × 1012), steep sub-threshold slope (18 mV/decade) and significantly change in analog/RF performance. The analog/RF figures of merit are analysed in term of transconductance (gm), output conductance (gds), gate to source capacitance (Cgs), gate to drain capacitance (Cgd), cutoff frequency (fT) and gain bandwidth (GBW) product. The proposed work would be beneficial for low power high frequency applications. The simulation results presented in this paper were carried out by using 2-D ATLAS.

Enhanced contrast and depth resolution in polarization imaging using elliptically polarized light.

Polarization gating is a popular and widely used technique in biomedical optics to sense superficial tissues (colinear detection), deeper volumes (crosslinear detection), and also selectively probe subsuperficial volumes (using elliptically polarized light). As opposed to the conventional linearly polarized illumination, we propose a new protocol of polarization gating that combines coelliptical and counter-elliptical measurements to selectively enhance the contrast of the images. This new method of eliminating multiple-scattered components from the images shows that it is possible to retrieve a greater signal and a better contrast for subsurface structures. In vivo experiments were performed on skin abnormalities of volunteers to confirm the results of the subtraction method and access subsurface information.