Band Pulse Research Articles

Increasing the two-photon photocurrent saturation limit in a quantum ratchet intermediate band solar cell

A quantum ratchet intermediate band solar cell based on a quantum well superlattice is investigated. The design is similar to that of a previously reported device, but it employs a stronger built-in electric field across the heterojunction; therefore, it works at higher illumination intensities before the photocurrent saturates due to photocarrier accumulation screening out the field and causing leveling of the bands. In this present device, saturation of the two-photon photocurrent occurred at a valence-to-intermediate band pulse energy of ∼4 nJ, approximately ten times greater than the previously reported device, making it more suitable for concentrator applications.

Ultrafast metamaterial all-optical switching based on coherent modulation.

We report a demonstration of an ultrafast all-optical switching with unique light control effects. The all-optical switching consists of a gold film with asymmetric split rings and a silica substrate. The device effectively controls the transmission and absorption of continuous pulses in the communication band (1200-1800 nm) and short pulses with a pulse duration of 80 fs by using the interaction of two coherent beams on nano-metamaterials with a thickness of only 50 nm. The metamaterial can achieve more than 90 % output control under continuous light irradiation. When the pulse duration is 80 fs, the switching contrast ratio is greater than 3 : 1 and the modulation bandwidth is greater than 12.5 THz. Switching time can be on the order of femtosecond. This paper provides a new structure for ultra-high speed optical data processing components in coherent networks.

Fivefold Helically Corrugated Waveguide for High-Power W-Band Gyro-Devices and Pulse Compression

The design, simulation, manufacture, and measurement of a W-band fivefold (5F) helically corrugated waveguide (HCW) is reported. The 5F HCW is based on the coupling of the traveling TE₃₁ and near cutoff TE₂₁ modes to create an operating eigenwave. The fabricated test structure has circular waveguide ports and features elliptical polarizer sections and broadband TE₁₁ to TE₃₁ mode converters on either side of the 5F HCW. The optimized mode converter design, based on a fourfold (4F) HCW, has a predicted power conversion efficiency greater than 90% from 89 to 102.5 GHz, and 96% peak efficiency at 94 GHz. The optimization of the 5F HCW geometry produced an eigenwave suitable for gyro-devices, but the optimization could equally well have been directed to applications such as pulse compression and microwave undulators. Analysis of simulated electric field profiles showed that the propagating power in the 5F HCW was increased by a factor of 6 over that in the 3F HCW at equivalent peak electric field strength. This is due to the larger diameter of the waveguide. Test structures were manufactured through a combination of precision machining of a sacrificial mandrel, copper growth by electroforming followed by removal of the aluminum mandrel by chemically etching. Measurements of the 5F HCW structure's dispersion showed excellent agreement with the prediction over the design range of 90-98 GHz.

Preparation and mode conversion application of narrowband hollow-core anti-resonant fiber

Owing to the unique characteristics of the hollow core fiber(HCF), more and more researchers pay attention to its application. Because the mode field is mainly limited to the core region of the fiber, which results in low non-linearity, ultra-low group velocity dispersion, low temperature sensitivity, and high material damage threshold. Based on the above, the HCF possesses some attractive nonlinear applications such as in transmission of high-power laser beams, sensing, ultra-wide band low-loss transmission, pulse compression and super-continuum generation. Besides, the HCFs can be further divided into the transmitting band-gap photonic crystal fiber(PBG-PCF) and the hollow-core anti-resonant fiber(HC-ARF). Compared with the PBG-PCF, the latter has wide light guiding characteristics caused by leaking modes. According to the research in the recent year, the HC-ARF has gradually approached to the performance of the PBG-PCF in its transmission loss, showing that it has potential applications in communications, sensing, aerospace, high-power laser transmission and other fields in the future. In addition, the HC-ARF with the special light-guiding properties has also become the important photonic device in the fields of fiber filters, mode conversion, etc. In this paper, a hollow-core anti-resonance fiber is studied and its light transmission performance in the spectral range of 500–1500 nm is verified. The optical loss measured at 980 nm wavelength is about 0.32 dB/m. It is found that a 980 nm multi-mode laser beam can be converted into a single-mode one after transmitting through the hollow core fiber we designed.

Research on Preparation and Mode Conversion Application of Narrowband Hollow-core Anti-resonant Fiber

Due to the unique characteristics of the hollow core fiber(HCF), more and more researchers pay attention to its application. Because the mode field is mainly limited to the core region of the fiber, which results in low non-linearity, ultra-low group velocity dispersion, low temperature sensitivity, and high material damage threshold. Based on above, there are some attractive nonlinear applications of the HCF, such as transmission of high-power laser beams, sensing, ultra-wide band low-loss transmission, pulse compression and super-continuum generation. Besides, the HCF can be further divided into the transmitting band-gap photonic crystal fiber(PBG-PCF) and the hollow-core anti-resonant fiber(HC-ARF). Compared with the PBG-PCF, the latter has wider light guiding characteristics caused by leaking modes. According to the research in the recent year, the HC-ARF has gradually approached the performance of the PBG-PCF in its transmission loss which shows that it has potential applications of communications, sensing, aerospace, high-power laser transmission and other fields in the future. In addition, the HC-ARF with the special light-guiding properties has also become the important photonic devices in the fields of fiber filters, mode conversion, etc. In this paper, a hollow-core anti-resonance fiber is studied and its light transmission performance in the spectral range of 500 ~ 1500 nm is verified. The optical loss measured at 980 nm wavelength is about 0.32 db/m. It is founded that a 980nm multi-mode laser beam can be converted into a singe-mode one after transmitting through the hollow core fiber we designed.

Ka-Band 100-kW Subnanosecond Pulse Generator Mode-Locked by a Nonlinear Cyclotron Resonance Absorber

We present the results of experiments on the generation of periodical trains of subnanosecond ${K}_{a}$-band pulses in the electron generator, which is based on passive mode locking. This technique is broadly used in laser physics for the generation of ultrashort pulses (USPs) but has not been previously employed in high-power microwave electronics. The microwave USP generator comprises a helical-waveguide gyrotron traveling wave tube and a saturable absorber in the feedback loop. Saturable absorption is implemented in an auxiliary section using the cyclotron resonance interaction with an initially rectilinear electron beam, for which nonlinear saturation is caused by the effect of the relativistic dependence of the gyrofrequency on the particle's energy. In agreement with theoretical predictions, periodical trains of 0.4-ns pulses with a peak power of 100 kW and repetition of 2.5 ns are measured. Phase coherence of radiated pulses is demonstrated based on analysis of the autocorrelation function. The experiments performed open a wide range of possibilities for the generation of coherent broadband radiation, which is in high demand for numerous applications.

Optical pulses generation of single-cycle and dual-UWB using square and Gaussian electric pulses

- In this paper, a method for generating transverse band (UWB) pulses, the basis of which is a large-scale interferometer with a resonator of small silicone rings capable of changing paired configuration, is reported. Single-cycle, dual-bandwidth signals are generated at the time of the Picosecond pulse, and the small ring amplifier is modulated with square and Gaussian electric pulses, respectively. Microwave photonic systems that work with large optical components suffer from large size, high energy consumption, high cost, and vulnerability to environmental disturbances. Therefore, it is highly desirable to assemble the microwave photonic system on a single chip to make it more compact, cheap, and low-consumption. They have a low spectrum. One of its applications is in short-range wireless telecommunications and high power for wireless transmission of large multimedia data. It can also be used in low speed and power mode for IoT applications such as precision internal positioning. Unlike the WiFi or Bluetooth distance estimation, which is based on signal intensity, the bandwidth signal has a very narrow pulse width, similar to the radar pulse, which enables it to estimate the position using pulse forward time and 10 cm accuracy. With an intensified modulator based on silicon photonics, one can very hopefully generate an adjustable microwave signal on the chip.

Mid-infrared 2.8 µm band laser output and pulse modulation

The mid-infrared 2.8 µm band laser has broad application value and development prospects in the fields of medicine, biology, military and remote sensing. At present, MIR 2.8 µm band lasers are mainly produced by solid-state lasers, fiber lasers, semiconductor lasers and chemical lasers, etc. The pulse modulation methods for this band lasers include electro-optical Q-switching, acousto-optic Q-switching, passive Q-switching, mechanical Q-switching and FTIR Q-switching, etc. The main technical difficulty lies in the discovery and utilization of high-performance and high-quality Q-switching new materials. In this paper, the output methods and pulse modulation methods of 2.8 µm band laser are summarized, and its development situation and existing problems are analyzed and prospected.

A Compact X-Band Microwave Pulse Compressor Using a Corrugated Cylindrical Cavity

Microwave pulse compressors based on a single resonant cavity operating at polarized modes can be super compact, and corrugated structures can transmit high-power, high-frequency microwave with very low loss. We present an $X$ -band (11.424 GHz) pulse compressor using a corrugated cavity with quarter-wavelength depth corrugations working at polarized HE 1-1-14 modes. The cavity has a high-quality factor ( $Q_{0}$ ) of 116 000 with an inner diameter of less than 7 cm and a length of less than 20 cm, which is more compact compared with smooth spherical and cylindrical cavities for equivalent quality factors. The klystron power can be compressed to a peak power of 150 MW in order to feed two high-gradient accelerating structures designed for the Tsinghua Thomson-scattering X-ray Source (TTX). Theory, design, measurements, and the high-power demonstration of the corrugated pulse compressor are presented in detail. Limitations such as breakdowns and temperature rise of using the corrugated structure as a storage element are also further analyzed.

Tutorial for analyzing coherent Raman spectra excited with chirped femtosecond sources

Coherent Raman spectroscopy (CRS) and imaging have been used successfully for the label-free visualization and analysis of functional and endogenous biomolecules in complex biological samples. The interest in implementing these methodologies worldwide in research laboratories has increased in recent years; however, many practical challenges are faced in the implementation process. One of them is identifying from scratch different coherent Raman signals when broadband femtosecond sources are utilized. We present a straightforward methodology to identify and analyze the multiple excited resonant SRS/CARS signals using a simple spectrophotometer in this work to expand the understanding of this particular branch of CRS. The coherent Raman experiments are conducted in the so-called temporal slit configuration using a broadband femtosecond laser source to obtain the excitation pump and Stokes beams and high group velocity dispersion glass to temporally stretch the pulses; but in a non-conventional and non-optimum configuration for CRS experiments neither for spectral focusing (single-frequency measurements) nor for mixing of a broadband pulse with a narrow band pulse (multiplexed detection). Despite that, we demonstrate our methodology's feasibility to extract and analyze complex to discern coherent Raman spectra. We use dimethyl sulfoxide (DMSO) and β-phase barium meta-borate crystal (BBO) and discuss molecular vibrations identified in the spectral range from 300 to 800 cm−1 from both kinds of CRS spectra, stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS).

Innovative Transient Study of Tri-Bandpass Negative Group Delay Applied to Microstrip Barcode-Circuit

A transient study of bandpass (BP) negative group delay (NGD) function is devoted in this paper. The transient analysis is applied to an original topology of NGD barcode-shape microstrip circuit. The performed investigation explains how to realize the transient analysis of tri-band NGD circuit. The time-domain (TD) parametrization of the test is established from the BP-NGD specifications of the circuit under test (CUT) based on the S-parameter model. The input signal is a Gaussian pulse characterized in function of the NGD bandwidth (BW) and center frequency. The feasibility of the BP-NGD transient study is illustrated with experimentation based on ultra-wide band (UWB) pulse generator. As proof-of-concept, barcode NGD circuit exhibiting tri-band NGD value-center frequency-bandwidth, (−5.9 ns, 2.128 GHz, 20 MHz), (−7.4 ns, 2.3 GHz, 14 MHz) and (−4.8 ns, 2.42 GHz, 14 MHz) has been fabricated and tested. The transient simulations and experiences confirm that the output signal envelopes of the barcode NGD prototype present leading and tailing edges in time-advance of input ones when the carrier frequency is set equal to the NGD center frequency.

Novel X -band transverse deflection structure with variable polarization

A collaboration between DESY, PSI and CERN has developed and built an advanced modular X-band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. The prototype of the novel X-band TDS, the polarizable $X$-band (PolariX) TDS, was fabricated at PSI following the high-precision tuning-free production process developed for the C-band Linac of the SwissFEL project. Bead-pull rf measurements were also performed at PSI to verify, in particular, that the polarization of the dipole fields does not have any rotation along the structure. The high-power test was performed at CERN and now the TDS is at DESY and has been installed in the FLASHForward beamline, where the first streaking experience with beam has been accomplished. We summarize in this paper the rf design of the TDS and its key components, such as the $X$-band pulse compressor, E-rotator, and phase shifter, the results of the bead-pull measurements and the high power test and finally the rf setup at DESY.

Proposal of UWB-PPM with Additional Time Shift for Positioning Technique in Nondestructive Environments

The ultra-wide band (UWB) technology has many advantages in positioning and measuring systems; however, powers of UWB signals rapidly reduce while traveling in propagation environments, hence detecting UWB signals are difficult. Various modulation techniques are applied for UWB signals to increase the ability for detecting the reflected signal from transmission mediums, such as pulse amplitude modulation (PAM), pulse position modulation (PPM), and so on. In this paper, we propose an ultra-wide band pulse position modulation technique with optimized additional time shift (UWB-PPM-ATS) to enhance the accuracy in locating buried object in nondestructive environments. Moreover, the Levenberg–Marquardt Fletcher algorithm (LMFA) is applied to determine the medium parameters and buried object location simultaneously. The influences of proposed modulation technique on determining system’s parameters, such as a propagation time, distance, and properties of the medium are analyzed. Calculation results indicate that the proposed UWB-PPM-ATS gives higher accuracy than the conventional one such as UWB-OOK and UWB-PPM in both homogeneous and heterogeneous environments. Furthermore, the LMFA with the proposed UWB-PPM-ATS outperforms the LMFA with the traditional modulation method, especially for unknown propagation environment.

Analysis on nonlinear response of RF filter under ultra wide band pulse environment

The experiments reveal, for the RF filter, the out-off-band transfer property under ultra wide band (UWB) pulses is essentially in agreement with that of continous wave (CW). However, for some frequencies in the in-band of the filter, the transfer function of UWB is much larger than 1. Moreover, the oscillating property is found in the time domain response of the filter. Therefore, based on the nonlinear passive intermodulation (PIM) and the Q-value, the response mechanisms of the filter are studied. The PIM of the filter shows nonlinear effects under the two different field strengths, which results in the limited universality of measurement results. Furthermore, the signal through the filter is predicted by making use of the two measured transfer functions. The predicting results under CW pulse are smaller than the measured ones in energy and peak power. In a word the response mechanisms of the filter under UWB pulse does differ from the that under CW pulse, i. e., the measured results of CW can’t be applied for the UWB effect analysis and evaluation.

High power RF operations studies at TARLA facility

Turkish Accelerator and Radiation Laboratory (TARLA) is a facility capable of accelerating an electron beam up to 40 MeV. Two beamlines were proposed to generate free-electron laser radiation and bremsstrahlung. The accelerator employs two normal conducting cavities, so-called buncher cavities: subharmonic buncher (SHB) and fundamental buncher (FB), and two cryomodules that house two TESLA cavities each. SHB operates in 260 MHz and FB in 1.3 GHz, and is powered by 1.5 kW and 500 W radio frequency (RF) amplifiers, respectively. Each TESLA cavity is driven by 18 kW saturated high-power solid-state amplifiers (SSA). In addition, a L band pulse compressor system is designed and implemented at the facility to actively promote high-power RF research. Currently, setup of a resonant ring test bench is approved to test the RF components under high power RF conditions. This paper describes the TARLA high power RF, RF controller, and network structures. High power tests and measurements of the RF components of the TARLA beamline are given. Outcomes from the operation of the L band pulse compressor are explained, and the resonant ring test stand is stated as a summary.

P6541Wrist band photoplethysmography pulse morphology-based autocorrelation analysis enables atrial fibrillation detection without the need of pulse detection

Abstract Background Atrial fibrillation (AF) is often asymptomatic and intermittent making its detection a major clinical challenge. A photoplethysmography (PPG) wrist band with algorithm-based detection of AF provides a promising solution for screening of AF. However, the shapes of individual pulse waveforms vary in AF decreasing pulse detection accuracy. Purpose The purpose of this study was to evaluate the utility of PPG wrist band pulse morphology in detection of AF. Methods A 5-minute PPG was recorded with a PPG wrist band from patients with AF or sinus rhythm. A simultaneously registered ECG served as the golden standard for the rhythm analysis and was interpreted by two cardiologists. In addition to using the inter-beat-interval (IBI) based AFEvidence algorithm in comparison, we extracted a feature straight from the PPG signal, without the need of pulse detection. This feature was calculated as the average of absolute autocorrelation values over different lags. The feature describes the regularity of the PPG signal and is decreased if the shape and periodicity of pulse waves vary. The performance of this PPG morphology-based method in detection of AF was evaluated and compared to the AFEvidence. Results The study population consisted of 213 patients (106 AF, 107 sinus rhythm). The sensitivity and specificity of PPG morphology-based autocorrelation AF detection method were 98.1% and 94.4%. For AFEvidence, the sensitivity and specificity were 96.2% and 98.1%, respectively (p=0.146 between the methods, McNemar test). PPG samples of AF and sinus rhythm Conclusions The PPG morphology-based autocorrelation method detects AF with good accuracy without the need of pulse detection. The method seems promising in detection of AF and should be studied further. Acknowledgement/Funding None

Compensation of Dispersion in Sinuous Antennas for Polarimetric Ground Penetrating Radar Applications

In order to improve the accuracy of subsurface target classification with ground penetrating radar (GPR) systems, it is desired to transmit and receive ultra-wide band pulses with varying combinations of polarization (a technique referred to as polarimetry). The sinuous antenna exhibits such desirable properties as ultra-wide bandwidth, polarization diversity, and low-profile form factor, making it an excellent candidate for the radiating element of such systems. However, sinuous antennas are dispersive since the active region moves with frequency along the structure, resulting in the distortion of radiated pulses. This distortion may be compensated in signal processing with accurately simulated or measured antenna phase information. However, in a practical GPR, the antenna performance may deviate from that simulated, accurate measurements may be impractical, and/or the dielectric loading of the environment may cause deviations. In such cases, it may be desirable to employ a simple dispersion model based on antenna design parameters which may be optimized in situ. This paper explores the dispersive properties of the sinuous antenna and presents a simple, adjustable, model that may be used to correct dispersed pulses. The dispersion model is successfully applied to both simulated and measured scenarios, thereby enabling the use of sinuous antennas in polarimetric GPR applications.

Detection of HV Winding Radial Deformation and PD in Power Transformer Using Stepped-Frequency Hyperboloid Method

Detection of winding deformation and partial discharge (PD) is essential for monitoring and failure risk assessment of power transformers. Recently, an online method based on electromagnetic waves has been proposed for detecting radial deformation (RD) in high-voltage (HV) transformer winding using ultra wide band pulses, called the hyperboloid method. In this method, a short pulse is transmitted toward HV winding and its reflection captured using a set of antennas. By comparing and analyzing signals in sound and deformed conditions, the RD can be detected. On the other hand, signals radiated from PD defect in transformers are generally appeared in the range of UHF band (0.3–3-GHz frequencies). In this paper, the hyperboloid method is proposed for implementation in UHF band, and the PD effect on the result of the hyperboloid method is investigated. Thus, a set of UHF sensors can be used for the detection of PD and detection and localization of RD defect. Results show that PD signals can affect the signal of the hyperboloid method and lead to wrong localization of RD. In order to solve this problem, the UHF stepped-frequency method is proposed, utilized, and tested on the HV winding of a 1.6-mega volt ampere (MVA) distribution transformer. Experimental results show the capability of the proposed method for detecting both defects using only one set of UHF antennas.

Chirp echo Fourier transform EPR-detected NMR

A new ultra-wide band (UWB) pulse EPR method is introduced for observing all nuclear frequencies of a paramagnetic center in a single shot. It is based on burning spectral holes with a high turning angle (HTA) pulse that excites forbidden transitions and subsequent detection of the hole pattern by a chirp echo. We term this method Chirp Echo Epr SpectroscopY (CHEESY)-detected NMR. The approach is a revival of FT EPR-detected NMR. It yields similar spectra and the same type of information as electron-electron double resonance (ELDOR)-detected NMR, but with a multiplex advantage. We apply CHEESY-detected NMR in Q band to nitroxides and correlate the hyperfine spectrum to the EPR spectrum by varying the frequency of the HTA pulse. Furthermore, a selective π pulse before the HTA pulse allows for detecting hyperfine sublevel correlations between transitions of one nucleus and for elucidating the coupling regime, the same information as revealed by the HYSCORE experiment. This is demonstrated on hexaaquamanganese(II). We expect that CHEESY-detected NMR is generally applicable to disordered systems and that our results further motivate the development of EPR spectrometers capable of coherent UWB excitation and detection, especially at higher fields and frequencies.

Two-Wave Cherenkov Oscillator With Moderately Oversized Slow-Wave Structure

This paper describes a new design of a relativistic Cherenkov oscillator with strong modulation of the e-beam current at the input of two-sectioned slow-wave structure, as well as numerical and experimental results on generation of few gigawatt-level $X$ -band pulses with pulse duration of up to 35 ns. Due to special phase shift between two sections and electrodynamic coupling between $E_{01}$ surface wave and $E_{02}$ volume mode, the first one is locked at the upper boundary of the passband and the second one gains more transparency. An electron beam can interact simultaneously with two waves with higher power conversion efficiencies, which in simulations amount up to 47% and 30% for high (~4 T) and low (~1 T) guiding magnetic fields, correspondingly. The tests of the geometry optimized in simulations were performed on the base of SINUS-7 high-current electron accelerator in the diode voltage range of 400–850 kV and current from 7 to 16 kA. The repeated and full-pulsewidth generation of about 1.5-GW microwave power is achieved only in the low magnetic field. The pulse shortening and the mode competition took place in the strong magnetic field. The results are considered as preliminary for creation of the efficient relativistic millimeter-wave oscillators at magnetic fields below the cyclotron resonance.