Low Peak Power Research Articles

Protonation tuned dipolar order mediated 1H→13C cross-polarization for dissolution-dynamic nuclear polarization experiments

A strategy of dipolar order mediated nuclear spin polarization transfer has recently been combined with dissolution-dynamic nuclear polarization (dDNP) and improved by employing optimized shaped radiofrequency pulses and suitable molecular modifications. In the context of dDNP experiments, this offers a promising means of transferring polarization from high-gamma 1H spins to insensitive 13C spins with lower peak power and lower energy compared with state-of-the-art cross-polarization schemes. The role of local molecular groups and the glassing matrix protonation level are both postulated to play a key role in the polarization transfer pathway via an intermediary reservoir of dipolar spin order. To gain appreciation of the mechanisms involved in the dipolar order mediated polarization transfer under dDNP conditions, we investigate herein the influence of the pivotal characteristics of the sample makeup: (i) revising the protonation level for the constituents of the DNP glass; and (ii) utilizing deuterated molecular derivatives. Experimental demonstrations are presented for the case of [1–13C]sodium acetate. We find that the proton sample molarity has a large impact on both the optimal parameters and the performance of the dipolar order mediated cross-polarization sequence, with the 13C signal build-up time drastically shortened in the case of high solvent protonation levels. In the case of a deuterated molecular derivative, we observe that the nearby 2H substituted methyl group is deleterious to the 1H→13C transfer phenomenon (particularly at low levels of sample protonation). Overall, increased solvent protonation makes the dipolar order governed polarization transfer significantly faster and more efficient. This study sheds light on the influential sample formulation traits which govern the dipolar order-controlled transfer of polarization and indicates that the polarization transfer efficiencies of deuterated molecules can be boosted and reach high performances simply by adequate solvent protonation.

Tunable Dual-Wavelength Bismuth Fiber Laser With 37.8-GHz Frequency Spacing

A tunable dual-wavelength Brillouin-bismuth fiber laser with a triple-Brillouin frequency spacing of ∼37.8 GHz was demonstrated by employing modular structures. The modular designs can be divided into two main cavities, whereby cavity 1 consisted of a 2-km single-mode fiber (SMF) and a loop mirror that was able to generate a single-spaced Brillouin shift, while cavity 2 comprised of 10-km dispersion compensating fiber (DCF) that was able to produce a double-spaced Brillouin shift. Based on this design, a stable dual-wavelength lasing was established with a low peak power fluctuation of 0.13 dB and 0.6 dB for the Brillouin pump (BP) and third Brillouin Stokes line (BS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ), respectively. By varying the center wavelength of the Brillouin pump, the dual-wavelength laser can be tuned across a 40 nm span, ranging from 1300 nm to 1340 nm. The frequency spacing of the Brillouin-bismuth fiber laser can also be easily switched between ∼12.6 GHz, ∼25.2 GHz, and ∼37.8 GHz by utilizing these modular structures. The proposed dual-wavelength laser has a promising potential for application as a low phase noise source for microwave generation.

On the Achievable Rate and Capacity for a Sample-Based Practical Photon-Counting Receiver

We investigate the achievable rate and capacity of a non-perfect photon-counting receiver. For the case of long symbol duration, the achievable rate under on-off keying modulation is investigated based on Kullback-Leibler (KL) divergence and Chernoff $\alpha$-divergence. We prove the tightness of the derived bounds for large peak power with zero background radiation with exponential convergence rate, and for low peak power of order two convergence rate. For large peak power with fixed background radiation and low background radiation with fixed peak power, the proposed bound gap is a small positive value for low background radiation and large peak power, respectively. Moreover, we propose an approximation on the achievable rate in the low background radiation and long symbol duration regime, which is more accurate compared with the derived upper and lower bounds in the medium signal to noise ratio (SNR) regime. For the symbol duration that can be sufficiently small, the capacity and the optimal duty cycle are is investigated. We show that the capacity approaches that of continuous Poisson capacity as $T_s=\tau\to0$. The asymptotic capacity is analyzed for low and large peak power. Compared with the continuous Poisson capacity, the capacity of a non-perfect receiver is almost lossless and loss with attenuation for low peak power given zero background radiation and nonzero background radiation, respectively. For large peak power, the capacity with a non-perfect receiver converges, while that of continuous Poisson capacity channel linearly increases. The above theoretical results are extensively validated by numerical results.

An optical parametric Bragg amplifier on a CMOS chip

Abstract We demonstrate a complementary metal–oxide–semiconductor (CMOS)-compatible optical parametric Bragg amplifier on an ultra-silicon-rich nitride chip. The amplifier design incorporates advantageous group index properties in a nonlinear Bragg grating to circumvent phase matching limitations arising from the bulk material and waveguide dispersion. The grating structure further augments the effective nonlinear parameter of 800 W−1/m, considerably lowering the power required for the observation of strong parametric gain. On/off optical parametric gain of 20 dB is achieved using a low peak power of 1.6 W, in good agreement with numerical calculations. This represents a 7 dB improvement in the parametric gain compared to the absence of grating enhancement which is attributed to the Bragg grating induced superior phase matching.

On the Development of a Low Peak-Power, High Repetition-Rate Laser Plasma Accelerator at IPEN

On the Development of a Low Peak-Power, High Repetition-Rate Laser Plasma Accelerator at IPEN

Single and combined effect of kinesio tape and warm-up on sprint cycling performance

BackgroundThe fact that kinesio tape may be capable to enhance muscle power would qualify it as practical tool to be considered during passive warm-up (WU) or coupled with active WU processes prior to power-based performance. Therefore, the aim of this study was to investigate the single and combined effect of kinesio tape (KT) and WU on sprint cycling performance.MethodsIn a repeated measure design, fifteen participants underwent six sessions to assess sprint cycling performance involving a combination of three taping conditions (without KT: NoKT; with KT positioned vertically over the thigh muscles KT; with KT positioned horizontally over the thigh muscles: Sham) with two pre-exercise routines (with WU: WU; without WU: NoWU) in a randomized order. Allometric scaling of peak power (PP) and average power (AP) values were considered for each sprint.ResultsKT-WU demonstrated the highest PP and AP with respect to the other conditions (p < 0.05), except for AP that was similar to Sham-WU (p > 0.05). Moreover, NoKT-NoWU showed the lowest PP and AP with respect to the other conditions (p < 0.05).ConclusionsOverall, our findings suggest that kinesio tape might be a possible tool to be combined with an active WU routine, inducing benefit on sprint performance. Moreover, KT may be considered a potential strategy to include within a passive WU, perhaps where an active WU is not feasible. However, as the influence of KT on muscle function is still unclear, our results should not be overinterpreted.

Boosting dissolution-dynamic nuclear polarization by multiple-step dipolar order mediated 1H→13C cross-polarization

Dissolution-dynamic nuclear polarization can be boosted by employing multiple-contact cross-polarization techniques to transfer polarization from 1H to 13C spins. The method is efficient and significantly reduces polarization build-up times, however, it involves high-power radiofrequency pulses in a superfluid helium environment which limit its implementation and applicability and prevent a significant scaling-up of the sample size. We propose to overcome this limitation by a stepwise transfer of polarization using a low-energy and low-peak power radiofrequency pulse sequence where the 1H→13C polarization transfer is mediated by a dipolar spin order reservoir. An experimental demonstration is presented for [1-13C]sodium acetate. A solid-state 13C polarization of ∼43.5% was achieved using this method with a build-up time constant of ∼5.1 minutes, leading to a ∼27.5% 13C polarization in the liquid-state after sample dissolution. The low-power multiple-step polarization transfer efficiency achieved with respect to the most advanced and highest-power multiple-contact cross-polarization approach was found to be ∼0.69.

Terahertz irradiation effects on the morphology and dynamics of actin biopolymer

Our recent experimental research on terahertz (THz) irradiation of actin filaments, which serve as representative biopolymer materials, is summarized in this review. We found that pulsed THz waves with energy density of ∼10−4 J cm−2 (∼108 W cm−2 at the peak) generate acoustic waves efficiently in the aqueous media. These acoustic waves propagated deeply into the water and demolished the actin filaments in living HeLa cells that were submerged into the cell culture medium. The results implied that THz pulsed irradiation affects the biomolecules in the tissues, even if these molecules are located a few millimeters away from the body surface. In contrast, irradiation using THz waves with lower peak power of the order of ∼W cm−2 induces the elongation of the actin biopolymer without thermal or acoustic effects. The polymerization of actin molecules plays essential roles in cell motility, growth, differentiation and gene expression. Therefore, our results indicate that THz waves could be applicable to artificial manipulation of cellular functions.

All-optical coherent pulse compression for dynamic laser ranging using an acousto-optic dual comb.

We demonstrate a new and simple dynamic laser ranging platform based on analog all-optical coherent pulse compression of modulated optical waveforms. The technique employs a bidirectional acousto-optic frequency shifting loop, which provides a dual-comb photonic signal with an optical bandwidth in the microwave range. This architecture simply involves a CW laser, standard telecom components and low frequency electronics, both for the dual-comb generation and for the detection. As a laser ranging system, it offers a range resolution of a few millimeters, set by a dual-comb spectral bandwidth of 24 GHz, and a precision of 20 µm for an integration time of 20 ms. The system is also shown to provide dynamic measurements at scanning rates in the acoustic range, including phase-sensitive measurements and Doppler shift velocimetry. In addition, we show that the application of perfect correlation phase sequences to the transmitted waveforms allows the ambiguity range to be extended by a factor of 10 up to ∼20 m. The system generates quasi-continuous waveforms with low peak power, which makes it possible to envision long-range telemetry or reflectometry requiring highly amplified signals.

Selection of laser pulse width for efficient generation of photoacoustic signals in liquid-filled thin capillary embedded in soft material

To design an instrumentation system for evaluating contrast agents of photoacoustic imaging, the optimal pulse width of the excitation laser is discussed in this paper. A pulsed semiconductor laser with a moderate pulse width (15–129 ns) and low peak power (1 W) is adopted in the proposed system. Black ink is selected as the reference sample, which is filled in a glass capillary embedded in a soft phantom. Our aim is that the pulse width matches the acoustic resonance of the target and the center frequency of the receiving transducer (5 MHz) to obtain sufficient strength of the ultrasonic signal with minimal laser power. A series of experiments reveal a clear relationship between the laser pulse width and the maximal amplitude of the resonance mode. Acoustic resonance occurs inside the capillary whose frequencies can be precisely predicted as the radial eigen mode. The laser pulse width and concentration of the sample showed little influence on these resonance frequencies as expected. To efficiently utilize the signal enhancement effect due to the resonance, several resonance mode candidates are investigated and discussed. It then becomes clear that the second angular and zeroth radial order mode is useful for capillaries with sub-millimeter inner diameters. It was demonstrated that the concentration of samples had very limited influence on the frequencies. Finally, consideration based on two delayed attenuating vibrations is successfully conducted to explain the experimental results.

Small All-Range Lidar for Asteroid and Comet Core Missions

We report the development of a new type of space lidar specifically designed for missions to small planetary bodies for both topographic mapping and support of sample collection or landing. The instrument is designed to have a wide dynamic range with several operation modes for different mission phases. The laser transmitter consists of a fiber laser that is intensity modulated with a return-to-zero pseudo-noise (RZPN) code. The receiver detects the coded pulse-train by correlating the detected signal with the RZPN kernel. Unlike regular pseudo noise (PN) lidars, the RZPN kernel is set to zero outside laser firing windows, which removes most of the background noise over the receiver integration time. This technique enables the use of low peak-power but high pulse-rate lasers, such as fiber lasers, for long-distance ranging without aliasing. The laser power and the internal gain of the detector can both be adjusted to give a wide measurement dynamic range. The laser modulation code pattern can also be reconfigured in orbit to optimize measurements to different measurement environments. The receiver uses a multi-pixel linear mode photon-counting HgCdTe avalanche photodiode (APD) array with near quantum limited sensitivity at near to mid infrared wavelengths where many fiber lasers and diode lasers operate. The instrument is modular and versatile and can be built mostly with components developed by the optical communication industry.

Stable to unstable differences in force–velocity-power profiling during chest presses and squats

Despite several studies investigating the effect of instability resistance exercises on neuromuscular performance, the force–velocity-power characteristics of muscles involved in lifting tasks and the underlying mechanisms have not been fully explored. This study investigates power-velocity and force–velocity relationships during resistance exercises performed on stable and unstable surfaces with different weights. A group of 63 physically active young men performed chest presses on the bench and Swiss ball, and squats on the firm surface and BOSU ball with weights from 20 kg to at least 85% of one-repetition maximum. Peak and/or mean values of power, velocity and force were analyzed. Results showed significantly lower peak power and force during chest presses on the Swiss ball as opposed to the bench at lower velocities (147.6 W and 176.0 N at 1.1 m·s−1, 108.7 W and 126.4 N at 1.3 m·s−1, 112.0 W and 72.7 N at 1.5 m·s−1; all at p < 0.01). Their values produced at lower velocities were also significantly lower during squats on the BOSU ball when compared to the firm surface (232.2 W and 257.1 N at 1.1 m·s−1, 228.2 W and 173.3 N at 1.2 m·s−1, 245.1 W and 156.8 N at 1.3 m·s−1, 254.5 W and 113.5 N at 1.4 m·s−1; all at p < 0.05). These significant differences between power produced during stable and unstable resistance exercises at lower velocities (or at higher loads) have to be taken into account in sports that require production of a high force in a short time. Because of the variable loading patterns under unstable conditions, it is necessary to quantify the optimal exercise load for each individual athlete.

Ultra-broadband mid-infrared supercontinuum generation in photonic-crystal pillar waveguides pumped at 1.82 μm

In this paper, we theoretically investigate the supercontinuum generation (SCG) spanning from near-infrared (NIR) to mid-infrared utilizing a novel photonic-crystal pillar waveguide (PCPW). The PCPW design and associated dispersion properties have been thoroughly studied and optimized, resulting in a flat and low dispersion profile from 1.67 to 7.31 µm with four zero dispersion wavelengths. Pumped at a relatively shorter NIR wavelength of 1.82 µm, the SCG of optimized PCPW possesses an ultra-broadband spectral broadening from 1 to 10 µm under pump pulses with a low peak power of 2 kW. The proposed PCPW can thus provide an efficient waveguide structure to generate ultra-broadband supercontinuum pumped by shorter wavelength laser sources of less peak power.

Experimental Study on Km-Range Long-Distance Measurement Using Silicon Photomultiplier Sensor with Low Peak Power Laser Pulse

Silicon photomultipliers (SiPM) have drawn considerable attention due to their superior sensitivity with a multi-pixel matrix structure. SiPM can be the choice of a detector for time of flight measurement which is one of the most promising applications in the field of light detection and ranging (LiDAR). In this work, we take advantage of SiPM and attempt to measure longer distances with a low peak power semiconductor laser under outdoor sunny and windy conditions. We achieved a long detection range of a few kilometers by using SiPM and a laser with a pulse energy of 9 µj at 0.905 µm and 3 dB enhancement in signal to noise ratio (SNR) by the implemented signal extraction algorithm. From the simulation performed, the minimum SNR value and detection probability were also determined for the outdoor field tests.

Energy Management Strategies for Hybrid Power Systems Considering Dynamic Characteristics of Power Sources

Due to the rising concern of environmental problems, fuel cell hybrid power systems have been proposed to be an ideal substitution to diesel engines. However, the hybrid power system has brought many challenges, one of which is the power splitting among different power generation technologies. In this paper, a wavelet transform and fuzzy logic based energy management strategy is proposed for a fuel cell/battery/ultra-capacitor hybrid power cruiser considering their dynamic characteristics. The energy demand of the cruiser is decoupled into different frequencies by wavelet transform and distributed to different energy sources according to their dynamic characteristics. To ensure long-term reliable operation of the hybrid power system, fuzzy logic is proposed to keep the state of charges of the battery and ultra-capacitor within safe range. The proposed energy management strategy is applied to a hybrid power cruiser in MATLAB/Simulink and two cases are studied considering different initial states of charge of the energy storage system. The results show that the proposed energy management strategy enables the fuel cell to supply about 50% of the high frequency power and reduce the peak power supplied by the fuel cell by 80% - 100% when the initial state of charge of the ultra-capacitor is low, and the fuel cell supplies around 400% higher than the low peak power and 20% of the high peak power when the initial state of charge of the battery is low.

Compact long-working-distance laser-diode-based photoacoustic microscopy with a reflective objective

Photoacoustic microscopy (PAM) has quickly developed into a noninvasive biomedical imaging technique to achieve detection, diagnosis, and monitoring. Compared with Q-switched neodymium-doped yttrium aluminum garnet or optical parametric oscillator lasers, a low-cost and small-size laser diode (LD) used as an alternative light source is conducive to achieving the miniaturization and integration for preclinical transformation. However, the LD’s low peak output power needs the high numerical aperture objective to attain tight focus, which limits the working distance (WD) of the system in only 2–3 mm, resulting in not achieving the backward coaxial confocal mode. Here, we present a compact visible LD-based PAM system with a reflective objective to achieve a 22 mm long WD and a 10 µm lateral resolution. Different depth subcutaneous microvascular networks in label-free mouse ears have successfully reappeared in vivo with a signal-to-noise ratio up to 14 dB by a confocal alignment. It will be a promising tool to develop into a handy tool for subcutaneous blood vessel imaging.

PTS-PAPR Reduction Technique for 5G Advanced Waveforms Using BFO Algorithm

Non-orthogonal multiple access (NOMA) will play an imperative part in an advanced 5G radio arrangement, owing to its numerous benefits such as improved spectrum adeptness, fast data rate, truncated spectrum leakage, and, so on. So far, NOMA undergoes from peak to average power ratio (PAPR) problem, which shrinks the throughput of the scheme. In this article, we propose a hybrid method, centered on the combination of advanced Partial transmission sequence (PTS), Selective mapping (SLM), and bacteria foraging optimization (BFO), known as PTS-BFO and SLM-PTS. PTS and SLM are utilized at the sender side and divide the NOMA into several sub-blocks. An optimal phase factor is achieved by the BFA and combined with the NOMA sub-block, where a low peak power value is obtained. Further, we estimate the bit error rate (BER) and PAPR of BFA in the SLM and PTS technique. The simulation outputs reveal that the PTS-BFO outperforms the traditional peak power minimization approaches and moderates the complexity of the system. It is concluded that the proposed algorithm is not explored for the NOMA waveform.

Detection of slags in structural steel sample using InfraRed thermal wave imaging

The estimation of defects in any material is a critical problem in the domain of InfraRed thermography (IRT). The paper presents simulation aspects of three-dimensional heat transfer model for a finite thickness structural steel sample having six different slag inclusions using a low peak power frequency modulated thermal wave imaging (FMTWI) and its digital counterpart digitized frequency modulated thermal wave imaging (DFMTWI) technique. The sample surface is subjected to proposed thermal heat flux and defect analysis was carried out by studying the thermal gradient over the test sample surface. Further, time domain pulse compression approach allowing better defect depth analysis has been discussed to evaluate the correlation coefficients and time delays for the proposed approaches. Results show better performance of the DFMTWI approach with high correlation coefficient values for all the defects with low time delays than the FMTWI approach.

Defect Detection Capabilities of Pulse Compression Based Infrared Non-Destructive Testing and Evaluation

Infrared Thermography is one of the widely used method for non-destructive testing and evaluation methods due to its merits (remote, full field, safe and quantitative inspection capabilities) for testing and evaluation of wide variety of materials (metals, semiconductors and composites). Among the various thermal non-destructive evaluation modalities such as pulse based and mono frequency excited modulated lock-in thermography, recently proposed matched filter based non-periodic infrared thermographic approaches gained their importance due to superior test resolution and sensitivity for detection of defects hidden inside the test material. Further, feasibility to implement with low peak power heat sources in moderate experimentation time in comparison with conventional (pulse based thermographic techniques and in a limited span of time in comparison with mono frequency lock-in) thermographic techniques makes these pulse compression favorable techniques more economical and reliable. The present manuscript demonstrates the advantages of pulse compression favorable frequency modulated thermal wave imaging approach for identification of flat bottom holes in a glass fibre reinforced polymer material. The obtained results have been compared with widely used principal component thermography by taking the signal to noise ratio as a figure of merit.

Estimation of Modulation Parameters of LPI Radar Using Cyclostationary Method

Low Probability of intercept (LPI) radars work on the principle of low peak-power and wide bandwidth. To achieve this, the LPI radars use special type of modulated waveforms which are difficult to intercept. The main tasks of intercept receivers are to detect, estimate and classify LPI signals even in the presence of high noise. Accurate estimation of the modulation parameters also provides information about threat to radar so that necessary counter measures could be initiated against the enemy radars. In the present work, Cyclo-stationary (CS) method is used to estimate the parameters of Polytime coded LPI signals. CS method is efficient for the analysis of periodic waveforms like LPI signals and finds applications in many fields such as array signal processing, estimation of direction of arrival, signal detection. Cyclic auto correlation function and the spectral correlation density function (SCD) which are the basis for CS analysis are computed for all the four types of polytime codes. Generation of all the four types of Polytime codes and computation of SCD coefficients are carried out using MATLAB. From the contour plot of SCD function, the parameters carrier frequency, bandwidth and code rate are measured. It is assumed that the received signal is not corrupted with any noise. The simulation results are compared with the values available in the literature. The maximum error of estimation is well within ± 6% for all the codes in the proposed method whereas the maximum error reported in the literature is 25.7%. Hence the proposed method is better. Since CS method is sensitive to sampling frequency, the analysis is repeated for three different sampling frequencies and in all cases, the estimation error is less than 6%.