On the Polishing Effect of Nanosecond Discharges in Vacuum

When a metal surface in ultra high vacuum is subjected to electric discharges with a sufficiently short duration the surface becomes perfectly smooth. This polishing is caused by the inertia of the molten metal within a cathode spot that prevents the formation of a crater by acceleration of the liquid. The present paper reports an investigation of this phenomenon in dependence on the discharge parameters. The effect was found to be determined by the pulse duration, it occurs with pulses of less than 10 nanoseconds. But also long discharges of 500 ns show a polishing if the current rise rate is below a critical value (0.5 — 1 A/ns), depending on the cathode material. Thus long discharges consist of elementary steps of about 10 ns duration, in accordance with the formation time of cathode craters. The polishing effect causes an abrupt decrease of the breakdown probability of rectangular high voltage pulses from one to zero at a critical pulse duration.     

Theoretical and experimental investigations of a passively mode-locked Nd: Glass laser

The presented theoretical model for a mode-locked Nd-glass laser simultaneously takes into account dynamics of the mode-locking dye, amplification saturation and radiation background. A systematic variation of laser parameters gives insight into the pulse formation process and allows to improve the laser design. The calculations show that it should be possible to decrease considerably the duration of light pulses of a mode-locked Nd-glass laser. Using a new mode-locking dye with a switching time of τ=2.7×10⁻¹² s we obtained stable laser operation and a pulse duration of 1.7×10⁻¹²s.     

A 532 nm molecular iodine optical frequency standard based on modulation transfer spectroscopy

We report construction of an iodine-stabilized laser frequency standard at 532 nm based on modulation transfer spectroscopy(MTS) technology with good reproducibility. A frequency stability of 2.5 × 10~(-14) at 1 s averaging time is achieved,and the frequency reproducibility has a relative uncertainty of 3.5×10~(-13), demonstrating the great stability of our setup.The systematic uncertainty of the iodine-stabilized laser frequency standard is evaluated, especially the contribution of the residual amplitude modulation(RAM). The contribution of the RAM in MTS cannot be evaluated directly. To solve this problem, we theoretically deduce the MTS signal with RAM under large modulation depth, and prove that the nonsymmetric shape of the MTS signal is directly related to the MTS effect. The non-symmetric shape factor r can be calibrated with a frequency comb, and in real experiments, this r value can be obtained by least-squares fitting of the MTS signal,from which we can infer the RAMinduced frequency shift. The full frequency uncertainty is evaluated to be 5.3 k Hz(corresponding to a relative frequency uncertainty of 9.4×10~(-12)). The corrected transition frequency has a difference from the BIPM-recommended value of 2 k Hz, which is within 1σ uncertainty, proving the validity of our evaluation.     

Rapid annealing of Fe-Si-B amorphous tapes by joule heating: Effects on magnetic and mechanical properties

We report a systematic study of relaxation effects in Fe-Si-B amorphous tapes rapidly annealed for short time at T≈800 K by Joule heating. It is found that this type of annealing in air can result in nearly the same degree of relaxation as obtained by two hours of conventional relaxation annealing in a furnace under inert gas or vacuum. The extent of relaxation as a function of current density and duration has been assessed by high precision calorimetric measurements and found to be highly reproducible. The effect of such rapid annealing on magnetic and mechanical properties are compared to those of conventional relaxation annealing for two hours at 655 K and found to be advantageous.     

Effects of the switching time in OPS/OBS networks

In this paper we present an analytical model, which considers the effects of the switching time on the network performance in service differentiated optical packet/burst switching (OPS/OBS) networks. Our results indicate that the switching time must be less than 10 % of the packet/burst duration in order to avoid any significant reductions in the network performance. Furthermore, regarding a network with full wavelength conversion, we show that the benefits of statistical resource sharing are almost non-existent for low priority traffic when the switching time is large.     

Localization of sound in rooms, III: Onset and duration effects

The steady-state sound field of a sine tone does not provide useful localization information in a room. Nevertheless, listeners can localize a sine tone in a room if it has an onset transient which allows the precedence effect to operate. In the present study, we made a quantitative assessment of onsets and the precedence effect by systematically varying onset duration from 0 s (impulsive), where the precedence effect is maximal, to 5 s, where there is no precedence effect at all. We also assessed listeners' sensitivity to the steady-state sound field under impulsive conditions by varying the total duration of tone pulses. Our experiments were conducted in a room with a single acoustical reflection having various directions and delays, and in an anechoic room. The results for tones of various frequencies (500 and 2000 Hz) and sound-pressure levels (65 and 40 dBA) indicate the following: Localization in rooms is facilitated by onsets even if the onsets are as long as 100 ms. The facilitation depends upon the peak intensity of the tone, as well as the onset duration, suggesting that onset rate is critical for the precedence effect; our results are most consistent with rate expressed as an increase in sound pressure per unit time. The facilitation also depends upon the reflection delay time for a room; gradual onsets take on much more importance for the precedence effect in rooms with long delays. As onsets begin to lose their effectiveness listeners become increasingly "misdirected" by invalid cues in the steady-state sound field. The pattern of misdirection suggests a perceptual averaging of cues over an interval more than an order of magnitude longer than previous estimates of the summation window for the precedence effect. The pattern of misdirection varies with the frequency of a tone, due to frequency-dependent interference effects in a room, but it is independent of signal level. Localization of an impulsive sine tone in rooms is very insensitive to the pulse duration; this suggests that binaural inhibition models of the precedence effect must be supplemented by an evaluative component that we term the "plausibility hypothesis."     

Errors in the Measurement of Cross-Correlated Relaxation Rates and How to Avoid Them

Cross-correlated relaxation rates Γ are commonly obtained from constant time experiments by measuring the effect of the desired cross-correlated relaxation on an appropriate coherence during the constant time T. These measurements are affected by systematic errors, which derive from undesired cross-correlated relaxation effects taking place before and after the constant time period T. In this paper we discuss the sources and the size of these errors in an example of two pulse sequences. Higher accuracy of the measured data can be obtained by recording a set of experiments with different T values. Cross-correlated relaxation rates are measured in constant time experiments either from the differential relaxation of multiplet components (J-resolved Γ experiments) or from the efficiency of magnetization transfer between two coherences (quantitative Γ experiments). In this paper we calculate analytically the statistical errors in both J-resolved and quantitative Γ experiments. These formulae provide the basis for the choice of the most efficient experimental approach and parameters for a given measurement time and size of the rate. The optimal constant time T for each method can be calculated and depends on the relaxation properties of the molecule under investigation. Moreover, we will show how to optimize the relative duration of cross and reference experiments in a quantitative Γ approach.     

Space charge effect and mirror charge effect in photoemission spectroscopy

We report the observation and systematic investigation of the space charge effect and mirror charge effect in photoemission spectroscopy. When pulsed light is incident on a sample, the photo-emitted electrons experience energy redistribution after escaping from the surface because of the Coulomb interaction between them (space charge effect) and between photo-emitted electrons and the distribution of mirror charges in the sample (mirror charge effect). These combined Coulomb interaction effects give rise to an energy shift and a broadening which can be on the order of 10 meV for a typical third-generation synchrotron light source. This value is comparable to many fundamental physical parameters actively studied by photoemission spectroscopy and should be taken seriously in interpreting photoemission data and in designing next generation experiments.     

可搬运锶光晶格钟系统不确定度的评估

可搬运光学原子钟在科学研究和工程应用中具有重要意义.本文测量了可搬运87Sr光晶格钟系统的主要频移,包括黑体辐射频移、碰撞频移、晶格光交流斯塔克频移、二阶塞曼频移等.首先实验上测量了磁光阱腔体表面的温度分布,分析了不同热源对原子团的影响,得到黑体辐射总的相对频移修正量为50.4×10^-16.相对不确定度为5.1×10^-17.然后利用分时自比对方法,评估了碰撞频移、晶格光交流斯塔克频移和二阶塞曼频移.结果表明,由黑体辐射引起的频移量最大,晶格光交流斯塔克频移的不确定度最大,系统总的相对频移修正量为58.8×10^-16,总不确定度为2.3×10^-16.该工作为可搬运87Sr光晶格钟之后的性能提升和应用提供了条件.     

Systematic treatment of fluctuations in a nonlinear oscillator

A systematic expansion method is developed to account for the effect of fluctuations on the motion of a damped Duffing oscillator. The expansion parameter α is the magnitude of the fluctuations. To first order in α we calculate all the correlation functions and the corresponding spectral densities. The relation of this expansion to an approximation method proposed by Nordholm and Zwanzig is also discussed.     

PIN限幅器的高功率微波单脉冲效应研究

基于PIN限幅器的等效电路模型,构建了PIN限幅器HPM效应ADS等效电路仿真模型,利用HPM注入实验和等效电路仿真相结合的方法,研究了单个微波脉冲作用下PIN限幅器的响应规律,获取了HPM作用结束后限幅器限幅持续时间与注入脉冲功率、脉宽的对应关系,并对限幅器的限幅持续过程进行了分析。仿真与实验结果表明:PIN限幅器限幅持续时间随着微波脉冲功率和脉宽的增大而变大,实验和仿真结果趋势一致,该研究使用的ADS等效电路模型可以应用于PIN限幅器的高功率微波瞬态响应特性分析研究。     

Self-similar amplification in fiber Bragg gratings written in fiber amplifiers

We show, by using numerical simulations, that self-similar pulses with a duration on the order of few nanoseconds and an energy on the order of 10?μJ can be obtained at the output of a fiber Bragg grating (FBG) written in a fiber amplifier. The evolution of the amplified pulses is determined by the combined effect of Kerr nonlinearity, normal-dispersion, gain, and gain saturation, which limit the pulse energy. The output pulse mainly depends on the initial pulse energy rather than on the initial pulse profile. The reduced group velocity in FBGs can significantly increase the total gain for a given amplifier length. Hence we find that the proposed amplification scheme can be highly advantageous for amplification of nanosecond-scale pulses in fiber amplifiers.     

A low-temperature and short-annealing process for metal oxide thin film transistors using deep ultraviolet light for roll-to-roll processing

Solution-processed metal oxide semiconductors have superior electron mobility and stability than solution-processed organic semiconductors. However, their fabrication requires a very-high-temperature and long-time annealing process. In this study, we utilized deep ultraviolet (DUV) light to decrease both the temperature and time of the annealing process. High external energy is required to break the organic bonds in a metal oxide film, which is generally supplied by a high-temperature annealing process carried out for a long duration.Alternatively, the required high energy can be supplied more efficiently by irradiating the metal oxide film with DUV light for a shorter duration. In this work, we used DUV light whose peaks at 172 nm instead of the generally used mercury lamp, peaking at 254 and 185 nm. Owing to this difference, thin film transistors (TFTs) could be fabricated on silicon wafers at a lower temperature and shorter duration as compared to the conditions used in previous studies. Various conditions, such as the heating temperature, duration of DUV irradiation, and N₂ flow rate, were optimized to control the heating temperature so as to achieve a mobility of 4.44 cm²/V·s and on–off ratio of 2 × 10⁷, which are much higher than those of a transistor annealed at 300 °C for 30 min (mobility, 1.31 cm²/V·s and on–off ratio, 7 × 10⁵).     

Spectral loudness summation as a function of duration

Loudness was measured as a function of signal bandwidth for 10-, 100-, and 1000-ms-long signals. The test and reference signals were bandpass-filtered noise spectrally centered at 2 kHz. The bandwidth of the test signal was varied from 200 to 6400 Hz. The reference signal had a bandwidth of 3200 Hz. The reference levels were 45, 55, and 65 dB SPL. The level to produce equal loudness was measured with an adaptive, two-interval, two-alternative forced-choice procedure. A loudness matching procedure was used, where the tracks for all signal pairs to be compared were interleaved. Mean results for nine normal-hearing subjects showed that the magnitude of spectral loudness summation depends on signal duration. For all reference levels, a 6- to 8-dB larger level difference between equally loud signals with the smallest (delta f = 200 Hz) and largest (delta f = 6400 Hz) bandwidth is found for 10-ms-long signals than for the 1000-ms-long signals. The duration effect slightly decreases with increasing reference loudness. As a consequence, loudness models should include a duration-dependent compression stage. Alternatively, if a fixed loudness ratio between signals of different duration is assumed, this loudness ratio should depend on the signal spectrum.     

Effect of gravity gradient in weak equivalence principle test

A high accuracy test of the weak equivalence principle(WEP) is of great scientific significance no matter whether its result is positive. We analyze the gravity gradient effect which is a main systematic error source in the test of WEP.The result shows that the uncompensated gravity gradient effect from the coupling term of the dominated gravity gradient multipole moment component q_(21) and the relative multipole field component Q_(21) contributes to an uncertainty of 1×10~(-11) on the E¨otv¨os parameter. We make a Q_(21) compensation to reduce the effect by about 20 times, and the limit of the test precision due to this coupling is improved to a level of a part in 10~(13).     

Influence of optical aberrations in an atomic gyroscope

In atom interferometry based on light-induced diffraction, the optical aberrations of the laser beam splitters are a dominant source of noise and systematic effect. In an atomic gyroscope, this effect is dramatically reduced by the use of two atomic sources. But it remains critical while coupled to fluctuations of atomic trajectories, and appears as a main source of noise to the long term stability. Therefore we measure these contributions in our set-up, using cold cesium atoms and stimulated Raman transitions.     

Spectral differences in the ability of temporal gaps to reset the mechanisms underlying overshoot

When very brief tonal signals are presented immediately after the onset of a gated noise masker, detectability can be 10-20 dB worse than when the signal is delayed by several hundred milliseconds, an effect known as the overshoot. It has long been known that, when an "onset" is created in an otherwise continuous, broadband masker by briefly turning it off and on again, the detectability of a brief signal presented soon after this temporal gap will decline gradually as the gap is increased from a few milliseconds to a few hundred milliseconds. In other words, the auditory system recovers to its quiescent, resting state following an adequate silent interval. Here, the broadband maskers consisted of three adjacent spectral bands--one centered on the frequency of the tonal signal, one low passed below the lower edge of the center band, and one high passed above the upper edge of the center band. The signal was a 2500-Hz tone having a total duration of 6 ms. In different blocks of trials, either all three bands, only the center band, or only the two flanking bands were temporally gapped by a duration ranging from 10-300 ms. When the center band was about 750 Hz wide (about 2.5 critical bandwidths), this differential gapping process resulted in typical recovery functions when all three bands (the entire spectrum) or when just the two flanking bands were gapped. However, when only the center band was gapped, there was no evident recovery--rather, detectability remained near the signal level required with a continuous masker, even for a gap duration of 300 ms.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental analysis of the fast magnetization dynamics in high perpendicular anisotropy Co/Pt nanostructures

We present preliminary results for magnetization dynamics in high perpendicular anisotropy Co/Pt cross-shaped nanostructures submitted to a single/train out-of-plane field pulses. For this, a fabrication process has been developed to obtain high-quality microwave test structures. Using extraordinary Hall effect, we measure quasistatic hysteresis loops while applying either a single or a train of field pulses of given amplitude (32 mT at maximum), variable duration (0.2–10 ns) and repetition frequency (1–100 kHz). We get that field pulses affect only one side of the hysteresis loops without any clear change in the squareness of the loop. Such behavior can be most probably attributed to pulse-induced nucleation of reverse domains in the cross area. The measured shift in coercive field decreases linearly with the logarithm of the pulse duration and two switching regimes that get connected for pulse duration around 1 ns have been observed. Switching probability with single pulse showed that field pulse of 10 ns and 32 mT of magnitude has the same effect of 2 mT static fields.     

Spectral loudness summation for sequences of short noise bursts

Recent loudness data of single noise bursts indicate that spectral loudness summation depends on signal duration. To gain insight into the mechanisms underlying this duration effect, loudness was measured as a function of signal bandwidth centered around 2 kHz for sequences of 10-ms noise bursts at various repetition rates and, for comparison, for single noise bursts of either 10- or 1000-ms duration. The test-signal bandwidth was varied from 200 to 6400 Hz. For the repeated noise bursts, the reference signal had a bandwidth of 400 Hz. For the single noise bursts, data were obtained for two reference bandwidths: 400 and 3200 Hz. In agreement with previous results, the magnitude of spectral loudness summation was larger for the 10-ms than for the 1000-ms noise bursts. The reference bandwidth had no significant effect on the results for the single noise bursts. Up to repetition rates of 50 Hz, the magnitude of spectral loudness summation for the sequences of noise bursts was the same as for the single short noise burst. The data indicate that the mechanism underlying the duration effect in spectral loudness is considerably faster than the time constant of about 100 ms commonly associated with the temporal integration of loudness.     

Radiation damping effects on the interaction of ultraintense laser pulses with an overdense plasma

A strong effect of radiation damping on the interaction of an ultraintense laser pulse with an overdense plasma slab is found and studied via a relativistic particle-in-cell simulation including ionization. Hot electrons generated by the irradiation of a laser pulse with a radiance of I lambda(2)>10(22) W microm(2)/cm(2) and duration of 20 fs can convert more than 35% of the laser energy to radiation. This incoherent x-ray emission lasts for only the pulse duration and can be intense. The radiation efficiency is shown to increase nonlinearly with laser intensity. Similar to cyclotron radiation, the radiation damping may restrain the maximal energy of relativistic electrons in ultraintense-laser-produced plasmas.