Fiber supercontinuum generators with dynamically controlled parameters

Various methods to dynamically control the supercontinuum (SC) parameters are analyzed. The possibility of variations in the SC power spectral density due to variations in the wavelength and pulse repetition rate of the pumping laser is considered. An increase in the SC coherence owing to the optimization of the pumppulse frequency modulation is discussed. A variation in the repetition rate of the SC pulses generated in the scheme with the two-wavelength pumping due to a variation in the frequency difference is studied.     

一种血流变参数在体实时探测方法

介绍了一种新的在体实时监测血流变参数的光学方法——光散射法。设计了一种实用的同轴多光纤探针装置。在装置中间,其中一根光纤用于传输入射激光,周围多根光纤与中心光纤等间隔,用于接收血液中的散射光。用扫描法布里-珀罗干涉仪产生散射光谱。结果表明,用该装置测得了含成分的液体、实血和不同血液成分的光散射光谱。     

Development of an optical time scale

A time standard based on the use of an optical oscillation period of a frequencystable He–Ne laser as a time scale is first described. We obtained highly frequency-stable oscillations in the SHF range that were locked to the oscillations of a He–Ne laser stabilized to an absorption resonance in methane at 3.39 m. A direct comparison of frequency stabilities of a rubidium standard and He–Ne/CH₄ laser has been made. The absolute measurement of the frequency of the He–Ne/CH₄ laser we performed gave a new value of frequency.This work was reported at the 3rd Frequency Standards and Metrology Symposium     

Nonlinear-optical transformation of nanosecond laser pulses and controlled supercontinuum generation in photonic-crystal fibers

Photonic-crystal fibers are shown to allow efficient spectral transformation of nanosecond laser pulses through parametric four-wave mixing and stimulated Raman scattering. Regimes providing highly efficient transformation of nanosecond laser pulses into white-light broadband radiation (supercontinuum) are identified. A strong parametric coupling between Stokes and anti-Stokes Raman sidebands around the wavelength of zero group-velocity dispersion is shown to increase the bandwidth and to improve the spectral quality of supercontinuum radiation.     

High-efficiency generation of a supercontinuum in an optical fiber

The results of experimental studies of high-efficiency generation of a supercontinuum in different types of single-mode optical fibers by pulses with a width of ～20 ps and with a wavelength widely tunable within the regions of normal and anomalous dispersion of the fibers are reported. A high efficiency of transformation of initially monochromatic radiation into a wide-spectrum supercontinuum with intense wings (in the range of 1000–2100 nm at a transformation efficiency of 95%) is demonstrated.     

Enhancement and broadening of extreme-ultraviolet supercontinuum in a relative phase controlled two-color laser field

We experimentally demonstrate the generation of an extreme-ultraviolet (XUV) supercontinuum in argon with a two-color laser field consisting of an intense 7 fs pulse at 800 nm and a relatively weak 37 fs pulse at 400 nm. By controlling the relative time delay between the two laser pulses, we observe enhanced high-order harmonic generation as well as spectral broadening of the supercontinuum. A method to produce isolated attosecond pulses with variable width and intensity is proposed.     

Predicting multivariate time series in real time with confidence intervals: Applications to renewable energy

We extend our earlier work on predicting a univariate time series in real time with confidence intervals (Hirata, et al., Renew. Energy 67, 35 (2014)) to a multivariate time series. We realize this extension by using the “p-norm” where p is smaller than 1. We compare the performance when p is 0.5 with that when p is 2 using solar irradiation data and wind data measured all over Japan.     

Characterization of the road surfaces in real time

The main factor in the propagation of traffic noise is the road surface, where the vehicles generate noise due to the contact between tire and pavement, in addition to the noise produced by the engine.     

Ultrasonic monitoring of zeolite synthesis in real time

Variations of the phase and amplitude of a transmitted ultrasonic wave package were monitored in real time during the synthesis of zeolite A and zeolite X. For both materials, characteristic changes of the measured attenuation and the sound velocity of ultrasonic waves traveling in the reaction fluid were observed, correlating with the processes of gel formation and zeolite crystallization, respectively. Aging effects of the reaction fluids are demonstrated. The observation of the onset of the zeolite crystallization was verified with ex-situ X-ray diffraction (XRD) measurements.     

Generation of an extreme ultraviolet supercontinuum in a two-color laser field

We theoretically investigate the high-order harmonic generation in a helium atom with a two-color optical field synthesized by an intense 6 fs pulse at 800 nm and a relatively weak 21.3 fs pulse at 400 nm. When the frequency-doubled pulse is properly time shifted with respect to the fundamental pulse, an ultrabroad extreme ultraviolet supercontinuum spectrum with a 148 eV spectral width can be generated which directly creates an isolated 65 as pulse even without phase compensation. We explain this extraordinary phenomenon by analyzing maximum electron kinetic energies at different return times.     

Interference detection of flaws in periodic objects in real time with adjustable sensitivity

A technique of interferometric testing for macroscopic defects in periodic objects is proposed which works in real time and with an adjustable measurement sensitivity. The possibility of compensating the aberrations of the interferometer by using a reference hologram is demonstrated. Interference patterns with different measurement sensitivity are presented which visualize flaws in a metal screen consisting of two overlapping grids. Zh. Tekh. Fiz. 69, 126–130 (October 1999)     

Estimation of the dead time period and parameters of an asynchronous alternative flow of events with unextendable dead time period

A problem of estimating the parameters of an asynchronous alternative flow of events with initiation of a superfluous event being a mathematical model of information flows of queries circulating in integrated service digital networks as well as a mathematical model of fluxes of elementary particles (photons, electrons, etc.) arriving at the recording equipment is considered. The conditions of flow observation are such that each registered event generates a dead time period during which other flow events are unobservable. The case of unextendable dead time period is investigated. The probability density of interarrival time in the flow under observation is found. The parameters of the initial asynchronous alternative flow with initiation of a superfluous event and a dead time period are estimated by the method of moments. Results of a statistical experiment realized for an imitational model are presented. They demonstrate fairly good properties of the estimates obtained. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 35–49, October, 2005.     

Frequency–time and time–space mappings with broadband and supercontinuum chirped pulses in coherent wave mixing and pump–probe techniques

Broadband and supercontinuum pulses with a linear chirp define a linear transform, mapping the difference between the instantaneous frequencies of pump pulses onto the delay time between these pulses. This delay between the pump pulses can be then mapped onto the spatial coordinate with the use of a broad-beam wave-mixing or pump–probe geometry. The new possibilities offered by these mappings for four-wave-mixing techniques are discussed. The spectral and temporal resolution of chirped-pulse wave-mixing and pump–probe techniques are examined. Single-shot multidimensional wave-mixing techniques using broadband and supercontinuum chirped pulses are discussed. PACS 42.65.Dr; 42.65.An     

Removal of sidebands in double-rotation NMR in real time

Double-rotation (DOR) is the only technique generally capable of yielding high-resolution NMR spectra of half-integer quadrupolar nuclei in one dimension for solids without the need for sophisticated coherence pathway selection. Unfortunately, due to the low outer rotor spinning frequencies currently available, the spectra often contain a large number of spinning sidebands which may overlap with the resonances of interest. We implement a simple, robust, and easy to use family of pulse sequences, which in practice are fully analogous to the 'total suppression of sidebands' (TOSS) sequences, to suppress all sidebands arising from the spinning of the outer rotor in DOR experiments. By removing the rotor phase dependence of the evolution of the sidebands, the sidebands destructively interfere with one another during the course of signal averaging to yield 'solution-like' spectra of half-integer quadrupolar nuclei in solids. Advantages and shortcomings of the method compared to other DOR sideband suppression methods are explored with the aid of simulations.     

Mechanical effect of van der waals interactions observed in real time in an ultracold Rydberg gas

We present time-resolved spectroscopic measurements of Rydberg-Rydberg interactions between two Rydberg atoms in an ultracold gas, revealing the pair dynamics induced by long-range van der Waals interactions between the atoms. By detuning the excitation laser, a specific pair distribution is prepared. Penning ionization on a microsecond time scale serves as a probe for the pair dynamics under the influence of the attractive long-range forces. Comparison with a Monte Carlo model not only explains all spectroscopic features but also gives quantitative information about the interaction potentials. The results imply that the interaction-induced ionization rate can be influenced by the excitation laser. Surprisingly, interaction-induced ionization is also observed for Rydberg states with purely repulsive interactions.     

Single-path interferometer for measuring fluid flows in real time with low-quality optics

An interferometric concept based on a modified version of the Fabry–Perot interferometry is proposed for measuring flow fields in real-time and some results are presented for demonstration. Being based on a single-path configuration of interfering beams, it is very convenient to build a simple compact measurement system. While allowing the deployment of low-quality optics including test-section windows through compensation of system errors, it is also immune to external vibration. In addition, it can easily allow large aperture and long pathlength of probing beams with good precision. These aforementioned features are very appropriate for measuring large flow fields including wind tunnel testing as well as conducting laboratory experiments without elaborate equipment.