Coherent anti-Stokes Raman scattering of slow light in a hollow planar periodically corrugated waveguide

Enhancement of coherent anti-Stokes Raman scattering (CARS) by molecular nitrogen in a hollow planar periodically corrugated waveguide is experimentally detected. The measured dependence of CARS efficiency on the thickness of the waveguide layer indicates that CARS enhancement under these conditions is at least partially due to the decrease in the group velocity of pump pulses around the photonic band gap.     

Theory of self-focusing in a hollow waveguide

We present a theoretical investigation of self-focusing in a hollow waveguide filled with noble gas. Our analysis was performed for a laser pulse that was predominantly in the fundamental mode and revealed the physical processes involved in self-focusing in a hollow waveguide. A critical power for self-focusing was obtained that was found to be substantially higher than the critical power for self-focusing in a bulk medium. Useful design criteria for pulse-compression systems are presented. We identify the parameter range for which the transverse variation of the pulse phase introduced by the Kerr nonlinearity is small.     

Wave-field formation in a hollow x-ray waveguide

Diffraction and refraction phenomena at the entrance of a hollow x-ray waveguide with weakly absorbing dielectric cladding layers are investigated using two independent approaches: (a) analytical and (b) numerical solutions of the wave equation in the paraxial (parabolic) approximation. It is shown that the wave penetrating through the cladding material substantially modifies the wave field near the waveguide entrance. It results in a significant increase of the total energy flux inside the guiding layer and in additional spatial modulation of the electromagnetic field.     

Probe of high-order harmonic generation in a hollow waveguide geometry using counterpropagating light

We use counterpropagating light to directly observe the coherent buildup of high harmonic generation in a hollow waveguide geometry. We measure, for the first time, coherence lengths for high photon energies that cannot be phase matched using conventional approaches. We also probe the transition through phase matching, the ionization level at which different harmonic orders are generated, and the change in the coherence length as the driving laser is depleted. These results directly prescribe the optimal structures or pulse trains required for implementing quasiphase matching.     

Vectorial vortex mode transformation for a hollow waveguide using Pancharatnam-Berry phase optical elements

Transformation and inverse transformation between a free-space linearly polarized beam and the vectorial vortex mode of a circular hollow waveguide by use of Pancharatnam-Berry phase optical elements is proposed. Demonstration was achieved by fabricating GaAs subwavelength gratings and utilizing a 300 microm diameter hollow metallic waveguide for 10.6 microm wavelength CO(2) laser radiation. The mode transformations and the excitation of a single vectorial mode inside the hollow waveguide were verified by full polarization measurements. In addition, the inverse mode transformation of the single vectorial mode excitation in the waveguide enabled us to experimentally obtain a linearly polarized bright spot with a high central lobe.     

Tunable infrared generation using third Stokes output from a waveguide Raman shifter

Tunable infrared output has been produced by stimulated Raman scattering of visible dye laser radiation in hydrogen gas using a capillary waveguide to enhance conversion to the third Stokes (S₃). With 568 nm pumping an output energy of 2 mJ is observed near 2 μ m, representing a 4% energy conversion efficiency into S₃). Higher wavelengths yield much lower energies (0.5 mJ at 3 μ m and 0.02 mJ at 4.55 μ m), reflecting the observed dependence of third Stokes output on the inverse of the fifth power of the generated wavelength.     

Generation of a single picosecond pulse using Raman backscattering

The second harmonic pulse train from a mode-locked NdYAG Self-Filtering Unstable Resonator has been compressed by a factor of 2.3 using Raman backscattering. Single pulses of 7.4 picoseconds at=0.68m and with 70 percent success probability have been obtained.     

锥形空心银波导的聚焦特性

利用时域有限差分(FDTD)方法数值演示了一种能光学引导和聚焦激光的锥形空心银波导,数值模拟结果表明这种锥形空心银波导能把激光聚焦成一个极小的、直径只有1 μm、强度高度局域性的光斑.对锥形波导能光学引导和聚焦激光的物理机理作了分析和探索,并进一步探讨了激光倾斜入射、波导几何结构对锥形波导聚焦特性造成的影响,这些研究结果对于锥形光学的应用、快点火或产生高能带电粒子中锥靶结构的最佳设计具有重要的参考价值. 关键词： 锥形波导 聚焦特性 时域有限差分     

Backward Raman amplification in a plasma waveguide

Backward Raman amplification of a short laser pulse in a plasma waveguide is demonstrated. With a guided seed pulse of 0.8-microJ energy and a pump pulse of 345-mJ energy in a 9-mm-long optically preformed plasma waveguide, 910-fold energy amplification is achieved. Heating of the plasma by the long pump pulse is identified to be a key issue for plasma-waveguide-based backward Raman amplifiers.     

Polarization insensitive hollow optical waveguide

A polarization insensitive hollow optical waveguide is proposed. The propagation characteristics of orthogonal polarizations in the hollow waveguide are effectively controlled in simulation to provide polarization insensitivity by tailoring the parameters associated with the two mirrors—a high-index contrast grating (HCG) mirror and a distributed Bragg reflecting (DBR) mirror, on either side of an air-core. The polarization insensitivity is evidenced by a low polarization dependence loss of 1.36 dB/cm and a low modal birefringence of 1.01 × 10^? 4.     

A spherical scatterer inside a circular hollow dielectric waveguide

A theoretical investigation is presented of scattering characteristics of a perfectly conducting spherical object placed inside a quasi-optical transmission line of the millimeter and submillimeter waves in the form of a circular hollow dielectric waveguide (HDW). From the analytical expressions obtained, backscattering and extinction cross sections of this object are derived via the excitation coefficient of the dominantHE ₁₁ mode of the circular HDW and the HDW geometrical parameters. The agreement of the results with the corresponding data for the scattering of a plane homogeneous wave is shown.     

单水听器波导不变量被动测距

本文主要讨论利用声场干涉现象由单水听器被动测距的可行性及测距性能,为此提出了单水听器波导不变量被动测距方法,通过提取LOFAR图上干涉条纹、使用简正波模型计算波导不变量、频域相关法估计相对速度,最后依据干涉条纹方程得到声源距离估计量。数值仿真和海上实验结果验证了单水听器被动测距的可行性,并具备一定测距性能,在3 dB信噪比环境中,对于7 km处的运动声源,平均测距误差小于5%。本文方法具有设备简单、易于推广至阵列信号处理等特点,为声纳信号处理环境宽容性的提高及环境适配声纳的设计开拓了思路。     

Noncontact characterization of glucose by a waveguide microwave probe

We investigate the electromagnetic field interaction with a glucose aqueous solution using a microwave dielectric waveguide probe to evaluate the glucose concentrations. A microwave dielectric waveguide probe allows observation of the small variation of the glucose concentration changes in the range of 0–300 mg/ml by measuring the change of the microwave reflection coefficient. We could observe the effect of concentration change of glucose with a detectable resolution up to 0.5 mg/ml at an operating frequency of about f = 2.0–2.5 GHz. The change of the glucose concentration is directly related to the change of the reflection coefficient due to the electromagnetic interaction between the dielectric waveguide resonator and the glucose aqueous solution. The operational principal is explained by a plane-wave solution model. A glucose biosensor using a microwave dielectric waveguide probe provides a unique approach for glucose monitoring.     

Self-and cross-phase modulation accompanying third-harmonic generation in a hollow waveguide

The influence of self-and cross-phase modulation on third-harmonic generation in a hollow waveguide is investigated. Analytic solutions of the coupled equations for the slowly varying amplitudes of the pump pulse and the third harmonic in a gas-filled hollow waveguide are obtained with consideration of self-and cross-phase modulation and first-order dispersion effects. The possibility of controlling the nonlinear phase trajectory of the third harmonic by cross-phase modulation is demonstrated. Zh. éksp. Teor. Fiz. 115, 1561–1579 (May 1999)     

Probing crystallographic orientation of a single GaN nanotube using polarized Raman imaging

We report the study of crystallographic orientation of a highly anisotropic square‐shaped single wurtzite GaN nanotube (NT) probed by polarized Raman imaging. The polarization‐dependent Raman intensities are collected in two mutually orthogonal directions with respect to the NT long axis. Variation in intensities of symmetry allowed A₁(LO) mode of GaN with two different polarization directions reveals the possible crystalline orientations in the NT. The polarized Raman spectral imaging illustrates the fact of inhomogeneous crystalline orientations along the edges of the NT facets owing to its finite wall thickness. The deviation of polarization selection rule for GaN is attributed to the geometrical anisotropy of the NT. Electron microscopic structural data confirms the spectral imaging analyses. Copyright © 2013 John Wiley & Sons, Ltd.     

Mode structure of hollow dielectric waveguide lasers

The mode structure of hollow dielectric waveguide lasers with free space sections and flat mirrors is studied theoretically and experimentally. The study covers the fundamental mode and the three most important higher order modes, and graphs are given which identify regions of high mode discrimination in the parameter space. Calculated coupling losses are verified experimentally by detailed studies of the output power of CO₂ lasers as a function of resonator geometry. The intensity profile inside and outside the resonator is calculated, and the profile outside the resonator is compared with experiments for the fundamental mode as well as for the higher order modes. It is shown that in general the fundamental mode is non-Gaussian, and that drastically different output characteristics are obtained for different choice of output plane. The paper identifies design criteria for obtaining single line and single mode oscillation over a wide tuning range, even in the densest region of the CO₂ laser line spectrum, and this is exemplified by a spectroscopic application.Supported by the Danish Science Research Councils under grants no. 5.17.4.6.19 and 5.17.4.1.23 and by FLS airloq     

Modeling of radar scattering conditions inside a circular hollow dielectric waveguide

A new ray representation of electromagnetic field inside a quasi — optical structure in the form of a circular hollow dielectric waveguide is suggested and confirms the possibility for the unusual application of such a waveguide as an off-beat microanechoic chamber for electromagnetic modeling in the near millimeter and submillimeter wave regions.     

Increase of the atomic phase density in a hollow laser waveguide

A study is made of the channeling of atoms in a narrowing hollow waveguide carrying on its inner surface a surface wave with positive detuning for the absorption line of an atom. The inelastic reflection of atoms from the surface light wave and the convergent geometry of the waveguide make it possible to decrease the temperature and increase the phase density of an ensemble of atoms introduced continuously into the hollow convergent waveguide from a magnetooptic trap, by a factor of 10⁵. It is suggested that such a waveguide be used to study collective phenomena in quantum-mechanical systems with a high density (Bose-Einstein condensate) and as a high-luminosity coherent source of cold atoms. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 10, 763–767 (25 May 1996)     

Nonlinear propagation dynamics of an ultrashort pulse in a hollow waveguide

We present a theoretical investigation of the self-focusing dynamics of femtosecond pulses in a hollow waveguide. We show that transverse effects play an important role in these dynamics, even for pulses that are significantly below the critical power for self-focusing in free space, and that excitation of higher-order modes of the waveguide results in the spreading of the pulse in time. Inclusion of self-steepening and space-time focusing in our model is necessary for properly capturing the pulse dynamics.     

Stimulated Raman amplification and high-order Raman sideband generation in a polymer waveguide on a printed circuit

The ultrafast Raman response of C-H vibrations in polymer waveguides on a printed circuit is shown to enable a high-gain amplification and high-order stimulated Raman transformation of ultrashort laser pulses. The pump and Stokes fields coupled by the C-H vibration mode with a vibration cycle of 11 fs give rise to multiple Raman sidebands, suggesting the way toward ultrafast optical data processing and few-cycle optical waveform synthesis on a printed-circuit polymer waveguide platform.