Optical propagation of the HE11 mode and Gaussian beams in hollow circular waveguides

The propagation of the HE₁₁ mode and Gaussian beams in hollow oversized circular waveguides is analyzed using optical theories. Different types of waveguides are considered : hollow dielectric or conducting waveguides, dielectric-lined waveguides, corrugated waveguides. General formulas are derived which give the power transmission through these different guides. The best wall materials and structures are determined from a comparison of the waveguide transmissions, at the infrared and millimeter wavelengths. The question of the coupling between the HE₁₁ mode and Gaussian beams is discussed and from a review of coupling coefficients derived before, an optimum value is pointed out. The problem of matching a Gaussian beam into circular waveguides in order to achieve the maximum power transmission is analyzed. These results are of interest for infrared lasers or waveguide applications and for Electron Cyclotron Wave (ECW) systems at the millimeter wavelength.     

Hybrid mode trasmission in 62-m corrugated waveguide

Experimental measurements by wavepacket reflectometry are carried out to verify the low transmission loss of hybrid mode on HE₁₁ in the corrugated waveguide with 88.9 mm in diameter. The HE₁₁ mode is injected into the 62-m straight circular corrugated waveguide and the beat between the HE₁₁ and HE₂₁ (including degenerated TE₀₁ and TM₀₂) modes is observed. The loss is too small to measure and inferred to be less than 2 db/km. The result shows that the use of HE₁₁ mode for electron cyclotron heating system is suitable.     

A dielectric rod waveguide coupled with metal rectangular waveguide

Measurements have been done in the millimeter wave region on a composite waveguide which comprises a dielectric rod waveguide connecting two metal rectangular waveguides. Such a waveguide has been used by us in a Josephson harmonic mixer installed in a small metal cryostat, to prevent the thermal invasion from outside environment and to transmit both signal and LO waves with small losses. The measured transmission loss, that is caused mainly by the coupling loss between metal rectangular waveguides (TE₁₀ mode) and a dielectric rod waveguide (HE₁₁ mode), has been less than 2dB in the frequency range of 52–104 GHz.     

Partially coherent non-paraxial vectorial Hermite-Gaussian beams and their far-field properities

The far-field theory of partially coherent vectorial non-paraxial beams is expanded and their analytical propagation expressions of the Wigner distribution function matrices and the cross-spectral-density matrices in free space are derived using the far-field approximation. Some interesting cases, in particular the vectorial non-paraxial partially coherent Hermite-Gaussian (HG) beams, are discussed and treated as special cases of our general expressions. It is shown that the f_σ and f parameters play an important role in determining vector and non-paraxiality of partially coherent HG beams. When two parameters are small enough, scalar and paraxial vectorial approximation is allowed; otherwise, non-paraxial vectorial approximation is applied. But the decided parameters additionally affect their far-field divergence angles.     

Partially coherent nonparaxial Hermite-Gaussian beams and their propagation properties

The concept of partially coherent nonparaxial Hermite-Gaussian (HG) beams is proposed. By using the generalized Rayleigh-Sommerfeld diffraction integral, the closed-form propagation equations of partially coherent nonparaxial HG beams in free space are derived. The on-axis intensity, far-field and paraxial expressions, and specifically, the free-space propagation equations of partially coherent nonparaxial Gaussian Schell-model beams are given, and treated as special cases of our results. It is found that the f and f_σ parameters play a crucial role in determining the nonparaxiality of partially coherent TEM_mn-mode HG beams. Only if the f and f_σ parameters are small enough, the paraxial approximation is applicable.     

Far-field intensity distribution, M factor of beams generated by Gaussian mirror resonator

We investigated M² factor and far-field distribution of beams generated by Gaussian mirror resonator. And we found usable analytical expressions of the M² factor and the far-field distribution intensity with respect to variation of diffraction parameters. Particular attention was paid to the parameters such as mirror spot size and reflectance of the Gaussian mirror.     

大气湍流对径向分布高斯列阵光束扩展和方向性的影响

采用积分变换的技巧,推导出了径向分布高斯列阵光束通过湍流大气传输的二阶矩束宽和远场发散角的解析公式,并详细研究了大气湍流对光束扩展和方向性的影响.研究表明,相干合成情况下,子光束数N越小、径向分布半径r₀越大,列阵光束扩展受湍流影响越小.相干较非相干合成时列阵光束的扩展小,但非相干合成时列阵光束扩展受湍流的影响比相干合成时的小.特别地,N足够小或r₀足够大时,相干与非相干合成列阵光束的远场束宽相等.另一方面,还给出了相干和非相干合成径向分布高斯列阵 关键词： 径向分布高斯列阵光束 大气湍流 相干和非相干合成 二阶矩束宽     

The beam propagation factor and far-field distribution of Bessel-modulated Gaussian beams

The explicit expressions for the beam propagation factor (M ² factor) and far-field distribution of Bessel-Modulated Gaussian beams with quadratic radial dependence are derived. The results are analyzed with numerical example.     

The Beam Propagation Factor of Nonparaxial Truncated Flattened Gaussian Beams

By using the second-order moment of the power density, the beam width, far-field divergence angle and M² factor of nonparaxial truncated flattened Gaussian (FG) beams are derived analytically. It is shown that the M² factor of nonparaxial truncated FG beams depends not only on the truncation parameter δ and beam order N, but also on the initial waist-width to wavelength ratio w₀/λ. The far-field divergence angle approaches an asymptotic value of θ_max=63.435° when the truncation parameter δ → 0. For the special cases of N = 0 and δ → ∞ our results reduce to those of nonparaxial truncated Gaussian beams and nonparaxial untruncated FG beams, respectively.     

Output mode characteristics of an in-phase locked gain waveguide array CO2 laser

In this paper,experimental and theoretical studies of the output mode characteristics of an in-phase locked gain waveguide array CO 2 laser are reported.The experimental results of the optical oscillation mode frequency,the far-field intensity distribution and the burnt pattern of the sliced waveguide array laser are obtained.A revised mode expression of the rectangle waveguide,which is suited for this waveguide array CO 2 laser,is proposed.The theoretical simulation results based on the revised mode expression are shown to be in good agreement with the experimental results.     

Variational analysis of Er:Ti:LiNbO3 waveguide lasers based on Gaussian/two-half Gaussian mode field distribution

Starting with two dimensional, scalar wave equation, a variational equation was established for the fundamental TE and TM modes guided in Ti:LiNbO₃ waveguides on the basis of assuming a symmetric Gaussian mode field function in the width direction and two-half Gaussian trial functions in the depth direction. The controllable waveguide fabrication parameters, including channel width, diffusion temperature, initial Ti-strip thickness and diffusion time, dependent of fundamental mode size, effective pump area, coupling efficiency between pump and laser modes, and the coupling loss between a Ti:LiNbO₃ waveguide and a fiber were numerically calculated for Z-cut Er:Ti:LiNbO₃ channel waveguide lasers at three possible emission wavelengths 1532,1563 and 1576 nm and two possible pump wavelengths 1480 and 980 nm. The calculated results were compared with those of Gaussian/Hermite–Gaussian mode field distribution in detail.     

Propagation properties of ultrashort pulsed beams with constant waist width in free space

Based on the Rayleigh diffraction integral and complex analytical signal representation, the strict propagation expression and its Fourier spectrum for ultrashort pulsed Gaussian beams with constant waist width are derived, which have the general applicable advantage, because the paraxial approximation, pulsed envelope representation and far-field approximation are not invoked. The far-field and paraxial expressions are obtained as the special cases of our general results. Numerical calculation results are given to illustrate the spatiotemporal propagation properties of few- and single-cycle pulsed Gaussian beams with constant waist width. A comparison with the paraxial results and previous work is also made.     

环形孔径高斯光束的远场特性

 讨论了环形孔径高斯光束的远场光斑能量分布,并给出了拟合表达式。首先推导了光束没有抖动时远场光斑的光能分布表达式,然后研究了各种不同中心遮拦和不同光束截断比, 在有以及没有激光束抖动的情况下,对高斯光束的远场环围能量的分布变化的影响。     

Generalized Malkmus line intensity distribution for CO2 infrared radiation in Doppler broadening regime

A new line intensity distribution function is introduced in order to improve the accuracy of statistical narrow-band (SNB) models in the Doppler line broadening regime and in a wide temperature range. This distribution function generalizes the Malkmus distribution through a parameter enabling to adjust the contribution of small line intensities. This new model is shown to enhance significantly SNB accuracy for CO₂ uniform column radiation, especially at low temperatures. For non-uniform columns, Lindquist-Simmons type approximations are derived for this new intensity distribution. Their results are in much closer agreement with line by line results than Curtis-Godson approximation ones when steep temperature gradients are considered.     

The Degenerate Vibrations of BCl3, BBr3 and BI3 with Application of Keating Coordinates

The experimental works of vibrational spectroscopy and normal coordinate analyses for BCl₃, BBr₃ and BI₃ are reviewed extensively. Harmonic force fields of the E' species are produced using isotopic frequencies and Coriolis constants as additional data, respectively. The usefulness of Keating coordinates versus valence coordinates as basis of force field approximations is discussed. The conclusions are not unequivocal, but they go in favour of the Keating coordinates when the reliability of the different computations is taken into account. Boron trichloride is treated specifically in some detail. Final force fields are proposed for the title molecules with the aid of the mass influence on Coriolis constants.     

Simulation study of semi-superjunction power MOSFET with SiGe pillar

The feasibility of applying the semi-superjunction (Semi-SJ) with SiGe-pillar (SGP) concept to Power MOSFET is studied in this paper. The electrical performances of SGP are compared with the conventional Power MOSFET through 3D device simulation work in terms of specific-on resistance (_Ron)$\left(R_{on}\right)$, breakdown-voltage (BV  ), the effect to change the Ge mole fraction in the SGP and the thermal stabilization. The results show that the _Ron$R_{on}$ is reduced by 44% on the base of BVs   reducing only 4.8%, tradeoff _Ron$R_{on}$ vs. BV and thermal stabilization of SGP are superior to that of conventional Semi-SJ since the strain effect inducing into the SGP structure in the low power device application.     

Electron diffraction data as a constraint in the determination of force field of thallous halide dimers

Electron diffraction data have been used as a constraint in the determination of force field for Tl₂F₂ having planar rhombic structure. The L-F approximation method, recently given by us, has also been applied to evaluate force constants for thallous halide dimers,e.g. T1₂F₂ and T1₂Cl₂. The results have been compared with the available experimental data in order to check the validity of the present work. It is concluded that non-bond experimental mean amplitudeU ₁..._Tl for Tl₂F₂ is capable of fixing the force field and L-F approximation gives reasonably good force fields for the two thallous halide dimers now under study.     

Propagation properties of vectorial elliptical Gaussian beams beyond the paraxial approximation

Starting from the vectorial Rayleigh diffraction integral formula and without using the far-field approximation, a solution of the wave equation beyond the paraxial approximation is found, which represents vectorial non-paraxial elliptical Gaussian beams in free space. The far-field expressions for non-paraxial Gaussian beams and elliptical Gaussian beams can be regarded as special cases treated in this paper. Some basic propagation properties of vectorial non-paraxial elliptical Gaussian beams, including the irradiance distribution, phase term, beam widths and divergence angles are studied. Numerical results are given and illustrated.