Warm cavity modes of free-electron laser resonators with on-axisholes

The optical mode structure and gain of a free-electron laser (FEL) resonator with holes on axis in the small optical signal regime is examined using a matrix formulation. A gain matrix, describing optical mode mixing and amplitude gain in the wiggler, is derived from the FEL evolution equations. A loss matrix, describing the effect on the transverse optical mode structure of the resonator end mirrors, is derived using the method of A.G. Fox and T. Li (1960). The laser matrix is the product of the gain and loss matrices. The eigenvectors and eigenvalues of the laser matrix give the transverse optical mode profile and gain of the resonator. The resonator of the Mark III infrared FEL at Duke University and a confocal resonator, for two holes sizes are examined. The results demonstrate the possibility of output coupling through the holes of the Mark III resonator, and the possibility of using the holes of the confocal resonator for gain control     

Magnetodynamical modes in a ferrite-filled coaxial cavity

The resonance frequencies of a coaxial ferrite-filled cavity and the field distribution in the cavity are calculated. There are three different groups of modes to be distinguished: the limit-TEM mode, the EH and HE modes, and modes independent of the zco-ordinate, which are TM modes. The eigenvalue equation for all modes is derived and discussed.     

Magnetodynamical modes in a spherical ferrite cavity

The axial-symmetrical modes of a spherical cavity containing magnetised-ferrite material are calculated. It can be shown that the different modes of the resonator are coupled by the gyrotropic medium. The field of the gyrotropic resonator is represented by an infinite sum of the eigenfunctions of the spherical resonator containing an isotropic medium. Under consideration of the boundary conditions the dependence of the resonance frequency on the magnetic-bias field may be obtained.     

Selection and stabilization of longitudinal modes by spacing of laser cavity components

The longitudinal mode spectrum of a solid-state ion laser can be greatly simplified and stabilized by spacing the rod and the mirrors according to a simple rule: the optical path between each end mirror and the nearest end of the rod should be an integral multiple of the optical length of the rod. Application of this rule can reduce the number, increase and regularize the frequency spacing, symmetrically distribute the intensities, and increase the temporal stabilization of the oscillating longitudinal modes. These remarkable effects were demonstrated with a continuous Nd:YAG laser that was constructed with several different spacings of cavity elements. The rule is probably the result of absorption loss that is localized at the surfaces of the rod. Other models, limitations, and generalizations of the rule are also discussed.     

Distributed feedback modes in a partially filled ring cavity

We have studied the threshold longitudinal modes of a structure composed of a ring cavity partially filled with a distributed feedback (DFB) medium. An eigenvalue equation and dispersion relation for the propagation constant, threshold gain, and mode location are derived and numerically solved for a number of cases. We show that the incommensurate nature of the unfilled ring cavity eigenfrequencies and DFB eigenfrequencies can lead to an enhancement of the frequency selectivity of the distributed feedback laser. The analysis is extended to consider finite linewidth and dispersion.     

Interacting solutions in erbium fibre laser

Novel behaviour from an FM mode-locked erbium fibre laser is reported. Selfsustaining, picosecond duration pulses which are not at the modulation frequency of 480 MHz have been observed. The pulses form complex pulse trains and seem to experience soliton interactions, causing them to execute complicated motions.<>     

Frequency locking of modes in a ring laser

The locking of two countertraveling ring laser modes due to light scattering is investigated. It is found that the mutual locking of two free-running oscillating modes is different from locking due to an externally injected signal. The text defines two kinds of mode-to-mode scattering: conservative and nonconservative. The former leads to no locking, to a high degree of approximation. Examples of conservative scatterers are nonabsorbing particles, small compared to a wavelength, and loss-free objects of larger size that represent only a weak perturbation of the dielectric constant in the cavity. The presence of two types of scatterers makes it impossible, in general, to calculate lockbands from measured scattering intensities from optical components such as mirrors. The relationship between the present theory, the conventional Adler theory, and measurable laser component properties such as scattering coefficients is discussed. The findings are of importance for the development of mirrors and optical coating processes in ring lasers.     

自成像列阵共振腔的分析——Ⅰ.Talbot共振腔

利用自成像效应进行半导体列阵激光器锁相是一种重要的外腔锁相技术,所构成的共振腔可分为Talbot腔和带相位补偿板的Lau腔。我们用Fox-Li方法计算了共振模式。本文给出了Talbot腔的计算结果和分析,表明同相和反相模的损耗随腔长变化存在临界点。     

自成像列阵共振腔的模式分析 ——Ⅱ.Lau共振腔

在对Talbot腔研究的基础上,继续分析Lau共振腔的模式结构和损耗特性。表明基模损耗最小,高阶模存在的条件是阶数低于单元数除以4。     

一种8字腔结构激光器中的双脉冲现象

设计了一种8字腔结构的激光器,用980 nm的泵浦源泵浦保偏掺铒光纤,得到了重复频率约是10 MHz双脉冲的输出,为了检验双脉冲的组成,在激光器的输出放置一个掺铒光纤放大器、偏振控制器和偏振分束,在不同的偏振态下获得了单脉冲的输出,证明双脉冲是偏振态不同的两个单脉冲组成的。     

外腔锁相中二极管列阵相邻单元间不同侧模的耦合系数

推导了锁相外腔中半导体激光器列阵相邻发光单元之间不同阶侧模的耦合系数,计算了耦合系数的幅度与外腔长度的关系。结果表明:幅度的极大值对应的外腔长度随侧模阶次增大而减小,不同阶次侧模耦合系数的最大幅度也随阶次降低而减小。上述结果意味着;要实现相邻单元间的基侧模耦合锁相,应该把腔长放在对应的极大值附近;同时也预示着如果腔长过短,可能会出现高阶侧模的外腔锁相。     

Analysis of modes in a free-standing nanowire cavity by FDTD simulation

The mode frequency and the quality factor of nanowire cavities are calculated for the intensity spectrum obtained by the finite-difference time-domain （FDTD） technique and the Pade approximation. In the free-standing nanowire cavity with the dielectric constant ε=6.0 and the length of 5μm, the quality factors of 130,159,and 151 are obtained for modes with frequency around 798 THz,at the cavity radius of 60 nm, 75 nm, and 90 nm, respectively. The obtained field distribution of the fundamental transverse mode shows that the mode field is confined very well by the nanowire cavity even when the radius of nanowire is much smaller than the mode wavelength.     

Room-temperature operation of a transverse-distributed-feedback cavity laser

A new type of transverse-distributed-feedback cavity laser is proposed. A threshold current of a two-dimensional mode is 190 mA, and an output power of 30 mW is obtained at 1.5Ith. The far-field pattern is stable up to a measured current of 2.1Ith.     

液芯激光腔中的倏逝波对LP_(om)模的放大作用

利用波导染料激光管中形成的“液芯光纤”证实了倏逝波对LP_(om)模的放大作用。     

Self-locking of transverse higher-order modes in a He-Ne laser

Self-locking of TEM10+ TEM01modes was observed in a He-Ne laser. The laser output was modulated with a frequency difference between two transverse modes. In this case two longitudinal modes operated, and the combination tone due to three of the modes pulled in the fourth.     

Resonant modes of a concentric spherical cavity with conicallystratified medium

An analysis on electromagnetic fields of a cavity formed by two concentric conducting spheres with a conically stratified medium is presented in this paper. Angular transmission formulation and the radial eigenfunction expansion are used to formulate the field components. Boundary matching methods are applied to obtain the characteristic equations containing various infinite series of spherical Hankel functions and Legendre functions of complex order for resonant frequencies. The first two resonant frequencies and field expansion coefficients are determined numerically. The distribution pattern of angular field components and the forms of typical electric field lines and magnetic field lines for the first resonant fields are also indicated     

Local beam deflector interated in a diode laser cavity

Deflection of a diode laser beam using a local deflector monolithically integrated in the cavity near an output facet is demonstrated. The index distribution in the deflector is adjusted by controlling the injection currents, and the laser beam is scanned over 9° by the prism effect of the deflector.     

Finite-element analysis of angularly dependent modes in a general RF periodic cavity

An analysis is presented for a circularly symmetric periodic structure for any angular dependence of the modes. The finite-element technique is applied and computations for the simple case of an iris loaded circular waveguide are compared with previously published results.     

New aspects of two transverse modes locking with multiple longitudinal modes in a He-Ne laser

The two different types of self-locking in TEM01+ TEM10modes with multiple longitudinal modes were observed in a He-Ne laser. In the locked state of the first type, two transverse modes are locked separately and the relative heights of adjacent pulses change with the measuring position on the modes. In the locked state of the second type, the transerse modes are quenched alternately, and the relative heights of adjacent pulses are the same on any part of the modes.