Design criteria for FIR waveguide laser cavities

The geometrical design parameters of coherently pumped far infrared waveguide laser cavities are analyzed with respect to minimization of pump power losses. The advantages of highly degenerate cavities and off axis displacement of the injection hole are outlined. Relations between the cavity parameters are given which simplify the design of cavities with high pumping efficiency.     

Polarizing grating coupler for high Q laser cavities

A coupling grating made in the last high-index layer of a highly reflective multilayer laser output mirror, located at the outside of the laser cavity, induces a significant fall of the reflection coefficient for one of the polarizations. The lasing polarization does not suffer more than 0.1% scattering. The understanding of device operation revealed by experiments shows the way for achieving an industrial manufacturing scheme, despite the poor control which layer-deposition technologies presently have on the layer index and thickness separately.     

Losses in fibre laser cavities

A passive cavity ring-down technique has been used to measure the intrinsic losses of a fibre laser cavity. The results show that very low cavity losses can be obtained using conventional mirrors butted to the fibre. Optimum output coupling for a typical cavity intrinsic loss is derived     

Characteristics of the dispersive free-electron laser

The dispersive free-electron laser (DFEL) was previously introduced as an optical klystron (OK) superimposed upon a free-electron laser (FEL). In this paper it is shown that with proper design this device provides a gain increase of the order of 4 over the gain of the OK (for equal lengths) with a gain-energy acceptance product approaching that of the FEL. Even when the transverse excursion of the electron beam exceeds the optical beam dimension, there is only a slight reduction in gain from the above value.     

Time-domain ABCD matrix formalism for laser mode-locking andoptical pulse transmission

ABCD matrix formalism in the time domain has been newly developed on the basis of laser beam and resonator analyses which were developed under a Gaussian paraxial approximation. We derive matrix elements for amplitude and frequency modulations, group velocity dispersion, optical bandpass filter dispersion, and lumped self-phase modulation under a parabolic approximation. Applications to AM, FM, and stretched-pulse laser mode-locking are described by using these time-domain matrices. An application to pulse transmission in a dispersion-allocated system is also described     

Stability analysis for laser diodes with short external cavities

Results of a numerical analysis of the stability of external cavity lasers with short external cavities are presented. If the external cavity is shorter than about 5 mm (air equivalent), the laser remains stable for any feedback from that cavity without any coherence collapse. The results can be considered also as guidelines for the design of laser diodes with integrated passive cavities.<>     

Coupling coefficients of coupled laser cavities

We discuss certain properties of the coupling coefficients for a specific model consisting of two coupled resonant cavities separated by a lossy coupling gap. The coupling coefficients are here defined in the framework of time-dependent coupled-cavity theory-not as end-fire power coupling between traveling waves of two adjacent waveguides. In particular, we explore the validity of a heuristic formula for the coupling coefficients proposed in an earlier publication. It turns out that, in this example, the heuristic formula is directly applicable only if the coupling gap is lossless and off-resonance, but it becomes inapplicable if the lossless gap approaches resonance. The heuristic formula remains useful, but requires a correction if the coupling gap is lossy. The phase angle of the complex coupling coefficient is found to be linearly dependent on the width of the coupling gap, assuming the value 0 (to within multiples of 2π) for an off-resonant gap and the value ofpi/2for a resonant gap. It is not the purpose of this letter to explore properties of c³lasers or to specify their optimum operating conditions. Only the validity of the approximate coupling function is to be investigated.     

Thermal effects in double prism dye laser cavities

Output power, beam divergence, and frequency stability in a double-prism dye laser cavity have been investigated as a function of temperature. For rhodamine 6G dye, it has been found that output power decreases by nearly 34 percent, beam divergence increases from 4.5 to 6.5 mrads, and the laser frequency is shifted by as much as 2 cm^-1, for an increase of 10°C above room temperature. The efficiency of the double-prism dye laser oscillator employed here was 18 percent (for N2laser pump) at a linewidth of 0.07 cm^-1(FWHM). Laser linewidth did not vary in the temperature range investigated here.     

GaAlAs激光器腔面减反射涂层

通过对波长９１０ｎｍ ＧａＡｓ／ＧａＡｌＡｓ激光器谐振腔面蒸镀ＺｒＯ２膜的工艺过程，从理论和实验上分析了涂层特性，透射率由无膜时６２％提高到蒸镀膜后的９４％以上，提高了激光器的激光输出功率和工作寿命，对器件端面起到了保护作用。     

Postgrowth tuning of semiconductor vertical cavities formultiple-wavelength laser arrays

Combined lateral-vertical oxidation of AlGaAs is investigated as a means of tuning the resonant wavelength of a semiconductor microcavity after the epitaxial growth. It is shown that this technique can provide arrays with a wavelength spread equal to the cavity's free spectral range with a single postgrowth processing step. Design issues for multiple-wavelength vertical-cavity laser arrays using this postgrowth tuning technique are discussed, comparing the performance of devices with all-semiconductor and partially or totally oxidized Bragg mirrors. Experimental results are presented on arrays with a 48-nm lasing span around 970 nm, using partially and totally oxidized mirrors     

Pitchfork bifurcation polarization bistability in laser diodes withexternal cavities

A new pitchfork bifurcation polarization bistability in laser diodes with a two-armed polarization-selective external cavity is examined theoretically and experimentally. The rate-equation analysis taking into account gain saturation has been carried out using the model for a laser diode whose laser thresholds of the TE and the TM modes can be changed independently through the changing of their photon lifetimes. It is shown from the analysis that pitchfork bifurcation polarization bistability appears when the laser thresholds for both modes are very close to each other and the switching between two stable states is obtained by means of a photon lifetime changing or a coherent or incoherent light injection. In the experiment, a 1.3-μm InGaAsP laser diodes with a T-shaped polarization-selective external cavity mas used. A new type of polarization bistability was observed when one arm was blocked and then recoupled. The two stable states mere also switched by means of an optical injection. All-optical flip-flop operation has been successfully demonstrated by using both TE and TM trigger inputs     

Beam-quality changes generated by thermally-induced sphericalaberration in laser cavities

Thermally-induced spherical aberration in Nd:YAG rods is investigated. Attention is concentrated on the so-called “intensity moment formalism” to analyze the beam-quality parameter of the emitted laser beams. A number of resonance conditions that certain beam-shape parameters of any stable laser mode should fulfill are also derived, and a comparison with previously reported numerical results is presented     

Switchable multiwavelength erbium-doped fiber laser with cascadedfiber grating cavities

We propose a new concept to produce switchable multiwavelength oscillations with a cascaded fiber Bragg grating overlapping cavity erbium-doped fiber laser. The laser can be designed to operate in multiwavelength or in wavelength switching modes. The different lines have different thresholds. For three-wavelength oscillation, the output powers are linear or piecewise linear functions of the input pump power. An output with a variation of only 1.5 dB has been achieved with an input pump power of 100 mW. For wavelength switching, three single-wavelength and two dual-wavelength operation regions have been obtained toy adjusting the input pump levels     

Astigmatic Gaussian beams produced by axially asymmetric laser cavities

Gaussian beams generated within astigmatic resonators are themselves astigmatic, having wavefront curvatures and spot sizes that are different when measured in two orthogonal directions. Expressions are derived for the confocal parameters, spot sizes, waist positions, and stability conditions of beams formed within spherical mirror resonators that contain one or more inclined plates (or Brewster-ended laser rods). An expression is also derived for the resonant frequencies of the TEMmnmode in such a resonator. It is shown that the frequency degeneracy between modes of the samem + nis lifted and the frequency splittings are calculated. The astigmatism produced by prisms used for dispersion is also considered and precautions are described for avoiding serious astigmatism in resonators containing such prisms.     

Spinor formalism for waveguides

The authors first prove that there exists a close relationship between the spinor fields and the electromagnetic transverse fields TE, TM.Then the spinor formalism is applied to the waveguide theory and explicit formulae are given for waveguides with rectangular or circular cross section. An interesting feature of the spinor formalism is to require only two components.     

二极管激光阵列在Talbot外腔锁相中的超模分析

采用数值计算的方法,对二极管激光阵列在Talbot腔、1/2Talbot腔和1/4Talbot腔中锁相时,同相模和异相模的分布进行了计算。结果表明:同相模在Talbot腔中成像位置没改变,在1/2Talbot腔中成像的位置有d/2的偏移,成像均没有产生相移;在1/4Talbot腔中同相模的分布是两组Talbot像的相干叠加,一组成像位置没有改变,产生-π/4的相移,另一组成像位置有d/2的偏移,产生π/4的相移。异相模在Talbot腔和1/2Talbot腔中成像位置均没有改变,在Talbot腔中异相模产生-π/2的相移,而在1/2Talbot腔中产生-π/4的相移;在1/4Talbot腔中异相模也是两组Talbot像的相干叠加,一组成像位置向左偏移d/4 ,一组向右偏移d/4 ,均产生-π/8的相移。所得结果给出了二级管激光阵列在Talbot外腔中同相模和异相模的分布规律。     

Electroluminescence properties of a whispering-gallery-mode laser with coupled disk cavities

Whispering-gallery-mode (WGM) lasers (emission wavelength λ = 2.1–2.4 μm) with coupled disk cavities connected by a bridge are developed on the basis of a GaInAsSb/GaAlAsSb quantum-well nano-heterostructure and their emission spectra and optical far-field patterns are studied. Almost single-mode lasing in one spatial mode is observed in a wide range of supply currents. The emission wavelength grows with increasing current due to heating of the laser, and this phenomenon can be used in diode-laser spectroscopy. An assumption is made that the flux of generated emission can pass in lasers of this kind from one cavity to the other and back along the cavity-connecting bridge. It is found that strong narrowing of the laser emission pattern occurs with increasing current near the plane separating the coupled cavities.     

Cavity decay rate and relaxation oscillation frequency inunconventional laser cavities

Measuring the relaxation oscillation frequency ω_r versus the normalized pumping rate r can provide a useful technique for determining either cavity or atomic parameters in many different kinds of lasers. Measurements of relaxation frequency versus pumping rate in a Nd:YAG laser using a gain-guided unstable-cavity design were recently found, however, to yield values of cavity decay rate which were unreasonably large compared to other estimates of the cavity losses. This difficulty has been resolved by a closer look at the relaxation oscillation dynamics in this type of laser. We find that in nonorthogonal laser cavities with nonuniform gain distributions the energy decay rate of the cavity oscillation mode usually employed in the relaxation frequency formula must be replaced by a different decay rate relevant to oscillation mode perturbations. A numerical simulation including this more general effect gives values very close to our experimental results, confirming the validity of this modified analysis     

Formation conditions of random laser cavities in annealed ZnO epilayers

The possibilities to realize room-temperature random laser action in ZnO epilayers with MgO as the buffer layer are studied. It is found that the formation of random laser cavities inside the ZnO epilayers can be achieved by post-growth annealing. Incoherent and coherent random lasing phenomena are observed from ZnO epilayers with (220)- and [200]-oriented MgO buffer layers, respectively. Lasing linewidth of the ZnO epilayers with incoherent and coherent feedback under 355-nm optical excitation is found to be /spl sim/4 and /spl sim/0.4 nm, respectively.