Aligned ZnO nanorod arrays fabricated on Si substrate by solution deposition

Aligned ZnO nanorod arrays were fabricated by chemical solution deposition based on Si substrate which was spin coated with ZnO colloid as nucleation seeds. Their microstructures were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The results indicated that ZnO nanorods nucleated and grew vertically on Si substrates along the [0 0 1] direction with single-crystalline structure. The diameter of ZnO nanorods was greatly affected by the grain size of ZnO seeds. Room-temperature photoluminescence of nanorods has a strong emission band at about 384 nm.     

Plasmonic leaky‐mode lasing in active semiconductor nanowires

Leaky modes are below‐cutoff waveguide modes that lose part of their energy to the continuum of radiation modes during propagation. In photonic nanowire lasers, leaky modes have to compete with almost lossless above‐cutoff modes and are therefore usually prevented from crossing the lasing threshold. The situation is drastically different in plasmonic nanowire systems where the above‐cutoff plasmonic modes are very lossy because of their strong confinement to the metal surface. Due to gain guiding, the threshold gain of the hybrid electric leaky mode does not increase strongly with reduced wire diameter and stays below that of all other modes, making it possible to observe leaky‐mode lasing. Plasmonic ZnO nanowire lasers operating in the gain‐guided regime could be used as coherent sources of surface plasmon polaritons at the nanoscale or as surface plasmon emitting diodes with an emission angle that depends on the nanowire diameter and the color of the surface plasmon polariton.

     

Properties and laser oscillation of the (Nd,Y) pentaphosphate system

We report on fluorescence and other properties of the system (Nd, Y)P₅O₁₄. With a single crystal of 1.32 mm length containing approximately one atomic percent yttrium we obtained pulsed laser oscillation at 1.05 microns wavelength with peak powers exceeding 200 Watts.     

Single-photon and three-photon absorption induced whispering-gallery mode lasing in ZnO micronails

The ZnO micronails were synthesized by the vapor phase transport method. The heads of the micronails show hexagonal disk structure which is suitable for the whispering-gallery mode lasing microcavity. Under the excitation of a nanosecond pulse at 355 nm, the single-photon absorption induced lasing was stimulated in the micronail with the head diameter of 3.0 μm, the whispering gallery mode and Fabry-Pérot mode lasing were investigated. Under the excitation of femtosecond laser pulses at 804 nm, the second harmonic generation and the three-photon absorption induced photoluminescence were observed from a bulk of micronails, then an individual micronail with the diameter of 9.1 μm was employed to realize the three-photon absorption induced whispering-gallery mode lasing.     

Laser theory for semiconductor quantum dots in microcavities

Quantum dots (QDs) used as active material in microresonators are currently of strong topical interest due to breakthroughs in growth and device structuring. From the theory side, however, atomic models are still used to analyse the emission from these semiconductor systems, despite known differences between QDs and atoms. We introduce a semiconductor laser theory based on a microscopic approach with the goal of better describing the characteristic behaviour of QD-based laser devices and to show differences from predictions based on atomic models.     

纳米ZnO粉末中随机激光现象

实验采用三倍频Nd:YAG(波长355 nm，脉宽8ns，频率30Hz) 脉冲激光器作为抽运光源，在ZnO纳米粉末(直径～100 nm)中发现了类似激光现象.并用环形腔理论模拟了ZnO的颗粒密度对平均自由程的影响，从理论上证明在纳秒级激光器的抽运下，ZnO纳米粉末也可以发射激光. 关键词： 类似激光 ZnO纳米粉末 平均自由程     

Random lasing in ZnO nanocrystals

Nanocrystalline ZnO powders can act as gain and scattering medium in a random laser where the light emission can be strongly amplified. In this work, we compare the luminescence properties of samples with different particle sizes in the regime of linear and nonlinear optics. In the high-excitation regime random lasing is observed in all samples. Here, the lasing threshold depends strongly on the size distribution in the ensemble. Additional characterization of the samples has been done by determining the absolute quantum efficiency of the radiative processes in the powder. The values are in the 10% range and the near-edge luminescence is strongly influenced by the particle sizes. We show that by annealing the nanocrystals coalesce to larger polycrystalline grains, which results in a new emission band at 3.333 eV due to the grain boundaries. Furthermore, it is found that in the annealed samples the threshold for random lasing could be considerably decreased.     

Microstructures evolution and physical properties of laser induced NbC modified nanocrystalline composites

The nanoscale quasicrystals (NQs), amorphous and ultrafine nanocrystals (UNs) modified hard composites are produced by laser cladding (LC) of the Ni60A-TiC-NbC-Sb mixed powders on the additive manufacturing (AM) TA1 titanium alloy. The LC technique is favorable to formations of icosahedral quasicrystals (I-phase) with five-fold symmetry due to its rapid cooling and solidification characteristics. The formation mechanism of this I-phase is explained here. Under the actions of NQs, amorphous and UNs, such LC composites exhibited an extremely high micro-hardness. UNs may also intertwin with amorphous, forming yarn-shape materials. This research provides essential theoretical basis to improve the quality of laser-treated composites.     

Elongated hexagonal ZnO micro-fence optical resonator

A highly symmetric ZnO micro-fence is prepared to form an optical resonator, which a symmetric array consisting of six elongated hexagonal microcolumns. It is found that the luminescence emission could be enhanced at the edge of ZnO micro-fence and the wavelength dependent light intensity could be influenced by its geometry. The optical characterization along with theoretical calculations and computer simulation analysis suggest that the Fabry-Perot and Cross-whispering gallery modes are generated in ZnO micro-fence. The individual ZnO micro-fence can regarded as an optical resonator structure. Furthermore, it is proposed that the source concentration around the substrate during the growth is a crucial factor for forming such a micro-fence.     

ZnCdO/ZnO – a new heterosystem for green‐wavelength semiconductor lasing

We report on our efforts to cultivate the ternary compound ZnCdO as a semiconductor laser material. Molecular beam epitaxy far from thermal equilibrium allows us to overcome the standard solubility limit and to fabricate alloys with band gaps ranging from 3.4 down to 2.1 eV. Optimized structures containing well‐defined quantum wells as active zones are capable of low‐threshold lasing under optical pumping up to room temperature. The longest lasing wavelength achieved so far is 510 nm.     

Single mode lasing in transversely multi‐moded PT‐symmetric microring resonators

Conventional techniques for transverse mode discrimination rely on introducing differential external losses to the different competing mode sets, enforcing single‐mode operation at the expense of additional losses to the desirable mode. We show how a parity‐time (PT) symmetric design approach can be employed to achieve single mode lasing in transversely multi‐moded microring resonators. In this type of system, mode selectivity is attained by judiciously utilizing the exceptional point dynamics arising from a complex interplay of gain and loss. The proposed scheme is versatile, robust to deviations from PT symmetry such as caused by fabrication inaccuracies or pump inhomogeneities, and enables a stable operation considerably above threshold while maintaining spatial and spectral purity. The experimental results presented here were obtained in InP‐based semiconductor microring arrangements and pave the way towards an entirely new class of chip‐scale semiconductor lasers that harness gain/loss contrast as a primary mechanism of mode selectivity.

     

Theoretical modelling of mode formation in Tm:YVO4 microchip lasers

Theoretical investigations of mode formation in a Tm³⁺:YVO₄ microchip laser are presented. Based on these new computations, we find a fair agreement between theoretical and experimental results obtained within a large pump power range and for two different pump beam sizes.     

ZnO粉末激光的研究

从ZnO粉末激光的实验现象出发,将激光泵浦下的ZnO粉末介质相互作用系统作为一个整体,并建立相应的物理模型。运用传输矩阵的方法数值模拟了该激光与ZnO粉末被泵浦的面积、功率和方向之间的关系。模拟结果在定性上与实验吻合。     

Single-mode lasing in a coupled twin circular-side-octagon microcavity

We demonstrate the curvature of coupled twin circular-side-octagon microcavity (TCOM) lasers as the degree of freedom to realize manipulation of mode quality ($Q$) factor and lasing characteristics. Numerical simulation results indicate that mode $Q$ factors varying from 10$^{4 }$ to 10$^{8}$, wavelength intervals of different transverse modes, and mode numbers for four-bounce modes can be manipulated for five different deformations. Global mode distributes throughout coupled microcavity with mode $Q$ factor around the order of 10$^{4 }$ or 10$^{5}$. Four-bounce modes lase with injection currents applied single microcavity. By pumping both microcavities simultaneously, single-mode lasing for global modes with side mode suppression ratios (SMSRs) of 30, 32, 32, 31, and 36 dB is achieved at the deformation of 0, 0.5, 1, 1.5, and 2 with four-bounce modes suppressed, respectively. Moreover, the linewidths less than 11 MHz for the single mode are obtained with the deformation of 2. The results show that the lasing modes can be efficiently manipulated considering variable curvature for TCOM lasers, which can promote practical applications of microcavity lasers.     

ZnO lasing in complex systems with tetrapods

A ZnO structure in the form of a core–shell wire was grown with a modified vapour transport and condensation method. The wire consists of a dense core which may play the role of a waveguide and a shell formed mainly from tetrapod-type crystallites. The high optical quality of the produced ZnO material is confirmed by continuous wave photoluminescence (PL) analysis demonstrating that low- temperature PL is related to the recombination of bound excitons, while room-temperature PL is due to free excitons. Good quality of the crystal structure is demonstrated also by the Raman spectrum. The shell of the wire exhibits room-temperature laser action due to lasing modes in tetrapods under the excitation by nanosecond laser pulses. The nature of the lasing modes is discussed. A simplified model for one of the possible modes is suggested.     

Impact of size upon lasing in ZnO microtetrapods

High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 μm have been grown by carbothermal chemical vapor deposition. Lasing with mode quality factors of 2500–3000 is demonstrated. The origin of laser resonator cavity is discussed as a function of the tetrapod size. It is shown that in big tetrapods with legs of 12 μm in length the laser emission lines are well explained by longitudinal Fabry–Pérot modes generated in cavities formed by individual tetrapod legs. The dispersion of the ZnO refractive index is experimentally determined from the position of lasing modes in the temperature interval from 10 to 300 K. It is shown that the lasing mode structure is seriously affected by the decrease of the tetrapod size. For a small tetrapod with a leg length of 1 μm, the lasing modes cannot be explained anymore by the formation of longitudinal Fabry–Pérot modes in separate tetrapod legs, and the generation of guided modes by multiple total internal reflections in single tetrapod legs or in pairs of legs should be taken into account. The correlations between the lasing threshold and the tetrapod size are discussed.     

束旋转90°对束变换环孔腔输出性能的影响

 使用积分方法和差分方法结合的快速计算方法，在实际燃烧驱动氟化氢化学激光器增益介质沿径向分布不均匀的情况下，考虑在光束变换环形孔径激光谐振腔的紧束段引入光束旋转90°对其输出性能的影响。计算结果显示：在无腔失调的情况下，在紧束段引入光束旋转对束变换环孔激光谐振腔输出功率及光束质量的改善并不显著；在存在腔失调的情况下，紧束段光束旋转对于输出功率和光束质量的改善有显著效果。     

Strong temperature and substrate effect on ZnO nanorod flower structures in modified chemical vapor condensation growth

We have reported low temperature growth (300 °C) of ZnO nanorod flower structures by depositing zinc acetate vapor on Ge (100) substrate in the form of a jet using chemical vapor condensation technique. The flowers were comprised of hierarchical arrangement of highly crystalline ZnO nanorods oriented isotropically around a common nucleus. The temperature window for stability of these structures was found to be very narrow and the formation of the flowers was highly depended on the type of the substrates used. The flower morphology changed to a different hemispherical shape when the growth temperature was increased by only 50 °C while decreasing the growth temperature of the same degrees resulted in an amorphous deposition of ZnO. The temperature and substrate effect has been explained on the basis of adatom kinetics during growth. X-ray diffraction and TEM study revealed wurtzite ZnO nanorods with lattice constants a and c of 3.2 and 5.19 Å, respectively. The flower structures showed strong room temperature photoluminescence having pure excitonic transition at around 3.298 eV.     

Saturated X-ray lasing in Ni-like Sn at 11.9 nm using the GRIP scheme

We report on gain-saturated operation of the 11.9 nm X-ray lasing line in Ni-like Sn using the grazing-incidence pumping scheme (GRIP). The experiments were done with 2-ps duration pump pulses and energies up to 5 J. Strong gain saturation with multi-microjoule output was measured for the Sn laser at a grazing angle of 30° and a pump pulse energy of 3 J. This was achieved with a 4.5%, 2-ps duration prepulse 2.4 ns ahead of the main pulse and also incident at grazing incidence. Increasing laser output was observed at GRIP angles up to 45°. At this angle, the minimum energy required for saturated lasing was determined as ∼2 J.