Low-threshold plasmonic lasing based on high-Q dipole void mode in a metallic nanoshell

We propose a novel type of plasmonic lasing nanostructure consisting of a metallic shell and a gain core. We demonstrate numerically that highly localized void modes of such metallodielectric core-shell nanoparticles have a very high quality factor. We found that the dipole void mode has a lasing threshold as low as 128 cm(-1) at 800 nm as a result of the unique mode distribution within the shell, due to a maximum field enhancement around the void center. The lasing condition for a symmetry-reduced silver nanocup is also investigated and the low plasmonic lasing threshold is sustained provided that the opening angle of the nanocup is smaller than 10°. Our proposal presents a new path toward plasmonic lasers with low gain threshold.     

Laser properties of some phthalocyanines

The lasing behavior of solutions of the phthalocyanines of aluminum, gallium, magnesium, and zinc was studied with nitrogen laser optical pumping. Aluminum phthalocyanine chloride showed simultaneous lasing at two wavelengths separated by approximately 70 nm. Gallium, magnesium, and zinc phthalocyanine each lased at only one wavelength. This behavior is explained in terms of some of the intrinsic physical properties of these phthalocyanines.     

Temperature dependent characteristics of InAs/GaAs quantum dot laser grown by gas source molecular beam epitaxy

We report on the temperature dependent lasing characteristics of InAs/GaAs quantum dot lasers under continuous wave mode. The five-stacked InAs quantum dots were grown by gas-source molecular beam epitaxy with slightly different thickness. Ridge waveguide laser with stripe width of 6 μm was processed on the growth structure. The characteristic temperature was measured as high as infinity in the temperature range of 80–180 k. With the increase of injection current, the lasing spectra of laser diode broaden gradually at low temperature of 80 k. However, when the operation temperature increases from 80 to 300 K, the width of lasing spectrum reduces gradually from 40 to 2.0 nm. The lasing process is obviously different from that of a reference quantum well laser which widens its width of lasing spectra by increasing operation temperature. These experiments demonstrate that a carrier transfer from the smaller size of dots into larger dots caused by thermal effect play an important role in the lasing characteristic of quantum dot lasers. In addition, the laser can operate at maximum temperature of 80 °C under continuous wave mode with a maximum output power of 52 mW from one facet at 20 °C. A wavelength thermal coefficient of 0.196 nm/K is obtained, which is 2.8 times lower than that of QW laser. The low wavelength thermal coefficient of quantum dot laser is mainly attributed to its broad gain profile and state filling effects.     

Whispering gallery mode microlasers and refractive index sensing based on single polymer fiber

The realization of whispering gallery mode (WGM) lasing in polymer fibers is hindered by an appropriate method to dissolve the polymer and the gain material. In this work, microfibers fabricated by directly drawing from a dye doped polymer solution are exhibited as high quality microlasers and microsensors. Multi‐mode and even single‐mode lasing is observed from the fiber under optical pumping at room temperature. The linewidth of lasing mode is narrower than 0.09 nm. The lasing mechanism is unambiguously verified by comprehensive spectroscopic analysis and ascribed to WGMs. Diameter‐ and polarization‐dependent lasing characteristics are systematically investigated, showing good agreement with the theoretical calculation. Particularly, application of the fiber laser for refractive index sensing based on resonant shift of lasing mode is demonstrated and the sensitivity up to about 300 nm/RIU is achieved. The promising potential of high quality polymer microfibers as optical sensors and multi‐function components for flexible photonic integrated systems is highly expected.     

类氖-锗电子碰撞激发X光激光的增益特性

 电子碰撞激发X光激光的增益特性依赖于电子密度Ne、电子温度Te、增益区宽度D R和介质速度梯度dv/dz等四个表征等离子体内部状态的参数。以类氖-锗离子为例研究了反转和增益特性对Te、Ne的依赖关系，并在典型的增益区宽度（D R=100 μm）和介质速度梯度（dv/dz=1.3×10⁹s^-1）下讨论了共振线俘获对增益特性影响，给出波长为19.6nm, 23.2nm和23.6nm三条激光线的增益目标区域。还讨论了双电子复合过程对离子布居的重要影响。     

Obtaining Single Picosecond Pulses in a Short-Cavity Dye Laser with Switching of Lasing to the Saturable Absorber

A new method of lasing of single picosecond pulses in a short-cavity dye laser with spatial separation of the lasing medium and the saturable absorber in the case of pumping by nanosecond pulses with energies much higher than the oscillation threshold has been developed and experimentally realized. The method is based on the use of a high-Q, external cavity tuned to the amplification wavelength of the saturable absorber. The first picosecond pulse is lased at a lasing-medium wavelength and the subsequent pulses are lased at a saturable-absorber amplification wavelength.     

Theoretical study on the lasing plasmon of a split ring for label-free detection of single molecules and single nanoparticles

This paper reports the plasmonic lasing of a split ring filled with gain material in water. The lasing mode(1500 nm)is far from the pump mode(980 nm), which can depress the detection noise from the pump light. The laser intensities of the two modes simultaneously increase by more than 10~3 in amplitude, which can intensify the absorption efficiency of the pumping light and enhance the plasmonic lasing. The plasmonic lasing is a sensitive sensor. When a single protein nanoparticle(n = 1.5, r = 1.25 nm) is trapped in the gap of the split ring, the lasing spectrum moves by 0.031 nm, which is much larger than the detection limit of 10~(-5) nm. Moreover, the lasing intensity is also very sensitive to the trapped nanoparticle. It reduces to less than 1/600 when a protein nanoparticle(n = 1.5, r = 1.25 nm) is trapped in the gap.     

Switchable erbium-doped fiber ring laser based on Sagnac loop mirror incorporating few-mode high birefringence fiber

Without the need of any other additional filtering device, a triple-wavelength switchable erbium-doped fiber ring laser based on Sagnac loop mirror incorporating a piece of few-mode high birefringence fiber is newly proposed and experimentally demonstrated. Three potential lasing wavelengths at about 2.0 nm interval with the side mode suppression ratio higher than 40 dB can be switched mainly by adjusting a polarization controller next to the few-mode high birefringence fiber in the Sagnac loop. In addition to the stable single-line lasing operation, simultaneous dual- and triple-line oscillations are also highly stable at room temperature with suppressing the intrinsic homogeneous gain broadening of the erbium-doped fiber.     

室温下稳定的多波长掺铒光纤激光器的研究

通过在线形谐振腔中引入一段缠绕在压电陶瓷上的单模光纤作为正弦相位调制器,使得激射波长的损耗不固定,抑制由于掺铒光纤的均匀展宽效应引起的模式竞争,从而避免了在室温下不稳定的单波长激射,实现了多波长掺铒光纤激光器的稳定输出。为了获得平坦的多波长输出,在谐振腔里使用了一个损耗峰位于1530nm处的长周期光纤光栅,以获得较为平坦的增益谱。通过两个3dB耦合器制成的反射型梳状滤波器的滤波作用,实验中观察到稳定的多波长激射,相邻波长间隔约为0．45nm。中心9个波长的输出功率平坦度为10dB,边模抑制比大于25dB。     

Self-tuned quantum dot gain in photonic crystal lasers

We demonstrate that very few (2-4) quantum dots as a gain medium are sufficient to realize a photonic-crystal laser based on a high-quality nanocavity. Photon correlation measurements show a transition from a thermal to a coherent light state proving that lasing action occurs at ultralow thresholds. Observation of lasing is unexpected since the cavity mode is in general not resonant with the discrete quantum dot states and emission at those frequencies is suppressed. In this situation, the quasicontinuous quantum dot states become crucial since they provide an energy-transfer channel into the lasing mode, effectively leading to a self-tuned resonance for the gain medium.     

Sustained kilowatt lasing in a free-electron laser with same-cell energy recovery

Jefferson Laboratory's kW-level infrared free-electron laser utilizes a superconducting accelerator that recovers about 75% of the electron-beam power. In achieving first lasing, the accelerator operated "straight ahead" to deliver 38-MeV, 1.1-mA cw current for lasing near 5 &mgr;m. The waste beam was sent directly to a dump while producing stable operation at up to 311 W. Utilizing the recirculation loop to send the electron beam back to the linac for energy recovery, the machine has now recovered cw average currents up to 5 mA, and has lased cw with up to 1720 W output at 3.1 &mgr;m.     

Dual-Wavelength Erbium Fiber Laser in a Simple Ring Cavity

Abstract

By controlling the cavity loss of the modes using a variable optical attenuator, specific intensities of distributed modes can be fed back into the erbium-doped fiber to produce signals without mode competition, thus resulting in stable lasing as a means to overcome mode competition in a homogenous gain medium. Two lasing signals were obtained with peak powers of approximately ?3.475 dBm and ?4.386 dBm for wavelengths of 1,540 nm and 1,548 nm, respectively, with a side mode suppression ratio of more than 43 dB.     

Laser performance studies of para-(phenylene-ethynylene) polymers in organic solvents

The lasing performance of the polymers poly(2,5-dioctadecyloxy-paraphenylene-ethynylene-co-2,5-thienyl) (OPT) and poly(2,5-dioctadecyloxy-paraphenylene-ethynylene-co-2,5-pyridinyl) (OPP) in organic solvents was studied. A two-mirror resonator was transversally pumped using single pulses of the second harmonic of a mode-locked ruby laser. OPT in tetrahydrofuran lased in the region from 480 nm to 525nm and OPP in tetrahydrofuran showed laser action in the region from 460 nm to 490nm. The polymer solutions are characterized by absorption and fluorescence spectroscopic analysis. Effective stimulated emission cross-sections are reported. High excited-state absorption cross-sections and residual ground-state absorption reduce the lasing efficiency. This revised version was published online in November 2006 with corrections to the Cover Date.     

Suppression of parasitic lasing in high energy, high repetition rate Ti:sapphire laser amplifiers

Transverse parasitic lasing is well known for limiting the signal gain and the pulse energy that can be extracted from Ti:sapphire petawatt amplifiers. We have developed a technique for suppressing these parasitic lasing modes based on perfect refractive index-matching liquid doped with a broad-bandwidth absorber to suppress the transverse lasing while ensuring proper heat removal from the Ti:sapphire crystal. The 800 nm laser output with a bandwidth of 41 nm (FWHM) and peak energy of 22.7 J at a repetition rate of 1 Hz is demonstrated.     

光纤回音壁模式的三波段激光辐射研究

将石英光纤浸入低折射率的激光染料溶液中构成圆柱形微腔.采用沿光纤轴向光抽运的消逝波激励增益方式,获得了沿光纤轴向长距离的激光染料增益,受激辐射光在圆柱形微腔中回音壁模式的支持下形成激光振荡.在直径为288 μm的同一根光纤外分三段分别填入罗丹明6G、罗丹明610和罗丹明640激光染料乙二醇溶液,实现了波长分别在567～575 nm、605～614 nm和656～666 nm三个不同波段的回音壁模式激光振荡,用一根光纤同时获得了红、橙、黄三种不同颜色的激光辐射.对实验所获得的回音壁模式激光光谱做了模式标定,依据标定的模式数计算了各种模式以及抽运光在光纤截面的强度分布.计算结果表明,激光增益区域总是局限在圆柱形微腔回音壁模式的模场区域内,由此可以显著地提高抽运效率,增加抽运光沿光纤轴向的增益长度.     

A 795 nm gain coupled distributed feedback semiconductor laser based on tilted waveguides

The 795 nm distributed feedback lasers have great application in pumping the Rb D1 transition. In this paper, in order to realize specific 795 nm lasing, we designed tilted ridge distributed feedback lasers based on purely gain coupled effect induced by periodic current injection windows through changing the angle of the tilted ridge. The fabricated devices were cleaved into 2 mm-cavity-length, including 5 tilted angles. The peak output powers of all devices were above 30 m W.Single longitudinal mode lasing was realized in all tilted Fabry–Perot cavities using periodic current injection windows,with side mode suppression ratio over 30 d B. The total wavelength range covered 8.656 nm at 20℃. It was disclosed theoretically and experimentally that the output powers, threshold currents, and central wavelengths of the tilted ridge purely gain coupled DFB lasers were relevant to the tilted angles. The results will be instructive for future design of DFB laser arrays with different central wavelengths.     

Optically pumped GaN/AlGaN quantum well intersubband terahertz laser

We propose an optically pumped nonpolar GaN/AlGaN quantum well (QW) active region design for terahertz (THz) lasing in the wavelength range of 30 μm～ 40 μm and operating at room temperature. The fast longitudinal optical (LO) phonon scattering in GaN/AlGaN QWs is used to depopulate the lower laser state, and more importantly, the large LO phonon energy is utilized to reduce the thermal population of the lasing states at high temperatures. The influences of temperature and pump intensity on gain and electron densities are investigated. Based on our simulations, we predict that with a sufficiently high pump intensity, a room temperature operated THz laser using a nonpolar GaN/AlGaN structure is realizable.     

Dual-cavity dual-output multi-wavelength fiber laser based on nonlinear polarization rotation effect

We demonstrate a multi-wavelength fiber laser based on nonlinear polarization rotation (NPR) in dual-cavity configuration with two output ports. The laser employs a piece of erbium doped fiber (EDF) and semiconductor optical amplifier (SOA) as the gain medium in a separate cavity. By incorporating PCF in the dual cavity the non-linear polarization rotation (NPR) effect is enhanced and thus higher output and more oscillating lasing can be achieved. The laser produces three strong lines with a spacing of 2.40 nm and side mode suppression ratio (SMSR) of more than 10 dB at 1535 nm region. Another output produces 8 lines of optical comb with a spacing of 0.54 at 1570 nm region.     

非线性吸收诱导掺镱光纤激光器中的光学双稳

研究了在掺镱光纤激光器中观察到的光学双稳态现象.激光信号光和驻留泵浦光的双稳特性来源于激光器在小信号和增益饱和两种情况下,掺镱光纤对信号的非线性吸收导致的激光器内腔非线性损耗.同时分析了把泵浦光中的光学双稳行为通过分叉的腔结构扩展到切换式双波长光纤激光器的可行性.     

Stable room-temperature multi-wavelength lasing oscillations in a Brillouin–Raman fiber ring laser

A stable room-temperature multi-wavelength Brillouin–Raman fiber laser with a ring cavity configuration was proposed and experimentally investigated. An obvious suppressant effect for unstable mode hopping of multi-wavelength lasing oscillations induced by deeply saturated effect was observed in the ring cavity configuration. Stable room-temperature multi-wavelength lasing oscillations with more than 30 lasing lines and wavelength spacing of 0.076 nm were obtained with only 250 mW Raman pump power and a section of high nonlinear fiber with a length of 1.5 km. The lasing output is so stable that the maximum power fluctuations for the foremost three Stokes lines over more than 20 min of observation were less than 0.30 dB. The lasing stability of the laser was also compared with a linear cavity configuration with the same gain components and pump conditions. While using the linear laser cavity configuration, obvious mode hopping was observed. The minimum value of the maximum power fluctuations at all lasing lines over more than 10 min of observation was more than 0.90 dB.