Mode-locking of quasi-continuous lasers

A simple rate-equation theory is developed which indicates that the combination of nonlinear amplification and nonlinear absorption may be responsible for ultrashort pulse generation in a mode-locked quasi-continuous laser system in the absence of commensurately short relaxation times. It is tentatively proposed that this mechanism is responsible for picosecond pulse generation in the mode-locked dye laser.     

Mode-locking dynamics of synchronously-pumped colour-centre lasers

A theoretical model has been developed for studying the steady-state pulse shaping dynamics of a synchronously-pumped colour-centre laser. A wide range of results is presented detailing effects on the mode-locking process of pump pulse power and width, laser bandwidth, cavity mismatch and, stochastic noise. From the results, we identify conditions which lead to the formation of single and multiple pulses. We show this can be understood on the basis of a simple scaling law between the principal laser parameters.     

Mode-locking of diode laser-pumped solid-state lasers

Mode-locked diode-pumped solid state lasers have become important sources for efficient and reliable short pulse generation. We review techniques for active mode-locking of diode-pumped lasers, highlighting techniques which have produced much shorter pulse durations than previous technologies and extended operating repetition rates to the several gigahertz regime. To achieve even shorter pulse durations a series of nonlinear passive mode-locking techniques have been developed. Self-starting additive pulse mode-locking, resonant passive mode-locking and self-mode-locking of diode-pumped solid-state lasers are described.     

Mode-locking of He - Ne lasers with saturable organic dyes

The organic dyes cresyl violet, cresyl violet acetate and nile blue A were found to act as saturable absorbers for mode-locking of 6328 Å He-Ne lasers. The width of the obtained optical pulses is proportional to the inverse of the pulse energy. The minimum pulse width obtained is 220 psec.     

Mode-locking of fiber lasers induced by residual polarization dependent loss of cavity components

We found experimentally that under strong pumping, mode locking could self-start in a fiber laser even without inserting a polarizer or a mode locker in the cavity. It was identified that the mode locking was caused by the large residual polarization dependent loss (PDL) of a cavity component. We have experimentally determined the strength of PDL in our fiber lasers. Our results show that in order to exclude the nonlinear polarization rotation (NPR) mode locking effect in a fiber laser one has to carefully select the intracavity components.     

Coupled-resonator optical waveguides doped with nanocrystals

Microsphere resonators doped with semiconductor nanocrystals are explored as building blocks for coupled-resonator optical waveguides (CROWs). The evolution of individual cavity modes into coherently coupled waveguide modes is studied using polarization-sensitive microphotoluminescence spectroscopy. To demonstrate the formation of multisphere photon states, we use a bent linear array of microresonators and probe the properties of the cavity photon field by the spatially and spectrally resolved measurement of the nanocrystal emission. Photon mode coupling is evidenced by the observed mode splitting and emission intensity distributions along the CROW structure.     

溶胶-凝胶法制备PbS量子点玻璃的研究

采用溶胶-凝胶法合成了半导体PbS量子点掺杂的Na₂O-B₂O₃-SiO₂玻璃,研究了不同热处理工艺对玻璃结构的影响,利用多种表征手段研究了量子点掺杂玻璃中的微晶结构及其光学性能.孔径分析结果表明随着热处理温度的升高玻璃内部孔径不断减小,最终孔结构几乎完全消失;红外光谱分析表明玻璃网络结构在较低温度下己经形成,随温度的升高不断密实化; X射线光电子能谱证明了玻璃中存在PbS,高分辨透射电镜表征了玻璃基质中掺杂的微晶结构是PbS,统计计算表明,玻璃中微晶的平均粒径尺寸为3.5nm;吸收光谱分析发现,微晶掺杂玻璃的吸收边界较PbS的块体材料发生了明显的蓝移,产生了量子尺寸效应;通过Z扫描技术测得其非线性折射率γ为-2.03×10^-14cm²/GW. 关键词： PbS量子点 半导体 非线性光学效应 溶胶-凝胶法     

Mode-locked diode-pumped vanadate lasers operated with PbS quantum dots

The use of glasses doped with PbS nanocrystals as intracavity saturable absorbers for passive Q-switching and mode locking of c-cut Nd:Gd_0.7Y_0.3VO₄, Nd:YVO₄, and Nd:GdVO₄ lasers is investigated. Q-switching yields pulses as short as 35 ns with an average output power of 435 mW at a repetition rate of 6–12 kHz at a pump power of 5–6 W. Mode locking through a combination of PbS nanocrystals and a Kerr lens results in 1.4 ps long pulses with an average output power of 255 mW at a repetition rate of 100 MHz.     

Mode-locking of high power lasers by a combination of intensity and time dependent Q-switching

A new method for simultaneous mode-looking and Q-switching of high power lasers by a combination of intensity and time dependent Q-switching is described. The two Q-switching mechanisms are achieved by equipping the laser with a device, here called the “Electro-Opto-Optical Modulator” (EOOM). The modulator, which is driven by the optical field which it modulates in addition to an external electric field, contains nonlinear media which exhibit a large optical as well as dc Kerr effect. The advantages of this combined Q-switching compared with a pure intensity dependent Q-switching are that the generation of the model-locked pulses can be predetermined in time and that the length of the Kerr active medium can be decreased.     

Experimental study on tellurite laser glass doped with neodymium

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 5, pp. 781–785, May, 1990.     

Glasses of heavy metal and gallium oxides doped with neodymium

Abstract

Optical and physical properties of a new family of Nd: BPG (Bi₂O₃-PbO-Ga₂O₃) glasses are presented at 1 mol% Nd doping level. Knoop hardness of 321 kg/mm² and density of 4.63 g/cm³ were measured. These high refractive index glasses present a very large absorption cross section of 2.5 × 10^?20 cm² at 800 nm. Emission occurs at three bands centered at 877 nm, 1066 nm and 1341 nm with a fluorescence lifetime associated to these transitions of 110 μs. At 1066 nm, the spectral linewidth is 30 nm. These properties make these glasses good candidates for laser action.     

Spectral-luminescent characteristics of fluorophosphate glasses with zinc sulfide nanocrystals

Fluorophosphate glasses doped with ZnS are studied. The properties of ZnS nanocrystals formed are determined using X-ray-diffraction analysis and optical spectroscopy. The size and the band-gap width of these crystals are determined by the Tauc method. It is shown that ZnS nanocrystals luminesce in the visible spectral region with a low (2–3%) absolute quantum yield.     

Comparative analysis of Raman spectra of PbS macro- and nanocrystals

A comparative analysis of the Raman spectra of bulk PbS and PbS nanocrystals with average diameters of 6.6 and 3.8 nm has been performed. It is shown that the bands due to the LO phonons at the Γ point of the Brillouin zone dominate in the first- and second-order Raman spectra of the nanocrystals. Based on the analysis of the relative band intensities for the first- and second-order spectra a qualitative conclusion is drawn: the electron-LO-phonon interaction in PbS nanocrystals increases with a decrease in their size.     

Combined mechanical-color center passive Q-switching of neodymium lasers

A combined mechanical LiF:F^-₂ color center passive Q-switch was used for YAG: Nd lasers. This system gives monopulse emission when each of the switches used alone give multiple pulse generation. Energy in switched regime represents up to 0.7–0.8 from that in free-generation regime, for the same pump energy. Pulse duration is considerably shorter than for the case when only one of the switches is used, leading to monopulse emission with very high peak power in the neodymium lasers.     

Preparation and characterization of neodymium tin oxide pyrochlore nanocrystals by the hydrothermal method

Fine powder of Nd₂Sn₂O₇ nanocrystals with a phase-pure pyrochlore structure were synthesized at low temperatures (200 °C) for 12 h through the hydrothermal method in alkaline medium. The pH value of the solution was adjusted by addition of 1.0 M NaOH solution to reach 11, and basically above 11 was shown to accelerate the crystallization process. The samples were characterized by X-ray diffraction and Fourier Transformed InfraRed spectra. Scanning electron microscopy was used for morphologic evolution. Furthermore, photoluminescence characterization and UV–VIS spectra of the Nd₂Sn₂O₇ pyrochlore nanocrystals showed clear luminescence and absorption peaks, and band gap energy were calculated using emission and absorption data.     

Luminescent properties of doped dielectric nanocrystals

Taking into account electron-phonon interaction effects, we have studied the radiative characteristics of doped nanoellipsoids in a dielectric medium with an arbitrary fraction of nanoparticles in a nanocomposite. The obtained analytical expressions for the radiative characteristics allow it to be concluded to what extent they are susceptible to changes in the phonon subsystem and electron-phonon interaction caused by the spatial confinement effect.