Papers by Keyword: Femtosecond

Abstract: Experiments were carried out in which the luminescence of color centers in lithium fluoride crystals was excited by two different femtosecond lasers with significantly different energies, durations and pulse repetition rates. It was established that in all experiments the main center, the luminescence of which was excited nonlinearly, was the F₃⁺ color center. Unusual experimental data were obtained; a laser with low pulse energy (4 nJ) excited triplet luminescence of these centers (570 nm) but did not excite singlet luminescence (540 nm). Another laser with a higher pulse energy (0.3 mJ), on the other hand, excited singlet luminescence and did not excite triplet luminescence. A proposed diagram of energy levels and quantum transitions is presented, explaining the possible mechanisms of nonlinear excitation of luminescence in these experiments.

Abstract: Monoclinic and orthorhombic phase of copper niobate was prepared by simple solid state reaction (700°C, 900°C for 12 hours). Formation of two polymorphic phases of CuNb₂O₆ was ascertained by XRD and FTIR analysis. FESEM showed the presence of pore networks in both phases. Third-order optical nonlinearity and their limiting behaviour were studied by Z-scan technique using Ti: Sapphire laser (800 nm, 150 fs, 80 MHz). Both phases of copper niobate exhibit reverse saturable absorption. The observed optical limiting action was ascribed due to two-photon absorption process. Monoclinic copper niobate shows almost 100 times stronger nonlinear absorption behaviour than orthorhombic copper niobate due to peculiar distortion of NbO₆ octahedra. Monoclinic copper niobate with high two photon absorption coefficient (85x10^-10 m/W) and low limiting threshold (0.21 μJ/cm²) can be a better alternate for benchmark optical limiters like carbon nanotubes.

Abstract: A fast laser texturing technique has been utilized to produce micro/nanosurface textures in Silicon by means of UV femtosecond laser. We have prepared good absorber surface for photovoltaic cells. The textured Silicon surface absorbs the incident light greater than the non-textured surface. The results show a photovoltaic current increase about 21.3% for photovoltaic cell with two-dimensional pattern as compared to the same cell without texturing.

Abstract: Surface Plasmon Polaritons (SPPs) Propagate along the Interface between Metal and Dielectric, so that Spps can Propagate along the Designed Interface, Spread to the Specified Region and Convert Back to Light Wave. through this Method, Modulated Light can be Guided to Setting Area and the Propagation Direction can be Changed. in this Paper, a Kind of all-Optical Switch Composed of Metallic Isosceles Triangle is Introduced. the Principle of the all-Optical Switch is this. Firstly, the Modulated Light is Converted into Spps in the Metal Triangle at the Bottom Corner. then, Spps Propagate along Designed Interface between Metal and Dielectric. Finally, Spps Become Scattered Light in the Vertex of Triangle where the Signal Light also Become Scattered Light. Two Scattering Light Interfere Cancellation to Achieve the Goal that the Modulation with very Low Power Light can Control the Signal Light. the most Remarkable Advantage of the all-Optical Switch is that the Incident Angle of Modulated Light does Not Require Strictly. as Long as the Light Intensity and Phase of Light is Proper, the Aim of Extinction can be Achieve. the Reaction Speed of the all-Optical Switch is Nearly the Speed of Light. Response Time is 0.9 Femtosecond. Extinction Ratio is about 34.93558dB.The Entire Structure Size is only 1.81μm× 1μm(x×z). The all-Optical Switch has the Characteristics of Low Threshold Power, Small Size and Easily Integrated. in the Case of Relatively High Extinction, the Switch can Control Signal of any Channel. it is Able to be Applied to High-Speed, Large Capacity, Channel Spacing of 0.8nm DWDM Optical Network

Abstract: Pico and femtosecond lasers present a growing interest for industrials applications such as surface structuring [1] or thin film selective ablation [2]. Indeed, they combine the unique capacity to process any type of material (dielectrics, semiconductors, metals) with an outstanding precision and a reduced affected zone. We report on results about surface engraving of metals (Al, Cu, Mo, Ni), semiconductor (Si) and polymer (PC) using a picosecond thin disk Yb:YAG-amplifier. The pulse duration of this source can be changed using two different configurations: direct amplification of a 34ps-oscillator on one hand, and 1ps-chirped pulse amplification (CPA) scheme on the other hand. The results obtained with this thin disk laser are compared to ones achieved with two commercial femtosecond lasers respectively based on Yb-doped crystals and fibers, and operating at similar output power levels (up to 15Watt).