Investigation on broadband near-infrared emission and energy transfer in Er-Tm codoped germanate glasses

Broadband near-infrared emission has been investigated in a new type host composition of Er³⁺-Tm³⁺ codoped germanate glass. A broadband emission extend from 1350 to 1675 nm with the full width at half maximum (FWHM) around 138 nm is obtained in the germanate glass which codoped with 0.2 wt.% Er₂O₃ and 0.8 wt.% Tm₂O₃. The energy transfer between Er³⁺ and Tm³⁺ plays an important role in the emission mechanism, which is evidenced by the visible upconversion and the lifetime of Er³⁺:⁴I_13/2 level effected by the addition of Tm₂O₃. And energy transfer efficiency from Er³⁺ to Tm³⁺ reaches 76% for the highest Tm³⁺ concentration of 0.8 wt.%. These results suggest that this glass would be a promising material for broadband light source and broadband amplifier for the wavelength division multiplexing transmission systems.     

Surface ablation of RbTiOPO4 by femtosecond laser

We report here the results obtained in surface ablation of RbTiOPO₄ single crystals by femtosecond laser. We fabricated and characterized one-dimensional (1D) diffraction gratings with different lattice spacings of 15 and 20 μm, and with a sub-modulation of the period introduced in the later. The optical and electronic microscopy characterization and filling factor analysis of these diffraction gratings are reported. We also show that the roughness generated on the grooves by the ablation process can be improved by chemical etching.     

A random laser made of nematic liquid crystal doped with a laser dye

We report on random laser emission obtained in 5CB and E7 nematic liquid crystal (LC) mixtures doped with 1% weight to weight ratio of DCM laser dye. The LC cell was used as asymmetric planar waveguide were emission was collected from the edge of the sample. Variable stripe length method was utilized to estimate the gain and the losses coefficients. Both systems have shown the threshold energy fluence in order of several mJ/cm². In both cases above Fredericks potential, significant increase of emission intensity was observed due to the increase of light scattering on liquid crystalline domains. Moreover the use of fifth order of diffraction grating covered with thin alumina film resulted in strong multimode and directional laser emission.     

掺Er3+:Al2O3平面光波导的溶胶-凝胶制备

掺铒光波导主要用来制作光波导放大器。采用溶胶-凝胶法制备了透明、稳定的掺铒的铝硅酸盐玻璃溶胶;使用浸渍提拉法或旋转涂敷法,并通过放在乙醇蒸汽中干燥,可在玻璃表面得到均匀的凝胶膜;最后样品在一定温度下烧结;通过多次重复涂敷-烧结这一工艺流程可以形成厚的硅酸盐玻璃膜层并得到波导结构。使用显微镜研究了凝胶膜表面性质,通过棱镜耦合法测量了波导的有效折射率Nm,也测定了所制备波导的吸收光谱。溶胶-凝胶法在制作均匀性好、高掺铒浓度的铝硅酸盐玻璃光波导上具有优势。     

飞秒激光空间选择性诱导玻璃微结构及应用

利用飞秒激光与玻璃的非线性相互作用，可以对玻璃进行空间选择性微观改性与修饰，赋予新的光功能．本文介绍飞秒激光的持点及其对玻璃微结构的改性，以及近年来利用飞秒激光进行玻璃的缺陷控制、光活性离子(稀土、过渡和重金属离子)价态操作、微晶析出与折射率调控及其在光开关、波分复用、波导型有源器件、光子晶体等微光学器件的制备及光学集成领域应用的进展．     

Spectra and laser properties of Er, Yb:phosphate glasses

The effects of Al₂O₃, Yb₂O₃, Er₂O₃ and OH on spectral properties of P₂O₅·Na₂O·SrO·Al₂O₃·Yb₂O₃·Er₂O₃ erbium phosphate glass were studied. 5, 8, 13 mol% Al₂O₃, 4, 5, 6, 7 and 8 mol% Yb₂O₃ and 0.05, 0.2, 0.4 mol% Er₂O₃ were used. It was found Al₂O₃ improves fluorescent lifetime of Er³⁺ ions, but the integrated absorption cross-section of Er³⁺ ions decreases with the increase of Al₂O₃ concentration. Evaluating from energy transfer efficiency of Yb³⁺ to Er³⁺ and spectral parameters of Yb³⁺ and Er³⁺, lower Al₂O₃ content, 6 mol% Yb₂O₃ and 0.2–0.4 mol% Er₂O₃ are preferred for LD pumped microchip laser application. OH groups in glass greatly affect fluorescent intensity and lifetime of Er³⁺, Yb³⁺:phosphate glass. The OH absorption coefficient at 3000 cm⁻¹ should be <1 cm⁻¹ for laser applications. Pumped with a 2 W, 974 nm InGaAs laser diode, CW laser centered at 1530 nm with slope efficiency of 10.6% and maximum output of 43 mW was achieved in our 2 mm thick Er³⁺, Yb³⁺:phosphate glass at room temperature.     

Random lasing in a dye-doped polymer thin film waveguide deposited on a Si surface microstructured by femtosecond laser ablation

Random laser action with ~8 nm of bandwidth from a special waveguide structure is reported. The waveguide structure is composed of a layer of rhodamine 6G-doped PMMA film and a silicon substrate with a microstructured surface induced by a femtosecond laser. The silicon substrate featured two-dimensional island-like microstructures with average sizes ranging from 0.8 μm to 3 μm and average heights at about 0.7 μm. A red-shift of laser peak positions and decrease of threshold were observed with decreasing size of silicon surface microstructures. The spectra at different probe directions were also measured, and the results reveal that the waveguide laser action is strongly confined within ±10° from the direction of the edge. The lasing modes emitted from the edge of the waveguide are found to be mainly transverse electric-polarized. Our experiments demonstrate a promising method to achieve waveguide random lasers.     

Fabrication of ridge waveguide on the ion-implanted TGG crystal by femtosecond laser ablation

The ridge waveguide on the TGG crystal has been fabricated through the combination of the ion implantation and the femtosecond laser ablation. Firstly, optical planar waveguide was formed on the top surface of TGG crystal by ion implantation. To investigate the damage induced by the 6.0?MeV Si ion implantation at a dose of 2.0 × 10¹⁵ ions/cm², the vacancy distribution was obtained by the SRIM simulation programme. Subsequently, the ridge waveguide with a width of 20?µm was produced by femtosecond laser ablation. The optical guiding properties of the ridge TGG waveguide were measured at the near-infrared wavelength (976?nm) by the end-face coupling technique. The work demonstrated that the manufactured waveguide structure possesses the ability to confine the light into guided mode, making it potentially valuable in integrated devices.     

Refractive index variations induced by femtosecond laser direct writing in the bulk of As2S3 glass at high repetition rate

This paper deals with the refractive index variation (Δn) induced by femtosecond laser irradiation in the bulk of As₂S₃ glass in a high repetition rate regime. Extensive measurements of spatially resolved Δn profiles of photowritten channels are reported for various values of the pulse energy. Nearly Gaussian profiles are obtained for energy slightly above the threshold whereas at higher energies the structure of Δn is more complex with a negative core surrounded by a positive ring. A thermal model is applied to reproduce the behaviour of the overall structure diameter.     

Diffraction gratings inside bulk azodye-doped hybrid inorganic-organic materials by a femtosecond laser

We have investigated diffraction gratings fabricated inside bulk azodye-doped hybrid inorganic-organic materials by a focused near-IR 800 nm femtosecond laser directly. The first-order diffraction of the grating was measured using a 632.8 nm He-Ne laser. By changing the laser parameters such as the laser power, the scanning speed, and the grating period, we found that the first-order Bragg diffraction efficiency was strongly dependent on the parameters of the femtosecond laser. The results showed that the first-order Bragg diffraction efficiency can be increased when decreasing the laser power or increasing the grating periods and the scanning speed of the laser. The mechanisms were also analyzed briefly.     

Noncrystalline micromachining of amorphous alloys using femtosecond laser pulses

Femtosecond laser micromachining of a Zr-based amorphous alloy in air, including measuring the ablation threshold, micro-drilling and trenching, was investigated. The threshold of ablating this amorphous alloy was determined by experiment. Laser-induced ablation and associated damage were examined by means of optical microscope, scanning electron microscopy, transmission electron microscopy and electron diffraction diagram. The results show that conventional processing method induced defects in the vicinity of machined area, such as crystallization, molten trace and spatter, were absent in femtosecond laser ablation area with selected parameters. This indicates that femtosecond laser ablation is a promising method for micromachining amorphous alloys without crystallization.     

Passively Q-switched Nd:YVO4 waveguide laser using graphene as a saturable absorber

We report on passively Q-switched lasers in femtosecond laser written waveguide in Nd:YVO₄ crystal. Using graphene as a saturable absorber, passively Q-switched waveguide laser operations are achieved along both TE and TM polarizations with single modal profiles. Furthermore, all-angle linear light pump was utilized to investigate the thorough information of the polarization effects of the laser, showing that the optimum polarization for laser generation is TE. The maximum average output power is estimated to be 129 mW with 12.2% slope efficiency, corresponding to single-pulse energy of 8.1 nJ, pulse duration of 25.0 ns and repetition rate of 16.3 MHz.     

Fabrication of spiral-shaped microfluidic channels in glass by femtosecond laser

Long spiral-shaped microfluidic channels in glass have been fabricated by femtosecond laser direct writing. After hydrofluoric acid etching and post baking, the laser modified regions in glass formed hollow microstructures. The diameter size and the screw-pitch of the channels can be set freely. The experimental results showed that the etched internal surface of the microchannel by hydrofluoric acid will become smoother after the subsequent baking. The incident laser power and scanning speed can also influence the channel quality.     

Greatly enhanced infrared normal spectral emissivity of microstructured silicon using a femtosecond laser

The infrared normal spectral emissivity of microstructured silicon prepared by femtosecond laser irradiation in SF₆ was measured for the wavelength range 2.5 μm to 25 μm. Greatly enhanced emissivity compared to that of flat silicon was observed over the entire wavelength range. For a sample with 13-14 μm high spikes, the emissivity at a temperature of 100 °C is approximately 0.96. The emissivity decreases slightly in the wavelength region above 8 μm, but remains higher than 0.9 over most of the measured wavelength range. Also the average emissivity is less than Nextel- Velvet-811-21 Coating, it can be used stably at more wide temperatures from 100 °C to 400 °C. These results show the potential for microstructured silicon to be used as a flat blackbody source or silicon-based pyroelectric and microbolometer devices.     

Luminescence quenching and recovering in photo-thermo-refractive silver-ion doped glasses

A spectroscopic investigation of luminescent centers transformation in photo-thermo-refractive glass by using ultraviolet (UV) nanosecond laser pulses with radiation wavelength 355 nm was performed. Initially the glass was irradiated by UV lamp and thermal-treated that causes a neutral silver molecular clusters luminescence in a visible spectral region. After the laser irradiation a luminescence quenching was observed in the irradiated region. The thermal treatment below glass transition temperature restores the luminescence of silver molecular clusters with complex spatial distribution of luminescence intensity inside the irradiated region. UV lamp irradiation achieves the same result without any inhomogeneity. The observed effects are caused by photoionization and reduction of subnanosized silver molecular clusters with the participation of cerium and antimony ions.     

Photo-thermo-refractive glass co-doped with Nd as a new laser medium

Photo-thermo-refractive (PTR) glass demonstrates refractive index change after exposure to UV radiation followed by a thermal treatment that enables recording of high efficiency holographic optical elements. This work demonstrates feasibility of function of this material as a complex optical medium which posseses both photosensitive and luminescent properties and paves a way for creation of monolythic solid state lasers where resonator components can be holographically recorded inside of a laser medium. It was found, that incorporating of Nd³⁺ ions in PTR glass does not affect photosensitivity required for hologram recording. It was demonstrated that emission wavelength, spectral width, and cross section of Nd³⁺ luminescence in PTR glass are typical for silicate laser glasses and Nd-doped PTR glass can be considered as a promising laser medium for monolithic solid state lasers.     

X-ray diffraction of permalloy nanoparticles fabricated by laser ablation in water

Permalloy (NiFeMo) nanoparticles were fabricated by laser ablation of bulk material in water with a UV pulsed laser. Transmission electron microscope images showed that approximately spherical particles about 50 nm in diameter were formed in the ablation process. All diffraction peaks corresponding to the bulk material were present in the nanoparticles. In addition to these peaks several new peaks were observed in the nanoparticles, which were attributed to nickel oxide.     

Nanoparticle formation by the debris produced by femtosecond laser ablation of silicon in ambient air

The debris produced by femtosecond laser ablation (180 fs, 775 nm, 1 kHz) of Si in ambient air is deposited around the ablated craters in a circular zone with diameters between ~ 40 and 300 μm for laser fluences (F) in the region F = 0.2-8 J/cm². The debris consists of nanoparticles. The mean height of the nanoparticles increases with laser fluence (from ~ 70 to 500 nm for fluences in the range F = 0.25-4.38 J/cm²) but at high fluences (F = 8 J/cm²) becomes equal to ~ 170 nm. The average horizontal dimension of the nanoparticles increases with laser fluence. Their average vertical dimension increases in proportion to their average horizontal dimension, but at high fluences becomes much smaller than their corresponding average horizontal dimension. The nanoparticles were found to be single crystals with d spacing of 1.71 ± 0.08 Å (corresponding to {311}).     

The fabrication of index-modulated grating coupler in a polymeric waveguide using two-photon initiated photopolymerization

A simple process suitable for fabrication of volume phase grating coupler in planar optical waveguide by two-photon initiated polymerization is presented. The volume phase grating has been written by scanning femtosecond laser pulses directly on the polymeric thin-film through a high numerical aperture lens. The areas of the index-modulated grating without morphology are 1.5 mm × 1.5 mm. The microstructure feature of coupling grating was illustrated. The corresponding index modulation reaches 0.03. We demonstrated the implementation of input coupling by this grating into the polymeric waveguide film. The measured coupling efficiency was about 11%.     

Pulsed laser deposition of indium tin oxide nanowires in argon and helium

Nanowires of indium tin oxide (ITO) were grown on catalyst-free amorphous glass substrates at relatively low temperature of 250 °C in argon and helium ambient by the Nd:YAG pulsed laser deposition technique. All the ITO samples showed crystalline structure due to substrate heating and the (400) X-ray diffraction peak became relatively stronger as the pressure was increased. The surface morphology was also changed from compact, polycrystalline thin-film layers to a dendritic layer consisting of nanowires for some limited pressure ranges. The transition from the normal thin-film structure to nanowires was likely due to the vapor-liquid-solid mechanism but under catalyst-free condition. These nanowires tended to grow perpendicularly on the glass substrate, as observed with the transmission electron microscopy (TEM), which also confirmed that these nanowires were crystalline.