Nonlinear absorption and upconversion properties of two-photon absorption dye: ASPI

Two-photon absorption (TPA) cross sections of an organic dye, trans-4-[p-(N-hydroxyethyl-N-methylamino)tyryl]-N-methylpyridinium iodide (abbreviated as ASPI), from 720 to 1100 nm have been measured by using nonlinear transmittance method, which reflect the TPA degrees of the dye at different wavelengths. The maximum TPA wavelength is located at 930 nm. The upconversion efficiencies of ASPI in dimethyl formamide and benzyl alcohol at different pump wavelengths have also been measured. There is 90 nm red shift for the highest upconversion wavelength as comparing with the strongest TPA wavelength. The influences of the solvents on the TPA-induced emission spectrum and the conversion efficiencies have also been given.     

Tunable nonlinear absorption of hydrogenated nanocrystalline silicon

Nonlinear absorption (NLA) of hydrogenated nanocrystalline silicon (nc-Si:H) has been investigated through the open aperture Z-scan method for the photon energy of the incident irradiance slightly less than the bandgap of the sample. NLA responses have been observed to be highly sensitive to the wavelength and intensity of the incident irradiance as well as to the bandgap of the sample, indicating greatly tunable NLA of nc-Si:H. The band tail of nc-Si:H appears to play a crucial role in such NLA responses.     

Laser absorption in short-lived metal and nanoplasmas

We have studied the absorption of 100 fs, 806 nm laser pulses in both bulk and nanoparticulate forms of copper as a function of the electric field intensity as well as polarization. In particular, we have investigated the changes in absorption over a wide range of intensity (over four orders of magnitude) which enables us to study the transition of a metal to plasma. We have found that, even in its nanoparticulate form, the onset of plasma formation occurs in copper when the incident light field intensity is about 10¹⁴ W^cm-2. The values of the dielectric permittivities, calculated using the Drude theory, deviate from the room temperature values beyond the onset of plasma formation.     

Multi-photon absorption in mercury

Three-and four-photon resonant excitations of the mercury atom from its ground state have been observed and their dependence on the polarization of the incident light investigated. The energies of the nG states (n = 5 to 13) have been measured. In addition two photon excitation from the ground state to the 6³P states (J = 1 and 2) were observed. The pressure dependence of the relative signal sizes is briefly reported.     

X-ray absorption study of light emitting silicon nanocrystals

X-ray absorption spectra obtained by total electron yield (TEY) at the Si absorption K-edge have been measured to have chemical and structural information about Si nanocrystals (Si-nc) produced by plasma-enhanced chemical vapour deposition (PECVD). The TEY technique has been employed to investigate the formation of Si-nc and the modification of the silica matrix as a function of annealing temperature (500–1250°C) and of silicon content in the film (35–46 at%). The amount of silicon present in the Si-nc has been evaluated by TEY. Thanks to Rutherford backscattering spectrometry measurements, the amount of Si atoms bonded to oxygen and to nitrogen, incorporated by PECVD, has been assessed. A compositional model that interprets the experimental findings is presented.     

FEL诱导半导体材料非线性光吸收

应用北京自由电子激光(BFEL)对典型的红外光电子材料Hg_1-xCd_xTe ,InSb和InAs进行了非线性光吸收研究.利用FEL的高光子密度和皮秒量级的短脉冲宽度特性，研究了双光子吸收(TPA)以及光生载流子吸收(FCA)共同作用机理，从实验上直接证实了在强入射能量下，FCA是不可忽略的光吸收过程，提取了精确的自由载流子吸收截面参数. 关键词： FEL 双光子吸收 光生载流子吸收 吸收截面 载流子寿命     

Hypersonic absorption in amorphous polymers by light scattering

Brillouin lines have been observed in the spectrum of light scattered by poly(methylmethacrylate) and, for the first time, for poly(vinylchloride). The line widths have been measured, by a special technique, as a function of temperature. The attenuation per wavelength of thermal phonons below the glass transition temperature is almost constant over a wide frequency range (5 MHz to 10 GHz). The attentuation is ascribed to the mechanical strain field round static imperfections. Above the glass transition temperature the attenuation is associated with the well-known mechanical ∝ process. The Rayleigh light scattered by these polymers and their transparency is also discussed.     

Two-photon absorption in hexagonal-CdS

The “composite sample technique” has been used to investigate the two-photon absorption coefficient (β) of CdS at 3.91 eV. The absolute value of β and its optical anisotropy have been studied for samples with different carrier densities. The present results may provide a new interpretation of experiments on CdS and other semiconductors reported in the literature.     

Nonisothermal absorption in thermotransformers

The results obtained using simple models of combined heat and mass transfer in nonisothermal vapor or gas absorption by aqueous solutions are generalized. The models take into account specific properties of two-phase binary systems used in absorbers of thermotransformers (heat pumps and refrigerators). Some authors have already cited certain of the results, including criterial dependences obtained via exact solutions, in reference books and monographs. This paper represents a wider spectrum of problems. The Russian, more detailed version of the article, was published as a book.     

准连续激光调制吸收谱的多谐波分析

使用准连续二极管激光器进行多重调制光谱检测时,发现吸收光谱信号中存在着丰富的倍频、和频以及差频成分;从激光与气体吸收谱线的非线性作用角度研究了倍频、和频及差频等信号存在的必然性;从实验角度对信号特征进行研究,发现其中有些和频、差频成分的幅度比传统调谐二极管激光吸收光谱技术中的二次谐波信号的幅度更大,有望在准连续调制谱技术中提高检测的灵敏度。     

Saturable absorption and reverse saturable absorption on silver particles with different shapes

Micro/nanostructured silver particles with different shapes (flower, wire, and rod) have been prepared and characterized. All the open aperture z-scan curves of silver microrods and silver nanoflowers present a typical reverse saturable absorption. With the increase of incident intensity, the nonlinear absorption coefficients and the third-order optical susceptibilities ImX⁽³⁾ of nanoflowers increase, but those of silver microrods decrease. Moreover, the silver nanowires show the conversion from saturable absorption to reverse saturable absorption. There was no definite correlation between incident intensity and nonlinear absorption coefficient (β) under the conditions studied herein. And nonlinear optical properties of micro/nanostructured silver particles are dependent on the particle shape in suspensions at 800 nm.     

Fine structure of two-photon absorption in CdS

We have observed the fine structure of the P-excitons (A, n = 2) in Cds through two-photon absorption. The strengths of absorption peaks of P-excitons and their dependence on the polarization of the light agree with predictions of a four-band model of two-photon absorption. Additional two-photon absorption peaks were identified as phasematched two-step two-photon processes involving second harmonic polarizations.     

Optical losses and absorption cross-section of silicon nanocrystals

 Si-rich silicon oxide and SiO₂ (SRSO)/SiO₂ multilayer (ML) samples were grown by reactive magnetron sputtering and then annealed at high temperature to induce the formation of Si-nc with mean size of 3-4 nm and density of about 3.5×10¹⁸ cm⁻³ as deduced from high resolution TEM micrographs. Refractive index and thickness have been determined by m-line measurements, which have shown a birefringence of about 1.5% due to the ML structure. Rib-loaded waveguides have been fabricated to measure propagation losses in the visible-infrared range. The analysis of the different contributions to optical losses such as Mie scattering and scattering due to waveguide roughness has allowed us to isolate the contribution due to the absorption losses and thus to extract the absorption cross-section at different wavelengths. Values of about 3.5×10⁻¹⁸ cm² have been found at 830 nm, increasing with decreasing of the wavelength.     

Infrared absorption cross sections for methanol

Infrared absorption cross sections for methanol, CH₃OH, have been determined near 3.4 and 10 μm from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125HR) and a multipass cell with a maximum optical path length of 19.3 m. Methanol/dry synthetic air mixtures were prepared and spectra were recorded at 0.015 cm^?1 resolution (calculated as 0.9/MOPD) at a number of temperatures and pressures (50–760 Torr and 204–296 K) appropriate for atmospheric conditions. Intensities were calibrated using composite methanol spectra taken from the Pacific Northwest National Laboratory (PNNL) IR database. The new measurements in the 10 μm region indicate problems with the existing methanol spectroscopic line parameters in the HITRAN database, which will impact the accuracy of satellite retrievals.     

Quantum absorption refrigerator

A quantum absorption refrigerator driven by noise is studied with the purpose of determining the limitations of cooling to absolute zero. The model consists of a working medium coupled simultaneously to hot, cold, and noise baths. Explicit expressions for the cooling power are obtained for Gaussian and Poisson white noise. The quantum model is consistent with the first and second laws of thermodynamics. The third law is quantified; the cooling power J(c) vanishes as J(c) ∝ T(c)(α), when T(c)→0, where α=d+1 for dissipation by emission and absorption of quanta described by a linear coupling to a thermal bosonic field, where d is the dimension of the bath.     

Periodic microwave absorption in superconducting whiskers

The microwave absorption and structural studies of BiSrCaCuO (2212) whiskers have been performed. The low-angle boundaries in the (a, b) and (a, c) planes have been observed. The periodic microwave absorption signal indicated the flux quantization in a system of weak links and superconducting loops formed on the boundaries. Regular character of this signal suggests possible applications in SQUID magnetometry. Lower Josephson critical fieldH _clJ=1.6 Oe and the critical temperatureT _c=89 K have been determined. The Josephson penetration depth was estimated from the Ginzgurg-Landau, and Clem models.     

Multiphoton absorption and luminescence of osmium tetroxide

Both the multiphoton absorption and the luminescence brightness of osmium tetroxide induced by absorption of temporally smooth CO₂ 10P(20) laser pulses of 10 and 40 ns FWHM have been measured for pressures in the range 6.7 to 200 Pa. A dependence of these phenomena on laser pulse length is observed. Comparison of the luminescence brightness to the average excitation shows that the distribution of the multiphoton excitation depends on the laser pulse intensity for the two pulse lengths studied.Issued as AECL Contribution No. 8806     

水下弹性微穿孔吸声结构吸声系数研究

利用模态叠加法建立了水介质微穿孔板的数学模型,基于声电类比法得到其等效电路模型。研究了弹性微穿孔板和弹性背腔对垂直入射吸声系数的影响。与空气介质中的微穿孔板不同,水下微穿孔板因结构阻抗不足,难以取得满意的吸声效果,为此提出了增强型微穿孔吸声结构,并在水介质阻抗管内对理论结果予以验证。结果表明,随着增强型弹性微穿孔板弯曲刚度的增大,其在[20,2000]Hz范围内的平均吸声系数得到提高,逐步趋近于刚性微穿孔板的结果,弹性背板使微穿孔吸声结构的吸声峰向低频移动,低频吸声效果得到提高。      

Two-photon absorption and two-photon-induced absorption of some organic liquids at 347.15 nm

The two-photon absorption cross-sections and effective excited- state absorption cross-sections at 347.15nm of the organic liquids ethylene glycol, methanol, ethanol, tetrahydrofuran, glycerol, cyclohexane, 1,4-dioxane, 1,2-dichloroethane, dichloromethane, chloroform, dimethylsulfoxide, N,N-dimethylformamide, o-xylene, m- xylene, p-xylene and xylene (isomer mixture) have been determined using second harmonic picosecond pulses of a mode-locked ruby laser system. Linear and circular polarized pump pulse transmission measurements were performed to determine the two linear independent two-photon absorption susceptibility components. Linear polarized probe pulse transmission measurements after pump-pulse passage were carried out to determine excited singlet state relaxation times.     

Far infrared absorption of a-GeSe

Far infrared absorption measurements have been made on a series of a-Ge_xSe_1?x films with near equiatomic compositions. The only sharp feature is an absorption line at 260cm^-1, and the compositional dependance of this feature is correctly described by a model in which the Ge(Se) atoms are 4(2) fold co-ordinated. There is no evidence in our amorphous samples of any absorption band in the frequency range (160?190cm^?1) of the major IR active modes of 3:3 fold co-ordinated crystalline GeSe.