Observation of enhanced two-photon absorption in ZnS quantum dots at an ultraviolet wavelength

Two-photon absorption(2PA) in zinc sulphide(ZnS) and Mn2+-doped ZnS quantum dots is reported by the z-scan technique,with nanosecond pulsed laser radiation at 355 nm.The observed values of the 2PA cross section of all the samples are 105 times larger than that of bulk ZnS.     

Photoacoustic spectroscopy with quantum cascade distributed-feedback lasers

We present photoacoustic (PA) spectroscopy measurements of carbon dioxide, methanol, and ammonia. The light source for the excitation was a single-mode quantum cascade distributed-feedback laser, which was operated in pulsed mode at moderate duty cycle and slightly below room temperature. Temperature tuning resulted in a typical wavelength range of 3cm(-1)at a linewidth of 0.2cm(-1). The setup was based on a Herriott multipass arrangement around the PA cell; the cell was equipped with a radial 16-microphone array to increase sensitivity. Despite the relatively small average laser power, the ammonia detection limit was 300 parts in 10(9)by volume.     

Very efficient two-photon induced photo-tautomerization in non-symmetrical phthalocyanines

In this work we demonstrate that non-symmetrically substituted phthalo-naphthalocyanine molecule can have extremely large 2PA cross section in near-resonance conditions of excitation. We also show the possibility to switch between its two tautomeric forms upon two-photon excitation at 77 K. By measuring 2PA cross section, quantum efficiency of transformation in these two forms, as well as quantum yield of fluorescence, we evaluate the figure of merit for fast re-writable 3D information storage and show that this figure meets the criteria of reliable and fast (one bit per one femtosecond pulse) 2PA writing or reading.     

Quantum ratchets in dissipative chaotic systems

Using the method of quantum trajectories, we study a quantum chaotic dissipative ratchet appearing for particles in a pulsed asymmetric potential in the presence of a dissipative environment. The system is characterized by directed transport emerging from a quantum strange attractor. This model exhibits, in the limit of small effective Planck constant, a transition from quantum to classical behavior, in agreement with the correspondence principle. We also discuss parameter values suitable for the implementation of the quantum ratchet effect with cold atoms in optical lattices.     

Nonlinear Optics to Glucose Sensing: Multifunctional Nitrogen and Boron Doped Carbon Dots with Solid-State Fluorescence in Nanoporous Silica Films

Multifunctional triple color photoluminescent (PL) nitrogen–boron doped carbon quantum dots (CQDs) with high quantum yield (QY) of 58% are fabricated by one step femtosecond pulsed laser irradiation of a single precursor (2-aminopyrimidine-5-boronic acid) in solution. In situ generated non-linear and linear emissions are used to monitor CQDs formation which results in enhanced second harmonic generation, two photon absorption (2PA), and linear fluorescence; implying triple mode emission. These CQDs present blue, green, and possible red color rendering which are mostly independent to the respective excitation wavelengths (λ) with large stokes shift of 100 nm. Solid-state photoluminescence with QY of 46% is achieved by incorporating CQDs into thin transparent nanoporous silica (pSiO₂) films (thickness 50 µm) to form a CQDs-pSiO₂ composite which exhibits reverse saturable absorption at λ = 800 nm with 2PA coefficient and excited state absorption cross-section of 4.94 × 10⁻¹⁰ m W⁻¹ and 6.23 × 10⁻¹⁷ cm², respectively. CQDs-pSiO₂ is also sensitive to glucose concentration down to 1.0 mg dL⁻¹ in a wide linear range up to 100 mg dL⁻¹. This work therefore demonstrates facile, controllable, and up-scalable bottom-up fabrication of CQDs forming multifunctional solid-state CQDs-pSiO₂ with proven application in optical limiting and glucose sensing.     

Fluorescence Quantum Yield Determination of Propylparaben Using Flow Injection Spectroscopy

The determination of the fluorescence quantum yield of Propylparaben is introduced and applied to L-tyrosine as a standard by a new approach that can be applied to the pharmaceutical compound utilised in this study. The quantum yield is a critical figure of quality for the optical nature of a fluorophore. Numerous investigations have considered the glitter in both pharmaceutical and nature compounds for its medical and industrial significance. A straightforward method is detailed here to decide the quantum yield of Propylparaben in solution as an element of the fluorescence concentration. For this reason, L-Tyrosine is chosen as a fluorescence standard perspective to gauge the Propylparaben fluorescence quantum yield. The impacts of pH, solvents and flow rate on the assessment of quantum yield and quantum efficiency, for the reference and the solutions of Propylparaben, have been investigated. The results indicated that these parameters significantly influence the accuracy of the method. Diverse methods are concentrated on to represent distinctive quantum yield advancements with the quantum efficiency. The impact of these parameters was likewise considered. In this study, the application of the single method may be taken into consideration to compute quantum yield of Propylparaben, which was 0.36, and this is an exceptionally basic and general technique to solve the imperative issue of luminescence quantum yield assurance of other fluorescence compounds.     

The determination of pair distance distributions by pulsed ESR using Tikhonov regularization

Pulsed ESR techniques with the aid of site-directed spin labeling have proven useful in providing unique structural information about proteins. The determination of distance distributions in electron spin pairs directly from the dipolar time evolution of the pulsed ESR signals by means of the Tikhonov regularization method is reported. The difficulties connected with numerically inverting this ill-posed mathematical problem are clearly illustrated. The Tikhonov regularization with the regularization parameter determined by the L-curve criterion is then described and tested to confirm its accuracy and reliability. The method is applied to recent experimental results on doubly labeled proteins that have been studied using two pulsed ESR techniques, double quantum coherence (DQC) ESR and double electron-electron resonance (DEER). The extracted distance distributions are able to provide valuable information about the conformational constraints in various partially folded states of proteins. This study supplies a mathematically reliable method for extracting pair distributions from pulsed ESR experimental data and has extended the use of pulsed ESR to provide results of greater value for structural biology.     

Measurement of Absolute Fluorescence Quantum Yield of Basic Fuchsin Solution Using a Dual-Beam Thermal Lens Technique

The dual beam thermal lens technique is an effective method for the measurement of fluorescence quantum yield of dye solutions. The concentration-dependent quantum yield of a novel dye of triaminotriphenylmethane family in ethanol is studied using this technique. The absolute fluorescence quantum yield is measured and is observed that the reduction in the quantum yield is due to the non-radiative relaxation of the absorbed energy.     

Photoacoustic detection of ozone using a quantum cascade laser

A 9.5-m pulsed quantum cascade laser (QCL) and a differential photoacoustic (PA) detector were used to measure trace concentrations of 100 ppbv ozone at ambient pressure with high selectivity. The QCL was tuned by temperature variation between -41 °C and 30.6 °C and the corresponding wavelengths were determined by the PA spectrum of CO₂. Good agreement was found between the measured PA spectrum and the simulated HITRAN spectrum of ozone. The PA signal showed a linear dependence on the ozone concentration in the investigated 4300–100 ppbv range. In comparison with recently published results, in which a similar QCL in combination with an optical absorption analysis technique was applied, an improvement in the ozone-detection sensitivity by a factor of about 200 was achieved. PACS 42.62.Fi; 82.80.Kq; 82.80.Gk; 92.60.Sz     

High quantum yield of photochemical reactions of protoporphyrin-IX induced by powerful ultrashort laser pulses

The action of powerful pulsed picosecond radiation from a Nd: YAG laser (λ=530 nm, pulse energy: 0.01 J, intensity: 2GW/cm²) and an argon laser (λ=515 nm, power: 50 mW) on protoporphyrin-IX dimethylether in three solvents (trichlormethane, carbon tetrachloride, dioxane) has been studied. Under continuous irradiation the quantum yield and resulting products do not differ materially from the ones produced under mercury lamp irradiation. When irradiation is performed by powerful laser pulses of picosecond duration the quantum yield of photodecomposition of protoporphyrin-IX dimethylether inereases substantially: by 10 in dioxane, by 4 in carbon tetrachloride and by 100 in trichlormethane. It is assumed that a quite different mechanism of multistep excitation is responsible for photodecomposition under powerful picosecond pulses.     

The photoelectrochemical properties of phenylseleniumdiimide films

The photoelectrochemical properties of organoselenium semiconductors (diphenylseleniumdiimide, N,N-(bis-p-methoxyphenyl)seleniumdiimide, N,N-(bis-m-methoxyphenyl)seleniumdiimide, and N,N-(bis-p-bromophenyl)seleniumdiimide) were studied in a photovoltaic system containing an electrolytic contact (metal-semiconductor-electrolyte-metal). The deposition of films on platinum substrates by evaporation of solutions in dimethylsulfoxide produced a porous coating, the photopotential of even most active diphenylse-leniumdiimide did not exceed 91 m V, and short-circuit current did not exceed 0.88 μA. The film of diphenylseleniumdiimide of the same thickness (400 nm) obtained by sublimation in a vacuum (10^?7 torr, 160°C) had photopotential up to 300 mV and short circuit current up to 2.21 μA. The dependence of photocurrent and current quantum yield on electrolyte pH and the thickness of pigment films and the photovoltaic characteristics of pigmented electrodes under pulsed irradiation were studied. The maximum values obtained were photopotential U _ph = 400 mV, photocurrent I _ph = 26 μA, current quantum yield under stationary irradiation η = 8.5%, and quantum yield under pulsed irradiation η* = 23%.     

Second-Order Correlation Function of the Photon Emission from a Single Quantum Dot

The photon correlation of photon emission from a single quantum dot with cw excitation and pulsed excitation is investigated in details. To calculate the second-order correlation function for optical pumping, we deduce rate equations with a simplified two-level model under cw excitation and present the master equation approach in the interaction picture to the study of evolution of a three-level system under pulsed excitation. In addition, we report photon correlation measurements on a single self-assembled In0.5Ga0.5As quantum dot, which show strong antibunching behaviour under both the conditions of cw and pulsed excitations. The calculated results are in agreement with the experimental measurements.     

Difference-frequency pulse generation in quantum well heterolasers

It is shown that mid-to far-infrared (IR) and terahertz (THz) pulse generation via difference-frequency mixing in quantum well (QW) dual-wavelength heterolasers can be rather efficient under the modelocking regime for one or both lasing fields even at room temperature. In such a device, the long-wavelength field is produced in the process of intracavity difference-frequency mixing of two optical fields: continuous wave (CW) and pulsed (or both pulsed), due to the resonant intersubband quantum coherence in QWs, as well as due to the nonresonant second-order semiconductor bulk nonlinearity. The mode-locking regime of the optical generation allows one to significantly enhance the pulsed driving fields in comparison with those under CW operation and, therefore, substantially increase the output difference-frequency power. Within a simple model, an explicit formula for the intensity and shape of the generated IR or THz pulse is derived. It is shown that this method is capable of producing picosecond pulses at a ∼ 1-GHz repetition rate with a peak power of the order of 1 W and ≲0.2 mW at 10 and 50 μm wavelengths, respectively. Original Text ? Astro, Ltd., 2007.     

Entanglement of two interacting electrons in a driven double quantum dot structure

We study the case where two interacting electrons in a double quantum dot structure are driven resonantly by a pulsed electromagnetic field and present a method that is based on controlled rotation for the creation of maximally entangled two-electron states.     

Chaotic filtering of moving atoms in pulsed optical lattices by control of dynamical localization

We propose a mechanism for a velocity-selective device which would allow packets of cold atoms traveling in one direction through a pulsed optical lattice to pass undisturbed, while dispersing atoms traveling in the opposite direction. The mechanism is generic and straightforward: for a simple quantum kicked rotor pulsed with unequal periods, the quantum suppression of momentum diffusion (dynamical localization) yields momentum localization lengths L which are no longer isotropic, as in the standard case, but vary smoothly and controllably with initial momentum.     

Coherent repopulating hyperfine-structure levels by pulsed resonance fields and the quantum computer problem

A new method of polarization of atoms and nuclei by pulsed bichromatic resonance radio-frequency fields is proposed to produce an initial state of a quantum computer constructed with the use of cubits representing impurity atoms in a solid matrix having the hyperfine structure. It is shown that this method can provide strong polarization without using ultralow temperatures. The problem is considered for the interaction of three-and four-level systems with bichromatic and two-phase fields.     

One-color one-beam pumping of Er(3+)-doped ZBLAN glasses for a three-dimensional two-step excitation display

We demonstrate a one-color one-beam pumping method for a three-dimensional two-step excitation fluorescent display with Er(3+) -doped ZBLAN glass. A localized green fluorescent spot is obtained by use of a focused pump-light beam at 979 nm. The quantum efficiency of the two-step excitation fluorescence is investigated in a time-dependent analysis and an experiment with a pulsed pump light.     

基于室温脉冲量子级联激光器的NO气体检测中的光谱处理方法研究

报导了采用基于室温脉冲量子级联激光器的脉内光谱检测技术,利用中心波长为1904 cm^-1的量子级联激光器,在实验室对NO气体样品进行检测的研究结果. 针对单线直接吸收光谱反演算法进行了研究,介绍了基线拟合的最小二乘算法以获取其吸光度,根据HITRAN数据库中相应吸收谱线的吸收线强,采用扫描积分实现了气体浓度的反演,避免了标气标定造成的误差及污染;通过拟合残差分析得到了系统的检测限,达到34×10^-6 m. 关键词： 量子级联激光器 中红外 多项式拟合 扫描积分     

Effect of the parameters of pulsed anodic formation of porous silicon on its luminescent,paramagnetic, and electrotransport properties

We present the data on changes in the properties of porous silicon formed at the current pulse modulation in the range of 0.1–1 Hz with the aim to modulate the properties of porous silicon in a nanoscale range. It is demonstrated that the use of the pulsed mode of formation of porous silicon with a period of a few tenths of a second can dramatically affect the photoluminescence quantum yield and other properties of the material. There is a correlation of the luminescent, electrotransport, and paramagnetic properties of porous silicon formed under different modes.