Side-hole to anti-hole conversion in time-resolved spectral hole burning of ruby: Long-lived spectral holes due to ground state level population storage

We report time-resolved transient spectral hole burning of Verneuil-grown 20 ppm and ca. 0.6 ppm ruby (Al₂O₃:Cr³⁺) in zero field and low magnetic fields B∥c at 4 K. The hole-burning spectroscopy of the 20 ppm sample implies relatively rapid cross relaxation in the ⁴A₂ ground state on the ∼1 ms timescale both in zero field and in low magnetic fields, B∥c, up to 0.2 T. In the 0.6 ppm sample, side-hole to anti-hole conversion is observed both in zero field and in low magnetic fields. This conversion is caused by population storage in ⁴A₂ ground state levels. Spin-lattice relaxation, on the 200 ms timescale, is directly observed from the time dependence of the resonant hole and anti holes in B∥c, consistent with a very low cross-relaxation rate. However, in zero field cross relaxation in the ⁴A₂ ground state is still a significant relaxation mechanism for the 0.6 ppm sample resulting in hole decay in ∼50 ms.     

Measurement of unstable burning velocities of iso-octane–air mixtures at high pressure and the derivation of laminar burning velocities

A new technique is reported for measuring burning velocities at high pressures in the final stages of two inwardly propagating flame kernels in an explosion bomb. The flames were initiated at diametrically opposite spark electrodes, close to the wall, in quiescent mixtures. Measurements of pressure and flame kernel propagation speeds by high-speed photography showed the burning velocities to be elevated above the corresponding laminar burning velocities as a result of the developing flame instabilities. The enhancement increased with increase in pressure and decreased with increase in Markstein number. When the Markstein number was negative, instabilities could be appreciable, as could the enhancement. For the iso-octane–air mixtures investigated, where the mixtures had well-characterised Markstein numbers or critical Peclet numbers at the relevant pressures and temperatures, it was possible to explain the enhancement quantitatively by the spherical explosion flame instability theory of Bechtold and Matalon, provided the critical Peclet number was that observed experimentally, and allowance was made for the changing pressure. With this theoretical procedure, it was possible to derive values of laminar burning velocity from the measured values of burning velocity over a wide range of equivalence ratios, pressures, and temperatures. The values became less reliable at the higher temperatures and pressures as the data on Markstein and critical Peclet numbers became less certain. It was found that with iso-octane as the fuel the laminar burning velocity decreased during isentropic compression.     

Modeling study of non-line-narrowed hole-burned spectra in weakly coupled dimers and multi-chromophoric molecular assemblies

Several different models have been proposed to explain the origin of the complex anti-hole features observed in hole-burned (HB) spectra of excitonically coupled systems such as photosynthetic complexes. This lack of consensus presents a serious constraint on the interpretation of HB spectra and the underlying electronic structures of these systems. To resolve this problem we present results of modeling studies of non-resonant HB spectra taking uncorrelated excitation energy transfer and excitonic interactions into account. Simplified analytical results are compared with Monte Carlo simulations in which excitonic interactions are explicitly taken into account in order to disentangle a number of distinct effects. It is shown that these effects can accurately account for both hole shapes and the broad anti-hole structure observed in excitonically coupled systems. We argue that these models will provide a necessary framework for probing the electronic structure of these systems via HB spectroscopy.     

色谱法测定催化剂中碳含量操作条件研究

根据燃烧-色谱法的原理建立了催化剂碳含量的测定方法并开发了催化剂高温定碳仪,通过考察燃烧温度、载气流速、桥流等对催化剂碳含量测定的影响,确定了测定催化剂碳含量的最佳操作条件。实验结果表明,在确定的最佳操作条件下,测定的催化剂碳含量与化学法基本相同。     

Tris(2‐aminoethyl)amine‐based ferrocene‐terminated dendrimers as burning rate catalysts for ammonium perchlorate‐based propellant decomposition

Ferrocene‐based derivatives show potential application as burning rate catalysts (BRCs) for solid composite propellants. However, migration problems of simple ferrocene‐based derivatives limit their application as BRCs in solid composite propellants. To overcome the migration problems of ferrocene‐based BRCs and to enhance the burning rate of ammonium perchlorate (AP)‐based propellants, zero‐ to second‐generation tris(2‐aminoethyl)amine‐based ferrocene‐terminated dendrimers (G0, G1 and G2) were synthesized. The structures of G0, G1 and G2 were confirmed using ¹H NMR, Fourier transform infrared and UV–visible spectroscopies. The electrochemical behavior of G0, G1 and G2 was investigated using cyclic voltammetry. It was found that G0, G1 and G2 showed redox behavior due to the presence of ferrocene and this redox behavior was diffusion controlled over the investigated scan range. The burning rate catalytic effect of G0, G1 and G2 on thermal decomposition of AP was investigated using thermogravimetry and differential thermogravimetry. G0, G1 and G2 showed good catalytic effect on the thermal decomposition of AP. Anti‐migration studies showed that migration of G0, G1 and G2 was much slower than that of 2,2‐bis(ethylferrocenyl)propane (catocene) and ferrocene.     

FTIR spectroscopic investigation of oxygen spillover especially through the gas-phase. A reaction interesting in coke burning

Oxygen spillover through the gas phase was investigated, using FTIR spectroscopy to measure the reaction kinetics of the oxidation of benzoic acid, adsorbed to γ-alumina, in the absence and presence of a neighboring Pt grid. It could be shown that oxygen, activated on Pt may increase the oxidation rate, though there is no contact between Pt and the benzoic acid.     

Persistent hole burning in semiconductor nanocrystals

The persistent spectral hole burning (PSHB) phenomenon was found to occur in many kinds of nanocrystalline semiconductors, such as CdSe, CdS, CuCl, CuBr and CuI, embedded in crystals, glass or polymers. In inhomogeneously broadened exciton absorption spectra of these nanocrystals, the spectral hole and its associated structure were created by the narrow-band laser excitation and were conserved for more than several hours at 2 K. Hole depth grew in proportion to the logarithm of the burning fluence. Thermally-annealing and light-induced hole-filling phenomena were observed. The hole burning takes place by the tunneling process through potential barriers with broadly distributed barrier height and thickness. Unusual luminescence behaviors related to the PSHB phenomena were also observed. They are luminescence elongation with increase of the light exposure and hole burning in the luminescence spectrum. The observed PSHB phenomena are explained by the exciton localization and the succeeding ionization of nanocrystals. The energy of the photoionized nanocrystal is released from the original energy and the new energies depend on the spatial arrangement of the trapped carriers. Quantum confinement of carriers and resulting strong Coulomb interaction between confined carriers and trapped carriers are essential for the energy change. Possible applications of the PSHB phenomenon is discussed.     

Stability performance of short cavity Er-doped fiber lasers

An experimental study of stability between two types of short-cavity laser configurations is carried out. The short-cavity lasers are comprised of one or two pairs of wavelength-matched FBGs, encompassing a short length of highly-doped Er-fiber, to create effectively single- or dual-wavelength fiber lasers. The laser performance in terms of the laser output power and laser stability in relation to the gain medium length was investigated experimentally, analyzed and reported in this letter.     

A theoretical analysis of the effects of erbium ion pair on the dynamics of an optical gain stabilized fiber amplifier

In this paper, the effects of ion-pair formation on the gain dynamics of multi cavity optical automatic gain control erbium doped fiber amplifier is modelled. The inhomogeneous Cabezas simple model is used to write the rate and propagation equations for the active medium. The solution of the governing equations shows that in high concentration of the erbium ions, depending on the pumping rate, the relaxation oscillations are converted to nT-Periodic or even to chaotic behavior. Although the high concentration erbium ion in the optical amplifiers decreases the conversion efficiency and increases the threshold pump power, amplitude of the transient effects is reduced in the multi feedback-loop WDM amplifiers relative to the low concentration erbium ions multi feedback-loop optical amplifiers and ion-pairs, which act as a saturable absorber to compensate the gain tilt caused by the OAGC laser spectral hole burning. The theoretical results are in complete agreement with the previous published experimental results.     

持久光谱烧孔动力学的理论模型和实验研究

建立了单光子光化烧孔的三能级模型，求解了反映质子转位变构机制的速率方程组，推导了成孔过程的动力学特性，获得了可与实验进行比较的解析解．用时域和频域两种方法测量了ＴＨＰ／ＰＭＭＡ和ＴＭＰ／ＰＭＭＡ薄膜样品光谱烧孔的动力学过程，得到与理论分析一致的规律，并测得了有效成孔速率和成孔时间等参数．这些参数对于评价频域光存贮材料性能有一定意义．