Synchronization between optically injected semiconductor lasers on undamped relaxation oscillations

Seeding light from a laser into the cavity of a second one is a simple experiment largely encountered in optical domain (Stover, H.L., Steier, W.H.: Appl. Phys. Lett. 8, 91–93 (1966); Lang, R.: IEEE J. Quant. Elect. 18(6), 976–983 (1982)). With an unidirectional coupling, optical injection is a basic tool to study synchronization process between oscillators. The dynamics induced in this experiment have been extensively described, theoretically and experimentally (Simpson, T.B. et al.: Quant. Semiclassical Opt. 9(5), 765–784 (1997); Wieczorek S.: Opt. Commun. 172, 279–295 (1999); Blin, S.: Comptes Rendus de la Phys. 4(6), 687–699 (2003)) but mainly when the seeded light is a continuous wave (CW). In this paper, we describe the synchronization on an undamped relaxation regime. In order to study the degree of correlation between the two synchronized lasers (TL and RL), we use a cascade of two optical injections (Guignard, C.: Conference on Lasers and Electro Optics—the Europeen Quant. Electronics Conference (CLEO-EQEC), Munich (Germany), EC1M (2003)) thus three lasers: Master-transmitter laser (TL)-receiver laser (RL). The seeding by a field showing undamped relaxations can be directly compared with the optical injection by a CW signal, especially when the injected power and the detuning between the TL and RL frequencies are varied. Synchronization on undamped relaxation are shown to occur at values of the optical injected power and detuning, for which the RL is in the locked or wave-mixing regime when it is seeded by a CW. However, additional tongues of synchronization also exist at detuning equal to the relaxation oscillation frequency (ROF).     

Structural Investigation of the High Spin→Low Spin Relaxation Dynamics of the Porous Coordination Network [Fe(pz)Pt(CN)4]⋅2.6 H2O

The Hoffman‐type coordination compound [Fe(pz)Pt(CN)₄] ? 2.6 H₂O (pz=pyrazine) shows a cooperative thermal spin transition at around 270 K. Synchrotron powder X‐Ray diffraction studies reveal that a quantitative photoinduced conversion from the low‐spin (LS) state into the high‐spin (HS) state, based on the light‐induced excited spin‐state trapping effect, can be achieved at 10 K in a microcrystalline powder. Time‐resolved measurements evidence that the HS→LS relaxation proceeds by a two‐step mechanism: a random HS→LS conversion at the beginning of the relaxation is followed by a nucleation and growth process, which proceeds until a quantitative HS→LS transformation has been reached.     

Switching of the polarization state of a vertical cavity surface-emitting laser using polarized feedback

We show that the light of a commercial vertical cavity surface-emitting laser with polarized optical feedback can be switched between two linear polarization eigenstates. The flip occurs when the feedback phase is scanned by either the external cavity length or the injection current.     

Regiodivergent synthesis of pyrazino-indolines vs. triazocines via α-imino carbenes addition to imidazolidines

Hexahydropyrazinoindoles were prepared in a single step from N-sulfonyl triazoles and imidazolidines. Under dirhodium catalysis, α-imino carbenes were generated and formed nitrogen ylide intermediates that, after subsequent aminal opening, afforded the pyrazinoindoles predominantly via formal [1,2]-Stevens and tandem Friedel–Crafts cyclizations. Of mechanistic importance, a regiodivergent reactivity was engineered through the use of a specific unsymmetrically substituted imidazolidine that promoted the exclusive formation of 8-membered ring 1,3,6-triazocines. Based on DFT calculations, an original Curtin–Hammett-like situation was demonstrated for the mechanism. Further derivatizations led to functionalized tetrahydropyrazinoindoles in high yields.

Hexahydropyrazinoindoles are prepared in a single step from N-sulfonyl triazoles and imidazolidines. Of mechanistic importance, a regiodivergent reactivity can be engineered towards the exclusive formation of 8-membered ring 1,3,6-triazocines.     

Multistate Aggregation-Induced Chiroptical Properties of Enantiopure Disulfide-Mediated Bispyrene Macrocycles

A chiral bispyrene macrocycle designed for exclusive intermolecular excimer fluorescence upon aggregation was synthesized by a double hydrothiolation of a bis-enol ether macrocycle followed by intramolecular oxidation of free thiols. Unusually high stereoselectivity was achieved for the thiol-ene additions under templated conditions and Et₃B/O₂ radical initiation. After enantiomer separation (chiral stationary phase HPLC), aqueous conditions provoked aggregation. Detailed structural evolution was afforded by ECD/CPL monitoring. Three regimes can be observed and characterized by strong modifications in chiroptical patterns under, at, or above a 70 % H₂O : THF threshold. In luminescence, high g_lum dissymmetry factors values were obtained, up to 0.022, as well as a double sign inversion of CPL signals during the aggregation, a behavior rationalized by time-dependent density functional theory (TDDFT) calculations. Langmuir layers of enantiopure disulfide macrocycles were formed at the air–water interface and transferred onto solid substrates to afford Langmuir–Blodgett films, which were then studied by AFM and UV/ECD/fluorescence/CPL.     

Transient dimer formation in supercritical carbon dioxide as seen from Raman scattering

The polarized and depolarized Raman profiles of supercritical CO(2) have been measured in the region of the nu(2) bending mode (forbidden transition at about 668 cm(-1)) and for the Fermi dyad (1285 and 1388 cm(-1)) along the isotherms 307, 309, 313, and 323 K in a reduced density domain 0.04相似文献   

Medium‐Sized Rings versus Macrocycles through Rhodium‐Catalyzed Ring‐Expansion Reactions of Cyclic Acetals

α‐Diazo β‐ketoesters and diketones react with cyclic acetals under Rh^II catalysis to yield unprecedented polyoxygenated 8‐ and 9‐membered rings in one pot. The reactions occur under mild conditions with yields up to 90 %. A perfect regioselectivity is obtained, which can be rationalized through a mechanistic hypothesis that considers 1) the formation of an oxonium ylide, 2) its transformation into an unsaturated acyclic oxocarbenium electrophilic intermediate, and 3) an intramolecular nucleophilic attack in a direct application of Baldwin’s rules.     

Asymmetric synthesis of ethano-Tröger bases using CuTC-catalyzed diazo decomposition reactions

Nonracemic ethano-bridged Tr?ger bases are prepared using CuTC-catalyzed decompositions of diazo compounds. Excellent levels of diastereo- and enantio-control (dr and ee up to 12:1 and 95% respectively) are now obtained with aryl diazoketone precursors.     

Carbon dioxide in 1-butyl-3-methylimidazolium acetate. I. Unusual solubility investigated by Raman spectroscopy and DFT calculations

The unusual solubility of carbon dioxide in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been studied by Raman spectroscopy and DFT calculations. It is shown that the solubility results from the existence of two distinct solvation regimes. In the first one (CO(2) mole fraction ≤ 0.35), the usual Fermi dyad is not observed, a fact never reported before for binary mixtures with organic liquids or ionic liquids (IL). Strong experimental evidence complemented by effective DFT modeling shows that this regime is dominated by a chemical reaction leading to the carboxylation of the imidazolium ring accompanied by acetic acid formation. The reactive scheme proposed involves two concerted mechanisms, which are a proton exchange process between the imidazolium cation and the acetate anion and the carboxylation process itself initiated from the formation of "transient" CO(2)-1-butyl-3-methylimidazole 2-ylidene carbene species. In that sense, CO(2) triggers the carboxylation reaction. Moreover, this dynamic picture circumvents consideration of a long-lived carbene formation in dense phase. The second regime is characterized by the detection of the CO(2) Fermi dyad showing that the carboxylation reaction has been strongly moderated. This finding has been interpreted as due to the interaction of the acetic acid molecules with the COO group of acetate anions involved in monodentate forms with the cation. The observation of the Fermi doublet allows us to infer that CO(2) essentially preserves its linear geometry and that the nature and strength of the interactions with its environment should be comparable to those existing in organic liquids and other IL as well. These results have been supported by DFT calculations showing that the CO(2) molecule interacts with energetically equivalent coexisting structures and that its geometry departs only slightly from the linearity. Finally, we find that the CO(2) solvation in Bmim Ac and 1-butyl-3-methylimidazolium trifluoroacetate (Bmim TFA) cannot be straightforwardly compared neither in the first regime due to the existence of a chemical reaction nor in the second regime because CO(2) interacts with a variety of environments not only consisting of ions pairs like in Bmim TFA but also with carboxylate and acetic acid molecule.