Tuning the frequency of ultrashort laser pulses by a cross-phase-modulation-induced shift in a photonic crystal fiber

Femtosecond pulses of fundamental Cr:forsterite laser radiation are used as a pump field to tune the frequency of copropagating second-harmonic pulses of the same laser through cross-phase modulation in a photonic crystal fiber. Sub-100-kW femtosecond pump pulses coupled into a photonic crystal fiber with an appropriate dispersion profile can shift the central frequency of the probe field by more than 100 nm, suggesting a convenient way to control propagation and spectral transformations of ultrashort laser pulses.     

Photochemical electrocyclization of the indolinylphenylethenes involving a C-N bond formation

[reaction: see text] A novel oxidative photodehydrocyclization of indolinylphenylethenes to a polycyclic heteroaromatic cation with good yields was described. Starting from the trans derivative, the phototransformation is a multistep process. The process includes two photochemical reactions and a trans-cis isomerization reaction, followed by an 1-aza-1,3,5-hexatrienic electrocyclic reaction involving the formation of a C-N bond. The cyclized product gives the stable heteroaromatic cations from hydride elimination with oxygen from air or iodine.     

Supramolecular architecture of crown-containing styryl dyes: Part I. Crystal and molecular structures of the acetonitrile solvate monohydrate of the potassium iodide complex with benzo-15-crown-5 ether dye based on methylquinoline iodide

The structure of a single crystal of the acetonitrile solvate monohydrate of the potassium iodide complex with benzo-15-crown-5 ether dye based on methylquinoline iodide (I) is determined by X-ray diffraction. It is established that the single crystal contains positively charged molecules of benzocrown ether photodye (D), K⁺ cations, I^? anions, and water and acetonitrile solvate molecules in the ratio 1: 0.5: 1.5: 1: 1, respectively. The K⁺ cation and one of the I^? anions occupy special positions along the twofold axis. The K⁺ cation is coordinated by ten oxygen atoms of the crown ether fragments of two D molecules to form the [D ₂K]³⁺ complex. Inside the complex, two aromatic quinoline fragments are involved in a stacking interaction. The crossed mutual arrangement of the ethylene fragments and the considerable distance between them exclude the occurrence of intramolecular photochemical [2 + 2]cycloaddition reactions. In the crystal, the [D ₂K]³⁺ cationic complexes form stacks along the b axis. The adjacent complexes in a stack are related through the center of symmetry and, therefore, are arranged in a head-to-tail manner. The double bonds of the neighboring molecular cations D in a stack are strictly parallel to each other and are separated by a distance of 3.754 Å. This geometry is favorable to the intermolecular cycloaddition reaction that should result in the formation of the syn head-to-tail isomer.     

Principles for control of photochemical reactions in molecularly organized microsystems

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2197–2210, October, 1990.     

Phosphorescence of aromatic molecules in complexes with crystalline β-cyclodextrin at room temperature

The rate constants for the quenching by oxygen of triplet states of aromatic molecules (naphthalenes-d₈ and-h₈, phenanthrene) forming inclusion complexes with crystalline β-cyclodextrin in water at 290 K are equal to 900–1300 L mol⁻¹s⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1450–1453, August, 1997.     

Microjoule supercontinuum generation by stretched megawatt femtosecond laser pulses in a large-mode-area photonic-crystal fiber

Microjoule supercontinuum generation is demonstrated using a large-mode-area photonic-crystal fiber (PCF) pumped by an amplified stretched-pulse output of a mode-locked Cr:forsterite laser. A PCF with a mode area of 380 μm² is employed to transform 300-fs Cr:forsterite laser pulses with a peak-power of a few megawatts into a supercontinuum radiation with a spectrum spanning from 700 to 1800 nm and a total energy of 1.15 μJ.     

Coherent anti-Stokes Raman scattering microspectroscopy of silicon components with a photonic-crystal fiber frequency shifter

Coherent anti-Stokes Raman scattering (CARS) microspectroscopy of silicon components is demonstrated with pump and probe fields delivered by a mode-locked Cr:forsterite laser and the frequency-shifted soliton output of a photonic-crystal fiber as a Stokes field. CARS microspectroscopy is shown to allow a visualization of microscale features and defects on the surface of silicon wafers, offering much promise for online diagnostics of electronic and photonic silicon chip components.     

Hydrolytic Stability and Photostability of Boron Complexes of Dibenzoylmethane with Various Substituents at the Boron Atom

High Energy Chemistry - The basic photophysical characteristics and the hydrolytic stability and photostability of dibenzoylmethanatoboron complexes containing various substituents at the boron...     

Influence of monolayer state on spectroscopy and photoisomerization of an amphiphilic styryl-pyridinium dye on a solid substrate

The spectroscopy and photochromic properties of transferred monolayers of the amphiphilic styryl-pyridinium dye 4-(3',4'-dimethoxystyryl)-N-octadecylpyridinium perchlorate (DMPOP) were studied at different conditions during their transfer. The emission maxima of the monolayers transferred from the air-water interface in the liquid-expanded phase are strongly dependent on the surface pressure applied during the transfer process, even at values when the area per molecule is 2-3 times larger than the area occupied by a chromophore. In monolayers transferred from the liquid-condensed phase, the presence of a different kind of aggregates was observed. The fluorescence emission properties of the monolayers can be reversibly modulated by photoinduced E-Z isomerization. A blue shift up to 72 nm in the emission maximum, depending on the transfer conditions of the films, can be obtained by irradiation with blue light, and partially recovered (a red shift of up to 26 nm) with UV radiation. The rate at which the first process (E-->Z) takes place is drastically reduced in monolayers transferred from the liquid-condensed phase as compared to those transferred from the liquid-expanded one. However, the rate of the reverse reaction (Z-->E) is not significantly altered. These properties make DMPOP a promising material for the preparation of Langmuir-Blodgett films, whose properties can be effectively controlled by the transfer conditions and subsequently optically modulated, for potential applications as photonics devices for data storage.