M. A. Semenov

Experimental determination and interpretation of the fluorescence and fluorescence excitation spectra of chrysene cooled in a supersonic jet

The fluorescence and fluorescence excitation spectra of jet-cooled chrysene are measured. The frequencies of in-plane vibrations in the ground and first excited singlet electronic states, as well as the relative intensities of transitions between them, are calculated with the MO/M8ST method. Based on these data, experimental spectra are interpreted. In the fluorescence excitation spectrum, the position of the line of the 0–0 transition (28 195 ± 1 cm−1), which is the most intense, is determined. In the experimental fluorescence excitation spectrum, 21 lines correspond to fundamental vibrations (altogether, 37 lines are attributed). This supports our assignment and is consistent with the group-theoretical analysis of vibronic interactions. Upon excitation at the frequency of the 0–0 transition, 10 lines corresponding to the excitation of fundamental vibrations are detected, and all 17 lines observed are attributed. In the fluorescence excitation spectrum, the standard deviation between the calculated and measured frequencies of attributed fundamental vibrations is 19 cm−1, while that in the fluorescence spectrum is 15 cm−1.

Experimental measurement and calculation of the line intensities in vibronic spectra of jet-cooled anthracene

The intensities of vibronic lines are experimentally measured in fluorescence and fluorescence excitation spectra of jet-cooled anthracene. An original method is developed for calculating geometrical parameters of benzene hydrocarbons in the ground and excited electronic states. Using these parameters, the intensities of vibronic lines in fluorescence and absorption spectra of anthracene are calculated in the Franck-Condon approximation taking into account the mixing of all the twelve normal coordinates of totally symmetric vibrational modes. After correction for the quantum yield of fluorescence, good agreement is obtained between the calculated line intensities in the absorption spectrum and the measured line intensities in the fluorescence excitation spectrum. Based on these data, a new assignment of the lines in the fluorescence excitation spectrum corresponding to totally symmetric modes 7 and 8 is suggested.

Fine-structure spectroscopy of 2-methylnaphthalene cooled in a supersonic jet

The fluorescence and fluorescence excitation spectra of 2-methylnaphthalene molecules cooled in a supersonic jet are measured. The frequencies of vibrations in the S0 and S1 states, as well as the relative intensities of electronic-vibrational transitions in the fluorescence and fluorescence excitation spectra, are calculated with the semiempirical MO/M8ST method. The intensities are calculated in the Franck-Condon approximation taking into account the mixing of all the 38 totally symmetric normal vibrations. Based on the calculations, most observed spectral lines are assigned. It is shown that the calculation accuracy of the method is high enough for it to be used to interpret the spectra of molecules of aromatic compounds such as substituted naphthalenes. It is found that the main contribution to the fluorescence spectrum is made by four optically active vibrations.

Diode-pumped dye laser

This letter reports diode pumping for dye lasers. We offer a pulsed dye laser with an astigmatism-compensated three-mirror cavity and side pumping by blue laser diodes with 200 ns pulse duration. Eight dyes were tested. Four dyes provided a slope efficiency of more than 10% and the highest slope efficiency (18%) was obtained for laser dye Coumarin 540A in benzyl alcohol.

Experimental determination and interpretation of fluorescence and fluorescence excitation spectra of 1,2-benzanthracene cooled in supersonic jet

We measured the fluorescence and fluorescence excitation spectra of supersonic jet-cooled 1,2-benzanthracene. Using the MO/M8ST method, we calculated the frequencies of in-plane vibrations in the ground and first excited singlet electronic states, and, in the Franck-Condon approximation, we calculated the intensities of transitions between them. Experimental spectra are interpreted based on these data. In the fluorescence excitation spectrum, the position of the line of the 0–0 transition (26535 ± 1 cm−1), which is the most intense, is determined.

New efficient laser dyes for the red region of the spectrum. Part 1. Peri-indenones

We report the generation characteristics of ethanol solutions of twenty newly synthesised dyes belonging to peri-indenones, including benzanthrones and phenalemines. The tuning curves of these dyes, generating light in the orange and red spectral regions, are measured, and the wavelength tuning ranges are determined. The dependence of the generation energy on the pump energy in a non-selective cavity is measured. It is shown that some of the synthesised dyes surpass the widely used laser dyes in the energy efficiency and the width of the wavelength tuning range.

New efficient laser dyes for the red spectral range. Part 2. Pyrone derivatives

We report the generation characteristics of ethanol solutions of some dyes belonging to the derivatives of 2H- and 4H- pyrones, as well as of some structurally similar model fluorophores. The tuning curves of these dyes generating light in the orange and red spectral regions are measured, and the wavelength tuning ranges are determined. The dependences of the generated energy on the pump energy in a non-selective cavity are also measured. It is shown that some of the studied compounds possess better characteristics than those of widely used laser dyes in these spectral regions.

Generation of a regular sequence of short-pulse microtrains with a discretely varied repetition period

In the Nd:YAG lamp-pumped laser controlled by optoelectronic negative feedback based on an electro-optic DKDP crystal, the mode of generation of a millisecond sequence of short-pulse microtrains with a discretely varied repetition period was implemented. The microtrain repetition periods are fixed and controlled by resonances of shear acoustic oscillations of the crystal. The cavity design allowed selective excitation of the first ten acoustic modes in the period range of 8–0.5 µs.

Synthesis and investigation of new organophosphorus dyes of green and red luminescence

On the basis of amino derivatives of N-phenylnaphthalimide, naphthoylenebenzimidazole, benzanthrone, and phenalenone new phosphorus-containing luminophores containing phosphonomethyl and phosphazo groups in their structures were synthesized. Luminiscence spectrum and excitation characteristics of compounds obtained were studied. Some of the synthesized substances were proposed for application as effective laser dyes for green and red spectral regions with a wide range of retuning.

An Electrodynamic Pulsed Valve for Molecular Beams

The pulsed valve with an electromagnetic drive, based on a permanent magnet and a movable coil, is intended to obtain pulsed molecular beams. It is controlled by small currents of a few amperes and, thus, does not produce considerable electrodynamic disturbances. An electric control circuit of the valve provides for reduced mechanical stress on the movable coil. The frequency of the valve actuation is controlled in a range of 5–50 Hz; the gas pulse duration is regulated within the limits of 0.2–4 ms (FWHM). This device is suggested for application in the spectroscopy of complex molecules in molecular beams.