V. A. Petukhov

Submicrosecond regular and chaotic nonlinear dynamics in a pulsed picosecond Nd:YAG laser with millisecond pumping

We propose and study both numerically and experimentally a feedback-controlled laser system capable of generating regular bursts with a submicrosecond period. Bursting is obtained in a laser that is controlled by a combination of feedbacks in which the negative feedback loop action is delayed by one cavity round trip with respect to the positive one, and the period is adjusted by relative feedback sensitivity. The proper combination of feedbacks is realized in a Nd:YAG laser with millisecond pumping by means of a single optoelectronic negative feedback unit that utilizes the signal reflected from an intracavity Pockels cell polarizer. Regular bursting (microgroups of picosecond pulses) with controlled periods from 25 to 75 cavity round trips is obtained experimentally. The development of chaotic dynamics displayed by the system at a higher pumping level differs from the Feigenbaum scenario.

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.

Vibronic Structures of the Ground and Excited Singlet Electronic States of Dimethylnaphthalenes Cooled in a Supersonic Jet

Abstract Fluorescence excitation and dispersed fluorescence spectra of jet-cooled naphthalene and 2,6-, 2,7-dimethylnaphthalenes have been measured. The frequencies of optical active vibrations in the ground and first excited singlet states have been determined. The new technique for calculation of planar vibration frequencies of polycyclic benzenoid hydrocarbons in the excited electronic states has been developed. The vibration frequencies in the ground and first excited singlet states of these molecules were calculated using the developed technique and the Ohnos model. The interpretation of vibronic spectral lines based on the comparison of the calculated and experimental data was made. The calculation rms errors for the vibration frequencies in the ground electronic states of the investigated molecules do not exceed 20 cm−1 and are approximately 1.5 times higher for excited states without additional adjustment of parameters for individual molecules.

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.

Analysis of the Electronic Vibrational Spectra of Bisanthene by Calculating Normal Modes

At 4.2 K, the quasiline fluorescence and fluorescence-excitation spectra (in the region of the S1 ← S0- and S2 ← S0 transitions) of bisanthene in n-hexane have been obtained. Using the MO/M8ST method, the calculation of the Ag normal modes in the S0, S1, and S2 electronic states was carried out for the bisanthene molecule; the relative intensities of the transitions in the corresponding vibronic spectra were also calculated. The analysis of the results of calculations and experiment made it possible to draw conclusions on the form of the modes for a number of normal vibrations which are active in the bisanthene vibronic spectra.

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.