New laser dyes based on derivatives of 3-(2-benzimidazolyl)coumarin are proposed that lase under lamp and coherent (nanosecond and microsecond) pumping in the spectral range 420-700 nm and feature a high generation efficiency reaching 40% under coherent pumping (1% when lamp-pumped) and an increased operational life that surpasses that for most popular laser dyes. The nature of the substituents in the 6-and 7-positions of the coumarin ring and the ionic structure of the dyes are found to influence their spectral and lasing characteristics. Introduction.Organic dyes and related compounds that lase upon pumping by nanosecond laser pulses are currently very common. However, the number of lasing dyes is much smaller for non-monochromatic pumping by lamp pulses. This is due to photophysical and photochemical processes occurring in the cavity under the influence of the pumping radiation. Furthermore, the spectral range in which lasing occurs is overlapped unevenly by effectively lasing and photostable dyes [1]. For this reason, the search for new effectively lasing dyes with increased photochemical stability is a critical problem.The use of coumarin derivatives as lasing media in dye lasers is very interesting [2]. This is due to the fact that this class of compounds has the best energy characteristics and photostability in the blue-green spectral region [3]. The clearly pronounced polarization of their molecular structure enables the range of laser spectral tuning to be expanded using solvation effects [4][5][6][7].New compounds of this class, derivatives of 3-(2-benzimidazolyl)coumarin, were previously reported [8]. They were investigated with powerful non-coherent pumping. As a result, the studies found that the new coumarin dyes lasing upon lamp pumping in the spectral range 503-580 nm had high lasing efficiency (up to 1%) and photochemical stability (3-5 times greater than rhodamine 6G). However, the spectral-luminescent characteristics of the new compounds and the lasing parameters under coherent pumping conditions were not studied.Herein the spectral-luminescent characteristics and lasing parameters of 3-(2-benzimidazolyl)coumarin derivatives are studied under coherent pumping by radiation from an excimer XeCl-laser.Experimental Setup and Measurement Method. Figure 1 shows a diagram of the setup on which the lasing parameters of EtOH solutions of the coumarin dyes were studied. The pumping source was an electrical-discharge excimer XeCl-laser with emission energy 180-200 mJ and wavelength 308 nm. The excitation pulse duration was 60 ns. Radiation from the XeCl-laser was focused by a cylindrical lens (f = 10 cm) onto a cuvette with the dye. The dye laser cavity with base L = 15 cm was formed by a mirror (reflection coefficient R = 100%) and stack (R = 20%). The dye laser pulse energy and pumping control energy were measured using IMO-2N meters. The broad-band laser spectrum was recorded using an STE ′ -1 spectrograph. The dye laser emission was directed into the spectrograph using an optical fiber with inner dia...

A comparative analysis of the spectral-luminescent characteristics and generation parameters of a number of 3-imidazopyridylcoumarin derivatives has been carried out under nano-and microsecond excitation by coherent and incoherent light. New coumarin dyes are offered that feature the ability to lase under different types of pumping in the spectral range 525-580 nm; high lasing efficiency reaching 20% and 1% under laser and lamp pumping, respectively; and high photochemical stability (3-5 times higher than that of rhodamine 6G) under conditions of powerful nonmonochromatic pumping.Introduction. About 500 laser dyes of various classes have now been studied [1]. Relationships between their molecular structural features and spectral-luminescent and generation characteristics have been established. Recommendations for the synthesis of highly efficient compounds with long operational lifetimes have been developed. As a result, generation in the spectral range from the near UV to the near IR has been achieved [2][3][4][5][6][7][8]. Recently liquid solutions have been replaced by solid-state matrices [9][10][11][12]. However, such a broad spectral range does not mean that dyes that generate with high efficiency, are photochemically stable to UV pumping, and have increased operational lifetimes are available over all ranges. In particular, such "gaps" exist in the green-yellow spectral range where the known dye unsubstituted rhodamine cannot satisfy the whole set of parameters. Therefore, it seemed interesting to use coumarin dyes that are currently capable of generating from the blue to the red spectral range and exhibit high conversion efficiency and photochemical stability [2-4, 7-10].Experimental. Spectral luminescent characteristics of dye solutions were studied on the nanosecond pulsed spectrofluorimeter that was described before [8]. Fluorescence decay times were measured using the laboratory setup operating in time-correlated single-photon counting mode that was described before [11].Generation parameters of EtOH solutions of coumarin dyes with microsecond pumping were studied in a dye laser converter (Fig. 1). The source of microsecond coherent pumping was a dye laser (DL) based on an upgraded version of the coaxial lamp-cuvette construction of Dzyubenko [13]. The DL cavity was formed by a planar dielectric mirror with R = 100% and a stop of three plane-parallel plates of K-8 glass, which in this instance was the optimum exit mirror. The flash loop included 10 K75-48 low-inductance capacitors of total capacitance 2.2 μF connected in parallel and an IRT-6 ignition discharger. The input potential was 17 kV. The lamp discharge gap was filled with Xe at 20-30 Torr pressure. The pulsed pumping light pulse length at the 0.5 level was 2 μs with a 0.8 μs rise time. The pumping pulse electrical energy was 300 J. The first stage (A) of the laser converter used solutions of the studied coumarins for the pumping lamp (noncoherent). The cavity of the second stage (B) of the laser converter was formed by a planar blank mirror ...

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Electrothermal devices exhibit increasing secondary effects upon downscaling. These effects alter their temperature profiles and thermal energy distributions. Based on scaling laws, we show that the Thomson effect is increased over Joule heating as the structures are sized down. Thermal models are upgraded to take into account this secondary effect, and finite element simulations together with experimental runs validate them.