Spectral-Luminescent and Lasing Properties of Aminocoumarin Derivatives in Thin Polymer Films

The absorption and fluorescence spectra and the lasing ability of aminocoumarin derivatives in thin polymer layers (0.5–0.8 μm) based on the copolymer methylmethacrylate with a methacrylic acid and the copolymer methylmethacrylate with glycidylmethacrylate formed by coating of optically transparent glass substrates have been studied. It is found that the intensity of absorption and luminescence as well as the lasing resource of coumarins are determined by the structure of the latter and by the nature of the polymer medium. Compositions based on the copolymer methylmethacrylate with glycidylmethacrylate and aminocoumarin derivatives with a fluorized methyl group at the 4th molecular position can be of interest in optical technologies (light transformers, amplifiers). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 464–467, July–August, 2005.     

Theoretical investigation of photoprocesses in complex organic compounds upon high-power laser excitation

A procedure of theoretical investigations into the dynamics of energy level populations of organic molecules upon high-power laser excitation is developed that allows information on stimulated emission of molecules, gain and lasing spectra, dynamics of lasing pulses, populations of the ground and excited states, and influence of the induced absorption on lasing of the organic molecules to be obtained. Laws of changing of the above-indicated processes are established for two pyran substitutes. Results of theoretical and experimental investigations are well correlated. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 51–60, March, 2009.     

Lasing of a DCM dye layer in carbazole-based films

We have studied the spectral and lasing properties of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) in polyepoxypropylcarbazole (PEPK), polybutylcarbazole (PBK), and polyvinylcarbazole (PVK) films when excited by emission from a XeCl laser (λ = 308 nm) and the second harmonic of a YAGNd laser (λ = 532 nm). Stimulated emission was excited without an external cavity in the traveling wave mode in films of thickness 0.5–0.8 μm, obtained by the centrifuging method. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 177–181, March–April, 2006.     

Two-photon—induced fluorescence and electronic structure of substituted dicyanomethylene pyrans in solutions under femtosecond excitation

The method of two-quantum etalon is used to determine the two-photon absorption cross sections of eight dicyanomethylene (DCM) pyran dyes (DCM derivatives). Measurements of two-photon absorption of femtosecond Ti: sapphire-laser (λ = 800 nm, τ = 100 fs, and f = 89 MHz) radiation have been carried out. The nature of nonlinear excitation has been confirmed by the dependence of the fluorescence intensity on the excitation radiation intensity, which is close to a square-law one. Based on the measured two-photon absorption cross sections, the sizes of delocalized π-electronic clouds of DCM dye molecules with different substitutes are estimated in solvents with different polarity parameters. It is demonstrated that an increase in the polarity parameter of the solvent causes the two-photon absorption cross sections and sizes of delocalized π-electronic clouds of DCM, DCM-doa, DCM-17, DCM-5M, and DCM-11 dyes to increase. It is demonstrated that the size of the delocalized π-electronic cloud and the quantum fluorescence yield of the DCM-ul dye decrease with increasing polarity of the solvent despite the growth of the two-photon absorption cross section. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 69–73, November, 2005.     

Quenching of fluorescence for fluoro derivatives of the laser dye DCM in polar solutions

We used fluorescence spectroscopy and nanosecond flash photolysis to study the photophysical properties of the laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylamino)styryl-4H-pyran (DCM) and its two fluoro derivatives: (E)-2-〈2-[2-(4-dimethylaminophenyl)ethenyl]-6-trifluoromethyl-4H-4-pyranylidene〉malononitrile (DCMF3) and (E)-2-〈2-[2-(4-dimethylaminophenyl)ethenyl]-6-n-heptafluoro-propyl-4H-4-pyranylidene〉 malononitrile (DCMF7), in nonpolar n-hexane, mixtures of low-polarity toluene and polar dimethylsulfoxide (DMSO), n-propanol at room temperature and at 77 K. The fluorescence quantum yield Φ_fl of the laser dye DCM increases linearly as the polarity of the binary solvent mixture (toluene+DMSO) increases, from 0.08 in toluene to 0.80 in DMSO. The dependence of Φ_fl on the polarity of the mixture toluene+DMSO for DCMF3 and DCMF7 reaches a maximum for a small amount (∼2 vol.%) of added polar DMSO; and with further increase in the DMSO concentration (≥50 vol.%), the fluorescence of the fluoro derivatives of DCM is practically completely quenched. The quantum yield for intersystem crossing Φ_ST for DCM, DCMF3, and DCMF7 is no greater than 0.01 in solutions of different polarities. We discuss the mechanisms for nonradiative deactivation of the electronic excitation energy for the fluoro derivatives compared with DCM. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 606–612, September–October, 2006.     

3-(2-Benzimidazolyl)coumarin derivatives —highly effective laser media

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.     

New laser dyes based on 3-imidazopyridylcoumarin derivatives

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 6 G) under conditions of powerful nonmonochromatic pumping.     

Lasing action of rhodamine B in polyacrylic acid films

 Rhodamine B (Rh-B) has been embedded in PolyAcrylic acid (PAA) films. The materials are studied for the laser action with nitrogen laser excitation. The lasing efficiency of Rh-B/PAA films is comparable to that of rhodamine 6G in methanol. There is a 50% reduction in the laser intensity of the films with 2600 pulses from the N₂ laser (2 Hz). The photostability of these materials is far superior to that of other polymeric materials and is comparable to that of sol–gel materials. Received: 22 May 1996 /Revised version: 10 July 1996     

Spectral-luminescence and lasing properties of several morpholine derivatives of naphathalimide in different solvents

The spectral-luminescence properties, lasing ability, and time-resolved gain spectra of three morpholine derivatives of naphthalimide (substituted in position 4) in polar (ethanol and dimethylformanide) and nonpolar (diethyl ester and toluene) solvents are investigated. It is found that rotation of the morpholine group about the single bond connecting the group with the rest molecule takes place, which results in a shift of the gain spectrum towards the longwave region and decrease of the fluorescence quantum yield. Deceased. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 603–606, September–October, 1997.     

Active media for lasers based on colored epoxy and triazine-containing polymers

The problems of the synthesis of active media for lasers based on colored thermoreactive polymers are examined, and the lasing characteristics of the active media are investigated. Zh. Tekh. Fiz. 67, 71–76 (October 1997)     

Lasing efficiency of dyes incorporated into a nanoporous glass-polymer composite

We have used microsecond coherent pumping to study the lasing efficiency of active elements based on a nanoporous glass-polymer composite activated by organic dyes, as a function of the spectral composition of the pump within the main absorption band of the dye. We have shown that under the indicated excitation conditions, the lasing efficiency can exceed 40% and can be comparable with the lasing of liquid elements. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 708–716, September–October, 2008.     

Distributed feedback dye laser holographically induced in improved organic–inorganic photocurable nanocomposites

Distributed feedback (DFB) lasing in permanent volume transmission gratings formed in a laser dye-doped organic–inorganic nanocomposite has been investigated. DFB laser cavities were fabricated using one-step two-beam holographic exposure of Pyrromethene 567 (PM567) doped photopolymerizable acrylate monomers containing inorganic (LaPO₄) nanoparticles. Compared to the formulation previously utilized, the material composition presented provides longer lifetime of the laser. Spectral and polarization properties, input–output and stability characteristics of the laser output have been investigated by varying the material composition and the patterning parameters. DFB lasing emission of the second and the third diffraction orders has been demonstrated. The spectral linewidth of ∼0.08 nm has been observed at a pump energy threshold of about 0.2 μJ/pulse for the second-order DFB lasing when pumped with 532 nm 500 ps laser pulses. Spectral tuning of the lasing output over ∼56 and ∼7 nm was obtained by varying the grating period and the content of inorganic nanoparticles in the polymer matrix, respectively.     

Passive Q-switching of erbium glass laser by magnesium aluminosilicate sitall with cobalt ions

We have studied the radiation output parameters for an erbium glass laser, lasing at a wavelength of 1.54 μm, with passive Q-switching by means of a cobalt-containing magnesium aluminosilicate sitall compared with a saturable absorber based on a magnesium aluminum spinel crystal with cobalt ions. We have shown that the output characteristics of the laser emission when using sitall are not inferior to the analogous characteristics of a laser based on a spinel crystal, and are practically independent of the temperature of the saturable absorber in the range 0°C–80°C. The duration (energy) of the output pulses was 70 nsec (∼4 mJ), the energy dispersion of the radiation pulse relative to the average value was no greater than 3%, the beam divergence was 2.8 mrad, the laser beam quality factor was M² = 1.2. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 126–131, January–February, 2007.     

A linear cavity multiwavelength fiber laser with adjustable lasing line number for fixed spectral regions

We report an experimental demonstration of muliwavelength erbium-doped fiber laser with adjustable wavelength number based on a power-symmetric nonlinear optical loop mirror (NOLM) in a linear cavity. The intensity-dependent loss (IDL) induced by the NOLM is used to suppress the mode competition and realize the stable multiwavelength oscillation. The controlling of the wavelength number is achieved by adjusting the strength of IDL, which is dependent on the pump power. As the pump power increases from 40 to 408 mW, 1–7 lasing line(s) at fixed wavelength around 1601 nm are obtained. The output power stability is also investigated. The most power fluctuation of single wavelength is less than 0.9 dB, when the wavelength number is increased from 1–7.     

Modeling the cw lasing regime for diode-pumped solid state lasers

In terms of a system of balance equations, we propose a model for describing the operation of lasers based on solid-state quasi-three-level active media in the cw lasing regime with longitudinal pumping by emission from diode lasers, taking into account the spatial distribution of the pump and lasing light beams. We model the operation of lasers based on the active crystals Yb³⁺:NaLa(MoO₄)₂ and Yb³⁺:YVO₄, taking into account the proposed spatial distribution function of the intensity and the emission spectrum of the pump. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 55–60, January–February, 2007.     

Characteristic properties of ZnO random laser pumped by nanosecond pulses

Investigations of UV radiation spectra of powdered zinc oxide and its unordered film were conducted. The samples were pumped by 3-rd harmonics of the two-stage Nd:YAG-laser (λ=355 nm) with pulse duration ∼10 ns. Maximum density of energy of pumping pulses was about 150 mJ/cm². With some of our samples, we achieved lasing. The threshold values of the pumping energy density occurred higher than those under picosecond pumping approximately for one-two orders of magnitude. It was shown that the threshold of lasing and the character of lasing spectra depend on the morphology of particles forming a powder. The long-wavelength shift of the maximum of lasing spectra with a rise of the pumping was observed. It was interpreted as a result of participation of electron–hole plasma recombination in the process of lasing. A chaotic character of lasing spectra was observed and partially analyzed. PACS 42.55.Zz; 78.55.Et; 42.70.Hj     

Generation of acoustically distributed feedback lasers based on gyrotropic crystals

Oscillation conditions were determined for acoustically distributed feedback (ADFB) lasers based on gyrotropic uniaxial and cubic crystals. The lasing threshold was shown to be higher for the modes with clockwise polarization than for those with counterclockwise polarization. It is established that the regions of maximal amplification for clockwise (counterwise) waves of the gyrotropic crystal are displaced in the direction of decreased (increased) phase detuning, respectively, relative to amplification regions that correspond to the absence of crystal gyrotropy. The ADFB laser was shown to be capable of generating at the Bragg frequency. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 331–335, May–June, 2008.     

High-quality MBE growth of AlχGa1-χ As-based THz quantum cascade lasers

High-quality GaAs-based quantum cascade laser (QCL) structures for the terahertz (THz) emission have been grown by solid source molecular-beam epitaxy. Ex-situ high-resolution x-ray diffraction shows that layer thickness and its control is the most critical growth aspect and that the lasing potential of the structure can be determined by the thickness accuracy of the layers. For our samples, the thickness tolerance for working lasing structures emitting approximately 100 μm was determined to be minimally above 1% for a 15 μm active region which was composed of 54.6 nm cascade cells. Increasing interface roughness adversely affects the lasing threshold and power. Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia     

Spectroscopic characteristics of erbiumand ytterbium-activated laser media

Judd–Ofelt parameters (Ω₂ = 5.09∙10^–20, Ω₄ = 0.92∙10^–20, and Ω₆ = 0.63∙10^–20 cm²) and oscillator strengths of fundamental optical transitions involved in lasing at wavelength 1.54 μm have been calculated for borosilicophosphate glass co-activated with Er³⁺ and Tb³⁺ ions based on experimental luminescence and absorption spectra and refractive indices. The results were used to determine the emission (6∙10^–23 cm²) and absorption (5∙10^–21 cm²) cross sections for λ = 1.54 μm and the gain cross section as a function of inverse population levels.     

Diagnoctics development at JINR for ILC and FEL ultrashort electron bunches

Different methods for diagnostics of ultrashort electron bunches are developed at JINR-DESY collaboration within the framework of the FLASH and XFEL projects and JINR participation in the ILC project. The main peculiarity of these accelerator complexes is related to formation of ultrashort electron bunches with r.m.s. length 20–300 μm. Novel diagnostics is required to provide femtoscaie time resolution in the modem FEL like FLASH and future XFEL and ILC projects. Photon diagnostics developed at JINR-DESY collaboration for ultrashort bunches is based on calorimetric measurements and detection of undulator radiation. The MCP-based radiation detectors are effectively used at FLASH for pulse energy measurements. The infrared undulator constructed at JINR and installed at FLASH is used for longitudinal bunch shape measurements and for two-color lasing provided by the FIR and VUV undulators. Two-color lasing in pump-probe experiments permits one to investigate dynamics of atomic and molecular systems with time resolution of 100–500 fs. A special magnetic spectrometer is planning to be used at ILC for measurements of average electron energy in each bunch. The first test spectrometer measurements were performed within the JINR-DESY-SLAC collaboration. A special synchrotron radiation detector applied for measurement of bunch average electron energy was constructed at JINR.