Rosa Weigand

Solvent dependence of the inhibition of intramolecular charge-transfer in N-substituted 1,8-naphthalimide derivatives as dye lasers

Abstract Fluorescence, lasing efficiency and photostability of the 4-methoxy and 4-acetamide-N-substituted 1,8-naphthalimide derivatives in alcohols have been investigated. An intramolecular charge-transfer (CT) inhibits the fluorescence and laser emission in the derivatives with an amino terminal group in the side chain. The addition of protons (acetic acid) quenches the intramolecular CT, and a high lasing efficiency in the green-blue zone of the spectrum is obtained with a N 2 pulsed laser ( FWHM ∼- 5.5 ns). The results have been interpreted on the basis of the acidity, polarity and viscosity of the solvents. Photostability tests with a pulsed N 2 laser and a Xe lamp (150 W) show good behavior for all molecules, except in ethylene glycol.

Characterization of broadband few-cycle laser pulses with the d-scan technique

We present an analysis and demonstration of few-cycle ultrashort laser pulse characterization using second-harmonic dispersion scans and numerical phase retrieval algorithms. The sensitivity and robustness of this technique with respect to noise, measurement bandwidth and complexity of the measured pulses is discussed through numerical examples and experimental results. Using this technique, we successfully demonstrate the characterization of few-cycle pulses with complex and structured spectra generated from a broadband ultrafast laser oscillator and a high-energy hollow fiber compressor.

Cascaded nondegenerate four-wave-mixing technique for high-power single-cycle pulse synthesis in the visible and ultraviolet ranges

We present a new technique to synthesize high-power single-cycle pulses in the visible and ultraviolet ranges by coherent superposition of a multiband octave-spanning spectrum obtained by highly-nondegenerate cascaded four-wave mixing of femtosecond pulses in bulk isotropic nonresonant media. The generation of coherent spectra spanning over two octaves in bandwidth is experimentally demonstrated using a thin fused silica slide. Full characterization of the intervening multicolored fields using frequency-resolved optical gating, where multiple cascaded orders have been measured simultaneously for the first time, supports the possibility of direct synthesis of near-single-cycle 2.2 fs visible-UV pulses without recurring to complex amplitude or phase control, which should enable many applications in science and technology.

N-substituted 1,8-naphthalimide derivatives as high efficiency laser dyes

Abstract A study of the photophysical properties of novel N -substituted 1,8-naphthalimide derivatives was performed in our laboratory. Some derivatives with a methoxy group in position 4 of the naphthalic ring have a high fluorescence quantum yield. The lasing efficiency of these compounds in acetonitrile solution, using an N 2 laser as the pumping system, is reported.

Generation of femtosecond paraxial beams with arbitrary spatial distribution

We present an approach to generate paraxial laser beams with arbitrary spatial distribution in the femtosecond time regime. The proposed technique is based upon a pair of volume phase holographic gratings working in parallel arrangement. It exploits the spatial coherence properties of the incoming laser beam in a compact and robust setup that mitigates angular and spatial chirp. The gratings were recorded in a photopolymerizable glass with a high optical damage threshold and a large optical throughput. Setup performance is studied and experimentally demonstrated by generating Laguerre-Gaussian femtosecond pulses.

Generation of high-energy vacuum UV femtosecond pulses by multiple-beam cascaded four-wave mixing in a transparent solid

The generation of ultrashort vacuum UV (VUV) pulses by nondegenerate cascaded four-wave mixing of femtosecond pulses in a thin slide of a large band-gap transparent solid is numerically demonstrated. Using a novel noncollinear multiple-beam configuration, cascaded four-wave mixing of amplified 30 fs Ti:sapphire laser pulses at 800 nm, and their second harmonic in lithium fluoride results in the generation of VUV radiation down to 134 nm with energies in the μJ range and durations comparable to those of the pump pulses. The proposed geometry is advantageous in large dispersion scenarios, namely for generating radiation close to absorption bands. Hence these results set this technique as a promising way to efficiently generate ultrashort VUV radiation in solids for several applications in science and technology.

Aminopyrido[2,3-c]-1,2,6-thiadiazine 2,2-dioxides as laser dyes

Abstract Measurements of the spectral and temporal characteristics and energy efficiency of the neutral and acidic species of 4-amino-1,7-dimethylpyrido[2,3-c]-1,2,6-thiadiazine 2,2-dioxide (compound N1 ) and 4-amino-7,8-dimethylpyrido[2,3-c]-1,2,6-thiadiazine 2,2-dioxide (compound N2 ) in dimethylsulphoxide and acetonitrile have been performed. Continuous lasing of N1 from 0 to 1 M total proton concentration reveals simultaneous lasing of the neutral (N) and acidic (A) species of N1 .

A simple experiment on slow light in ruby

We describe a simple, reliable, and inexpensive experiment for teaching the basic features of slow light propagation using a solid saturable absorber at room temperature. The experiment is accessible to undergraduate and graduate students. We provide an explanation and analysis based on the coherent population oscillations model, which describes the propagation of light across a ruby crystal.

Inline self-diffraction dispersion-scan of over octave-spanning pulses in the single-cycle regime

We present an implementation of dispersion-scan based on self-diffraction (SD d-scan) and apply it to the measurement of over octave-spanning sub-4-fs pulses. The results are compared with second-harmonic generation (SHG) d-scan. The efficiency of the SD process is derived theoretically and compared with the spectral response retrieved by the d-scan algorithm. The new SD d-scan has a robust inline setup and enables measuring pulses with over-octave spectra, single-cycle durations, and wavelength ranges beyond those of SHG crystals, such as the ultraviolet and the deep-ultraviolet.

Orientational self-bleaching for pulsed dye lasers with polarized pumping

The dynamics of pulsed pumped dye lasers with transversal excitation geometry with linearly polarized pumping when the absorption dipole is perpendicular to the emission dipole have been theoretically and experimentally investigated. The theoretical model is based on balance equations and takes orientational relaxation processes into account. Experimental results have been obtained on Rhodamine 6G in Ethyleneglycol under pulsed transversal polarized pumping from a N2 laser. The theoretical and experimental results obtained allow us to call the new effect: orientational self-bleaching.