Tunable electronic Raman laser at 16 μm

6s–9s electronic Raman scattering in caesium vapour is used to generate tunable 16m radiation. Output energies in excess of 8 J were obtained, with peak powers in the kilowatt range.     

Profiling primaquine metabolites in primary human hepatocytes using UHPLC‐QTOF‐MS with 13C stable isotope labeling

Therapeutic efficiency and hemolytic toxicity of primaquine (PQ), the only drug available for radical cure of relapsing vivax malaria are believed to be mediated by its metabolites. However, identification of these metabolites has remained a major challenge apparently due to low quantities and their reactive nature. Drug candidates labeled with stable isotopes afford convenient tools for tracking drug‐derived metabolites in complex matrices by liquid chromatography‐tandem mass spectrometry (LC‐MS‐MS) and filtering for masses with twin peaks attributable to the label. This study was undertaken to identify metabolites of PQ from an in vitro incubation of a 1:1 w/w mixture of ¹³C₆‐PQ/PQ with primary human hepatocytes. Acquity ultra‐performance LC (UHPLC) was integrated with QTOF‐MS to combine the efficiency of separation with high sensitivity, selectivity of detection and accurate mass determination. UHPLC retention time, twin mass peaks with difference of 6 (originating from ¹³C₆‐PQ/PQ), and MS‐MS fragmentation pattern were used for phenotyping. Besides carboxy‐PQ (cPQ), formed by oxidative deamination of PQ to an aldehyde and subsequent oxidation, several other metabolites were identified: including PQ alcohol, predictably generated by oxidative deamination of PQ to an aldehyde and subsequent reduction, its acetate and the alcohol's glucuronide conjugate. Trace amounts of quinone‐imine metabolites of PQ and cPQ were also detected which may be generated by hydroxylation of the PQ/cPQ quinoline ring at the 5‐position and subsequent oxidation. These findings shed additional light on the human hepatic metabolism of PQ, and the method can be applied for identification of reactive PQ metabolites generated in vivo in preclinical and clinical studies. Copyright © 2013 John Wiley & Sons, Ltd.     

Undamped relaxation oscillations due to self-gain-switching of laser dye mixtures

Undamped relaxation oscillations were observed from a short, simple dye laser using a laser dye mixture which was pumped at 337 nm using ns pulses. The dye solution contained Rh101 as first laser dye, together with DTDCI in double function as saturable absorber and second laser dye. Two trains of intense laser pulses were generated near 619 and 685 nm, with pulse durations of ca. 4 and 2 times the resonator transit time, respectively. This method of short-pulse generation is related to double mode-locking of dye lasers. Model calculations are used to describe the pulse generation by self-gain-switching, and to estimate radiative and nonradiative contributions towards saturation of the absorber dye.     

Femtosecond transient absorption with chirped pump and supercontinuum probe: Perturbative calculation of transient spectra with general lineshape functions, and simplifications

Femtosecond transient UV/vis absorption spectra of molecules in solution show vibronic structure initially while pump and probe pulses overlap, superimposed on bands which broaden and shift on several time scales. Third-order perturbation theory is used simulate and understand such spectra under experimental conditions, i.e., with chirped pump pulses and 40–80 fs pump/probe correlation time. The electronic system is coupled to a solvent bath whose fluctuations enter through a lineshape function g(t). This approach has two advantages. (i) In the general case when g(t) is modelled realistically it provides a distinction of coherent and sequential contributions to early transient spectra. The time-zero stimulated emission band can be extracted, giving access to the relaxation function for the emission frequency. (ii) For limiting forms of g(t) corresponding to the Bloch approximation and to inhomogeneous broadening the threefold time integrals underlying the theory reduce to a single integral. In such cases the lineshape formulation of transient absorption spectra can be used for data fitting.     

Spectrally narrow, long-term stable optical frequency reference based on a Eu3+:Y2SiO5 crystal at cryogenic temperature

Using an ultrastable continuous-wave laser at 580 nm we performed spectral hole burning of Eu(3+):Y(2)SiO(5) at a very high spectral resolution. The essential parameters determining the usefulness as a macroscopic frequency reference, linewidth, temperature sensitivity, and long-term stability, were characterized using a H-maser stabilized frequency comb. Spectral holes with a linewidth as low as 6 kHz were observed and the upper limit of the drift of the hole frequency was determined to be 5±3 mHz/s. We discuss the necessary requirements for achieving ultrahigh stability in laser frequency stabilization to these spectral holes.     

Fluorescence excitation spectra of jet-cooled amino-phthalimides

We report the fluorescence excitation spectra of the ππ¹ transition of jet-cooled 3-amino-, 3-amino-N-methyl-, and 4-amino-N-methyl-phthalimide. The spectra are dominated by a long progression of a vibrational mode v' ≈ 210 cm^-1 in combination with a few vibrational fundamentals of the excited state. The long electronic lifetimes and structural diversity of these compounds make them ideally suited for the study of intramolecular vibronic relaxation.     

Mapping CTTS dynamics of Na- in tetrahydrofurane with ultrafast multichannel pump-probe spectroscopy

Using multichannel femtosecond spectroscopy we have followed Na- charge transfer to solvent (CTTS) dynamics in THF solution. Absorption of the primary photoproducts in the visible, resolved here for the first time, consists of an asymmetric triplet centered at 595 nm, which we assign to a metastable incompletely solvated neutral atomic sodium species. Decay of this feature within approximately 1 ps to a broad and structureless solvated neutral is accompanied by broadening and loss of spectral detail. Kinetic analysis shows that both the spectral structure and the decay of this band are independent of the excitation photon frequency in the range 400-800 nm. With different pump-probe polarizations the anisotropy in transient transmission has been charted and its variation with excitation wavelength surveyed. The anisotropies are assigned to the reactant bleach, indicating that due to solvent-induced symmetry breaking, the CTTS absorption band of Na- is made up of discreet orthogonally polarized sub bands. None of the anisotropy in transient absorption could be associated with the photoproduct triplet band even at the earliest measurable time delays. Along with the documented differences in the spatial distribution of ejected electrons across the tested excitation wavelength range, these results lead us to conclude that photoejection is extremely rapid, and that loss of correlations between the departing electron and its neutral core is faster than our time resolution of approximately 60 fs.