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R E Goetz, T A Isaev, B Nikoobakht, R Berger, C P Koch
Photoelectron circular dichroism refers to the forward/backward asymmetry in the photoelectron angular distribution with respect to the propagation axis of circularly polarized light. It has recently been demonstrated in femtosecond multi-photon photoionization experiments with randomly oriented camphor and fenchone molecules [C. Lux et al., Angew. Chem., Int. Ed. 51, 4755 (2012) and C. S. Lehmann et al., J. Chem. Phys. 139, 234307 (2013)]. A theoretical framework describing this process as (2+1) resonantly enhanced multi-photon ionization is constructed, which consists of two-photon photoselection from randomly oriented molecules and successive one-photon ionization of the photoselected molecules...
January 14, 2017: Journal of Chemical Physics
Xiaojuan Dai, Di Song, Kunhui Liu, Hongmei Su
5-Iodouracil (5-IU) can be integrated into DNA and acts as a UV sensitive chromophore suitable for probing DNA structure and DNA-protein interactions based on the photochemical reactions of 5-IU. Here, we perform joint studies of time-resolved Fourier transform infrared (TR-FTIR) spectroscopy and ab initio calculations to examine the state-specific photochemical reaction mechanisms of the 5-IU. The fact that uracil (U) is observed in TR-FTIR spectra after 266 nm irradiation of 5-IU in acetonitrile and ascribed to the product of hydrogen abstraction by the uracil-5-yl radical (U·) provides experimental evidence for the C-I bond homolysis of 5-IU...
January 14, 2017: Journal of Chemical Physics
Kathrin J Mohler, Bernhard J Bohn, Ming Yan, Gwénaëlle Mélen, Theodor W Hänsch, Nathalie Picqué
We extend the technique of multiplex coherent Raman spectroscopy with two femtosecond mode-locked lasers to oscillators of a pulse repetition frequency of 1 GHz. We demonstrate a spectra of liquids, which span 1100  cm<sup>-1</sup> of Raman shifts. At a resolution of 6  cm<sup>-1</sup>, their measurement time may be as short as 5 μs for a refresh rate of 2 kHz. The waiting period between acquisitions is improved 10-fold compared to previous experiments with two lasers of 100-MHz repetition frequencies...
January 15, 2017: Optics Letters
Xavier Audier, Naveen Balla, Hervé Rigneault
We demonstrate femtosecond pump-probe transient absorption spectroscopy using a programmable dispersive filter as an ultra-fast delay line. Combined with fast synchronous detection, this delay line allows for recording of 6 ps decay traces at 34 kHz. With such acquisition speed, we perform single point pump-probe spectroscopy on bulk samples in 80 μs and hyperspectral pump-probe imaging over a field of view of 100 μm in less than a second. The usability of the method is illustrated in a showcase experiment to image and discriminate between two pigments in a mixture...
January 15, 2017: Optics Letters
A I Chernov, M A Kozhaev, I V Savochkin, D V Dodonov, P M Vetoshko, A K Zvezdin, V I Belotelov
In most of the previous studies of the spin wave optical generation in magnetic dielectrics, the backward volume spin waves were excited. Here we modified the parameters of the circularly polarized optical pump beams emitted by femtosecond laser to reveal surface spin waves in bismuth iron garnet thin film. Beams that are larger than 10 μm in diameter generate both surface and volume spin waves with only one spectral peak near the ferromagnetic resonance. On the contrary, narrower beams excite predominantly surface spin waves of higher frequency, providing an additional peak in the spin wave spectrum...
January 15, 2017: Optics Letters
N Lilienfein, C Hofer, S Holzberger, C Matzer, P Zimmermann, M Trubetskov, V Pervak, I Pupeza
We address the challenge of increasing the bandwidth of high-finesse femtosecond enhancement cavities and demonstrate a broad spectrum spanning 1800  cm<sup>-1</sup> (195 nm) at -10  dB around a central wavelength of 1050 nm in an EC with an average finesse exceeding 300. This will benefit a host of spectroscopic applications, including transient absorption spectroscopy, direct frequency comb spectroscopy, and Raman spectroscopy. The pulse circulating in the EC is composed of only 5.4 optical cycles, at a kilowatt-level average power...
January 15, 2017: Optics Letters
Jason C Ng, Peter R Herman, Li Qian
Second harmonic generation (SHG) is demonstrated in femtosecond laser written waveguides in fused silica through a combination of thermal poling and laser-based quasi-phase-matching (QPM) techniques. Quasi-phase-matching was controlled by the periodic erasure of induced nonlinearity through femtosecond laser erasure. A maximum SHG conversion efficiency of 6.6±0.5×10<sup>-5</sup>%/W is reported for the fundamental wavelength of 1552.8 nm with a phase-matching bandwidth of 4.4 nm for a 10.0 mm long waveguide...
January 15, 2017: Optics Letters
Peter Spenst, Ryan M Young, Brian T Phelan, Michel Keller, Jakub Dostál, Tobias Brixner, Michael R Wasielewski, Frank Würthner
A series of semi-rigid perylene bisimide (PBI) macrocycles with varied ring size containing two to nine PBI chromophores were synthesized in a one-pot reaction and their photophysical properties were characterized by fluorescence, steady-state and transient absorption spectroscopy as well as femtosecond stimulated Raman spectroscopy. These macrocycles show solvent-dependent conformational equilibria and excited-state properties. In dichloromethane the macrocycles prevail in wide-stretched conformations and exhibit upon photoexcitation symmetry-breaking charge separation followed by charge recombination to triplet states, which photosensitize singlet oxygen formation...
January 12, 2017: Journal of the American Chemical Society
Furong Wang, Uli Schmidhammer, Aurélien de La Lande, Mehran Mostafavi
Oxidation by the ultra-short lived radical cation of water, H2O˙(+), can potentially take place at the interface of water and numerous heterogeneous systems involved in radiation therapy, energy and environmental industries. The oxidation processes induced by H2O˙(+) can be mimicked in highly concentrated solutions where the nearest neighbors of H2O˙(+) may be molecules other than water. The reactivity of H2O˙(+) and D2O˙(+) is probed in hydrogenated and deuterated sulfuric acid solutions of various concentrations...
January 12, 2017: Physical Chemistry Chemical Physics: PCCP
Maria Gallego, Joaquin Calbo, Rafael M Krick-Calderon, Paula Pla, Ya-Chu Hsieh, Emilio Manuel Pérez, Yao-Ting Wu, Enrique Orti, Dirk M Guldi, Nazario Martin
The association behavior of an electron-donating, bowl-shaped, truxene-based tetrathiafulvalene (truxTTF) with two corannulene-based fullerene fragments -C32H12 and C38H14- is investigated in several solvents. Formation of 1:1 complexes is followed by absorption titrations and complemented by density functional theory (DFT) calculations. The binding constants are in the range of log Ka 2.9-3.5. DFT calculations reveal that the conformation in which the 1,3-dithiole ring of truxTTF is placed inside the concave cavity of the corannulene derivative is the most stable arrangement...
January 11, 2017: Chemistry: a European Journal
Changcheng Jiang, Philip J Young, Samantha Brown-Xu, Judith C Gallucci, Malcolm H Chisholm
Four photophysically interesting dimolybdenum paddlewheel compounds are synthesized and characterized: I and II contain amide ligand (N,3-diphenyl-2-propynamide), and III and IV contain thioamide ligand (N,3-diphenyl-2-propynethioamide). I and III are trans-Mo2L2(O2C-T(i)PB)2-type compounds, and II and IV are Mo2L4-type compounds, where O2C-T(i)PB is 2,4,6-triisopropylbenzoate. I-IV display strong light absorption due to metal to ligand charge transfer (MLCT) transitions from molybdenum to the amide/thioamide ligands...
January 11, 2017: Inorganic Chemistry
C Elias Eckert, Jagdeep Kaur, Clemens Glaubitz, Josef Wachtveitl
We report femtosecond time-resolved absorption change measurements of the photoinduced deactivation dynamics of a microbial rhodopsin in the ultraviolet-visible and mid-infrared range. The blue light quenching process is recorded in green proteorhodopsin's (GPR) primary proton donor mutant E108Q from the deprotonated 13-cis photointermediate. The return of GPR to the dark state occurs in two steps, starting with the photoinduced 13-cis to all-trans reisomerization of the retinal. The subsequent Schiff base reprotonation via the primary proton acceptor (D97) occurs on a nanosecond time scale...
January 11, 2017: Journal of Physical Chemistry Letters
S Mondal, Q Wei, W J Ding, H A Hafez, M A Fareed, A Laramée, X Ropagnol, G Zhang, S Sun, Z M Sheng, J Zhang, T Ozaki
We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20-200 THz)...
January 10, 2017: Scientific Reports
Christophe Panthier, Florent Costantini, Jean Claude Rigal-Sastourné, Antoine Brézin, Chadi Mehanna, Mikael Guedj, Dominique Monnet
PURPOSE: To compare the shape of the capsulotomy, its change, and its impact on visual quality over 1 year using the femtosecond laser system from the manual technique. METHODS: In this two-center cross-sectional study from May 2012 to June 2013, each patient had femtosecond laser-assisted cataract surgery in one eye (FLACS group) and conventional phacoemulsification cataract surgery in the other eye (CPCS group). An evaluation of the capsulotomy was performed using retroillumination slit-lamp photographs at 7 days, 6 months, and 1 year after surgery...
January 1, 2017: Journal of Refractive Surgery
Gustavo K Marino, Marcony R Santhiago, Steven E Wilson
PURPOSE: To characterize the location and regularity of the opaque bubble layer (OBL) in the corneal stroma after femtosecond laser-assisted LASIK (FS-LASIK) flap generation. METHODS: In this prospective study, 30 eyes of 15 patients who had FS-LASIK surgery for myopia, astigmatism, and/or hyperopia were included. Screen captures were obtained at the end of the flap creation and the eyes with hard type OBL were immediately imaged with anterior segment optical coherence tomography...
January 1, 2017: Journal of Refractive Surgery
Rohit Shetty, Rushad Shroff, Kalyani Deshpande, Roshan Gowda, Sumeet Lahane, Chaitra Jayadev
PURPOSE: To analyze refractive outcomes of wavefront-optimized (WFO) ablation and topography-guided custom ablation (TCAT) profiles using the Allegretto Wave excimer laser platform (Alcon Laboratories, Inc., Fort Worth, TX) in the treatment of myopia. METHODS: Sixty eyes of 30 patients who underwent LASIK were included in this prospective interventional study. WFO ablation was performed in one eye (WFO group) and TCAT in the fellow eye (TCAT group). The WaveLight FS200 femtosecond laser (Alcon Laboratories, Inc...
January 1, 2017: Journal of Refractive Surgery
Agnieszka A Gil, Sergey P Laptenok, Jarrod B French, James N Iuliano, Andras Lukacs, Christopher R Hall, Igor V Sazanovich, Gregory M Greetham, Adelbert Bacher, Boris Illarionov, Markus Fischer, Peter J Tonge, Stephen R Meech
The rational engineering of photosenor proteins underpins the field of optogenetics, in which light is used for spatio-temporal control of cell signalling. Optogenetic elements function by converting electronic excitation of an embedded chromophore into structural changes on the μs-sec timescale, which then modulate the activity of output domains responsible for biological signalling. Using time resolved vibrational spectroscopy coupled with isotope labelling we have mapped the structural evolution of the LOV2 domain of the flavin binding phototropin Avena sativa (AsLOV2) over 10 decades of time, reporting structural dynamics between 100 femtoseconds and one millisecond after optical ex-citation...
January 9, 2017: Journal of Physical Chemistry. B
Geun Young Jin, Yung Sam Kim
2D IR echo spectroscopy, with high sensitivity and femtosecond time resolution, enables us to understand structure and ultrafast dynamics of molecular systems. Application of this experimental technique on weakly absorbing samples, however, had been limited by the precise and unambiguous phase determination of the echo signals. In this study, we propose a new experimental scheme that significantly increases the phase stability of the involved IR pulses. We have demonstrated that the incorporation of phase-resolved heterodyne-detected transient grating (PR-HDTG) spectroscopy greatly enhances the capabilities of 2D IR spectroscopy...
January 9, 2017: Journal of Physical Chemistry. A
Sizuo Luo, Wenhui Hu, Jiaqi Yu, Ruihan Zhu, Lanhai He, Xiaokai Li, Pan Ma, Chuncheng Wang, Fuchun Liu, Wim G Roeterdink, Steven Stolte, Dajun Ding
Rotational dynamics of quantum state selected and un-selected CH3I molecules in intense femtosecond laser fields has been studied. The orientation and alignment evolutions are derived from a pump-probe measurement and in good agreement with the numerical results from the time dependent Schrödinger equation (TDSE) calculation. The different rotational transitions through nonresonant Raman process have been assigned from the Fourier analysis of the orientation and alignment revivals. These revivals are derived from a pump-probe measurement and in good agreement with the numerical results from the time dependent Schr¨odinger equation (TDSE) calculation...
January 9, 2017: Journal of Physical Chemistry. A
Heewon Yang, Byungheon Han, Junho Shin, Dong Hou, Hayun Chung, In Hyung Baek, Young Uk Jeong, Jungwon Kim
Ultrafast electron-based coherent radiation sources, such as free-electron lasers (FELs), ultrafast electron diffraction (UED) and Thomson-scattering sources, are becoming more important sources in today's ultrafast science. Photocathode laser is an indispensable common subsystem in these sources that generates ultrafast electron pulses. To fully exploit the potentials of these sources, especially for pump-probe experiments, it is important to achieve high-precision synchronization between the photocathode laser and radio-frequency (RF) sources that manipulate electron pulses...
January 9, 2017: Scientific Reports
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