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Mohammad Taghinejad, Hossein Taghinejad, Zihao Xu, Yawei Liu, Sean P Rodrigues, Kyu-Tae Lee, Tianquan Lian, Ali Adibi, Wenshan Cai
The optical Kerr nonlinearity of plasmonic metals provides enticing prospects for developing reconfigurable and ultracompact all-optical modulators. In nanostructured metals, the coherent coupling of light energy to plasmon resonances creates a nonequilibrium electron distribution at an elevated electron temperature that gives rise to significant Kerr optical nonlinearities. Although enhanced nonlinear responses of metals facilitate the realization of efficient modulation devices, the intrinsically slow relaxation dynamics of the photoexcited carriers, primarily governed by electron-phonon interactions, impedes ultrafast all-optical modulation...
January 15, 2018: Advanced Materials
Yongchang Dong, Sergii Chertopalov, Kathleen Maleski, Babak Anasori, Longyu Hu, Sriparna Bhattacharya, Apparao M Rao, Yury Gogotsi, Vadym N Mochalin, Ramakrishna Podila
MXenes comprise a new class of 2D transition metal carbides, nitrides, and carbonitrides that exhibit unique light-matter interactions. Recently, 2D Ti3 CNTx (Tx represents functional groups such as OH and F) was found to exhibit nonlinear saturable absorption (SA) or increased transmittance at higher light fluences, which is useful for mode locking in fiber-based femtosecond lasers. However, the fundamental origin and thickness dependence of SA behavior in MXenes remain to be understood. 2D Ti3 C2 Tx thin films of different thicknesses are fabricated using an interfacial film formation technique to systematically study their nonlinear optical properties...
January 15, 2018: Advanced Materials
Claudia Corredor-Ortega, Roberto Gonzalez-Salinas, María José Montero, Rocío González-Flores, Allan Collura-Merlier, Guadalupe Cervantes-Coste, Erick Mendoza-Schuster, Cecilio Velasco-Barona
No abstract text is available yet for this article.
January 10, 2018: Journal of AAPOS: the Official Publication of the American Association for Pediatric Ophthalmology and Strabismus
Surajit Kayal, Khokan Roy, Siva Umapathy
Ultrafast torsional dynamics plays an important role in the photoinduced excited state dynamics. Tetraphenylethylene (TPE), a model system for the molecular motor, executes interesting torsional dynamics upon photoexcitation. The photoreaction of TPE involves ultrafast internal conversion via a nearly planar intermediate state (relaxed state) that further leads to a twisted zwitterionic state. Here, we report the photoinduced structural dynamics of excited TPE during the course of photoisomerization in the condensed phase by ultrafast Raman loss (URLS) and femtosecond transient absorption (TA) spectroscopy...
January 14, 2018: Journal of Chemical Physics
Shirin Ghanbari, Ksenia A Fedorova, Andrey B Krysa, Edik U Rafailov, Arkady Major
An Alexandrite laser passively mode-locked using an InP/InGaP quantum-dot semiconductor saturable absorber mirror (QD-SESAM) was demonstrated. The laser was pumped at 532 nm and generated pulses as short as 380 fs at 775 nm with an average output power of 295 mW. To the best of our knowledge, this is the first report on a passively mode-locked femtosecond Alexandrite laser using a SESAM in general and a QD-SESAM in particular.
January 15, 2018: Optics Letters
Zhi Wang, Lan Jiang, Xiaowei Li, Andong Wang, Zhulin Yao, Kaihu Zhang, Yongfeng Lu
We proposed combining temporally shaped (double-pulse train) laser pulses with spatially shaped (Bessel beam) laser pulses. By using a temporally shaped femtosecond laser Bessel-beam-assisted chemical etching method, the energy deposition efficiency was improved by adjusting the pulse delay to yield a stronger material modification and, thus, a higher etching depth. The etching depth was enhanced by a factor of 13 using the temporally shaped Bessel beam. The mechanism of etching depth enhancement was elucidated by localized transient-free electrons dynamics-induced structural and morphological changes...
January 1, 2018: Optics Letters
O Kosareva, M Esaulkov, N Panov, V Andreeva, D Shipilo, P Solyankin, A Demircan, I Babushkin, V Makarov, U Morgner, A Shkurinov, A Savel'ev
We individually control polarizations of 800 and 400 nm beams, which form a two-color femtosecond plasma filament in air irradiating a linear-to-elliptical THz signal. We detected a threshold-like appearance of THz ellipticity at the angle of ∼85° between the fundamental and second-harmonic field polarization directions. The simulations confirm the abrupt change of THz polarization and reveal that the weak ellipticity of the second harmonic is sufficient to generate essentially elliptical THz radiation.
January 1, 2018: Optics Letters
Shuo Yang, Daniel Homa, Gary Pickrell, Anbo Wang
This Letter introduces a fiber Bragg grating (FBG) in a micro-single-crystal sapphire fiber (micro-SFBG) for sensing applications in high-temperature and harsh environments. The FBG was fabricated by a point-by-point method via an IR-femtosecond laser in a large-diameter sapphire fiber that was then wet-hot acid etched to achieve microfiber size, which culminated in fabricating and characterizing a 9.6 μm diameter micro-SFBG. The refractive index measurement ranging from 1 to 1.75 and temperature measurement from room temperature to 1400°C are also reported...
January 1, 2018: Optics Letters
Viktória Csajbók, Zsolt Bedőházi, Benedek J Nagy, Péter Dombi
Laser-induced damage threshold is a fundamental figure of merit of femtosecond optical components used in large-scale laser systems. We tested a series of ultrafast mirrors featuring high band-gap dielectric materials as well as improved design and coating techniques. In a broad range of the damage test pulse train involving between 10 and 100,000 pulses (40 fs, 800 nm), pure dielectric high reflectors exhibit around 1.5  J/cm2 and hybrid Ag-multilayer mirrors can exhibit well above 1.2  J/cm2 damage threshold...
January 10, 2018: Applied Optics
Xiaoliang Wang, Daru Chen, Haitao Li, Lijuan She, Qiong Wu
The random fiber laser (RFL), which is a milestone in laser physics and nonlinear optics, has attracted considerable attention recently. Most previously reported RFLs are based on distributed feedback of Rayleigh scattering amplified through the stimulated Raman-Brillouin scattering effect in single-mode fibers, which require long-distance (tens of kilometers) single-mode fibers and high threshold, up to watt level, due to the extremely small Rayleigh scattering coefficient of the fiber. We proposed and demonstrated a half-open-cavity RFL based on a segment of an artificially controlled backscattering single-mode fiber with a length of 210 m, 310 m, or 390 m...
January 10, 2018: Applied Optics
Chao-Bo Yang, Ping He, David Escofet-Martin, Jiang-Bo Peng, Rong-Wei Fan, Xin Yu, Derek Dunn-Rankin
In this paper, three ultrashort-pulse coherent anti-Stokes Raman scattering (CARS) thermometry approaches are summarized with a theoretical time-domain model. The difference between the approaches can be attributed to variations in the input field characteristics of the time-domain model. That is, all three approaches of ultrashort-pulse (CARS) thermometry can be simulated with the unified model by only changing the input fields features. As a specific example, the hybrid femtosecond/picosecond CARS is assessed for its use in combustion flow diagnostics; thus, the examination of the input field has an impact on thermometry focuses on vibrational hybrid femtosecond/picosecond CARS...
January 10, 2018: Applied Optics
Smriti Sahu, Rituraj Sharma, K V Adarsh, Anbarasu Manivannan
Rapid and reversible switching between amorphous and crystalline phases of phase-change material promises to revolutionize the field of information processing with a wide range of applications including electronic, optoelectronics, and photonic memory devices. However, achieving faster crystallization is a key challenge. Here, we demonstrate femtosecond-driven transient inspection of ultrafast crystallization of as-deposited amorphous Ge1Sb2Te4 and Ge1Sb4Te7 thin films induced by a series of 120 fs laser pulses...
January 10, 2018: Applied Optics
L Dworak, S Roth, M P Scheffer, A S Frangakis, J Wachtveitl
CdTe core and CdTe/CdSe core/shell quantum dots (QD) are investigated with steady state and time-resolved spectroscopic methods. The coating of the CdTe core with a 0.7 nm thick CdSe shell shifts the lowest exciton absorption band to the red by more than 70 nm making the CdTe/CdSe QD an interesting candidate for application in solar energy conversion. Femtosecond transient absorption measurements are applied to study the photoinduced electron transfer (ET) to the molecular acceptor methylene blue (MB). ET times after single excitation of the QD are determined for different MB : QD ratios...
January 12, 2018: Nanoscale
A Cesaretti, B Carlotti, F Elisei, C G Fortuna, A Spalletti
The excited state dynamics of two quadrupolar polyaromatic N-methylpyridinium cations have been fully investigated in order to acquire detailed information on their photo-induced behavior. The two molecules are symmetric push-pull compounds having a D-π-A+-π-D motif, with the same electron-acceptor central unit (A = N-methylpyridinium) and two distinctive electron-donor polyaromatic side groups (D), namely naphthyl and pyrenyl substituents. Both molecules undergo charge transfer during the absorption, as revealed by a significant solvatochromism exhibited with solvent polarity, but the fate of their excited state was found to be markedly different...
January 12, 2018: Physical Chemistry Chemical Physics: PCCP
Kenji Goya, Yusuke Fuchiwaki
In this study, we demonstrate the precise control of fluid flow using femtosecond (FS) laser-induced microstructures. A microgroove structure inscribed on a poly(methyl methacrylate) (PMMA) substrate functions as a superhydrophilic membrane similar to paper. We first estimated the flow rate for pure water on microgrooves fabricated at various laser fluences in the range from 9.2 to 100.8 J/cm2. The results showed that the flow rate could be tuned in the range from 0.30 to 12.07 μL/s by varying the laser irradiation parameters...
2018: Analytical Sciences: the International Journal of the Japan Society for Analytical Chemistry
Hendrik Böhnke, Julia Bahrenburg, Xiaonan Ma, Katharina Röttger, Christian Näther, Michał F Rode, Andrzej L Sobolewski, Friedrich Temps
Molecular switches based on proton transfer that are photochromic and can be interconverted by light at different wavelengths back and forth between two thermodynamically stable tautomeric states in solution at room temperature are rare to date. We report on a study of the ultrafast conversion of the bistable proton transfer switch N-(3-pyridinyl)-2-pyridinecarboxamide (NPPCA) to a corresponding iminol after photoexcitation at λpump ≈ 265 nm by means of femtosecond time-resolved broad-band and single-colour transient electronic absorption spectroscopy (TEAS), transient fluorescence spectroscopy (TFLS), and transient vibrational absorption spectroscopy (TVAS) in acetonitrile solution...
January 10, 2018: Physical Chemistry Chemical Physics: PCCP
Manan Machida, Yasutaka Nakajima, Maria Leilani Torres-Mapa, Dag Heinemann, Alexander Heisterkamp, Mitsuhiro Terakawa
The integration of metal microstructures and soft materials is promising for the realization of novel optical and biomedical devices owing to the flexibility and biocompatibility of the latter. Nevertheless, the fabrication of three-dimensional metal structures within a soft material is still challenging. In this study, we demonstrate the fabrication of a silver diffraction grating inside a biocompatible poly(ethylene glycol) diacrylate (PEGDA) hydrogel by using a 522-nm femtosecond laser via multi-photon photoreduction of silver ions...
January 9, 2018: Scientific Reports
Dennis K P Ng, Xiao-Fei Chen, Mohamed El-Khouly, Kei Ohkubo, Shunichi Fukuzumi
A series of light-harvesting conjugates based on a zinc(II) phthalocyanine core with either two or four boron dipyrromethene (BODIPY) or porphyrin units have been synthesized and characterized. The conjugation of BODIPY/porphyrin units can extend the absorptions of the phthalocyanine core to cover most of the visible region. Upon addition of an imidazole-substituted C60 (C60Im), it can axially bind to the zinc(II) center of the phthalocyanine core via metal-ligand interactions. The resulting complexes form photosynthetic antenna-reaction center mimics in which the BODIPY/porphyrin units serve as the antennas to capture the light and transfer the energy to the phthalocyanine core via efficient excitation energy transfer...
January 6, 2018: Chemistry: a European Journal
Masahiko Iyoda, Hideyuki Shimizu, Kyu Hyung Park, Hiroyuki Otani, Shinobu Aoyagi, Tohru Nishinaga, Yoshio Aso, Dongho Kim
A Saturn-like 1:1 complex composed of macrocyclic oligothiophene (E-8T7A) and [60]fullerene (C60) has been synthesized to investigate the interaction between macrocyclic oligothiophenes and C60 in solution and the solid state. Since the Saturn-like 1:1 complex E-8T7A·C60 is mainly stabilized by van der Waals interactions between C60 and sulfur atoms of macrocyclic E-8T7A, C60 is rather weakly incorporated in the macroring in solution. In the solid state, however, the Saturn-like 1:1 complex is preferentially formed to produce single crystals or nano-structured polymorphs...
January 5, 2018: Chemistry: a European Journal
Leonardo Mastropasqua, Mario Nubile, Niccolò Salgari, Rodolfo Mastropasqua
PURPOSE: To investigate the in vivo effect of a novel femtosecond laser-assisted procedure termed stromal lenticule addition keratoplasty for advanced keratoconus. METHODS: Ten patients with stage III and IV stable keratoconus were included. Negative meniscus-shaped stromal lenticules were produced from corneoscleral eye bank buttons with a refractive lenticule extraction procedure with a 500-kHz VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany). Recipient corneas underwent a modified femtosecond laser flap-cut procedure to produce an intrastromal pocket and lenticules were implanted...
January 1, 2018: Journal of Refractive Surgery
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