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Sample records for local two-photon couplings

  1. Local Two-Photon Couplings and the J=0 Fixed Pole in Real and Virtual Compton Scattering

    SciTech Connect

    Brodsky, Stanley J.; Llanes-Estrada, Felipe J.; Szczepaniak, Adam P.

    2008-12-05

    The local coupling of two photons to the fundamental quark currents of a hadron gives an energy-independent contribution to the Compton amplitude proportional to the charge squared of the struck quark, a contribution which has no analog in hadron scattering reactions. We show that this local contribution has a real phase and is universal, giving the same contribution for real or virtual Compton scattering for any photon virtuality and skewness at fixed momentum transfer squared t. The t-dependence of this J = 0 fixed Regge pole is parameterized by a yet unmeasured even charge-conjugation form factor of the target nucleon. The t = 0 limit gives an important constraint on the dependence of the nucleon mass on the quark mass through the Weisberger relation. We discuss how this 1=x form factor can be extracted from high energy deeply virtual Compton scattering and examine predictions given by models of the H generalized parton distribution.

  2. Control and enhancement of interferometric coupling between two photonic qubits

    NASA Astrophysics Data System (ADS)

    Stárek, R.; Mičuda, M.; Straka, I.; Miková, M.; Ježek, M.; Filip, R.; Fiurášek, J.

    2016-04-01

    We theoretically investigate and experimentally demonstrate a procedure for conditional control and enhancement of an interferometric coupling between two qubits encoded into states of bosonic particles. Our procedure combines local coupling of one of the particles to an auxiliary mode and single-qubit quantum filtering. We experimentally verify the proposed procedure using a linear optical setup where qubits are encoded into quantum states of single photons and coupled at a beam splitter with a fixed transmittance. With our protocol, we implement a range of different effective transmittances, demonstrate both enhancement and reduction of the coupling strength, and observe dependence of two-photon bunching on the effective transmittance. To make our analysis complete, we also theoretically investigate a more general scheme where each particle is coupled to a separate auxiliary mode and show that this latter scheme enables us to achieve higher implementation probability. We show that our approach can be extended also to other kinds of qubit-qubit interactions.

  3. Two photon couplings of the lightest isoscalars from BELLE data

    DOE PAGESBeta

    Dai, Ling -Yun; Pennington, Michael R.

    2014-07-07

    Amplitude Analysis of two photon production of ππ and K¯K, using S-matrix constraints and fitting all available data, including the latest precision results from Belle, yields a single partial wave solution up to 1.4 GeV. The two photon couplings of the σ/f0(500), f0(980) and f2(1270) are determined from the residues of the resonance poles.

  4. Two photon couplings of the lightest isoscalars from BELLE data

    SciTech Connect

    Dai, Ling -Yun; Pennington, Michael R.

    2014-07-07

    Amplitude Analysis of two photon production of ππ and K¯K, using S-matrix constraints and fitting all available data, including the latest precision results from Belle, yields a single partial wave solution up to 1.4 GeV. The two photon couplings of the σ/f0(500), f0(980) and f2(1270) are determined from the residues of the resonance poles.

  5. Correlated two-photon transport in a one-dimensional waveguide side-coupled to a nonlinear cavity

    SciTech Connect

    Liao Jieqiao; Law, C. K.

    2010-11-15

    We investigate the transport properties of two photons inside a one-dimensional waveguide side-coupled to a single-mode nonlinear cavity. The cavity is filled with a nonlinear Kerr medium. Based on the Laplace transform method, we present an analytic solution for the quantum states of the two transmitted and reflected photons, which are initially prepared in a Lorentzian wave packet. The solution reveals how quantum correlation between the two photons emerges after the scattering by the nonlinear cavity. In particular, we show that the output wave function of the two photons in position space can be localized in relative coordinates, which is a feature that might be interpreted as a two-photon bound state in this waveguide-cavity system.

  6. Two-photon Anderson localization in a disordered quadratic waveguide array

    NASA Astrophysics Data System (ADS)

    Bai, Y. F.; Xu, P.; Lu, L. L.; Zhong, M. L.; Zhu, S. N.

    2016-05-01

    We theoretically investigate two-photon Anderson localization in a χ (2) waveguide array with off-diagonal disorder. The nonlinear parametric down-conversion process would enhance both the single-photon and the two-photon Anderson localization. In the strong disorder regime, the two-photon position correlation exhibits a bunching distribution around the pumped waveguides, which is independent of pumping conditions and geometrical structures of waveguide arrays. Quadratic nonlinearity can be supplied as a new ingredient for Anderson localization. Also, our results pave the way for engineering quantum states through nonlinear quantum walks.

  7. Two-photon microscopy as a tool to study blood flow and neurovascular coupling in the rodent brain

    PubMed Central

    Shih, Andy Y; Driscoll, Jonathan D; Drew, Patrick J; Nishimura, Nozomi; Schaffer, Chris B; Kleinfeld, David

    2012-01-01

    The cerebral vascular system services the constant demand for energy during neuronal activity in the brain. Attempts to delineate the logic of neurovascular coupling have been greatly aided by the advent of two-photon laser scanning microscopy to image both blood flow and the activity of individual cells below the surface of the brain. Here we provide a technical guide to imaging cerebral blood flow in rodents. We describe in detail the surgical procedures required to generate cranial windows for optical access to the cortex of both rats and mice and the use of two-photon microscopy to accurately measure blood flow in individual cortical vessels concurrent with local cellular activity. We further provide examples on how these techniques can be applied to the study of local blood flow regulation and vascular pathologies such as small-scale stroke. PMID:22293983

  8. Enhanced-locality fiber-optic two-photon-fluorescence live-brain interrogation

    SciTech Connect

    Fedotov, I. V.; Doronina-Amitonova, L. V.; Sidorov-Biryukov, D. A.; Fedotov, A. B.; Anokhin, K. V.; Kilin, S. Ya.; Sakoda, K.; Zheltikov, A. M.

    2014-02-24

    Two-photon excitation is shown to substantially enhance the locality of fiber-based optical interrogation of strongly scattering biotissues. In our experiments, a high-numerical-aperture, large-core-are fiber probe is used to deliver the 200-fs output of a 100-MHz mode-locked ytterbium fiber laser to samples of live mouse brain, induce two-photon fluorescence of nitrogen–vacancy centers in diamond markers in brain sample. Fiber probes with a high numerical aperture and a large core area are shown to enable locality enhancement in fiber-laser–fiber-probe two-photon brain excitation and interrogation without sacrificing the efficiency of fluorescence response collection.

  9. The Correlated Two-Photon Transport in a One-Dimensional Waveguide Coupling to a Hybrid Atom-Optomechanical System

    NASA Astrophysics Data System (ADS)

    Liu, Jingyi; Zhang, Wenzhao; Li, Xun; Yan, Weibin; Zhou, Ling

    2016-06-01

    We investigate the two-photon transport properties inside one-dimensional waveguide side coupled to an atom-optomechanical system, aiming to control the two-photon transport by using the nonlinearity. By generalizing the scheme of Phys. Rev. A 90, 033832, we show that Kerr nonlinearity induced by the four-level atoms is remarkable and can make the photons antibunching, while the nonlinear interaction of optomechanical coupling participates in both the single photon and the two photon processes so that it can make the two photons exhibiting bunching and antibunching.

  10. A scheme for two-photon lasing with two coupled flux qubits in circuit quantum electrodynamics

    NASA Astrophysics Data System (ADS)

    Huang, Wen; Zou, Xu-Bo; Guo, Guang-Can

    2015-06-01

    We theoretically study the system of a superconducting transmission line resonator coupled to two interacting superconducting flux qubits. It is shown that under certain conditions the resonator mode can be tuned to two-photon resonance between the ground state and the highest excited state while the middle excited states are far-off resonance. Furthermore, we study the steady-state properties of the flux qubits and resonator, such as the photon statistics, the spectrum and squeezing of the resonator, and demonstrate that two-photon laser can be implemented with current experimental technology. Project supported by the National Fundamental Research Program of China (Grant No. 2011cba00200), the National Natural Science Foundation of China (Grant No. 11274295), and the Doctor Foundation of Education Ministry of China (Grant No. 20113402110059).

  11. Stimulated photon emission and two-photon Raman scattering in a coupled-cavity QED system

    PubMed Central

    Li, C.; Song, Z.

    2016-01-01

    We study the scattering problem of photon and polariton in a one-dimensional coupled-cavity system. Analytical approximate analysis and numerical simulation show that a photon can stimulate the photon emission from a polariton through polariton-photon collisions. This observation opens the possibility of photon-stimulated transition from insulating to radiative phase in a coupled-cavity QED system. Inversely, we also find that a polariton can be generated by a two-photon Raman scattering process. This paves the way towards single photon storage by the aid of atom-cavity interaction. PMID:26877252

  12. Describing two-photon absorptivity of fluorescent proteins with a new vibronic coupling mechanism.

    PubMed

    Drobizhev, M; Makarov, N S; Tillo, S E; Hughes, T E; Rebane, A

    2012-02-01

    Fluorescent proteins (FPs) are widely used in two-photon microscopy as genetically encoded probes. Understanding the physical basics of their two-photon absorption (2PA) properties is therefore crucial for creation of two-photon brighter mutants. On the other hand, it can give us better insight into molecular interactions of the FP chromophore with a complex protein environment. It is known that, compared to the one-photon absorption spectrum, where the pure electronic transition is the strongest, the 2PA spectrum of a number of FPs is dominated by a vibronic transition. The physical mechanism of such intensity redistribution is not understood. Here, we present a new physical model that explains this effect through the "Herzberg-Teller"-type vibronic coupling of the difference between the permanent dipole moments in the ground and excited states (Δμ) to the bond-length-alternating coordinate. This model also enables us to quantitatively describe a large variability of the 2PA peak intensity in a series of red FPs with the same chromophore through the interference between the "Herzberg-Teller" and Franck-Condon terms. PMID:22224830

  13. Two-photon transport in a waveguide coupled to a cavity in a two-level system

    SciTech Connect

    Shi, T.; Sun, C. P.; Fan Shanhui

    2011-12-15

    We study two-photon effects for a cavity quantum electrodynamics system where a waveguide is coupled to a cavity embedded in a two-level system. The wave function of two-photon scattering is exactly solved by using the Lehmann-Symanzik-Zimmermann reduction. Our results about quantum statistical properties of the outgoing photons explicitly exhibit the photon blockade effects in the strong-coupling regime. These results agree with the observations of recent experiments.

  14. Origin-independent two-photon circular dichroism calculations in coupled cluster theory.

    PubMed

    Friese, Daniel H; Hättig, Christof; Rizzo, Antonio

    2016-05-21

    We present the first origin-independent approach for the treatment of two-photon circular dichroism (TPCD) using coupled cluster methods. The approach is assessed concerning its behavior on the choice of the basis set and different coupled cluster methods. We also provide a comparison of results from CC2 with those from density functional theory using the CAM-B3LYP functional. Concerning the basis set we note that in most cases an augmented triple zeta basis or a doubly augmented double zeta basis is needed for reasonably converged results. In the comparison of different coupled cluster methods results from CCSD, CC3 and CC2 have been found to be quite similar in most cases, while CCS results differ remarkably from the results at the higher levels. However, this proof-of-principle study also shows that further benchmarking of DFT and CC2 against accurate coupled cluster reference values (e.g. CCSD or CC3) is needed. PMID:27140590

  15. Simultaneous control of emission localization and two-photon absorption efficiency in dissymmetrical chromophores

    SciTech Connect

    Tretiak, Sergei

    2009-01-01

    The aim of the present work is to demonstrate that combined spectral tuning of fluorescence and two-photon absorption (TPA) properties of multipolar chromophores can be achieved by introduction of slight electronic chemical dissymmetry. In that perspective, two novel series of structurally related chromophores have been designed and studied: a first series based on rod-like quadrupolar chromophores bearing different electron-donating (D) end groups and a second series based on three-branched octupolar chromophores built from a trigonal donating moiety and bearing various acceptor (A) peripheral groups. The influence of the electronic dissymmetry is investigated by combined experimental and theoretical studies of the linear and nonlinear optical properties of dissymmetric chromophores compared to their symmetrical counterparts. In both types of systems (i.e. quadrupoles and octupoles) experiments and theory reveal that excitation is essentially delocalized and that excitation involves synchronized charge redistribution between the different D and A moieties within the multipolar structure (i.e. concerted intramolecular charge transfer). In contrast, the emission stems only from a particular dipolar subunit bearing the strongest D or A moieties due to fast excitation localization after excitation prior to emission. Hence control of emission characteristics (polarization and emission spectrum) in addition to localization can be achieved by controlled introduction of electronic dissymmetry (i.e. replacement of one of the D or A end-groups by a slightly stronger D{prime} or A{prime} units). Interestingly dissymmetrical functionalization of both quadrupolar and octupolar compounds does not lead to significant loss in TPA responses and can even be beneficial due to the spectral broadening and peak position tuning that it allows. This study thus reveals an original molecular engineering route strategy allowing major TPA enhancement in multipolar structures due to concerted

  16. Polymer waveguides self-organized by two-photon photochemistry for self-aligned optical couplings with wide misalignment tolerances

    NASA Astrophysics Data System (ADS)

    Yoshimura, Tetsuzo; Takeda, Daisuke; Sato, Takuya; Kinugasa, Yoshihiko; Nawata, Hideyuki

    2016-03-01

    Self-organized optical waveguides formed in a photopolymer using two-photon photochemistry is proposed for self-aligned optical couplings involving nano-scale optical devices with wide tolerances in lateral misalignments. Simulations based on the finite-difference time-domain method revealed that on introducing a 400-nm write beam and a 780-nm write beam into the two-photon photopolymer respectively from two 600-nm-wide waveguides facing each other with 32 μm gap a self-aligned coupling waveguide called a two-photon self-organized lightwave network (SOLNET) is formed between the two waveguides. The lateral misalignment tolerance was found to be 3000 nm, which is five times larger than the misalignment limit of ~600 nm in waveguides formed by conventional one-photon photochemistry. Preliminary experiments demonstrated that the two-photon SOLNETs are formed between multimode optical fibers by introducing a 448-nm write beam and a 780-nm (or 856-nm) write beam from the fibers into a photosensitive organic/inorganic hybrid material, SUNCONNECT®, with doped camphorquinone (or biacetyl).

  17. Theory of coherent polarization anisotropy in time-resolved two-photon ionization of isolated molecules. Effects of Coriolis couplings

    NASA Astrophysics Data System (ADS)

    Sato, S.; Nomura, Y.; Fujimura, Y.

    1987-09-01

    Effects of vibration-rotation (Coriolis) couplings on the coherent polarization anisotropy are theoretically studied in a time-resolved two-photon ionization of a symmetric top molecule. This polarization anisotropy originates from a coherent excitation of the resonant rovibronic molecular eigenstates (rovibronic coherence) whose zeroth order states are mixed through the Coriolis coupling. Expressions for the time-dependent degree of polarization after the coherent excitation of the rovibronic states produced by the Coriolis coupling are derived as a function of the delay time in the pump-probe two-photon ionization. Model calculations of the time-dependent degree of polarization as well as the probabilities of the two-photon ionization are performed to demonstrate the Coriolis coupling effects in the low excess energy regions of the resonant intermediate state. It is shown that oscillatory behaviors in the time-dependent degree of polarization should be observed as a result of the creation of the rovibronic coherence. It is demonstrated that oscillations of the degree of polarization involve both contribution of the purely rotational J-coherence and that of the rovibronic coherence in the resonant manifold when the rotational branches are coherently excited and the characteristic rotation-vibration interaction energy is larger than a typical free rotational energy under jet-cooled condition.

  18. Two-photon excitation cross section in light and intermediate atoms in frozen-core LS-coupling approximation

    NASA Technical Reports Server (NTRS)

    Omidvar, K.

    1980-01-01

    Using the method of explicit summation over the intermediate states two-photon absorption cross sections in light and intermediate atoms based on the simplistic frozen-core approximation and LS coupling have been formulated. Formulas for the cross section in terms of integrals over radial wave functions are given. Two selection rules, one exact and one approximate, valid within the stated approximations are derived. The formulas are applied to two-photon absorptions in nitrogen, oxygen, and chlorine. In evaluating the radial integrals, for low-lying levels, the Hartree-Fock wave functions, and for high-lying levels, hydrogenic wave functions obtained by the quantum-defect method have been used. A relationship between the cross section and the oscillator strengths is derived.

  19. Highly Charged Ruthenium(II) Polypyridyl Complexes as Lysosome-Localized Photosensitizers for Two-Photon Photodynamic Therapy.

    PubMed

    Huang, Huaiyi; Yu, Bole; Zhang, Pingyu; Huang, Juanjuan; Chen, Yu; Gasser, Gilles; Ji, Liangnian; Chao, Hui

    2015-11-16

    Photodynamic therapy (PDT) is a noninvasive medical technique that has received increasing attention over the last years and been applied for the treatment of certain types of cancer. However, the currently clinically used PDT agents have several limitations, such as low water solubility, poor photostability, and limited selectivity towards cancer cells, aside from having very low two-photon cross-sections around 800 nm, which limits their potential use in TP-PDT. To tackle these drawbacks, three highly positively charged ruthenium(II) polypyridyl complexes were synthesized. These complexes selectively localize in the lysosomes, an ideal localization for PDT purposes. One of these complexes showed an impressive phototoxicity index upon irradiation at 800 nm in 3D HeLa multicellular tumor spheroids and thus holds great promise for applications in two-photon photodynamic therapy. PMID:26447888

  20. ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS: Local Control of Two-Photon Absorption in a Six-Level Atomic System by Using a Coherent Perturbation Field

    NASA Astrophysics Data System (ADS)

    Jia, Wen-Zhi; Wang, Shun-Jin

    2009-11-01

    If a coherent perturbation field is used to couple the excited level of the coupling transition in the five-level K-type atom with another higher excited level, the two-photon electromagnetically induced transparency can be locally modulated by altering the parameters of the additional perturbation field. With different detunings of the coherent perturbation field, the absorption peak or transparency window with sharp and high-contrast spectral feature can be generated in the two-photon absorption spectrum. The physical interpretation of these phenomena is given in terms of the dressed states.

  1. Plasmon-enhanced two-photon-induced isomerization for highly-localized light-based actuation of inorganic/organic interfaces.

    PubMed

    Lim, Chang-Keun; Li, Xin; Li, Yue; Drew, Kurt L M; Palafox-Hernandez, J Pablo; Tang, Zhenghua; Baev, Alexander; Kuzmin, Andrey N; Knecht, Marc R; Walsh, Tiffany R; Swihart, Mark T; Ågren, Hans; Prasad, Paras N

    2016-02-21

    Two-photon initiated photo-isomerization of an azobenzene moiety adsorbed on silver nanoparticles (Ag NPs) is demonstrated. The azobenzene is linked to a materials-binding peptide that brings it into intimate contact with the Ag NP surface, producing a dramatic enhancement of its two-photon absorbance. An integrated modeling approach, combining advanced conformational sampling with Quantum Mechanics/Capacitance Molecular Mechanics and response theory, shows that charge transfer and image charges in the Ag NP generate local fields that enhance two-photon absorption of the cis isomer, but not the trans isomer, of adsorbed molecules. Moreover, dramatic local field enhancement is expected near the localized surface plasmon resonance (LSPR) wavelength, and the LSPR band of the Ag NPs overlaps the azobenzene absorbance that triggers cis to trans switching. As a result, the Ag NPs enable two-photon initiated cis to trans isomerization, but not trans to cis isomerization. Confocal anti-Stokes fluorescence imaging shows that this effect is not due to local heating, while the quadratic dependence of switching rate on laser intensity is consistent with a two-photon process. Highly localized two-photon initiated switching could allow local manipulation near the focal point of a laser within a 3D nanoparticle assembly, which cannot be achieved using linear optical processes. PMID:26830974

  2. In vivo stoichiometry monitoring of G protein coupled receptor oligomers using spectrally resolved two-photon microscopy

    NASA Astrophysics Data System (ADS)

    Stoneman, M. R.; Singh, D. R.; Raicu, V.

    2010-02-01

    Resonance Energy Transfer (RET) between a donor molecule in an electronically excited state and an acceptor molecule in close proximity has been frequently utilized for studies of protein-protein interactions in living cells. Typically, the cell under study is scanned a number of times in order to accumulate enough spectral information to accurately determine the RET efficiency for each region of interest within the cell. However, the composition of these regions may change during the course of the acquisition period, limiting the spatial determination of the RET efficiency to an average over entire cells. By means of a novel spectrally resolved two-photon microscope, we were able to obtain a full set of spectrally resolved images after only one complete excitation scan of the sample of interest. From this pixel-level spectral data, a map of RET efficiencies throughout the cell is calculated. By applying a simple theory of RET in oligomeric complexes to the experimentally obtained distribution of RET efficiencies throughout the cell, a single spectrally resolved scan reveals stoichiometric and structural information about the oligomer complex under study. This presentation will describe our experimental setup and data analysis procedure, as well as an application of the method to the determination of RET efficiencies throughout yeast cells (S. cerevisiae) expressing a G-protein-coupled receptor, Sterile 2 α factor protein (Ste2p), in the presence and absence of α-factor - a yeast mating pheromone.

  3. Plasmon-enhanced two-photon-induced isomerization for highly-localized light-based actuation of inorganic/organic interfaces

    NASA Astrophysics Data System (ADS)

    Lim, Chang-Keun; Li, Xin; Li, Yue; Drew, Kurt L. M.; Palafox-Hernandez, J. Pablo; Tang, Zhenghua; Baev, Alexander; Kuzmin, Andrey N.; Knecht, Marc R.; Walsh, Tiffany R.; Swihart, Mark T.; Ågren, Hans; Prasad, Paras N.

    2016-02-01

    Two-photon initiated photo-isomerization of an azobenzene moiety adsorbed on silver nanoparticles (Ag NPs) is demonstrated. The azobenzene is linked to a materials-binding peptide that brings it into intimate contact with the Ag NP surface, producing a dramatic enhancement of its two-photon absorbance. An integrated modeling approach, combining advanced conformational sampling with Quantum Mechanics/Capacitance Molecular Mechanics and response theory, shows that charge transfer and image charges in the Ag NP generate local fields that enhance two-photon absorption of the cis isomer, but not the trans isomer, of adsorbed molecules. Moreover, dramatic local field enhancement is expected near the localized surface plasmon resonance (LSPR) wavelength, and the LSPR band of the Ag NPs overlaps the azobenzene absorbance that triggers cis to trans switching. As a result, the Ag NPs enable two-photon initiated cis to trans isomerization, but not trans to cis isomerization. Confocal anti-Stokes fluorescence imaging shows that this effect is not due to local heating, while the quadratic dependence of switching rate on laser intensity is consistent with a two-photon process. Highly localized two-photon initiated switching could allow local manipulation near the focal point of a laser within a 3D nanoparticle assembly, which cannot be achieved using linear optical processes.Two-photon initiated photo-isomerization of an azobenzene moiety adsorbed on silver nanoparticles (Ag NPs) is demonstrated. The azobenzene is linked to a materials-binding peptide that brings it into intimate contact with the Ag NP surface, producing a dramatic enhancement of its two-photon absorbance. An integrated modeling approach, combining advanced conformational sampling with Quantum Mechanics/Capacitance Molecular Mechanics and response theory, shows that charge transfer and image charges in the Ag NP generate local fields that enhance two-photon absorption of the cis isomer, but not the trans isomer

  4. Impact of electronic coupling, symmetry, and planarization on one- and two-photon properties of triarylamines with one, two, or three diarylboryl acceptors.

    PubMed

    Makarov, Nikolay S; Mukhopadhyay, Sukrit; Yesudas, Kada; Brédas, Jean-Luc; Perry, Joseph W; Pron, Agnieszka; Kivala, Milan; Müllen, Klaus

    2012-04-19

    We have performed a study of the one- and two-photon absorption properties of a systematically varied series of triarylamino-compounds with one, two, or three attached diarylborane arms arranged in linear dipolar, bent dipolar, and octupolar geometries. Two-photon fluorescence excitation spectra were measured over a wide spectral range with femtosecond laser pulses. We found that on going from the single-arm to the two- and three-arm systems, the peak in two-photon absorption (2PA) cross-section is suppressed by factors of 3-11 for the lowest excitonic level associated with the electronic coupling of the arms, whereas it is enhanced by factors of 4-8 for the higher excitonic level. These results show that the coupling of arms redistributes the 2PA cross-section between the excitonic levels in a manner that strongly favors the higher-energy excitonic level. The experimental data on one- and two-photon cross-sections, ground- and excited-state transition dipole moments, and permanent dipole moment differences between the ground and the lowest excited states were compared to the results obtained from a simple Frenkel exciton model and from highly correlated quantum-chemical calculations. It has been found that planarization of the structure around the triarylamine moiety leads to a sizable increase in peak 2PA cross-section for the lowest excitonic level of the two-arm system, whereas for the three-arm system, the corresponding peak was weakened and shifted to lower energy. Our studies show the importance of the interarm coupling, number of arms, and structural planarity on both the enhancement and the suppression of two-photon cross-sections in multiarm molecules. PMID:22429020

  5. Calculation of two-photon absorption strengths with the approximate coupled cluster singles and doubles model CC2 using the resolution-of-identity approximation.

    PubMed

    Friese, Daniel H; Hättig, Christof; Ruud, Kenneth

    2012-01-21

    An implementation of two-photon absorption matrix elements using the approximate second-order coupled-cluster singles and doubles model CC2 is presented. In this implementation we use the resolution-of-the-identity approximation for the two-electron repulsion integrals to reduce the computational cost. To avoid storage of large arrays we introduce in addition a numerical Laplace transformation of orbital energy denominators for the response of the doubles amplitudes. The error due to the numerical Laplace transformation is found to be negligible. Using this new implementation, we performed a series of benchmark calculations on substituted benzene and azobenzene derivatives to get reference values for TD-DFT results. We show that results obtained with the Coulomb-attenuated B3LYP functional are in reasonable agreement with the coupled-cluster results, whereas other density functionals which do not have a long-range correction give considerably less accurate results. Applications to the AF240 dye molecule and a weakly bound molecular tweezer complex demonstrate that this new RI-CC2 implementation allows for the first time to compute two-photon absorption cross sections with a correlated wave function method for molecules with more than 70 atoms and to apply this method for benchmarking TD-DFT calculations on molecules which are of particular relevance for experimental studies of two-photon absorption. PMID:22130199

  6. Strong interlayer coupling mediated giant two-photon absorption in MoS e2 /graphene oxide heterostructure: Quenching of exciton bands

    NASA Astrophysics Data System (ADS)

    Sharma, Rituraj; Aneesh, J.; Yadav, Rajesh Kumar; Sanda, Suresh; Barik, A. R.; Mishra, Ashish Kumar; Maji, Tuhin Kumar; Karmakar, Debjani; Adarsh, K. V.

    2016-04-01

    A complex few-layer MoS e2 /graphene oxide (GO) heterostructure with strong interlayer coupling was prepared by a facile hydrothermal method. In this strongly coupled heterostructure, we demonstrate a giant enhancement of two-photon absorption that is in stark contrast to the reverse saturable absorption of a weakly coupled MoS e2 /GO heterostructure and saturable absorption of isolated MoS e2 . Spectroscopic evidence of our study indicates that the optical signatures of isolated MoS e2 and GO domains are significantly modified in the heterostructure, displaying a direct coupling of both domains. Furthermore, our first-principles calculations indicate that strong interlayer coupling between the layers dramatically suppresses the MoS e2 excitonic bands. We envision that our findings provide a powerful tool to explore different optical functionalities as a function of interlayer coupling, which may be essential for the development of device technologies.

  7. ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS: Incoherently Coupled Grey-Grey Spatial Soliton Pairs in Biased Two-Photon Photovoltaic Photorefractive Crystals

    NASA Astrophysics Data System (ADS)

    Su, Yan-Li; Jiang, Qi-Chang; Ji, Xuan-Mang

    2010-05-01

    The incoherently coupled grey-grey screening-photovoltaic spatial soliton pairs are predicted in biased two-photon photovoltaic photorefractive crystals under steady-state conditions. These grey-grey screening-photovoltaic soliton pairs can be established provided that the incident beams have the same polarization, wavelength, and are mutually incoherent. The grey-grey screening-photovoltaic soliton pairs can be considered as the united form of grey-grey screening soliton pairs and open or closed-circuit grey-grey photovoltaic soliton pairs.

  8. Anomalous photon-gauge boson coupling contribution to the exclusive vector boson pair production from two photon exchange in pp collisions at 13 TeV

    SciTech Connect

    Martins, D. E.; Vilela Pereira, A.; Sá Borges, J.; Rebello Teles, P.

    2015-04-10

    We study the W and Z pair production from two-photon exchange in proton-proton collisions at the LHC in order to evaluate the contributions of anomalous photon-gauge boson couplings, that simulates new particles and couplings predicted in many Standard Model (SM) extensions. The experimental results of W{sup +} W{sup −} exclusive production (pp → pW{sup +}W{sup −} p) at 7 TeV from the CMS collaboration [1] updates the experimental limits on anomalous couplings obtained at the Large Electron-Positron Collider (LEP). This motivates our present analysis hopefully anticipating the expected results using the Precision Proton Spectrometer (PPS) to be installed as part of CMS. In this work, we consider the W{sup +}W{sup −} exclusive production to present the p{sub T} distribution of the lepton pair corresponding to the SM signal with p{sub T} (e, μ) > 10 GeV. Next, we consider the photon-gauge boson anomalous couplings by calculating, from the FPMC and MadGraph event generators, the process γγ → W{sup +}W{sup −} from a model with gauge boson quartic couplings, by considering a 1 TeV scale for new physical effects. We present our results for an integrated luminosity of 5 fb{sup −1} at center-of-mass energy of 7 TeV and for an integrated luminosity of 100 fb{sup −1} at 13 TeV. We present our preliminary results for Z pair exclusive production from two-photon exchange with anomalous couplings, where the ZZγγ quartic coupling is absent in the SM. We calculate the total cross section for the exclusive process and present the four lepton invariant mass distribution. Finally we present an outlook for the present analysis.

  9. Localized lipid autoxidation initiated by two-photon irradiation within single oil droplets in oil-in-water emulsions.

    PubMed

    Raudsepp, Piret; Brüggemann, Dagmar A; Knudsen, Jes C; Andersen, Mogens L

    2016-05-15

    The initiation of lipid autoxidation within single oil droplets in Tween-20-stabilized oil-in-water emulsion was achieved by highly focused two-photon (2P) irradiation at excitation wavelength (λex) 700 nm. The radical formation was enhanced by inclusion of the photo-cleavable radical initiator di-tert-butyl peroxide (DTBP) into the droplets, and demonstrated with confocal microscopy using radical-sensitive probe BODIPY(665/676). The radical chain reactions progressed up to 60 μm; however, there were no indications of oxidation in neighboring droplets demonstrating that radicals and oxidized probe molecules were not able to migrate between oil droplets. In addition, the spatial propagation of lipid autoxidation increased with the degree of oil unsaturation. PMID:26776033

  10. Quantum input-output theory for optical cavities with arbitrary coupling strength: Application to two-photon wave-packet shaping

    NASA Astrophysics Data System (ADS)

    Raymer, M. G.; McKinstrie, C. J.

    2013-10-01

    We develop quantum-optical input-output theory for resonators with arbitrary coupling strength, and for input fields whose spectrum can be wider than the cavity free-spectral range, while ensuring that the field-operator commutator relations in space-time variables are correct. The cavity-field commutator exhibits a series of space-time “echoes,” representing causal connections of certain space-time points by light propagation. We apply the theory to two-photon wave-packet shaping by cavity reflection, which displays a remarkable illustration of dispersion cancellation. We also show that the theory is amenable to inclusion of intracavity absorbing and emitting atoms, allowing, for example, dissipative losses within the cavity to be incorporated in a quantum mechanically correct way.

  11. Two-Photon Flow Cytometry

    NASA Technical Reports Server (NTRS)

    Zhog, Cheng Frank; Ye, Jing Yong; Norris, Theodore B.; Myc, Andrzej; Cao, Zhengyl; Bielinska, Anna; Thomas, Thommey; Baker, James R., Jr.

    2004-01-01

    Flow cytometry is a powerful technique for obtaining quantitative information from fluorescence in cells. Quantitation is achieved by assuring a high degree of uniformity in the optical excitation and detection, generally by using a highly controlled flow such as is obtained via hydrodynamic focusing. In this work, we demonstrate a two-beam, two- channel detection and two-photon excitation flow cytometry (T(sup 3)FC) system that enables multi-dye analysis to be performed very simply, with greatly relaxed requirements on the fluid flow. Two-photon excitation using a femtosecond near-infrared (NIR) laser has the advantages that it enables simultaneous excitation of multiple dyes and achieves very high signal-to-noise ratio through simplified filtering and fluorescence background reduction. By matching the excitation volume to the size of a cell, single-cell detection is ensured. Labeling of cells by targeted nanoparticles with multiple fluorophores enables normalization of the fluorescence signal and thus ratiometric measurements under nonuniform excitation. Quantitative size measurements can also be done even under conditions of nonuniform flow via a two-beam layout. This innovative detection scheme not only considerably simplifies the fluid flow system and the excitation and collection optics, it opens the way to quantitative cytometry in simple and compact microfluidics systems, or in vivo. Real-time detection of fluorescent microbeads in the vasculature of mouse ear demonstrates the ability to do flow cytometry in vivo. The conditions required to perform quantitative in vivo cytometry on labeled cells will be presented.

  12. Two Photon Polymerization of Ormosils

    NASA Astrophysics Data System (ADS)

    Matei, A.; Zamfirescu, M.; Jipa, F.; Luculescu, C.; Dinescu, M.; Buruiana, E. C.; Buruiana, T.; Sima, L. E.; Petrescu, S. M.

    2010-10-01

    In this work, 3D structures of hybrid polymers—ORMOSILS (organically modified silicates) were produced via Two Photon Polymerization (2PP) of hybrid methacrylates based on silane derivates. Synthetic routes have been used to obtain series of hybrid monomers, their structure and purity being checked by NMR Spectroscopy and Fourier Transform Infrared Spectroscopy. Two photon polymerization method (a relatively new technology which allows fast micro and nano processing of three-dimensional structures with application in medical devices, tissue scaffolds, photonic crystals etc) was used for monomers processing. As laser a Ti: Sapphire laser was used, with 200 fs pulse duration and 2 kHz repetition rate, emitting at 775 nm. A parametric study on the influence of the processing parameters (laser fluence, laser scanning velocity, photo initiator) on the written structures was carried out. The as prepared polymeric scaffolds were tested in mesenchymal stem cells and fibroblasts cell cultures, with the aim of further obtaining bone and dermal grafts. Cells morphology, proliferation, adhesion and alignment were analyzed for different experimental conditions.

  13. Two-photon flow cytometry

    NASA Astrophysics Data System (ADS)

    Zhong, Cheng F.; Ye, Jing Yong; Myc, Andrzej; Thomas, Thommey P.; Bielinska, Anna; Baker, James R., Jr.; Norris, Theodore B.

    2005-03-01

    Flow cytometry is a powerful technique for obtaining quantitative information from fluorescence in cells. Quantization is achieved by assuring a high degree of uniformity in the optical excitation and detection, generally by using a highly controlled flow such as is obtained via hydrodynamic focusing. In this work, we demonstrate a two-beam, two-channel detection and two-photon excitation flow cytometry (T3FC) system that enables multi-dye analysis to be performed very simply, with greatly relaxed requirements on the fluid flow. Two-photon excitation using a femtosecond near-infrared (NIR) laser has the advantages that it enables simultaneous excitation of multiple dyes and achieves very high signal-to-noise ratio through simplified filtering and fluorescence background reduction. By matching the excitation volume to the size of a cell, single-cell detection is ensured. Labeling of cells by targeted nanoparticles with multiple fluorophores enables normalization of the fluorescence signal and thus ratiometric measurements under nonuniform excitation. Quantitative size measurements can also be done even under conditions of nonuniform flow via a two-beam layout. This innovative detection scheme not only considerably simplifies the fluid flow system and the excitation and collection optics, it opens the way to quantitative cytometry in simple and compact microfluidics systems, or in vivo.

  14. Two-photon double ionization of helium

    NASA Astrophysics Data System (ADS)

    van der Hart, Hugo W.; Feng, Liang; McKenna, Claire

    2003-12-01

    The combination of B-spline basis sets with R-matrix theory has provided a powerful tool for the description of double ionization processes. We demonstrate this first by investigating electron-impact ionization of Li2+. By applying the Floquet Ansatz, the same techniques can be employed to describe multiphoton double ionization processes through the R-matrix Floquet approach. Results for two-photon double ionization of He confirm the lower values of time-dependent close-coupling calculations compared to perturbation theory. The approach can be extended to quasi-two-electron systems through the use of model potentials. This is demonstrated by calculating photoionization cross sections near threshold for the m = 0 level of the 4s4p 1Po state of calcium.

  15. Two-photon absorption cross sections within equation-of-motion coupled-cluster formalism using resolution-of-the-identity and Cholesky decomposition representations: Theory, implementation, and benchmarks

    NASA Astrophysics Data System (ADS)

    Nanda, Kaushik D.; Krylov, Anna I.

    2015-02-01

    The equation-of-motion coupled-cluster (EOM-CC) methods provide a robust description of electronically excited states and their properties. Here, we present a formalism for two-photon absorption (2PA) cross sections for the equation-of-motion for excitation energies CC with single and double substitutions (EOM-CC for electronically excited states with single and double substitutions) wave functions. Rather than the response theory formulation, we employ the expectation-value approach which is commonly used within EOM-CC, configuration interaction, and algebraic diagrammatic construction frameworks. In addition to canonical implementation, we also exploit resolution-of-the-identity (RI) and Cholesky decomposition (CD) for the electron-repulsion integrals to reduce memory requirements and to increase parallel efficiency. The new methods are benchmarked against the CCSD and CC3 response theories for several small molecules. We found that the expectation-value 2PA cross sections are within 5% from the quadratic response CCSD values. The RI and CD approximations lead to small errors relative to the canonical implementation (less than 4%) while affording computational savings. RI/CD successfully address the well-known issue of large basis set requirements for 2PA cross sections calculations. The capabilities of the new code are illustrated by calculations of the 2PA cross sections for model chromophores of the photoactive yellow and green fluorescent proteins.

  16. Two-photon absorption cross sections within equation-of-motion coupled-cluster formalism using resolution-of-the-identity and Cholesky decomposition representations: Theory, implementation, and benchmarks

    SciTech Connect

    Nanda, Kaushik D.; Krylov, Anna I.

    2015-02-14

    The equation-of-motion coupled-cluster (EOM-CC) methods provide a robust description of electronically excited states and their properties. Here, we present a formalism for two-photon absorption (2PA) cross sections for the equation-of-motion for excitation energies CC with single and double substitutions (EOM-CC for electronically excited states with single and double substitutions) wave functions. Rather than the response theory formulation, we employ the expectation-value approach which is commonly used within EOM-CC, configuration interaction, and algebraic diagrammatic construction frameworks. In addition to canonical implementation, we also exploit resolution-of-the-identity (RI) and Cholesky decomposition (CD) for the electron-repulsion integrals to reduce memory requirements and to increase parallel efficiency. The new methods are benchmarked against the CCSD and CC3 response theories for several small molecules. We found that the expectation-value 2PA cross sections are within 5% from the quadratic response CCSD values. The RI and CD approximations lead to small errors relative to the canonical implementation (less than 4%) while affording computational savings. RI/CD successfully address the well-known issue of large basis set requirements for 2PA cross sections calculations. The capabilities of the new code are illustrated by calculations of the 2PA cross sections for model chromophores of the photoactive yellow and green fluorescent proteins.

  17. Two Photon Exchange for Exclusive Pion Electroproduction

    SciTech Connect

    Afanaciev, Andrei V.; Aleksejevs, Aleksandrs G.; Barkanova, Svetlana G.

    2013-09-01

    We perform detailed calculations of two-photon-exchange QED corrections to the cross section of pion electroproduction. The results are obtained with and without the soft-photon approximation; analytic expressions for the radiative corrections are derived. The relative importance of the two-photon correction is analyzed for the kinematics of several experiments at Jefferson Lab. A significant, over 20%, effect due to two-photon exchange is predicted for the backward angles of electron scattering at large transferred momenta.

  18. Interference and complementarity for two-photon hybrid entangled states

    SciTech Connect

    Nogueira, W. A. T.; Santibanez, M.; Delgado, A.; Saavedra, C.; Neves, L.; Lima, G.; Padua, S.

    2010-10-15

    In this work we generate two-photon hybrid entangled states (HESs), where the polarization of one photon is entangled with the transverse spatial degree of freedom of the second photon. The photon pair is created by parametric down-conversion in a polarization-entangled state. A birefringent double-slit couples the polarization and spatial degrees of freedom of these photons, and finally, suitable spatial and polarization projections generate the HES. We investigate some interesting aspects of the two-photon hybrid interference and present this study in the context of the complementarity relation that exists between the visibility of the one-photon and that of the two-photon interference patterns.

  19. Relative fine-structure intensities in two-photon excitation

    NASA Technical Reports Server (NTRS)

    Crosley, D. R.; Bischel, W. K.

    1984-01-01

    A discrepancy is pointed out between experimental determinations of the relative intensities for different fine-structure components of the two-photon transitions 2p3P 3p3P in oxygen and 2p3 4S0 - 2p2 3p4D0 in nitrogen, which agreed well with calculations involving a single virtual intermediate level, and a two-photon selection rule dJ not equal to one, derived in a purely theoretical and erroneous treatment of these transitions. Five other experiments are also briefly examined, with the conclusion that relative fine-structure intensities in two-photon transitions are well understood as straightforward extensions of angular momentum coupling in single-photon cases, in accordance with allowed dJ = 0, + or -1, and + or -2 transitions.

  20. Two-Photon Physics in Hadronic Processes

    SciTech Connect

    Carl Carlson; Marc Vanderhaeghen

    2007-11-01

    Two-photon exchange contributions to elastic electron-scattering are reviewed. The apparent discrepancy in the extraction of elastic nucleon form factors between unpolarized Rosenbluth and polarization transfer experiments is discussed, as well as the understanding of this puzzle in terms of two-photon exchange corrections. Calculations of such corrections both within partonic and hadronic frameworks are reviewed. In view of recent spin-dependent electron scattering data, the relation of the two-photon exchange process to the hyperfine splitting in hydrogen is critically examined. The imaginary part of the two-photon exchange amplitude as can be accessed from the beam normal spin asymmetry in elastic electron-nucleon scattering is reviewed. Further extensions and open issues in this field are outlined.

  1. An Interactive Approach to Two-Photon Microscopy

    NASA Astrophysics Data System (ADS)

    So, Peter T. C.; Yu, Weiming; Ragan, Tim; Gratton, Enrico

    1996-03-01

    Typical fluorescence microscopy is a method for passive observation. Novel two-photon microscopy has typical excitation volume on the order of 0.1 femtoliter. This ability to selectively excite a small region in a sample has opened new opportunities for interactive experimentation. Two emerging interactive two-photon techniques will be described. Single particle tracking has been applied to the study of protein diffusion and interaction. The traditional approach is limited to monitoring two dimensional motions with video rate time resolution. We have developed a 3-D two-photon particle tracking instrument. Using a real-time feedback system, we can interactively follow the position of the diffusing fluorescent particle by maximizing detected intensity. This system has been used to study the process of antigen endocytosis of macrophage. (2) There are no reliable manipulation methods for objects, such as virus particles, of sizes below 0.1 micrometer but larger than atomic dimensions. Two-photon excitation can initiate localized chemical reaction for nanomanipulation. Consider the diffusion of an object in a photo-polymerizable medium. By locally polymerizing the medium adjacent to the object, we can break the spatial symmetry of the diffusion of the object and interactively direct its motion. [Supported by NIH grant RR03155.

  2. Two-Photon Laser Scanning Microscopy

    NASA Astrophysics Data System (ADS)

    Nimmerjahn, A.; Theer, P.; Helmchen, F.

    Since its inception more than 15 years ago, two-photon laser scanning microscopy (2PLSM) has found widespread use in biological and medical research. Two-photon microscopy is based on simultaneous absorption of two photons by fluorophores and subsequent fluorescence emission, a process which under normal illumination conditions is highly improbable. Theoretically described around 1930 by Maria Göppert-Mayer [1], the first experimental demonstration of two-photon excitation had to await the invention of the laser, which produced sufficiently high light intensities to observe two-photon absorption events [2]. Only after the development of ultrafast lasers providing subpicosecond light pulses with high peak power intensities, however, two-photon-excited fluorescence became practical in a laser-scanning microscope [3]. Since then 2PLSM has developed into the method of choice for high-resolution imaging in living animals (reviewed in [4,5]). One of the main reasons is the low sensitivity of 2PLSM to light scattering, which enables imaging relatively deep inside biological tissue and direct observation of the dynamic behavior of cells in their native environment. In this chapter, we introduce the physical principles governing 2PLSM and briefly describe the key instrument components. We give an overview of fluorescence labeling techniques and how they are combined with 2PLSM for functional imaging and photomanipulation in living tissue. Finally, we discuss limitations and provide some future perspectives.

  3. Two-Photon-Pumped Perovskite Semiconductor Nanocrystal Lasers.

    PubMed

    Xu, Yanqing; Chen, Qi; Zhang, Chunfeng; Wang, Rui; Wu, Hua; Zhang, Xiaoyu; Xing, Guichuan; Yu, William W; Wang, Xiaoyong; Zhang, Yu; Xiao, Min

    2016-03-23

    Two-photon-pumped lasers have been regarded as a promising strategy to achieve frequency up-conversion for situations where the condition of phase matching required by conventional approaches cannot be fulfilled. However, their practical applications have been hindered by the lack of materials holding both efficient two-photon absorption and ease of achieving population inversion. Here, we show that this challenge can be tackled by employing colloidal nanocrystals of perovskite semiconductors. We observe highly efficient two-photon absorption (with a cross section of 2.7 × 10(6) GM) in toluene solutions of CsPbBr3 nanocrystals that can excite large optical gain (>500 cm(-1)) in thin films. We have succeeded in demonstrating stable two-photon-pumped lasing at a remarkable low threshold by coupling CsPbBr3 nanocrystals with microtubule resonators. Our findings suggest perovskite nanocrystals can be used as excellent gain medium for high-performance frequency-up-conversion lasers toward practical applications. PMID:26938656

  4. Two-photon uncageable enzyme inhibitors bearing targeting vectors.

    PubMed

    Anstaett, Philipp; Pierroz, Vanessa; Ferrari, Stefano; Gasser, Gilles

    2015-10-01

    The activity of two cyclooxygenase-2 enzyme inhibitors, Celecoxib and Lumiracoxib, could be suppressed by coupling to photo-labile protecting groups, so-called photocages. These groups could be further functionalized with a peptide targeting vector for specific cellular delivery. The enzyme inhibition potential of the cyclooxygenase-2 inhibitors could be regained upon two-photon excitation with tissue-transparent near-IR light at 800 nm. PMID:26314377

  5. Two-photon vibrational spectroscopy for biosciences based on surface-enhanced hyper-Raman scattering

    PubMed Central

    Kneipp, Janina; Kneipp, Harald; Kneipp, Katrin

    2006-01-01

    Two-photon excitation is gaining rapidly in interest and significance in spectroscopy and microscopy. Here we introduce a new approach that suggests versatile optical labels suitable for both one- and two-photon excitation and also two-photon-excited ultrasensitive, nondestructive chemical probing. The underlying spectroscopic effect is the incoherent inelastic scattering of two photons on the vibrational quantum states called hyper-Raman scattering (HRS). The rather weak effect can be strengthened greatly if HRS takes place in the local optical fields of gold and silver nanostructures. This so-called surface-enhanced HRS (SEHRS) is the two-photon analogue to surface-enhanced Raman scattering (SERS). SEHRS provides structurally sensitive vibrational information complementary to those obtained by SERS. SEHRS combines the advantages of two-photon spectroscopy with the structural information of vibrational spectroscopy and the high-sensitivity and nanometer-scale local confinement of plasmonics-based spectroscopy. We infer effective two-photon cross-sections for SEHRS on the order of 10−46 to 10−45 cm4·s, similar to or higher than the best “action” cross-sections (product of the two-photon absorption cross-section and fluorescence quantum yield) for two-photon fluorescence, and we demonstrate HRS on biological structures such as single cells after incubation with gold nanoparticles. PMID:17088534

  6. Chimeras in networks with purely local coupling

    NASA Astrophysics Data System (ADS)

    Laing, Carlo R.

    2015-11-01

    Chimera states in spatially extended networks of oscillators have some oscillators synchronized while the remainder are asynchronous. These states have primarily been studied in networks with nonlocal coupling, and more recently in networks with global coupling. Here, we present three networks with only local coupling (diffusive, to nearest neighbors) which are numerically found to support chimera states. One of the networks is analyzed using a self-consistency argument in the continuum limit, and this is used to find the boundaries of existence of a chimera state in parameter space.

  7. Two-photon induced polymer nanomovement.

    PubMed

    Ishitobi, Hidekazu; Shoji, Satoru; Hiramatsu, Tsunemi; Sun, Hong-Bo; Sekkat, Zouheir; Kawata, Satoshi

    2008-09-01

    We present the first report of two-photon induced plastic surface deformation in solid polymer films. Exposure of azo polymer films, which absorb in the visible range (lambda(max) = 480 nm), to intense 920 nm irradiation leads to polarization dependent photofluidic polymer nanomovement caused by photoselective two-photon trans <-->cis isomerization. The deformations were induced by a gradient of light intensity; and strongly depend on the wavelength and the polarization direction of the incident laser light and the position of the focused spot with respect to the plane of the polymer film. PMID:18773020

  8. Two-Photon Fluorescence Correlation Spectroscopy

    NASA Technical Reports Server (NTRS)

    Zimmerli, Gregory A.; Fischer, David G.

    2002-01-01

    We will describe a two-photon microscope currently under development at the NASA Glenn Research Center. It is composed of a Coherent Mira 900 tunable, pulsed Titanium:Sapphire laser system, an Olympus Fluoview 300 confocal scanning head, and a Leica DM IRE inverted microscope. It will be used in conjunction with a technique known as fluorescence correlation spectroscopy (FCS) to study intracellular protein dynamics. We will briefly explain the advantages of the two-photon system over a conventional confocal microscope, and provide some preliminary experimental results.

  9. A [111]-Cut Si Hemisphere Two-Photon Response Photodetector

    NASA Astrophysics Data System (ADS)

    Liu, Xiu-Huan; Chen, Zhan-Guo; Jia, Gang; Wang, Hai-Yan; Gao, Yan-Jun; Li, Yi

    2011-11-01

    Properties of two-photon response in a [111]-cut nearly-intrinsic Si hemisphere photodetector are studied. The measured photocurrent of the photodetector responding to the 1.32μm continuous wave laser shows a quadratic dependence on the coupled optical power and is saturated with the bias voltage. Also, the photocurrent is independent of polarization. Such properties are in good agreement with the theory of two-photon absorption. The isotropic photocurrent generated from the [111]-cut Si hemisphere is compared to the anisotropic one induced in the [110]-cut Si sample and the ratio of χxxxx/χxxyy for silicon performing at 1.32 μm is calculated to be 2.4 via the fitted function of the anisotropic photocurrent from the [110]-cut sample.

  10. Meson production in two-photon interactions at LHC energies

    SciTech Connect

    Da Silva, D. T.; Goncalves, V. P.; Sauter, W. K.

    2013-03-25

    The LHC opens a new kinematical regime at high energy, where several questions related to the description of the high-energy regime of the Quantum Chromodynamics (QCD) remain without satisfactory answers. Some open questions are the search for non-q-bar q resonances, the determination of the spectrum of q-bar q states and the identification of states with anomalous {gamma}{gamma} couplings. A possible way to study these problems is the study of meson production in two-photon interactions. In this contribution we calculate the meson production in two-photon interactions at LHC energies considering proton - proton collisions and estimate the total cross section for the production of the mesons {pi}, a, f, {eta} and {chi}.

  11. Local Land-Atmosphere Coupling (Invited)

    NASA Astrophysics Data System (ADS)

    Ek, M.; Santanello, J. A.; Jacobs, C.; Tuinenburg, O.

    2010-12-01

    The GEWEX Land-Atmosphere System Study / Local Coupling (GLASS/LoCo) project seeks to understand the role of local land-atmosphere coupling in the evolution of surface fluxes, and land and atmospheric state variables including clouds. The theme of land-atmosphere interaction is a research area that is rapidly developing; new research has evolved in modeling and observing the degree of land-atmosphere coupling on local scales. Questions of interest are (1) what is the nature and strength of this coupling, and (2) how does this change, i.e. for different temporal and spatial scales, geographic regions, and changing climates. As such, this is an important issue on both weather and climate time scales. The GLASS/LoCo working group is investigating the role of surface hydrology (e.g. soil moisture) and interaction with the evolving atmospheric boundary layer and boundary-layer (top) entrainment and boundary-layer clouds, from both the observational perspective and using coupled land-atmosphere models.

  12. Scattering of entangled two-photon states.

    PubMed

    Schotland, John C; Cazé, A; Norris, Theodore B

    2016-02-01

    We consider the scattering of entangled two-photon states from collections of small particles. We also study the related Mie problem of scattering from a sphere. In both cases, we calculate the entropy of entanglement and investigate the influence of the entanglement of the incident field on the entanglement of the scattered field. PMID:26907393

  13. Two-photon production of ω pairs

    NASA Astrophysics Data System (ADS)

    Albrecht, H.; Hamacher, T.; Hofmann, R. P.; Kirchhoff, T.; Mankel, R.; Nau, A.; Nowak, S.; Reßing, D.; Schröder, H.; Schulz, H. D.; Walter, M.; Wurth, R.; Hast, C.; Kapitza, H.; Kolanoski, H.; Kosche, A.; Lange, A.; Lindner, A.; Schieber, M.; Siegmund, T.; Spaan, B.; Thurn, H.; Töpfer, D.; Wegener, D.; Eckstein, P.; Frankl, C.; Graf, J.; Schmidtler, M.; Schramm, M.; Schubert, K. R.; Schwierz, R.; Waldi, R.; Reim, K.; Wegener, H.; Eckmann, R.; Kuipers, H.; Mai, O.; Mundt, R.; Oest, T.; Reiner, R.; Schmidt-Parzefall, W.; Stiewe, J.; Werner, S.; Ehret, K.; Hofmann, W.; Hüpper, A.; Knöpfle, K. T.; Spengler, J.; Krieger, P.; Macfarlane, D. B.; Prentice, J. D.; Saull, P. R. B.; Tzamariudaki, K.; van de Water, R. G.; Yoon, T.-S.; Schneider, M.; Weseler, S.; Kernel, G.; Križan, P.; Križnič, E.; Podobnik, T.; Živko, T.; Balagura, V.; Barsuk, S.; Belyaev, I.; Chistov, R.; Danilov, M.; Eiges, V.; Gershtein, L.; Gershtein, Yu.; Golutvin, A.; Igonkina, O.; Korolko, I.; Kostina, G.; Litvintsev, D.; Pakhlov, P.; Semenov, S.; Snizhko, A.; Tichomirov, I.; Zaitsev, Yu.; Argus Collaboration

    1996-02-01

    A maximum likelihood analysis of ARGUS data on two-photon production of π+π+π0π0π-π- is presented. A small fraction of events is due to the production of omega pairs. The γγ → ωω cross section has its maximum value close to threshold.

  14. Oxygen Microscopy by Two-Photon-Excited Phosphorescence

    PubMed Central

    Finikova, Olga S.; Lebedev, Artem Y.; Aprelev, Alexey; Troxler, Thomas; Gao, Feng; Garnacho, Carmen; Muro, Silvia; Hochstrasser, Robin M.; Vinogradov, Sergei A.

    2009-01-01

    High-resolution images of oxygen distributions in microheterogeneous samples are obtained by two-photon laser scanning microscopy (2P LSM), using a newly developed dendritic nanoprobe with internally enhanced two-photon absorption (2PA) cross-section. In this probe, energy is harvested by a 2PA antenna, which passes excitation onto a phosphorescent metalloporphyrin via intramolecular energy transfer. The 2P LSM allows sectioning of oxygen gradients with near diffraction-limited resolution, and lifetime-based acquisition eliminates dependence on the local probe concentration. The technique is validated on objects with a priori known oxygen distributions and applied to imaging of pO2 in cells. PMID:18663708

  15. Quantum correlation of path-entangled two-photon states in waveguide arrays with defects

    SciTech Connect

    Dou, Yiling; Xu, Lei; Han, Bin; Bo, Fang; Xu, Jingjun; Zhang, Guoquan

    2014-04-15

    We study the quantum correlation of path-entangled states of two photons in coupled one-dimensional waveguide arrays with lattice defects. Both off-diagonal and diagonal defects are considered, which show different effects on the quantum correlation of path-entangled two-photon states. Two-photon bunching or anti-bunching effects can be observed and controlled. The two photons are found to have a tendency to bunch at the side lobes with a repulsive off-diagonal defect, and the path-entanglement of the input two-photon state can be preserved during the propagation. We also found that defect modes may play an important role on the two-photon correlation of path-entangled states in the waveguide arrays. Due to the quantum interference effect, intriguing evolution dynamics of the two-photon correlation matrix elements with oscillation frequencies being either twice of or the same as that of a classical light wave, depending on the position of the correlation matrix element, is observed. Our results show that it is possible to manipulate the two-photon correlation properties of path-entangled states in waveguide arrays with lattice defects.

  16. Magnetic two-photon scattering and two-photon emission - Cross sections and redistribution functions

    NASA Technical Reports Server (NTRS)

    Alexander, S. G.; Meszaros, P.

    1991-01-01

    The magnetic two-photon scattering cross section is discussed within the framework of QED, and the corresponding scattering redistribution function for this process and its inverse, as well as the scattering source function are calculated explicitly. In a similar way, the magnetic two-photon emission process which follows the radiative excitation of Landau levels above ground is calculated. The two-photon scattering and two-photon emission are of the same order as the single-photon magnetic scattering. All three of these processes, and in optically thick cases also their inverses, are included in radiative transport calculations modeling accreting pulsars and gamma-ray bursters. These processes play a prominent role in determining the relative strength of the first two cyclotron harmonics, and their effects extend also to the higher harmonics.

  17. Two-photon physics as a probe of hadron dynamics

    SciTech Connect

    Brodsky, S.J.

    1981-05-01

    Two-photon collisions provide an ideal laboratory for testing many features of quantum chromodynamics, especially the interplay between the vector-meson-dominated and point-like hadronic interactions of the photon. A number of QCD applications are discussed, including: jet and single-particle production at large transverse momentum; the photon structure function and its relationship to the ..gamma.. ..-->.. q anti q wave function; and the possible role of gluonium states in the ..gamma gamma.. ..-->.. rho/sup 0/rho/sup 0/ channel. Evidence that even low momentum transfer photon-hadron interactions are sensitive to the point-like ..gamma.. ..-->.. q anti q coupling is discussed.

  18. Denoising Two-Photon Calcium Imaging Data

    PubMed Central

    Malik, Wasim Q.; Schummers, James; Sur, Mriganka; Brown, Emery N.

    2011-01-01

    Two-photon calcium imaging is now an important tool for in vivo imaging of biological systems. By enabling neuronal population imaging with subcellular resolution, this modality offers an approach for gaining a fundamental understanding of brain anatomy and physiology. Proper analysis of calcium imaging data requires denoising, that is separating the signal from complex physiological noise. To analyze two-photon brain imaging data, we present a signal plus colored noise model in which the signal is represented as harmonic regression and the correlated noise is represented as an order autoregressive process. We provide an efficient cyclic descent algorithm to compute approximate maximum likelihood parameter estimates by combing a weighted least-squares procedure with the Burg algorithm. We use Akaike information criterion to guide selection of the harmonic regression and the autoregressive model orders. Our flexible yet parsimonious modeling approach reliably separates stimulus-evoked fluorescence response from background activity and noise, assesses goodness of fit, and estimates confidence intervals and signal-to-noise ratio. This refined separation leads to appreciably enhanced image contrast for individual cells including clear delineation of subcellular details and network activity. The application of our approach to in vivo imaging data recorded in the ferret primary visual cortex demonstrates that our method yields substantially denoised signal estimates. We also provide a general Volterra series framework for deriving this and other signal plus correlated noise models for imaging. This approach to analyzing two-photon calcium imaging data may be readily adapted to other computational biology problems which apply correlated noise models. PMID:21687727

  19. A Two-Photon Fluorescent Probe for Lysosomal Thiols in Live Cells and Tissues

    NASA Astrophysics Data System (ADS)

    Fan, Jiangli; Han, Zhichao; Kang, Yao; Peng, Xiaojun

    2016-01-01

    Lysosome-specific fluorescent probes are exclusive to elucidate the functions of lysosomal thiols. Moreover, two-photon microscopy offers advantages of less phototoxicity, better three dimensional spatial localization, deeper penetration depth and lower self-absorption. However, such fluorescent probes for thiols are still rare. In this work, an efficient two-photon fluorophore 1,8-naphthalimide-based probe conjugating a 2,4-dinitrobenzenesulfonyl chloride and morpholine was designed and synthesized, which exhibited high selectivity and sensitivity towards lysosomal thiols by turn-on fluorescence method quantitatively and was successfully applied to the imaging of thiols in live cells and tissues by two-photon microscopy.

  20. A Two-Photon Fluorescent Probe for Lysosomal Thiols in Live Cells and Tissues

    PubMed Central

    Fan, Jiangli; Han, Zhichao; Kang, Yao; Peng, Xiaojun

    2016-01-01

    Lysosome-specific fluorescent probes are exclusive to elucidate the functions of lysosomal thiols. Moreover, two-photon microscopy offers advantages of less phototoxicity, better three dimensional spatial localization, deeper penetration depth and lower self-absorption. However, such fluorescent probes for thiols are still rare. In this work, an efficient two-photon fluorophore 1,8-naphthalimide-based probe conjugating a 2,4-dinitrobenzenesulfonyl chloride and morpholine was designed and synthesized, which exhibited high selectivity and sensitivity towards lysosomal thiols by turn-on fluorescence method quantitatively and was successfully applied to the imaging of thiols in live cells and tissues by two-photon microscopy. PMID:26794434

  1. Two-Photon Small Molecule Enzymatic Probes.

    PubMed

    Qian, Linghui; Li, Lin; Yao, Shao Q

    2016-04-19

    Enzymes are essential for life, especially in the development of disease and on drug effects, but as we cannot yet directly observe the inside interactions and only partially observe biochemical outcomes, tools "translating" these processes into readable information are essential for better understanding of enzymes as well as for developing effective tools to fight against diseases. Therefore, sensitive small molecule probes suitable for direct in vivo monitoring of enzyme activities are ultimately desirable. For fulfilling this desire, two-photon small molecule enzymatic probes (TSMEPs) producing amplified fluorescent signals based on enzymatic conversion with better photophysical properties and deeper penetration in intact tissues and whole animals have been developed and demonstrated to be powerful in addressing the issues described above. Nonetheless, currently available TSMEPs only cover a small portion of enzymes despite the distinct advantages of two-photon fluorescence microscopy. In this Account, we would like to share design principles for TSMEPs as potential indicators of certain pathology-related biomarkers together with their applications in disease models to inspire more elegant work to be done in this area. Highlights will be addressed on how to equip two-photon fluorescent probes with features amenable for direct assessment of enzyme activities in complex pathological environments. We give three recent examples from our laboratory and collaborations in which TSMEPs are applied to visualize the distribution and activity of enzymes at cellular and organism levels. The first example shows that we could distinguish endogenous phosphatase activity in different organelles; the second illustrates that TSMEP is suitable for specific and sensitive detection of a potential Parkinson's disease marker (monoamine oxidase B) in a variety of biological systems from cells to patient samples, and the third identifies that TSMEPs can be applied to other enzyme

  2. Two photon excitation of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Pindzola, M. S.

    1977-01-01

    A standard perturbation expansion in the atom-radiation field interaction is used to calculate the two photon excitation cross section for 1s(2) 2s(2) 2p(4) p3 to 1s(2) 2s(2) 2p(3) (s4) 3p p3 transition in atomic oxygen. The summation over bound and continuum intermediate states is handled by solving the equivalent inhomogeneous differential equation. Exact summation results differ by a factor of 2 from a rough estimate obtained by limiting the intermediate state summation to one bound state. Higher order electron correlation effects are also examined.

  3. Two-Photon Ionization of Metastable Helium

    NASA Astrophysics Data System (ADS)

    Czechanski, James Poremba

    There have been relatively few investigations of multiphoton ionization from metastable helium. Of particular interest has been the work of Haberland et al. 1987 and Haberland and Oschwald 1988. In both the 1987 and 1988 papers they have described the two photon ionization of metastable helium. In each of these studies they have reported the occurrence of unexplained structure along the wings of their resonance profiles. Upon the performance of similar measurements by this study, the unexplained structure is not seen and the agreement of the experiment's measurements with the theoretical shape of the resonance curves has been good. To experimentally verify these resonance effects, we have used a tunable dye laser in conjunction with a time of flight mass spectrometer to create and detect ions from metastable helium by two-photon absorption. The use of a metastable state instead of the ground state is advantageous because of its proximity to the ionization continuum and its extended lifetime. Using a metastable state as a starting point for multiphoton absorption requires fewer photons to reach the ionization threshold. The extended lifetime of the state also makes it easy to access experimentally. For helium the singlet metastable state 2^1 S lies at 20.61 eV above the ground level with a natural lifetime of close to a millisecond. Two photons of 501.7 nm and 504.35 nm are required for the ionization processes in resonance with the 3^1P and the 3^1D states. This thesis is the accounting of the experimental process involved in the measurement of the dipole and quadrupole resonances of two photon ionization from singlet metastable helium. The study includes the description of the laser, electron gun assembly for metastable helium creation, and the time of flight mass spectrometer. A discussion of the theory of multiphoton processes is included along with the discussion of the data, its reduction and analysis, and a comparison with theoretical prediction. This study

  4. Combined two-photon microscopy and angiographic optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Kim, Bumju; Wang, Tae Jun; Li, Qingyun; Nam, Jutaek; Hwang, Sekyu; Chung, Euiheon; Kim, Sungjee; Kim, Ki Hean

    2013-08-01

    A combined two-photon microscopy (TPM) and angiographic optical coherence tomography (OCT) is developed, which can provide molecular, cellular, structural, and vascular information of tissue specimens in vivo. This combined system is implemented by adding an OCT vasculature visualization method to the previous combined TPM and OCT, and then is applied to in vivo tissue imaging. Two animal models, a mouse brain cranial window model and a mouse ear cancer model, are used. Both molecular, cellular information at local regions of tissues, and structural, vascular information at relatively larger regions are visualized in the same sections. In vivo tissue microenvironments are better elucidated by the combined TPM and angiographic OCT.

  5. Dicyanostilbene-derived two-photon fluorescence dyes with large two-photon absorption cross sections

    NASA Astrophysics Data System (ADS)

    Huang, Chibao; Lin, Changhua; Ren, Anxiang; Yang, Nianfa

    2011-12-01

    Four dicyanostilbene-derived two-photon fluorescence (TPF) dyes were synthesized as the model compounds to systematically study the effect of the dicyano and the terminal substituent on the two-photon absorption (TPA). These four compounds ( DSO, DCY, DTO and DPH) exhibit very large two-photon absorption cross sections ( δ). DCY (A- π-A) with the terminal cyano group has especially high fluorescence quantum yield (0.71) and relatively large δ (1480 GM), while DPH (D- π-A) with the substitutedamino group at its terminus possesses the largest δ (2800 GM) and the longest emission wavelength (620 nm). The idealest terminal substituent should not be the alkoxy group but the substitutedamino group. This class of dicyanostilbene dyes possess small molecule size, large δ (830-2800 GM), long-wavelength emission (459-620 nm) and large Stokes shift (80-206 nm), and are ideal chromophores for TPF labels and probes.

  6. Encoded multisite two-photon microscopy

    PubMed Central

    Ducros, Mathieu; Houssen, Yannick Goulam; Bradley, Jonathan; de Sars, Vincent; Charpak, Serge

    2013-01-01

    The advent of scanning two-photon microscopy (2PM) has created a fertile new avenue for noninvasive investigation of brain activity in depth. One principal weakness of this method, however, lies with the limit of scanning speed, which makes optical interrogation of action potential-like activity in a neuronal network problematic. Encoded multisite two-photon microscopy (eMS2PM), a scanless method that allows simultaneous imaging of multiple targets in depth with high temporal resolution, addresses this drawback. eMS2PM uses a liquid crystal spatial light modulator to split a high-power femto-laser beam into multiple subbeams. To distinguish them, a digital micromirror device encodes each subbeam with a specific binary amplitude modulation sequence. Fluorescence signals from all independently targeted sites are then collected simultaneously onto a single photodetector and site-specifically decoded. We demonstrate that eMS2PM can be used to image spike-like voltage transients in cultured cells and fluorescence transients (calcium signals in neurons and red blood cells in capillaries from the cortex) in depth in vivo. These results establish eMS2PM as a unique method for simultaneous acquisition of neuronal network activity. PMID:23798397

  7. 3D single-molecule tracking using one- and two-photon excitation microscopy

    NASA Astrophysics Data System (ADS)

    Liu, Cong; Perillo, Evan P.; Zhuang, Quincy; Huynh, Khang T.; Dunn, Andrew K.; Yeh, Hsin-Chih

    2014-03-01

    Three dimensional single-molecule tracking (3D-SMT) has revolutionized the way we study fundamental cellular processes. By analyzing the spatial trajectories of individual molecules (e.g. a receptor or a signaling molecule) in 3D space, one can discern the internalization or transport dynamics of these molecules, study the heterogeneity of subcellular structures, and elucidate the complex spatiotemporal regulation mechanisms. Sub-diffraction localization precision, sub-millisecond temporal resolution and tens-of-seconds observation period are the benchmarks of current 3D-SMT techniques. We have recently built two molecular tracking systems in our labs. The first system is a previously reported confocal tracking system, which we denote as the 1P-1E-4D (one-photon excitation, one excitation beam, and four fiber-coupled detectors) system. The second system is a whole new design that is based on two-photon excitation, which we denote as the 2P-4E-1D (two-photon excitation, four excitation beams, and only one detector) system. Here we compare these two systems based on Monte Carlo simulation of tracking a diffusing fluorescent molecule. Through our simulation, we have characterized the limitation of individual systems and optimized the system parameters such as magnification, z-plane separation, and feedback gains.

  8. Two-photon imaging and analysis of neural network dynamics

    NASA Astrophysics Data System (ADS)

    Lütcke, Henry; Helmchen, Fritjof

    2011-08-01

    The glow of a starry night sky, the smell of a freshly brewed cup of coffee or the sound of ocean waves breaking on the beach are representations of the physical world that have been created by the dynamic interactions of thousands of neurons in our brains. How the brain mediates perceptions, creates thoughts, stores memories and initiates actions remains one of the most profound puzzles in biology, if not all of science. A key to a mechanistic understanding of how the nervous system works is the ability to measure and analyze the dynamics of neuronal networks in the living organism in the context of sensory stimulation and behavior. Dynamic brain properties have been fairly well characterized on the microscopic level of individual neurons and on the macroscopic level of whole brain areas largely with the help of various electrophysiological techniques. However, our understanding of the mesoscopic level comprising local populations of hundreds to thousands of neurons (so-called 'microcircuits') remains comparably poor. Predominantly, this has been due to the technical difficulties involved in recording from large networks of neurons with single-cell spatial resolution and near-millisecond temporal resolution in the brain of living animals. In recent years, two-photon microscopy has emerged as a technique which meets many of these requirements and thus has become the method of choice for the interrogation of local neural circuits. Here, we review the state-of-research in the field of two-photon imaging of neuronal populations, covering the topics of microscope technology, suitable fluorescent indicator dyes, staining techniques, and in particular analysis techniques for extracting relevant information from the fluorescence data. We expect that functional analysis of neural networks using two-photon imaging will help to decipher fundamental operational principles of neural microcircuits.

  9. Two-Photon Fluorescence Microscope for Microgravity Research

    NASA Technical Reports Server (NTRS)

    Fischer, David G.; Zimmerli, Gregory A.; Asipauskas, Marius

    2005-01-01

    A two-photon fluorescence microscope has been developed for the study of biophysical phenomena. Two-photon microscopy is a novel form of laser-based scanning microscopy that enables three-dimensional imaging without many of the problems inherent in confocal microscopy. Unlike one-photon optical microscopy, two-photon microscopy utilizes the simultaneous nonlinear absorption of two near-infrared photons. However, the efficiency of two-photon absorption is much lower than that of one-photon absorption, so an ultra-fast pulsed laser source is typically employed. On the other hand, the critical energy threshold for two-photon absorption leads to fluorophore excitation that is intrinsically localized to the focal volume. Consequently, two-photon microscopy enables optical sectioning and confocal performance without the need for a signal-limiting pinhole. In addition, there is a reduction (relative to one-photon optical microscopy) in photon-induced damage because of the longer excitation wavelength. This reduction is especially advantageous for in vivo studies. Relative to confocal microscopy, there is also a reduction in background fluorescence, and, because of a reduction in Rayleigh scattering, there is a 4 increase of penetration depth. The prohibitive cost of a commercial two-photon fluorescence-microscope system, as well as a need for modularity, has led to the construction of a custom-built system (see Figure 1). This system includes a coherent mode-locked titanium: sapphire laser emitting 120-fs-duration pulses at a repetition rate of 80 MHz. The pulsed laser has an average output power of 800 mW and a wavelength tuning range of 700 to 980 nm, enabling the excitation of a variety of targeted fluorophores. The output from the laser is attenuated, spatially filtered, and then directed into a confocal scanning head that has been modified to provide for side entry of the laser beam. The laser output coupler has been replaced with a dichroic filter that reflects the

  10. Experimental realization of a two-photon Raman laser

    NASA Astrophysics Data System (ADS)

    Brown, William J.

    1999-11-01

    This thesis describes the development of a novel quantum oscillator known as a two-photon Raman laser. It is based on two-photon stimulated emission in strongly driven potassium atoms. Two-photon lasers were first proposed in the 1960's, but only recently have such devices been experimentally realized. The two-photon Raman laser is an important step forward as it provides the first opportunity to study the turn-on behavior, instabilities, and noise properties of a pure two-photon optical device. The necessary ingredients for a two-photon laser are a medium displaying two-photon laser beam amplification and an optical resonator. In my two-photon Raman laser the amplification arises from a multi-photon process in which state-prepared potassium atoms undergo two-photon Raman transitions. This amplification process was studied using a high-density, small-Doppler-width potassium atomic beam that was driven by a strong pump laser and probed by a weak probe laser. I observed two-photon Raman amplification for a range of pump laser frequencies, atomic beam number densities, and probe beam powers. The two-photon Raman gain is linearly dependent on the input probe power as expected for a two-photon process. This gain mechanism is also spectrally isolated from other mechanisms occurring in strongly driven potassium atoms. The optical resonator consists of a sub-confocal high finesse cavity. The cavity is constructed so that the two-photon Raman process will lase while all other processes are suppressed. The cavity buildup is sufficient to support lasing given the maximum two-photon Raman gain observed in the amplification experiment. Using this apparatus I have observed two-photon lasing. In agreement with theoretical predictions, an external photon source is required to initiate two-photon lasing. I initiated the two-photon laser using an externally injected pulse of light and using a frequency degenerate one-photon process. The two-photon Raman laser threshold was mapped as

  11. LASERS IN MEDICINE: Two-photon excitation of aluminium phthalocyanines

    NASA Astrophysics Data System (ADS)

    Meshalkin, Yu P.; Alfimov, E. E.; Vasil'ev, N. E.; Denisov, A. N.; Makukha, V. K.; Ogirenko, A. P.

    1999-12-01

    A demonstration is given of the feasibility of two-photon excitation of aluminium phthalocyanine and of the pharmaceutical preparation 'Fotosens', used in photodynamic therapy. The excitation source was an Nd:YAG laser emitting at the 1064 nm wavelength. The spectra of the two-photon-excited luminescence were obtained and the two-photon absorption cross sections were determined.

  12. Two photon annihilation operators and squeezed vacuum

    NASA Technical Reports Server (NTRS)

    Roy, Anil K.; Mehta, C. L.; Saxena, G. M.

    1993-01-01

    Inverses of the harmonic oscillator creation and annihilation operators by their actions on the number states are introduced. Three of the two photon annihilation operators, viz., a(sup +/-1)a, aa(sup +/-1), and a(sup 2), have normalizable right eigenstates with nonvanishing eigenvalues. The eigenvalue equation of these operators are discussed and their normalized eigenstates are obtained. The Fock state representation in each case separates into two sets of states, one involving only the even number states while the other involving only the odd number states. It is shown that the even set of eigenstates of the operator a(sup +/-1)a is the customary squeezed vacuum S(sigma) O greater than.

  13. Two-photon fluorescence anisotropy imaging

    NASA Astrophysics Data System (ADS)

    Li, Wei; Wang, Yi; Shao, Hanrong; He, Yonghong; Ma, Hui

    2006-09-01

    We have developed a novel method for imaging the fluorescence intensity and anisotropy by two-photon fluorescence microscopy and tested its capability in biological application. This method is applied to model sample including FITC and FITC-CD44 antibody solution and also FITC-CD44 stained cells. The fluorescence anisotropy (FA) of FITC-CD44ab solution is higher than the FITC solution with the same concentration. The fluorescence in cell sample has even higher FA than in solution because the rotation diffusion is restrained in membrane. The method is employed to study the effect of berberine a kind of Chinese medicine, on tumor metastasis. The results indicated that tumor cell membrane fluidity is decreasing with increasing the concentration of berberine in culture medium.

  14. Photorejuvenation observation based on two photon microscopy

    NASA Astrophysics Data System (ADS)

    Wu, Shu-lian; Li, Hui; Xiao, Zheng-ying; Xie, Shu-sen

    2008-12-01

    With low risk of complications and little down-time, the non-ablative photo-rejuvenation is playing an increasing role in the therapy of the photo-damaged skin, but the appraisal standard is different. This paper mainly observed the effect of the mouse skin irradiated by intense pulse light source through two photo microscopy in sub-micrometer. The spectrum and morphological imaging between pre- and post-irradiated by Intense Pulse Light (IPL) were obtained from two photon microscopy respectively. The outcome showed that non-ablative IPL irradiated the aging mouse skin got the better effect, and then have gained the changes of spectrum intensity and corresponding photon numbers in a rectangular area, these probable achieve the mechanism of light irradiated skin. The intention of this was offer the theory basis in clinic.

  15. Two-photon imaging of stem cells

    NASA Astrophysics Data System (ADS)

    Uchugonova, A.; Gorjup, E.; Riemann, I.; Sauer, D.; König, K.

    2008-02-01

    A variety of human and animal stem cells (rat and human adult pancreatic stem cells, salivary gland stem cells, dental pulpa stem cells) have been investigated by femtosecond laser 5D two-photon microscopy. Autofluorescence and second harmonic generation have been imaged with submicron spatial resolution, 270 ps temporal resolution, and 10 nm spectral resolution. In particular, NADH and flavoprotein fluorescence was detected in stem cells. Major emission peaks at 460nm and 530nm with typical mean fluorescence lifetimes of 1.8 ns and 2.0 ns, respectively, were measured using time-correlated single photon counting and spectral imaging. Differentiated stem cells produced the extracellular matrix protein collagen which was detected by SHG signals at 435 nm.

  16. The CLAS Two Photon Exchange Experiment

    NASA Astrophysics Data System (ADS)

    Adikaram, Dasuni; Bennett, Robert; Weinstein, Larry; Rimal, Dipak; Khetarpal, Puneet; Raue, Brian

    2013-04-01

    There is a large discrepancy between the proton electron form factor (GE^p(Q^2)) measured using the Rosenbluth separation and polarization transfer methods. The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section. The TPE contribution can be extracted in a model-independent way from the measured ratio of the cross sections of positron-proton and electron-proton elastic scattering. This ratio was measured in Hall B at Jefferson Lab using a simultaneous mixed tertiary beam of electrons and positrons incident on a liquid hydrogen target in the center of the CLAS detector in 2010-2011. In this talk, the experimental techniques to produce e^+/e^- beam, the analysis techniques to identify the elastic scattering events, and some preliminary results will be presented.

  17. The CLAS Two Photon Exchange Experiment

    NASA Astrophysics Data System (ADS)

    Adikaram, Dasuni; CLAS Collaboration

    2013-10-01

    There is a large discrepancy between the proton electron form factor (GEp(Q2)) measured using the Rosenbluth separation and polarization transfer methods. The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section. The TPE contribution can be extracted in a model-independent way from the measured ratio of the cross sections of positron-proton and electron-proton elastic scattering. This ratio was measured in Hall B at Jefferson Lab using a simultaneous mixed tertiary beam of electrons and positrons incident on a liquid hydrogen target in the center of the CLAS detector in 2010-2011. This talk will present the analysis techniques used to identify the elastic scattering events, and some preliminary results at Q2 = 1.4 (GeV/c)2.

  18. Two-Photon Fluorescence Microscopy Developed for Microgravity Fluid Physics

    NASA Technical Reports Server (NTRS)

    Fischer, David G.; Zimmerli, Gregory A.; Asipauskas, Marius

    2004-01-01

    Recent research efforts within the Microgravity Fluid Physics Branch of the NASA Glenn Research Center have necessitated the development of a microscope capable of high-resolution, three-dimensional imaging of intracellular structure and tissue morphology. Standard optical microscopy works well for thin samples, but it does not allow the imaging of thick samples because of severe degradation caused by out-of-focus object structure. Confocal microscopy, which is a laser-based scanning microscopy, provides improved three-dimensional imaging and true optical sectioning by excluding the out-of-focus light. However, in confocal microscopy, out-of-focus object structure is still illuminated by the incoming beam, which can lead to substantial photo-bleaching. In addition, confocal microscopy is plagued by limited penetration depth, signal loss due to the presence of a confocal pinhole, and the possibility of live-cell damage. Two-photon microscopy is a novel form of laser-based scanning microscopy that allows three-dimensional imaging without many of the problems inherent in confocal microscopy. Unlike one-photon microscopy, it utilizes the nonlinear absorption of two near-infrared photons. However, the efficiency of two-photon absorption is much lower than that of one-photon absorption because of the nonlinear (i.e., quadratic) electric field dependence, so an ultrafast pulsed laser source must typically be employed. On the other hand, this stringent energy density requirement effectively localizes fluorophore excitation to the focal volume. Consequently, two-photon microscopy provides optical sectioning and confocal performance without the need for a signal-limiting pinhole. In addition, there is a reduction in photo-damage because of the longer excitation wavelength, a reduction in background fluorescence, and a 4 increase in penetration depth over confocal methods because of the reduction in Rayleigh scattering.

  19. Dynamics of two-photon paired superradiance

    NASA Astrophysics Data System (ADS)

    Yoshimura, M.; Sasao, N.; Tanaka, M.

    2012-07-01

    We develop for dipole-forbidden transition a dynamical theory of two-photon paired superradiance (PSR). This is a cooperative process characterized by two photons emitted back to back with equal energies. By irradiating the trigger laser from two target ends, with its frequency tuned at the half energy between two levels, a macroscopically coherent state of medium and fields dynamically emerges as time evolves, and a large signal of amplified output occurs with a time delay. The basic semiclassical equations in 1+1 space-time dimensions are derived for the field-plus-medium system to describe the space-time evolution of the entire system and are numerically solved to demonstrate the existence of both explosive and weak PSR phenomena in the presence of relaxation terms. The explosive PSR event terminates accompanying a sudden release of most of the energy stored in the target. Our numerical simulations are performed using the vibrational transition X1Σg+v=1→0 of a para-H2 molecule and taking many different excited atom number densities and different initial coherences between the metastable and the ground states. In an example with a number density close to O(1021 cm-3) and a high initial coherence, the explosive event terminates several nanoseconds after the trigger irradiation, when the phase relaxation time larger than O(10 ns) is taken. After PSR events the system is expected to follow a steady-state solution which is obtained by analytic means and is made of many objects of field condensates endowed with a topological stability.

  20. Two-photon resonant second harmonic generation in atomic xeon

    SciTech Connect

    Shi, Y. J.; Al-Basheer, W.; Thompson, R. I.

    2009-03-07

    Vacuum ultraviolet (VUV) radiation at 124.8 nm (9.93 eV) was produced from two-photon resonant second harmonic generation (SHG) in a xeon gaseous medium and used to probe molecular samples of acetone, furan, thiophene, ammonia, and methane. The mass spectra recorded from the species with ionization energies below 9.93 eV were dominated by the parent ions. The parent ions were only observed when the incident UV radiation was tuned to resonate with the two-photon transition 5p{sup 5}({sup 2}P{sub 3/2}{sup 0})6p[1/2]{sub 0}(leftarrow)5p{sup 6} {sup 1}S{sub 0} of Xe at 80 119.474 cm{sup -1}. The pressure dependence and the resonant nature of the parent ions observed support the mechanism for SHG as the ionization-initiated electric field induced SHG via the third-order nonlinear susceptibility {chi}{sup (3)}, which is enhanced by the coupling between the 5p{sup 5}({sup 2}P{sub 3/2}{sup 0})6p[1/2]{sub 0} and the nearby 5p{sup 5}({sup 2}P{sub 3/2}{sup 0})5d[1/2]{sub 1} states of Xe atoms.

  1. Two-photon-induced singlet fission in rubrene single crystal

    NASA Astrophysics Data System (ADS)

    Ma, Lin; Galstyan, Gegham; Zhang, Keke; Kloc, Christian; Sun, Handong; Soci, Cesare; Michel-Beyerle, Maria E.; Gurzadyan, Gagik G.

    2013-05-01

    The two-photon-induced singlet fission was observed in rubrene single crystal and studied by use of femtosecond pump-probe spectroscopy. The location of two-photon excited states was obtained from the nondegenerate two-photon absorption (TPA) spectrum. Time evolution of the two-photon-induced transient absorption spectra reveals the direct singlet fission from the two-photon excited states. The TPA absorption coefficient of rubrene single crystal is 52 cm/GW at 740 nm, as obtained from Z-scan measurements. Quantum chemical calculations based on time-dependent density functional theory support our experimental data.

  2. Two-Photon Imaging of Microbial Immunity in Living Tissues

    PubMed Central

    Herz, Jasmin; Zinselmeyer, Bernd H.; McGavern, Dorian B.

    2013-01-01

    The immune system is highly evolved and can respond to infection throughout the body. Pathogen-specific immune cells are usually generated in secondary lymphoid tissues (e.g., spleen, lymph nodes) and then migrate to sites of infection where their functionality is shaped by the local milieu. Because immune cells are so heavily influenced by the infected tissue in which they reside, it is important that their interactions and dynamics be studied in vivo. Two-photon microscopy is a powerful approach to study host-immune interactions in living tissues, and recent technical advances in the field have enabled researchers to capture movies of immune cells and infectious agents operating in real time. These studies have shed light on pathogen entry and spread through intact tissues as well as the mechanisms by which innate and adaptive immune cells participate in thwarting infections. This review focuses on how two-photon microscopy can be used to study tissue-specific immune responses in vivo, and how this approach has advanced our understanding of host-immune interactions following infection. PMID:22846498

  3. Two-photon quantum walk in a multimode fiber

    PubMed Central

    Defienne, Hugo; Barbieri, Marco; Walmsley, Ian A.; Smith, Brian J.; Gigan, Sylvain

    2016-01-01

    Multiphoton propagation in connected structures—a quantum walk—offers the potential of simulating complex physical systems and provides a route to universal quantum computation. Increasing the complexity of quantum photonic networks where the walk occurs is essential for many applications. We implement a quantum walk of indistinguishable photon pairs in a multimode fiber supporting 380 modes. Using wavefront shaping, we control the propagation of the two-photon state through the fiber in which all modes are coupled. Excitation of arbitrary output modes of the system is realized by controlling classical and quantum interferences. This report demonstrates a highly multimode platform for multiphoton interference experiments and provides a powerful method to program a general high-dimensional multiport optical circuit. This work paves the way for the next generation of photonic devices for quantum simulation, computing, and communication. PMID:27152325

  4. Two-photon quantum walk in a multimode fiber.

    PubMed

    Defienne, Hugo; Barbieri, Marco; Walmsley, Ian A; Smith, Brian J; Gigan, Sylvain

    2016-01-01

    Multiphoton propagation in connected structures-a quantum walk-offers the potential of simulating complex physical systems and provides a route to universal quantum computation. Increasing the complexity of quantum photonic networks where the walk occurs is essential for many applications. We implement a quantum walk of indistinguishable photon pairs in a multimode fiber supporting 380 modes. Using wavefront shaping, we control the propagation of the two-photon state through the fiber in which all modes are coupled. Excitation of arbitrary output modes of the system is realized by controlling classical and quantum interferences. This report demonstrates a highly multimode platform for multiphoton interference experiments and provides a powerful method to program a general high-dimensional multiport optical circuit. This work paves the way for the next generation of photonic devices for quantum simulation, computing, and communication. PMID:27152325

  5. Search for two-photon production of f{sub J}(2220)/{xi}(2230) at CLEO

    SciTech Connect

    Galik, Richard S.

    1997-05-20

    We use the CLEO detector at the Cornell e{sup +}e{sup -} storage ring, CESR, to search for the two-photon production of the glueball candidate f{sub J}(2220) in its decay to K{sub s}K{sub s}. We present a restrictive upper limit on the product of the two-photon partial width and the K{sub s}K{sub s} branching fraction, {gamma}{sub {gamma}}{sub {gamma}}{center_dot}B{sub K{sub s}}{sub K{sub s}} for this narrow resonance. We use this limit to calculate a lower limit on the stickiness, which is a measure of the two-gluon coupling relative to the two-photon coupling. This limit on stickiness indicates that the f{sub J}(2220) has substantial glueball content.

  6. Two-photon excited UV fluorescence for protein crystal detection

    PubMed Central

    Madden, Jeremy T.; DeWalt, Emma L.; Simpson, Garth J.

    2011-01-01

    Two-photon excited ultraviolet fluorescence (TPE-UVF) microscopy is explored for sensitive protein-crystal detection as a complement to second-order nonlinear optical imaging of chiral crystals (SONICC). Like conventional ultraviolet fluorescence (UVF), TPE-UVF generates image contrast based on the intrinsic fluorescence of aromatic residues, generally producing higher fluorescence emission within crystals than the mother liquor by nature of the higher local protein concentration. However, TPE-UVF has several advantages over conventional UVF, including (i) insensitivity to optical scattering, allowing imaging in turbid matrices, (ii) direct compatibility with conventional optical plates and windows by using visible light for excitation, (iii) elimination of potentially damaging out-of-plane UV excitation, (iv) improved signal to noise through background reduction from out-of-plane excitation and (v) relatively simple integration into instrumentation developed for SONICC. PMID:21931215

  7. Four-dimensional multi-site two-photon excitation

    NASA Astrophysics Data System (ADS)

    Daria, Vincent R.; Stricker, Christian; Bowman, Richard; Bachor, Hans-A.; Redman, Stephen

    2010-02-01

    We use the holographic method to project an arbitrary array of diffraction-limited focal spots suitable for multi-site twophoton excitation. The spot array can be projected arbitrarily within a three-dimensional (3D) volume, while the fourth dimension in time is attributed to high temporal resolution via high-speed non-iterative calculation of the hologram using a video graphics accelerator board. We show that the spots have sufficient energy and spatiotemporal photon density for localized two-photon excitation at individual spots in the array. The significance of this work points to 3D microscopy, non-linear micro-fabrication, volume holographic optical storage and biomedical instrumentation. In neuroscience, timecritical release of neurotransmitters at multiple sites within complex dendritic trees of neurons can lead to insights on the mechanisms of information processing in the brain.

  8. Two-photon excited UV fluorescence for protein crystal detection

    SciTech Connect

    Madden, Jeremy T.; DeWalt, Emma L.; Simpson, Garth J.

    2011-10-01

    Complementary measurements using SONICC and TPE-UVF allow the sensitive and selective detection of protein crystals. Two-photon excited ultraviolet fluorescence (TPE-UVF) microscopy is explored for sensitive protein-crystal detection as a complement to second-order nonlinear optical imaging of chiral crystals (SONICC). Like conventional ultraviolet fluorescence (UVF), TPE-UVF generates image contrast based on the intrinsic fluorescence of aromatic residues, generally producing higher fluorescence emission within crystals than the mother liquor by nature of the higher local protein concentration. However, TPE-UVF has several advantages over conventional UVF, including (i) insensitivity to optical scattering, allowing imaging in turbid matrices, (ii) direct compatibility with conventional optical plates and windows by using visible light for excitation, (iii) elimination of potentially damaging out-of-plane UV excitation, (iv) improved signal to noise through background reduction from out-of-plane excitation and (v) relatively simple integration into instrumentation developed for SONICC.

  9. Ordering of azobenzenes by two-photon isomerization.

    PubMed

    Ishitobi, Hidekazu; Sekkat, Zouheir; Kawata, Satoshi

    2006-10-28

    We report on light induced orientation by two-photon isomerization of azobenzenes in films of polymer. The dynamics of isomerization and orientation by one-photon absorption and two-photon absorption (TPA) are similar, and TPA creates a degree of molecular orientation which is comparable to that achieved by single-photon isomerization, in agreement with the theoretical predictions of two-photon isomeric orientation. PMID:17092131

  10. Two-photon absorption in Hg 2Cl 2 crystals

    NASA Astrophysics Data System (ADS)

    Pelant, I.; Ambrož, M.; Hála, J.; Kohlová, V.; Barta, Č.

    1985-01-01

    Violet luminescence (396 nm) of Hg 2Cl 2 single crystals was observed under excitation of green light (∼ 500 nm) of a pulsed dye laser at liquid helium temperature. The effect is interpreted as due to the two-photon absorption process. The two-photon excitation spectrum of the luminescence was measured in the wavelength range 475-530 nm. Possible mechanisms of the two-photon transition are outlined.

  11. Ordering of azobenzenes by two-photon isomerization

    SciTech Connect

    Ishitobi, Hidekazu; Sekkat, Zouheir; Kawata, Satoshi

    2006-10-28

    We report on light induced orientation by two-photon isomerization of azobenzenes in films of polymer. The dynamics of isomerization and orientation by one-photon absorption and two-photon absorption (TPA) are similar, and TPA creates a degree of molecular orientation which is comparable to that achieved by single-photon isomerization, in agreement with the theoretical predictions of two-photon isomeric orientation.

  12. Resonance production in two-photon interactions

    SciTech Connect

    Roe, N.A.

    1989-02-01

    Resonance production in two-photon interactions is studied using data collected with the ASP detector at the PEP e/sup +/e/sup /minus// storage ring located at the Stanford Linear Accelerator Center. The ASP detector is a non-magnetic lead-glass calorimeter constructed from 632 lead-glass bars. It covers 94% of 4..pi.. in solid angle, extending to within 20/degree/ of the beamline. Lead-scintillator calorimeters extend the coverage to within 21 mr of the beamline on both sides. Energy resolution of ..sqrt..E/10%, where E is the energy is GeV, is achieved for electrons and photons in the lead-glass calorimeter, and particle trajectories are reconstructed with high efficiency. A total luminosity of 108 pb/sup /minus/1/ was collected with the ASP detector at a center-of-mass energy of 29 GeV. The observed process is e/sup +/e/sup /minus// ..-->.. e/sup +/e/sup /minus//..gamma..*..gamma..* ..-->.. e/sup +/e/sup /minus//X, is a pseudoscalar resonance (J/sup PC/ = 0/sup /minus/+/) and ..gamma..* is a virtual (mass /ne/ 0) photon. The outgoing electrons scatter down the beampipe and are not detected. The observed resonances are the /eta/ and /eta/' mesons, with masses of 549 and 958 MeV, respectively. They are detected in the ..gamma gamma.. decay mode; a total of 2380 +- 49 /eta/ ..-->.. ..gamma gamma.. and 568 +- 26 /eta/' ..-->.. ..gamma gamma.. events are observed. From the number of events, the detection efficiency, and the calculated production cross sections the radiative widths, GAMMA/sub ..gamma gamma../, of the /eta/ and /eta/' were measured and found to be: GAMMA/sub ..gamma gamma../(/eta/) = .481 +- .010 +- .047keV and GAMMA/sub ..gamma gamma../(/eta/') = 4.71 +- .22 +- .70keV. These results are in good agreement with the world average values. 67 refs., 42 figs., 20 tabs.

  13. Large two-atom two-photon vacuum Rabi oscillations in a high-quality cavity

    SciTech Connect

    Pathak, P.K.; Agarwal, G.S.

    2004-10-01

    We predict a large cooperative effect involving two-atom two-photon vacuum Rabi oscillations in a high-quality cavity. The two-photon emission occurs as a result of simultaneous deexcitation of both atoms with two-photon resonance condition {omega}{sub 1}+{omega}{sub 2}{approx_equal}{omega}{sub a}+{omega}{sub b}, where {omega}{sub 1},{omega}{sub 2} are the atomic transition frequencies and {omega}{sub a},{omega}{sub b} are the frequencies of the emitted photons. The actual resonance condition depends on the vacuum Rabi couplings. The effect can be realized either with identical atoms in a bimodal cavity or with nonidentical atoms in a single-mode cavity.

  14. Investigation of two-photon absorption induced excited state absorption in a fluorenyl-based chromophore.

    PubMed

    Li, Changwei; Yang, Kun; Feng, Yan; Su, Xinyan; Yang, Junyi; Jin, Xiao; Shui, Min; Wang, Yuxiao; Zhang, Xueru; Song, Yinglin; Xu, Hongyao

    2009-12-01

    Two-photon absorption induced excited state absorption in the solution of a new fluorenyl-based chromophore is investigated by a time-resolved pump-probe technique using femtosecond pulses. With the help of an additional femtosecond open-aperture Z-scan technique, numerical simulations based on a three-energy level model are used to interpret the experimental results, and we determine the nonlinear optical parameters of this new chromophore uniquely. Large two-photon absorption cross section and excited state absorption cross section for singlet excited state are obtained, indicating a good candidate for optical limiting devices. Moreover, the influence of two-beam coupling induced energy transfer in neat N,N'-dimethylformamide solvent is also considered, although this effect is strongly restrained by the instantaneous two-photon absorption. PMID:19894682

  15. A multidimensional screening method for the selection of two-photon enhanced fluorescent proteins

    NASA Astrophysics Data System (ADS)

    Stoltzfus, Caleb; Barnett, Lauren; Rebane, Aleksander; Hughes, Thomas; Drobizhev, Mikhail; Wicks, Geoffrey; Mikhailov, Alexandr

    2014-03-01

    Two-photon excitation of fluorescent proteins (FPs) is widely used in imaging whole organisms or living tissues. Many different FPs are now available but these proteins have only been optimized for their one-photon properties. We have developed a technique for screening entire libraries of E. coli colonies expressing FPs that utilizes multiple wavelengths of linear excitation as well as two-photon excitation. Single mutations in a particular protein that affect one or twophoton properties are easily identified, providing new views of structure/function relationships. An amplified femtosecond Ti:sapphire laser and a spectrally filtered lamp source are used to acquire the fluorescence signals of up to ~1000 E. coli colonies on a standard Petri dish. Automation of the analysis and acquisition of the fluorescent signals makes it feasible to rapidly screen tens of thousands of colonies. In a proof of principle experiment with the commonly used EGFP, we used two rounds of error prone PCR and selection to evolve new proteins with shifted absorption and increased two-photon cross sections at 790nm. This method of screening, coupled with careful measurements of photo bleaching dynamics and two-photon cross sections, should make it possible to optimize a wide variety of fluorescent proteins and biosensors for use in two-photon microscopes.

  16. Titanium: Sapphire laser as an excitation source in two-photon spectroscopy

    SciTech Connect

    Fisher, W.G.; Wachter, E.A.; Armas, M.; Seaton, C.

    1997-02-01

    The passively mode-locked titanium:sapphire laser provides new opportunities for acquiring two-photon spectral data in the near-infrared, a region not commonly accessible to synchronously pumped dye lasers. This source generates pulses with peak powers near 100 kW at average powers over 1 W and is capable of yielding two-photon signals roughly two orders of magnitude larger than is possible with synchronously pumped dye lasers. However, the multimode output of this laser exhibits significant temporal and spectral pulse profile variations as the laser wavelength is tuned. As a consequence, peak powers of the titanium:sapphire laser can vary independently from average power across the tuning range. This wavelength dependence, coupled with the quadratic dependence of the two-photon signal upon the instantaneous power of the laser, precludes simple average power correction of nonlinear spectral band shapes. Here, we investigate the key properties of the titanium:sapphire laser as an excitation source for two-photon spectroscopy. We also identify a chemical reference suitable for obtaining source-corrected excitation spectra in the near-infrared using a double-beam, ratiometric approach; this is based on a source-independent two-photon excitation spectrum for the laser dye coumarin-480 that has been obtained with a single-frequency titanium:sapphire laser. From these data, correction factors are generated for correction of multimode source data. {copyright} {ital 1997} {ital Society for Applied Spectroscopy}

  17. Two-photon interference with true thermal light

    SciTech Connect

    Zhai Yanhua; Zhang Da; Wu Lingan; Chen Xihao

    2005-10-15

    Two-photon interference and 'ghost' imaging with entangled light have attracted much attention since the last century because of features such as nonlocality and subwavelength effects. Recently, it has been found that pseudothermal light can mimic certain effects of entangled light. We report here the first observation of two-photon interference with true thermal light.

  18. Two-photon fluorescence excitation spectroscopy of biological molecules

    NASA Astrophysics Data System (ADS)

    Meshalkin, Yuri P.; Alfimov, E. E.; Groshev, D. E.; Makukha, V. K.

    1996-06-01

    The UV fluorescence spectra of aromatic amino-acids and some proteins at two photon excitation by second harmonic of Nd:YAG laser are received. Two-photon absorption cross sections of tryptophan, tyrosine, phenylalanine and proteins: bovine serum albumin, lysozyme, trypsin, (alpha) - chymotrypsinogen and pepsin at wavelength 532 nm were measured by means of the two-quantum standard method.

  19. Quantum information processing with narrow band two-photon state

    NASA Astrophysics Data System (ADS)

    Lu, Yajun

    Application of quantum sources in communication and information processing are believed to bring a new revolution to the on-going information age. The generation of applicable quantum sources such as single photon state and two-photon state, appears to be one of the most difficult in experimental quantum optics. Spontaneous Parametric Down-Conversion (PDC) is known to generate two-photon state, but bandwidth problem makes it less applicable in quantum information processing. The aim of this work is to generate a narrow band two-photon state and apply it to quantum information processing. We start by developing a cavity enhanced PDC device to narrow the bandwidth of the two-photon state. Direct measurement of the bandwidth of the generated state has been made and the quantum theory of such a device has been investigated. An application of this narrow band two-photon state is to generate anti-bunched photons for quantum cryptography, based on the quantum interference between the two-photon state and a coherent state. The feasibility of this scheme for pulsed pump is also investigated. When applying the concept of mode locking in lasers to a two-photon state, we have mode-locked two-photon state which exhibits a comb-like correlation function and may be used for engineering of quantum states in time domain. Other applications such as demonstration of single photon nonlocality, nonlinear sign gate in quantum computation, and direct measurement of quantum beating, will also be addressed.

  20. Two-photon upconversion affected by intermolecule correlations near metallic nanostructures

    NASA Astrophysics Data System (ADS)

    Osaka, Yoshiki; Yokoshi, Nobuhiko; Ishihara, Hajime

    2016-04-01

    We investigate an efficient two-photon upconversion process in more than one molecule coupled to an optical antenna. In the previous paper [Y. Osaka et al., Phys. Rev. Lett. 112, 133601 (2014), 10.1103/PhysRevLett.112.133601], we considered the two-photon upconversion process in a single molecule within one-dimensional input-output theory and revealed that controlling the antenna-molecule coupling enables the efficient upconversion with radiative loss in the antenna suppressed. In this paper, aiming to propose a way to enhance the total probability of antenna-photon scattering, we extend the model to the case of multiple molecules. In general, the presence of more than one molecule decreases the upconversion probability because they equally share the energy of the two photons. However, it is shown that we can overcome the difficulty by controlling the intermolecule coupling. Our result implies that, without increasing the incident photon number (light power), we can enlarge the net probability of the two-photon upconversion.

  1. Two-Photon Fluorescence Spectroscopy and Imaging of 4-Dimethylaminonaphthalimide-Peptide and Protein Conjugates

    PubMed Central

    McLean, Alan M.; Socher, Elke; Varnavski, Oleg; Clark, Travis B.

    2014-01-01

    We report detailed photophysical studies on the two-photon fluorescence processes of the solvatochromic fluorophore 4-DMN as a conjugate of the important calmodulin (CaM) and the associated CaM-binding peptide M13. Strong two-photon fluorescence enhancement has been observed which is associated with calcium binding. It is found that the two-photon absorption cross-section is strongly dependent on the local environment surrounding the 4-DMN fluorophore in the CaM conjugates, providing sensitivity between sites of fluorophore attachment. Utilizing time-resolved measurements, the emission dynamics of 4-DMN under various environmental (solvent) conditions are analyzed. In addition, anisotropy measurements reveal that the 4-DMN-S38C-CaM system has restricted rotation in the calcium-bound calmodulin. To establish the utility for cellular imaging, two-photon fluorescence microscopy studies were also carried out with the 4-DMN-modified M13 peptide in cells. Together, these studies provide strong evidence that 4-DMN is a useful probe in two-photon imaging, with advantageous properties for cellular experiments. PMID:24245815

  2. Synthesis of Two-Photon Materials and Two-Photon Liquid Crystals

    NASA Technical Reports Server (NTRS)

    Subramaniam, Girija

    2001-01-01

    The duration of the grant was interrupted by two major accidents that the PI met with-- an auto accident in Pasadena, CA during her second summer at JPL which took almost eight months for recovery and a second accident during Fall 2000 that left her in crutches for the entire semester. Further, the time released agreed by the University was not given in a timely fashion. The candidate has been given post-grant expire time off. In spite of all these problems, the PI synthesized a number of new two-photon materials and studied the structure-activity correlation to arrive at the best-optimized structure. The PI's design proved to be one of the best in the sense that these materials has a hitherto unreported two-photon absorption cross section. Many materials based on PI's design was later made by the NASA colleague. This is Phase 1. Phase II of this grant is to orate liquid crystalline nature into this potentially useful materials and is currently in progress. Recent observations of nano- and pico-second response time of homeotropically aligned liquid crystals suggest their inherent potentials to act as laser hardening materials, i.e., as protective devices against short laser pulses. The objective of the current project is to exploit this potential by the synthesis of liquid crystals with high optical nonlinearity and optimizing their performance. The PI is trying structural variations to bring in liquid crystalline nature without losing the high two-photon cross section. Both Phase I and Phase II led to many invited presentations and publications in reputed journals like 'Science' and 'Molecular Crystals'. The list of presentations and reprints are enclosed. Another important and satisfying outcome of this grant is the opportunity that this grant offered to the budding undergraduate scientists to get involved in a visible research of international importance. All the students had a chance to learn a lot during research, had the opportunity to present their work at

  3. Chimera-type states induced by local coupling

    NASA Astrophysics Data System (ADS)

    Clerc, M. G.; Coulibaly, S.; Ferré, M. A.; García-Ñustes, M. A.; Rojas, R. G.

    2016-05-01

    Coupled oscillators can exhibit complex self-organization behavior such as phase turbulence, spatiotemporal intermittency, and chimera states. The latter corresponds to a coexistence of coherent and incoherent states apparently promoted by nonlocal or global coupling. Here we investigate the existence, stability properties, and bifurcation diagram of chimera-type states in a system with local coupling without different time scales. Based on a model of a chain of nonlinear oscillators coupled to adjacent neighbors, we identify the required attributes to observe these states: local coupling and bistability between a stationary and an oscillatory state close to a homoclinic bifurcation. The local coupling prevents the incoherent state from invading the coherent one, allowing concurrently the existence of a family of chimera states, which are organized by a homoclinic snaking bifurcation diagram.

  4. Chimera-type states induced by local coupling.

    PubMed

    Clerc, M G; Coulibaly, S; Ferré, M A; García-Ñustes, M A; Rojas, R G

    2016-05-01

    Coupled oscillators can exhibit complex self-organization behavior such as phase turbulence, spatiotemporal intermittency, and chimera states. The latter corresponds to a coexistence of coherent and incoherent states apparently promoted by nonlocal or global coupling. Here we investigate the existence, stability properties, and bifurcation diagram of chimera-type states in a system with local coupling without different time scales. Based on a model of a chain of nonlinear oscillators coupled to adjacent neighbors, we identify the required attributes to observe these states: local coupling and bistability between a stationary and an oscillatory state close to a homoclinic bifurcation. The local coupling prevents the incoherent state from invading the coherent one, allowing concurrently the existence of a family of chimera states, which are organized by a homoclinic snaking bifurcation diagram. PMID:27300877

  5. Chimera states in purely local delay-coupled oscillators

    NASA Astrophysics Data System (ADS)

    Bera, Bidesh K.; Ghosh, Dibakar

    2016-05-01

    We study the existence of chimera states in a network of locally coupled chaotic and limit-cycle oscillators. The necessary condition for chimera state in purely local coupled oscillators is discussed. At first, we numerically observe the existence of chimera or multichimera states in the locally coupled Hindmarsh-Rose neuron model. We find that delay time in the nonlinear local coupling reduces the domain of the coherent island in the parameter space of the synaptic coupling strength and time delay, and thus the coherent region can be completely eliminated once the time delay exceeds a certain threshold. We then consider another form of nonlinearity in the local coupling, and the existence of chimera states is observed in the time-delayed Mackey-Glass system and in a Van der Pol oscillator. We also discuss the effect of time delay in local coupling for the existence of chimera states in Mackey-Glass systems. The nonlinearity present in the coupling function plays a key role in the emergence of chimera or multichimera states. A phase diagram for the chimera state is identified over a wide parameter space.

  6. Exchange coupling between localized defect states in graphene nanoflakes

    NASA Astrophysics Data System (ADS)

    Droth, Matthias; Burkard, Guido

    2014-03-01

    Graphene nanoflakes are interesting because electrons are naturally confined in these quasi zero-dimensional structures, thus eluding the need for a bandgap. Defects inside the graphene lattice lead to localized states and the spins of two such localized states may be used for spintronics. We perform a tight-binding description on the entire system and, by virtue of a Schrieffer-Wolff-transformation on the bonding and antibonding states, we extract the coupling strength between the localized states. The coupling strength allows us to estimate the exchange coupling, which governs the dynamics of singlet-triplet spintronics.

  7. Two-photon induced polymerization of photo-driven microsensors

    NASA Astrophysics Data System (ADS)

    Lin, Chih-Lang; Wang, Irene; Bouriau, Michel; Casalegno, Roger; Andraud, Chantal; Baldeck, Patrice L.

    2004-10-01

    We report on the fabrication of photo-driven polymer microsensors for viscosimetry, velocimetry and micropump applications. They are readily made with a low-cost polymerization technique based on two-photon absorption. Microsensors are free-floating in the liquid to be characterized. A linearly-polarized optical tweezers is used to trap one sensor at the laser focal point and to generate the optical torque needed for local hydrodynamic measurements. Viscosity and velocity microsensors have slab shapes that align in the polarization direction. The local viscosity is deduced from the maximum rotation frequency generated by the rotating linear polarization, while the fluid velocity is obtained by measuring the maximum angle that equilibrates the optical torque and drag torque. Experimental results are in good agreement with theoretical calculations. The micropump is based on a micron-size Archimedes screw that rotates around its long axis when it is trapped at the focal point. The laser-induced rotation is due to the optical torque that is transferred by the laser scattering on the screw.

  8. Characterization of one- and two-photon photochemical uncaging efficiency.

    PubMed

    Specht, Alexandre; Bolze, Frederic; Nicoud, Jean Francois; Goeldner, Maurice

    2013-01-01

    The idea of using light to unleash biologically active compounds from inert precursors (uncaging) was introduced over 30 years ago. Recent efforts prompted the development of photoremovable protecting groups that have increased photochemical efficiencies for one- and two-photon excitation to allow more sophisticated applications. This requires characterization of one- and two-photon photochemical efficiencies of the uncaging processes.The present chapter focuses on the characterization of one-photon quantum yields and two-photon cross-sections. PMID:23494373

  9. Random access three-dimensional two-photon microscopy.

    PubMed

    Rózsa, Balázs; Katona, Gergely; Vizi, E Sylvester; Várallyay, Zoltán; Sághy, Attila; Valenta, Lásló; Maák, Pál; Fekete, Júlia; Bányász, Akos; Szipocs, Róbert

    2007-04-01

    We propose a two-photon microscope scheme capable of real-time, three-dimensional investigation of the electric activity pattern of neural networks or signal summation rules of individual neurons in a 0.6 mm x 0.6 mm x 0.2 mm volume of the sample. The points of measurement are chosen according to a conventional scanning two-photon image, and they are addressed by separately adjustable optical fibers. This allows scanning at kilohertz repetition rates of as many as 100 data points. Submicrometer spatial resolution is maintained during the measurement similarly to conventional two-photon microscopy. PMID:17356631

  10. Investigating femtosecond-laser-induced two-photon photoacoustic generation

    PubMed Central

    Urban, Ben E.; Yi, Ji; Yakovlev, Vladislav; Zhang, Hao F.

    2014-01-01

    Abstract. We investigated two-photon absorption-based photoacoustic generation and compared it with corresponding photoluminescence emission. Experimental results revealed expected quadratic dependences on the incident optical fluence in both photoacoustic and photoluminescence processes. We also investigated the influence of optical scattering on the generation of two-photon photoacoustic and photoluminescence signals and found that photoacoustic signals attenuated more slowly than photoluminescence signals when the optical scattering coefficient was increased, which was attributed to a weaker ultrasonic attenuation than that the optical attenuation in the scattering medium. Finally, we showed three-dimensional two-photon photoacoustic imaging. PMID:25084119

  11. Enhancement of two photon absorption properties and intersystem crossing by charge transfer in pentaaryl boron-dipyrromethene (BODIPY) derivatives.

    PubMed

    Küçüköz, B; Sevinç, G; Yildiz, E; Karatay, A; Zhong, F; Yılmaz, H; Tutel, Y; Hayvalı, M; Zhao, J; Yaglioglu, H G

    2016-05-11

    Novel BODIPY derivatives containing N,N-diphenylamine, 4-methoxyphenyl, 2,4-dimethoxyphenyl, triphenylamine, and 1-pyrene moieties were designed and synthesized for the first time by employing the palladium-catalyzed Suzuki-Miyaura coupling on pentaaryl boron dipyrromethene compounds. The effect of various moieties and charge transfer on linear and nonlinear optical absorption was investigated. It was found that moieties with strong electron donor properties and long conjugation lengths increase charge transfer and enhance intersystem crossing in the investigated compounds. Besides, the investigated compounds showed strong two photon absorption properties at near infrared wavelengths (800 nm and 900 nm), which is required for two photon photodynamic therapy. Two photon absorption cross section values were found to be 83, 454, 331, 472 and 413 GM for , , , and compounds at 800 nm wavelength, respectively. The highest two-photon absorption cross-section value was obtained for the compound containing a triphenylamine moiety due to its more efficient charge transfer characteristics. Strong two-photon absorption properties in the near infrared region, efficient intersystem crossing and heavy atom free nature of the investigated compounds make them good candidates for two photon photodynamic therapy applications. We believe that this work will be one of the leading studies for two-photon photodynamic therapy applications of pentaaryl BODIPY derivatives. PMID:27138347

  12. Two-Photon-Absorption Scheme for Optical Beam Tracking

    NASA Technical Reports Server (NTRS)

    Ortiz, Gerardo G.; Farr, William H.

    2011-01-01

    A new optical beam tracking approach for free-space optical communication links using two-photon absorption (TPA) in a high-bandgap detector material was demonstrated. This tracking scheme is part of the canonical architecture described in the preceding article. TPA is used to track a long-wavelength transmit laser while direct absorption on the same sensor simultaneously tracks a shorter-wavelength beacon. The TPA responsivity was measured for silicon using a PIN photodiode at a laser beacon wavelength of 1,550 nm. As expected, the responsivity shows a linear dependence with incident power level. The responsivity slope is 4.5 x 10(exp -7) A/W2. Also, optical beam spots from the 1,550-nm laser beacon were characterized on commercial charge coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) imagers with as little as 13.7 microWatts of optical power (see figure). This new tracker technology offers an innovative solution to reduce system complexity, improve transmit/receive isolation, improve optical efficiency, improve signal-to-noise ratio (SNR), and reduce cost for free-space optical communications transceivers.

  13. Imperfect traveling chimera states induced by local synaptic gradient coupling

    NASA Astrophysics Data System (ADS)

    Bera, Bidesh K.; Ghosh, Dibakar; Banerjee, Tanmoy

    2016-07-01

    In this paper, we report the occurrence of chimera patterns in a network of neuronal oscillators, which are coupled through local, synaptic gradient coupling. We discover a new chimera pattern, namely the imperfect traveling chimera state, where the incoherent traveling domain spreads into the coherent domain of the network. Remarkably, we also find that chimera states arise even for one-way local coupling, which is in contrast to the earlier belief that only nonlocal, global, or nearest-neighbor local coupling can give rise to chimera state; this find further relaxes the essential connectivity requirement of getting a chimera state. We choose a network of identical bursting Hindmarsh-Rose neuronal oscillators, and we show that depending upon the relative strength of the synaptic and gradient coupling, several chimera patterns emerge. We map all the spatiotemporal behaviors in parameter space and identify the transitions among several chimera patterns, an in-phase synchronized state, and a global amplitude death state.

  14. Imperfect traveling chimera states induced by local synaptic gradient coupling.

    PubMed

    Bera, Bidesh K; Ghosh, Dibakar; Banerjee, Tanmoy

    2016-07-01

    In this paper, we report the occurrence of chimera patterns in a network of neuronal oscillators, which are coupled through local, synaptic gradient coupling. We discover a new chimera pattern, namely the imperfect traveling chimera state, where the incoherent traveling domain spreads into the coherent domain of the network. Remarkably, we also find that chimera states arise even for one-way local coupling, which is in contrast to the earlier belief that only nonlocal, global, or nearest-neighbor local coupling can give rise to chimera state; this find further relaxes the essential connectivity requirement of getting a chimera state. We choose a network of identical bursting Hindmarsh-Rose neuronal oscillators, and we show that depending upon the relative strength of the synaptic and gradient coupling, several chimera patterns emerge. We map all the spatiotemporal behaviors in parameter space and identify the transitions among several chimera patterns, an in-phase synchronized state, and a global amplitude death state. PMID:27575131

  15. Strong and Coherent Coupling between Localized and Propagating Phonon Polaritons.

    PubMed

    Gubbin, Christopher R; Martini, Francesco; Politi, Alberto; Maier, Stefan A; De Liberato, Simone

    2016-06-17

    Following the recent observation of localized phonon polaritons in user-defined silicon carbide nanoresonators, here we demonstrate strong and coherent coupling between those localized modes and propagating phonon polaritons bound to the surface of the nanoresonator's substrate. In order to obtain phase matching, the nanoresonators have been fabricated to serve the double function of hosting the localized modes, while also acting as a grating for the propagating ones. The coherent coupling between long lived, optically accessible localized modes, and low-loss propagative ones, opens the way to the design and realization of phonon-polariton based coherent circuits. PMID:27367398

  16. Strong and Coherent Coupling between Localized and Propagating Phonon Polaritons

    NASA Astrophysics Data System (ADS)

    Gubbin, Christopher R.; Martini, Francesco; Politi, Alberto; Maier, Stefan A.; De Liberato, Simone

    2016-06-01

    Following the recent observation of localized phonon polaritons in user-defined silicon carbide nanoresonators, here we demonstrate strong and coherent coupling between those localized modes and propagating phonon polaritons bound to the surface of the nanoresonator's substrate. In order to obtain phase matching, the nanoresonators have been fabricated to serve the double function of hosting the localized modes, while also acting as a grating for the propagating ones. The coherent coupling between long lived, optically accessible localized modes, and low-loss propagative ones, opens the way to the design and realization of phonon-polariton based coherent circuits.

  17. Coupling Identical one-dimensional Many-Body Localized Systems

    NASA Astrophysics Data System (ADS)

    Bordia, Pranjal; Lüschen, Henrik P.; Hodgman, Sean S.; Schreiber, Michael; Bloch, Immanuel; Schneider, Ulrich

    2016-04-01

    We experimentally study the effects of coupling one-dimensional many-body localized systems with identical disorder. Using a gas of ultracold fermions in an optical lattice, we artificially prepare an initial charge density wave in an array of 1D tubes with quasirandom on-site disorder and monitor the subsequent dynamics over several thousand tunneling times. We find a strikingly different behavior between many-body localization and Anderson localization. While the noninteracting Anderson case remains localized, in the interacting case any coupling between the tubes leads to a delocalization of the entire system.

  18. Identifying parameters to describe local land-atmosphere coupling

    NASA Astrophysics Data System (ADS)

    Ek, M. B.; Jacobs, C. M.; Santanello, J. A.; Tuinenburg, O.

    2009-12-01

    The Global Energy and Water Cycle Experiment (GEWEX) Land-Atmosphere System Study / Local Coupling (GLASS/LoCo) project seeks to understand the role of local land-atmosphere coupling in the evolution of surface fluxes and boundary layer state variables including clouds. The theme of land-atmosphere interaction is a research area that is rapidly developing; after the well-known GLACE experiments and various diagnostic studies, new research has evolved in modeling and observing the degree of land-atmosphere coupling on local scales. Questions of interest are (1) how much is coupling related to local versus "remote" processes, (2) what is the nature and strength of coupling, and (3) how does this change (e.g. for different temporal and spatial scales, geographic regions, and changing climates). As such, this is an important issue on both weather and climate time scales. The GLASS/LoCo working group is investigating diagnostics to quantify land-atmosphere coupling. Coupling parameters include the roles of soil moisture and surface evaporative fraction as well as the evolving atmospheric boundary layer and boundary-layer entrainment. After suitable diagnostic parameters are identified, observational data and output from weather and climate models will be used to "map" land-atmosphere coupling in regards to (1)-(3) above.

  19. Two-Photon Fluorescence Microscopy for Biomedical Research

    NASA Technical Reports Server (NTRS)

    Fischer, David; Zimmerli, Greg; Asipauskas, Marius

    2007-01-01

    This viewgraph presentation gives an overview of two-photon microscopy as it applies to biomedical research. The topics include: 1) Overview; 2) Background; 3) Principles of Operation; 4) Advantages Over Confocal; 5) Modes of Operation; and 6) Applications.

  20. Pulse-shaping based two-photon FRET stoichiometry

    PubMed Central

    Flynn, Daniel C.; Bhagwat, Amar R.; Brenner, Meredith H.; Núñez, Marcos F.; Mork, Briana E.; Cai, Dawen; Swanson, Joel A.; Ogilvie, Jennifer P.

    2015-01-01

    Förster Resonance Energy Transfer (FRET) based measurements that calculate the stoichiometry of intermolecular interactions in living cells have recently been demonstrated, where the technique utilizes selective one-photon excitation of donor and acceptor fluorophores to isolate the pure FRET signal. Here, we present work towards extending this FRET stoichiometry method to employ two-photon excitation using a pulse-shaping methodology. In pulse-shaping, frequency-dependent phases are applied to a broadband femtosecond laser pulse to tailor the two-photon excitation conditions to preferentially excite donor and acceptor fluorophores. We have also generalized the existing stoichiometry theory to account for additional cross-talk terms that are non-vanishing under two-photon excitation conditions. Using the generalized theory we demonstrate two-photon FRET stoichiometry in live COS-7 cells expressing fluorescent proteins mAmetrine as the donor and tdTomato as the acceptor. PMID:25836193

  1. Two-photon directed evolution of green fluorescent proteins

    NASA Astrophysics Data System (ADS)

    Stoltzfus, Caleb R.; Barnett, Lauren M.; Drobizhev, Mikhail; Wicks, Geoffrey; Mikhaylov, Alexander; Hughes, Thomas E.; Rebane, Aleksander

    2015-07-01

    Directed evolution has been used extensively to improve the properties of a variety of fluorescent proteins (FPs). Evolutionary strategies, however, have not yet been used to improve the two-photon absorption (2PA) properties of a fluorescent protein, properties that are important for two-photon imaging in living tissues, including the brain. Here we demonstrate a technique for quantitatively screening the two-photon excited fluorescence (2PEF) efficiency and 2PA cross section of tens of thousands of mutant FPs expressed in E. coli colonies. We use this procedure to move EGFP through three rounds of two-photon directed evolution leading to new variants showing up to a 50% enhancement in peak 2PA cross section and brightness within the near-IR tissue transparency wavelength range.

  2. Photodamage of mesotetraphenylporphyrin under one- and two-photon excitation

    SciTech Connect

    Wen Yanan; Liu Yuqiang; Yang Zhenling; Yang Yanqiang; Guo Ximing

    2010-08-15

    Photoinduced damage behavior of mesotetraphenylporphyrin (TPP) under one- and two-photon excitation with femtosecond laser pulses is investigated in the present work. Quenching in the luminescent intensity is observed. Results suggest that laser irradiation on TPP mainly causes two simultaneously occurring photoprocesses: photodamage and formation of a porphine-type photoproduct. The damage rate exhibits a linear dependence on the incident light power in one-photon excitation, whereas in two-photon excitation, the power dependence of the damage rate turns out to be exponential. The photoproduct formed in one- and two-photon excitation is identical. This product, which is observed to possess superior photostability and two-photon absorbing ability compared with the original TPP sensitizer, is likely to be treated as a secondary photosensitizer in the activation process of photodynamic therapy (PDT). This work might be helpful for the drug evaluation in the practical application of PDT.

  3. Two-photon directed evolution of green fluorescent proteins

    PubMed Central

    Stoltzfus, Caleb R.; Barnett, Lauren M.; Drobizhev, Mikhail; Wicks, Geoffrey; Mikhaylov, Alexander; Hughes, Thomas E.; Rebane, Aleksander

    2015-01-01

    Directed evolution has been used extensively to improve the properties of a variety of fluorescent proteins (FPs). Evolutionary strategies, however, have not yet been used to improve the two-photon absorption (2PA) properties of a fluorescent protein, properties that are important for two-photon imaging in living tissues, including the brain. Here we demonstrate a technique for quantitatively screening the two-photon excited fluorescence (2PEF) efficiency and 2PA cross section of tens of thousands of mutant FPs expressed in E. coli colonies. We use this procedure to move EGFP through three rounds of two-photon directed evolution leading to new variants showing up to a 50% enhancement in peak 2PA cross section and brightness within the near-IR tissue transparency wavelength range. PMID:26145791

  4. Two photon processes in ZnO quantum dots

    NASA Astrophysics Data System (ADS)

    Maikhuri, Deepti; Purohit, S. P.; Mathur, K. C.

    2016-01-01

    The two-photon bound-bound (TPBB) and the two-photon bound-free (TPBF) processes are studied for the electron in the initial 1S state in the conduction band of the ZnO quantum dot (QD) embedded in the HfO2 and the AlN matrices. The energy and the wave functions of the QD are obtained by using the effective mass approximation with a finite barrier height at the dot-matrix interface. Using the second order perturbation theory results are obtained for the two-photon absorption coefficient and the photoelectric cross section. The photoelectric cross section ratio for the circularly to the linearly polarized photons is also obtained. It is observed that the two-photon processes depend significantly on the polarization of the incident beam, the dot size, and the surrounding matrix. It is found that the electric quadrupole interaction enhance the TPBF photoelectric cross section.

  5. Two-photon transitions to excited states in atomic hydrogen

    SciTech Connect

    Quattropani, A.; Bassani, F.; Carillo, S.

    1982-06-01

    Resonant two-photon transition rates from the ground state of atomic hydrogen to ns excited states have been computed as a function of photon frequencies in the length and velocity gauges in order to test the accuracy of the calculation and to discuss the rate of convergence over the intermediate states. The dramatic structure of the transition rates produced by intermediate-state resonances is exhibited. A two-photon transparency is found in correspondence to each resonance.

  6. The use of CNDO in spectroscopy. XV. Two photon absorption

    NASA Astrophysics Data System (ADS)

    Marchese, Francis T.; Seliskar, C. J.; Jaffé, H. H.

    1980-04-01

    Two-photon absorptivities have been calculated within the CNDO/S-CI molecular orbital framework of Del Bene and Jaffé utilizing the second order time dependent perturbation equations of Göppert-Mayer and polarization methods of McClain. Good agreement is found between this theory and experiment for transition energies, symmetries, and two-photon absorptivities for the following molecules: biphenyl, terphenyl, 2,2'-difluorobiphenyl, 2,2'-bipyridyl, phenanthrene, and the isoelectronic series: fluorene, carbazole, dibenzofuran.

  7. In Vivo Cell Tracking Using Two-Photon Microscopy.

    PubMed

    Malide, Daniela

    2016-01-01

    Recently we have explored and developed approaches imaging using confocal/two-photon microscopy, which enables simultaneous high-resolution assessment of specifically fluorescently marked cells in conjunction with structural components of the tissues visualized via harmonic generated signals. This approach uses commercially available confocal and two-photon laser microscope and automated user-interactive image analysis methods based on commercially available software packages allowing easy implementation in usual microscopy facilities. PMID:27283422

  8. Two-photon photovoltaic effect in gallium arsenide.

    PubMed

    Ma, Jichi; Chiles, Jeff; Sharma, Yagya D; Krishna, Sanjay; Fathpour, Sasan

    2014-09-15

    The two-photon photovoltaic effect is demonstrated in gallium arsenide at 976 and 1550 nm wavelengths. A waveguide-photodiode biased in its fourth quadrant harvests electrical power from the optical energy lost to two-photon absorption. The experimental results are in good agreement with simulations based on nonlinear wave propagation in waveguides and the drift-diffusion model of carrier transport in semiconductors. Power efficiency of up to 8% is theoretically predicted in optimized devices. PMID:26466255

  9. Voigt spectral profiles in two-photon resonance fluorescence

    SciTech Connect

    Alexanian, Moorad; Bose, Subir K.

    2007-11-15

    A recent work on two-photon fluorescence is extended by considering the pump field to be a coherent state, which represents a laser field operating well above threshold. The dynamical conditions are investigated under which the two-photon spectrum gives rise, in addition to a Lorentzian line shape at the pump frequency, to two Voigt spectral sideband profiles. Additional conditions are found under which the Voigt profile behaves like either a Gaussian or a Lorentzian line shape.

  10. Uniform silica nanoparticles encapsulating two-photon absorbing fluorescent dye

    SciTech Connect

    Wu Weibing; Liu Chang; Wang Mingliang; Huang Wei; Zhou Shengrui; Jiang Wei; Sun Yueming; Cui Yiping; Xu Chunxinag

    2009-04-15

    We have prepared uniform silica nanoparticles (NPs) doped with a two-photon absorbing zwitterionic hemicyanine dye by reverse microemulsion method. Obvious solvatochromism on the absorption spectra of dye-doped NPs indicates that solvents can partly penetrate into the silica matrix and then affect the ground and excited state of dye molecules. For dye-doped NP suspensions, both one-photon and two-photon excited fluorescence are much stronger and recorded at shorter wavelength compared to those of free dye solutions with comparative overall dye concentration. This behavior is possibly attributed to the restricted twisted intramolecular charge transfer (TICT), which reduces fluorescence quenching when dye molecules are trapped in the silica matrix. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells with low cytotoxicity. - Graphical abstract: Water-soluble silica NPs doped with a two-photon absorbing zwitterionic hemicyanine dye were prepared. They were found of enhanced one-photon and two-photon excited fluorescence compared to free dye solutions. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells.

  11. Primordial helium recombination. II. Two-photon processes

    SciTech Connect

    Hirata, Christopher M.; Switzer, Eric R.

    2008-04-15

    Interpretation of precision measurements of the cosmic microwave background (CMB) will require a detailed understanding of the recombination era, which determines such quantities as the acoustic oscillation scale and the Silk damping scale. This paper is the second in a series devoted to the subject of helium recombination, with a focus on two-photon processes in He i. The standard treatment of these processes includes only the spontaneous two-photon decay from the 2{sup 1}S level. We extend this treatment by including five additional effects, some of which have been suggested in recent papers but whose impact on He i recombination has not been fully quantified. These are: (i) stimulated two-photon decays; (ii) two-photon absorption of redshifted He i line radiation; (iii) two-photon decays from highly excited levels in He i (n{sup 1}S and n{sup 1}D, with n{>=}3); (iv) Raman scattering; and (v) the finite width of the 2{sup 1}P{sup o} resonance. We find that effect (iii) is highly suppressed when one takes into account destructive interference between different intermediate states contributing to the two-photon decay amplitude. Overall, these effects are found to be insignificant: they modify the recombination history at the level of several parts in 10{sup 4}.

  12. Two Photon Polymerization of Microneedles for Transdermal Drug Delivery

    PubMed Central

    Gittard, Shaun D.; Ovsianikov, Aleksandr; Chichkov, Boris N.; Doraiswamy, Anand; Narayan, Roger J.

    2010-01-01

    Importance of the field Microneedles are small-scale devices that are finding use for transdermal delivery of protein-based pharmacologic agents and nucleic acid-based pharmacologic agents; however, microneedles prepared using conventional microelectronics-based technologies have several shortcomings, which have limited translation of these devices into widespread clinical use. Areas covered in this review Two photon polymerization is a laser-based rapid prototyping technique that has been recently used for direct fabrication of hollow microneedles with a wide variety of geometries. In addition, an indirect rapid prototyping method that involves two photon polymerization and polydimethyl siloxane micromolding has been used for fabrication of solid microneedles with exceptional mechanical properties. What the reader will gain In this review, the use of two photon polymerization for fabricating in-plane and out-of-plane hollow microneedle arrays is described. The use of two photon polymerization-micromolding for fabrication of solid microneedles is also reviewed. In addition, fabrication of microneedles with antimicrobial properties is discussed; antimicrobial microneedles may reduce the risk of infection associated with formation of channels through the stratum corneum. Take home message It is anticipated that the use of two photon polymerization as well as two photon polymerization-micromolding for fabrication of microneedles and other microstructured drug delivery devices will increase over the coming years. PMID:20205601

  13. Three-dimensional two-photon laser fabrication for metals, polymers, and magneto-optical materials

    NASA Astrophysics Data System (ADS)

    Tanaka, Takuo; Ishikawa, Atsushi; Amemiya, Tomohiro

    2015-03-01

    The three-dimensional (3D) two-photon laser fabrication techniques for metal, polymer, and magneto-optical structures are presented. Two-photon-induced reduction of metal complex ions was developed to create 3D metal micro/nano structures. Owing to the inhibition of unwanted growth of metal nano crystals using surfactant molecules, we have successfully improved the spatial resolution of fabricated metal structures down to 100 nm in linewidth. Arbitrary shaped 3D silver structures with high electric conductivity were fabricated. Two-photon-induced photopolymerization technique has been applied for the photonic wire bonding. We have demonstrated the optical interconnection of III-V based DFB lasers and photo detectors by polymer wires with optical coupling loss less than 0.3dB. We also applied two-photon laser irradiation technique for the modification of the magnetic properties of cerium-substituted yttrium iron garnet crystal (CexY3-xFe5O12: Ce:YIG). A Ce:YIG layer was epitaxially-grown on a monomagnetic garnet (<111>-SGGG) substrate. 3D fs laser scanning in the Ce:YIG layer creates the micrometer patterns of both refractive index and magnetic properties change of the crystal. We demonstrated the micro/nanometer scale patterning of both optical and magnetic properties in the Ce:YIG crystal.

  14. Dynamics and two-photon absorption properties of chromophore functionalized semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Varaganti, Shankar; Gessesse, Mathias; Obare, Sherine O.; Ramakrishna, Guda

    2009-08-01

    Two photon absorption cross-sections and fluorescence dynamics of Riboflavin, Fluorescein 548, Coumarin 519 and Quinizarin adsorbed onto reactive (TiO2) and non-reactive (ZrO2) semiconductor nanoparticles have been investigated. These dye molecules are chosen because of their inherently different anchoring groups with which they can bind to semiconductor nanoparticles giving a handle to probe the influence of anchoring group as well as molecule-nanoparticle electronic coupling on the two-photon absorption and nonlinear optical properties. Two-photon excited fluorescence technique has been utilized to monitor the two photon absorption cross-sections and the dynamics of singlet states are followed with femto second fluorescence upconversion. Interesting cross-section trends have been observed where the TPA cross-section of chromophore on ZrO2 surface is similar or lower to that of the free dye while the cross-sections seem to be higher on the surface of reactive TiO2 nanoparticle surface. Fluorescence upconversion investigations were able to probe the electronic interactions of the chromophore with semiconductor nanoparticle and also the adsorption of the chromophores on the surface of the nanoparticle.

  15. Two-photon exchange between two three-level atoms in separate cavities

    SciTech Connect

    Alexanian, Moorad

    2011-02-15

    The temporal evolution of two coupled cavities, each containing a single three-level atom, is studied when the cavities exchange two coherent photons. The general state of the system is a linear superposition of symmetric and antisymmetric states with the symmetric states controlled by two of the four eigenfrequencies and the antisymmetric states by the other two. The system undergoes Rabi oscillations between the two symmetric (antisymmetric) states. There is state transfer between the cavities when both atoms are in the ground state and two photons are exchanged. In addition, there is also Rabi ''flopping'' whereby one atom is in the excited state and the other in the ground state and the roles are reversed in a periodic fashion by the exchange of two photons. The generation of entanglement can be explicitly given as a function of time. Models of coupled cavities are of interest in distributed quantum information and computation.

  16. Mitochondrial organization and motility probed by two-photon microscopy in cultured mouse brainstem neurons

    SciTech Connect

    Mueller, Michael . E-mail: mike@neuro-physiol.med.uni-goettingen.de; Mironov, Sergej L.; Ivannikov, Maxim V.; Schmidt, Joerg; Richter, Diethelm W.

    2005-02-01

    Two-photon microscopy of rhodamine 123-labeled mitochondria revealed that mitochondria of neurons cultured from mouse respiratory center form functionally coupled, dynamically organized aggregates such as chains and clusters, while single mitochondria were rarely seen. Mitochondrial chain structures predominate in dendrites, while irregularly shaped mitochondrial clusters are mostly found in the soma. Both types of mitochondrial structures showed chaotic Brownian motions and the mitochondrial chains also revealed well-directed movements. The latter dislocations were arrested upon mitochondrial depolarization or blockade of mitochondrial ATP synthesis. Depolymerization of microtubules by colchicine or nocodazole or inhibition of protein phosphatases by calyculin A disrupted mitochondrial chains and the mitochondria accumulated in the soma. Forskolin and IBMX reversibly blocked directed movements of mitochondria, but did not affect their overall spatial distribution. Thus, protein phosphorylation seems to control both mitochondrial transport and organization. Protein phosphorylation downstream of enhanced cytosolic cAMP levels apparently regulates the transition from motile to non-motile mitochondria, while phosphorylation resulting from inhibition of types 1 and 2A protein phosphatases massively disturbs mitochondrial organization. The complex phosphorylation processes seem to control the close interaction of mitochondria and cytoskeleton which may guarantee that mitochondria are immobilized at energetic hot spots and rearranged in response to changes in local energy demands.

  17. Two-Photon Absorption of Metal-Assisted Chromophores.

    PubMed

    Li, Xin; Rinkevicius, Zilvinas; Ågren, Hans

    2014-12-01

    Aiming to understand the effect of a metal surface on nonlinear optical properties and the combined effects of surface and solvent environments on such properties, we present a multiscale response theory study, integrated with dynamics of the two-photon absorption of 4-nitro-4'-amino-trans-stilbene physisorbed on noble metal surfaces, considering two such surfaces, Ag(111) and Au(111), and two solvents, cyclohexane and water, as cases for demonstration. A few conclusions of general character could be drawn: While the geometrical change of the chromophore induced by the environment was found to notably alter (diminish) the two-photon absorption cross section in the polar medium, the effects of the metal surface and solvent on the electronic structure of the chromophore surpasses the geometrical effects and leads to a considerably enhanced two-photon absorption cross section in the polar solvent. This enhancement of two-photon absorption arises essentially from the metal charge image induced enlargement of the difference between the dipole moment of the excited state and the ground state. The orientation-dependence of the two-photon absorption is found to connect with the lateral rotation of the chromophore, where the two-photon absorption reaches its maximum when the polarization of the incident light coincides with the long-axis of the chromophore. Our results demonstrate a distinct enhancement of the two-photon absorption by a metal surface and a polar medium and envisage the employment of metal-chromophore composite materials for future development of nonlinear optical materials with desirable properties. PMID:26583246

  18. Subject-level measurement of local cortical coupling.

    PubMed

    Vandekar, Simon N; Shinohara, Russell T; Raznahan, Armin; Hopson, Ryan D; Roalf, David R; Ruparel, Kosha; Gur, Ruben C; Gur, Raquel E; Satterthwaite, Theodore D

    2016-06-01

    The human cortex is highly folded to allow for a massive expansion of surface area. Notably, the thickness of the cortex strongly depends on cortical topology, with gyral cortex sometimes twice as thick as sulcal cortex. We recently demonstrated that global differences in thickness between gyral and sulcal cortex continue to evolve throughout adolescence. However, human cortical development is spatially heterogeneous, and global comparisons lack power to detect localized differences in development or psychopathology. Here we extend previous work by proposing a new measure - local cortical coupling - that is sensitive to differences in the localized topological relationship between cortical thickness and sulcal depth. After estimation, subject-level coupling maps can be analyzed using standard neuroimaging analysis tools. Capitalizing on a large cross-sectional sample (n=932) of youth imaged as part of the Philadelphia Neurodevelopmental Cohort, we demonstrate that local coupling is spatially heterogeneous and exhibits nonlinear development-related trajectories. Moreover, we uncover sex differences in coupling that indicate divergent patterns of cortical topology. Developmental changes and sex differences in coupling support its potential as a neuroimaging phenotype for investigating neuropsychiatric disorders that are increasingly conceptualized as disorders of brain development. R code to estimate subject-level coupling maps from any two cortical surfaces generated by FreeSurfer is made publicly available along with this manuscript. PMID:26956908

  19. A novel ratiometric two-photon fluorescent probe for imaging of Pd(2+) ions in living cells and tissues.

    PubMed

    Zhou, Liyi; Hu, Shunqin; Wang, Haifei; Sun, Hongyan; Zhang, Xiaobing

    2016-09-01

    Ratiometric two-photon fluorescent probes can not only eliminate interferences from environmental factors but also achieve deep-tissue imaging with improved spatial localization. To quantitatively track Pd(2+) in biosystems, herein, we reported a ratiometric two-photon fluorescent probe, termed as Np-Pd, which based on a D-π-A-structure two-photon fluorophore of the naphthalimide derivative and deprotection of aryl propargyl ethers by palladium species. The probe Np-Pd displayed a more than 25-fold enhancement towards palladium species with high sensitivity and selectivity. Additionally, the probe Np-Pd was further used for fluorescence imaging of Pd(2+) ions in living cells and tissues under two-photon excitation (820nm), which showed large tissue-imaging depth (19.6-184.6μm), and a high resolution for ratiometric imaging. PMID:27203231

  20. A novel ratiometric two-photon fluorescent probe for imaging of Pd2 + ions in living cells and tissues

    NASA Astrophysics Data System (ADS)

    Zhou, Liyi; Hu, Shunqin; Wang, Haifei; Sun, Hongyan; Zhang, Xiaobing

    2016-09-01

    Ratiometric two-photon fluorescent probes can not only eliminate interferences from environmental factors but also achieve deep-tissue imaging with improved spatial localization. To quantitatively track Pd2 + in biosystems, herein, we reported a ratiometric two-photon fluorescent probe, termed as Np-Pd, which based on a D-π-A-structure two-photon fluorophore of the naphthalimide derivative and deprotection of aryl propargyl ethers by palladium species. The probe Np-Pd displayed a more than 25-fold enhancement towards palladium species with high sensitivity and selectivity. Additionally, the probe Np-Pd was further used for fluorescence imaging of Pd2 + ions in living cells and tissues under two-photon excitation (820 nm), which showed large tissue-imaging depth (19.6-184.6 μm), and a high resolution for ratiometric imaging.

  1. Hybrid Theranostic Platform for Second Near-IR Window Light Triggered Selective Two-Photon Imaging and Photothermal Killing of Targeted Melanoma Cells.

    PubMed

    Tchounwou, Christine; Sinha, Sudarson Sekhar; Viraka Nellore, Bhanu Priya; Pramanik, Avijit; Kanchanapally, Rajashekhar; Jones, Stacy; Chavva, Suhash Reddy; Ray, Paresh Chandra

    2015-09-23

    Despite advances in the medical field, even in the 21st century cancer is one of the leading causes of death for men and women in the world. Since the second near-infrared (NIR) biological window light between 950 and 1350 nm offers highly efficient tissue penetration, the current article reports the development of hybrid theranostic platform using anti-GD2 antibody attached gold nanoparticle (GNP) conjugated, single-wall carbon nanotube (SWCNT) for second near-IR light triggered selective imaging and efficient photothermal therapy of human melanoma cancer cell. Reported results demonstrate that due to strong plasmon-coupling, two-photon luminescence (TPL) intensity from theranostic GNP attached SWCNT materials is 6 orders of magnitude higher than GNP or SWCNT alone. Experimental and FDTD simulation data indicate that the huge enhancement of TPL intensity is mainly due to strong resonance enhancement coupled with the stronger electric field enhancement. Due to plasmon coupling, the theranostic material serves as a local nanoantennae to enhance the photothermal capability via strong optical energy absorption. Reported data show that theranostic SWCNT can be used for selective two-photon imaging of melanoma UACC903 cell using 1100 nm light. Photothermal killing experiment with 1.0 W/cm(2) 980 nm laser light demonstrates that 100% of melanoma UACC903 cells can be killed using theranostic SWCNT bind melanoma cells after just 8 min of exposure. These results demonstrate that due to plasmon coupling, the theranostic GNP attached SWCNT material serves as a two-photon imaging and photothermal source for cancer cells in biological window II. PMID:26327304

  2. Two-Photon and Two-gluon Decays of 0{sup ++} and 2{sup ++} P-wave Heavy Quarkonium States

    SciTech Connect

    Pham, T. N.

    2010-12-22

    By neglecting the relative quark momenta in the propagator term, the two-photon and two-gluon decay amplitude of heavy quarkonia states can be written as a local heavy quark field operator matrix element which could be obtained from other processes or computed with QCD sum rules technique or lattice simulation, as shown in a recent work on {eta}{sub c,b} two-photon decays. In this talk, I would like to discuss a similar calculation on P-wave {chi}{sub c0,2} and {chi}{sub b0,2} two-photon decays. We show that the effective Lagrangian for the two-photon decays of the P-wave {eta}{sub c0,2} and {chi}{sub b0,2} is given by the heavy quark energy-momentum tensor local operator and its trace, the QQ scalar density. A simple expression for {chi}c0 two-photon and two-gluon decay rate in terms of the f{sub {chi}c0} decay constant, similar to that of {eta}{sub c} is obtained. From the existing QCD sum rules value for f{sub {chi}c0,} we get 5 keV for the {chi}{sub c0} two-photon width, somewhat larger than measurement.

  3. Two-photon flow cytometer with laser scanning Bessel beams

    NASA Astrophysics Data System (ADS)

    Wang, Yongdong; Ding, Yu; Ray, Supriyo; Paez, Aurelio; Xiao, Chuan; Li, Chunqiang

    2016-03-01

    Flow cytometry is an important technique in biomedical discovery for cell counting, cell sorting and biomarker detection. In vivo flow cytometers, based on one-photon or two-photon excited fluorescence, have been developed for more than a decade. One drawback of laser beam scanning two-photon flow cytometer is that the two-photon excitation volume is fairly small due to the short Rayleigh range of a focused Gaussian beam. Hence, the sampling volume is much smaller than one-photon flow cytometry, which makes it challenging to count or detect rare circulating cells in vivo. Bessel beams have narrow intensity profiles with an effective spot size (FWHM) as small as several wavelengths, making them comparable to Gaussian beams. More significantly, the theoretical depth of field (propagation distance without diffraction) can be infinite, making it an ideal solution as a light source for scanning beam flow cytometry. The trade-off of using Bessel beams rather than a Gaussian beam is the fact that Bessel beams have small concentric side rings that contribute to background noise. Two-photon excitation can reduce this noise, as the excitation efficiency is proportional to intensity squared. Therefore, we developed a two-photon flow cytometer using scanned Bessel beams to form a light sheet that intersects the micro fluidic channel.

  4. Strong coupling between localized and propagating plasmon polaritons.

    PubMed

    Balci, Sinan; Karademir, Ertugrul; Kocabas, Coskun

    2015-07-01

    We investigate plasmon-plasmon (PP) coupling in the strongly interacting regimes by using a tunable plasmonic platform consisting of triangular Ag nanoprisms placed nanometers away from Ag thin films. The nanoprisms are colloidally synthesized using a seed-mediated growth method and having size-tunable localized surface plasmon polariton (SPP) resonances immobilized on Si(3)N(4) films. The PP coupling between the localized SPPs of metal nanoprisms and the propagating SPPs of the metal film is controlled by the nanoprism concentration and the plasmon damping in the metal film. Results reveal that Rabi splitting energy determining the strength of the coupling can reach up to several hundreds meV, thus demonstrating the ultrastrong coupling occurring between localized and propagating SPPs. The metal nanoparticle-metal thin film hybrid system over the square-centimeter areas presented here provides a unique configuration to study PP coupling all the way from the weak to ultrastrong coupling regimes in a broad range of wavelengths. PMID:26125396

  5. Mechanism of two-photon excited hemoglobin fluorescence emission

    NASA Astrophysics Data System (ADS)

    Sun, Qiqi; Zheng, Wei; Wang, Jiannong; Luo, Yi; Qu, Jianan Y.

    2015-10-01

    Hemoglobin, one of the most important proteins in the human body, is composed of "heme" groups (iron-containing rings) and "globins" (proteins). We investigate the two-photon excited fluorescence of hemoglobin and its subunit components (heme and globin). We measure the hemoglobin fluorescence lifetime by using a streak camera of ps resolution and confirm that its lifetime is in femtosecond scale. In the study of the fluorescence properties of heme and globin, the experimental results reveal that heme is the sole fluorophore of hemoglobin. Hemoglobin fluorescence can be effectively excited only via two-photon process, because heme has a centrosymmetric molecular structure and two-photon allowed transition is forbidden for single-photon process and vice versa due to the Laporte parity selection rule.

  6. Mechanism of two-photon excited hemoglobin fluorescence emission.

    PubMed

    Sun, Qiqi; Zheng, Wei; Wang, Jiannong; Luo, Yi; Qu, Jianan Y

    2015-10-01

    Hemoglobin, one of the most important proteins in the human body, is composed of “heme” groups (iron-containing rings) and “globins” (proteins). We investigate the two-photon excited fluorescence of hemoglobin and its subunit components (heme and globin). We measure the hemoglobin fluorescence lifetime by using a streak camera of ps resolution and confirm that its lifetime is in femtosecond scale. In the study of the fluorescence properties of heme and globin, the experimental results reveal that heme is the sole fluorophore of hemoglobin. Hemoglobin fluorescence can be effectively excited only via two-photon process, because heme has a centrosymmetric molecular structure and two-photon allowed transition is forbidden for single-photon process and vice versa due to the Laporte parity selection rule. PMID:26506468

  7. Two-photon absorption of few-electron heavy ions

    SciTech Connect

    Surzhykov, A.; Indelicato, P.; Santos, J. P.; Amaro, P.; Fritzsche, S.

    2011-08-15

    The two-photon absorption of few-electron ions has been studied by using second-order perturbation theory and Dirac's relativistic equation. Within this framework, the general expressions for the excitation cross sections and rates are derived including a full account of the higher-order multipole terms in the expansion of the electron-photon interaction. While these expressions can be applied to any ion, independent of its particular shell structure, detailed computations are carried out for the two-photon absorption of hydrogen-, helium-, and berylliumlike ions and are compared with the available theoretical and experimental data. The importance of relativistic and nondipole effects in the analysis and computation of induced two-photon transitions is pointed out. Moreover, we discuss the potential of these transitions for atomic parity-violation studies in the high-Z domain.

  8. Two-photon imaging of the immune system.

    PubMed

    Dzhagalov, Ivan L; Melichar, Heather J; Ross, Jenny O; Herzmark, Paul; Robey, Ellen A

    2012-04-01

    Two-photon microscopy is a powerful method for visualizing biological processes as they occur in their native environment in real time. The immune system uniquely benefits from this technology as most of its constituent cells are highly motile and interact extensively with each other and with the environment. Two-photon microscopy has provided many novel insights into the dynamics of the development and function of the immune system that could not have been deduced by other methods and has become an indispensible tool in the arsenal of immunologists. In this unit, we provide several protocols for preparation of various organs for imaging by two-photon microscopy that are intended to introduce the new user to some basic aspects of this method. PMID:22470153

  9. Adaptive optics two-photon scanning laser fluorescence microscopy

    NASA Astrophysics Data System (ADS)

    Zhou, Yaopeng; Bifano, Thomas; Lin, Charles

    2011-03-01

    Two-photon fluorescence microscopy provides a powerful tool for deep tissue imaging. However, optical aberrations from illumination beam path limit imaging depth and resolution. Adaptive Optics (AO) is found to be useful to compensate for optical aberrations and improve image resolution and contrast from two-photon excitation. We have developed an AO system relying on a MEMS Deformable Mirror (DM) to compensate the optical aberrations in a two-photon scanning laser fluorescence microscope. The AO system utilized a Zernike polynomial based stochastic parallel gradient descent (SPGD) algorithm to optimize the DM shape for wavefront correction. The developed microscope is applied for subsurface imaging of mouse bone marrow. It was demonstrated that AO allows 80% increase in fluorescence signal intensity from bone cavities 145um below the surface. The AO-enhanced microscope provides cellular level images of mouse bone marrow at depths exceeding those achievable without AO.

  10. Cell assay using a two-photon-excited europium chelate

    PubMed Central

    Xiao, Xudong; Haushalter, Jeanne P.; Kotz, Kenneth T.; Faris, Gregory W.

    2011-01-01

    We report application of two-photon excitation of europium chelates to immunolabeling of epidermal growth factor receptor (EGFR) cell surface proteins on A431 cancer cells. The europium chelates are excited with two photons of infrared light and emit in the visible. Europium chelates are conjugated to antibodies for EGFR. A431 (human epidermoid carcinoma) cells are labeled with this conjugate and imaged using a multiphoton microscope. To minimize signal loss due to the relatively long-lived Eu3+ emission, the multiphoton microscope is used with scanning laser two-photon excitation and non-scanning detection with a CCD. The chelate labels show very little photobleaching (less than 1% during continuous illumination in the microscope for 20 minutes) and low levels of autofluorescence (less than 1% of the signal from labeled cells). The detection limit of the europium label in the cell assay is better than 100 zeptomoles. PMID:21833362

  11. Two-photon interference between disparate sources for quantum networking

    PubMed Central

    McMillan, A. R.; Labonté, L.; Clark, A. S.; Bell, B.; Alibart, O.; Martin, A.; Wadsworth, W. J.; Tanzilli, S.; Rarity, J. G.

    2013-01-01

    Quantum networks involve entanglement sharing between multiple users. Ideally, any two users would be able to connect regardless of the type of photon source they employ, provided they fulfill the requirements for two-photon interference. From a theoretical perspective, photons coming from different origins can interfere with a perfect visibility, provided they are made indistinguishable in all degrees of freedom. Previous experimental demonstrations of such a scenario have been limited to photon wavelengths below 900 nm, unsuitable for long distance communication, and suffered from low interference visibility. We report two-photon interference using two disparate heralded single photon sources, which involve different nonlinear effects, operating in the telecom wavelength range. The measured visibility of the two-photon interference is 80 ± 4%, which paves the way to hybrid universal quantum networks. PMID:23783585

  12. MEASUREMENT AND OPTIMIZATION OF LOCAL COUPLING FROM RHIC BPM DATA.

    SciTech Connect

    CALAGA, R.; ABEYTUNGE, S.; BAI, M.; FISCHER, W.; ET AL.

    2005-05-16

    Global coupling in RHIC is routinely corrected by using three skew quadrupole families to minimize the tune split ({Delta}Q{sub min}). In this paper we propose to re-optimize transverse coupling by minimizing the resonance driving terms (RDT's) and the coupling matrix (|{bar C}|/{gamma}{sup 2}) in two steps: (1) Identify locations with coupling sources by inspection of the driving terms and the C-matrix around the ring and minimize the discontinuities and (2) Find the best configuration of the three skew quadrupole families to minimize both {Delta}Q{sub min} and RDTs (f{sub 1001}). The measurements of f{sub 1001} and |{bar C}|/{gamma}{sup 2} at injection and top energy to identify local coupling sources are presented.

  13. Two-photon excitation photodynamic therapy with Photofrin

    NASA Astrophysics Data System (ADS)

    Karotki, Aliaksandr; Khurana, Mamta; Lepock, James R.; Wilson, Brian C.

    2005-09-01

    Photodynamic therapy (PDT) based on simultaneous two-photon (2-γ) excitation has a potential advantage of highly targeted treatment by means of nonlinear localized photosensitizer excitation. One of the possible applications of 2-γ PDT is a treatment of exodus age-related macular degeneration where highly targeted excitation of photosensitizer in neovasculature is vital for reducing collateral damage to healthy surrounding tissue. To investigate effect of 2-γ PDT Photofrin was used as an archetypal photosensitizer. First, 2-γ absorption properties of Photofrin in the 750 - 900 nm excitation wavelength range were investigated. It was shown that above 800 nm 2-γ interaction was dominant mode of excitation. The 2-γ cross section of Photofrin was rather small and varied between 5 and 10 GM (1 GM = 10-50 cm4s/photon) in this wavelength range. Next, endothelial cells treated with Photofrin were used to model initial effect of 2-γ PDT on neovasculature. Ultrashort laser pulses provided by mode-locked Ti:sapphire laser (pulse duration at the sample 300 fs, repetition rate 90 MHz, mean laser power 10 mW, excitation wavelength 850 nm) were used for the excitation of the photosensitizer. Before 2-γ excitation of the Photofrin cells formed a single continuous sheet at the bottom of the well. The tightly focused laser light was scanned repeatedly over the cell layer. After irradiation the cell layer of the control cells stayed intact while cells treated with photofrin became clearly disrupted. The light doses required were high (6300 Jcm(-2) for ~ 50% killing), but 2-γ cytotoxicity was unequivocally demonstrated.

  14. Single and two-photon fluorescence studies of linear and non-linear optical chromophores

    NASA Astrophysics Data System (ADS)

    Nicolaou, Nick

    The subject matter presented in this thesis concerns the structural and dynamic studies of new fluorescent probe molecules and the application of polarised fluorescence techniques and analysis to molecular motion, order and solvation in a highly ordered environment. Chapter 1 reviews recent group research providing a context to the work in this thesis, whilst Chapters 2 and 3 concern the study of fluorescent probe dynamics. Time resolved photoselection techniques were used to probe the order and full angular motion of Coumarin 6 and Coumarin 153 in the nematic and isotropic phases of the liquid crystal 5CB. The uptake of coumarin molecules into this host differs from previously studied (Xanthene) probes - in particular, Coumarin 6 is seen to adopt a disruptive position within the alkyl tails due to its size and hydrophobic nature this is discussed in Chapter 2. Furthermore, Coumarin 153 undergoes a substantial increase in dipole moment upon electronic excitation this led to a unique study of time dependent solvation dynamics in both a globally and locally structured environment. The presence of strong solvent- solute interactions necessitated the development of a new approach to the analysis of time resolved polarised fluorescence in ordered systems. This approach and the study of time dependent solvation dynamics in the isotropic and nematic phases of 5CB is presented in Chapter 3. Structural studies of new two-photon fluorescent probes in collaboration with CNRS Rennes and Los Alamos are described in the final two chapters. Large two-photon resonances in the green-visible were observed together with a fuller characterisation of those in the near IR. Polarised two-photon absorption and anisotropy measurements were used to examine the structure of the two-photon resonances. Finally, the stimulated emission depletion dynamics of a branched two-photon fluorophore were investigated and found to differ markedly from conventional (non-degenerate) fluorophores.

  15. Modulation of Attosecond Beating by Resonant Two-Photon Transition

    NASA Astrophysics Data System (ADS)

    Jiménez Galán, Álvaro; Argenti, Luca; Martín, Fernando

    2015-09-01

    We present an analytical model that characterizes two-photon transitions in the presence of autoionising states. We applied this model to interpret resonant RABITT spectra, and show that, as a harmonic traverses a resonance, the phase of the sideband beating significantly varies with photon energy. This phase variation is generally very different from the π jump observed in previous works, in which the direct path contribution was negligible. We illustrate the possible phase profiles arising in resonant two-photon transitions with an intuitive geometrical representation.

  16. Two-photon interference with non-identical photons

    NASA Astrophysics Data System (ADS)

    Liu, Jianbin; Zhou, Yu; Zheng, Huaibin; Chen, Hui; Li, Fu-li; Xu, Zhuo

    2015-11-01

    Two-photon interference with non-identical photons is studied based on the superposition principle in Feynman's path integral theory. The second-order temporal interference pattern is observed by superposing laser and pseudothermal light beams with different spectra. The reason why there is two-photon interference for photons of different spectra is that non-identical photons can be indistinguishable for the detection system when Heisenberg's uncertainty principle is taken into account. These studies are helpful to understand the second-order interference of light in the language of photons.

  17. A fluorescent benzothiazole probe with efficient two-photon absorption

    NASA Astrophysics Data System (ADS)

    Echevarria, Lorenzo; Moreno, Iván; Camacho, José; Salazar, Mary Carmen; Hernández, Antonio

    2012-11-01

    In this work, we report the two-photon absorption of 2-[4-(dimethylamino)phenyl]-1,3-benzothiazole-6-carbonitrile (DBC) in DMSO solution pumping at 779 nm with a 10 ns pulse laser-Nd:YAG system. The obtained two-photon absorption cross-section in DBC (407 ± 18 GM) is considerably high. Because DBC is a novel compound and have high values of fluorescence quantum yield, this result is expected to have an impact in biomolecules detection, diagnosis and treatment of cancer. Similar structures have previously been reported to show remarkable antitumour effects.

  18. Projection two-photon polymerization using a spatial light modulator

    NASA Astrophysics Data System (ADS)

    Yang, Liang; Li, Jiawen; Hu, Yanlei; Zhang, Chenchu; Lao, Zhaoxin; Huang, Wenhao; Chu, Jiaru

    2014-11-01

    The development of a high-efficiency projection two-photon polymerization (P2PP) process by using a liquid crystal spatial light modulator (SLM) is presented. Rapid fabrication of 2D patterned microstructures with P2PP is demonstrated, and the effect of laser pattern and exposure dose on the surface roughness of the fabricated microstructures is investigated. It is found that the distribution of laser intensity at the focal plane of objective has a significant effect on the profiles of microstructures. This unique technology has a promising approach to increase the efficiency of two-photon polymerization (2PP) and a parallel fabrication of complex 2D and 3D microstructures.

  19. Two-photon in vivo imaging of retinal microstructures

    NASA Astrophysics Data System (ADS)

    Schejter, Adi; Farah, Nairouz; Shoham, Shy

    2014-02-01

    Non-invasive fluorescence retinal imaging in small animals is an important requirement in an array of translational vision applications. Two-photon imaging has the potential for long-term investigation of healthy and diseased retinal function and structure in vivo. Here, we demonstrate that two-photon microscopy through a mouse's pupil can yield high-quality optically sectioned fundus images. By remotely scanning using an electronically tunable lens we acquire highly-resolved 3D fluorescein angiograms. These results provide an important step towards various applications that will benefit from the use of infrared light, including functional imaging of retinal responses to light stimulation.

  20. Spatial solitons in two-photon photorefractive media

    NASA Astrophysics Data System (ADS)

    Hou, Chunfeng; Pei, Yanbo; Zhou, Zhongxiang; Sun, Xiudong

    2005-05-01

    We provide a theory for spatial solitons due to the two-photon photorefractive effect based on the Castro-Camus model [Opt. Lett. 28, 1129 (2003)]. We present the evolution equation of one-dimensional spatial solitons in two-photon photorefractive media. In steady state and under appropriate external bias conditions, we obtain the dark and bright soliton solutions of the optical wave evolution equation, and also discuss the self-deflection of the bright solitons theoretically by taking into account the diffusion effect.

  1. Spatial solitons in two-photon photorefractive media

    SciTech Connect

    Hou Chunfeng; Pei Yanbo; Zhou Zhongxiang; Sun Xiudong

    2005-05-15

    We provide a theory for spatial solitons due to the two-photon photorefractive effect based on the Castro-Camus model [Opt. Lett. 28, 1129 (2003)]. We present the evolution equation of one-dimensional spatial solitons in two-photon photorefractive media. In steady state and under appropriate external bias conditions, we obtain the dark and bright soliton solutions of the optical wave evolution equation, and also discuss the self-deflection of the bright solitons theoretically by taking into account the diffusion effect.

  2. Parity-dependent localization in N strongly coupled chains

    NASA Astrophysics Data System (ADS)

    Weinmann, Dietmar; Evangelou, S. N.

    2014-10-01

    Anderson localization of wave functions at zero energy in quasi-one-dimensional (1D) systems of N disordered chains with interchain coupling t is examined. Localization becomes weaker than for the 1D disordered chain (t =0) when t is smaller than the longitudinal hopping t'=1, and localization becomes usually much stronger when t ≫t'. This is not so for all N. We find "immunity" to strong localization for open (periodic) lateral boundary conditions when N is odd (a multiple of 4), with localization that is weaker than for t =0 and rather insensitive to t when t ≫t'. The peculiar N dependence and a critical scaling with N are explained by a perturbative treatment in t'/t, and the correspondence to a weakly disordered effective chain is shown. Our results could be relevant for experimental studies of localization in photonic waveguide arrays.

  3. Two-photon excitation cross-section in light and intermediate atoms

    NASA Technical Reports Server (NTRS)

    Omidvar, K.

    1980-01-01

    The method of explicit summation over the intermediate states is used along with LS coupling to derive an expression for two-photon absorption cross section in light and intermediate atoms in terms of integrals over radial wave functions. Two selection rules, one exact and one approximate, are also derived. In evaluating the radial integrals, for low-lying levels, the Hartree-Fock wave functions, and for high-lying levels, hydrogenic wave functions obtained by the quantum defect method are used. A relationship between the cross section and the oscillator strengths is derived. Cross sections due to selected transitions in nitrogen, oxygen, and chlorine are given. The expression for the cross section is useful in calculating the two-photon absorption in light and intermediate atoms.

  4. Rational Design of Fluorescent Phthalazinone Derivatives for One- and Two-Photon Imaging.

    PubMed

    Yang, Lingfei; Zhu, Yuanjun; Shui, Mengyang; Zhou, Tongliang; Cai, Yuanbo; Wang, Wei; Xu, Fengrong; Niu, Yan; Wang, Chao; Zhang, Jun-Long; Xu, Ping; Yuan, Lan; Liang, Lei

    2016-08-22

    Phthalazinone derivatives were designed as optical probes for one- and two-photon fluorescence microscopy imaging. The design strategy involves stepwise extension and modification of pyridazinone by 1) expansion of pyridazinone to phthalazinone, a larger conjugated system, as the electron acceptor, 2) coupling of electron-donating aromatic groups such as N,N-diethylaminophenyl, thienyl, naphthyl, and quinolyl to the phthalazinone, and 3) anchoring of an alkyl chain to the phthalazinone with various terminal substituents such as triphenylphosphonio, morpholino, triethylammonio, N-methylimidazolio, pyrrolidino, and piperidino. Theoretical calculations were utilized to verify the initial design. The desired fluorescent probes were synthesized by two different routes in considerable yields. Twenty-two phthalazinone derivatives were synthesized and their photophysical properties were measured. Selected compounds were applied in cell imaging, and valuable information was obtained. Furthermore, the designed compounds showed excellent performance in two-photon microscopic imaging of mouse brain slices. PMID:27440529

  5. Programmable two-photon quantum interference in 103 channels in opaque scattering media

    NASA Astrophysics Data System (ADS)

    Wolterink, Tom A. W.; Uppu, Ravitej; Ctistis, Georgios; Vos, Willem L.; Boller, Klaus-J.; Pinkse, Pepijn W. H.

    2016-05-01

    We investigate two-photon quantum interference in an opaque scattering medium that intrinsically supports a large number of transmission channels. By adaptive spatial phase modulation of the incident wave fronts, the photons are directed at targeted speckle spots or output channels. From 103 experimentally available coupled channels, we select two channels and enhance their transmission to realize the equivalent of a fully programmable 2 ×2 beam splitter. By sending pairs of single photons from a parametric down-conversion source through the opaque scattering medium, we observe two-photon quantum interference. The programed beam splitter need not fulfill energy conservation over the two selected output channels and hence could be nonunitary. Consequently, we have the freedom to tune the quantum interference from bunching (Hong-Ou-Mandel-like) to antibunching. Our results establish opaque scattering media as a platform for high-dimensional quantum interference that is notably relevant for boson sampling and physical-key-based authentication.

  6. Two-photon light-sheet nanoscopy by fluorescence fluctuation correlation analysis.

    PubMed

    Chen, Xuanze; Zong, Weijian; Li, Rongqin; Zeng, Zhiping; Zhao, Jia; Xi, Peng; Chen, Liangyi; Sun, Yujie

    2016-05-21

    Advances in light-sheet microscopy have enabled the fast three-dimensional (3D) imaging of live cells and bulk specimens with low photodamage and phototoxicity. Combining light-sheet illumination with super-resolution imaging is expected to resolve subcellular structures. Actually, such kind of super-resolution light-sheet microscopy was recently demonstrated using a single-molecule localization algorithm. However, the imaging depth and temporal resolution of this method are limited owing to the requirements of precise single molecule localization and reconstruction. In this work, we present two-photon super-resolution light-sheet imaging via stochastic optical fluctuation imaging (2PLS-SOFI), which acquires high spatiotemporal resolution and excellent optical sectioning ability. 2PLS-SOFI is based on non-linear excitation of fluctuation/blinking probes using our recently developed fast two-photon three-axis digital scanned light-sheet microscope (2P3A-DSLM), which enables both deep penetration and thin sheet of light. Overall, 2PLS-SOFI demonstrates up to 3-fold spatial resolution enhancement compared with conventional two-photon light-sheet (2PLS) microscopy and about 40-fold temporal resolution enhancement compared with individual molecule localization-selective plane illumination microscopy (IML-SPIM). Therefore, 2PLS-SOFI is promising for 3D long-term, deep-tissue imaging with high spatiotemporal resolution. PMID:27121341

  7. Two-photon light-sheet nanoscopy by fluorescence fluctuation correlation analysis

    NASA Astrophysics Data System (ADS)

    Chen, Xuanze; Zong, Weijian; Li, Rongqin; Zeng, Zhiping; Zhao, Jia; Xi, Peng; Chen, Liangyi; Sun, Yujie

    2016-05-01

    Advances in light-sheet microscopy have enabled the fast three-dimensional (3D) imaging of live cells and bulk specimens with low photodamage and phototoxicity. Combining light-sheet illumination with super-resolution imaging is expected to resolve subcellular structures. Actually, such kind of super-resolution light-sheet microscopy was recently demonstrated using a single-molecule localization algorithm. However, the imaging depth and temporal resolution of this method are limited owing to the requirements of precise single molecule localization and reconstruction. In this work, we present two-photon super-resolution light-sheet imaging via stochastic optical fluctuation imaging (2PLS-SOFI), which acquires high spatiotemporal resolution and excellent optical sectioning ability. 2PLS-SOFI is based on non-linear excitation of fluctuation/blinking probes using our recently developed fast two-photon three-axis digital scanned light-sheet microscope (2P3A-DSLM), which enables both deep penetration and thin sheet of light. Overall, 2PLS-SOFI demonstrates up to 3-fold spatial resolution enhancement compared with conventional two-photon light-sheet (2PLS) microscopy and about 40-fold temporal resolution enhancement compared with individual molecule localization-selective plane illumination microscopy (IML-SPIM). Therefore, 2PLS-SOFI is promising for 3D long-term, deep-tissue imaging with high spatiotemporal resolution.

  8. Local-field correction in the strong-coupling regime

    SciTech Connect

    Hien, Tran Minh; Dung, Ho Trung; Welsch, Dirk-Gunnar

    2011-04-15

    The influence of the local-field correction on the strong atom-field coupling regime are investigated using the real-cavity model. The atom is positioned at the center of a multilayer sphere. Three types of mirrors are considered: perfectly reflecting, Lorentz band gap, and Bragg-distributed ones, with special emphasis on experimental practicability. In particular, the influence of the local field on the spectral resonance lines, the Rabi oscillation frequency and decay rate, and the condition indicating the occurrence of the strong-coupling regime are studied in detail. It is shown that the local-field correction gives rise to a structureless plateau in the density of states of the electromagnetic field. The level of the plateau rises with increasing material density and/or absorption, which may eventually destroy the strong-coupling regime. The effect of the local field is especially pronounced at high-material densities due to direct energy transfer from the guest atom to the medium. At lower material density and/or absorption, variation of the material density does not seem to affect much the strong-coupling regime, except for a small shift in the resonance frequency.

  9. Two-photon absorbing porphyrins for oxygen microscopy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Esipova, Tatiana V.; Vinogradov, Sergei A.

    2016-03-01

    The ability to quantify oxygen in vivo in 3D with high spatial and temporal resolution is invaluable for many areas of the biomedical science, including ophthalmology, neuroscience, cancer and stem biology. An optical method based on oxygen-dependent quenching of phosphorescence is being developed, that allows quantitative minimally invasive real-time imaging of partial pressure of oxygen (pO2) in tissue. In the past, dendritically protected phosphorescent oxygen probes with controllable quenching parameters and defined bio-distributions have been developed. More recently our probe strategy has extended to encompass two-photon excitable oxygen probes, which brought about first demonstrations of two-photon phosphorescence lifetime microscopy (2PLM) of oxygen in vivo, providing new valuable information for neuroscience and stem cell biology. However, current two-photon oxygen probes suffer from a number of limitations, such as low brightness and high cost of synthesis, which dramatically reduce imaging performance and limit usability of the method. Here we present an approach to new bright phosphorescent chromophores with internally enhanced two-photon absorption cross-sections, which pave a way to novel proves for 2PLM. In addition to substantial increase in performance, the new probes can be synthesized by much more efficient methods, thereby greatly reducing the cost of the synthesis and making the technique accessible to a broader range of researchers across different fields.

  10. Two-photon excitation endoscopy through a multimode optical fiber

    NASA Astrophysics Data System (ADS)

    Morales Delgado, Edgar E.; Psaltis, Demetri; Moser, Christophe

    2016-03-01

    The vast number of propagating solutions to the wave equation in multimode optical fibers represents a larger information capacity than provided by fiber bundles of the same diameter. Therefore, in the field of imaging, multimode fibers potentially allow the transmission of images with higher resolution. However, image transmission through multimode fibers is not direct as in the fiber bundle case, in which each of the fiber cores can relay a portion of the distal image. In multimode fiber transmission, a distribution of intensity is scrambled in time and space by the propagating modes, leading to a speckle-like pattern that does not resemble the initial distribution. Here, we demonstrate two-photon excitation imaging of fluorescent beads through a multimode optical fiber. We show that our method maintains the advantages of two-photon excitation microscopy compared to single-photon excitation such as reduced photo-bleaching, deeper penetration depth and sectioning capability. Our method is based on time-gated digital phase conjugation, which allows the generation of focused pulses on the other side of a multimode fiber. To acquire an image, the focused femtosecond pulse is scanned in a three-dimensional mesh, producing two-photon excitation on each spatial location of the sample. By collecting the fluorescence through the fiber, a 3D two-photon image is reconstructed.

  11. Multimodal dyes: toward correlative two-photon and electron microscopy

    NASA Astrophysics Data System (ADS)

    Bolze, Frédéric; Ftouni, Hussein; Nicoud, Jean-François; Leoni, Piero; Schwab, Yannick; Rehspringer, Jean-Luc; Mafouana, Rodrigues R.

    2013-03-01

    Nowadays, many crucial biological questions involve the observation of biological samples at different scales. Thus, optical microscopy can be associated to magnetic nuclear imaging allowing access to data from the cellular to the organ level, or can be associated to electron microscopy to reach the sub cellular level. We will describe here the design, synthesis and characterization of new bimodal probes, which can be used as dye in two-photon excited microscopy (TPEM) and electron dense markers in scanning and transmission electron microscopy (EM). In a first part, we will describe new molecular dyes with small organic systems grafted on metal atoms (Pt, Au). Such systems show good twophoton induced fluorescence and two-photon images of HeLa cells will be presented. In a second part, we will present hybrid organic-inorganic fluorescent systems with diketopyrrolopyrole-based dye grafted on iron oxide-silica core shell nanoparticles by peptide bond. Such systems present high two-photon absorption cross sections and good fluorescence quantum yields. These nanoparticles are rapidly internalized in HeLa cells and high quality two-photon images were performed with low laser power. Then we will present our results on correlative light-electron microscopy were twophoton and electron microscopy (both scanning and transmission) images were obtained on the same biological sample.

  12. Strong Local-Nonlocal Coupling for Integrated Fracture Modeling

    SciTech Connect

    Littlewood, David John; Silling, Stewart A.; Mitchell, John A.; Seleson, Pablo D.; Bond, Stephen D.; Parks, Michael L.; Turner, Daniel Z.; Burnett, Damon J.; Ostien, Jakob; Gunzburger, Max

    2015-09-01

    Peridynamics, a nonlocal extension of continuum mechanics, is unique in its ability to capture pervasive material failure. Its use in the majority of system-level analyses carried out at Sandia, however, is severely limited, due in large part to computational expense and the challenge posed by the imposition of nonlocal boundary conditions. Combined analyses in which peridynamics is em- ployed only in regions susceptible to material failure are therefore highly desirable, yet available coupling strategies have remained severely limited. This report is a summary of the Laboratory Directed Research and Development (LDRD) project "Strong Local-Nonlocal Coupling for Inte- grated Fracture Modeling," completed within the Computing and Information Sciences (CIS) In- vestment Area at Sandia National Laboratories. A number of challenges inherent to coupling local and nonlocal models are addressed. A primary result is the extension of peridynamics to facilitate a variable nonlocal length scale. This approach, termed the peridynamic partial stress, can greatly reduce the mathematical incompatibility between local and nonlocal equations through reduction of the peridynamic horizon in the vicinity of a model interface. A second result is the formulation of a blending-based coupling approach that may be applied either as the primary coupling strategy, or in combination with the peridynamic partial stress. This blending-based approach is distinct from general blending methods, such as the Arlequin approach, in that it is specific to the coupling of peridynamics and classical continuum mechanics. Facilitating the coupling of peridynamics and classical continuum mechanics has also required innovations aimed directly at peridynamic models. Specifically, the properties of peridynamic constitutive models near domain boundaries and shortcomings in available discretization strategies have been addressed. The results are a class of position-aware peridynamic constitutive laws for

  13. Two-photon imaging of a magneto-fluorescent indicator for 3D optical magnetometry.

    PubMed

    Lee, Hohjai; Brinks, Daan; Cohen, Adam E

    2015-10-19

    We developed an optical method to visualize the three-dimensional distribution of magnetic field strength around magnetic microstructures. We show that the two-photon-excited fluorescence of a chained donor-bridge-acceptor compound, phenanthrene-(CH2)12-O-(CH2)2-N,N-dimethylaniline, is sensitive to ambient magnetic field strength. A test structure is immersed in a solution of the magneto-fluorescent indicator and a custom two-photon microscope maps the fluorescence of this compound. The decay kinetics of the electronic excited state provide a measure of magnetic field that is insensitive to photobleaching, indicator concentration, or local variations in optical excitation or collection efficiency. PMID:26480460

  14. Intermediate vibrational coordinate localization with harmonic coupling constraints

    NASA Astrophysics Data System (ADS)

    Hanson-Heine, Magnus W. D.

    2016-05-01

    Optimized normal coordinates can significantly improve the speed and accuracy of vibrational frequency calculations. However, over-localization can occur when using unconstrained spatial localization techniques. The unintuitive mixtures of stretching and bending coordinates that result can make interpreting spectra more difficult and also cause artificial increases in mode-coupling during anharmonic calculations. Combining spatial localization with a constraint on the coupling between modes can be used to generate coordinates with properties in-between the normal and fully localized schemes. These modes preserve the diagonal nature of the mass-weighted Hessian matrix to within a specified tolerance and are found to prevent contamination between the stretching and bending vibrations of the molecules studied without a priori classification of the different types of vibration present. Relaxing the constraint can also be used to identify which normal modes form specific groups of localized modes. The new coordinates are found to center on more spatially delocalized functional groups than their fully localized counterparts and can be used to tune the degree of vibrational correlation energy during anharmonic calculations.

  15. Intermediate vibrational coordinate localization with harmonic coupling constraints.

    PubMed

    Hanson-Heine, Magnus W D

    2016-05-28

    Optimized normal coordinates can significantly improve the speed and accuracy of vibrational frequency calculations. However, over-localization can occur when using unconstrained spatial localization techniques. The unintuitive mixtures of stretching and bending coordinates that result can make interpreting spectra more difficult and also cause artificial increases in mode-coupling during anharmonic calculations. Combining spatial localization with a constraint on the coupling between modes can be used to generate coordinates with properties in-between the normal and fully localized schemes. These modes preserve the diagonal nature of the mass-weighted Hessian matrix to within a specified tolerance and are found to prevent contamination between the stretching and bending vibrations of the molecules studied without a priori classification of the different types of vibration present. Relaxing the constraint can also be used to identify which normal modes form specific groups of localized modes. The new coordinates are found to center on more spatially delocalized functional groups than their fully localized counterparts and can be used to tune the degree of vibrational correlation energy during anharmonic calculations. PMID:27250288

  16. Four new two-photon polymerization initiators with varying donor and conjugated bridge: Synthesis and two-photon activity

    NASA Astrophysics Data System (ADS)

    Hao, Fuying; Liu, Zhaodi; Zhang, Mingliang; Liu, Jie; Zhang, Shengyi; Wu, Jieying; Zhou, Hongping; Tian, YuPeng

    2014-01-01

    A specific series of dumbbell-shaped bis-carbazoles or bis-phenothiazines dyes (1, 2, 3 and 4) constructed with styrene or biphenylethyne as the π-bridge have been synthesized and characterized. Detailed spectral properties including linear absorption, one and two-photon fluorescence properties were investigated. The results show that extending conjugated chain and introducing donors have substantial effect on their photophysical properties. Among them, two-photon absorption cross sections (σ) of the four dyes in DMF determined by the Z-scan technique are successively increased from 1 to 4 with enhancing electron-donating ability and extending conjugated chain, but electron-donating ability has larger contribution to the σ values than extending conjugated chain based on the comparison of small molecules (D-π-D). Two-photon initiation polymerization (TPIP) microfabrication experiments have been carried out using compound 4 as an initiator under irradiation of 200 fs, 76 MHz femtosecond laser at 760 nm. The results confirm that the four dyes can be effectively used as organic two-photon photopolymerization initiators.

  17. Transmission of a microwave cavity coupled to localized Shiba states

    NASA Astrophysics Data System (ADS)

    Chirla, Razvan; Manolescu, Andrei; Moca, Cǎtǎlin Paşcu

    2016-04-01

    We consider a strongly correlated quantum dot, tunnel coupled to two superconducting leads and capacitively coupled to a single mode microwave cavity. When the superconducting gap is the largest energy scale, multiple Shiba states are formed inside the gap. The competition of these states for the ground state signals a quantum phase transition. We demonstrate that photonic measurements can be used to probe such localized Shiba states. Moreover, the quantum phase transition can be pinpointed exactly from the sudden change in the transmission signal. Calculations were performed using the numerical renormalization-group approach.

  18. Ultrasensitive mass sensing using mode localization in coupled microcantilevers

    SciTech Connect

    Spletzer, Matthew; Raman, Arvind; Wu, Alexander Q.; Xu Xianfan; Reifenberger, Ron

    2006-06-19

    We use Anderson or vibration localization in coupled microcantilevers as an extremely sensitive method to detect the added mass of a target analyte. We focus on the resonance frequencies and eigenstates of two nearly identical coupled gold-foil microcantilevers. Theoretical and experimental results indicate that the relative changes in the eigenstates due to the added mass can be orders of magnitude greater than the relative changes in resonance frequencies. Moreover this sensing paradigm possesses intrinsic common mode rejection characteristics thus providing an alternate way to achieve ultrasensitive mass detection under ambient conditions.

  19. Laser scanning stereomicroscopy for fast volumetric imaging with two-photon excitation and scanned Bessel beams

    NASA Astrophysics Data System (ADS)

    Yang, Yanlong; Zhou, Xing; Li, Runze; Van Horn, Mark; Peng, Tong; Lei, Ming; Wu, Di; Chen, Xun; Yao, Baoli; Ye, Tong

    2015-03-01

    Bessel beams have been used in many applications due to their unique optical properties of maintaining their intensity profiles unchanged during propagation. In imaging applications, Bessel beams have been successfully used to provide extended focuses for volumetric imaging and uniformed illumination plane in light-sheet microscopy. Coupled with two-photon excitation, Bessel beams have been successfully used in realizing fluorescence projected volumetric imaging. We demonstrated previously a stereoscopic solution-two-photon fluorescence stereomicroscopy (TPFSM)-for recovering the depth information in volumetric imaging with Bessel beams. In TPFSM, tilted Bessel beams were used to generate stereoscopic images on a laser scanning two-photon fluorescence microscope; upon post image processing we could successfully provide 3D perception of acquired volume images by wearing anaglyph 3D glasses. However, tilted Bessel beams were generated by shifting either an axicon or an objective laterally; the slow imaging speed and severe aberrations made it hard to use in real-time volume imaging. In this article, we report recent improvements of TPFSM with newly designed scanner and imaging software, which allows 3D stereoscopic imaging without moving any of the optical components on the setup. This improvement has dramatically improved focusing qualities and imaging speed so that the TPFSM can be performed potentially in real-time to provide 3D visualization in scattering media without post image processing.

  20. Compact two-photon laser-scanning microscope made from minimally modified commercial components

    NASA Astrophysics Data System (ADS)

    Iyer, Vijay; Hoogland, Tycho; Losavio, Bradley E.; McQuiston, A. R.; Saggau, Peter

    2002-06-01

    A compact two-photon laser-scanning microscope (TPLSM) was constructed using a diode-pumped, mode-locked Nd:YLF laser (Biolight 1000, Coherent Laser Group) and a small confocal laser scan-head (PCM2000, Nikon Bioscience). The laser emits at 1047nm and is fiber-coupled to a compact compressor unit producing a pulse-width of ~175fsec. Both the pulse compressor and confocal scan head were interfaced on a small optical breadboard that was directly attached to an upright research microscope (Eclipse E600FN, Nikon Bioscience). Two-photon fluorescence emitted from the specimen was collected into a multimode fiber and transmitted directly to an external PMT supplied with the Nikon confocal system. The modifications to the scanhead were minimal (a single mirror replacement) and did not interfere with its confocal function. The resulting system offers several advantages: compact size, turnkey operation, and the ability to translate the microscope rather than an often delicate specimen. In addition, it is possible to switch between confocal and two-photon operation, allowing for straightforward comparison. Using this compact TPLSM, we obtained structural and functional images from hippocampal neurons in living brain slices using commonly available fluorophores.

  1. Transverse target spin asymmetry in inclusive DIS with two-photon exchange

    SciTech Connect

    Afanasev, A.; Strikman, M.; Weiss, C.

    2008-01-01

    We study the transverse target spin dependence of the cross section for inclusive electron-nucleon scattering with unpolarized beam. Such dependence is absent in the one-photon exchange approximation (Christ-Lee theorem) and arises only in higher orders of the QED expansion, from the interference of one-photon and absorptive two-photon exchange amplitudes as well as from real photon emission (bremsstrahlung). We demonstrate that the transverse spin-dependent two-photon exchange cross section is free of QED infrared and collinear divergences. We argue that in DIS kinematics the transverse spin dependence should be governed by a 'partonlike' mechanism in which the two-photon exchange couples mainly to a single quark. We calculate the normal spin asymmetry in an approximation where the dominant contribution arises from quark-helicity flip due to interactions with nonperturbative vacuum fields (constituent quark picture) and is proportional to the quark transversity distribution in the nucleon. Such helicity-flip processes are not significantly Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark subprocess is of the order of the chiral symmetry breaking scale, {mu}{sub chiral}{sup 2}>>{lambda}{sub QCD}{sup 2}. We estimate the asymmetry in the kinematics of the planned Jefferson Lab Hall A experiment to be of the order 10{sup -4}, with different sign for proton and neutron. We also comment on the spin dependence in the limit of soft high-energy scattering.

  2. Transverse target spin asymmetry in inclusive DIS with two-photon exchange

    NASA Astrophysics Data System (ADS)

    Afanasev, A.; Strikman, M.; Weiss, C.

    2008-01-01

    We study the transverse target spin dependence of the cross section for inclusive electron-nucleon scattering with unpolarized beam. Such dependence is absent in the one-photon exchange approximation (Christ-Lee theorem) and arises only in higher orders of the QED expansion, from the interference of one-photon and absorptive two-photon exchange amplitudes as well as from real photon emission (bremsstrahlung). We demonstrate that the transverse spin-dependent two-photon exchange cross section is free of QED infrared and collinear divergences. We argue that in DIS kinematics the transverse spin dependence should be governed by a “partonlike” mechanism in which the two-photon exchange couples mainly to a single quark. We calculate the normal spin asymmetry in an approximation where the dominant contribution arises from quark-helicity flip due to interactions with nonperturbative vacuum fields (constituent quark picture) and is proportional to the quark transversity distribution in the nucleon. Such helicity-flip processes are not significantly Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark subprocess is of the order of the chiral symmetry breaking scale, μchiral2≫ΛQCD2. We estimate the asymmetry in the kinematics of the planned Jefferson Lab Hall A experiment to be of the order 10-4, with different sign for proton and neutron. We also comment on the spin dependence in the limit of soft high-energy scattering.

  3. Calculation of the spatial resolution in two-photon absorption spectroscopy applied to plasma diagnosis

    SciTech Connect

    Garcia-Lechuga, M.; Fuentes, L. M.; Grützmacher, K.; Pérez, C. Rosa, M. I. de la

    2014-10-07

    We report a detailed characterization of the spatial resolution provided by two-photon absorption spectroscopy suited for plasma diagnosis via the 1S-2S transition of atomic hydrogen for optogalvanic detection and laser induced fluorescence (LIF). A precise knowledge of the spatial resolution is crucial for a correct interpretation of measurements, if the plasma parameters to be analysed undergo strong spatial variations. The present study is based on a novel approach which provides a reliable and realistic determination of the spatial resolution. Measured irradiance distribution of laser beam waists in the overlap volume, provided by a high resolution UV camera, are employed to resolve coupled rate equations accounting for two-photon excitation, fluorescence decay and ionization. The resulting three-dimensional yield distributions reveal in detail the spatial resolution for optogalvanic and LIF detection and related saturation due to depletion. Two-photon absorption profiles broader than the Fourier transform-limited laser bandwidth are also incorporated in the calculations. The approach allows an accurate analysis of the spatial resolution present in recent and future measurements.

  4. Transverse target spin asymmetry in inclusive DIS with two-photon exchange

    SciTech Connect

    Andrei Afanasev; Mark Strikman; Christian Weiss

    2007-09-06

    We study the transverse target spin dependence of the cross section for the inclusive electron-nucleon scattering with unpolarized beam. Such dependence is absent in the one-photon exchange approximation (Christ-Lee theorem) and arises only in higher orders of the QED expansion, from the interference of one-photon and absorptive two-photon exchange amplitudes as well as from real photon emission (bremsstrahlung). We demonstrate that the transverse spin-dependent two-photon exchange cross section is free of QED infrared and collinear divergences. We argue that in DIS kinematics the transverse spin dependence should be governed by a "parton-like" mechanism in which the two-photon exchange couples mainly to a single quark. We calculate the normal spin asymmetry in an approximation where the dominant contribution arises from quark helicity flip due to interactions with non-perturbative vacuum fields (constituent quark picture) and is proportional to the quark transversity distribution in the nucleon. Such helicity-flip processes are not significantly Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark subprocess is of the order of the chiral symmetry breaking scale, mu^2_chiral>>Lambda^2_QCD. We estimate the asymmetry in the kinematics of the planned Jefferson Lab Hall A experiment to be of the order 10^-4, with different sign for proton and neutron. We also comment on the spin dependence in the limit of soft high-energy scattering.

  5. Two-photon Lee-Goldburg nuclear magnetic resonance: Simultaneous homonuclear decoupling and signal acquisition

    NASA Astrophysics Data System (ADS)

    Michal, Carl A.; Hastings, Simon P.; Lee, Lik Hang

    2008-02-01

    We present NMR signals from a strongly coupled homonuclear spin system, H1 nuclei in adamantane, acquired with simultaneous two-photon excitation under conditions of the Lee-Goldburg experiment. Small coils, having inside diameters of 0.36mm, are used to achieve two-photon nutation frequencies of ˜20kHz. The very large rf field strengths required give rise to large Bloch-Siegert shifts that cannot be neglected. These experiments are found to be extremely sensitive to inhomogeneity of the applied rf field, and due to the Bloch-Siegert shift, exhibit a large asymmetry in response between the upper and lower Lee-Goldburg offsets. Two-photon excitation has the potential to enhance both the sensitivity and performance of homonuclear dipolar decoupling, but is made challenging by the high rf power required and the difficulties introduced by the inhomogeneous Bloch-Siegert shift. We briefly discuss a variation of the frequency-switched Lee-Goldburg technique, called four-quadrant Lee-Goldburg (4QLG) that produces net precession in the x-y plane, with a reduced chemical shift scaling factor of 1/3.

  6. Two-photon Lee-Goldburg nuclear magnetic resonance: Simultaneous homonuclear decoupling and signal acquisition.

    PubMed

    Michal, Carl A; Hastings, Simon P; Lee, Lik Hang

    2008-02-01

    We present NMR signals from a strongly coupled homonuclear spin system, (1)H nuclei in adamantane, acquired with simultaneous two-photon excitation under conditions of the Lee-Goldburg experiment. Small coils, having inside diameters of 0.36 mm, are used to achieve two-photon nutation frequencies of approximately 20 kHz. The very large rf field strengths required give rise to large Bloch-Siegert shifts that cannot be neglected. These experiments are found to be extremely sensitive to inhomogeneity of the applied rf field, and due to the Bloch-Siegert shift, exhibit a large asymmetry in response between the upper and lower Lee-Goldburg offsets. Two-photon excitation has the potential to enhance both the sensitivity and performance of homonuclear dipolar decoupling, but is made challenging by the high rf power required and the difficulties introduced by the inhomogeneous Bloch-Siegert shift. We briefly discuss a variation of the frequency-switched Lee-Goldburg technique, called four-quadrant Lee-Goldburg (4QLG) that produces net precession in the x-y plane, with a reduced chemical shift scaling factor of 13. PMID:18266418

  7. Two-photon Lee-Goldburg nuclear magnetic resonance: Simultaneous homonuclear decoupling and signal acquisition

    SciTech Connect

    Michal, Carl A.; Hastings, Simon P.; Lee, Lik Hang

    2008-02-07

    We present NMR signals from a strongly coupled homonuclear spin system, {sup 1}H nuclei in adamantane, acquired with simultaneous two-photon excitation under conditions of the Lee-Goldburg experiment. Small coils, having inside diameters of 0.36 mm, are used to achieve two-photon nutation frequencies of {approx}20 kHz. The very large rf field strengths required give rise to large Bloch-Siegert shifts that cannot be neglected. These experiments are found to be extremely sensitive to inhomogeneity of the applied rf field, and due to the Bloch-Siegert shift, exhibit a large asymmetry in response between the upper and lower Lee-Goldburg offsets. Two-photon excitation has the potential to enhance both the sensitivity and performance of homonuclear dipolar decoupling, but is made challenging by the high rf power required and the difficulties introduced by the inhomogeneous Bloch-Siegert shift. We briefly discuss a variation of the frequency-switched Lee-Goldburg technique, called four-quadrant Lee-Goldburg (4QLG) that produces net precession in the x-y plane, with a reduced chemical shift scaling factor of 1/3.

  8. A Two-Photon E1-M1 Optical Clock

    NASA Astrophysics Data System (ADS)

    Alden, Emily A.

    Innovations in precision frequency measurement advance popular technologies such as global positioning systems (GPS), permit the testing of fundamental physics constants, and have the potential to measure local variations in gravity. Driving optical transitions for frequency measurement using an E1-M1 excitation scheme in a hot mercury (Hg) vapor cell is viable and could be the basis of a portable optical frequency standard with comparable accuracy to the most precise atomic clocks in the world. This dissertation explores the fundamental physics of the new E1-M1 method of high-precision frequency measurement in an optical, atomic clock and describes the construction of a high-power E1-M1 clock laser. The value of this new scheme compared to existing optical frequency standards is the simplicity and portability of the experimental setup. Such an optical frequency standard would permit frequency measurement in far-flung locations on earth and in space. Analysis of both the E1-M1 optical transition and thermal properties of the candidate clock atoms are presented. These models allow a stability estimate of an E1-M1 optical clock and recommend experimental settings to optimize the standard. The experimental work that has been performed in pursuit of observing the E1-M1 clock transition in Hg is also discussed. An optical clock operates by making a precision frequency measurement of a laser that has been brought into resonance with a clock atom's oscillator: a high quality atomic level transition. Group II type atoms, such as Hg, have the 1S0-3P0 transition that is an ideal basis for a clock. The E1-M1 excitation is performed by driving the two-photon allowed transition 1S0-3P1-3P0. This is in contrast to the single-photon E1 transition used in other systems. Single-photon schemes must use ultracold atoms to reduce atomic motion to attain high levels of accuracy. Driving the clock transition with a pair of degenerate counter-propagating photons in an E1-M1 scheme

  9. Communication: Improved pair approximations in local coupled-cluster methods

    SciTech Connect

    Schwilk, Max; Werner, Hans-Joachim; Usvyat, Denis

    2015-03-28

    In local coupled cluster treatments the electron pairs can be classified according to the magnitude of their energy contributions or distances into strong, close, weak, and distant pairs. Different approximations are introduced for the latter three classes. In this communication, an improved simplified treatment of close and weak pairs is proposed, which is based on long-range cancellations of individually slowly decaying contributions in the amplitude equations. Benchmark calculations for correlation, reaction, and activation energies demonstrate that these approximations work extremely well, while pair approximations based on local second-order Møller-Plesset theory can lead to errors that are 1-2 orders of magnitude larger.

  10. Spiral wave chimeras in locally coupled oscillator systems

    NASA Astrophysics Data System (ADS)

    Li, Bing-Wei; Dierckx, Hans

    2016-02-01

    The recently discovered chimera state involves the coexistence of synchronized and desynchronized states for a group of identical oscillators. In this work, we show the existence of (inwardly) rotating spiral wave chimeras in the three-component reaction-diffusion systems where each element is locally coupled by diffusion. A transition from spiral waves with the smooth core to spiral wave chimeras is found as we change the local dynamics of the system or as we gradually increase the diffusion coefficient of the activator. Our findings on the spiral wave chimera in the reaction-diffusion systems suggest that spiral chimera states may be found in chemical and biological systems that can be modeled by a large population of oscillators indirectly coupled via a diffusive environment.

  11. Two-photon-induced cycloreversion reaction of chalcone photodimers

    NASA Astrophysics Data System (ADS)

    Träger, J.; Härtner, S.; Heinzer, J.; Kim, H.-C.; Hampp, N.

    2008-04-01

    The photocleavage reaction of chalcone photodimers has been studied using a two-photon process. For this purpose, a novel chalcone dimer has been synthesized as a low molecular weight model substance for polymer bound chalcones and its photochemistry triggered by two-photon-absorption (2PA) has been investigated using a pulsed frequency-doubled Nd:YAG-laser. The 2PA-induced cycloreversion reaction selectively leads to the cleavage of the chalcone photodimers resulting in the formation of monomeric chalcone molecules. Hence, as an application chalcones can be used as a photosensitive linker which can be cleaved beyond an UV-absorbing barrier. The 2PA cross section of the chalcone photodimer was determined to be of 1.1 × 10 -49 cm 4 s photon -1 (11 GM).

  12. Three-dimensional micronanofabrication via two-photon-excited photoisomerization

    NASA Astrophysics Data System (ADS)

    Xia, Hong; Zhang, Wen-Yi; Wang, Fang-Fang; Wu, Dong; Liu, Xiang-Wei; Chen, Lei; Chen, Qi-Dai; Ma, Yu-Guang; Sun, Hong-Bo

    2009-08-01

    In this letter, laser micronanofabrication via two-photon absorption initiated isomerization was proposed and explored. Experimentally a cis-form rich poly[2,5-dihexyloxy-1,4-phenylene] vinylene)-alt-(2,5-diphenyl-1,4-phenylene vinylene)] (DPO-PPV) was used as the precursory material, which underwent pinpoint molecular conformational change upon the near-infrared femtosecond laser irradiation. Due to pronouncedly reduced solubility of trans-configuration molecules, the precipitate at the tiny volumes was implemented as voxels to construct two- and three-dimensional micronanostructures. This mechanism may provide an alternative enabling tool other than two-photon absorption initiated polymerization of resins for designable micronanofabrication of photonic or optoelectronic devices including organic electroluminescent devices, particularly those based on PPV and its derivatives.

  13. Extended cavity laser enhanced two-photon flow cytometry

    PubMed Central

    Tkaczyk, Eric R.; Tkaczyk, Alan H.; Katnik, Steve; Ye, Jing Yong; Luker, Kathryn E.; Luker, Gary D.; Myc, Andrzej; Baker, James R.; Norris, Theodore B.

    2015-01-01

    We demonstrate enhanced sensitivity in two-photon flow cytometry with an extended cavity laser excitation source. At low power, the home-built 20-MHz oscillator was able to detect a significantly larger fraction, in either phosphate buffered saline (PBS) or whole blood, of green fluorescent protein (GFP) –expressing MCA-207 cells cross-labeled with the membrane-binding lipophilic dye DiD. A geometrical model is used to explain unique features of the signals resulting from the different spatial distribution of DiD and GFP. These unique features include sub-square law scaling of unsaturated two-photon signal, a sigmoidal sensitivity curve for detection under varying powers for cell detection thresholds as low as a single photon, and uncorrelated signal strengths in two detection channels. PMID:19021327

  14. Direct frequency comb two-photon laser cooling and trapping

    NASA Astrophysics Data System (ADS)

    Long, Xueping; Jayich, Andrew; Campbell, Wesley C.

    2016-05-01

    Generating and manipulating high energy photons for spectroscopy on electric dipole transitions of atoms and molecules with deeply bound valence electrons is difficult. Further, laser cooling of such species is even more challenging for lack of laser power. A possible solution is to drive two-photon transitions. This may alleviate the photon energy problem and open the door to cold, trapped samples of highly desirable species with tightly bound electrons. We perform a proof of principle experiment with rubidium by driving a two-photon transition with an optical frequency comb. We perform optical cooling and extend this technique to trapping, where we are able to make a magneto-optical trap in one dimension. This work is supported by the National Science Foundation CAREER program.

  15. Thermal light two-photon imaging: magic mirrors

    NASA Astrophysics Data System (ADS)

    Scarcelli, Giuliano; Berardi, Vincenzo; Shih, Yanhua

    2005-08-01

    We show an experimental study of two-photon imaging using thermal light sources. It is interesting to see that the thermal source behaves like a mirror producing an equal size reproduction of a chosen object. We refer to such mirror as "magic" because the ghost image produced by the mirror is real in the sense that it lies in the real space and can be further imaged by a camera or an equivalent optical system. We also show that it is possible to overcome the main limitation towards the actual implementation of thermal light two-photon imaging, i.e. the poor contrast of the imaging pattern, by designing an appropriate correlation measurement scheme that is insensitive to the uncorrelated background noise.

  16. Integrated photoacoustic, confocal, and two-photon microscope

    PubMed Central

    Rao, Bin; Soto, Florentina; Kerschensteiner, Daniel; Wang, Lihong V.

    2014-01-01

    Abstract. The invention of green fluorescent protein and other molecular fluorescent probes has promoted applications of confocal and two-photon fluorescence microscopy in biology and medicine. However, exogenous fluorescence contrast agents may affect cellular structure and function, and fluorescence microscopy cannot image nonfluorescent chromophores. We overcome this limitation by integrating optical-resolution photoacoustic microscopy into a modern Olympus IX81 confocal, two-photon, fluorescence microscope setup to provide complementary, label-free, optical absorption contrast. Automatically coregistered images can be generated from the same sample. Imaging applications in ophthalmology, developmental biology, and plant science are demonstrated. For the first time, in a familiar microscopic fluorescence imaging setting, this trimodality microscope provides a platform for future biological and medical discoveries. PMID:24589986

  17. Two-photon microscopy using fiber-based nanosecond excitation.

    PubMed

    Karpf, Sebastian; Eibl, Matthias; Sauer, Benjamin; Reinholz, Fred; Hüttmann, Gereon; Huber, Robert

    2016-07-01

    Two-photon excitation fluorescence (TPEF) microscopy is a powerful technique for sensitive tissue imaging at depths of up to 1000 micrometers. However, due to the shallow penetration, for in vivo imaging of internal organs in patients beam delivery by an endoscope is crucial. Until today, this is hindered by linear and non-linear pulse broadening of the femtosecond pulses in the optical fibers of the endoscopes. Here we present an endoscope-ready, fiber-based TPEF microscope, using nanosecond pulses at low repetition rates instead of femtosecond pulses. These nanosecond pulses lack most of the problems connected with femtosecond pulses but are equally suited for TPEF imaging. We derive and demonstrate that at given cw-power the TPEF signal only depends on the duty cycle of the laser source. Due to the higher pulse energy at the same peak power we can also demonstrate single shot two-photon fluorescence lifetime measurements. PMID:27446680

  18. The potential of DABCO for two-photon amplification

    NASA Astrophysics Data System (ADS)

    Glownia, J. H.; Arjavalingam, G.; Sorokin, P. P.

    1985-05-01

    A study is made of the potential of triethylenediamine (DABCO) vapor for amplification of resonantly tuned picosecond pulses by two-photon stimulated emission (TPSE). Essential parameters needed to assess the feasibility of this experiment were determined. These include the absorption spectrum and population dynamics of the excited à state, and the (transient regime) Ã→X˜ two-photon cross section B. It is concluded that B is ˜5× too small to allow a demonstration of TPSE in a multipass ˜300 K DABCO cell, pressurized to ˜2 atm of H2, and end pumped with a ˜1 J KrF laser beam. Much higher gain exists for stimulated anti-Stokes Raman emission, which is predicted to be a practicable generating mechanism of picosecond UV (λ˜2600 Å) pulses, if a picosecond pump source near ˜2.5 μm can be found.

  19. Two-photon microscopy using fiber-based nanosecond excitation

    PubMed Central

    Karpf, Sebastian; Eibl, Matthias; Sauer, Benjamin; Reinholz, Fred; Hüttmann, Gereon; Huber, Robert

    2016-01-01

    Two-photon excitation fluorescence (TPEF) microscopy is a powerful technique for sensitive tissue imaging at depths of up to 1000 micrometers. However, due to the shallow penetration, for in vivo imaging of internal organs in patients beam delivery by an endoscope is crucial. Until today, this is hindered by linear and non-linear pulse broadening of the femtosecond pulses in the optical fibers of the endoscopes. Here we present an endoscope-ready, fiber-based TPEF microscope, using nanosecond pulses at low repetition rates instead of femtosecond pulses. These nanosecond pulses lack most of the problems connected with femtosecond pulses but are equally suited for TPEF imaging. We derive and demonstrate that at given cw-power the TPEF signal only depends on the duty cycle of the laser source. Due to the higher pulse energy at the same peak power we can also demonstrate single shot two-photon fluorescence lifetime measurements. PMID:27446680

  20. One- and two-photon detachment of O-

    NASA Astrophysics Data System (ADS)

    Génévriez, Matthieu; Urbain, Xavier; Dochain, Arnaud; Cyr, Alain; Dunseath, Kevin M.; Terao-Dunseath, Mariko

    2016-08-01

    Cross sections for one- and two-photon detachment of O-(1 s22 s22 p5P2o) have been determined in a joint experimental and theoretical study. The absolute measurement is based on the animated-crossed-beam technique, which is extended to the case of pulsed lasers, pulsed ion beams, and multiphoton detachment. The ab initio calculations employ R -matrix Floquet theory, with simple descriptions of the initial bound state and the residual oxygen atom which reproduce well the electron affinity and ground-state polarizability. For one-photon detachment, the measured and computed cross sections are in good mutual agreement, departing significantly from previous reference experiments and calculations. The generalized two-photon detachment cross section, measured at the Nd:YAG laser wavelength, is in good agreement with the R -matrix Floquet calculations. Long-standing discrepancies between theory and experiment are thus resolved.

  1. Combinatorial discovery of two-photon photoremovable protecting groups.

    PubMed

    Pirrung, Michael C; Pieper, Wolfgang H; Kaliappan, Krishna P; Dhananjeyan, Mugunthu R

    2003-10-28

    A design principle for a two-photon photochemically removable protecting group based on sequential one-photon processes has been established. The expected performance of such groups in spatially directed photoactivation/photodeprotection has been shown by a kinetic analysis. One particular molecular class fitting into this design, the nitrobenzyl ethers of o-hydroxycinnamates, has been presented. An initial demonstration of two-photon deprotection of one such group prompted further optimization with respect to photochemical deprotection rate. This was accomplished by the preparation and screening of a 135-member indexed combinatorial library. Optimum performance for lambda >350 nm deprotection in organic solvent was found with 4,5-dialkoxy and -cyano substitution in the nitrobenzyl group and 4-methoxy substitution in the cinnamate. PMID:14557545

  2. Nonstationary energy localization vs conventional stationary localization in weakly coupled nonlinear oscillators

    NASA Astrophysics Data System (ADS)

    Manevitch, Leonid I.; Kovaleva, Agnessa; Sigalov, Grigori

    2016-03-01

    In this paper we study the effect of nonstationary energy localization in a nonlinear conservative resonant system of two weakly coupled oscillators. This effect is alternative to the well-known stationary energy localization associated with the existence of localized normal modes and resulting from a local topological transformation of the phase portraits of the system. In this work we show that nonstationary energy localization results from a global transformation of the phase portrait. A key to solving the problem is the introduction of the concept of limiting phase trajectories (LPTs) corresponding to maximum possible energy exchange between the oscillators. We present two scenarios of nonstationary energy localization under the condition of 1:1 resonance. It is demonstrated that the conditions of nonstationary localization determine the conditions of efficient targeted energy transfer in a generating dynamical system. A possible extension to multi-particle systems is briefly discussed.

  3. Photochromic transformations in doped polymers upon two-photon excitation

    SciTech Connect

    Letuta, S N; Ketsle, G A; Lantukh, Yu D; Pashkevich, S N

    2001-10-31

    Physical photochromic transformations are studied in doped polymer films upon two-photon excitation. It is shown by the example of fluorescein halogen derivatives that the triplet-level population of molecules can be controlled by exciting the system by light into the T{sub 1} {yields} T{sub n} triplet - triplet absorption band of molecules. It is proposed to use this effect for fabrication of materials with controllable photochromic properties. (nonlinear optical phenomena and devices)

  4. Two-photon exchange and elastic electron-proton scattering

    SciTech Connect

    Peter Blunden; Wally Melnitchouk; John Tjon

    2003-06-01

    Two-photon exchange contributions to elastic electron-proton scattering cross sections are evaluated in a simple hadronic model including the finite size of the proton. The corrections are found to be small, but with a strong angular dependence at fixed Q{sup 2}. This is significant for the Rosenbluth technique for determining the ratio of electric and magnetic form factors of the proton, and partly reconciles the apparent discrepancy with the results of the polarization transfer technique.

  5. Relativistic Effects in Two Photon Decay of 0-+ Quarkonium

    NASA Astrophysics Data System (ADS)

    Zhou, H. Q.; Zou, B. S.

    Relativistic effects in two photon decay of 0-+ quarkonium are investigated with a relativistic phenomenological approach. Comparing with the non-relativistic approximation, the relativistic phenomenological approach gives corrections coming from three sources: qbar q relative momentum distribution, qbar q relative energy distribution and description of quark spinors in the meson. These relativistic effects are studied in detail for cbar c and sbar s systems.

  6. Simultaneous two-photon excitation of photodynamic therapy agents

    SciTech Connect

    Wachter, E.A.; Fisher, W.G. |; Partridge, W.P.; Dees, H.C.; Petersen, M.G.

    1998-01-01

    The spectroscopic and photochemical properties of several photosensitive compounds are compared using conventional single-photon excitation (SPE) and simultaneous two-photon excitation (TPE). TPE is achieved using a mode-locked titanium:sapphire laser, the near infrared output of which allows direct promotion of non-resonant TPE. Excitation spectra and excited state properties of both type 1 and type 2 photodynamic therapy (PDT) agents are examined.

  7. Two-photon exchange corrections to the pion form factor

    DOE PAGESBeta

    Peter G. Blunden; Melnitchouk, Wally; Tjon, John A.

    2010-01-06

    Here, we compute two-photon exchange corrections to the electromagnetic form factor of the pion, taking into account the finite size of the pion. Compared to the soft-photon approximation for the infrared divergent contribution which neglects hadron structure effects, the corrections are found to be ≲ 1% for small Q2 (Q2 < 0.1 GeV2), but increase to several percent for Q2 ≳ 1 GeV2 at extreme backward angles.

  8. Surface states controlled broadband enhancement of two-photon absorption

    SciTech Connect

    Zhou, Zhiqiang; Lu, Changgui; Xu, Shuhong; Jiang, Yuan; Yun, Binfeng; Wang, Chunlei; Cui, Yiping

    2013-12-02

    We demonstrate the controllable broadband enhancement of two-photon absorption in a wide spectral range from 710 nm to 960 nm by controlling the surface states of aqueous Co{sup 2+} doped CdTe quantum dots, which is consistent with the measurement results of surface potential and fluorescence decay. The enhancement can be tuned in the range between 1 and 1.7 by changing the dopant concentrations that determine the surface states.

  9. Exploring control parameters of two photon processes in solutions#

    PubMed Central

    GOSWAMI, DEBABRATA; NAG, AMIT

    2013-01-01

    Two-photon microscopy depends extensively on the two-photon absorption cross-sections of biologically relevant chromophores. High repetition rate (HRR) lasers are essential in multiphoton microscopy for generating satisfactory signal to noise at low average powers. However, HRR lasers generate thermal distortions in samples even with the slightest single photon absorption. We use an optical chopper with HRR lasers to intermittently ‘blank’ irradiation and effectively minimize thermal effects to result in a femtosecond z-scan setup that precisely measures the two-photon absorption (TPA) cross-sections of chromophores. Though several experimental factors impact such TPA measurements, a systematic effort to modulate and influence TPA characteristics is yet to evolve. Here, we present the effect of several control parameters on the TPA process that are independent of chromophore characteristics for femtosecond laser pulse based measurements; and demonstrate how the femtosecond laser pulse repetition rate, chromophore environment and incident laser polarization can become effective control parameters for such nonlinear optical properties. PMID:24098068

  10. New two-photon excitation chromophores for cellular imaging

    NASA Astrophysics Data System (ADS)

    D'Alfonso, Laura; Chirico, Giuseppe; Collini, Maddalena; Baldini, Giancarlo; Diaspro, Alberto; Ramoino, Paola; Abbotto, Alessandro; Beverina, Luca; Pagani, Giorgio A.

    2003-10-01

    The one photon and two photon excitation spectral properties (absorption, emission spectra, singlet lifetime) of a very efficient two photon absorber, dimethyl-pepep, have been measured in solution. The one photon excitation peak lye near 525 nm and the emission falls at 600 nm, where autofluorescence of cells is weak. The value of the singlet-triplet conversion rate, obtained by two-photon excitation fluorescence correlation spectroscopy, has a quadratic dependence on the excitation power and is comparable to that shown by the dye rhodamine. Preliminary results on stained cells from yeast Saccaromices cerevisiae and Paramecium primaurelia show that the dye preferentially stains DNA in the cell. A direct comparison with a DNA stainer, Dapi, is also performed. Some measurements of the dye functionalized to react with lysine and n-terminal residues of protein are presented. Moreover, this dye can be employed in order to follow in detail some cellular processes such as nuclei division. In vitro fluorescence titration of dimethyl-pepep with calf thymus DNA allowed to estimate the values of the dye-DNA association constant versus ionic strength, and an affinity close to that of ethidium bromide is found.

  11. Two-photon excited fluorescence emission from hemoglobin

    NASA Astrophysics Data System (ADS)

    Sun, Qiqi; Zeng, Yan; Zhang, Wei; Zheng, Wei; Luo, Yi; Qu, Jianan Y.

    2015-03-01

    Hemoglobin, one of the most important proteins in blood, is responsible for oxygen transportation in almost all vertebrates. Recently, we discovered two-photon excited hemoglobin fluorescence and achieved label-free microvascular imaging based on the hemoglobin fluorescence. However, the mechanism of its fluorescence emission still remains unknown. In this work, we studied the two-photon excited fluorescence properties of the hemoglobin subunits, heme/hemin (iron (II)/(III) protoporphyrin IX) and globin. We first studied the properties of heme and the similar spectral and temporal characteristics of heme and hemoglobin fluorescence provide strong evidence that heme is the fluorophore in hemoglobin. Then we studied the fluorescence properties of hemin, globin and methemoglobin, and found that the hemin may have the main effect on the methemoglobin fluorescence and that globin has tryptophan fluorescence like other proteins. Finally, since heme is a centrosymmetric molecule, that the Soret band fluorescence of heme and hemoglobin was not observed in the single photon process in the previous study may be due to the parity selection rule. The discovery of heme two-photon excited fluorescence may open a new window for heme biology research, since heme as a cofactor of hemoprotein has many functions, including chemical catalysis, electron transfer and diatomic gases transportation.

  12. Two-Photon Absorption in Organometallic Bromide Perovskites.

    PubMed

    Walters, Grant; Sutherland, Brandon R; Hoogland, Sjoerd; Shi, Dong; Comin, Riccardo; Sellan, Daniel P; Bakr, Osman M; Sargent, Edward H

    2015-09-22

    Organometallic trihalide perovskites are solution-processed semiconductors that have made great strides in third-generation thin film light-harvesting and light-emitting optoelectronic devices. Recently, it has been demonstrated that large, high-purity single crystals of these perovskites can be synthesized from the solution phase. These crystals' large dimensions, clean bandgap, and solid-state order have provided us with a suitable medium to observe and quantify two-photon absorption in perovskites. When CH3NH3PbBr3 single crystals are pumped with intense 800 nm light, we observe band-to-band photoluminescence at 572 nm, indicative of two-photon absorption. We report the nonlinear absorption coefficient of CH3NH3PbBr3 perovskites to be 8.6 cm GW(-1) at 800 nm, comparable to epitaxial single-crystal semiconductors of similar bandgap. We have leveraged this nonlinear process to electrically autocorrelate a 100 fs pulsed laser using a two-photon perovskite photodetector. This work demonstrates the viability of organometallic trihalide perovskites as a convenient and low-cost nonlinear absorber for applications in ultrafast photonics. PMID:26196162

  13. Depth and resolution characterization of two-photon photoacoustic spectroscopy for noninvasive subsurface chemical diagnostics

    NASA Astrophysics Data System (ADS)

    Dahal, Sudhir; Kiser, John B.; Cullum, Brian M.

    2011-05-01

    Photoacoustic spectroscopy is a powerful optical biopsy technique that enables rapid tumor diagnosis in situ. It has also been reported that photoacoustic spectroscopy can be used to diagnose pre-malignant tissue based on the chemical differences between healthy and pre-malignant tissues. Since the acoustic signals obtained from tissues in these analyses suffer from minimum damping, photoacoustic spectroscopy can be highly sensitive. This paper focuses on the characterization of a novel multiphoton excited photoacoustic methodology for margining of malignant and pre-malignant tissues. The two-photon excitation process in tissues using nanosecond laser pulses produces ultrasonic signals that transmit through tissue with minimal attenuation. Additionally, the two-photon excitation process is highly localized since only ballistic photons contribute to the excitation process; thereby eliminating potential absorption events in tissue not of interest (i.e., along the beam path) and increasing the spatial resolution of the diagnostic technique to that achievable via optics. This work characterizes the two-photon excitation process for photoacoustic signal measurements on a model dye. Using gelatin phantoms to mimic real tissues, tissue penetration studies were performed, revealing chemical species as deep as 1.3 cm in the tissue can easily be detected using this methodology. Furthermore, the resolution of this multiphoton excitation process was determined to be as great as 50 μm (near cellular level resolution).

  14. Two-Photon deep tissue ex vivo imaging of mouse dermal and subcutaneous structures

    NASA Astrophysics Data System (ADS)

    So, Peter; Kim, Hyun; Kochevar, Irene E.

    1998-10-01

    The non-invasive determination of deep tissue three dimensional structure and biochemistry is the ultimate goal of optical biopsy. Two-photon microscopy has been shown to be a particularly promising approach. The use of infrared radiation in two-photon microscopy is critical for deep tissue imaging since tissue absorption and scattering coefficients for infrared light are much lower than for shorter wavelengths. Equally important, tissue photodamage is localized to the focal region where fluorescence excitation occurs. This report demonstrates that, by means of high resolution two-photon microscopy, skin and subcutaneous tissue structures can be imaged utilizing their endogenous fluorescence. From a freshly prepared tissue punch of a mouse ear, we were able to 3D resolve both the living and cornified keratinocytes in the epidermis, the collagen/elastin fibers in the dermal layer and the cartilage in the subcutaneous layer. The ability to non-invasively acquire 3D structures of these tissue components may find application in areas such as non-invasive diagnosis of skin cancer and the study of wound healing processes.

  15. Applications of Two-Photon Absorption in Medicine and Biology Enabled by Specially Designed Biological Molecules

    NASA Astrophysics Data System (ADS)

    Drobizhev, M.

    2008-05-01

    We quantitatively study how the two-photon absorption (2PA) properties of biological molecules depend on their structure. 2PA is advantageous over regular one-photon absorption because of deeper penetration and more localized excitation in biological tissues. However, 2PA cross sections of biological chromophores are usually rather small to be useful in real life applications. Using quantum-mechanical few-level description of molecular electronic states, we interpret our data and predict new structures with considerably increased 2PA cross sections. These new materials either synthesized or genetically engineered make 2PA-based techniques applicable in medicine and biology. We show how our new porphyrin photosensitizers with drastically enhanced 2PA (˜1000 times compared to regular porphyrins) can be used for in vivo two-photon-induced closing of blood vessels in Age-Related Macular Degeneration. The second example describes the application of fluorescent proteins in two-photon laser microscopy of biological cells. We demonstrate how the 2PA properties of fluorescent proteins can be considerably improved by smart mutations of the environment of chromophore inside the protein.

  16. Quantum versus stochastic or hidden-variable fluctuations in two-photon interference effects

    NASA Astrophysics Data System (ADS)

    Su, C.; Wódkiewicz, K.

    1991-11-01

    In a series of experiments performed by Mandel and co-workers, nonclassical effects have been demonstrated in the interference of two photons generated in a process of parametric down-conversion. The nonclassical effects in the two-photon interference effects can be discussed in the framework of two different descriptions. In the first description, a stochastic theory of electromagnetic field fluctuations can be used in order to calculate the interference pattern. In the second description, a theory of hidden-variable fluctuations can be applied in order to calculate correlations of the interference pattern. A stochastic theory leads to statistical inequalities for the light intensities, while a local hidden-variable theory leads to Bell's inequalities. Using the Schwinger-boson representation of the angular momentum, we show that the two-photon interference effects can be described in terms of spin-correlated states. In particular, we show that the action of a beam splitter on the photons in a parametric down-conversion is equivalent to the production of an entangled state that is very similar to the well-known Einstein, Podolsky, and Rosen spin-singlet state. We show that the stochastic theory of two-photon fluctuations is not equivalent to a hidden-variable theory of photon correlations. We establish a range for which the stochastic theory fails but the hidden-variable theory is still possible. We compare our theoretical predictions with the experimental results and conclude that a violation of the stochastic theory has been clearly observed, while the violation of the hidden-variable theory is less pronounced.

  17. Tunable two-photon correlation in a double-cavity optomechanical system

    SciTech Connect

    Feng, Zhi-Bo; Zhang, Jian-Qi

    2015-12-15

    Correlated photons are essential sources for quantum information processing. We propose a practical scheme to generate pairs of correlated photons in a controllable fashion from a double-cavity optomechanical system, where the variable optomechanical coupling strength makes it possible to tune the photon correlation at our will. The key operation is based on the repulsive or attractive interaction between the two photons intermediated by the mechanical resonator. The present protocol could provide a potential approach to coherent control of the photon correlation using the optomechanical cavity.

  18. Observation of two-photon fluorescence for Rhodamine 6G in microbubble resonators.

    PubMed

    Cohoon, Gregory A; Kieu, Khanh; Norwood, Robert A

    2014-06-01

    We report an observation of multi-photon excitation of organic chromophores in microbubble whispering gallery mode resonators. High-Q microbubble resonators were formed by heating a pressurized fused silica capillary to form a hollow bubble that was then filled with liquid. In this work, the microbubble was filled with a solution of Rhodamine 6G dye. The resonator and dye were excited by evanescently coupling continuous wave (CW) light from a 980 nm laser diode using a tapered optical fiber. The two-photon fluorescence of the dye can be seen with pump powers as low as 700 μW. PMID:24875986

  19. Adiabatic two-photon quantum gate operations using a long-range photonic bus

    NASA Astrophysics Data System (ADS)

    Hope, Anthony P.; Nguyen, Thach G.; Mitchell, Arnan; Greentree, Andrew D.

    2015-03-01

    Adiabatic techniques have much potential to realize practical and robust optical waveguide devices. Traditionally, photonic elements are limited to coupling schemes that rely on proximity to nearest neighbour elements. We combine adiabatic passage with a continuum based long-range optical bus to break free from such topological restraints and thereby outline a new approach to photonic quantum gate design. We explicitly show designs for adiabatic quantum gates that produce a Hadamard, 50:50 and 1/3:2/3 beam splitter, and non-deterministic controlled NOT gate based on planar thin, shallow ridge waveguides. Our calculations are performed under conditions of one and two-photon inputs.

  20. Nonlinearly coupled localized plasmon resonances: Resonant second-harmonic generation

    NASA Astrophysics Data System (ADS)

    Ginzburg, Pavel; Krasavin, Alexey; Sonnefraud, Yannick; Murphy, Antony; Pollard, Robert J.; Maier, Stefan A.; Zayats, Anatoly V.

    2012-08-01

    The efficient resonant nonlinear coupling between localized surface plasmon modes is demonstrated in a simple and intuitive way using boundary integral formulation and utilizing second-order optical nonlinearity. The nonlinearity is derived from the hydrodynamic description of electron plasma and originates from the presence of material interfaces in the case of small metal particles. The coupling between fundamental and second-harmonic modes is shown to be symmetry selective and proportional to the spatial overlap between polarization dipole density of the second-harmonic mode and the square of the polarization charge density of the fundamental mode. Particles with high geometrical symmetry will convert a far-field illumination into dark nonradiating second-harmonic modes, such as quadrupoles. Effective second-harmonic susceptibilities are proportional to the surface-to-volume ratio of a particle, emphasizing the nanoscale enhancement of the effect.

  1. Localized patterns in homogeneous networks of diffusively coupled reactors

    NASA Astrophysics Data System (ADS)

    Moore, Peter K.; Horsthemke, Werner

    2005-06-01

    We study the influence of network topology on instabilities of the homogeneous steady state of diffusively coupled, monostable nonlinear cells. A particular focus are diffusion-induced instabilities, i.e., Turing instabilities. We present various theorems that make it possible to determine analytically the stability properties of networks with arbitrary topologies and general monostable dynamics of the individual cells. This work aims in particular to determine those topologies that will give rise to localized stationary patterns. Specific examples focus on well-stirred chemical reactors. The reactors are coupled by diffusion-like mass transfer, and the kinetics is given by the Lengyel-Epstein model, a two-variable scheme for the chlorine dioxide-iodine-malonic acid reaction.

  2. Two-Photon Optical Pulse Propagation in Sodium Vapor.

    NASA Astrophysics Data System (ADS)

    Rabbani, Syed Golam

    A detailed experimental study of two-photon coherent interaction of short optical pulses with a simple atomic system is carried out. A comparison of experimental results with the theory is also presented. The simple atomic system chosen was sodium vapor. The 3S_{1/2}-3P_ {1/2} transition was used for the one -photon interaction with a two-level system while 3S _{1/2}-3P_{1/2 }-4D_{3/2} transition was used for the two-photon interaction with a three-level system. Pulses from two single-axial-mode dye lasers, pumped synchronously by the second harmonic beam of an injection seeded Nd:YAG laser, propagate co -axially through a pyrex cell containing sodium vapor. The laser beams were focused to a diameter of about 200 μm and typical power was about 10 W, so that maximum intensities of 10^5 W/cm ^2 occurred in the Na cell. The intensity for the experiment was varied by using ND (neutral density) filters. For the two-level one-photon interaction; one of the dye lasers (Rhodamine B) was adjusted such that (lambda_1 = 589.6 nm) it was resonant with the 3S_{1/2} to 3P_{1/2} transition. For the two-photon interaction with the three-level system, the dye lasers were adjusted such that (lambda _1 = 589.6 nm and lambda_2 = 568.3 nm) they were resonant with the 3S _{1/2} to 3P_{1/2 } and 3P_{1/2} to 4D_{3/2} transition. That is lambda_1+lambda_2 were held at the 3S_{1/2} -4D_{3/2} two-photon transition. The wavelength lambda_2 was generated by the second dye laser where Rhodamine 6G was used as the gain medium. After passing through the cell, the laser pulses were focused on an aperture in order to image only a uniform -plane-wave region in the cell. The output of the aperture was then (separately lambda_1 and lambda_2) focused on two fast photodiodes, the output of which were displayed on two storage oscilloscope. The resonance of 3S _{1/2}-3P_{1/2 } transition is confirmed by collecting the D_1 fluorescence (589.6 nm) on a PMT by a fiber cable. Two-photon resonance condition

  3. Hyperspectral imaging of microalgae using two-photon excitation.

    SciTech Connect

    Sinclair, Michael B.; Melgaard, David Kennett; Reichardt, Thomas A.; Timlin, Jerilyn Ann; Garcia, Omar Fidel; Luk, Ting Shan; Jones, Howland D. T.; Collins, Aaron M.

    2010-10-01

    A considerable amount research is being conducted on microalgae, since microalgae are becoming a promising source of renewable energy. Most of this research is centered on lipid production in microalgae because microalgae produce triacylglycerol which is ideal for biodiesel fuels. Although we are interested in research to increase lipid production in algae, we are also interested in research to sustain healthy algal cultures in large scale biomass production farms or facilities. The early detection of fluctuations in algal health, productivity, and invasive predators must be developed to ensure that algae are an efficient and cost-effective source of biofuel. Therefore we are developing technologies to monitor the health of algae using spectroscopic measurements in the field. To do this, we have proposed to spectroscopically monitor large algal cultivations using LIDAR (Light Detection And Ranging) remote sensing technology. Before we can deploy this type of technology, we must first characterize the spectral bio-signatures that are related to algal health. Recently, we have adapted our confocal hyperspectral imaging microscope at Sandia to have two-photon excitation capabilities using a chameleon tunable laser. We are using this microscope to understand the spectroscopic signatures necessary to characterize microalgae at the cellular level prior to using these signatures to classify the health of bulk samples, with the eventual goal of using of LIDAR to monitor large scale ponds and raceways. By imaging algal cultures using a tunable laser to excite at several different wavelengths we will be able to select the optimal excitation/emission wavelengths needed to characterize algal cultures. To analyze the hyperspectral images generated from this two-photon microscope, we are using Multivariate Curve Resolution (MCR) algorithms to extract the spectral signatures and their associated relative intensities from the data. For this presentation, I will show our two-photon

  4. Rate for annihilation of galactic dark matter into two photons

    NASA Technical Reports Server (NTRS)

    Giudice, Gian F.; Griest, Kim

    1989-01-01

    A calculation of the cross section for neutralino-neutralino annihilation into two photons is performed and applied to dark matter in the galactic halo to find the counting rate in a large gamma ray detector such as EGRET (Energetic Gamma Ray Experiment Telescope) or ASTROGAM. Combining constraints from particle accelerators with the requirement that the neutralinos make up the dark matter, it is found that rates of over a few dozen events per year are unlikely. The assumptions that go into these conclusions are listed. Other particle dark matter candidates which could give larger and perhaps observable signals are suggested.

  5. Direct two-photon double ionization of H2

    NASA Astrophysics Data System (ADS)

    Simonsen, A. S.; Sørngård, S. A.; Nepstad, R.; Førre, M.

    2012-06-01

    We have studied the process of direct (nonsequential) two-photon double ionization of molecular hydrogen (H2). Solving the time-dependent Schrödinger equation by an ab initio method, total (generalized) and single-differential cross sections are obtained at photon energies from 26 to 33 eV. Both parallel and perpendicular orientation of the molecule with respect to the laser polarization direction are considered, and the results are compared with previously calculated cross sections at 30 eV, as well as the predictions of a simple model.

  6. Two-photon microscopy of nanoparticles and biotissues

    NASA Astrophysics Data System (ADS)

    Rivera, Judith Noemi

    Biomedical Imaging is an important tool in medical research and clinical practice. From understanding the fundamental processes involved in our biological makeup to its use in diagnostics in helping determine what ails us, the advancements in imaging and microscopy have helped shape our view of the world and nature. Microscopy in particular is often used to study the smallest of cells and their dynamical properties while attempting to minimally change the sample being studied. My research objective is largely divided into two parts. The first part consists of designing a video-rate raster scanning two-photon microscope that is faster than current commercially available two-photon microscopes, while maintaining the high-quality optical resolution of the system. This fast scanning mechanism proves to be an essential component in biomedical imaging due to the fact that many biological processes are dynamic and require the use of imaging systems with a high degree of temporal resolution in order to study. The second objective of my research is to implement the microscope, building it up component by component, and then demonstrating its high speed imaging capabilities, in which I have been largely successful. Current commercially available two-photon microscopes have imaging speeds on the order of 2 frames per second; however, our imaging system currently has a video-rate imaging speed at 30 frames per second. In addition, with further improvements and changes to the electronics that control our mirrors, we hope to soon achieve imaging speeds of up to 300 frames per second. Since my goal is to increase the temporal resolvability of images while imaging a fast moving, dynamic biological system, I also helped design and construct a second two-photon microscope that theoretically has the ability to temporally resolve the images on the order of several thousand of frames per second. However, given the high image acquisition period of our relatively low peak power laser, we

  7. Two Photon Decays of Charmonia from Lattice QCD

    SciTech Connect

    Jozef Dudek; Robert Edwards

    2006-07-12

    We make the first calculation in lattice QCD of two-photon decays of mesons. Working in the charmonium sector, using the LSZ reduction to relate a photon to a sum of hadronic vector eigenstates, we compute form-factors in both the space-like and time-like domains for the transitions {eta}{sub c} {yields} {gamma}*{gamma}* and {chi}{sub c0} {yields} {gamma}*{gamma}*. At the on-shell point we find approximate agreement with experimental world-average values.

  8. Polarization rotation under two-photon Raman resonance for magnetometry

    SciTech Connect

    Pradhan, S.; Behera, R.; Das, A. K.

    2012-04-23

    The polarization rotation and coherent population trapping signal arising due to two photon process using linearly polarized light are found to be significantly enhanced for a Zeeman degenerate system. The zero crossing of the dispersive profile is found to be shifting proportional to the applied magnetic field, albeit the absorptive profile position remains invariant for a slightly imbalanced orthogonal circular polarization component. It provides an alternative method for precise measurement of vector magnetic field without requirement of a bias field. The use of polarization rotation signal for magnetic field measurement offers added advantage due to improved signal to noise ratio.

  9. Imaging nanowire plasmon modes with two-photon polymerization

    SciTech Connect

    Gruber, Christian; Trügler, Andreas; Hohenester, Ulrich; Ditlbacher, Harald; Hohenau, Andreas; Krenn, Joachim R.; Hirzer, Andreas; Schmidt, Volker

    2015-02-23

    Metal nanowires sustain propagating surface plasmons that are strongly confined to the wire surface. Plasmon reflection at the wire end faces and interference lead to standing plasmon modes. We demonstrate that these modes can be imaged via two-photon (plasmon) polymerization of a thin film resist covering the wires and subsequent electron microscopy. Thereby, the plasmon wavelength and the phase shift of the nanowire mode picked up upon reflection can be directly retrieved. In general terms, polymerization imaging is a promising tool for the imaging of propagating plasmon modes from the nano- to micro-scale.

  10. Nonlinear Dual-Comb Spectroscopy with Two-Photon Excitation

    NASA Astrophysics Data System (ADS)

    Meek, S. A.; Hipke, A.; Hansch, T. W.; Picque, N.

    2013-06-01

    Dual frequency comb spectroscopy has proven to be a powerful method for acquiring broadband, high resolution spectra with measurement times that are much shorter than in traditional moving-mirror Fourier transform spectroscopy. Because the measurements are carried out with femtosecond lasers, this technique has great potential for decreasing the measurement times and improving the signal-to-noise ratio of nonlinear spectroscopic measurements, such as two-photon excitation or Raman processes. In the case of two-photon excitation, an entire spectrum can be obtained at a given signal level using dual-comb spectroscopy in the same time that a measurement of a single transition frequency would be obtained with a continuous laser of the same average power. In this presentation, I will show the latest results in extending the dual-comb technique to two-photon excitation spectroscopy, with measurements on gas-phase rubidium and liquid-phase dye samples. In our realization of dual-comb spectroscopy, two frequency combs with slightly different repetition rates are combined on a beam splitter and directed into a sample, and we measure the intensity of the resulting fluorescence as a function of time. Because of the different repetition rates, the time delay between a pulse from the first comb and the next pulse from the second comb changes linearly with time, simulating the action of the moving mirror in a traditional Michelson interferometer. The Fourier transform of the measured time-domain interferogram produces a radio-frequency spectrum that can be directly converted to a broadband optical spectrum through a linear scaling of the frequency. To achieve the highest possible resolution, it is necessary to compensate the residual relative fluctuations of the repetition rate and the carrier-envelope offset frequency of the frequency combs. Measuring RF beatnotes of each comb with two CW lasers provides two error signals that can be used to correct the recorded interferograms

  11. Metastable Krypton Beam Source via Two-Photon Pumping Technique

    SciTech Connect

    Wong, W.W.; Young, L.

    2003-01-01

    Metastable beams of rare gas atoms have wide applications in chemical analysis of samples, as well as in aiding understanding of fundamental processes and physical attributes. Most current sources of metastable rare gas atomic beams, however, are limited in their flux density, which greatly reduces their utility in applications such as low level trace analysis and precision measurements. Previous work has demonstrated feasibility of metastable krypton production via two-photon pumping, and this paper extends that possibility into beam form. Further optimization on this scheme, moreover, promises 100-fold increase of metastable krypton flux density over that of an rf-driven discharge.

  12. Two-photon entanglement in multiqubit bidirectional-waveguide QED

    NASA Astrophysics Data System (ADS)

    Mirza, Imran M.; Schotland, John C.

    2016-07-01

    We study entanglement generation and control in bidirectional-waveguide QED driven by a two-photon Gaussian wave packet. In particular, we focus on how increasing the number of qubits affects the overall average pairwise entanglement in the system. We also investigate how the presence of a second photon can introduce nonlinearities, thereby manipulating the generated entanglement. In addition, we show that, through the introduction of chirality and small decay rates, entanglement can be stored and enhanced up to factors of 2 and 3, respectively. Finally, we analyze the influence of finite detunings and time-delays on the generated entanglement.

  13. Two-photon tomography using on-chip quantum walks.

    PubMed

    Titchener, James G; Solntsev, Alexander S; Sukhorukov, Andrey A

    2016-09-01

    We present an approach to quantum tomography based on first expanding a quantum state across extra degrees of freedom and then exploiting the introduced sparsity to perform reconstruction. We formulate its application to photonic circuits and show that measured spatial photon correlations at the output of a specially tailored discrete-continuous quantum walk can enable full reconstruction of any two-photon spatially entangled and mixed state at the input. This approach does not require any tunable elements, so it is well suited for integration with on-chip superconducting photon detectors. PMID:27607977

  14. Two-Photon Photochemical Generation of Reactive Enediyne

    PubMed Central

    Poloukhtine, Andrei; Popik, Vladimir V.

    2008-01-01

    p-Quinoid cyclopropenone-containing enediyne precursor (1) has been synthesized by mono-cyclopropanation of one of the triple bonds in p-dimethoxy substituted 3,4-benzocyclodeca-1,5-diyne followed by oxidative demethylation. Cyclopropenone 1 is stable up to 90°C but readily produces reactive enediyne 2 upon single-photon (Φ300nm = 0.46) or two-photon (σ800 nm = 0.5 GM) photolysis. The photo-product 2 undergoes Bergman cyclization at 40°C with the life time of 88 h. PMID:16958537

  15. Two-photon spectroscopy of excitons with entangled photons

    SciTech Connect

    Schlawin, Frank; Mukamel, Shaul

    2013-12-28

    The utility of quantum light as a spectroscopic tool is demonstrated for frequency-dispersed pump-probe, integrated pump-probe, and two-photon fluorescence signals which show Ramsey fringes. Simulations of the frequency-dispersed transmission of a broadband pulse of entangled photons interacting with a three-level model of matter reveal how the non-classical time-bandwidth properties of entangled photons can be used to disentangle congested spectra, and reveal otherwise unresolved features. Quantum light effects are most pronounced at weak intensities when entangled photon pairs are well separated, and are gradually diminished at higher intensities when different photon pairs overlap.

  16. Two-Photon Exchange in (Semi-)Inclusive DIS

    SciTech Connect

    Schlegel, Marc; Metz, Andreas

    2009-01-01

    In this note we consider effects of a Two-Photon Exchange (TPE) in inclusive DIS and semi-inclusive DIS (SIDIS). In particular, transverse single spin asymmetries are generated in inclusive DIS if more than one photon is exchanged between the lepton and the hadron. We briefly summarize the TPE in DIS in the parton model and extend our approach to SIDIS, where a new leading twist $\\sin(2\\phi)$ contribution to the longitudinal beam spin asymmetry shows up. Possible TPE effects for the Sivers and the Collins asymmetries in SIDIS are power-suppressed.

  17. Two-Photon Exchange in (Semi-)Inclusive DIS

    SciTech Connect

    Schlegel, M.; Metz, A.

    2009-08-04

    In this note we consider effects of a Two-Photon Exchange (TPE) in inclusive DIS and semi-inclusive DIS (SIDIS). In particular, transverse single spin asymmetries are generated in inclusive DIS if more than one photon is exchanged between the lepton and the hadron. We briefly summarize the TPE in DIS in the parton model and extend our approach to SIDIS, where a new leading twist sin(2{phi}) contribution to the longitudinal beam spin asymmetry shows up. Possible TPE effects for the Sivers and the Collins asymmetries in SIDIS are power-suppressed.

  18. Two-photon exchange corrections to the pion form factor

    SciTech Connect

    Peter G. Blunden; Melnitchouk, Wally; Tjon, John A.

    2010-01-06

    Here, we compute two-photon exchange corrections to the electromagnetic form factor of the pion, taking into account the finite size of the pion. Compared to the soft-photon approximation for the infrared divergent contribution which neglects hadron structure effects, the corrections are found to be ≲ 1% for small Q2 (Q2 < 0.1 GeV2), but increase to several percent for Q2 ≳ 1 GeV2 at extreme backward angles.

  19. Two-photon exchange in electron-trinucleon elastic scattering

    NASA Astrophysics Data System (ADS)

    Kobushkin, A. P.; Timoshenko, Ju. V.

    2013-10-01

    We discuss two-photon exchange (TPE) in elastic electron scattering off the trinucleon systems, 3He and 3H. The calculations are done in the semirelativistic approximation with the trinucleon wave functions obtained with the Paris and CD-Bonn nucleon-nucleon potentials. An applicability area of the model is wide enough and includes the main part of kinematical domain where experimental data exist. All three TPE amplitudes (generalized form factors) for electron 3He elastic scattering are calculated. We find that the TPE amplitudes are a few times more significant in the scattering of electrons off 3He then in the electron-proton scattering.

  20. Two-photon interferences with degenerate and nondegenerate paired photons

    NASA Astrophysics Data System (ADS)

    Liu, Chang; Chen, J. F.; Zhang, Shanchao; Zhou, Shuyu; Kim, Yoon-Ho; Loy, M. M. T.; Wong, G. K. L.; Du, Shengwang

    2012-02-01

    We generate narrow-band frequency-tunable entangled photon pairs from spontaneous four-wave mixing in three-level cold atoms and study their two-photon quantum interference after a beam splitter. We find that the path-exchange symmetry plays a more important role in the Hong-Ou-Mandel interference than the temporal or frequency indistinguishability, and observe coalescence interference for both degenerate and nondegenerate photons. We also observe a quantum beat in the same experimental setup using either slow or fast detectors.

  1. Using ac dipoles to localize sources of beam coupling impedance

    NASA Astrophysics Data System (ADS)

    Biancacci, N.; Tomás, R.

    2016-05-01

    The beam coupling impedance is one of the main sources of beam instabilities and emittance blow up in circular accelerators. A refined machine impedance evaluation is therefore required in order to understand and model intensity dependent effects and instabilities that may limit the machine performance. For this reason, many impedance source localization techniques have been developed. In this work we present the impedance localization technique based on the observation of phase advance versus intensity at the beam position monitors using ac dipoles to force betatron oscillations. We present analytical formulas for the interpretation of measurements together with simulations to benchmark and illustrate the equations. Studies on the method accuracy for different Fourier transform algorithms are presented as well as first exploratory measurements performed in the LHC.

  2. Fully integrated reflection-mode photoacoustic, two-photon, and second harmonic generation microscopy in vivo

    PubMed Central

    Song, Wei; Xu, Qiang; Zhang, Yang; Zhan, Yang; Zheng, Wei; Song, Liang

    2016-01-01

    The ability to obtain comprehensive structural and functional information from intact biological tissue in vivo is highly desirable for many important biomedical applications, including cancer and brain studies. Here, we developed a fully integrated multimodal microscopy that can provide photoacoustic (optical absorption), two-photon (fluorescence), and second harmonic generation (SHG) information from tissue in vivo, with intrinsically co-registered images. Moreover, using a delicately designed optical-acoustic coupling configuration, a high-frequency miniature ultrasonic transducer was integrated into a water-immersion optical objective, thus allowing all three imaging modalities to provide a high lateral resolution of ~290 nm with reflection-mode imaging capability, which is essential for studying intricate anatomy, such as that of the brain. Taking advantage of the complementary and comprehensive contrasts of the system, we demonstrated high-resolution imaging of various tissues in living mice, including microvasculature (by photoacoustics), epidermis cells, cortical neurons (by two-photon fluorescence), and extracellular collagen fibers (by SHG). The intrinsic image co-registration of the three modalities conveniently provided improved visualization and understanding of the tissue microarchitecture. The reported results suggest that, by revealing complementary tissue microstructures in vivo, this multimodal microscopy can potentially facilitate a broad range of biomedical studies, such as imaging of the tumor microenvironment and neurovascular coupling. PMID:27576922

  3. Fully integrated reflection-mode photoacoustic, two-photon, and second harmonic generation microscopy in vivo.

    PubMed

    Song, Wei; Xu, Qiang; Zhang, Yang; Zhan, Yang; Zheng, Wei; Song, Liang

    2016-01-01

    The ability to obtain comprehensive structural and functional information from intact biological tissue in vivo is highly desirable for many important biomedical applications, including cancer and brain studies. Here, we developed a fully integrated multimodal microscopy that can provide photoacoustic (optical absorption), two-photon (fluorescence), and second harmonic generation (SHG) information from tissue in vivo, with intrinsically co-registered images. Moreover, using a delicately designed optical-acoustic coupling configuration, a high-frequency miniature ultrasonic transducer was integrated into a water-immersion optical objective, thus allowing all three imaging modalities to provide a high lateral resolution of ~290 nm with reflection-mode imaging capability, which is essential for studying intricate anatomy, such as that of the brain. Taking advantage of the complementary and comprehensive contrasts of the system, we demonstrated high-resolution imaging of various tissues in living mice, including microvasculature (by photoacoustics), epidermis cells, cortical neurons (by two-photon fluorescence), and extracellular collagen fibers (by SHG). The intrinsic image co-registration of the three modalities conveniently provided improved visualization and understanding of the tissue microarchitecture. The reported results suggest that, by revealing complementary tissue microstructures in vivo, this multimodal microscopy can potentially facilitate a broad range of biomedical studies, such as imaging of the tumor microenvironment and neurovascular coupling. PMID:27576922

  4. Two-photon experiments in the frequency domain

    NASA Astrophysics Data System (ADS)

    Mbodji, I.; Olislager, L.; Woodhead, E.; Galmes, B.; Cussey, J.; Furfaro, L.; Emplit, P.; Massar, S.; Phan Huy, K.; Merolla, J.-M.

    2012-06-01

    We report on the study of two-photon interference in the frequency domain. Bell and Hong-Ou-Mandel experiments are investigated. These experiments involve the manipulation of photons in the frequency domain, using off-the-shelf telecommunication components such as electro-optic phase modulators and narrow-band frequency filters. In the first experiment, photon pairs entangled in frequency are created and separated. Each photon is then directed through an independent electro-optic phase modulator. Variation of the radio-frequency parameters of the modulation gives rise to a well-controlled Bessel-shape two-photon interference pattern in the frequency domain. This is efficiently measured with narrow-band frequency filters and superconducting single photon detectors. Experimental measurements exhibit high visibilities (over 99 percent both for net and raw visibilities) and allow the (theoretically proven) optimal violation of a Bell inequality for our setup (by more than 18 standard deviations). The second experiment is a Hong-Ou-Mandel experiment in the frequency domain. We show that a grating (spatial domain) or a phase modulator (temporal domain) can be seen as a frequency beam splitter. A broadband spectrum of photon pairs is divided into two interleaved frequency combs, each one used as an independent input to this acting beam splitter. A theoretical calculation shows clear photon anti-bunching behavior.

  5. Imaging of Protein Crystals with Two-Photon Microscopy

    SciTech Connect

    Padayatti, Pius; Palczewska, Grazyna; Sun, Wenyu; Palczewski, Krzysztof; Salom, David

    2012-05-02

    Second-order nonlinear optical imaging of chiral crystals (SONICC), which portrays second-harmonic generation (SHG) by noncentrosymmetric crystals, is emerging as a powerful imaging technique for protein crystals in media opaque to visible light because of its high signal-to-noise ratio. Here we report the incorporation of both SONICC and two-photon excited fluorescence (TPEF) into one imaging system that allows visualization of crystals as small as 10 {mu}m in their longest dimension. Using this system, we then documented an inverse correlation between the level of symmetry in examined crystals and the intensity of their SHG. Moreover, because of blue-green TPEF exhibited by most tested protein crystals, we also could identify and image SHG-silent protein crystals. Our experimental data suggest that the TPEF in protein crystals is mainly caused by the oxidation of tryptophan residues. Additionally, we found that unspecific fluorescent dyes are able to bind to lysozyme crystals and enhance their detection by TPEF. We finally confirmed that the observed fluorescence was generated by a two-photon rather than a three-photon process. The capability for imaging small protein crystals in turbid or opaque media with nondamaging infrared light in a single system makes the combination of SHG and intrinsic visible TPEF a powerful tool for nondestructive protein crystal identification and characterization during crystallization trials.

  6. Interpreting two-photon imaging data of lymphocyte motility.

    PubMed

    Meyer-Hermann, Michael E; Maini, Philip K

    2005-06-01

    Recently, using two-photon imaging it has been found that the movement of B and T cells in lymph nodes can be described by a random walk with persistence of orientation in the range of 2 minutes. We interpret this new class of lymphocyte motility data within a theoretical model. The model considers cell movement to be composed of the movement of subunits of the cell membrane. In this way movement and deformation of the cell are correlated to each other. We find that, indeed, the lymphocyte movement in lymph nodes can best be described as a random walk with persistence of orientation. The assumption of motility induced cell elongation is consistent with the data. Within the framework of our model the two-photon data suggest that T and B cells are in a single velocity state with large stochastic width. The alternative of three different velocity states with frequent changes of their state and small stochastic width is less likely. Two velocity states can be excluded. PMID:16089770

  7. Coherent Two Photon Production in Superconductor-Semiconductor Heterostructures

    NASA Astrophysics Data System (ADS)

    Baireuther, Paul; Vekhter, Ilya; Schmalian, Jörg

    2012-02-01

    Connecting a thin (direct band gap) p-n junction to a superconductor allows Cooper pairs to tunnel into the junction. This leads to an enhancement of the luminescence at the junction via Cooper pair based radiative recombination[1,2], an effect that has recently been observed experimentally[3]. Due to the proximity-induced Cooper pairs in the junction, anomalous photon production related to coherent two photon processes becomes allowed. Using a simple model for direct band gap luminescence we study a superconductor-p-n-superconductor heterostructure where the two photon state depends on the relative phase between the two superconductors. We investigate to what extend the production rate of entangled photons is controlled by the phase difference between the attached superconductors. [1] E. Hanamura, Phys. Stat. Sol. (b) 234, 166 (2002). [2] Y. Asano, I. Suemune, H. Takayanagi, and E. Hanamura, Phys. Rev. Lett. 103, 187001 (2009). [3] I. Suemune, T. Akazaki, K. Tanaka, M. Jo, K. Uesugi, M. Endo1, H. Kumano, E. Hanamura, H. Takayanagi, M. Yamanishi and H. Kan, Jpn. Journ. of Appl. Phys. 45, 9264 (2006).

  8. Two-photon imaging using a flexible endoscope

    NASA Astrophysics Data System (ADS)

    Riemann, Iris; Schenkl, Selma; Le Harzic, Ronan; Sauer, Daniel; Ehlers, Alexander; Messerschmidt, Bernhard; Bückle, Rainer; König, Karsten

    2008-02-01

    Two-photon autofluorescence imaging offers the analysis of cells and tissues without the need of taking biopsies, staining and complicated confocal detection systems. Therefore, it is of special interest for non- or minimal invasive clinical diagnostics. Until now, two-photon imaging was performed only on superficial surfaces like skin or of biopsies. To extend this technique to deeper tissues or inside the body the optical properties have to be reduced to endoscopical sizes. This can be achieved by tiny GRIN-optics, based on a radial gradient in the reflective index. A newly developed GRIN-lens assembly with increased numerical aperture is of special interest which is shown by the quality of tissue constituents and cell autofluorescence images. A fiber directs the laser light to the specimen in an assembly like an endoscope. This well-characterized photonic crystal fiber supports the high laser power of the femtosecond excitation impulses without the generation of non-linearities. A sensitive PMT detector detects the fluorescence. First fluorescence images using a fiber-GRIN lens combination were taken.

  9. Multidimensional two-photon imaging of diseased skin

    NASA Astrophysics Data System (ADS)

    Cicchi, R.; Sestini, S.; De Giorgi, V.; Massi, D.; Lotti, T.; Pavone, F. S.

    2008-02-01

    We used combined two photon intrinsic fluorescence (TPE), second harmonic generation microscopy (SHG), fluorescence lifetime imaging microscopy (FLIM), and multispectral two photon emission detection (MTPE) to investigate different kinds of human cutaneous ex-vivo skin lesions. Morphological and spectroscopic analyses allowed to characterize both healthy and pathological skin samples, including tumors, as well as to discriminate between healthy and diseased tissue, in a good agreement with common routine histology. In particular, we examined tissue samples from normal and pathological scar tissue (keloid), and skin tumors, including basal cell carcinoma (BCC) and malignant melanoma (MM). By using combined TPE-SHG microscopy we investigated morphological features of different skin regions, as BCC, tumor-stroma interface, healthy dermis, fibroblastic proliferation, and keloids. The SHG to autofluorescence aging index of dermis (SAAID) score was used to characterize each region, finding differences between BCC, healthy skin, tumor-stroma interface, keloids, and fibroblastic proliferation. Further comparative analysis of healthy skin and neoplastic samples was performed using FLIM. In particular, BCC showed a blue-shifted fluorescence emission, a higher absorption at 800 nm excitation wavelength, and a slightly longer mean fluorescence lifetime. MM showed a lifetime distribution similar to the corresponding melanocytic nevus (MN) lifetime distribution for the slow lifetime component, and different for the fast lifetime component.

  10. Two-Photon-Induced Fluorescence of Isomorphic Nucleobase Analogs

    PubMed Central

    Lane, Richard S. K.; Jones, Rosemary; Sinkeldam, Renatus W.

    2014-01-01

    Five isomorphic fluorescent uridine mimics have been subjected to two-photon (2P) excitation analysis to investigate their potential applicability as non-perturbing probes for the single-molecule detection of nucleic acids. We find that small structural differences can cause major changes in the two-photon excitation probability, with the 2P cross sections varying by over one order of magnitude. Two of the probes, both furan-modified uridine analogs, have the highest 2P cross sections (3.8 GM and 7.6 GM) reported for nucleobase analogs, using a conventional Ti:sapphire laser for excitation at 690 nm; they also have the lowest emission quantum yields. In contrast, the analogs with the highest reported quantum yields have the lowest 2P cross sections. The structure-photophysical property relationship presented here is a first step towards the rational design of emissive nucleobase analogs with controlled 2P characteristics. The results demonstrate the potential for major improvements through judicious structural modifications. PMID:24604669