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Sample records for doppler-free two-photon optogalvanic

  1. Doppler-Free Two-Photon Absorption Spectroscopy of Naphthalene Assisted by AN Optical Frequency Comb

    NASA Astrophysics Data System (ADS)

    Nishiyama, Akiko; Matsuba, Ayumi; Misono, Masatoshi

    2014-06-01

    Optical frequency combs are powerful tools for precise frequency measurements in various wavelength regions. The combs have been applied not only to metrology, but also to molecular spectroscopy. Recently, we studied high resolution spectroscopy of iodine molecule assisted by an optical frequency comb. In the study, the comb was used for frequency calibration of a scanning dye laser. In this study, we developed a frequency calibration scheme with a comb and an acousto-optic modulator to realize more precise frequency measurement in a wide frequency range. And the frequency calibration scheme was applied to Doppler-free two-photon absorption (DFTPA) spectroscopy of naphthalene. Naphthalene is one of the prototypical aromatic molecules, and its detailed structure and dynamics in excited states have been reported. We measured DFTPA spectra of A^1B1u(v4=1) ← X^1A_g(v=0) transition around 298 nm. A part of obtained spectra is shown in the figure. The spectral lines are rotationally resolved and the resolution is about 100 kHz. The horizontal axis was calibrated by the developed frequency calibration system employing the comb. The uncertainties of the calibrated frequencies were determined by the fluctuations of the comb modes which were stabilized to a GPS-disciplined clock. A. Nishiyama, D. Ishikawa, and M. Misono, J. Opt. Soc. Am. B 30, 2107 (2013).

  2. Plasma magnetic field diagnostic using two-photon Doppler-free LIF

    NASA Astrophysics Data System (ADS)

    Yoon, Young Dae; Bellan, Paul

    2015-11-01

    A detailed description of a new plasma B field diagnostic using Doppler-free two-photon laser-induced fluorescence is presented. The diagnostic is based on a method previously developed in the context of rubidium vapor experiments. Two counter-propagating 393nm diode laser beams are directed into an argon plasma to excite Ar-II ions from 3s2 3p4 4 s4P1 / 2 ⟶ 3s2 3p4 4 p4S3 / 2 ⟶ 3s2 3p4 4 d4P3 / 2 . These levels involve two similar (392.86 and 393.25nm) transition wavelengths, so the two counter-propagating beams effectively cancel out the Doppler effect. The excited ions then decay to the 3s2 3p4 4 p4P1 / 2 level, emitting a 324.98nm line which is to be detected by a photomultiplier tube. The Zeeman splitting -- normally unobservable because of the large Doppler broadening -- of the resultant fluorescence is then to be analyzed, yielding the magnetic field of the particular location. This method is expected to provide a 3-D localized, non-perturbing measurement of magnetic fields. An experimental implementation is currently in progress.

  3. Doppler-free two-photon absorption spectroscopy of rovibronic transition of naphthalene calibrated with an optical frequency comb

    NASA Astrophysics Data System (ADS)

    Nishiyama, A.; Nakashima, K.; Matsuba, A.; Misono, M.

    2015-12-01

    We performed Doppler-free two-photon absorption spectroscopy of naphthalene using an optical frequency comb as a frequency reference. Rotationally resolved rovibronic spectra were observed, and absolute frequencies of the rovibronic transitions were determined with an uncertainty of several tens of kHz. The resolution and precision of our system are finer than the natural width of naphthalene. We assigned 1466 lines of the Q (Ka) Q (J) transition and calculated molecular constants. We attribute systematic spectral line shifts to the Coriolis interaction, and discuss the origin of the spectral linewidths.

  4. Doppler-free two-photon spectroscopy on the S 1 ← S 0 origin band of 1,4-diazabicyclo[2,2,2]octane (DABCO)

    NASA Astrophysics Data System (ADS)

    Berden, Giel; Groot, Tim; van der Veldt, Tony; Meijer, Gerard

    1997-01-01

    The rotationally resolved two-photon excitation spectrum of the Q-branch ( ΔJ = 0) of the O 00 band in the S 1 ← S 0 transition of DABCO was recorded in a cell at room temperature. Two counterpropagating narrow bandwidth laser beams were used for Doppler-free excitation. The observed linewidth was 20 MHz. Analysis of the spectra provides the change upon electronic excitation of the rotational constants.

  5. Local Electric Field Strength in a Hollow Cathode Determined by Stark Splitting of the 2S Level of Hydrogen Isotopes by Optogalvanic Spectroscopy

    SciTech Connect

    Perez, C.; Rosa, M. I. de la; Gruetzmacher, K.; Fuentes, L. M.; Gonzalo, A. B.

    2008-10-22

    In this work we present Doppler-free two-photon optogalvanic spectroscopy as a tool to measure the electric field strength in the cathode fall region of a hollow cathode discharge via the Stark splitting of the 2S level of atomic deuterium. The strong electric field strength present in the hollow cathode is determined for various discharge conditions which allows studying the corresponding variations of the cathode fall, and its changes with discharge operation time.

  6. Doppler-free two-photon excitation spectroscopy and the Zeeman effect of the 1401 band of the S1 1B2u<--S0 1A1g transition of benzene-d6

    NASA Astrophysics Data System (ADS)

    Wang, Jinguo; Doi, Atsushi; Kasahara, Shunji; Katô, Hajime; Baba, Masaaki

    2004-11-01

    The Doppler-free two-photon excitation spectrum and the Zeeman effect of the 1401 band of the S1←S0 transition of C6D6 were measured from 39 842 to 39 856 cm-1. The Zeeman splittings of the Q(K)Q(J) lines of a given J were observed to increase proportionally with K2 and reach a maximum at K=J. The Zeeman splittings of the Q(K=J)Q(J) lines were observed to increase proportionally with J. The observed Zeeman splittings are identified as originating from the electronic orbital angular momentum arising from a mixing of the S1 1B2u and S2 1B1u states via J-L coupling. No perturbation originating from an interaction with a triplet state was observed. It became clear from the Zeeman effect that rotationally resolved levels of the S1 state are not mixed with a triplet state. Therefore, it is concluded that nonradiative decay of an isolated benzene molecule excited to the S1 state occurs through the intramolecular vibrational-rotational mixing within the S1 state even in the low vibrational levels.

  7. dc discharge cell for laser optogalvanic spectroscopy

    NASA Technical Reports Server (NTRS)

    Webster, C. R.

    1983-01-01

    A dc electrical discharge cell for laser optogalvanic spectroscopy has been designed and tested. Signal optimization is achieved through the use of adjustable electrode positions and an orthogonal geometry between the probe laser and the discharge axis. Results are presented for visible dye laser and infrared diode laser studies of selected neutral, radical, and ion species.

  8. 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.

  9. Efficient reflection via four-wave mixing in a Doppler-free electromagnetically-induced-transparency gas system

    SciTech Connect

    Zhou, Hai-Tao; Wang, Dan; Zhang, Jun-Xiang; Wang, Da-Wei; Zhu, Shi-Yao

    2011-11-15

    We experimentally demonstrate the high-efficiency reflection of a probe field in {Lambda}-type three-level atoms of cesium vapor driven by two counterpropagating coupling fields. More than 60% of reflection efficiency is observed at the phase-matching angle. The underlying mechanism theoretically is investigated as the four-wave mixing is enhanced by the electromagnetically-induced transparency. Both of the two Doppler-free two-photon resonances (one for the probe and co-propagating fields, the other for the reflected and the counterpropagation fields) play an important role in satisfying the phase matching in the reflection direction. The phase compensation due to the anomalous dispersion and the decrease of effective absorption length in the atomic system allow the efficient reflection to be observed in a wide range of incident angles of the probe field and detunings of the coupling field.

  10. Study of the anode plasma double layer: optogalvanic detectors

    SciTech Connect

    Gurlui, S.; Dimitriu, D.; Strat, M.; Strat, Georgeta

    2006-01-15

    The experimental and theoretical results show that the anode double layer (DL) is a very sensitive plasma formation suitable for fine optogalvanic studies. The obtained results demonstrate that the parameters of the oscillations sustained by a DL (frequency, amplitude) can be used as optogalvanic detectors.

  11. Quantitative studies of the Optogalvanic Effect and Optogalvanic Line Ratio Spectroscopy (OGLRS)

    NASA Astrophysics Data System (ADS)

    Whitehead, C. J.; Stewart, R. S.; Chavez-Chavez, A.

    We have developed the technique of Optogalvanic Line Ratio Spectroscopy (OGLRS) in which simultaneous optogalvanic and absorption measurements are made on both lines for a pair of transitions under the same discharge conditions. This removes the need for accurate knowledge of the difficult-to-determine discharge dynamic impedance, and leaves terms describing the kinetics of the excited states of the particlar transitions selected. We believe OGLRS has considerable advantages because all the necessary experimental data can be determined accurately and compared with the theoretical model for the line ratio. We have measured and tested line ratios for a large number of neon 1s-2p transitions in the positive column as well as preliminary testing in the negative glow of a hollow-cathode discharge. For cases where the optogalvanic line ratio is strongly dependent on the particular states involved in the two transitions, we have shown that OGLRS may be successfully used as a sensitive test of important kinetic processes such as direct and indirect collisional population mixing and wall losses due to diffusion and resonance radiation trapping.

  12. Towards a portable optical clock based on a two-photon transition

    NASA Astrophysics Data System (ADS)

    Potnis, Shreyas; Jackson, Shira; Vutha, Amar

    2016-05-01

    Optical clocks based on narrow linewidth atomic transitions have achieved an unprecedented level of precision. These clocks rely on tight confinement of atoms by light, to mitigate Doppler shifts and atomic recoil, with the trapping light appropriately tuned to a ``magic'' wavelength to eliminate light shifts. An alternative approach is construct optical clocks using inherently Doppler-free two-photon transitions, which can lead to a substantially simplified architecture. The short cycle time and large atom numbers available with such a scheme enable rapid, high signal-to-noise measurements, paving the way for portable and autonomous clocks. We report on experimental progress towards constructing an optical clock based on the 4s21S0 --> 4 s 3 d1D2 two-photon transition in laser cooled 40Ca atoms.

  13. 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.

  14. 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.

  15. 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.

  16. Microplasma source for optogalvanic spectroscopy of nanogram samples

    SciTech Connect

    Berglund, M.; Thornell, G.; Persson, A.

    2013-07-21

    The demand for analysis of smaller samples in isotopic ratio measurements of rare isotopes is continuously rising with the development of new applications, particularly in biomedicine. Interesting in this aspect are methods based on optogalvanic spectroscopy, which have been reported to facilitate both {sup 13}C-to-{sup 12}C and {sup 14}C-to-{sup 12}C ratio measurements with high sensitivity. These methods also facilitate analysis of very small samples, down to the microgram range, which makes them very competitive to other technologies, e.g., accelerator mass spectroscopy. However, there exists a demand for moving beyond the microgram range, especially from regenerative medicine, where samples consist of, e.g., DNA, and, hence, the total sample amount is extremely small. Making optogalvanic spectroscopy of carbon isotopes applicable to such small samples, requires miniaturization of the key component of the system, namely the plasma source, in which the sample is ionized before analysis. In this paper, a novel design of such a microplasma source based on a stripline split-ring resonator is presented and evaluated in a basic optogalvanic spectrometer. The investigations focus on the capability of the plasma source to measure the optogalvanic signal in general, and the effect of different system and device specific parameters on the amplitude and stability of the optogalvanic signal in particular. Different sources of noise and instabilities are identified, and methods of mitigating these issues are discussed. Finally, the ability of the cell to handle analysis of samples down to the nanogram range is investigated, pinpointing the great prospects of stripline split-ring resonators in optogalvanic spectroscopy.

  17. Microplasma source for optogalvanic spectroscopy of nanogram samples

    NASA Astrophysics Data System (ADS)

    Berglund, M.; Thornell, G.; Persson, A.

    2013-07-01

    The demand for analysis of smaller samples in isotopic ratio measurements of rare isotopes is continuously rising with the development of new applications, particularly in biomedicine. Interesting in this aspect are methods based on optogalvanic spectroscopy, which have been reported to facilitate both 13C-to-12C and 14C-to-12C ratio measurements with high sensitivity. These methods also facilitate analysis of very small samples, down to the microgram range, which makes them very competitive to other technologies, e.g., accelerator mass spectroscopy. However, there exists a demand for moving beyond the microgram range, especially from regenerative medicine, where samples consist of, e.g., DNA, and, hence, the total sample amount is extremely small. Making optogalvanic spectroscopy of carbon isotopes applicable to such small samples, requires miniaturization of the key component of the system, namely the plasma source, in which the sample is ionized before analysis. In this paper, a novel design of such a microplasma source based on a stripline split-ring resonator is presented and evaluated in a basic optogalvanic spectrometer. The investigations focus on the capability of the plasma source to measure the optogalvanic signal in general, and the effect of different system and device specific parameters on the amplitude and stability of the optogalvanic signal in particular. Different sources of noise and instabilities are identified, and methods of mitigating these issues are discussed. Finally, the ability of the cell to handle analysis of samples down to the nanogram range is investigated, pinpointing the great prospects of stripline split-ring resonators in optogalvanic spectroscopy.

  18. Applications of Doppler-Free Saturation Spectroscopy for Edge Physics Studies

    SciTech Connect

    Martin, Elijah H; Caughman, John B; Isler, Ralph C; Bell, Gary L

    2016-01-01

    Doppler-free saturation spectroscopy provides a very powerful method to obtained detailed information about the electronic structure of the atom through measurement of the spectral line profile. This is achieved through a significant decrease in the Doppler broadening and essentially an elimination of the instrument broadening inherent to passive spectroscopic techniques. In this paper we will present the technique and associated physics of Doppler-free saturation spectroscopy in addition to how one selects the appropriate transition. Simulations of H spectra will be presented to illustrate the increased sensitivity to both electric field and electron density measurements.

  19. 14C Analysis via Intracavity Optogalvanic Spectroscopy

    PubMed Central

    Murnick, Daniel; Dogru, Ozgur; Ilkmen, Erhan

    2010-01-01

    A new ultra sensitive laser-based analytical technique, intracavity optogalvanic spectroscopy (ICOGS), allowing extremely high sensitivity for detection of 14C-labeled carbon dioxide has recently been demonstrated. Capable of replacing accelerator mass spectrometers (AMS) for many applications, the technique quantifies zeptomoles of 14C in sub micromole CO2 samples. Based on the specificity of narrow laser resonances coupled with the sensitivity provided by standing waves in an optical cavity, and detection via impedance variations, limits of detection near 10−15 14C/12C ratios have been obtained with theoretical limits much lower. Using a 15 W 14CO2 laser, a linear calibration with samples from 5 × 10−15 to >1.5 × 10−12 in 14C/12C ratios, as determined by AMS, was demonstrated. Calibration becomes non linear over larger concentration ranges due to interactions between CO2 and buffer gas, laser saturation effects and changes in equilibration time constants. The instrument is small (table top), low maintenance and can be coupled to GC or LC input. The method can also be applied to detection of other trace entities. Possible applications include microdosing studies in drug development, individualized sub therapeutic tests of drug metabolism, carbon dating and real time monitoring of atmospheric radiocarbon. PMID:20448803

  20. 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.

  1. Optogalvanic intracavity quantitative detector and method for its use

    DOEpatents

    Zalewski, E.F.; Keller, R.A.; Apel, C.T.

    1981-02-25

    The disclosure relates to an optogalvanic intracavity detector and method for its use. Measurement is made of the amount of light absorbed by atoms, small molecules and ions in a laser cavity utilizing laser-produced changes in plasmas containing the same atoms, molecules or ions.

  2. Optogalvanic intracavity quantitative detector and method for its use

    DOEpatents

    Zalewski, Edward F.; Keller, Richard A.; Apel, Charles T.

    1983-01-01

    The disclosure relates to an optogalvanic intracavity detector and method for its use. Measurement is made of the amount of light absorbed by atoms, small molecules and ions in a laser cavity utilizing laser-produced changes in plasmas containing the same atoms, molecules, or ions.

  3. Optogalvanic intracavity quantitative detector and method for its use

    DOEpatents

    Zalewski, E.F.; Keller, R.A.; Apel, C.T.

    1983-09-06

    The disclosure relates to an optogalvanic intracavity detector and method for its use. Measurement is made of the amount of light absorbed by atoms, small molecules and ions in a laser cavity utilizing laser-produced changes in plasmas containing the same atoms, molecules, or ions. 6 figs.

  4. Optogalvanic spectrum of argon in the visible wavelength region 4150-6700 A

    NASA Technical Reports Server (NTRS)

    Reddy, B. R.; Venkateswarlu, P.; George, M. C.

    1990-01-01

    Optogalvanic spectrum of argon has been investigated in the visible wavelength region 4150-6700 A by axially irradiating a hollow cathodic discharge with an excimer pumped dye laser. About 180 transitions have been recorded and a majority of them have been identified using the Jl-coupling scheme. The optogalvanic spectrum in the regions 4300-5300 and 6010-6700 A is being reported in detail for the first time. The optogalvanic signal intensities are found to agree with atomic transition probabilities. A technique has been discussed to record a maximum number of transitions in optogalvanic effect.

  5. Optogalvanic single-color multiphoton ionization spectroscopy of uranium in a hollow cathode discharge

    SciTech Connect

    Levesque, S.; Babin, F.; Gagne, J.M.

    1993-12-01

    Single color multiphoton ionization spectra of atoms can be obtained using the fast pulsed ({approximately} 10{sup {minus}9} s) optogalvanic signal generated by photoionization in the dark space of a hollow cathode discharge. Such spectra have been measured for uranium in the spectral range of rhodamine 6G with a high laser bandwidth excitation (0.3 cm{sup {minus}1}). In the process of ascribing an ionization scheme to each line through the known levels of uranium, many possibilities appear. In order to help the authors select the correct scheme, they perturbed the atomic level population distribution by optical pumping of the 16900.37 cm{sup {minus}1} level ({sup 7}M{sub 7}). The spectrum obtained this way show many new strong lines. They try to explain these lines by a three photon resonant or quasi-resonant scheme, using known levels of uranium, or by a two photon scheme from the 16900.37 cm{sup {minus}1} level. In both perturbed and unperturbed spectra, many ionization schemes are still possible for each line. For this reason the authors have performed higher resolution scans of selected lines (in particular 5915.4{angstrom}) in order to confirm the existence of more than one scheme for many lines.

  6. Improved optogalvanic detection with voltage biased Langmuir probes

    NASA Astrophysics Data System (ADS)

    Persson, A.; Berglund, M.; Salehpour, M.

    2014-12-01

    Optogalvanic detectors show great potential for infrared spectroscopy, especially in cavity enhanced techniques where they, in contrast to ordinary absorption detectors, can perform intracavity measurements. This enables them to utilize the signal-to-noise ratio improvement gained from the extended effective path length inside an optical cavity, without losing signal strength due to the limited amount of light exiting through the rear mirror. However, if optogalvanic detectors are to become truly competitive, their intrinsic sensitivity and stability has to be improved. This, in turn, requires a better understanding of the mechanisms behind the generation of the optogalvanic signal. The study presented here focuses on an optogalvanic detector based on a miniaturized stripline split-ring resonator plasma source equipped with Langmuir probes for detecting the optogalvanic signal. In particular, the effect of applying a constant bias voltage to one of the probes is investigated, both with respect to the sensitivity and stability, and to the mechanism behind the generation of the signal. Experiments with different bias voltages at different pressures and gas composition have been conducted. In particular, two different gas compositions (pure CO2 and 0.25% CO2 in 99.75% N2) at six different pressures (100 Pa to 600 Pa) have been studied. It has been shown that probe biasing effectively improves the performance of the detector, by increasing the amplitude of the signal linearly over one order of magnitude, and the stability by about 40% compared with previous studies. Furthermore, it has been shown that relatively straightforward plasma theory can be applied to interpret the mechanism behind the generation of the signal, although additional mechanisms, such as rovibrational excitation from electron-molecule collisions, become apparent in CO2 plasmas with electron energies in the 1-6 eV range. With the achieved performance improvement and the more solid theoretical

  7. Improved optogalvanic detection with voltage biased Langmuir probes

    SciTech Connect

    Persson, A.; Salehpour, M.; Berglund, M.

    2014-12-28

    Optogalvanic detectors show great potential for infrared spectroscopy, especially in cavity enhanced techniques where they, in contrast to ordinary absorption detectors, can perform intracavity measurements. This enables them to utilize the signal-to-noise ratio improvement gained from the extended effective path length inside an optical cavity, without losing signal strength due to the limited amount of light exiting through the rear mirror. However, if optogalvanic detectors are to become truly competitive, their intrinsic sensitivity and stability has to be improved. This, in turn, requires a better understanding of the mechanisms behind the generation of the optogalvanic signal. The study presented here focuses on an optogalvanic detector based on a miniaturized stripline split-ring resonator plasma source equipped with Langmuir probes for detecting the optogalvanic signal. In particular, the effect of applying a constant bias voltage to one of the probes is investigated, both with respect to the sensitivity and stability, and to the mechanism behind the generation of the signal. Experiments with different bias voltages at different pressures and gas composition have been conducted. In particular, two different gas compositions (pure CO{sub 2} and 0.25% CO{sub 2} in 99.75% N{sub 2}) at six different pressures (100 Pa to 600 Pa) have been studied. It has been shown that probe biasing effectively improves the performance of the detector, by increasing the amplitude of the signal linearly over one order of magnitude, and the stability by about 40% compared with previous studies. Furthermore, it has been shown that relatively straightforward plasma theory can be applied to interpret the mechanism behind the generation of the signal, although additional mechanisms, such as rovibrational excitation from electron-molecule collisions, become apparent in CO{sub 2} plasmas with electron energies in the 1–6 eV range. With the achieved performance improvement and

  8. 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.

  9. Rotational analysis for the Doppler-free photoelectron spectrum of water using the spectator model.

    PubMed

    Ford, Mark S; Müller-Dethlefs, Klaus; Kitajima, M; Tanaka, H; Tamenori, Y; De Fanis, A; Ueda, Kyoshi

    2010-10-28

    A photoelectron spectrum of H(2)O has been recorded at a resolution of 2 meV under Doppler-free conditions. Complex rotational structures appear in the individual vibrational states of the electronic X̃(+ 2)B(1) and Ã(+ 2)A(2) states in H(2)O(+). The rotational structures are analyzed and well reproduced using a spectator orbital model developed for rotationally resolved photoelectron spectroscopy. PMID:20879775

  10. 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.

  11. Determination of the Relative Two-photon Absorption Cross-section Between Xenon and Hydrogen

    NASA Astrophysics Data System (ADS)

    Elliott, Drew; Scime, Earl; McCarren, Dustin; Vandervort, Robert; Soderholm, Mark

    2014-10-01

    Two-photon Absorption Laser Induced Fluorescence (TALIF) is a non-perturbative method for measuring the density and temperature of neutral hydrogen in a fusion plasma. Calibration of a TALIF system, for absolute density measurements, requires a measurement of a known density of particles under controlled conditions. Since hydrogen is diatomic, hydrogen TALIF system calibration requires measurements of target cold monatomic gas with a two-photon transition from the ground state and fluorescence decay at accessible energies. Here we present single-sided TALIF (angular momentum change of 2) measurements of a new transition in xenon with absorption and emission wavelengths nearly identical to those of the hydrogen TALIF sequence (the n = 3 to n = 2 emission in hydrogen is at 656.27 nm whereas it is at 655.99 nm in xenon). The xenon calibration approach provides the first opportunity for absolute calibration of Doppler-free (angular momentum change of 0) hydrogen TALIF. We first measure the relative TALIF absorption cross section between xenon and krypton and then use the known cross section ratio between the krypton and hydrogen transitions to calculate the relative xenon-hydrogen cross section. Single isotope xenon samples are used to remove the confounding factors of isotopic and hyperfine splitting.

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. Observation of Doppler-free electromagnetically induced transparency in atoms selected optically with specific velocity

    SciTech Connect

    Yu, Hoon; Kim, Kwan Su; Kim, Jung Dong; Lee, Hyun Kyung; Kim, Jung Bog

    2011-11-15

    We observed an electromagnetically induced transparency signal in a four-level system with optically selected rubidium atoms at specific velocities in a room-temperature vaporized cell. Since the atoms behave like cold atoms in the selected atomic view, the observed signals coincide with a trapped atomic system. According to this result, we can observe Doppler-free signals, which correspond from 1.2 to 1.0 K in a Doppler-broadened medium. And the selected atoms have velocity components of {+-}(131 {+-} 3) MHz per wave number. Our experimental results can provide insight for research in cold media.

  17. Diode laser excited optogalvanic spectroscopy of glow discharges

    SciTech Connect

    Barshick, C.M.; Shaw, R.W.; Post-Zwicker, A., Young, J.P.; Ramsey, J.M.

    1996-10-01

    The development of diode-laser-excited isotopically-selective optogalvanic spectroscopy (OGS) of uranium metal, oxide and fluoride in a glow discharge (GD) is presented. The technique is useful for determining isotopic ratios of {sup 235}U/({sup 235}U + {sup 238}U) in the above samples. The precision and accuracy of this determination is evaluated, and a study of experimental parameters pertaining to optimization of he measurement is discussed. Application of the GD-OGS to other f-transition elements is also described.

  18. 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.

  19. Stripline split-ring resonator with integrated optogalvanic sample cell

    NASA Astrophysics Data System (ADS)

    Persson, Anders; Berglund, Martin; Thornell, Greger; Possnert, Göran; Salehpour, Mehran

    2014-04-01

    Intracavity optogalvanic spectroscopy (ICOGS) has been proposed as a method for unambiguous detection of rare isotopes. Of particular interest is 14C, where detection of extremely low concentrations in the 1:1015 range (14C: 12C), is of interest in, e.g., radiocarbon dating and pharmaceutical sciences. However, recent reports show that ICOGS suffers from substantial problems with reproducibility. To qualify ICOGS as an analytical method, more stable and reliable plasma generation and signal detection are needed. In our proposed setup, critical parameters have been improved. We have utilized a stripline split-ring resonator microwave-induced microplasma source to excite and sustain the plasma. Such a microplasma source offers several advantages over conventional ICOGS plasma sources. For example, the stripline split-ring resonator concept employs separated plasma generation and signal detection, which enables sensitive detection at stable plasma conditions. The concept also permits in situ observation of the discharge conditions, which was found to improve reproducibility. Unique to the stripline split-ring resonator microplasma source in this study, is that the optogalvanic sample cell has been embedded in the device itself. This integration enables improved temperature control and more stable and accurate signal detection. Significant improvements are demonstrated, including reproducibility, signal-to-noise ratio, and precision.

  20. Laser optogalvanic wavelength calibration with a commercial hollow cathode iron - neon discharge lamp

    NASA Technical Reports Server (NTRS)

    Zhu, Xinming; Nur, Abdullahi H.; Misra, Prabhakar

    1994-01-01

    351 optogalvanic transitions have been observed in the 337 - 598 nm wavelength region using an iron - neon hollow cathode discharge lamp and a pulsed tunable dye laser. 223 of these have been identified as transitions associated with neon energy levels. These optogalvanic transitions have allowed, in conjunction with interference fringes recorded concomitantly with an etalon, the calibration of the dye laser wavelength with 0.3/cm accuracy.

  1. A tunable Doppler-free dichroic lock for laser frequency stabilization

    NASA Astrophysics Data System (ADS)

    Singh, Vivek; Tiwari, V. B.; Mishra, S. R.; Rawat, H. S.

    2016-08-01

    We propose and demonstrate a laser frequency stabilization scheme which generates a dispersion-like tunable Doppler-free dichroic lock (TDFDL) signal. This signal offers a wide tuning range for lock point (i.e. zero-crossing) without compromising on the slope of the locking signal. The method involves measurement of magnetically induced dichroism in an atomic vapour for a weak probe laser beam in the presence of a counter-propagating strong pump laser beam. A simple model is presented to explain the basic principles of this method to generate the TDFDL signal. The spectral shift in the locking signal is achieved by tuning the frequency of the pump beam. The TDFDL signal is shown to be useful for locking the frequency of a cooling laser used for magneto-optical trap (MOT) for 87 Rb atoms.

  2. 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

  3. 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

  4. 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.

  5. 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

  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. 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.

  8. 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

  9. 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.

  10. Nonselective and polarization effects in time-resolved optogalvanic spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhechev, D.; Steflekova, V.

    2016-02-01

    Three interfering effects in optogalvanic (OG) spectroscopy are identified in a hollow cathode discharge (HCD) - OG detector. The laser beam is found to generate two nonselective processes, namely photoelectron emission (PE) from the cathode surface with a sub-breakdown bias applied, and nonresonant space ionization. The convolution of these galvanic contributions was determined experimentally as an instrumental function and a deconvolution procedure to determine the actual OG signal was developed. Specific plasma conductance is detected dependent on the polarization of the laser beam irradiating. Linearly/circularly polarized light beam is found to induce OG signals differ in amplitude (and their shape parameters in the time-resolved OG signals (TROGS)). The phenomena coherence and specific conductance are found to be in causal relationship. The additional conductance due to coherent states of atoms manifests itself as an intrinsic instrumental property of OG detector.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Doppler-free spectroscopy of metastable calcium in a discharge heat pipe

    NASA Astrophysics Data System (ADS)

    Hansen, Dirk; Hemmerich, Andreas

    2005-08-01

    We report on Doppler-free frequency modulation spectroscopy and polarization spectroscopy in a discharge heat pipe of yet unexplored transitions connecting the metastable P23(4s4p) state of calcium atoms with the multiply excited states P23(4p4p) and D33(4s3d) . Calcium vapor is efficiently produced in a heat pipe operating in a small Pyrex cell filled with 2torr of neon. A dc discharge running at 500V efficiently populates the metastable triplet states. Narrow resonances with bandwidths of a few tens of MHz with excellent signal-to-noise ratios are observed, well suited as references for laser frequency stabilization. Examination of the Zeeman shifts lets us determine the Landé g factors of the excited states and compare them with the predictions based on the Russel-Saunders coupling scheme. We describe an economic, simple, and robust experimental setup that should work for other alkaline-earth-metal atoms like Mg and Sr, as well as for other solid elements with insufficient vapor pressures at room temperature.

  1. Doppler-free spectroscopy on the Cs D1 line with a dual-frequency laser.

    PubMed

    Hafiz, Moustafa Abdel; Coget, Grégoire; De Clercq, Emeric; Boudot, Rodolphe

    2016-07-01

    We report on Doppler-free laser spectroscopy in a Cs vapor cell using a dual-frequency laser system tuned on the Cs D1 line. Using counter-propagating beams with crossed linear polarizations, an original sign reversal of the usual saturated absorption dip and large increase in Doppler-free atomic absorption is observed. This phenomenon is explained by coherent population trapping (CPT) effects. The impact of laser intensity and light polarization on absorption profiles is reported in both single-frequency and dual-frequency regimes. In the latter, frequency stabilization of two diode lasers was performed, yielding a beat note fractional frequency stability at the level of 3×10-12 at 1 s averaging time. These performances are about an order of magnitude better than those obtained using a conventional single-frequency saturated absorption scheme. PMID:27367081

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. Doppler-Free Spectroscopy Measurements of Isotope Shifts and Hyperfine Components of Near-IR Xenon Lines

    SciTech Connect

    Mazouffre, S.; Pawelec, E.; Tran Bich, N.; Sadeghi, N.

    2006-01-15

    Xenon is currently used as propellant gas in electric thrusters, in which ejection of corresponding ions produces the desired thrust. As such a gas contains 9 stable isotopes, a non-intrusive determination of the velocity distribution function of atoms and ions in the thruster plasma plume, by means of absorption or fluorescence techniques, requires a precise knowledge of the line structure. We used Doppler-free Lamb-dip spectroscopy to determine isotopic shifts and hyperfine components of odd isotopes of several spectral lines of Xe atom and Xe+ ion in the 825 - 835 nm range.

  11. 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

  12. 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

  13. 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

  14. 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.

  15. 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

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. 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}.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. Anomalous optogalvanic line shapes of argon metastable transitions in a hollow cathode lamp

    NASA Technical Reports Server (NTRS)

    Ruyten, W. M.

    1993-01-01

    Anomalous optogalvanic line shapes were observed in a commercial hollow cathode lamp containing argon buffer gas. Deviations from Gaussian line shapes were particularly strong for transitions originating from the 3P2 metastable level of argon. The anomalous line shapes can be described reasonably well by the assumption that two regions in the discharge are excited simultaneously, each giving rise to a purely Gaussian line shape, but with different polarities, amplitudes, and linewidths.

  13. Intracavity OptoGalvanic Spectroscopy not suitable for ambient level radiocarbon detection.

    PubMed

    Paul, Dipayan; Meijer, Harro A J

    2015-09-01

    IntraCavity OptoGalvanic Spectroscopy as a radiocarbon detection technique was first reported by the Murnick group at Rutgers University, Newark, NJ, in 2008. This technique for radiocarbon detection was presented with tremendous potentials for applications in various fields of research. Significantly cheaper, this technique was portrayed as a possible complementary technique to the more expensive and complex accelerator mass spectrometry. Several groups around the world started developing this technique for various radiocarbon related applications. The IntraCavity OptoGalvanic Spectroscopy setup at the University of Groningen was constructed in 2012 in close collaboration with the Murnick group for exploring possible applications in the fields of radiocarbon dating and atmospheric monitoring. In this paper we describe a systematic evaluation of the IntraCavity OptoGalvanic Spectroscopy setup at Groningen for radiocarbon detection. Since the IntraCavity OptoGalvanic Spectroscopy setup was strictly planned for dating and atmospheric monitoring purposes, all the initial experiments were performed with CO2 samples containing contemporary levels and highly depleted levels of radiocarbon. Because of recurring failures in differentiating the two CO2 samples, with the radiocarbon concentration 3 orders of magnitude apart, CO2 samples containing elevated levels of radiocarbon were prepared in-house and experimented with. All results obtained thus far at Groningen are in sharp contrast to the results published by the Murnick group and rather support the results put forward by the Salehpour group at Uppsala University. From our extensive test work, we must conclude that the method is unsuited for ambient level radiocarbon measurements, and even highly enriched CO2 samples yield insignificant signal. PMID:26252648

  14. Intracavity optogalvanic spectroscopy: Is there any evidence of a radiocarbon signal?

    NASA Astrophysics Data System (ADS)

    Persson, Anders; Salehpour, Mehran

    2015-10-01

    In 2008, the first report of an ultrasensitive method for ro-vibrational spectrometry of radiocarbon dioxide was published. The method, called intracavity optogalvanic spectroscopy (ICOGS), claimed a sensitivity and limit-of-detection comparable to accelerator mass spectroscopy. ICOGS was claimed to utilize the isotope-dependent ro-vibrational absorption lines of carbon dioxide in the infrared spectrum. In order to facilitate unambiguous detection of radiocarbon, the sample was placed inside the cavity of a radiocarbon dioxide laser. This intracavity approach was claimed to increase the sensitivity by seven orders of magnitude compared with traditional optogalvanic methods. However, despite the methodical and thorough efforts of several research groups worldwide, these claims have not been possible to reproduce. Instead, we have previously reported serious deviations from the original results, where we found that ICOGS suffers from considerable problems with the stability and reproducibility of the optogalvanic signal, and that misinterpretations of these uncertainties likely are the explanation for the claimed sensitivity in the first reports. Having identified the stability and reproducibility of the detection as major concerns, we decided to improve the setup by with state-of-the-art plasma source technology. Deploying a custom-made stripline split-ring resonator optogalvanic detector, we have now investigated the applicability of ICOGS to radiocarbon detection even further. Measurements have been made with a wide range of parameters including different gas mixtures at various pressures and wavelengths. We have also conducted measurements with gas flowing through the sample cell to investigate the effect of plasma induced decomposition of the sample. Still, we have seen no indications of a significant radiocarbon signal in a concentration range between 0.29 Modern and 9.7 Modern, i.e., the range of interest to the radiocarbon community. Hence, our conclusions

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  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. 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

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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}.

  7. 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

  8. 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).

  9. 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

  10. 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.

  11. 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.

  12. 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)

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. On a focal point instability in (B3Πg - C3Πu)N2 optogalvanic circuit with hollow cathode

    NASA Astrophysics Data System (ADS)

    Gencheva, V.

    2016-03-01

    The (B3Πg, v = 0 - C3 Πu, v = 0) N2 dynamic optogalvanic signals have been registered illuminating an Al hollow cathode lamp with a pulsed N2 laser generating at the wavelength of 337.1nm. The dynamic optogalvanic signal (DOGS) at certain discharge current of 8 mA is a harmonic oscillator due to a focal point instability produced by our optogalvanic circuit. This damped harmonic oscillator can be described as a solution of linear second order homogeneous differential equation. The oscillation frequency is estimated from the registered DOGS using Fourier synthesis. The analytical description of the damped harmonic DOGS is obtained.

  3. 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

  4. Discharge cell for optogalvanic spectroscopy having orthogonal relationship between the probe laser and discharge axis

    NASA Technical Reports Server (NTRS)

    Webster, C. R. (Inventor)

    1986-01-01

    A method and apparatus for an optogalvanic spectroscopy system are disclosed. Orthogonal geometry exists between the axis of a laser probe beam and the axis of a discharge created by a pair of spaced apart and longituduinally aligned high voltage electrodes. The electrodes are movable to permit adjustment of the location of a point in the discharge which is to irradiated by a laser beam crossing the discharge region. The cell dimensions are selected so that the cross section of the discharge region is substantly comparable in size to the cross section of the laser beam passing orthogonally through the discharge region.

  5. Doppler-free spectroscopy of mercury at 253.7 nm using a high-power, frequency-quadrupled, optically pumped external-cavity semiconductor laser.

    PubMed

    Paul, Justin; Kaneda, Yushi; Wang, Tsuei-Lian; Lytle, Christian; Moloney, Jerome V; Jones, R Jason

    2011-01-01

    We have developed a stable, high-power, single-frequency optically pumped external-cavity semiconductor laser system and generate up to 125 mW of power at 253.7 nm using successive frequency doubling stages. We demonstrate precision scanning and control of the laser frequency in the UV to be used for cooling and trapping of mercury atoms. With active frequency stabilization, a linewidth of <60 kHz is measured in the IR. Doppler-free spectroscopy and stabilization to the 6(1)S(0)-6(3)P(1) mercury transition at 253.7 nm is demonstrated. To our knowledge, this is the first demonstration of Doppler-free spectroscopy in the deep UV based on a frequency-quadrupled, high-power (>1 W) optically pumped semiconductor laser system. The results demonstrate the utility of these devices for precision spectroscopy at deep-UV wavelengths. PMID:21209687

  6. Term values of even parity np‧ (n=10-16) states of neon determined by two-step optogalvanic spectroscopy

    NASA Astrophysics Data System (ADS)

    Ami, Norihiro; Wada, Akihide; Adachi, Yukio; Hirose, Chiaki

    1988-12-01

    Term values of even parity np' ( n = 10-16 with primed letter denoting the electronic states on the 2P 1/2 ion core state) levels of neon have been determined from the observation of Stark-induced np'-3p' transitions by two-step optogalvanic spectroscopy.

  7. 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

  8. 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

  9. 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.

  10. 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.

  11. 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.

  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. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Spin-dependent, optogalvanic effects of laser-pumped He(2/3/S1) atoms

    NASA Astrophysics Data System (ADS)

    Schearer, L. D.; Tin, Pedetha

    1989-10-01

    Spin-dependent optogalvanic effects of laser-pumped He(2/3/S1) atoms are demonstrated. As helium atoms are excited with an IR tunable laser, changes in the conductivity of helium radio-frequency discharge are observed. With approximately 1 mW/sq cm of tunable laser power near 1.083 microns, the intensity-modulated optogalvanic effect signals are obtained as the laser is tuned through the D0(2/3/S1-2/3/P0), D1(2/3/S1-2/3/P1), and D2(2/3/S1-2/3/P2) transitions at 1.082908, 1.083025, and 1.083034 microns, respectively. If the laser emission is now circularly polarized and directed onto the helium discharge cell with the applied field parallel to the pump axis, some of the metastable atoms are oriented with their electronic spins along the field direction, modulating the coil current. One of the important applications of spin-polarized ensembles of metastable 4He is in extremely sensitive magnetic-field measuring devices.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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

  16. 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).

  17. Temperature dependence of the two photon absorption in indium arsenide

    SciTech Connect

    Berryman, K.W.; Rella, C.W.

    1995-12-31

    Nonlinear optical processes in semiconductors have long been a source of interesting physics. Two photon absorption (TPA) is one such process, in which two photons provide the energy for the creation of an electron-hole pair. Researchers at other FEL centers have studied room temperature TPA in InSb, InAs, and HgCdTe. Working at the Stanford Picosecond FEL Center, we have extended and refined this work by measuring the temperature dependence of the TPA coefficient in InAs over the range from 80 to 350 K at four wavelengths: 4.5, 5.06, 6.01, and 6.3 microns. The measurements validate the functional dependence of recent band structure calculations with enough precision to discriminate parabolic from non-parabolic models, and to begin to observe smaller effects, such as contributions due to the split-off band. These experiments therefore serve as a strong independent test of the Kane band theory, as well as providing a starting point for detailed observations of other nonlinear absorption mechanisms.

  18. 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.

  19. Two-photon multiplane imaging of neural circuits (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yang, Weijian; Miller, Jae-eun K.; Carrillo-Reid, Luis; Pnevmatikakis, Eftychios; Paninski, Liam; Peterka, Darcy S.; Yuste, Rafael

    2016-03-01

    Imaging the neuronal activity throughout the brain with high temporal and spatial resolution is an important step in understanding how the brain works. Two-photon laser scanning microscopy with fluorescent calcium indicators has enabled this type of experiments in vivo. Most of these microscopes acquire images serially, with a single laser beam, limiting the overall imaging speed. To overcome this limit, multiple beamlets can be used to image in parallel multiple regions. Here, we demonstrate a novel scheme of a two-photon laser-scanning microscope that can simultaneously record neuronal activity at multiple planes of the sample with a single photomultiplier tube. A spatial light modulator is used to generate the designated multiple beamlets, and a constrained non-negative matrix factorization algorithm is used to demix the signals from multiple scanned planes. We simultaneously record neuronal activity of multiple layers of a mouse cortex at 10 fps in vivo. This novel imaging scheme provides a powerful tool for mapping the brain activity.

  20. 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

  1. 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.

  2. Photosensitizer-doped conjugated polymer nanoparticles for simultaneous two-photon imaging and two-photon photodynamic therapy in living cells

    NASA Astrophysics Data System (ADS)

    Shen, Xiaoqin; Li, Lin; Wu, Hao; Yao, Shao Q.; Xu, Qing-Hua

    2011-12-01

    Photosensitizer doped conjugated polymer nanoparticles have been prepared by incorporating polyoxyethylene nonylphenylether (CO-520) into the nanoparticles using a re-precipitation method. The conjugated polymer, poly[9,9-dibromohexylfluorene-2,7-ylenethylene-alt-1,4-(2,5-dimethoxy)phenylene] (PFEMO), was used as the host matrix to disperse tetraphenylporphyrin (TPP) and an energy donor to enhance the two-photon excitation properties of TPP. These CO-520 incorporated, TPP-doped PFEMO nanoparticles are stable and have low cytotoxicity in the dark. The TPP emission of the nanoparticles was found to be enhanced by about 20 times by PFEMO under two-photon excitation. The nanoparticles showed significantly enhanced two-photon excitation singlet oxygen generation efficiency and two-photon photodynamic therapy activity in cancer cells. These composite nanoparticles display features required for ideal photosensitizers, such as low cytotoxicity in the dark and efficient two-photon photodynamic activity under laser radiation. In addition, these novel nano-photosensitizers allow simultaneous in vivo monitoring by two-photon fluorescence imaging during two-photon photodynamic treatment. These photosensitizer-doped conjugated polymer nanoparticles can act as novel photosensitizing agents for two-photon photodynamic therapy and related applications.Photosensitizer doped conjugated polymer nanoparticles have been prepared by incorporating polyoxyethylene nonylphenylether (CO-520) into the nanoparticles using a re-precipitation method. The conjugated polymer, poly[9,9-dibromohexylfluorene-2,7-ylenethylene-alt-1,4-(2,5-dimethoxy)phenylene] (PFEMO), was used as the host matrix to disperse tetraphenylporphyrin (TPP) and an energy donor to enhance the two-photon excitation properties of TPP. These CO-520 incorporated, TPP-doped PFEMO nanoparticles are stable and have low cytotoxicity in the dark. The TPP emission of the nanoparticles was found to be enhanced by about 20 times by PFEMO

  3. Two-Photon Voltmeter for Measuring a Molecular Electric Field**

    PubMed Central

    Rebane, Aleksander; Wicks, Geoffrey; Drobizhev, Mikhail; Cooper, Thomas; Trummal, Aleksander; Uudsemaa, Merle

    2015-01-01

    We present a new approach for determining the strength of the dipolar solute-induced reaction field, along with the ground- and excited-state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one-photon and two-photon absorption measurements. We verify the approach on two benchmark chromophores N,N-dimethyl-6-propionyl-2-naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum-chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0–107 V cm−1, and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute–solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close-range molecular interaction. PMID:25958849

  4. Exploring Entangled Two-Photon Absorption in Molecules

    NASA Astrophysics Data System (ADS)

    Caraher, John

    2014-05-01

    Goodson and colleagues have reported anomalously large cross-sections (of order σ =10-17 cm2) for the two-photon absorption of entangled photons in a number of molecules. This poster reports on attempts to replicate and expand upon their results for one of these, zinc tetraphenylporphyrin (Zn TPP) in chloroform solution. It will also discuss the interpretation of the Goodson group's experimental data, particularly their results regarding entanglement area and entanglement time (the spatial and temporal widths of the fourth-order coherence functions, respectively). Results of direct measurement of entanglement time (via a Hong-Ou-Mandel interferometer) for a laser and optical system essentially identical to the one used in Goodson's work will be presented and compared with their reported values. Supported by the DePauw University Faculty Development Committee.

  5. Two-photon decays of η _c from lattice QCD

    NASA Astrophysics Data System (ADS)

    Chen, Ting; Chen, Ying; Gong, Ming; Lei, Yu-Hong; Li, Ning; Liu, Chuan; Liu, Yu-Bin; Liu, Zhaofeng; Ma, Jian-Ping; Qiu, Wei-Feng; Wang, Zhan-Lin; Zhang, Jian-Bo

    2016-07-01

    We present an exploratory lattice study for the two-photon decay of η _c using N_f=2 twisted mass lattice QCD gauge configurations generated by the European Twisted Mass Collaboration. Two different lattice spacings of a=0.067 fm and a=0.085 fm are used in the study, both of which are of physical size of 2 fm. The decay widths are found to be 1.025(5) KeV for the coarser lattice and 1.062(5) KeV for the finer lattice, respectively, where the errors are purely statistical. A naive extrapolation toward the continuum limit yields Γ ˜eq 1.122(14) KeV, which is smaller than the previous quenched result and most of the current experimental results. Possible reasons are discussed.

  6. 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.

  7. High numerical aperture hybrid optics for two-photon polymerization.

    PubMed

    Burmeister, Frank; Zeitner, Uwe D; Nolte, Stefan; Tünnermann, Andreas

    2012-03-26

    We report on an immersion hybrid optics specially designed for focusing ultrashort laser pulses into a polymer for direct laser writing via two-photon polymerization. The hybrid optics allows for well-corrected focusing over a large working distance range of 577 μm with a numerical aperture (NA) of 1.33 and low internal dispersion. We combine the concepts of an aplanatic solid immersion lens (ASIL) for achieving a high NA with a diffractive optical element (DOE) for correction of aberrations. To demonstrate the improvements for volume structuring of the polymer, we compare the achievable structure sizes of our optics with a commercially available oil-immersion objective (100x, NA=1.4). PMID:22453471

  8. Clinical multiphoton tomography and clinical two-photon microendoscopy

    NASA Astrophysics Data System (ADS)

    König, Karsten; Bückle, Rainer; Weinigel, Martin; Elsner, Peter; Kaatz, Martin

    2009-02-01

    We report on applications of high-resolution clinical multiphoton tomography based on the femtosecond laser system DermaInspectTM with its flexible mirror arm in Australia, Asia, and Europe. Applications include early detection of melanoma, in situ tracing of pharmacological and cosmetical compounds including ZnO nanoparticles in the epidermis and upper dermis, the determination of the skin aging index SAAID as well as the study of the effects of anti-aging products. In addition, first clinical studies with novel rigid high-NA two-photon 1.6 mm GRIN microendoscopes have been conducted to study the effect of wound healing in chronic wounds (ulcus ulcera) as well as to perform intrabody imaging with subcellular resolution in small animals.

  9. Two-photon quantum interference for an undergraduate lab

    NASA Astrophysics Data System (ADS)

    Ourjoumtsev, A.; Dheur, M.-C.; Avignon, T.; Jacubowiez, L.

    2015-11-01

    We present a simple setup allowing undergraduate students to reproduce the Hong-Ou-Mandel experiment during a half-day labwork session and observe the coalescence of two indistinguishable photons merging on a balanced beamsplitter. This two-photon interference effect, fundamentally related to the bosonic character of the photons, is commonly used in the fields of quantum communication and computing to test the indistinguishability of two single-photon wavepackets. The setup makes use of very few optical elements and requires little alignement that can be performed by students themselves. It allows them to gather essential experimental skills related to parametric crystals, fibre optics and single-photon detection, and to transpose abstract concepts of quantum physics to a hands-on experiment in the lab.

  10. Two-photon voltmeter for measuring a molecular electric field.

    PubMed

    Rebane, Aleksander; Wicks, Geoffrey; Drobizhev, Mikhail; Cooper, Thomas; Trummal, Aleksander; Uudsemaa, Merle

    2015-06-22

    We present a new approach for determining the strength of the dipolar solute-induced reaction field, along with the ground- and excited-state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one-photon and two-photon absorption measurements. We verify the approach on two benchmark chromophores N,N-dimethyl-6-propionyl-2-naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum-chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0-10(7)  V cm(-1) , and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute-solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close-range molecular interaction. PMID:25958849

  11. Fluorescent Pluronic nanodots for in vivo two-photon imaging.

    PubMed

    Maurin, Mathieu; Vurth, Laeticia; Vial, Jean-Claude; Baldeck, Patrice; Marder, Seth R; Van der Sanden, Boudewijn; Stephan, Olivier

    2009-06-10

    We report the synthesis of new nanosized fluorescent probes based on bio-compatible polyethylene-polypropylene glycol (Pluronic) materials. In aqueous solution, mini-emulsification of Pluronic with a high fluorescent di-stryl benzene-modified derivative, exhibiting a two-photon absorption cross section as high as 2500 Goeppert-Mayer units at 800 nm, leads to nanoparticles exhibiting a hydrodynamic radius below 100 nm. We have demonstrated that these new probes with luminescence located in the spectral region of interest for bio-imaging (the yellow part of the visible spectrum) allow deep (500 microm) bio-imaging of the mice brain vasculature. The dose injected during our experiments is ten times lower when compared to the classical commercial rhodamine-B isothicyanate-Dextran system but gives similar results to homogeneous blood plasma staining. The mean fluorescent signal intensity stayed constant during more than 1 h. PMID:19448291

  12. Fluorescent Pluronic nanodots for in vivo two-photon imaging

    NASA Astrophysics Data System (ADS)

    Maurin, Mathieu; Vurth, Laeticia; Vial, Jean-Claude; Baldeck, Patrice; Marder, Seth R.; Sanden, Boudewijn Van der; Stephan, Olivier

    2009-06-01

    We report the synthesis of new nanosized fluorescent probes based on bio-compatible polyethylene-polypropylene glycol (Pluronic) materials. In aqueous solution, mini-emulsification of Pluronic with a high fluorescent di-stryl benzene-modified derivative, exhibiting a two-photon absorption cross section as high as 2500 Goeppert-Mayer units at 800 nm, leads to nanoparticles exhibiting a hydrodynamic radius below 100 nm. We have demonstrated that these new probes with luminescence located in the spectral region of interest for bio-imaging (the yellow part of the visible spectrum) allow deep (500 µm) bio-imaging of the mice brain vasculature. The dose injected during our experiments is ten times lower when compared to the classical commercial rhodamine-B isothicyanate-Dextran system but gives similar results to homogeneous blood plasma staining. The mean fluorescent signal intensity stayed constant during more than 1 h.

  13. Two-Photon Fluorescence Tracking of Colloidal Clusters.

    PubMed

    Roy, Debjit; Mondal, Dipankar; Goswami, Debabrata

    2016-07-01

    In situ dynamics of colloidal cluster formation from nanoparticles is yet to be addressed. Using two-photon fluorescence (TPF) that has been amply used for single particle tracking, we demonstrate in situ measurement of effective three-dimensional optical trap stiffness of nanoparticles and their aggregates without using any position sensitive detector. Optical trap stiffness is an essential measure of the strength of an optical trap. TPF is a zero-background detection scheme and has excellent signal-to-noise-ratio, which can be easily extended to study the formation of colloidal cluster of nanospheres in the optical trapping regime. TPF tracking can successfully distinguish colloidal cluster from its monomer. PMID:27165039

  14. Evidence for a spin-1 particle produced by two photons

    NASA Astrophysics Data System (ADS)

    Aihara, H.; Alston-Garnjost, M.; Avery, R. E.; Barbaro-Galtieri, A.; Barker, A. R.; Barnes, A. V.; Barnett, B. A.; Bauer, D. A.; Bengtsson, H.-U.; Bintinger, D. L.; Bobbink, G. J.; Bolognese, T. S.; Bross, A. D.; Buchanan, C. D.; Buijs, A.; Caldwell, D. O.; Clark, A. R.; Cowan, G. D.; Crane, D. A.; Dahl, O. I.; Derby, K. A.; Eastman, J. J.; Eberhard, P. H.; Edberg, T. K.; Eisner, A. M.; Enomoto, R.; Erné, F. C.; Fujii, T.; Gary, J. W.; Gorn, W.; Hauptman, J. M.; Hofmann, W.; Huth, J. E.; Hylen, J.; Kamae, T.; Kaye, H. S.; Kees, K. H.; Kenney, R. W.; Kerth, L. T.; Ko, Winston; Koda, R. I.; Kofler, R. R.; Kwong, K. K.; Lander, R. L.; Langeveld, W. G.; Layter, J. G.; Linde, F. L.; Lindsey, C. S.; Loken, S. C.; Lu, A.; Lu, X.-Q.; Lynch, G. R.; Madaras, R. J.; Maeshima, K.; Magnuson, B. D.; Marx, J. N.; Masek, G. E.; Mathis, L. G.; Matthews, J. A.; Maxfield, S. J.; Melnikoff, S. O.; Miller, E. S.; Moses, W.; McNeil, R. R.; Nemethy, P.; Nygren, D. R.; Oddone, P. J.; Paar, H. P.; Park, D. A.; Park, S. K.; Pellett, D. E.; Pripstein, M.; Ronan, M. T.; Ross, R. R.; Rouse, F. R.; Schwitkis, K. A.; Sens, J. C.; Shapiro, G.; Shapiro, M. D.; Shen, B. C.; Slater, W. E.; Smith, J. R.; Steinman, J. S.; Stevenson, M. L.; Stork, D. H.; Strauss, M. G.; Sullivan, M. K.; Takahashi, T.; Thompson, J. R.; Toge, N.; Toutounchi, S.; van Tyen, R.; van Uitert, B.; Vandalen, G. J.; van Daalen Wetters, R. F.; Vernon, W.; Wagner, W.; Wang, E. M.; Wang, Y. X.; Wayne, M. R.; Wenzel, W. A.; White, J. T.; Williams, M. C.; Wolf, Z. R.; Yamamoto, H.; Yellin, S. J.; Zeitlin, C.; Zhang, W.-M.

    1986-11-01

    Two-photon production of K08K+/-π-/+ states has been studied by the TPC/Two-Gamma experiment at the SLAC storage ring PEP. A resonance of mass 1.42 GeV was seen when one of the photons was quite virtual but not when both photons were nearly real. Production of a spin-1 meson, which cannot be made by two real photons, would fit these observations. The Q2 dependence of the data in the resonance region agrees with this spin assignment and is incompatible with a spin-0 hypothesis. The mass and width of the resonance are similar to those of the E meson, which has been assigned JP=0- and JP=1+ by different experiments.

  15. 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

  16. Nonsequential two-photon double ionization of helium

    NASA Astrophysics Data System (ADS)

    Feist, J.; Nagele, S.; Pazourek, R.; Persson, E.; Schneider, B. I.; Collins, L. A.; Burgdörfer, J.

    2008-04-01

    We present accurate time-dependent ab initio calculations on fully differential and total integrated (generalized) cross sections for the nonsequential two-photon double ionization of helium at photon energies from 40 to 54 eV. Our computational method is based on the solution of the time-dependent Schrödinger equation and subsequent projection of the wave function onto Coulomb waves. We compare our results with other recent calculations and discuss the emerging similarities and differences. We investigate the role of electronic correlation in the representation of the two-electron continuum states, which are used to extract the ionization yields from the fully correlated final wave function. In addition, we study the influence of the pulse length and shape on the cross sections in time-dependent calculations and address convergence issues.

  17. 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

  18. High contrast two-photon imaging of fingermarks

    NASA Astrophysics Data System (ADS)

    Stoltzfus, Caleb R.; Rebane, Aleksander

    2016-04-01

    Optically-acquired fingermarks are widely used as evidence across law enforcement agencies as well as in the courts of law. A common technique for visualizing latent fingermarks on nonporous surfaces consists of cyanoacrylate fuming of the fingerprint material, followed by impregnation with a fluorescent dye, which under ultra violet (UV) illumination makes the fingermarks visible and thus accessible for digital recording. However, there exist critical circumstances, when the image quality is compromised due to high background scattering, high auto-fluorescence of the substrate material, or other detrimental photo-physical and photo-chemical effects such as light-induced damage to the sample. Here we present a novel near-infrared (NIR), two-photon induced fluorescence imaging modality, which significantly enhances the quality of the fingermark images, especially when obtained from highly reflective and/or scattering surfaces, while at the same time reducing photo-damage to sensitive forensic samples.

  19. 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

  20. Superparamagnetic microrobots: fabrication by two-photon polymerization and biocompatibility.

    PubMed

    Suter, Marcel; Zhang, Li; Siringil, Erdem C; Peters, Christian; Luehmann, Tessa; Ergeneman, Olgac; Peyer, Kathrin E; Nelson, Bradley J; Hierold, Christofer

    2013-12-01

    This work presents the fabrication and controlled actuation of swimming microrobots made of a magnetic polymer composite (MPC) consisting of 11-nm-diameter magnetite (Fe3O4) nanoparticles and photocurable resin (SU-8). Two-photon polymerization (TPP) is used to fabricate the magnetic microstructures. The material properties and the cytotoxicity of the MPC with different nanoparticle concentrations are characterized. The live/dead staining tests indicate that MPC samples with varied concentrations, up to 10 vol.%, have negligible cytotoxicity after 24 h incubation. Fabrication parameters of MPC with up to 4 vol.% were investigated. We demonstrate that the helical microdevices made of 2 vol.% MPC were capable of performing corkscrew motion in water applying weak uniform rotating magnetic fields. PMID:23846247

  1. Two-photon exchange effect studied with neural networks

    SciTech Connect

    Graczyk, Krzysztof M.

    2011-09-15

    An approach to the extraction of the two-photon exchange (TPE) correction from elastic ep scattering data is presented. The cross-section, polarization transfer (PT), and charge asymmetry data are considered. It is assumed that the TPE correction to the PT data is negligible. The form factors and TPE correcting term are given by one multidimensional function approximated by the feedforward neural network (NN). To find a model-independent approximation, the Bayesian framework for the NNs is adapted. A large number of different parametrizations is considered. The most optimal model is indicated by the Bayesian algorithm. The obtained fit of the TPE correction behaves linearly in {epsilon} but it has a nontrivial Q{sup 2} dependence. A strong dependence of the TPE fit on the choice of parametrization is observed.

  2. High contrast two-photon imaging of fingermarks.

    PubMed

    Stoltzfus, Caleb R; Rebane, Aleksander

    2016-01-01

    Optically-acquired fingermarks are widely used as evidence across law enforcement agencies as well as in the courts of law. A common technique for visualizing latent fingermarks on nonporous surfaces consists of cyanoacrylate fuming of the fingerprint material, followed by impregnation with a fluorescent dye, which under ultra violet (UV) illumination makes the fingermarks visible and thus accessible for digital recording. However, there exist critical circumstances, when the image quality is compromised due to high background scattering, high auto-fluorescence of the substrate material, or other detrimental photo-physical and photo-chemical effects such as light-induced damage to the sample. Here we present a novel near-infrared (NIR), two-photon induced fluorescence imaging modality, which significantly enhances the quality of the fingermark images, especially when obtained from highly reflective and/or scattering surfaces, while at the same time reducing photo-damage to sensitive forensic samples. PMID:27053515

  3. Measurement of two-photon exchange effects in CLAS

    NASA Astrophysics Data System (ADS)

    Rimal, Dipak; Raue, Brian; Adikaram, Dasuni; Weinstein, Lawrence

    2014-03-01

    There is a significant discrepancy between the Rosenbluth and the polarization transfer measurements of the proton's electric to magnetic form factor ratio GEp/GEp. One possible explanation of this discrepancy is the contribution from two-photon exchange (TPE) effects, which are not typically accounted for in standard radiative corrections. The ratio of positron-proton to electron-proton elastic scattering cross sections, R =σ/(e+ p) σ (e- p) , provides a model independent measurement of the TPE contribution to elastic electron-proton scattering. We measured this ratio at Jefferson Lab using a mixed electron-positron beam. Both electrons and positrons were elastically scattered from a liquid hydrogen target. The resulting scattered particles were detected in CLAS. The experimental details and results will be discussed. U.S. Dept. of Energy.

  4. 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.

  5. High contrast two-photon imaging of fingermarks

    PubMed Central

    Stoltzfus, Caleb R.; Rebane, Aleksander

    2016-01-01

    Optically-acquired fingermarks are widely used as evidence across law enforcement agencies as well as in the courts of law. A common technique for visualizing latent fingermarks on nonporous surfaces consists of cyanoacrylate fuming of the fingerprint material, followed by impregnation with a fluorescent dye, which under ultra violet (UV) illumination makes the fingermarks visible and thus accessible for digital recording. However, there exist critical circumstances, when the image quality is compromised due to high background scattering, high auto-fluorescence of the substrate material, or other detrimental photo-physical and photo-chemical effects such as light-induced damage to the sample. Here we present a novel near-infrared (NIR), two-photon induced fluorescence imaging modality, which significantly enhances the quality of the fingermark images, especially when obtained from highly reflective and/or scattering surfaces, while at the same time reducing photo-damage to sensitive forensic samples. PMID:27053515

  6. Whole Brain Imaging with Serial Two-Photon Tomography

    PubMed Central

    Amato, Stephen P.; Pan, Feng; Schwartz, Joel; Ragan, Timothy M.

    2016-01-01

    Imaging entire mouse brains at submicron resolution has historically been a challenging undertaking and largely confined to the province of dedicated atlasing initiatives. This has limited systematic investigations into important areas of neuroscience, such as neural circuits, brain mapping and neurodegeneration. In this article, we describe in detail Serial Two-Photon (STP) tomography, a robust, reliable method for imaging entire brains with histological detail. We provide examples of how the basic methodology can be extended to other imaging modalities, such as Optical Coherence Tomography (OCT), in order to provide unique contrast mechanisms. Furthermore, we provide a survey of the research that STP tomography has enabled in the field of neuroscience, provide examples of how this technology enables quantitative whole brain studies, and discuss the current limitations of STP tomography-based approaches. PMID:27047350

  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. Arbitrary-scan imaging for two-photon microscopy

    NASA Astrophysics Data System (ADS)

    Botcherby, Edward; Smith, Christopher; Booth, Martin; Juskaitis, Rimas; Wilson, Tony

    2010-02-01

    In this paper, we present details of a scanning two-photon fluorescence microscope we have built with a nearisotropic scan rate. This means that the focal spot can be scanned at high speed along any direction in the specimen, without introducing systematic aberrations. We present experimental point spread function measurements for this system using an Olympus 0.8 NA 40X water dipping objective lens that demonstrates an axial range of operation greater than 200 μm. We give details of a novel actuator device used to displace the focusing element and demonstrate axial scan responses up to 3.5 kHz. Finally, we present a bioscience application of this system to image dendritic processes that follow non-linear paths in three-dimensional space. The focal spot was scanned along one such process at 400 Hz with an axial range of more than 90 μm.

  9. Two-photon exchange in proton elastic scattering

    NASA Astrophysics Data System (ADS)

    Bernauer, Jan C.

    2015-10-01

    Recent interest in the proton electromagnetic form factors is partly motivated by the discrepancy found in the determination of the electric-to-magnetic form factor ratio using different techniques. Results from scattering experiments using the Rosenbluth technique indicate that the form factor ratio is constant as a function of Q2 while experiments employing polarization show a clear, roughly linear, decline of the ratio. A possible explanation is the typically unaccounted for contribution of hard two-photon exchange to the scattering process. Theoretical calculations show large variations, many indicating an effect of the right sign and magnitude. Direct verification was sought by experiments at VEPP-3, Jefferson Lab and by the OLYMPUS collaboration at DESY. In the talk, I will discuss the OLYMPUS experiment and the current state of experimental and theoretical results.

  10. Classes of two-photon states defined by linear interactions and destructive two-photon quantum interference in a single mode

    NASA Astrophysics Data System (ADS)

    Lund, A. P.

    2015-11-01

    We describe a two-photon quantum interference effect which differs from the Hong-Ou-Mandel effect in that the destructive quantum inference occurs on a component of the state where two photons are in a single output mode while maintaining the two-photon events in the alternative mode. This effect is manifestly nonclassical but requires more sophisticated technology to observe than the Hong-Ou-Mandel effect. The theory outlined in this paper can also be used to classify two-photon states into classes which are related by the ability to transform the states within the class by using only linear optical interactions. This theory shows that there is an infinite number of these classes of two photon states when there are two or more modes which can support the photons.

  11. Two-photon absorption spectrum of the photoinitiator Lucirin TPO-L

    NASA Astrophysics Data System (ADS)

    Mendonca, C. R.; Correa, D. S.; Baldacchini, T.; Tayalia, P.; Mazur, E.

    2008-03-01

    Two-photon absorption induced polymerization provides a powerful method for the fabrication of intricate three-dimensional microstructures. Recently, Lucirin TPO-L was shown to be a photoinitiator with several advantageous properties for two-photon induced polymerization. Here we measure the two-photon absorption cross-section spectrum of Lucirin TPO-L, which presents a maximum of 1.2 GM at 610 nm. Despite its small two-photon absorption cross-section, it is possible to fabricate excellent microstructures by two-photon polymerization due to the high polymerization quantum yield of Lucirin TPO-L. These results indicate that optimization of the two-photon absorption cross-section is not the only material parameter to be considered when searching for new photoinitiators for microfabrication via two-photon absorption.

  12. Intracavity Optogalvanic Spectroscopy, A New Ultra-sensitive Analytical Technique for 14C Analysis

    PubMed Central

    Murnick, Daniel E.; Dogru, Ozgur; Ilkmen, Erhan

    2009-01-01

    We show a new ultra-sensitive laser based analytical technique, intracavity optogalvanic spectroscopy, allowing extremely high sensitivity for detection of 14C labeled carbon dioxide. Capable of replacing large accelerator mass spectrometers, the technique quantifies attomoles of 14C in submicrogram samples. Based on the specificity of narrow laser resonances coupled with the sensitivity provided by standing waves in an optical cavity and detection via impedance variations, limits of detection near 10-15 14C:12C ratios are obtained. Using a 15W 14CO2 laser, a linear calibration with samples from 10-15 to >2 × 10-12 in 14C:12C ratios, as determined by accelerator mass spectrometry, is demonstrated. Possible applications include microdosing studies in drug development, individualized sub-therapeutic tests of drug metabolism, carbon dating and real time monitoring of atmospheric radiocarbon. The method can also be applied to detection of other trace entities. PMID:18533685

  13. Development of laser optogalvanic spectroscopy as a probe of alkali atoms in an MHD environment

    SciTech Connect

    Monts, D.L.; Qian, S.; Cook, R.L.; Shepard, W.S.

    1995-02-01

    Application of Laser Optogalvanic Spectroscopy (LOGS) to MHD combustion systems requires selection of an appropriate alkali atom electronic transition to monitor. These studies suggest that in MHD combustion systems, it is desirable to use cesium, which occurs as an impurity in potassium compounds, as a surrogate for potassium rather than to directly monitor potassium in order to obtain reliable determinations of seed concentration. Studies were also performed to investigate the effect of electrode corrosion on the normalized LOGS signal intensity at a fixed wavelength (578.238 nm). During six-hour experiments in a near-stoichiometric flame, the normalized LOGS signal intensity decreased by 40-50% for a -960 V rod electrode and by 10-20% for a -500 V rod electrode. These changes are attributed to buildup of an oxide coating on the electrode, reducing the collection efficiency of the electrode.

  14. Comparative Study of Electric Field Measurement in Glow Discharges using Laser Optogalvanic Spectroscopy

    SciTech Connect

    Hussain, Shahid; Saleem, M.; Baig, M. A.

    2008-10-22

    The net electric field inside low-pressure glow discharges has been measured using laser optogalvanic spectroscopy of 1s2s {sup 1}S{sub 0}{yields}np{sup 1}P{sub 1} Rydberg series of atomic helium. Three different types of discharges, an inductively coupled RF discharge cell operating at 4 MHz, a homemade DC discharge cell and a commercial see-through hollow cathode lamp have been used for these studies. The Rydberg series terminates earlier in the high electric field discharge as compared to that in the low electric field discharge. The net electric field also produces shift and broadens the observed spectral lines especially in the high lying Rydberg transitions. The electric field has been determined from the series termination and also from the energy shift of the observed transitions.

  15. Optimization of Doppler-free magnetically induced dichroic locking spectroscopy on the 1S0-3P1 transition of a neutral mercury atom

    NASA Astrophysics Data System (ADS)

    Liu, Hongli; Yin, Shiqi; Qian, Jun; Xu, Zhen; Wang, Yuzhu

    2013-04-01

    Doppler-free dichroic locking (DFDL) spectroscopy on the 1S0-3P1 transition of neutral mercury (Hg) atoms is observed in a 5 mm long vapour cell. The performance of the DFDL signal, such as its slope and amplitude, is investigated in detail. The optimal axial magnetic field and cell temperature (optical depth) for the observed seven transitions are also highlighted. We also demonstrate an important application of DFDL spectroscopy in the frequency stabilization of an ultraviolet laser on the transition of 200Hg.

  16. Doppler-free approach to optical pumping dynamics in the 6S_1/2‑5D_5/2 electric quadrupole transition of cesium vapor

    NASA Astrophysics Data System (ADS)

    Chan, Eng Aik; Aljunid, Syed Abdullah; Zheludev, Nikolay I.; Wilkowski, David; Ducloy, Martial

    2016-05-01

    The $6S_{1/2}-5D_{5/2}$ electric quadrupole transition is investigated in Cesium vapor at room temperature via nonlinear Doppler-free 6P-6S-5D three-level spectroscopy. Frequency-resolved studies of individual E2 hyperfine lines allow one to analyze optical pumping dynamics, polarization selection rules and line intensities. It opens the way to studies of transfer of light orbital angular momentum to atoms, and the influence of metamaterials on E2 line spectra.

  17. Two-Photon Ghost Image and Interference-Diffraction

    NASA Technical Reports Server (NTRS)

    Shih, Y. H.; Sergienko, A. V.; Pittman, T. B.; Strekalov, D. V.; Klyshko, D. N.

    1996-01-01

    One of the most surprising consequences of quantum mechanics is entanglement of two or more distance particles. The two-particle entangled state was mathematically formulated by Schrodinger. Based on this unusual quantum behavior, EPR defined their 'physical reality' and then asked the question: 'Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?' One may not appreciate EPR's criterion of physical reality and insist that 'no elementary quantum phenomenon is a phenomenon until it is a recorded phenomenon'. Optical spontaneous parametric down conversion (SPDC) is the most effective mechanism to generate an EPR type entangled two-photon state. In SPDC, an optical beam, called the pump, is incident on a birefringent crystal. The pump is intense enough so that nonlinear effects lead to the conversion of pump photons into pairs of photons, historically called signal and idler. Technically, the SPDC is said to be type-1 or type-2, depending on whether the signal and idler beams have parallel or orthogonal polarization. The SPDC conversion efficiency is typically on the order of 10(exp -9) to 10(exp -11), depending on the SPDC nonlinear material. The signal and idler intensities are extremely low, only single photon detection devices can register them. The quantum entanglement nature of SPDC has been demonstrated in EPR-Bohm experiments and Bell's inequality measurements. The following two experiments were recently performed in our laboratory, which are more closely related to the original 1935 EPR gedankenezperiment. The first experiment is a two-photon optical imaging type experiment, which has been named 'ghost image' by the physics community. The signal and idler beams of SPDC are sent in different directions, so that the detection of the signal and idler photons can be performed by two distant photon counting detectors. An aperture object (mask) is placed in front of the signal photon detector and illuminated by the signal beam through a

  18. Characterization of two-photon polymerization process using Raman microspectroscopy

    NASA Astrophysics Data System (ADS)

    Jiang, L. J.; Zhou, Y. S.; Xiong, W.; Gao, Y.; Baldacchini, T.; Silvain, J.-F.; Jiang, L.; Lu, Y. F.

    2014-03-01

    Two-photon polymerization (TPP) is a promising micro/nanofabrication technique, which is capable of fabricating 3D micro/nanostructures beyond the diffraction limit of light. However, the study of TPP process with a focus on the dependence of degree of conversion on TPP parameters using a non-destructive and efficient method is still lacking. We studied the quantitative relationships between the TPP parameters and the cross-linking of an acrylic-based IP-L 780 photoresist via systematic Raman characterization. The differences in the Raman spectra between the non-polymerized and the polymerized IP-L 780 photoresists were observed by probing the excitation of carbon-carbon double bond (C=C) vibrations. We obtained the relationship between the degree of conversion in TPP and the Raman spectra of the IP-L 780 resin, in which the intensity of the characteristic Raman peak of IP-L 780 at 1635 cm-1 decreases with the increase of the TPP laser dose. A mathematic model of the degree of conversion with respective to the TPP parameters, including laser average power and writing speed, has been established. The method provides a simple and effective way to characterize and optimize the TPP micro/nanofabrication processes. The established model for the degree of conversion as the function of TPP parameters will contribute to the advanced 3D TPP micro/nanofabrication by providing a guidance to optimize the laser doses, voxel sizes, and the mechanical strength of the polymers.

  19. Two-photon holographic optogenetics of neural circuits (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yang, Weijian; Carrillo-Reid, Luis; Peterka, Darcy S.; Yuste, Rafael

    2016-03-01

    Optical manipulation of in vivo neural circuits with cellular resolution could be important for understanding cortical function. Despite recent progress, simultaneous optogenetic activation with cellular precision has either been limited to 2D planes, or a very small numbers of neurons over a limited volume. Here we demonstrate a novel paradigm for simultaneous 3D activation using a low repetition rate pulse-amplified fiber laser system and a spatial light modulator (SLM) to project 3D holographic excitation patterns on the cortex of mice in vivo for targeted volumetric 3D photoactivation. This method is compatible with two-photon imaging, and enables the simultaneous activation of multiple cells in 3D, using red-shifted opsins, such as C1V1 or ReaChR, while simultaneously imaging GFP-based sensors such as GCaMP6. This all-optical imaging and 3D manipulation approach achieves simultaneous reading and writing of cortical activity, and should be a powerful tool for the study of neuronal circuits.

  20. Photodynamic therapy by nonresonant two-photon excitation

    NASA Astrophysics Data System (ADS)

    Koenig, Karsten; Riemann, Iris; Fischer, Peter

    1999-07-01

    Intracellular photodynamic reactions by nonlinear excitation of porphyrin photosensitizers have been induced using near infrared ultrashort laser pulses at 200 fs pulse width, 80 MHz pulse repetition rate and 2 mW mean laser power. In particular, a highly focused 780 nm pulsed laser scanning beam was employed at a frame rate of 1/16 s-1 (60 microsecond(s) pixel dwell time) to expose Photofrin-labeled and aminolevulinic acid (ALA)-labeled Chinese hamster ovary cells. Intracellular accumulation and photobleaching of the fluorescent photosensitizers protoporphyrin IX and Photofrin have been studied by non-resonant two-photon fluorescence excitation. Subsequent scanning of the sensitizer-labeled cells resulted in reduced cloning efficiency of 50% and 0% after about 13 scans (approximately equals 10 mJ) and 50 scans, respectively, in the case of Photofrin accumulation (5 (mu) g/ml) and after about 24 scans and 100 scans in the case of ALA administration (1.5 mg/ml). Live/dead assays revealed the loss of vitality of most of cells after 50 scans for Photofrin-labeled cells and 100 scans for ALA-labeled cells. Sensitizer-free control cells could be scanned more than 250 times (1.1 h) without impact on the reproduction behavior, morphology, and vitality.

  1. 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.

  2. Higgs boson decay to two photons and dispersion relations

    NASA Astrophysics Data System (ADS)

    Melnikov, Kirill; Vainshtein, Arkady

    2016-03-01

    We discuss the computation of the Higgs boson decay amplitude to two photons through the W -loop using dispersion relations. The imaginary part of the form factor FW(s ) that parametrizes this decay is unambiguous in four dimensions. When it is used to calculate the unsubtracted dispersion integral, the finite result for the form factor FW(s ) is obtained. However, the FW(s ) obtained in this way differs by a constant term from the result of a diagrammatic computation, based on dimensional regularization. It is easy to accommodate the missing constant by writing a once-subtracted dispersion relation for FW(s ) but it is unclear why the subtraction needs to be done. The goal of this paper is to investigate this question in detail. We show that the correct constant can be recovered within a dispersive approach in a number of ways that, however, either require an introduction of an ultraviolet regulator or unphysical degrees of freedom; unregulated and unsubtracted computations in the unitary gauge are insufficient, in spite of the fact that such computations give a finite result.

  3. Formation of Alkali Hydrides via Two-photon Excitation

    NASA Astrophysics Data System (ADS)

    Juarros, Elizabeth; Kirby, Kate; Coté, Robin

    2006-05-01

    Alkali hydride molecules are very polar, exhibiting large ground-state dipole moments. Ultracold sources of alkali atoms and hydrogen have been created in the laboratory. We explore theoretically the feasibility of forming such molecules from a mixture of the ultracold atomic gases, employing a two-photon stimulated radiative association process -- Raman excitation. The triplet ground state for lithium hydride is of particular interest since it supports only one bound ro-vibrational level. Using accurate molecular potential energy curves and dipole transition moments, we have calculated the rate coefficients for populating the bound ro-vibrational level of the a^3&+circ; state of LiH via the excited b^3π state. We have found that significant molecule formation rates can be realized with laser intensities and atomic densities that are attainable experimentally. Also, we have calculated the rate coefficients for populating all the vibrational levels of the X^1&+circ; state of LiH via the excited B^1π state. In this case, we have found that significant formation rates into the upper vibrational levels can be realized. We examine the spontaneous emission cascade which takes place from these upper vibrational levels on a timescale of milliseconds, and calculate the resulting rotational populations in v=0. We show that photon emission in the cascade process does not contribute to trap loss.

  4. Two-photon autofluorescence spectroscopy of oral mucosa tissue

    NASA Astrophysics Data System (ADS)

    Edward, Kert; Shilagard, Tuya; Qiu, Suimin; Vargas, Gracie

    2011-03-01

    The survival rate for individuals diagnosed with oral cancer is correlated with the stage of detection. Thus the development of novel techniques for the earliest possible detection of malignancies is of critical importance. Single photon (1P) autofluorescence spectroscopy has proven to be a powerful diagnostic tool in this regard, but 2P (two photon) spectroscopy remains essentially unexplored. In this investigation, a spectroscopic system was incorporated into a custom-built 2P laser scanning microscope. Oral cancer was induced in the buccal pouch of Syrian Golden hamsters by tri-weekly topical application of 9,10-dimethyl-1,2-benzanthracene (DMBA).Three separated sites where investigated in each hamster at four excitation wavelengths from 780 nm to 890 nm. A Total of 8 hamsters were investigated (4 normal and 4 DMBA treated). All investigated sites were imaged via 2p imaging, marked for biopsy, processed for histology and H&E staining, and graded by a pathologist. The in vivo emission spectrum for normal, mild/high grade dysplasia and squamous cell carcinoma is presented. It is shown that the hamsters with various stages of dysplasia are characterized by spectral differences as a function of depth and excitation wavelength, compared to normal hamsters.

  5. Two-Photon Absorption in Conjugated Energetic Molecules.

    PubMed

    Bjorgaard, Josiah A; Sifain, Andrew E; Nelson, Tammie; Myers, Thomas W; Veauthier, Jacqueline M; Chavez, David E; Scharff, R Jason; Tretiak, Sergei

    2016-07-01

    Time-dependent density functional theory (TD-DFT) was used to investigate the relationship between molecular structure and the one- and two-photon absorption (OPA and TPA, respectively) properties of novel and recently synthesized conjugated energetic molecules (CEMs). The molecular structures of CEMs can be strategically altered to influence the heat of formation and oxygen balance, two factors that can contribute to the sensitivity and strength of an explosive material. OPA and TPA are sensitive to changes in molecular structure as well, influencing the optical range of excitation. We found calculated vertical excitation energies to be in good agreement with experiment for most molecules. Peak TPA intensities were found to be significant and on the order of 10(2) GM. Natural transition orbitals for essential electronic states defining TPA peaks of relatively large intensity were used to examine the character of relevant transitions. Modification of molecular substituents, such as additional oxygen or other functional groups, produces significant changes in electronic structure, OPA, and TPA and improves oxygen balance. The results show that certain molecules are apt to undergo nonlinear absorption, opening the possibility for controlled, direct optical initiation of CEMs through photochemical pathways. PMID:27257984

  6. Two-photon excited photoconversion of cyanine-based dyes

    PubMed Central

    Kwok, Sheldon J. J.; Choi, Myunghwan; Bhayana, Brijesh; Zhang, Xueli; Ran, Chongzhao; Yun, Seok-Hyun

    2016-01-01

    The advent of phototransformable fluorescent proteins has led to significant advances in optical imaging, including the unambiguous tracking of cells over large spatiotemporal scales. However, these proteins typically require activating light in the UV-blue spectrum, which limits their in vivo applicability due to poor light penetration and associated phototoxicity on cells and tissue. We report that cyanine-based, organic dyes can be efficiently photoconverted by nonlinear excitation at the near infrared (NIR) window. Photoconversion likely involves singlet-oxygen mediated photochemical cleavage, yielding blue-shifted fluorescent products. Using SYTO62, a biocompatible and cell-permeable dye, we demonstrate photoconversion in a variety of cell lines, including depth-resolved labeling of cells in 3D culture. Two-photon photoconversion of cyanine-based dyes offer several advantages over existing photoconvertible proteins, including use of minimally toxic NIR light, labeling without need for genetic intervention, rapid kinetics, remote subsurface targeting, and long persistence of photoconverted signal. These findings are expected to be useful for applications involving rapid labeling of cells deep in tissue. PMID:27029524

  7. Two-photon excited photoconversion of cyanine-based dyes

    NASA Astrophysics Data System (ADS)

    Kwok, Sheldon J. J.; Choi, Myunghwan; Bhayana, Brijesh; Zhang, Xueli; Ran, Chongzhao; Yun, Seok-Hyun

    2016-03-01

    The advent of phototransformable fluorescent proteins has led to significant advances in optical imaging, including the unambiguous tracking of cells over large spatiotemporal scales. However, these proteins typically require activating light in the UV-blue spectrum, which limits their in vivo applicability due to poor light penetration and associated phototoxicity on cells and tissue. We report that cyanine-based, organic dyes can be efficiently photoconverted by nonlinear excitation at the near infrared (NIR) window. Photoconversion likely involves singlet-oxygen mediated photochemical cleavage, yielding blue-shifted fluorescent products. Using SYTO62, a biocompatible and cell-permeable dye, we demonstrate photoconversion in a variety of cell lines, including depth-resolved labeling of cells in 3D culture. Two-photon photoconversion of cyanine-based dyes offer several advantages over existing photoconvertible proteins, including use of minimally toxic NIR light, labeling without need for genetic intervention, rapid kinetics, remote subsurface targeting, and long persistence of photoconverted signal. These findings are expected to be useful for applications involving rapid labeling of cells deep in tissue.

  8. Measurement of two-photon exchange effect with CLAS

    SciTech Connect

    Raue, Brian A

    2010-08-01

    The structure of the proton is one the most important and most studied topics in nuclear physics. However, discrepant measurements of the proton's electromagnetic form factor ratio, GE/GM, seriously jeopardize a definitive understanding of the proton's structure. Measurements of GEGM using the Rosenbluth separation technique disagree with those using polarization transfer methods by about a factor of three at Q2~5.6 GeV2. It has been hypothesized that this discrepancy is due to two-photon exchange (TPE) effects that are not part of the usual radiative corrections. Theoretical corrections for the TPE effect are difficult due to the fact that a large number of excited nucleon states can contribute to the process. However, the TPE effect can be directly determined by measuring the ratio of the positron-proton to electron-proton elastic scattering cross sections, R = sigma(e+)/sigma(e-), as the TPE effect changes sign with respect to the charge of the incident particle. A brief test run of a modified beamline and the CLAS detector at Jefferson Lab has resulted in the most precise measurements of the R to date. We will present results from the test run covering Q2<0.8 GeV2 and 0.78<=epsilon<=0.97. In addition, the test run demonstrated the feasibility of producing a mixed electron/positron beam of good quality so that the measurements can be extended up to Q2~3.0 GeV2.

  9. Perturbative QCD predictions for two-photon exchange

    SciTech Connect

    Borisyuk, Dmitry; Kobushkin, Alexander

    2009-02-01

    We study two-photon exchange (TPE) in the elastic electron-nucleon scattering at high Q{sup 2} in the framework of perturbative quantum chromodynamics. The obtained TPE amplitude is of order {alpha}/{alpha}{sub s} with respect to Born approximation. Its shape and value are sensitive to the choice of nucleon wave function, thus study of TPE effects can provide important information about nucleon structure. With the wave functions based on quantum chromodynamics sum rules, TPE correction to the electron-proton cross section has a negative sign, is almost linear in {epsilon}, and grows logarithmically with Q{sup 2} up to 7% at Q{sup 2}=30 GeV{sup 2}. The results of existing hadronic calculations, taking into account just the nucleon intermediate state, can be smoothly connected with the perturbative quantum chromodynamics result near Q{sup 2}{approx}3 GeV{sup 2}. Above this point two methods disagree, which implies that the hadronic approach becomes inadequate at high Q{sup 2}. Other relevant observables, such as the electron/positron cross section ratio, are also discussed.

  10. Review of two-photon exchange in electron scattering

    SciTech Connect

    J. Arrington, P. G. Blunden, W. Melnitchouk

    2011-10-01

    We review the role of two-photon exchange (TPE) in electron-hadron scattering, focusing in particular on hadronic frameworks suitable for describing the low and moderate Q^2 region relevant to most experimental studies. We discuss the effects of TPE on the extraction of nucleon form factors and their role in the resolution of the proton electric to magnetic form factor ratio puzzle. The implications of TPE on various other observables, including neutron form factors, electroproduction of resonances and pions, and nuclear form factors, are summarized. Measurements seeking to directly identify TPE effects, such as through the angular dependence of polarization measurements, nonlinear epsilon contributions to the cross sections, and via e+p to e-p cross section ratios, are also outlined. In the weak sector, we describe the role of TPE and gamma-Z interference in parity-violating electron scattering, and assess their impact on the extraction of the strange form factors of the nucleon and the weak charge of the proton.

  11. Two photon absorption in high power broad area laser diodes

    NASA Astrophysics Data System (ADS)

    Dogan, Mehmet; Michael, Christopher P.; Zheng, Yan; Zhu, Lin; Jacob, Jonah H.

    2014-03-01

    Recent advances in thermal management and improvements in fabrication and facet passivation enabled extracting unprecedented optical powers from laser diodes (LDs). However, even in the absence of thermal roll-over or catastrophic optical damage (COD), the maximum achievable power is limited by optical non-linear effects. Due to its non-linear nature, two-photon absorption (TPA) becomes one of the dominant factors that limit efficient extraction of laser power from LDs. In this paper, theoretical and experimental analysis of TPA in high-power broad area laser diodes (BALD) is presented. A phenomenological optical extraction model that incorporates TPA explains the reduction in optical extraction efficiency at high intensities in BALD bars with 100μm-wide emitters. The model includes two contributions associated with TPA: the straightforward absorption of laser photons and the subsequent single photon absorption by the holes and electrons generated by the TPA process. TPA is a fundamental limitation since it is inherent to the LD semiconductor material. Therefore scaling the LDs to high power requires designs that reduce the optical intensity by increasing the mode size.

  12. Nonlinear Pulse Propagation Near a Two-Photon Resonance

    NASA Astrophysics Data System (ADS)

    Rodrigues, Augusto Da Silveira

    The propagation of light pulses whose spectra are in the vicinity of a material two-photon resonance is studied. We derive the appropriate form for the nonlinear polarization. In the limit of fast material response (as compared to the pulse duration) we obtain a wave equation that includes a new term that reflects the nonlinearly dispersive nature of the propagation. We find that nonlinear dispersion leads to self-steepening, and asymmetric spectral modulation, which in the absence of linear dispersion eventually leads to an optical shock formation. However, second-order linear dispersion is eventually able to stop the steepening and we show that a new set of solitons are supported by the system, resulting from the interplay of linear dispersion, intensity dependent refractive-index, and nonlinear dispersion. We assess the effects of third-order linear dispersion on these pulses and show that for realistic values of the parameters and not too large propagation distances they remain relatively stable. We study also the evolution of ultra-short pulses in a medium whose relaxation time is comparable to the pulses duration, and apply those results to the study of femtosecond pulse propagation in quantum dot doped waveguides.

  13. 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.

  14. Synergistic Two-Photon Absorption Enhancement in Photosynthetic Light Harvesting

    NASA Astrophysics Data System (ADS)

    Chen, Kuo-Mei; Chen, Yu-Wei; Gao, Ting-Fong

    2012-06-01

    The grand scale fixation of solar energies into chemical substances by photosynthetic reactions of light-harvesting organisms provides Earth's other life forms a thriving environment. Scientific explorations in the past decades have unraveled the fundamental photophysical and photochemical processes in photosynthesis. Higher plants, green algae, and light-harvesting bacteria utilize organized pigment-protein complexes to harvest solar power efficiently and the resultant electronic excitations are funneled into a reaction center, where the first charge separation process takes place. Here we show experimental evidences that green algae (Chlorella vulgaris) in vivo display a synergistic two-photon absorption enhancement in their photosynthetic light harvesting. Their absorption coefficients at various wavelengths display dramatic dependence on the photon flux. This newly found phenomenon is attributed to a coherence-electronic-energy-transfer-mediated (CEETRAM) photon absorption process of light-harvesting pigment-protein complexes of green algae. Under the ambient light level, algae and higher plants can utilize this quantum mechanical mechanism to create two entangled electronic excitations adjacently in their light-harvesting networks. Concerted multiple electron transfer reactions in the reaction centers and oxygen evolving complexes can be implemented efficiently by the coherent motion of two entangled excitons from antennae to the charge separation reaction sites. To fabricate nanostructured, synthetic light-harvesting apparatus, the paramount role of the CEETRAM photon absorption mechanism should be seriously considered in the strategic guidelines.

  15. Spatial distribution of the optogalvanic signal in a microplasma detector for lab-on-a-chip gas analysis

    NASA Astrophysics Data System (ADS)

    Persson, A.; Berglund, M.

    2016-07-01

    Gas sensors are characterized by their sensitivity and selectivity. This is preferably combined with versatility, where the selectivity can be altered, without complex modifications and whiteout losing sensitivity. If aimed at lab-on-a-chip applications, the sensor also must be able to analyze small samples. Today, sensors combining selectivity and versatility for chip-level gas analysis are scarce; however, this paper investigates how miniaturized optogalvanic spectroscopy can fill this gap. By studying the spatial distribution of the optogalvanic signal inside a microplasma, it is shown that the signal is generated in the minuscule gas volume of the sheath surrounding the plasma probe that collects it. Nevertheless, a strong and stable spectroscopic signal can be extracted from the sheath, and the sample concentrations can be calculated using straightforward plasma theory. The minimum detectable absorption and the noise equivalent absorption sensitivity of the system are estimated to be less than 1.4  ×  10‑9 Hz‑0.5 and 2.8  ×  10‑9 cm‑1 Hz‑0.5, respectively, without cavity enhancement. Combined with inherited versatility from absorption spectroscopy and the capability of handling sub-nanogram samples, this makes optogalvanic spectrometry an excellent candidate for future lab-on-a-chip gas analyzers.

  16. 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.

  17. Two photon microscopy for studies of xenobiotics in human skin

    NASA Astrophysics Data System (ADS)

    Simonsson, Carl; Smedh, Maria; Jonson, Charlotte; Karlberg, Ann-Therese; Ericson, Marica B.

    2007-07-01

    For successful uptake and distribution of drugs from transdermal formulations, it is important to understand the skin barrier function. Innovative advances in modern microscopy have provided valuable tools to study the interaction between the skin and xenobiotics. Two-photon microscopy (TPM) allows non-invasive visualization of fluorescent compounds in the skin. The advantages of TPM over conventional confocal microscopy are better light penetration into highly scattering and absorbing tissue such as human skin, improved detection efficiency, limited out of focus photobleaching and reduced phototoxic effects. We present TPM as an alternative non-invasive in vitro method to study chemical penetration enhancement of fluorescent model drugs. The permeability of sulforhodamine B (SRB) through human epidermis was measured with vertical diffusion cells. The absorption was visualized using TPM after 24 h passive diffusion. We have evaluated variations in physicochemical parameters controlling dermal drug uptake induced by the penetration enhancer oleic acid according to methods previously described by Yu et al. Optical sectioning by TPM was compared with cryosectioning. Oleic acid significantly increased penetration of sulforhodamine. TPM images demonstrate a four-fold increase in the partition coefficient. In addition, a six-fold increase in the concentration gradient was found over stratum corneum. Better light penetration and detection efficiency increase maximum imaging depth in TPM compared to conventional confocal microscopy, however loss of signal due to scattering and absorption is still significant and will affect distribution profiles generated by optical sectioning. A true concentration profile cannot be established without better knowledge about signal losses in the skin.

  18. Measurement of two-photon exchange effect with CLAS

    SciTech Connect

    Raue, Brian A.

    2010-08-05

    The structure of the proton is one the most important and most studied topics in nuclear physics. However, discrepant measurements of the proton's electromagnetic form factor ratio, G{sub E}/G{sub M}, seriously jeopardize a definitive understanding of the proton's structure. Measurements of G{sub E}G{sub M} using the Rosenbluth separation technique disagree with those using polarization transfer methods by about a factor of three at Q{sup 2{approx}}5.6 GeV{sup 2}. It has been hypothesized that this discrepancy is due to two-photon exchange (TPE) effects that are not part of the usual radiative corrections. Theoretical corrections for the TPE effect are difficult due to the fact that a large number of excited nucleon states can contribute to the process. However, the TPE effect can be directly determined by measuring the ratio of the positron-proton to electron-proton elastic scattering cross sections, R = {sigma}(e{sup +})/{sigma}(e{sup -}), as the TPE effect changes sign with respect to the charge of the incident particle. A brief test run of a modified beamline and the CLAS detector at Jefferson Lab has resulted in the most precise measurements of the R to date. We will present results from the test run covering Q{sup 2}<0.8 GeV{sup 2} and 0.78{<=}{epsilon}{<=}0.97. In addition, the test run demonstrated the feasibility of producing a mixed electron/positron beam of good quality so that the measurements can be extended up to Q{sup 2{approx}}3.0 GeV{sup 2}.

  19. Laser Optogalvanic Spectroscopy pf Neon and Argon in a Discharge Plasma and its Significance for Microgravity Combustion

    NASA Technical Reports Server (NTRS)

    Misra, Prabhakar; Haridass, C.; Major, H.

    1999-01-01

    A detailed study of combustion mechanisms in flames, employing laser-based diagnostics, has provided good knowledge and understanding of the physical phenomena, and led to better characterization of the dynamical and chemical combustion processes, both under low-gravity (in space) and normal gravity (in ground based facilities, e.g. drop towers). Laser induced fluorescence (LIF), laser-induced incandescence (LII) and LIF thermometry have been widely used to perform nonintrusive measurements and to better understand combustion phenomena. Laser optogalvanic (LOG) spectroscopy has well-established applications in ion mobility measurements, atomic and molecular spectroscopy, ionization rates, recombination rates, velocity measurements and as a combustion probe for trace element detection. Absorption spectra of atomic and molecular species in flames can be obtained via LOG spectroscopy by measuring the voltage and current changes induced by laser irradiation. There are different kinds of processes that contribute to a discharge current, namely: (1) electron impact ionization, (2) collisions among the excited atoms of the discharge species and (3) Penning ionization. In general, at higher discharge currents, the mechanism of electron impact ionization dominates over Penning ionization, whereby the latter is hardly noticeable. In a plasma, whenever the wavelength of a laser coincides with the absorption of an atomic or molecular species, the rate of ionization of the species momentarily increases or decreases due to laser-assisted acceleration of collisional ionization. Such a rate of change in the ionization is monitored as a variation in the transient current by inserting a high voltage electrode into the plasma. Optogalvanic spectroscopy in discharges has been useful for characterizing laser line-widths and for providing convenient calibration lines for tunable dye lasers in the ultraviolet, visible and infrared wavelength regions. Different kinds of quantitative

  20. Two-photon decay of excited levels in hydrogen: The ambiguity of the separation of cascades and pure two-photon emission

    NASA Astrophysics Data System (ADS)

    Labzowsky, L.; Solovyev, D.; Plunien, G.

    2009-12-01

    The problem of the evaluation of the two-photon decay width of excited states in hydrogen is considered. Two different approaches to the evaluation of the width including cascades channels are employed: the summation of the transition probabilities for various decay channels and the evaluation of the imaginary part of the Lamb shift. As application, the two-photon decay channels for the 3s level of the hydrogen atom are evaluated, including the cascade transition probability 3s-2p-1s . An important role is assigned to the two-photon decays in astrophysics context, since processes of this kind provide a possibility for the decoupling of radiation and matter in the early universe. We demonstrate the ambiguity of separation of the “pure” two-photon contribution and criticize the existing methods for such a separation.

  1. Transitional behavior between self-Kerr and cross-Kerr effects by two photons

    SciTech Connect

    Koshino, Kazuki

    2007-06-15

    The transitional behavior of the two-photon Kerr effect between the self-Kerr and cross-Kerr cases is investigated. To this end, we have developed a semiclassical method for evaluating the two-photon Kerr effect that is applicable to any two-photon input state. It is revealed that the maximum Kerr effect is obtained when the second photon is input with a delay time that corresponds to the absorption time of the first photon by the optical material.

  2. Efficient selective two-photon excitation by tailored quantum-correlated photons

    SciTech Connect

    Oka, Hisaki

    2010-06-15

    We theoretically investigate two-photon excitation by correlated photons with energy anticorrelation. A three-level atomic system is used to evaluate selectivity and efficiency of two-photon excitation. It is shown that tailored squeezing of two-photon probability distribution concurrently enhances excitation efficiency and high-contrast selective excitation, without phase manipulation or pulse-shaping techniques. We also discuss candidates to generate such squeezed photons in real material systems.

  3. Two-photon approximation in the theory of electron recombination in hydrogen

    SciTech Connect

    Solovyev, D.; Labzowsky, L.

    2010-06-15

    A rigorous quantum electrodynamics theory of the multiphoton decay of excited states in a hydrogen atom is presented. The ''two-photon'' approximation is formulated which is limited by the one- and two-photon transitions including cascade transitions with two-photon links. This may be helpful for the strict description of the recombination process in a hydrogen atom and, in principle, for the history of hydrogen recombination in the early universe.

  4. A ratiometric two-photon fluorescent probe for fluoride ion imaging in living cells and zebrafish.

    PubMed

    Hu, Wei; Zeng, Lingyu; Wang, Yanying; Liu, Zhihong; Ye, Xiaoxue; Li, Chunya

    2016-09-21

    Using 6-hydroxyl-quinoline-2-benzothiazole (HQB) as a two-photon fluorophore and tert-butyldiphenylsilyl as a recognition domain for F(-), a ratiometric two-photon fluorescent fluoride probe, QF, was synthesized and fully characterized. QF displays both one- and two-photon ratiometric responses towards fluoride ions in aqueous solution. QF was enabled to detect exogenous fluoride ions in living cells by a ratiometric method. Two-photon microscopic imaging of fluoride ions in living HeLa cells and zebrafish has also been achieved. QF has been demonstrated to be an excellent fluorescent probe with high selectivity, low cytotoxicity and good photostability. PMID:27353376

  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. Two-photon absorption and nonlinear polariton effects in organic crystals

    SciTech Connect

    Johnson, C.K.

    1981-01-01

    Two-photon excitation (TPE) and second harmonic generation (SHG) have been studied in phenanthrene crystals at low temperatures (2 to 6K) in order to investigate mechanisms of two-photon absorption (TPA), the relationship between TPE and SHG, and polariton effects. The transition studied is of special interest because it is both one- and two-photon allowed in the dipole approximation. Consequently, polariton states and SHG play a role in the two-photon process. In the polariton model, both TPA and SHG are understood as resulting from the process of polariton fusion.

  7. Two-photon absorption and spectroscopy of the lowest two-photon transition in small donor-acceptor-substituted organic molecules

    NASA Astrophysics Data System (ADS)

    Beels, Marten T.; Biaggio, Ivan; Reekie, Tristan; Chiu, Melanie; Diederich, François

    2015-04-01

    We determine the dispersion of the third-order polarizability of small donor-acceptor substituted organic molecules using wavelength-dependent degenerate four-wave mixing experiments in solutions with varying concentrations. We find that donor-acceptor-substituted molecules that are characterized by extremely efficient off-resonant nonlinearities also have a correspondingly high two-photon absorption cross section. The width and shape of the first two-photon resonance for these noncentrosymmetric molecules follows what is expected from their longest wavelength absorption peak, and the observed two-photon absorption cross sections are record high when compared to the available literature data, the size of the molecule, and the fundamental limit for two-photon absorption to the lowest excited state, which is essentially determined by the number of conjugated electrons and the excited-state energies. The two-photon absorption of the smallest molecule, which only has 16 electrons in its conjugated system, is one order of magnitude larger than for the molecule called AF-50, a reference molecule for two-photon absorption [O.-K. Kim et al., Chem. Mater. 12, 284 (2000), 10.1021/cm990662r].

  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. Gold nanorods as dual photo-sensitizing and imaging agents for two-photon photodynamic therapy

    NASA Astrophysics Data System (ADS)

    Zhao, Tingting; Shen, Xiaoqin; Li, Lin; Guan, Zhenping; Gao, Nengyue; Yuan, Peiyan; Yao, Shao Q.; Xu, Qing-Hua; Xu, Guo Qin

    2012-11-01

    Gold nanorods with three different aspect ratios were prepared and their dual capabilities for two-photon imaging and two-photon photodynamic therapy have been demonstrated. These gold nanorods exhibit large two-photon absorption action cross-sections, about two orders of magnitude larger than small organic molecules, which makes them suitable for two-photon imaging. They can also effectively generate singlet oxygen under two-photon excitation, significantly higher than traditional photosensitizers such as Rose Bengal and Indocyanine Green. Such high singlet oxygen generation capability under two-photon excitation was ascribed to their large two-photon absorption cross-sections. Polyvinylpyrrolidone (PVP) coated gold nanorods displayed excellent biocompatibility and high cellular uptake efficiency. The two-photon photodynamic therapy effect and two-photon fluorescence imaging properties of PVP coated gold nanorods have been successfully demonstrated on HeLa cells in vitro using fluorescence microscopy and indirect XTT assay method. These gold nanorods thus hold great promise for imaging guided two-photon photodynamic therapy for the treatment of various malignant tumors.Gold nanorods with three different aspect ratios were prepared and their dual capabilities for two-photon imaging and two-photon photodynamic therapy have been demonstrated. These gold nanorods exhibit large two-photon absorption action cross-sections, about two orders of magnitude larger than small organic molecules, which makes them suitable for two-photon imaging. They can also effectively generate singlet oxygen under two-photon excitation, significantly higher than traditional photosensitizers such as Rose Bengal and Indocyanine Green. Such high singlet oxygen generation capability under two-photon excitation was ascribed to their large two-photon absorption cross-sections. Polyvinylpyrrolidone (PVP) coated gold nanorods displayed excellent biocompatibility and high cellular uptake efficiency

  10. Two-photon absorption in tetraphenylporphycenes: are porphycenes better candidates than porphyrins for providing optimal optical properties for two-photon photodynamic therapy?

    PubMed

    Arnbjerg, Jacob; Jiménez-Banzo, Ana; Paterson, Martin J; Nonell, Santi; Borrell, José I; Christiansen, Ove; Ogilby, Peter R

    2007-04-25

    Porphycenes are structural isomers of porphyrins that have many unique properties and features. In the present work, the resonant two-photon absorption of 2,7,12,17-tetraphenylporphycene (TPPo) and its palladium(II) complex (PdTPPo) has been investigated. The data obtained are compared to those from the isomeric compound, meso-tetraphenylporphyrin (TPP). Detection of phosphorescence from singlet molecular oxygen, O2(a(1)Delta(g)), produced upon irradiation of these compounds, was used to obtain two-photon excitation spectra and to quantify two-photon absorption cross sections, delta. In the spectral region of 750-850 nm, the two-photon absorption cross sections at the band maxima for both TPPo and PdTPPo, delta = 2280 and 1750 GM, respectively, are significantly larger than that for TPP. This difference is attributed to the phenomenon of so-called resonance enhancement; for the porphycenes, the two-photon transition is nearly resonant with a comparatively intense one-photon Q-band transition. The results of quantum mechanical calculations using density functional quadratic response theory are in excellent agreement with the experimental data and, as such, demonstrate that comparatively high-level quantum chemical methods can be used to interpret and predict nonlinear optical properties from such large molecular systems. One important point realized through these experiments and calculations is that one must exercise caution when using qualitative molecular-symmetry-derived arguments to predict the expected spectral relationship between allowed one- and two-photon transitions. From a practical perspective, this study establishes that, in comparison to porphyrins and other tetrapyrrolic macrocyclic systems, porphycenes exhibit many desirable attributes for use as sensitizers in two-photon initiated photodynamic therapy. PMID:17397157

  11. TWO-PHOTON EXCHANGE IN ELECTRON-PROTON ELASTIC SCATTERING: THEORY UPDATE

    SciTech Connect

    Andrei Afanasev

    2007-05-21

    Recent theoretical developments in the studies of two-photon exchange effects in elastic electron-proton scattering are reviewed. Two-photon exchange mechanism is considered a likely source of discrepancy between polarized and unpolarized experimental measurements of the proton electric form factor at momentum transfers of several GeV$^2$. This mechanism predicts measurable effects that are currently studied experimentally.

  12. Two-photon excitation of chlorin-e6-C15 monomethyl ester for photodynamic therapy

    NASA Astrophysics Data System (ADS)

    Chen, Ping; Zhao, P. D.; Guo, P.; Lin, Lie; Liu, J. Wei; Yu, Q.

    2005-01-01

    Two-photon-induced fluorescence spectrum and lifetime of Chlorin-e6-C15 Monomethyl Ester in tetrahydrofura (THF) are experimentally examined with femtosecond laser pulses at 800 nm from a Ti:sapphire laser. The two-photon excited fluorescence spectra of the molecule are basically similar to those obtained by one-photon excitation. The lifetimes of two-photon and one-photon excitation fluorescence of this molecule in the solution are of the order of 5.2 ns and 4.8 ns respectively. Our experimental results indicate that the two-photon-induced photodynamic processes of Chlorin-e6-C15 Monomethyl Ester are similar to one-photon-induced photodynamic processes. The two-photon absorption cross section of the molecule is measured at 800 nm as about σ2' ~ 29.1 x 10-50 cm4 " s/photon. As an example for two-photon photodynamic therapy, we also further examine the cell-damaging effects of the Ester. Our preliminary results of cell viability test indicate that Chlorin-e6-C15 Monomethyl Ester can effectively damage the liver cancer cells BEL-7402 under two-photon irradiation. Our results suggest Chlorin-e6-C15 Monomethyl Ester may become a potential two-photon phototherapeutic agent.

  13. 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.

  14. Effect of morphology and solvent on two-photon absorption of nano zinc oxide

    SciTech Connect

    Kavitha, M.K.; Haripadmam, P.C.; Gopinath, Pramod; Krishnan, Bindu; John, Honey

    2013-05-15

    Highlights: ► ZnO nanospheres and triangular structures synthesis by novel precipitation technique. ► The effect of precursor concentration on the size and shape of nano ZnO. ► Open aperture Z-scan measurements of the ZnO nanoparticle dispersions. ► Nanospheres exhibit higher two photon absorption coefficient than triangular nanostructures. ► Nanospheres dispersed in water exhibit higher two photon absorption coefficient than its dispersion in 2-propanol. - Abstract: In this paper, we report the effect of morphology and solvent on the two-photon absorption of nano zinc oxide. Zinc oxide nanoparticles in two different morphologies like nanospheres and triangular nanostructures are synthesized by novel precipitation technique and their two-photon absorption coefficient is measured using open aperture Z-scan technique. Experimental results show that the zinc oxide nanospheres exhibit higher two-photon absorption coefficient than the zinc oxide triangular nanostructures. The zinc oxide nanospheres dispersed in water exhibit higher two-photon absorption coefficient than that of its dispersion in 2-propanol. The zinc oxide nanospheres dispersed in water shows a decrease in two-photon absorption coefficient with an increase in on-axis irradiance. The result confirms the dependence of shape and solvent on the two-photon absorption of nano zinc oxide.

  15. Second harmonic generation and two-photon luminescence from colloidal gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Yashunin, D. A.; Korytin, A. I.; Smirnov, A. I.; Stepanov, A. N.

    2016-03-01

    Second harmonic generation and two-photon luminescence from colloidal gold nanoparticles in the 980-1300 nm wavelength range of exciting femtosecond radiation were investigated experimentally. The measured polarization and spectral characteristics of the second harmonic and two-photon luminescence demonstrate that the observed nonlinear optical signal is determined by the dimers constituting several percent of the total nanoparticle number.

  16. Optimizing single-nanoparticle two-photon microscopy by in situ adaptive control of femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Li, Donghai; Deng, Yongkai; Chu, Saisai; Jiang, Hongbing; Wang, Shufeng; Gong, Qihuang

    2016-07-01

    Single-nanoparticle two-photon microscopy shows great application potential in super-resolution cell imaging. Here, we report in situ adaptive optimization of single-nanoparticle two-photon luminescence signals by phase and polarization modulations of broadband laser pulses. For polarization-independent quantum dots, phase-only optimization was carried out to compensate the phase dispersion at the focus of the objective. Enhancement of the two-photon excitation fluorescence intensity under dispersion-compensated femtosecond pulses was achieved. For polarization-dependent single gold nanorod, in situ polarization optimization resulted in further enhancement of two-photon photoluminescence intensity than phase-only optimization. The application of in situ adaptive control of femtosecond pulse provides a way for object-oriented optimization of single-nanoparticle two-photon microscopy for its future applications.

  17. Folate receptor targeting silica nanoparticle probe for two-photon fluorescence bioimaging

    PubMed Central

    Wang, Xuhua; Yao, Sheng; Ahn, Hyo-Yang; Zhang, Yuanwei; Bondar, Mykhailo V.; Torres, Joseph A.; Belfield, Kevin D.

    2010-01-01

    Narrow dispersity organically modified silica nanoparticles (SiNPs), diameter ~30 nm, entrapping a hydrophobic two-photon absorbing fluorenyl dye, were synthesized by hydrolysis of triethoxyvinylsilane and (3-aminopropyl)triethoxysilane in the nonpolar core of Aerosol-OT micelles. The surface of the SiNPs were functionalized with folic acid, to specifically deliver the probe to folate receptor (FR) over-expressing Hela cells, making these folate two-photon dye-doped SiNPs potential candidates as probes for two-photon fluorescence microscopy (2PFM) bioimaging. In vitro studies using FR over-expressing Hela cells and low FR expressing MG63 cells demonstrated specific cellular uptake of the functionalized nanoparticles. One-photon fluorescence microscopy (1PFM) imaging, 2PFM imaging, and two-photon fluorescence lifetime microscopy (2P-FLIM) imaging of Hela cells incubated with folate-modified two-photon dye-doped SiNPs were demonstrated. PMID:21258480

  18. Studies on pulsed optogalvanic effect in Eu/Ne hollow cathode discharge.

    PubMed

    Saini, V K; Kumar, P; Dixit, S K; Nakhe, S V

    2014-07-01

    The optogalvanic (OG) effect has been observed in a Eu/Ne hollow cathode discharge lamp using pulsed laser irradiation. An OG spectrum is recorded in dye laser wavelength region 574–602 nm using a boxcar-averager. In total 41 atomic lines are observed. Of these, 38 lines are assigned to neon transitions. Two lines observed corresponding to wavelengths 576.519 and 601.815 nm are assigned to europium transitions; (4f 7 6s 2 , S 8 7/2 →4f 7 6s6p , zP 6 7/2 ) and (4f 7 6s 2 , S 8 7/2 →4f 7 6s6p , zP 8 9/2 ), respectively, and the remaining line at 582.475 nm could not be assigned. The effect of the discharge current on europium as well as neon OG signals is also studied. At moderate discharge current values, an extra positive peak is observed in neon OG signal for the transition (1s 5 →2p 2 ) at 588.189 nm, which is explained by Penning-ionization process using the quasi-resonant energy transfer interactions between excited neon and europium atoms lying in 2p 2 and D 10 9/2 states, respectively. PMID:25089996

  19. Laser-induced optogalvanic signal oscillations in miniature neon glow discharge plasma.

    PubMed

    Saini, V K

    2013-06-20

    Laser-induced optogalvanic (OG) signal oscillations detected in miniature neon glow discharge plasma are investigated using a discharge equivalent-circuit model. The damped oscillations in OG signal are generated when a pulsed dye laser is tuned to a specific neon transition (1s5→2p2) at 588.2 nm under the discharge conditions where dynamic resistance changes its sign. Penning ionization via quasi-resonant energy transfer collisions between neon gas atoms in metastable state and sputtered electrode atoms in ground state is discussed to explain the negative differential resistance properties of discharge plasma that are attributed to oscillations in the OG signal. The experimentally observed results are simulated by analyzing the behavior of an equivalent discharge-OG circuit. Good agreement between theoretically calculated and experimental results is observed. It is found that discharge plasma is more sensitive and less stable in close vicinity to dynamic resistance sign inversion, which can be useful for weak-optical-transition OG detection. PMID:23842186

  20. Penning type of ionizing energy transfer collisions in a Hg-Ar discharge detected by the optogalvanic effect

    NASA Technical Reports Server (NTRS)

    Reddy, B. R.; Venkateswarlu, P.; George, M. C.

    1989-01-01

    The temporal evolution of the optogalvanic signals has been investigated in detail in a Hg-argon discharge by irradiating it with an excimer pumped dye laser. The signals at 4510.7, 4596 and 4628.4 A exhibited anomalous behavior. Analysis of the data revealed that the excited Ar and Hg atoms respectively in the 1P1 and 3P1 states participated in energy transfer collisions, causing atomic mercury to excite to an ionized energy state, while simultaneously the argon atom relaxes to its ground state.

  1. Correlated two-photon generation by diamond atomic system in Yb atoms

    NASA Astrophysics Data System (ADS)

    Yoon, Tai Hyun; Song, Minsoo

    2011-05-01

    We study a non-degenerate correlated two-photon generation with narrow bandwidths of 50 MHz by using a diamond atomic system in the collimated Yb atomic beam. We excited the 6s2 1S0 atoms into the 6s7s 1S0 excited state by the resonant two-photon transition via the intermediate 6s6p 1P1 state. Then, the excited atoms decay spontaneously into the 6s2 1S0 ground state via the inter-combination 6s6p 3P1 state. We are focusing on the closed-loop two-photon absorption/excitation path through which correlated two photons having the wavelengths of 611.3 nm (Stokes) and 556.8 nm (anti-Stokes) can be generated efficiently. We performed first a two-photon absorption spectroscopy for the 1S0-1P1-1S0 two-photon transitions. An ECDL at 399 nm was used to excite the 1S0-1P1 transition and another ECDL at 1077 nm was used to excite the 1P1-1S0 transition. From the spontaneous two-photon emission process, we were able to detect correlated two-photons at 611.3 nm and 555.8 nm at the plane perpendicular to the excitation beams, and parallel to the Yb atomic beam. We detected a few times of 106 photons per second both at the idler and signal beams at the condition of two-photon resonance with the detection solid angle of only 0.01 sr. We also performed an optical switching and modulation experiments of the photon-pair by optically switching and frequency modulation of the 399-nm driving field.

  2. The two-photon exchange contribution to elastic electron-nucleon scattering at large momentum transfer

    SciTech Connect

    Andrei V. Afanasev; Stanley J. Brodsky; Carl E. Carlson; Yu-Chun Chen; Marc Vanderhaeghen

    2005-01-01

    We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer by using a quark-parton representation of virtual Compton scattering. We thus can relate the two-photon exchange amplitude to the generalized parton distributions which also enter in other wide angle scattering processes. We find that the interference of one- and two-photon exchange contribution is able to substantially resolve the difference between electric form factor measurements from Rosenbluth and polarization transfer experiments.

  3. 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

  4. Dicke coherent narrowing in two-photon and Raman spectroscopy of thin vapor cells

    NASA Astrophysics Data System (ADS)

    Dutier, Gabriel; Todorov, Petko; Hamdi, Ismahène; Maurin, Isabelle; Saltiel, Solomon; Bloch, Daniel; Ducloy, Martial

    2005-10-01

    The principle of coherent Dicke narrowing in a thin vapor cell, in which sub-Doppler spectral line shapes are observed under a normal irradiation for a λ/2 thickness, is generalized to two-photon spectroscopy. Only the sum of the two wave vectors must be normal to the cell, making the two-photon scheme highly versatile. A comparison is provided between the Dicke narrowing with copropagating fields, and the residual Doppler broadening occurring with counterpropagating geometries. The experimental feasibility is discussed on the basis of a first observation of a two-photon resonance in a 300-nm-thick Cs cell. Extension to the Raman situation is finally considered.

  5. Two-Photon Optical Interrogation of Individual Dendritic Spines with Caged Dopamine

    PubMed Central

    2013-01-01

    We introduce a novel caged dopamine compound (RuBi-Dopa) based on ruthenium photochemistry. RuBi-Dopa has a high uncaging efficiency and can be released with visible (blue-green) and IR light in a two-photon regime. We combine two-photon photorelease of RuBi-Dopa with two-photon calcium imaging for an optical imaging and manipulation of dendritic spines in living brain slices, demonstrating that spines can express functional dopamine receptors. This novel compound allows mapping of functional dopamine receptors in living brain tissue with exquisite spatial resolution. PMID:23672485

  6. 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.

  7. Control of two-photon double ionization of helium with intense chirped attosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Barmaki, S.; Lanteigne, P.; Laulan, S.

    2014-06-01

    We study the two-photon double-ionization process of the helium atom by solving numerically the nonrelativistic, time-dependent Schrödinger equation in its full dimensionality. We investigate with intense chirped attosecond laser pulses of 23.5-nm wavelength the two-photon absorption near and above the sequential threshold. We show how it is possible by adjusting the chirp parameter to control the electronic transitions inside the atom, thereby reinforcing or weakening the ionization process. Attosecond chirped laser pulses offer a promising way to probe and control the two-photon double ionization of helium when compared with attosecond transform-limited pulses.

  8. Quinoline-based two-photon fluorescent probe for nitric oxide in live cells and tissues.

    PubMed

    Dong, Xiaohu; Heo, Cheol Ho; Chen, Shiyu; Kim, Hwan Myung; Liu, Zhihong

    2014-01-01

    A two-photon fluorescent probe (QNO) for nitric oxide is reported. The probe is designed with a photoinduced electron transfer (PeT) mechanism and shows 12-fold fluorescence enhancement toward NO. Adopting a quinoline derivative as the fluorophore, QNO has a large two-photon action cross section value of 52 GM and long-wavelength emission. It also features high selectivity, low cytotoxicity, and pH insensitivity. By utilizing two-photon microscopy (TPM), QNO can detect NO in live cells and live tissues at a depth of 90-180 μm. PMID:24341482

  9. {Delta} resonance contribution to two-photon exchange in electron-proton scattering

    SciTech Connect

    S. Kondratyuk; P. G. Blunden; W. Melnitchouk; J. A. Tjon

    2005-06-01

    We calculate the effects on the elastic electron-proton scattering cross section of the two-photon exchange contribution with an intermediate {Delta} resonance. The {Delta} two-photon exchange contribution is found to be smaller in magnitude than the previously evaluated nucleon contribution, with an opposite sign at backward scattering angles. The sum of the nucleon and {Delta} two-photon exchange corrections has the angular dependence compatible with both the polarization transfer and the Rosenbluth methods of measuring the nucleon electromagnetic form factors.

  10. 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.

  11. Studies on the optogalvanic effect and isotope-selective excitation of ytterbium in a hollow cathode discharge lamp using a pulsed dye laser.

    PubMed

    Kumar, Pankaj; Kumar, Jitendra; Prakash, Om; Saini, Vinod K; Dixit, Sudhir K; Nakhe, Shankar V

    2013-09-01

    This paper presents studies on the pulsed optogalvanic effect and isotope-selective excitation of Yb 555.648 nm (0 cm(-1) → 17 992.007 cm(-1)) and 581.067 nm (17 992.007 cm(-1) → 35 196.98 cm(-1)) transitions, in a Yb/Ne hollow cathode lamp. The Yb atoms were excited by narrow linewidth (500-1000 MHz) Rh110 and Rh6G dye based pulsed lasers. Optogalvanic signal inversion for ground state transition at 555.648 nm was observed beyond a hollow cathode discharge current of 8.5 mA, in contrast to normal optogalvanic signal at 581.067 nm up to maximum current of 14 mA. The isotope-selective excitation studies of Yb were carried out by recording Doppler limited optogalvanic signals as a function of dye laser wavelength. For the 581.067 nm transition, three even isotopes, (172)Yb, (174)Yb, and (176)Yb, and one odd isotope, (171)Yb, were clearly resolved. These data were compared with selective isotope excitation by 10 MHz linewidth continuous-wave dye laser. For 555.648 nm transition, isotopes were not clearly resolved, although isotope peaks of low modulation were observed. PMID:24067634

  12. Note: Derivation of two-photon circular dichroism—Addendum to “Two-photon circular dichroism” [J. Chem. Phys. 62, 1006 (1975)

    SciTech Connect

    Friese, Daniel H.

    2015-09-07

    This addendum shows the detailed derivation of the fundamental equations for two-photon circular dichroism which are given in a very condensed form in the original publication [I. Tinoco, J. Chem. Phys. 62, 1006 (1975)]. In addition, some minor errors are corrected and some of the derivations in the original publication are commented.

  13. Enhanced two-photon absorption using entangled states and small mode volumes

    SciTech Connect

    You Hao; Hendrickson, S. M.; Franson, J. D.

    2009-10-15

    We calculate the rate of two-photon absorption for frequency-entangled photons in a tapered optical fiber whose diameter is comparable to the wavelength of the light. The confinement of the electric field in the transverse direction increases the intensity associated with a single photon, while the two-photon absorption rate is further enhanced by the fact that the sum of the frequencies of the two photons is on resonance with the upper atomic state, even though each photon has a relatively broad linewidth. As a result, the photons are effectively confined in all three dimensions and the two-photon absorption rate for frequency-entangled photons in a tapered fiber was found to be comparable to that for unentangled photons in a microcavity with a small mode volume.

  14. Two-photon-exchange effects in the electro-excitation of the $\\Delta$ resonance

    SciTech Connect

    Vladimir Pascalutsa; Carl E. Carlson; Marc Vanderhaghen

    2005-09-15

    We evaluate the two-photon exchange contribution to the eN {yields} e{Delta}(1232) {yields} e{pi}N process at large momentum transfer with the aim of a precision study of the ratios of electric quadrupole (E2) and Coulomb quadrupole (C2) to the magnetic dipole (M1) {gamma}* N{Delta} transitions. We relate the two-photon exchange amplitude to the N {yields} {Delta} generalized parton distributions and obtain a quantitative estimate of the two-photon effects. The two-photon exchange corrections to the C2/M1 ratio depend strongly on whether this quantity is obtained from an interference cross section or from the Rosenbluth-type cross sections, in similarity with the elastic, eN {yields} eN, process.

  15. Measurement of Two-Photon Absorption Cross Section of Metal Ions by a Mass Sedimentation Approach.

    PubMed

    Ma, Zhuo-Chen; Chen, Qi-Dai; Han, Bing; Liu, Xue-Qing; Song, Jun-Feng; Sun, Hong-Bo

    2015-01-01

    The photo-reduction of metal ions in solution induced by femtosecond laser is an important and novel method for fabricating three-dimensional metal microstructures. However, the nonlinear absorption cross section of metal ions remains unknown because its measurement is difficult. In the present study, a method based on Two-Photon Excited Sedimentation (TPES) is proposed to measure the two-photon absorption cross section (TPACS) of metal ions in solution. The power-squared dependence of the amount of sediment on the excitation intensity was confirmed, revealing that 800 nm femtosecond laser induced reduction of metal ions was a two photon absorption process. We believe that the proposed method may be applied to measure the TPACS of several metal ions, thereby opening a new avenue towards future analysis of two-photon absorption materials. PMID:26657990

  16. Two-photon fluorescence correlation spectroscopy with high count rates and low background using dielectric microspheres

    PubMed Central

    Aouani, Heykel; Schön, Peter; Brasselet, Sophie; Rigneault, Hervé; Wenger, Jérôme

    2010-01-01

    Two-photon excitation fluorescence is a powerful technique commonly used for biological imaging. However, the low absorption cross section of this non-linear process is a critical issue for performing biomolecular spectroscopy at the single molecule level. Enhancing the two-photon fluorescence signal would greatly improve the effectiveness of this technique, yet current methods struggle with medium enhancement factors and/or high background noise. Here, we show that the two-photon fluorescence signal from single Alexa Fluor 488 molecules can be enhanced up to 10 times by using a 3 µm diameter latex sphere while adding almost no photoluminescence background. We report a full characterization of the two-photon fluorescence enhancement by a single microsphere using fluorescence correlation spectroscopy. This opens new routes to enhance non-linear optical signals and extend biophotonic applications. PMID:21258531

  17. Fluorescence upconversion properties of a class of improved pyridinium dyes induced by two-photon absorption

    NASA Astrophysics Data System (ADS)

    Xu, Guibao; Hu, Dawei; Zhao, Xian; Shao, Zongshu; Liu, Huijun; Tian, Yupeng

    2007-06-01

    We report the fluorescence upconversion properties of a class of improved pyridinium toluene- p-sulfonates having donor- π-acceptor (D- π-A) structure under two-photon excitation at 1064 nm. The experimental results show that both the two-photon excited (TPE) fluorescence lifetime and the two-photon pumped (TPP) energy upconversion efficiency were increased with the enhancement of electron-donating capability of the donor in the molecule. It is also indicated that an overlong alkyl group tends to result in a weakened molecular conjugation, leading to a decreased two-photon absorption (TPA) cross section. By choosing the donor, we can obtain a longest fluorescence lifetime of 837 ps, a highest energy upconversion efficiency of ˜6.1%, and a maximum TPA cross-section of 8.74×10 -48 cm 4 s/photon in these dyes.

  18. Method and apparatus for producing laser radiation following two-photon excitation of a gaseous medium

    DOEpatents

    Bischel, William K. [Menlo Park, CA; Jacobs, Ralph R. [Livermore, CA; Prosnitz, Donald [Hamden, CT; Rhodes, Charles K. [Palo Alto, CA; Kelly, Patrick J. [Fort Lewis, WA

    1979-02-20

    Method and apparatus for producing laser radiation by two-photon optical pumping of an atomic or molecular gaseous medium and subsequent lasing action. A population inversion is created as a result of two-photon absorption of the gaseous species. Stark tuning is utilized, if necessary, in order to tune the two-photon transition into exact resonance. In particular, gaseous ammonia (NH.sub.3) or methyl fluoride (CH.sub.3 F) is optically pumped by a pair of CO.sub.2 lasers to create a population inversion resulting from simultaneous two-photon excitation of a high-lying vibrational state, and laser radiation is produced by stimulated emission of coherent radiation from the inverted level.

  19. Method and apparatus for producing laser radiation following two-photon excitation of a gaseous medium

    DOEpatents

    Bischel, W.K.; Jacobs, R.R.; Prosnitz, D.P.; Rhodes, C.K.; Kelly, P.J.

    1979-02-20

    Method and apparatus are disclosed for producing laser radiation by two-photon optical pumping of an atomic or molecular gaseous medium and subsequent lasing action. A population inversion is created as a result of two-photon absorption of the gaseous species. Stark tuning is utilized, if necessary, in order to tune the two-photon transition into exact resonance. In particular, gaseous ammonia (NH[sub 3]) or methyl fluoride (CH[sub 3]F) is optically pumped by a pair of CO[sub 2] lasers to create a population inversion resulting from simultaneous two-photon excitation of a high-lying vibrational state, and laser radiation is produced by stimulated emission of coherent radiation from the inverted level. 3 figs.

  20. Super-resolution two-photon microscopy via scanning patterned illumination

    PubMed Central

    Urban, Ben E.; Yi, Ji; Chen, Siyu; Dong, Biqin; Zhu, Yongling; DeVries, Steven H.; Backman, Vadim; Zhang, Hao F.

    2015-01-01

    We developed two-photon scanning patterned illumination microscopy (2P-SPIM) for super-resolution two-photon imaging. Our approach used a traditional two-photon microscopy setup with temporally modulated excitation to create patterned illumination fields. Combing nine different illuminations and structured illumination reconstruction, super-resolution imaging was achieved in two-photon microscopy. Using 2P-SPIM we achieved a lateral resolution of 141 nm, which represents an improvement by a factor of 1.9 over the corresponding diffraction limit. We further demonstrated super-resolution cellular imaging by 2P-SPIM to image actin cytoskeleton in mammalian cells and three-dimensional imaging in highly scattering retinal tissue. PMID:25974523

  1. Experimental observation of sub-Rayleigh quantum imaging with a two-photon entangled source

    SciTech Connect

    Xu, De-Qin; Song, Xin-Bing; Li, Hong-Guo; Zhang, De-Jian; Wang, Hai-Bo; Xiong, Jun Wang, Kaige

    2015-04-27

    It has been theoretically predicted that N-photon quantum imaging can realize either an N-fold resolution improvement (Heisenberg-like scaling) or a √(N)-fold resolution improvement (standard quantum limit) beyond the Rayleigh diffraction bound, over classical imaging. Here, we report the experimental study on spatial sub-Rayleigh quantum imaging using a two-photon entangled source. Two experimental schemes are proposed and performed. In a Fraunhofer diffraction scheme with a lens, two-photon Airy disk pattern is observed with subwavelength diffraction property. In a lens imaging apparatus, however, two-photon sub-Rayleigh imaging for an object is realized with super-resolution property. The experimental results agree with the theoretical prediction in the two-photon quantum imaging regime.

  2. Measurement of Two-Photon Absorption Cross Section of Metal Ions by a Mass Sedimentation Approach

    PubMed Central

    Ma, Zhuo-Chen; Chen, Qi-Dai; Han, Bing; Liu, Xue-Qing; Song, Jun-Feng; Sun, Hong-Bo

    2015-01-01

    The photo-reduction of metal ions in solution induced by femtosecond laser is an important and novel method for fabricating three-dimensional metal microstructures. However, the nonlinear absorption cross section of metal ions remains unknown because its measurement is difficult. In the present study, a method based on Two-Photon Excited Sedimentation (TPES) is proposed to measure the two-photon absorption cross section (TPACS) of metal ions in solution. The power-squared dependence of the amount of sediment on the excitation intensity was confirmed, revealing that 800 nm femtosecond laser induced reduction of metal ions was a two photon absorption process. We believe that the proposed method may be applied to measure the TPACS of several metal ions, thereby opening a new avenue towards future analysis of two-photon absorption materials. PMID:26657990

  3. Y-shaped two-photon absorbing molecules with an imidazole-thiazole core

    NASA Technical Reports Server (NTRS)

    Feng, Ke; De Boni, Leonardo; Misoguti, Lino; Mendonca, C. R.; Meador, Michael; Hsu, Fu-Lian; Bu, Xiu R.

    2004-01-01

    Two new classes of two-photon absorbing Y-shaped molecules have been developed to possess an imidazole-thiazole core and a stilbene-type conjugation pathway with either nitro or sulfonyl as terminal electron-accepting group.

  4. Two-photon vibrational excitation of air by long-wave infrared laser pulses

    NASA Astrophysics Data System (ADS)

    Palastro, J. P.; Peñano, J.; Johnson, L. A.; Hafizi, B.; Wahlstrand, J. K.; Milchberg, H. M.

    2016-08-01

    Ultrashort long-wave infrared (LWIR) laser pulses can resonantly excite vibrations in N2 and O2 through a two-photon transition. The absorptive vibrational component of the ultrafast optical nonlinearity grows in time, starting smaller than but quickly surpassing the electronic, rotational, and vibrational refractive components. The growth of the vibrational component results in a novel mechanism of third-harmonic generation, providing an additional two-photon excitation channel, fundamental + third harmonic. The original and emergent two-photon excitations drive the resonance exactly out of phase, causing spatial decay of the absorptive vibrational nonlinearity. This nearly eliminates two-photon vibrational absorption. Here we present simulations and analytical calculations demonstrating how these processes modify the ultrafast optical nonlinearity in air. The results reveal nonlinear optical phenomena unique to the LWIR regime of ultrashort pulse propagation in the atmosphere.

  5. An ethylene-glycol decorated ruthenium(ii) complex for two-photon photodynamic therapy.

    PubMed

    Boca, Sanda C; Four, Mickaël; Bonne, Adeline; van der Sanden, Boudewijn; Astilean, Simion; Baldeck, Patrice L; Lemercier, Gilles

    2009-08-14

    A novel water-soluble Ru(ii) complex has been prepared, which represents a promising new class of selective two-photon sensitizers for use in photodynamic therapy within a confined space. PMID:19617993

  6. Cooperative Veratryle and Nitroindoline Cages for Two-Photon Uncaging in the NIR.

    PubMed

    Cueto Diaz, Eduardo; Picard, Sébastien; Klausen, Maxime; Hugues, Vincent; Pagano, Paolo; Genin, Emilie; Blanchard-Desce, Mireille

    2016-07-25

    Tandem uncaging systems in which a two-photon absorbing module and a cage moiety, linked via a phosphorous clip, that act together by Förster resonance energy transfer (FRET) have been developed. A library of these compounds, using different linkers and cages (7-nitroindolinyl or nitroveratryl) has been synthesized. The investigation of their uncaging and two-photon absorption properties demonstrates the scope and versatility of the engineering strategy towards efficient two-photon cages and reveals surprising cooperative and topological effects. The interactions between the 2PA module and the caging moiety are found to promote cooperative effects on the 2PA response while additional processes that enhance the uncaging efficiency are operative in well-oriented nitroindoline-derived dyads. These synergic effects combine to lead to record two-photon uncaging cross-section values (i.e., up to 20 GM) for uncaging of carboxylic acids. PMID:27346866

  7. Observation of Nondegenerate Two-Photon Gain in GaAs.

    PubMed

    Reichert, Matthew; Smirl, Arthur L; Salamo, Greg; Hagan, David J; Van Stryland, Eric W

    2016-08-12

    Two-photon lasers require materials with large two-photon gain (2PG) coefficients and low linear and nonlinear losses. Our previous demonstration of large enhancement of two-photon absorption in semiconductors for very different photon energies translates directly into enhancement of 2PG. We experimentally demonstrate nondegenerate 2PG in optically excited bulk GaAs via femtosecond pump-probe measurements. 2PG is isolated from other pump induced effects through the difference between measurements performed with parallel and perpendicular polarizations of pump and probe. An enhancement in the 2PG coefficient of nearly 2 orders of magnitude is reported. The results point a possible way toward two-photon semiconductor lasers. PMID:27563962

  8. Observation of Nondegenerate Two-Photon Gain in GaAs

    NASA Astrophysics Data System (ADS)

    Reichert, Matthew; Smirl, Arthur L.; Salamo, Greg; Hagan, David J.; Van Stryland, Eric W.

    2016-08-01

    Two-photon lasers require materials with large two-photon gain (2PG) coefficients and low linear and nonlinear losses. Our previous demonstration of large enhancement of two-photon absorption in semiconductors for very different photon energies translates directly into enhancement of 2PG. We experimentally demonstrate nondegenerate 2PG in optically excited bulk GaAs via femtosecond pump-probe measurements. 2PG is isolated from other pump induced effects through the difference between measurements performed with parallel and perpendicular polarizations of pump and probe. An enhancement in the 2PG coefficient of nearly 2 orders of magnitude is reported. The results point a possible way toward two-photon semiconductor lasers.

  9. Two-Photon Neuronal and Astrocytic Stimulation with Azobenzene-Based Photoswitches

    PubMed Central

    2015-01-01

    Synthetic photochromic compounds can be designed to control a variety of proteins and their biochemical functions in living cells, but the high spatiotemporal precision and tissue penetration of two-photon stimulation have never been investigated in these molecules. Here we demonstrate two-photon excitation of azobenzene-based protein switches and versatile strategies to enhance their photochemical responses. This enables new applications to control the activation of neurons and astrocytes with cellular and subcellular resolution. PMID:24857186

  10. Two-Photon Exchange in Elastic Electron-Proton Scattering: A QCD Factorization Approach

    SciTech Connect

    Kivel, Nikolai; Vanderhaeghen, Marc

    2009-08-28

    We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer Q{sup 2}. It is shown that the leading two-photon exchange amplitude behaves as 1/Q{sup 4}, and can be expressed in a model independent way in terms of the leading twist nucleon distribution amplitudes. Using several models for the nucleon distribution amplitudes, we provide estimates for existing data and for ongoing experiments.

  11. Controlling the Cavity Structures of Two-Photon-Pumped Perovskite Microlasers.

    PubMed

    Zhang, Wei; Peng, Lan; Liu, Jie; Tang, Aiwei; Hu, Jin-Song; Yao, Jiannian; Zhao, Yong Sheng

    2016-06-01

    Low-threshold two-photon-pumped (TPP) perovskite microcavity lasers are achieved in crystal perovskite 1D or 2D microstructures fabricated through a liquid-phase self-assembly method assisted by two distinct surfactant soft templates. The lasing actions from the perovskite materials exhibit a shape-dependent microcavity effect, which is subsequently utilized for the modulation of the lasing modes and for the achievement of two-photon-pumped single-mode perovskite microlasers. PMID:27007487

  12. Two-photon ionization of atomic hydrogen with elliptically polarized light

    NASA Technical Reports Server (NTRS)

    Kassaee, A.; Rustgi, M. L.; Long, S. A. T.

    1988-01-01

    The theory of two-photon ionization of a hydrogenic state in the nonrelativistic dipole approximation is generalized for elliptically polarized light. An application to the metastable 2S state of atomic hydrogen is made. Significant differences in the angular distribution of the outgoing electrons are found depending upon the polarization of the photons. It is claimed that two-photon ionization employing elliptically polarized photons from lasers may provide an additional test for the theories of multiphoton ionization.

  13. The two-photon excitation cross section of 6MAP, a fluorescent adenine analogue.

    PubMed

    Stanley, Robert J; Hou, Zhanjia; Yang, Aiping; Hawkins, Mary E

    2005-03-01

    6MAP is a fluorescent analogue of adenine that undergoes Watson-Crick base pairing and base stacking in double-stranded DNA. The one-photon absorption spectrum of 6MAP is characterized by a maximum around 330 nm with moderate quantum yield fluorescence centered at about 420 nm. To take advantage of this probe for confocal and single-molecule microscopy, it would be advantageous to be able to excite the analogue via two photons. We report the first determination of the two-photon excitation cross section and spectrum for 6MAP from 614 to 700 nm. The power dependence of the fluorescence indicates that emission results from the absorption of two photons. The one-photon and two-photon emission line shapes are identical within experimental error. A study of the concentration dependence of the fluorescence yield for one-photon excitation shows no measurable quenching up to about 5 microM. The maximum in the two-photon excitation spectrum gives a two-photon cross section, delta(TPE), of 3.4 +/- 0.1 Goeppert-Mayer (G.M.) at 659 nm, which correlates well with the one-photon absorption maximum. This compares quite favorably with cross sections of various naturally fluorescent biological molecules such as flavins and nicotiamide. In addition, we have also obtained the two-photon-induced fluorescence emission spectrum of quinine sulfate. It is approximately the same as that for one-photon excitation, suggesting that two-photon excitation of quinine sulfate may be used for calibration purposes. PMID:16851408

  14. Three-Dimensional Control of DNA Hybridization by Orthogonal Two-Color Two-Photon Uncaging.

    PubMed

    Fichte, Manuela A H; Weyel, Xenia M M; Junek, Stephan; Schäfer, Florian; Herbivo, Cyril; Goeldner, Maurice; Specht, Alexandre; Wachtveitl, Josef; Heckel, Alexander

    2016-07-25

    We successfully introduced two-photon-sensitive photolabile groups ([7-(diethylamino)coumarin-4-yl]methyl and p-dialkylaminonitrobiphenyl) into DNA strands and demonstrated their suitability for three-dimensional photorelease. To visualize the uncaging, we used a fluorescence readout based on double-strand displacement in a hydrogel and in neurons. Orthogonal two-photon uncaging of the two cages is possible, thus enabling complex scenarios of three-dimensional control of hybridization with light. PMID:27294300

  15. Two-Photon Entanglement and EPR Experiments Using Type-2 Spontaneous Parametric Down Conversion

    NASA Technical Reports Server (NTRS)

    Sergienko, A. V.; Shih, Y. H.; Pittman, T. B.; Rubin, M. H.

    1996-01-01

    Simultaneous entanglement in spin and space-time of a two-photon quantum state generated in type-2 spontaneous parametric down-conversion is demonstrated by the observation of quantum interference with 98% visibility in a simple beam-splitter (Hanburry Brown-Twiss) anticorrelation experiment. The nonlocal cancellation of two-photon probability amplitudes as a result of this double entanglement allows us to demonstrate two different types of Bell's inequality violations in one experimental setup.

  16. The second- and the fourth-order interferences observed in a two-photon interferometer

    NASA Astrophysics Data System (ADS)

    Qiu, Jing; Zhang, Yong-Sheng; Han, Shen-Sheng; Gui, You-Zhen

    2016-05-01

    We design a two-photon interferometer in which the second-order interference of 'two-photon' can be observed. This is realized by introducing a relative phase shift between different path combinations which the photon pairs choose to take. In this interferometer, both the second- and the fourth-order interferences occur when we adjust the time delay continuously. This phenomenon can help us get a better understanding of the second- and the fourth-order interferences.

  17. Serial two-photon tomography: an automated method for ex-vivo mouse brain imaging

    PubMed Central

    Ragan, Timothy; Kadiri, Lolahon R.; Venkataraju, Kannan Umadevi; Bahlmann, Karsten; Sutin, Jason; Taranda, Julian; Arganda-Carreras, Ignacio; Kim, Yongsoo; Seung, H. Sebastian

    2011-01-01

    Here we describe an automated method, which we call serial two-photon (STP) tomography, that achieves high-throughput fluorescence imaging of mouse brains by integrating two-photon microscopy and tissue sectioning. STP tomography generates high-resolution datasets that are free of distortions and can be readily warped in 3D, for example, for comparing multiple anatomical tracings. This method opens the door to routine systematic studies of neuroanatomy in mouse models of human brain disorders. PMID:22245809

  18. Nonlocality of high-dimensional two-photon orbital angular momentum states

    SciTech Connect

    Aiello, A.; Oemrawsingh, S. S. R.; Eliel, E. R.; Woerdman, J. P.

    2005-11-15

    We propose an interferometric method to investigate the nonlocality of high-dimensional two-photon orbital angular momentum states generated by spontaneous parametric down conversion. We incorporate two half-integer spiral phase plates and a variable-reflectivity output beam splitter into a Mach-Zehnder interferometer to build an orbital angular momentum analyzer. This setup enables testing the nonlocality of high-dimensional two-photon states by repeated use of the Clauser-Horne-Shimony-Holt inequality.

  19. Spatial-mode two-photon interference at a beam splitter

    SciTech Connect

    Deng, L.-P.; Dang, G.-F.; Wang, K.

    2006-12-15

    We present a general theory on the interference of a two-photon wave packet associated with spatial modes at a beam splitter. We find that the topological symmetry of the two-photon angular spectrum governs the nature of the two-photon interference. We distinguish between the coalescence interference and anticoalescence interference according to the decrease or increase of the coincidence probability in the absence of interference, respectively, and demonstrate that the symmetric and antisymmetric two-photon angular spectra are responsible for perfect coalescence interference and anticoalescence interference, respectively. Then we prove that anticoalescence interference never occurs for two independent photons, and it turns out that anticoalescence interference is the signature of two-photon entanglement. On the basis of this feature, we propose a special Mach-Zehnder interferometer, incorporated with two spiral phase plates, which can change the interference from a coalescence to an anticoalescence type only for a two-photon entangled state. The scheme is simple and straightforward compared with a test of Bell's inequality.

  20. A two-photon ratiometric fluorescent probe enables spatial coordinates determination of intracellular pH.

    PubMed

    Wang, Junjie; Sun, Yuming; Zhang, Weijia; Liu, Yong; Yu, Xiaoqiang; Zhao, Ning

    2014-11-01

    We reported a two-photon ratiometric fluorescent probe for detecting intracellular pH. When excited with 800 nm laser, an optimal output of laser as the routine equipment of two-photon fluorescence microscopy, the two-photon excited fluorescence of this probe showed distinct emission peak shift as large as 109 nm upon the change of pH values in vitro. Very importantly, the experiment results show that this probe has large two-photon absorption cross-section at pH 4.5 at 800 nm of 354 g, which ranks it as one of the best two-photon ratiometric fluorescent pH probes, and its working pH value is between 4.0 and 8.0 which could fit the intracellular pH range. Moreover, utilizing this probe, the two-photon ratiometric fluorescent images in living cells have been obtained, and the spatial coordinates of intracellular pH can be mapped. At the same time, the probe also exhibited selectivity, photostability and membrane permeability. And the photophysical properties of this probe in various solvents indicated that these photophysical properties variations are due to an intramolecular charge transfer process. At last, the imaging depth of the probe in liver biopsy slices was investigated. The experimental results demonstrated the maximum imaging depth can arrive 66 µm in living rat liver tissues. PMID:25127590

  1. Rapid prototyping of electrochromatography chips for improved two-photon excited fluorescence detection.

    PubMed

    Hackl, Claudia; Beyreiss, Reinhild; Geissler, David; Jezierski, Stefan; Belder, Detlev

    2014-04-15

    In the present study, we introduce two-photon excitation at 532 nm for label-free fluorescence detection in chip electrochromatography. Two-photon excitation at 532 nm offers a promising alternative to one-photon excitation at 266 nm, as it enables the use of economic chip materials instead of fused silica. In order to demonstrate these benefits, one-photon and two-photon induced fluorescence detection are compared in different chip layouts and materials with respect to the achievable sensitivity in the detection of polycyclic aromatic hydrocarbons (PAHs). Customized chromatography chips with cover or bottom slides of different material and thickness are produced by means of a rapid prototyping method based on liquid-phase lithography. The design of thin bottom chips (180 μm) enables the use of high-performance immersion objectives with low working distances, which allows one to exploit the full potential of two-photon excitation for a sensitive detection. The developed method is applied for label-free analysis of PAHs separated on a polymer monolith inside polymer glass sandwich chips made from fused silica or soda-lime glass. The obtained limits of detection range from 40 nM to 1.95 μM, with similar sensitivities in fused silica thin bottom chips for one-photon and two-photon excitation. In deep-UV non- or less-transparent devices two-photon excitation is mandatory for label-free detection of aromatics with high sensitivity. PMID:24666258

  2. Study of the Rb D 2-line splitting in a strong transverse magnetic field with Doppler-free spectroscopy in a nanocell

    NASA Astrophysics Data System (ADS)

    Sargsyan, A.; Hakhumyan, G.; Tonoyan, A.; Petrov, P. A.; Vartanyan, T. A.

    2015-08-01

    Atomic transitions of 85Rb and 87Rb isotopes in a strong transverse magnetic field with induction of up to 7 kG have been studied experimentally. High spectral resolution is achieved owing to the application of the linear Doppler-free spectroscopy method to a nanometric thin cell with the thickness of L = λ/2 = 390 nm, where λ is the wavelength of laser emission tuned to the resonance with the Rb D 2-line (λ/2-method). It has been observed that the number of atomic transitions in the transmission spectrum of linearly polarized (π) radiation decreases from 64 down to 20 transitions as the field strength increases above B > 5 kG. Four atomic transitions (two of 85Rb and two of 87Rb), which are forbidden in the absence of magnetic field, acquire significant strength in the strong magnetic field. Experimental results are in a good agreement with theory. Several practical applications of alkali-vapor-filled nanometric thin cells have been proposed.

  3. Symmetry-suppressed two-photon transitions induced by hyperfine interactions and magnetic fields

    SciTech Connect

    Kozlov, M. G.; English, D.; Budker, D.

    2009-10-15

    Two-photon transitions between atomic states of total electronic angular-momentum J{sub a}=0 and J{sub b}=1 are forbidden when the photons are of the same energy. This selection rule is analogous to the Landau-Yang theorem in particle physics that forbids decays of vector particle into two photons. It arises because it is impossible to construct a total angular-momentum J{sub 2{gamma}}=1 quantum-mechanical state of two photons that is permutation symmetric, as required by Bose-Einstein statistics. In atoms with nonzero nuclear spin, the selection rule can be violated due to hyperfine interactions. Two distinct mechanisms responsible for the hyperfine-induced two-photon transitions are identified, and the hyperfine structure of the induced transitions is evaluated. The selection rule is also relaxed, even for zero-nuclear-spin atoms, by application of an external magnetic field. Once again, there are two similar mechanisms at play: Zeeman splitting of the intermediate-state sublevels, and off-diagonal mixing of states with different total electronic angular momentum in the final state. The present theoretical treatment is relevant to the ongoing experimental search for a possible Bose-Einstein-statistics violation using two-photon transitions in barium, where the hyperfine-induced transitions have been recently observed, and the magnetic-field-induced transitions are being considered both as a possible systematic effect, and as a way to calibrate the measurement.

  4. 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.

  5. 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

  6. Pseudopotential calculations and photothermal lensing measurements of two-photon absorption in solids

    SciTech Connect

    White, W.T. III

    1985-11-04

    We have studied two-photon absorption in solids theoretically and experimentally. We have shown that it is possible to use accurate band structure techniques to compute two-photon absorption spectra within 15% of measured values in a wide band-gap material, ZnS. The empirical pseudopotential technique that we used is significantly more accurate than previous models of two-photon absorption in zinc blende materials, including present tunneling theories (which are essentially parabolic-band results in disguise) and the nonparabolic-band formalism of Pidgeon et al. and Weiler. The agreement between our predictions and previous measurements allowed us to use ZnS as a reference material in order to validate a technique for measuring two-photon absorption that was previously untried in solids, pulsed dual-beam thermal lensing. With the validated technique, we examined nonlinear absorption in one other crystal (rutile) and in several glasses, including silicates, borosilicates, and one phosphate glass. Initially, we believed that the absorption edges of all the materials were comparable; however, subsequent evidence suggested that the effective band-gap energies of the glasses were above the energy of two photons in our measurement. Therefore, we attribute the nonlinear absorption that we observed in glasses to impurities or defects. The measured nonlinear absorption coefficients were of the order of a few cm/TW in the glasses and of the order of 10 cm/GW in the crystals, four orders of magnitude higher than in glasses. 292 refs.

  7. 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}

  8. Sulfonated aluminum phthalocyanines for two-photon photodynamic cancer therapy: the effect of the excitation wavelength

    NASA Astrophysics Data System (ADS)

    Wang, J.; Li, W.; Yu, H. B.; Cheung, N. H.; Chen, J. Y.

    2014-03-01

    Sulfonated aluminum phthalocyanine (AlPcS) is a well-studied photosensitizer which has been widely used in research and in clinical applications of the photodynamic therapy of cancers. Conventionally, one-photon excitation was used, but it was unknown whether two-photon excitation of AlPcS was equally effective. In this study, the two-photon absorption cross sections of AlPcS at near infrared wavelengths were deduced from femtosecond (fs) laser-induced fluorescence. We found that the two-photon absorption cross section of AlPcS was strongly dependent on the excitation wavelength. It was about 19 GM when excited at 800 nm, but grew to 855 GM when excited at 750 nm. The 750 nm fs-laser-induced fluorescence images of AlPcS in human nasopharyngeal carcinoma cells were clearly visible while the corresponding images were very dim when excited at 800 nm. Singlet oxygen production was 13 times higher when excited at 750 nm relative to 800 nm. Our subsequent in vitro experiments showed that 750 nm two-photon excitation with an unfocused fs laser beam damaged cancer cells in a light-dose-dependent manner typical of photodynamic therapy (PDT). The killing at 750 nm was about 9-10 times more efficient than at 800 nm. These results demonstrated for the first time that AlPcS has good potential for two-photon PDT of cancers.

  9. Excitation Spectra and Brightness Optimization of Two-Photon Excited Probes

    PubMed Central

    Mütze, Jörg; Iyer, Vijay; Macklin, John J.; Colonell, Jennifer; Karsh, Bill; Petrášek, Zdeněk; Schwille, Petra; Looger, Loren L.; Lavis, Luke D.; Harris, Timothy D.

    2012-01-01

    Two-photon probe excitation data are commonly presented as absorption cross section or molecular brightness (the detected fluorescence rate per molecule). We report two-photon molecular brightness spectra for a diverse set of organic and genetically encoded probes with an automated spectroscopic system based on fluorescence correlation spectroscopy. The two-photon action cross section can be extracted from molecular brightness measurements at low excitation intensities, while peak molecular brightness (the maximum molecular brightness with increasing excitation intensity) is measured at higher intensities at which probe photophysical effects become significant. The spectral shape of these two parameters was similar across all dye families tested. Peak molecular brightness spectra, which can be obtained rapidly and with reduced experimental complexity, can thus serve as a first-order approximation to cross-section spectra in determining optimal wavelengths for two-photon excitation, while providing additional information pertaining to probe photostability. The data shown should assist in probe choice and experimental design for multiphoton microscopy studies. Further, we show that, by the addition of a passive pulse splitter, nonlinear bleaching can be reduced—resulting in an enhancement of the fluorescence signal in fluorescence correlation spectroscopy by a factor of two. This increase in fluorescence signal, together with the observed resemblance of action cross section and peak brightness spectra, suggests higher-order photobleaching pathways for two-photon excitation. PMID:22385865

  10. Angular correlations in the two-photon decay of heliumlike heavy ions

    SciTech Connect

    Surzhykov, A.; Fratini, F.; Volotka, A.; Santos, J. P.; Indelicato, P.; Plunien, G.; Stoehlker, Th.; Fritzsche, S.

    2010-04-15

    The two-photon decay of heavy, helium-like ions is investigated based on second-order perturbation theory and Dirac's relativistic equation. Special attention has been paid to the angular emission of the two photons (i.e., how the angular correlation function depends on the shell structure of the ions in their initial and final states). Moreover, the effects from the (electric and magnetic) nondipole terms in the expansion of the electron-photon interaction are discussed. Detailed calculations have been carried out for the two-photon decay of the 1s2s {sup 1}S{sub 0}, 1s2s {sup 3}S{sub 1}, and 1s2p {sup 3}P{sub 0} states of helium-like Xe{sup 52+}, Au{sup 77+}, and U{sup 90+} ions.

  11. 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.

  12. 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

  13. Two-photon decay of K -shell vacancies in silver atoms

    NASA Astrophysics Data System (ADS)

    Mokler, P. H.; Schäffer, H. W.; Dunford, R. W.

    2004-09-01

    The spectral distributions for the two-photon decay modes of singly K -shell ionized silver atoms are determined by x-ray-x-ray coincidence measurements. AgK -shell vacancies were induced by nuclear electron capture decay of radioactive cadmium isotopes Cd109 and two-photon coincidences were taken back to back (180°) and at a 90° opening angle for the emission. Each of the two-photon transitions from the 2s , 3s , and 3d states exhibits unique angular and spectral distributions. The measurements agree nicely with relativistic self-consistent field calculations of Tong Our results also confirm and extend the earlier experimental data of Ilakovac and co-workers with improved accuracy.

  14. Two-Photon Frequency Comb Excitation of Rubidium Atoms in External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Vujičić, N.; Ban, T.; Skenderović, H.; Vdović, S.; Pichler, G.

    2008-10-01

    In the present experiment the 5S-5D two-photon transitions in 85Rb and 87Rb atoms as a result of the interaction of the femtosecond frequency comb with atomic levels of both rubidium isotopes are investigated. The main problem in studying of two-photon transitions is in optimization of the excitation efficiency of the desired state. There are two general cases: those transition with an intermediate resonance those in which the pulse spectrum is far detuned from an intermediate resonance. In order to investigate the dependence of the two-photon fluorescence signal as a result of interaction of the frequency comb with perturbed energy-level pattern an external magnetic field was applied.

  15. Near-IR Two-Photon Fluorescent Sensor for K(+) Imaging in Live Cells.

    PubMed

    Sui, Binglin; Yue, Xiling; Kim, Bosung; Belfield, Kevin D

    2015-08-19

    A new two-photon excited fluorescent K(+) sensor is reported. The sensor comprises three moieties, a highly selective K(+) chelator as the K(+) recognition unit, a boron-dipyrromethene (BODIPY) derivative modified with phenylethynyl groups as the fluorophore, and two polyethylene glycol chains to afford water solubility. The sensor displays very high selectivity (>52-fold) in detecting K(+) over other physiological metal cations. Upon binding K(+), the sensor switches from nonfluorescent to highly fluorescent, emitting red to near-IR (NIR) fluorescence. The sensor exhibited a good two-photon absorption cross section, 500 GM at 940 nm. Moreover, it is not sensitive to pH in the physiological pH range. Time-dependent cell imaging studies via both one- and two-photon fluorescence microscopy demonstrate that the sensor is suitable for dynamic K(+) sensing in living cells. PMID:26258885

  16. Exact analysis of the response of quantum systems to two-photons using a QSDE approach

    NASA Astrophysics Data System (ADS)

    Pan, Yu; Dong, Daoyi; Zhang, Guofeng

    2016-03-01

    We introduce the quantum stochastic differential equation (QSDE) approach to exactly analyze the response of quantum systems to a continuous-mode two-photon input. The QSDE description of the two-photon process allows us to integrate the input-output analysis with the quantum network theory, and so the analytical computability of the output state of a general quantum system can be addressed within this framework. We show that the time-domain two-photon output states can be exactly calculated for a large class of quantum systems including passive linear networks, optomechanical oscillators and two-level emitter in waveguide systems. In particular, we propose to utilise the results for the exact simulation of the stimulated emission as well as the study of the scattering of two-mode photon wave packets.

  17. 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.

  18. Active stabilization of a fiber-optic two-photon interferometer using continuous optical length control.

    PubMed

    Cho, Seok-Beom; Kim, Heonoh

    2016-05-16

    The practical realization of long-distance entanglement-based quantum communication systems strongly rely on the observation of highly stable quantum interference between correlated single photons. This task must accompany active stabilization of the optical path lengths within the single-photon coherence length. Here, we provide two-step interferometer stabilization methods employing continuous optical length control and experimentally demonstrate two-photon quantum interference using an actively stabilized 6-km-long fiber-optic Hong-Ou-Mandel interferometer. The two-step active control techniques are applied for measuring highly stable two-photon interference fringes by scanning the optical path-length difference. The obtained two-photon interference visibilities with and without accidental subtraction are found to be approximately 90.7% and 65.4%, respectively. PMID:27409920

  19. Two-photon imaging of spatially extended neuronal network dynamics with high temporal resolution

    PubMed Central

    Lillis, Kyle P.; Eng, Alfred; White, John A.; Mertz, Jerome

    2008-01-01

    We describe a simple two-photon fluorescence imaging strategy, called targeted path scanning (TPS), to monitor the dynamics of spatially extended neuronal networks with high spatiotemporal resolution. Our strategy combines the advantages of mirror-based scanning, minimized dead time, ease of implementation, and compatibility with high-resolution low-magnification objectives. To demonstrate the performance of TPS, we monitor the calcium dynamics distributed across an entire juvenile rat hippocampus (>1.5mm), at scan rates of 100Hz, with single cell resolution and single action potential sensitivity. Our strategy for fast, efficient two-photon microscopy over spatially extended regions provides a particularly attractive solution for monitoring neuronal population activity in thick tissue, without sacrificing the signal to noise ratio or high spatial resolution associated with standard two-photon microscopy. Finally, we provide the code to make our technique generally available. PMID:18539336

  20. Visible-wavelength two-photon excitation microscopy for fluorescent protein imaging.

    PubMed

    Yamanaka, Masahito; Saito, Kenta; Smith, Nicholas I; Arai, Yoshiyuki; Uegaki, Kumiko; Yonemaru, Yasuo; Mochizuki, Kentaro; Kawata, Satoshi; Nagai, Takeharu; Fujita, Katsumasa

    2015-10-01

    The simultaneous observation of multiple fluorescent proteins (FPs) by optical microscopy is revealing mechanisms by which proteins and organelles control a variety of cellular functions. Here we show the use of visible-light based two-photon excitation for simultaneously imaging multiple FPs. We demonstrated that multiple fluorescent targets can be concurrently excited by the absorption of two photons from the visible wavelength range and can be applied in multicolor fluorescence imaging. The technique also allows simultaneous single-photon excitation to offer simultaneous excitation of FPs across the entire range of visible wavelengths from a single excitation source. The calculation of point spread functions shows that the visible-wavelength two-photon excitation provides the fundamental improvement of spatial resolution compared to conventional confocal microscopy. PMID:26238663

  1. A mitochondria-targeted ratiometric two-photon fluorescent probe for biological zinc ions detection.

    PubMed

    Ning, Peng; Jiang, Jiacheng; Li, Longchun; Wang, Shuxin; Yu, Haizhu; Feng, Yan; Zhu, Manzhou; Zhang, Buchang; Yin, Hang; Guo, Qingxiang; Meng, Xiangming

    2016-03-15

    A mitochondria-targeted ratiometric two-photon fluorescent probe (Mito-MPVQ) for biological zinc ions detection was developed based on quinolone platform. Mito-MPVQ showed large red shifts (68 nm) and selective ratiometric signal upon Zn(2+) binding. The ratio of emission intensity (I488 nm/I420 nm) increases dramatically from 0.45 to 3.79 (ca. 8-fold). NMR titration and theoretical calculation confirmed the binding of Mito-MPVQ and Zn(2+). Mito-MPVQ also exhibited large two-photon absorption cross sections (150 GM) at nearly 720 nm and insensitivity to pH within the biologically relevant pH range. Cell imaging indicated that Mito-MPVQ could efficiently located in mitochondria and monitor mitochondrial Zn(2+) under two-photon excitation with low cytotoxicity. PMID:26528806

  2. Visible-wavelength two-photon excitation microscopy for fluorescent protein imaging

    NASA Astrophysics Data System (ADS)

    Yamanaka, Masahito; Saito, Kenta; Smith, Nicholas I.; Arai, Yoshiyuki; Uegaki, Kumiko; Yonemaru, Yasuo; Mochizuki, Kentaro; Kawata, Satoshi; Nagai, Takeharu; Fujita, Katsumasa

    2015-10-01

    The simultaneous observation of multiple fluorescent proteins (FPs) by optical microscopy is revealing mechanisms by which proteins and organelles control a variety of cellular functions. Here we show the use of visible-light based two-photon excitation for simultaneously imaging multiple FPs. We demonstrated that multiple fluorescent targets can be concurrently excited by the absorption of two photons from the visible wavelength range and can be applied in multicolor fluorescence imaging. The technique also allows simultaneous single-photon excitation to offer simultaneous excitation of FPs across the entire range of visible wavelengths from a single excitation source. The calculation of point spread functions shows that the visible-wavelength two-photon excitation provides the fundamental improvement of spatial resolution compared to conventional confocal microscopy.

  3. Up-conversion dynamics for temporally entangled two-photon pulses

    SciTech Connect

    Nakatani, Masatoshi; Shimizu, Ryosuke; Koshino, Kazuki

    2011-01-15

    We analyze the up conversion of a two-photon pulse having temporal entanglement on the basis of a full quantum formalism that treats both photons and optical media quantum mechanically. We derive a formula of the up-converted photon wave function, which is applicable to arbitrary input two-photon states for a three-level system, as the simplest second-order nonlinear optical system. As the input, we employ three kinds of temporally entangled two-photon pulses: correlated, uncorrelated, and anticorrelated. We observe the up-conversion efficiency and the temporal profile of the up-converted photon. Our results reveal the crossover behavior of the up conversion from anticorrelation to correlation and show how the temporal correlation in the input is reflected in the up-conversion process.

  4. Two-photon absorption in the relativistic four-component Hartree-Fock approximation.

    PubMed

    Henriksson, Johan; Norman, Patrick; Jensen, Hans Jørgen Aa

    2005-03-15

    A first implementation of the single residue of the quadratic response function in the four-component Hartree-Fock approximation is presented. The implementation is based on a Kramers paired molecular orbital basis and takes full advantage of time and spatial symmetry reductions in a quaternion formulation-in analogy with the previous work on the quadratic response function [J. Chem. Phys. 121, 6145 (2004)]. Sample calculations are given in terms of the monochromatic and coherent two-photon absorption cross sections in the noble gases. The relativistic two-photon selection rule DeltaJ = {0,+/-2} allows for nonrelativistically spin-forbidden transitions, and, even in neon, strong two-photon absorption is shown to occur for the X (1)S(0)-->2 (3)P(2) transition. It is argued that relevant comparisons between nonrelativistic and relativistic calculations must be performed at the level of integrated absorption cross sections. PMID:15836200

  5. Electron capture of dopants in two-photonic ionization in a poly(methyl methacrylate) solid

    SciTech Connect

    Tsuchida, Akira; Sakai, Wataru; Nakano, Mitsuru; Yamamoto, Masahide

    1992-10-29

    Behavior of the electron produced by two-photonic excitation of an aromatic donor in a poly(methyl methacrylate) solid was studied by the addition of the electron scavengers to the system. According to the Perrin type analysis for the two-photonically ejected electron, the capture radii (R{sub c}) of the scavengers examined were estimated to be from 8 to 40 {Angstrom}. For the two-photonically ejected electrons, R{sub c} is a capture radius for thermalized electrons. In this case the parent electron donor is not necessarily within this radius. On the other hand, for the fluorescence quenching, the distance between the donor and acceptor is within the static quenching radius (R{sub q}) of the donor. 13 refs., 4 figs., 2 tabs.

  6. Molecular rovibrational dynamics investigated by two-photon wavepacket interferometry with phase-locked pulse pairs

    NASA Astrophysics Data System (ADS)

    Cao, Ying; Zhang, Liang; Yang, Yan; Sun, Zhenrong; Wang, Zugeng

    2007-07-01

    Time-resolved two-photon fluorescence spectra have been investigated based on wavepacket interferometry (WPI), and the wavepacket dynamics of the excited states for 4-dicyanomethylene-2-methyl-6- p-dimethyl-aminostryryl-4H-pyran (DCM) is determined by phase-locked femtosecond pulse pairs. A relative phase between the femtosecond pulse pairs can be maintained as the delay line scanning, and so the two-photon fluorescence signals will be observed to appear periodically recurring features. It indicates the constructive or destructive interference between two-photon wavepackets on the molecular excited states. The experimental results show that the phase-locked WPI has the potential applications in the wavepacket dynamics of the complicated molecular systems.

  7. Two-photon decay of K-shell vacancies in silver atoms

    SciTech Connect

    Mokler, P.H.; Schaeffer, H.W.; Dunford, R. W.

    2004-09-01

    The spectral distributions for the two-photon decay modes of singly K-shell ionized silver atoms are determined by x-ray-x-ray coincidence measurements. Ag K-shell vacancies were induced by nuclear electron capture decay of radioactive cadmium isotopes {sup 109}Cd and two-photon coincidences were taken back to back (180 deg.) and at a 90 deg. opening angle for the emission. Each of the two-photon transitions from the 2s, 3s, and 3d states exhibits unique angular and spectral distributions. The measurements agree nicely with relativistic self-consistent field calculations of Tong et al. Our results also confirm and extend the earlier experimental data of Ilakovac and co-workers with improved accuracy.

  8. Highly selective population of two excited states in nonresonant two-photon absorption

    NASA Astrophysics Data System (ADS)

    Zhang, Hui; Zhang, Shi-An; Sun, Zhen-Rong

    2011-08-01

    A nonresonant two-photon absorption process can be manipulated by tailoring the ultra-short laser pulse. In this paper, we theoretically demonstrate a highly selective population of two excited states in the nonresonant two-photon absorption process by rationally designing a spectral phase distribution. Our results show that one excited state is maximally populated while the other state population is widely tunable from zero to the maximum value. We believe that the theoretical results may play an important role in the selective population of a more complex nonlinear process comprising nonresonant two-photon absorption, such as resonance-mediated (2+1)-three-photon absorption and (2+1)-resonant multiphoton ionization.

  9. Long-term two-photon neuroimaging with a photostable AIE luminogen

    PubMed Central

    Qian, Jun; Zhu, Zhenfeng; Leung, Chris Wai Tung; Xi, Wang; Su, Liling; Chen, Guangdi; Qin, Anjun; Tang, Ben Zhong; He, Sailing

    2015-01-01

    In neuroscience, fluorescence labeled two-photon microscopy is a promising tool to visualize ex vivo and in vivo tissue morphology, and track dynamic neural activities. Specific and highly photostable fluorescent probes are required in this technology. However, most fluorescent proteins and organic fluorophores suffer from photobleaching, so they are not suitable for long-term imaging and observation. To overcome this problem, we utilize tetraphenylethene-triphenylphosphonium (TPE-TPP), which possesses aggregation-induced emission (AIE) and two-photon fluorescence characteristics, for neuroimaging. The unique AIE feature of TPE-TPP makes its nanoaggregates resistant to photobleaching, which is useful to track neural cells and brain-microglia for a long period of time. Two-photon fluorescence of TPE-TPP facilitates its application in deep in vivo neuroimaging, as demonstrated in the present paper. PMID:25909029

  10. Long-term two-photon neuroimaging with a photostable AIE luminogen.

    PubMed

    Qian, Jun; Zhu, Zhenfeng; Leung, Chris Wai Tung; Xi, Wang; Su, Liling; Chen, Guangdi; Qin, Anjun; Tang, Ben Zhong; He, Sailing

    2015-04-01

    In neuroscience, fluorescence labeled two-photon microscopy is a promising tool to visualize ex vivo and in vivo tissue morphology, and track dynamic neural activities. Specific and highly photostable fluorescent probes are required in this technology. However, most fluorescent proteins and organic fluorophores suffer from photobleaching, so they are not suitable for long-term imaging and observation. To overcome this problem, we utilize tetraphenylethene-triphenylphosphonium (TPE-TPP), which possesses aggregation-induced emission (AIE) and two-photon fluorescence characteristics, for neuroimaging. The unique AIE feature of TPE-TPP makes its nanoaggregates resistant to photobleaching, which is useful to track neural cells and brain-microglia for a long period of time. Two-photon fluorescence of TPE-TPP facilitates its application in deep in vivo neuroimaging, as demonstrated in the present paper. PMID:25909029

  11. Images of photoreceptors in living primate eyes using adaptive optics two-photon ophthalmoscopy

    PubMed Central

    Hunter, Jennifer J.; Masella, Benjamin; Dubra, Alfredo; Sharma, Robin; Yin, Lu; Merigan, William H.; Palczewska, Grazyna; Palczewski, Krzysztof; Williams, David R.

    2011-01-01

    In vivo two-photon imaging through the pupil of the primate eye has the potential to become a useful tool for functional imaging of the retina. Two-photon excited fluorescence images of the macaque cone mosaic were obtained using a fluorescence adaptive optics scanning laser ophthalmoscope, overcoming the challenges of a low numerical aperture, imperfect optics of the eye, high required light levels, and eye motion. Although the specific fluorophores are as yet unknown, strong in vivo intrinsic fluorescence allowed images of the cone mosaic. Imaging intact ex vivo retina revealed that the strongest two-photon excited fluorescence signal comes from the cone inner segments. The fluorescence response increased following light stimulation, which could provide a functional measure of the effects of light on photoreceptors. PMID:21326644

  12. Images of photoreceptors in living primate eyes using adaptive optics two-photon ophthalmoscopy.

    PubMed

    Hunter, Jennifer J; Masella, Benjamin; Dubra, Alfredo; Sharma, Robin; Yin, Lu; Merigan, William H; Palczewska, Grazyna; Palczewski, Krzysztof; Williams, David R

    2010-01-01

    In vivo two-photon imaging through the pupil of the primate eye has the potential to become a useful tool for functional imaging of the retina. Two-photon excited fluorescence images of the macaque cone mosaic were obtained using a fluorescence adaptive optics scanning laser ophthalmoscope, overcoming the challenges of a low numerical aperture, imperfect optics of the eye, high required light levels, and eye motion. Although the specific fluorophores are as yet unknown, strong in vivo intrinsic fluorescence allowed images of the cone mosaic. Imaging intact ex vivo retina revealed that the strongest two-photon excited fluorescence signal comes from the cone inner segments. The fluorescence response increased following light stimulation, which could provide a functional measure of the effects of light on photoreceptors. PMID:21326644

  13. Two-photon patterning of a polymer containing Y-shaped azochromophores

    SciTech Connect

    Ambrosio, A.; Orabona, E.; Maddalena, P.; Camposeo, A.; Polo, M.; Neves, A. A. R.; Pisignano, D.; Carella, A.; Borbone, F.; Roviello, A.

    2009-01-05

    We report on the patterning of the free surface of azo-based polymer films by means of mass migration driven by one- or two-photon absorption. A symmetric donor-acceptor-donor structured Y-shaped azochromophore is specifically synthesized to enhance two-photon absorption in the polymer. The exposure of the polymer film to a focused laser beam results in light-driven mass migration for both one- and two-photon absorptions. Features with subdiffraction resolution (250 nm) are realized and the patterning dynamics is investigated as a function of the light dose. Furthermore, functional photonic structures, such as diffraction gratings with periods ranging between 0.5 and 2.0 {mu}m, have been realized.

  14. 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.

  15. Source-corrected two-photon excited fluorescence measurements between 700 and 880 nm

    SciTech Connect

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

    1998-04-01

    Passively mode-locked titanium:sapphire (Ti:S) lasers are capable of generating a high-frequency train of transform-limited subpico-second pulses, producing peak powers near 10{sup 5}thinspW at moderate average powers. The low energy per pulse ({lt}20 nJ) permits low fluence levels to be maintained in tightly focused beams, reducing the possibility of saturating fluorescence transitions. These properties, combined with a wavelength tunability from approximately 700 nm to 1 {mu}m, provide excellent opportunities for studying simultaneous two-photon excitation (TPE). However, pulse formation is very sensitive to a variety of intracavity parameters, including group velocity dispersion compensation, which leads to wavelength-dependent pulse profiles as the wavelength is scanned. This wavelength dependence can seriously distort band shapes and apparent peak heights during collection of two-photon spectral data. Since two-photon excited fluorescence is proportional to the product of the peak and average powers, it is not possible to obtain source-independent spectra by using average power correction schemes alone. Continuous-wave, single-mode lasers can be used to generate source-independent two-photon data, but these sources are four to five orders of magnitude less efficient than the mode-locked Ti:S laser and are not practical for general two-photon measurements. Hence, a continuous-wave, single-mode Ti:S laser has been used to collect a source-independent excitation spectrum for the laser dye Coumarin 480. This spectrum may be used to correct data collected with multimode sources; this possibility is demonstrated by using a simple ratiometric method to collect accurate TPE spectra with the mode-locked Ti:S laser. An approximate value of the two-photon cross section for Coumarin 480 is also given. {copyright} {ital 1998} {ital Society for Applied Spectroscopy}

  16. Semiclassical evaluation of the two-photon cross-Kerr effect

    SciTech Connect

    Koshino, Kazuki

    2006-11-15

    When two distinguishable photons are simultaneously input into a nonlinear system, the output photons undergo nonlinear optical effects of the cross-Kerr type. Theoretical quantification of this two-photon cross-Kerr effect requires, in principle, a fully quantum-mechanical analysis involving heavy computation. In this paper, we propose a method for evaluating the two-photon cross-Kerr effect using a semiclassical optical response theory. The semiclassical method enables precise evaluation of the cross-Kerr effect with greatly reduced computation. The validity of the method is confirmed using a model nonlinear system.

  17. Two-photon exchange contribution to proton form factors in the time-like region

    SciTech Connect

    Chen, D. Y.; Dong, Y. B.; Zhou, H. Q.

    2008-10-15

    We estimate the two-photon exchange contribution to the process e{sup +}+e{sup -}{yields}p+p . The two-photon exchange corrections to double spin polarization observables and form factors in the time-like region are calculated. The corrections are found to be small in magnitude but with a strong angular dependence at fixed momentum transfer. These two features are the same as those in the space-like region. In future experiments, the double spin polarization observable P{sub z} deserves to be considered.

  18. Demonstration of a programmable source of two-photon multiqubit entangled states

    SciTech Connect

    Cialdi, Simone; Brivio, Davide; Paris, Matteo G. A.

    2010-04-15

    We suggest and demonstrate a novel source of two-photon multipartite entangled states which exploits the transverse spatial structure of spontaneous parametric down-conversion together with a programmable spatial light modulator (SLM). The one-dimensional SLM is used to perform polarization entanglement purification and to realize arbitrary phase gates between polarization and momentum degrees of freedom of photons. We experimentally demonstrate our scheme by generating two-photon three-qubit linear cluster states with high fidelity using a diode laser pump with a limited coherence time and power on the crystal as low as {approx}2.5 mW.

  19. Non-degenerate two photon absorption enhancement for laser dyes by precise lock-in detection

    NASA Astrophysics Data System (ADS)

    Xue, B.; Katan, C.; Bjorgaard, J. A.; Kobayashi, T.

    2015-12-01

    This study demonstrates a measurement system for a non-degenerate two-photon absorption (NDTPA) spectrum. The NDTPA light sources are a white light super continuum beam (WLSC, 500 ˜ 720 nm) and a fundamental beam (798 nm) from a Ti:Sapphire laser. A reliable broadband NDTPA spectrum is acquired in a single-shot detection procedure using a 128-channel lock-in amplifier. The NDTPA spectra for several common laser dyes are measured. Two photon absorption cross section enhancements are found in the experiment and validated by theoretical calculation for all of the chromophores.

  20. Two-photon fluorescence imaging of embryo with much less damage than confocal imaging

    NASA Astrophysics Data System (ADS)

    Liu, Bian; Xu, Hui; Jin, Lei; Ma, Hui; Chen, Die Yan

    2002-09-01

    Two-photon Laser Scanning Microscopy (TPLSM) is a novel technique based on the two-photon excitation of fluorophore. In this paper, TPLSM and traditional confocal microscopy are introduced. And the influence of femtosecond near-infrared (NIR) illumination on mouse embryos is investigated for the first time. The result shows that NIR laser has much less damage to embryos than blue laser and proves that TPLSM is superior to conventional confocal microscopy in keeping sample alive. TPLSM enables us to make a continuous observation for a longer time on embryogenesis.

  1. TWO-PHOTON TISSUE IMAGING: SEEING THE IMMUNE SYSTEM IN A FRESH LIGHT

    PubMed Central

    Cahalan, Michael D.; Parker, Ian; Wei, Sindy H.; Miller, Mark J.

    2009-01-01

    Many lymphocyte functions, such as antigen recognition, take place deep in densely populated lymphoid organs. Because direct in vivo observation was not possible, the dynamics of immune-cell interactions have been inferred or extrapolated from in vitro studies. Two-photon fluorescence excitation uses extremely brief (<1 picosecond) and intense pulses of light to ‘see’ directly into living tissues, to a greater depth and with less phototoxicity than conventional imaging methods. Two-photon microscopy, in combination with newly developed indicator molecules, promises to extend single-cell approaches to the in vivo setting and to reveal in detail the cellular collaborations that underlie the immune response. PMID:12415310

  2. Two-photon fluorescence properties of curcumin as a biocompatible marker for confocal imaging

    NASA Astrophysics Data System (ADS)

    Kumar, Abhishek; Li, Lian; Chaturvedi, Akanksha; Brzostowski, Joseph; Chittigori, Joshna; Pierce, Susan; Samuelson, Lynne A.; Sandman, Daniel; Kumar, Jayant

    2012-05-01

    Two-photon (TP) fluorescence properties of an antioxidant and anti-tumor molecule, curcumin, were investigated. The two-photon absorption (TPA) action cross-section was measured in organic solvents and found to be 6 GM in tetrahydrofuran and 2 GM in dimethyl sulfoxide. The measured TPA cross-section is comparable to that of rhodamine 6G. One-photon and TP confocal microscopy has demonstrated that curcumin is internalized in cells and can be used for imaging applications. Our investigation indicates that curcumin is a viable biocompatible TP fluorescent marker.

  3. Fluorenyl porphyrins for combined two-photon excited fluorescence and photosensitization

    NASA Astrophysics Data System (ADS)

    Mongin, Olivier; Hugues, Vincent; Blanchard-Desce, Mireille; Merhi, Areej; Drouet, Samuel; Yao, Dandan; Paul-Roth, Christine

    2015-04-01

    The two-photon absorption (2PA), the luminescence and the photosensitization properties of porphyrin-cored fluorenyl dendrimers and meso-substituted fluorenylporphyrin monomer, dimer and trimer are described. In comparison with model tetraphenylporphyrin, these compounds combine enhanced (non-resonant) 2PA cross-sections in the near infrared and enhanced fluorescence quantum yields, together with maintained singlet oxygen generation quantum yields. 'Semi-disconnection' between fluorenyl groups and porphyrins (i.e. direct meso substitution) proved to be more efficient than non-conjugated systems (based on efficient FRET between fluorenyl antennae and porphyrins). These results are of interest for combined two-photon imaging and photodynamic therapy.

  4. Nonsequential Two-Photon Double Ionization of Atoms: Identifying the Mechanism

    NASA Astrophysics Data System (ADS)

    Førre, Morten; Selstø, Sølve; Nepstad, Raymond

    2010-10-01

    We develop an approximate model for the process of direct (nonsequential) two-photon double ionization of atoms. Employing the model, we calculate (generalized) total cross sections as well as energy-resolved differential cross sections of helium for photon energies ranging from 39 to 54 eV. A comparison with results of ab initio calculations reveals that the agreement is at a quantitative level. We thus demonstrate that this complex ionization process can be described by the simple model, providing insight into the underlying physical mechanism. Finally, we use the model to calculate generalized cross sections for the two-photon double ionization of neon in the nonsequential regime.

  5. Measurement of Electron Beam Polarization from Unstrained Bulk GaAs via Two Photon Photoemission

    SciTech Connect

    J L McCarter, T J Gay, J Hansknecht, M Poelker, M L Stutzman

    2011-06-01

    This paper describes measurements of the beam polarization and quantum efficiency for photoemission using two-photon excitation from unstrained bulk GaAs illuminated with pulsed, high intensity 1560nm laser light. Quantum efficiency is linearly proportional to 1560nm peak laser intensity, which was varied in three independent ways, indicating that the emitted electrons are promoted from the valence to the conduction band via two-photon absorption. Beam polarization was measured using a microMott polarimeter, with a value of 16.8(4)% polarization at 1560nm, which is roughly half the measured value of 33.4(8)% using 778 nm light.

  6. Two-photon excitation improves multifocal structured illumination microscopy in thick scattering tissue

    PubMed Central

    Ingaramo, Maria; York, Andrew G.; Wawrzusin, Peter; Milberg, Oleg; Hong, Amy; Weigert, Roberto; Shroff, Hari; Patterson, George H.

    2014-01-01

    Multifocal structured illumination microscopy (MSIM) provides a twofold resolution enhancement beyond the diffraction limit at sample depths up to 50 µm, but scattered and out-of-focus light in thick samples degrades MSIM performance. Here we implement MSIM with a microlens array to enable efficient two-photon excitation. Two-photon MSIM gives resolution-doubled images with better sectioning and contrast in thick scattering samples such as Caenorhabditis elegans embryos, Drosophila melanogaster larval salivary glands, and mouse liver tissue. PMID:24706872

  7. Preparation of entangled states of two photons in several spatial modes

    SciTech Connect

    Lemr, Karel; Fiurasek, Jaromir

    2008-02-15

    We describe a protocol capable of preparing an arbitrary state of two photons in several spatial modes using pairs of photons generated by spontaneous parametric down conversion, linear optical elements, and single-photon detectors or postselection. The protocol involves unitary and nonunitary transformations realizable by beam splitters and phase shifters. Nonunitary transformations are implemented by attenuation filters. The protocol contains several optimization capabilities with the goal of improving overall probability of its success. We also show how entangled two-photon states required for quantum computing with linear optics can be prepared using a very simple and feasible scheme.

  8. Arduino Due based tool to facilitate in vivo two-photon excitation microscopy.

    PubMed

    Artoni, Pietro; Landi, Silvia; Sato, Sebastian Sulis; Luin, Stefano; Ratto, Gian Michele

    2016-04-01

    Two-photon excitation spectroscopy is a powerful technique for the characterization of the optical properties of genetically encoded and synthetic fluorescent molecules. Excitation spectroscopy requires tuning the wavelength of the Ti:sapphire laser while carefully monitoring the delivered power. To assist laser tuning and the control of delivered power, we developed an Arduino Due based tool for the automatic acquisition of high quality spectra. This tool is portable, fast, affordable and precise. It allowed studying the impact of scattering and of blood absorption on two-photon excitation light. In this way, we determined the wavelength-dependent deformation of excitation spectra occurring in deep tissues in vivo. PMID:27446677

  9. Global analysis of proton elastic form factor data with two-photon exchange corrections

    SciTech Connect

    J. Arrington; W. Melnitchouk; J. A. Tjon

    2007-09-01

    We use the world's data on elastic electron-proton scattering and calculations of two-photon exchange effects to extract corrected values of the proton's electric and magnetic form factors over the full Q^2 range of the existing data. Our analysis combines the corrected Rosenbluth cross section and polarization transfer data, and is the first extraction of G_Ep and G_Mp including explicit two-photon exchange corrections and their associated uncertainties. In addition, we examine the angular dependence of the corrected cross sections, and discuss the possible nonlinearities of the cross section as a function of epsilon.

  10. Non-degenerate two photon absorption enhancement for laser dyes by precise lock-in detection

    SciTech Connect

    Xue, B.; Katan, C.; Bjorgaard, J. A.; Kobayashi, T.

    2015-12-15

    This study demonstrates a measurement system for a non-degenerate two-photon absorption (NDTPA) spectrum. The NDTPA light sources are a white light super continuum beam (WLSC, 500 ∼ 720 nm) and a fundamental beam (798 nm) from a Ti:Sapphire laser. A reliable broadband NDTPA spectrum is acquired in a single-shot detection procedure using a 128-channel lock-in amplifier. The NDTPA spectra for several common laser dyes are measured. Two photon absorption cross section enhancements are found in the experiment and validated by theoretical calculation for all of the chromophores.

  11. Teleportation of entangled states without Bell-state measurement via a two-photon process

    NASA Astrophysics Data System (ADS)

    dSouza, A. D.; Cardoso, W. B.; Avelar, A. T.; Baseia, B.

    2011-02-01

    In this letter we propose a scheme using a two-photon process to teleport an entangled field state of a bimodal cavity to another one without Bell-state measurement. The quantum information is stored in a zero- and two-photon entangled state. This scheme requires two three-level atoms in a ladder configuration, two bimodal cavities, and selective atomic detectors. The fidelity and success probability do not depend on the coefficients of the state to be teleported. For convenient choices of interaction times, the teleportation occurs with fidelity close to the unity.

  12. Insights into esophagus tissue architecture using two-photon confocal microscopy

    NASA Astrophysics Data System (ADS)

    Liu, Nenrong; Wang, Yue; Feng, Shangyuan; Chen, Rong

    2013-08-01

    In this paper, microstructures of human esophageal mucosa were evaluated using the two-photon laser scanning confocal microscopy (TPLSCM), based on two-photon excited fluorescence (TPEF) and second harmonic generation (SHG). The distribution of epithelial cells, muscle fibers of muscularis mucosae has been distinctly obtained. Furthermore, esophageal submucosa characteristics with cancer cells invading into were detected. The variation of collagen, elastin and cancer cells is very relevant to the pathology in esophagus, especially early esophageal cancer. Our experimental results indicate that the MPM technique has the much more advantages for label-free imaging, and has the potential application in vivo in the clinical diagnosis and monitoring of early esophageal cancer.

  13. Arduino Due based tool to facilitate in vivo two-photon excitation microscopy

    PubMed Central

    Artoni, Pietro; Landi, Silvia; Sato, Sebastian Sulis; Luin, Stefano; Ratto, Gian Michele

    2016-01-01

    Two-photon excitation spectroscopy is a powerful technique for the characterization of the optical properties of genetically encoded and synthetic fluorescent molecules. Excitation spectroscopy requires tuning the wavelength of the Ti:sapphire laser while carefully monitoring the delivered power. To assist laser tuning and the control of delivered power, we developed an Arduino Due based tool for the automatic acquisition of high quality spectra. This tool is portable, fast, affordable and precise. It allowed studying the impact of scattering and of blood absorption on two-photon excitation light. In this way, we determined the wavelength-dependent deformation of excitation spectra occurring in deep tissues in vivo. PMID:27446677

  14. Polarization-induced control of two-photon excited fluorescence in a chiral polybinaphthyl

    NASA Astrophysics Data System (ADS)

    Zeng, Yi; Wang, Changshun; Zhao, Fuli; Huang, Xiaobo; Cheng, Yixiang

    2011-08-01

    The fluorescence behavior of a chiral polybinaphthyl excited with 100fs800nm laser pulses was investigated in tetrahydrofuran solution. The peak fluorescence intensity versus the input irradiance was measured to meet a square dependence, giving evidence for two-photon excited fluorescence (TPF). The variations of the TPF intensity were found to be strongly modulated by the different polarized incident lights and tightly depend on the linearly polarized component of the incident light. Furthermore, combining with the characteristics of chiral molecules, the two-photon polarization ratio was studied to reveal the symmetry of the involved excited states.

  15. Three-dimensional Polycaprolactone Structures Fabricated by Two-Photon Polymerization

    NASA Astrophysics Data System (ADS)

    Claeyssens, F.; Hasan, E. A.; Gaidukeviciute, A.; Achilleos, D. S.; Ranella, A.; Reinhardt, C.; Ovsianikov, A.; Shizhou, X.; Fotakis, C.; Vamvakaki, M.; Chichkov, B. N.; Farsari, Maria

    2010-11-01

    Two-photon polymerization has been employed to fabricate three-dimensional structures using the biodegradable triblock copolymer poly(ɛ-caprolactone-co-trimethylenecarbonate)-b-poly(ethylene glycol)-b-poly(ɛ-caprolactone-co-trimethylenecarbonate) with 4,4'-bis(diethylamino)benzophenone as the photoinitiator. The fabricated structures were of good quality and had four micron resolution. Initial cytotoxicity tests show that the material does not affect cell proliferation. These studies demonstrate the potential of two-photon polymerization as a technology for the fabrication of biodegradable scaffolds for tissue engineering.

  16. Two-photon excitation of atoms by ultrashort electromagnetic pulses in a discrete spectrum

    NASA Astrophysics Data System (ADS)

    Astapenko, V. A.; Sakhno, S. V.

    2016-07-01

    The paper is devoted to the theoretical investigation of two-photon excitation of atom in a discrete energy spectrum by ultrashort electromagnetic pulses of femto- and subfemtosecond ranges of durations. An analytical expression for the total probability of the process is derived. Numerical simulations are made for hydrogen and sodium atoms. It is shown that the total probability of the process is nonlinear function of pulse duration and character of this function depends strongly on the frequency detuning of pulse carrier frequency from two-photon resonance.

  17. Two-photon-excited fluorescence spectroscopy of atomic fluorine at 170 nm

    NASA Technical Reports Server (NTRS)

    Herring, G. C.; Dyer, Mark J.; Jusinski, Leonard E.; Bischel, William K.

    1988-01-01

    Two-photon-excited fluorescence spectroscopy of atomic fluorine is reported. A doubled dye laser at 286-nm is Raman shifted in H2 to 170 nm (sixth anti-Stokes order) to excite ground-state 2P(0)J fluorine atoms to the 2D(0)J level. The fluorine atoms are detected by one of two methods: observing the fluorescence decay to the 2PJ level or observing F(+) production through the absorption of an additional photon by the excited atoms. Relative two-photon absorption cross sections to and the radiative lifetimes of the 2D(0)J states are measured.

  18. In Vivo Two-Photon Fluorescence Kinetics of Primate Rods and Cones

    PubMed Central

    Sharma, Robin; Schwarz, Christina; Williams, David R.; Palczewska, Grazyna; Palczewski, Krzysztof; Hunter, Jennifer J.

    2016-01-01

    Purpose The retinoid cycle maintains vision by regenerating bleached visual pigment through metabolic events, the kinetics of which have been difficult to characterize in vivo. Two-photon fluorescence excitation has been used previously to track autofluorescence directly from retinoids and pyridines in the visual cycle in mouse and frog retinas, but the mechanisms of the retinoid cycle are not well understood in primates. Methods We developed a two-photon fluorescence adaptive optics scanning light ophthalmoscope dedicated to in vivo imaging in anesthetized macaques. Using pulsed light at 730 nm, two-photon fluorescence was captured from rods and cones during light and dark adaptation through the eye's pupil. Results The fluorescence from rods and cones increased with light exposure but at different rates. During dark adaptation, autofluorescence declined, with cone autofluorescence decreasing approximately 4 times faster than from rods. Rates of autofluorescence decrease in rods and cones were approximately 4 times faster than their respective rates of photopigment regeneration. Also, subsets of sparsely distributed cones were less fluorescent than their neighbors immediately following bleach at 565 nm and they were comparable with the S cone mosaic in density and distribution. Conclusions Although other molecules could be contributing, we posit that these fluorescence changes are mediated by products of the retinoid cycle. In vivo two-photon ophthalmoscopy provides a way to monitor noninvasively stages of the retinoid cycle that were previously inaccessible in the living primate eye. This can be used to assess objectively photoreceptor function in normal and diseased retinas. PMID:26903225

  19. Theory of two-photon interactions with broadband down-converted light and entangled photons

    SciTech Connect

    Dayan, Barak

    2007-10-15

    When two-photon interactions are induced by down-converted light with a bandwidth that exceeds the pump bandwidth, they can obtain a behavior that is pulselike temporally, yet spectrally narrow. At low photon fluxes this behavior reflects the time and energy entanglement between the down-converted photons. However, two-photon interactions such as two-photon absorption (TPA) and sum-frequency generation (SFG) can exhibit such a behavior even at high power levels, as long as the final state (i.e., the atomic level in TPA, or the generated light in SFG) is narrow-band enough. This behavior does not depend on the squeezing properties of the light, is insensitive to linear losses, and has potential applications. In this paper we describe analytically this behavior for traveling-wave down conversion with continuous or pulsed pumping, both for high- and low-power regimes. For this we derive a quantum-mechanical expression for the down-converted amplitude generated by an arbitrary pump, and formulate operators that represent various two-photon interactions induced by broadband light. This model is in excellent agreement with experimental results of TPA and SFG with high-power down-converted light and with entangled photons [Dayan et al., Phys. Rev. Lett. 93, 023005 (2004); 94, 043602 (2005); Pe'er et al., ibid. 94, 073601 (2005)].

  20. Two-Photon Absorbing Nanocrystal Sensors for Ratiometric Detection of Oxygen

    PubMed Central

    McLaurin, Emily J.; Greytak, Andrew B.; Bawendi, Moungi G.; Nocera, Daniel G.

    2012-01-01

    Two nanocrystal-osmium(II) polypyridyl (NC-Os(II)PP) conjugates have been designed to detect oxygen in biological environments. Polypyridines appended with a single free amine were linked with facility to a carboxylic acid functionality of a semiconductor NC overlayer to afford a biologically stable amide bond. The Os(II)PP complexes possess broad absorptions that extend into the red spectral region; this absorption feature makes them desirable acceptors of energy from NC donors. Fluorescence resonance energy transfer (FRET) from the NC to the Os(II)PP causes an enhanced Os(II)PP emission with a concomitant quenching of the NC emission. Owing to the large two-photon absorption cross-section of the NCs, FRET from NC to the Os(II)PP can be established under two-photon excitation conditions. In this way, two-photon processes of metal polypyridyl complexes can be exploited for sensing. The emission of the NC is insensitive to oxygen, even at 1 atm, whereas excited states of both osmium complexes are quenched in the presence of oxygen. The NC emission may thus be used as an internal reference to correct for fluctuations in the photoluminescence intensity signal. These properties taken together establish NC-Os(II)PP conjugates as competent ratiometric, two-photon oxygen sensors for application in biological microenvironments. PMID:19697933

  1. Imaging marine virus CroV and its host Cafeteria roenbergensis with two-photon microscopy

    NASA Astrophysics Data System (ADS)

    Cao, Bin; Chakraborty, Sayan; Sun, Wenqing; Aghvami, Seyedmohammadali; Fischer, Matthias G.; Qian, Wei; Xiao, Chuan; Li, Chunqiang

    2014-02-01

    We use two-photon microscopy to monitor the infection process of marine zooplankton, Cafeteria roenbergensis (C.roenbergensis), by Cafeteria roenbergensis virus (CroV), a giant DNA virus named after its host. Here, we image C.roenbergensis in culture by two-photon excited NADH autofluorescence at video-rate (30 frame/s), and the movement of C.roenbergensis is recorded in live videos. Moreover, CroV is stained with DNA dye SYBR gold and recorded simultaneously with this two-photon microscope. We observed the initial infection moment with this method. The result demonstrates the potential use of two-photon microscopy to investigate the fast dynamic interaction between C.roenbergensis with virus CroV. After catching this initial moment, we will freeze the sample in liquid nitrogen for cryo-electron microscopy (EM) study to resolve the virus-host interaction at molecular level. The long-term goal is to study similar fast moving pathogen-host interaction process which could lead to important medical applications.

  2. Video-rate two-photon excited fluorescence lifetime imaging system with interleaved digitization

    PubMed Central

    Dow, Ximeng Y.; Sullivan, Shane Z.; Muir, Ryan D.; Simpson, Garth J.

    2016-01-01

    A fast (up to video rate) two-photon excited fluorescence lifetime imaging system based on interleaved digitization is demonstrated. The system is compatible with existing beam-scanning microscopes with minor electronics and software modification. Proof-of-concept demonstrations were performed using laser dyes and biological tissue. PMID:26176453

  3. Phosphorescent probes for two-photon microscopy of oxygen (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Vinogradov, Sergei A.; Esipova, Tatiana V.

    2016-03-01

    The ability to quantify oxygen in vivo in 3D with high spatial and temporal resolution is much needed in many areas of biological research. Our laboratory has been developing the phosphorescence quenching technique for biological oximetry - an optical method that possesses intrinsic microscopic capability. In the past we have developed dendritically protected oxygen probes for quantitative imaging of oxygen in tissue. More recently we expanded our design on special two-photon enhanced phosphorescent probes. These molecules brought about first demonstrations of the two-photon phosphorescence lifetime microscopy (2PLM) of oxygen in vivo, providing new information for neouroscience and stem cell biology. However, current two-photon oxygen probes suffer from a number of limitations, such as sub-optimal brightness and high cost of synthesis, which dramatically reduce imaging performance and limit usability of the method. In this paper we discuss principles of 2PLM and address the interplay between the probe chemistry, photophysics and spatial and temporal imaging resolution. We then present a new approach to brightly phosphorescent chromophores with internally enhanced two-photon absorption cross-sections, which pave a way to a new generation of 2PLM probes.

  4. A two-photon activatable amino acid linker for the induction of fluorescence.

    PubMed

    Friedrich, Felix; Klehs, Kathrin; Fichte, Manuela A H; Junek, Stephan; Heilemann, Mike; Heckel, Alexander

    2015-10-28

    A new one- and two-photon activatable fluorophore based on ATTO565 was developed using a photolabile linker that simultaneously acts as a quencher. It is especially interesting for protein and peptide applications because it can be incorporated by standard peptide chemistry. The application of the new fluorogenic construct in super-resolution microscopy of antibody conjugates is shown. PMID:26343765

  5. Rapid Prototyping of Chemical Microsensors Based on Molecularly Imprinted Polymers Synthesized by Two-Photon Stereolithography.

    PubMed

    Gomez, Laura Piedad Chia; Spangenberg, Arnaud; Ton, Xuan-Anh; Fuchs, Yannick; Bokeloh, Frank; Malval, Jean-Pierre; Tse Sum Bui, Bernadette; Thuau, Damien; Ayela, Cédric; Haupt, Karsten; Soppera, Olivier

    2016-07-01

    Two-photon stereolithography is used for rapid prototyping of submicrometre molecularly imprinted polymer-based 3D structures. The structures are evaluated as chemical sensing elements and their specific recognition properties for target molecules are confirmed. The 3D design capability is exploited and highlighted through the fabrication of an all-organic molecularly imprinted polymeric microelectromechanical sensor. PMID:27145145

  6. HSA-based phosphorescent probe for two-photon in vitro visualization.

    PubMed

    Chelushkin, Pavel S; Nukolova, Natalia V; Melnikov, Alexei S; Serdobintsev, Pavel Yu; Melnikov, Pavel A; Krupenya, Dmitry V; Koshevoy, Igor O; Burov, Sergey V; Tunik, Sergey P

    2015-08-01

    Two-photon microscopy reveals several advantages over conventional one since it provides higher spatial resolution as well as deeper penetration into the sample under study. The development of suitable two-photon probes is one of the most challenging tasks in this area. Here we present phosphorescent non-covalent adduct of human serum albumin and Au-Ag alkynyl-diphosphine complex, [Au14Ag4(C2Ph)12(PPh2C6H4PPh2)6][PF6]4, which exhibits high cross section of two-photon-induced luminescence (δTPE) within large near-infrared excitation wavelength region (700-800 nm) with maximum δTPE about 38 GM at 740 nm. This feature makes it a promising probe for multiphoton bioimaging as demonstrated by successful visualization of glioma C6 cells and various tissues by two-photon confocal microscopy both in planar and z-stacking modes. Additionally, the broad excitation region enables optimization of the signal-to-background auto-fluorescence ratio via variation of excitation wavelength. PMID:25864999

  7. Gaussian beam in two-photon fluorescence imaging of rat brain microvessel

    PubMed Central

    Shi, Lingyan; Rodríguez-Contreras, Adrián; Alfano, Robert R.

    2014-01-01

    Abstract. The critical optical properties of a Gaussian laser beam in two-photon or multiphoton fluorescence imaging, including the beam spot size, depth of focus, and intensity profile, are investigated for spatially locating nanoscale solutes in and surrounding the microvessels of rat brain. PMID:25490048

  8. Location of the lowest exciton in C 60 single crystal by two-photon excitation spectroscopy

    NASA Astrophysics Data System (ADS)

    Muccini, M.; Danieli, R.; Zamboni, R.; Taliani, C.; Mohn, H.; Müller, W.; ter Meer, H. U.

    1995-10-01

    Two-photon excitation of C 60 single crystal at 4 K shows a sharp band at 1.846 eV which is assigned to the lowest forbidden Frenkel singlet exciton of T 1g symmetry. This assignment is supported by the analysis of Herzberg-Teller induced photoluminescence.

  9. Atomic Dipole Squeezing in the Correlated Two-Mode Two-Photon Jaynes-Cummings Model

    NASA Technical Reports Server (NTRS)

    Dong, Zhengchao; Zhao, Yonglin

    1996-01-01

    In this paper, we study the atomic dipole squeezing in the correlated two-mode two-photon JC model with the field initially in the correlated two-mode SU(1,1) coherent state. The effects of detuning, field intensity and number difference between the two field modes are investigated through numerical calculation.

  10. Two-photon finite-pulse model for resonant transitions in attosecond experiments

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    We present an analytical model capable of describing two-photon ionization of atoms with attosecond pulses in the presence of intermediate and final isolated autoionizing states. The model is based on the finite-pulse formulation of second-order time-dependent perturbation theory. It approximates the intermediate and final states with Fano's theory for resonant continua, and it depends on a small set of atomic parameters that can either be obtained from separate ab initio calculations or be extracted from a few selected experiments. We use the model to compute the two-photon resonant photoelectron spectrum of helium below the N =2 threshold for the RABITT (reconstruction of attosecond beating by interference of two-photon transitions) pump-probe scheme, in which an XUV attosecond pulse train is used in association with a weak IR probe, obtaining results in quantitative agreement with those from accurate ab initio simulations. In particular, we show that (i) the use of finite pulses results in a homogeneous redshift of the RABITT beating frequency, as well as a resonant modulation of the beating frequency in proximity to intermediate autoionizing states; (ii) the phase of resonant two-photon amplitudes generally experiences a continuous excursion as a function of the intermediate detuning, with either zero or 2 π overall variation.

  11. LANTHANIDE ENHANCE LUMINESCENCE (LEL) WITH ONE AND TWO PHOTON EXCITATION OF QUANTUM DYES LANTHANIDE (III) - MACROCYCLES

    EPA Science Inventory

    Title: Lanthanide Enhance Luminescence (LEL) with one and two photon excitation of Quantum Dyes? Lanthanide(III)-Macrocycles
    Principal Author:
    Robert C. Leif, Newport Instruments
    Secondary Authors:
    Margie C. Becker, Phoenix Flow Systems
    Al Bromm, Virginia Commonw...

  12. Real-time tracking mitochondrial dynamic remodeling with two-photon phosphorescent iridium (III) complexes.

    PubMed

    Huang, Huaiyi; Yang, Liang; Zhang, Pingyu; Qiu, Kangqiang; Huang, Juanjuan; Chen, Yu; Diao, JiaJie; Liu, Jiankang; Ji, Liangnian; Long, Jiangang; Chao, Hui

    2016-03-01

    Mitochondrial fission and fusion control the shape, size, number, and function of mitochondria in the cells of organisms from yeast to mammals. The disruption of mitochondrial fission and fusion is involved in severe human diseases such as Parkinson's disease, Alzheimer's disease, metabolic diseases, and cancers. Agents that can real-time track the mitochondrial dynamics are of great importance. However, the short excitation wavelengths and rapidly photo-bleaching properties of commercial mitochondrial dyes render them unsuitable for tracking mitochondrial dynamics. Thus, mitochondrial targeting agents that exhibit superior photo-stability under continual light irradiation, deep tissue penetration and at intrinsically high three-dimensional resolutions are urgently needed. Two-photon-excited compounds employ low-energy near-infrared light and have emerged as a non-invasive tool for real-time cell imaging. Here, cyclometalated Ir(III) complexes (Ir1-Ir5) are demonstrated as one- and two-photon phosphorescent probes for the real-time imaging and tracking of mitochondrial fission and fusion. The results indicate that Ir2 is well suited for two-photon phosphorescent tracking of mitochondrial fission and fusion in living cells and in Caenorhabditis elegans (C. elegans). This study provides a practical use for mitochondrial targeting two-photon phosphorescent Ir(III) complexes. PMID:26796044

  13. Video-rate two-photon excited fluorescence lifetime imaging system with interleaved digitization.

    PubMed

    Dow, Ximeng Y; Sullivan, Shane Z; Muir, Ryan D; Simpson, Garth J

    2015-07-15

    A fast (up to video rate) two-photon excited fluorescence lifetime imaging system based on interleaved digitization is demonstrated. The system is compatible with existing beam-scanning microscopes with minor electronics and software modification. Proof-of-concept demonstrations were performed using laser dyes and biological tissue. PMID:26176453

  14. 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.

  15. Experimental and theoretical study of two-photon absorption in nitrofuran derivatives: Promising compounds for photochemotherapy

    NASA Astrophysics Data System (ADS)

    De Boni, L.; Correa, D. S.; Silva, D. L.; Gonçalves, P. J.; Zilio, S. C.; Parra, G. G.; Borissevitch, I. E.; Canuto, S.; Mendonca, C. R.

    2011-01-01

    We report experimental and theoretical studies of the two-photon absorption spectrum of two nitrofuran derivatives: nitrofurantoine, (1-(5-nitro-2-furfurilideneamine)-hidantoine) and quinifuryl, 2-(5'-nitro-2'-furanyl)ethenyl-4-{N-[4'-(N,N-diethylamino)-1'-methylbutyl]carbamoyl} quinoline. Both molecules are representative of a family of 5-nitrofuran-ethenyl-quinoline drugs that have been demonstrated to display high toxicity to various species of transformed cells in the dark. We determine the two-photon absorption cross-section for both compounds, from 560 to 880 nm, which present peak values of 64 GM for quinifuryl and 20 GM for nitrofurantoine (1 GM = 1×10-50cm4.s.photon-1). Besides, theoretical calculations employing the linear and quadratic response functions were carried out at the density functional theory level to aid the interpretations of the experimental results. The theoretical results yielded oscillator strengths, two-photon transition probabilities, and transition energies, which are in good agreement with the experimental data. A higher number of allowed electronic transitions was identified for quinifuryl in comparison to nitrofurantoine by the theoretical calculations. Due to the planar structure of both compounds, the differences in the two-photon absorption cross-section values are a consequence of their distinct conjugation lengths.

  16. 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.

  17. Quantum Authencryption with Two-Photon Entangled States for Off-Line Communicants

    NASA Astrophysics Data System (ADS)

    Ye, Tian-Yu

    2016-02-01

    In this paper, a quantum authencryption protocol is proposed by using the two-photon entangled states as the quantum resource. Two communicants Alice and Bob share two private keys in advance, which determine the generation of two-photon entangled states. The sender Alice sends the two-photon entangled state sequence encoded with her classical bits to the receiver Bob in the manner of one-step quantum transmission. Upon receiving the encoded quantum state sequence, Bob decodes out Alice's classical bits with the two-photon joint measurements and authenticates the integrity of Alice's secret with the help of one-way hash function. The proposed protocol only uses the one-step quantum transmission and needs neither a public discussion nor a trusted third party. As a result, the proposed protocol can be adapted to the case where the receiver is off-line, such as the quantum E-mail systems. Moreover, the proposed protocol provides the message authentication to one bit level with the help of one-way hash function and has an information-theoretical efficiency equal to 100 %.

  18. Carbon quantum dot-NO photoreleaser nanohybrids for two-photon phototherapy of hypoxic tumors.

    PubMed

    Fowley, Colin; McHale, Anthony P; McCaughan, Bridgeen; Fraix, Aurore; Sortino, Salvatore; Callan, John F

    2015-01-01

    We report a conjugate between carbon quantum dots and a NO photoreleaser able to photogenerate the anticancer NO radical via an energy transfer mechanism. This nanohybrid proved toxic to cancer cells in vitro and significantly reduced tumor volume in mice bearing human xenograft BxPC-3 pancreatic tumors upon two-photon excitation with the highly biocompatible 800 nm light. PMID:25388953

  19. Dinuclear ruthenium(II) polypyridyl complexes as single and two-photon luminescence cellular imaging probes.

    PubMed

    Xu, Wenchao; Zuo, Jiarui; Wang, Lili; Ji, Liangnian; Chao, Hui

    2014-02-28

    A new series of dinuclear ruthenium(II) polypyridyl complexes, which possess larger π-conjugated systems, good water solubility and pH resistance, and high photostability, were developed to act as single and two-photon luminescence cellular imaging probes. PMID:24418839

  20. New long-wave and highly efficient two-photon fluorophores for multiphoton microscopy

    NASA Astrophysics Data System (ADS)

    Gvishi, Raz; Berkovic, Garry; Kotler, Zvi; Krief, P.; Becker, J. Y.; Khodorkovsky, Vladimir

    2001-04-01

    An important ingredient in improving Multi Photon Laser Scanning Microscopy, MPLSM, is the development of efficient exogenous two-photon fluorescent (TPF) probes. Here we report on a new class of two-photon fluorophores, specifically designed in order to maximize their efficiency in potential MPLSM applications. The fluorophores possess a symmetric Donor-Acceptor-Donor (D-n-A-n-D) structure with varying conjugation length and have strong donors and acceptors. We have studied the two-photon excitation (TPE) properties of these fluorophores and found the following properties: (1) Very large two-photon absorption coefficients (6 > 1000 GM); (2) Peak TP excitation wavelength which are strongly shifted to the red ((lambda) 1 micrometer); (3) Large fluorescence quantum efficiency; (4) Large Stokes shifts of the fluorescence bands. These properties make them particularly suitable for imaging thicker samples, relying on the large improvement in TPE cross-sections and the reduced attenuation at both the excitation and emission wavelengths. We also describe TPE fluorescence anisotropy experiments revealing the tensorial shape of the fluorophores.

  1. Projective measurement of the two-photon polarization state: Linear optics approach

    SciTech Connect

    Grudka, Andrzej; Wojcik, Antoni

    2002-12-01

    We present a method of implementation of general projective measurement of the two-photon polarization state with the use of linear optics elements only. The scheme presented succeeds with a probability of at least 1/16. For some specific measurements (e.g., parity measurement) this probability reaches 1/4.

  2. Two-photon photoemission from a copper cathode in an X -band photoinjector

    NASA Astrophysics Data System (ADS)

    Li, H.; Limborg-Deprey, C.; Adolphsen, C.; McCormick, D.; Dunning, M.; Jobe, K.; Raubenheimer, T.; Vrielink, A.; Vecchione, T.; Wang, F.; Weathersby, S.

    2016-02-01

    This paper presents two-photon photoemission from a copper cathode in an X -band photoinjector. We experimentally verified that the electron bunch charge from photoemission out of a copper cathode scales with laser intensity (I) square for 400 nm wavelength photons. We compare this two-photon photoemission process with the single photon process at 266 nm. Despite the high reflectivity (R ) of the copper surface for 400 nm photons (R =0.48 ) and higher thermal energy of photoelectrons (two-photon at 200 nm) compared to 266 nm photoelectrons, the quantum efficiency of the two-photon photoemission process (400 nm) exceeds the single-photon process (266 nm) when the incident laser intensity is above 300 GW /cm2 . At the same laser pulse energy (E ) and other experimental conditions, emitted charge scales inversely with the laser pulse duration. A thermal emittance of 2.7 mm-mrad per mm root mean square (rms) was measured on our cathode which exceeds by sixty percent larger compared to the theoretical predictions, but this discrepancy is similar to previous experimental thermal emittance on copper cathodes with 266 nm photons. The damage of the cathode surface of our first-generation X -band gun from both rf breakdowns and laser impacts mostly explains this result. Using a 400 nm laser can substantially simplify the photoinjector system, and make it an alternative solution for compact pulsed electron sources.

  3. 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.

  4. Design and synthesis of new optical-power-limiting chromophores with enhanced two-photon absorption

    NASA Astrophysics Data System (ADS)

    Spangler, Charles W.; Elandaloussi, El H.; Casstevens, Martin K.; Kumar, Deepak N.; Weibel, John F.; Burzynski, Ryszard

    1999-10-01

    There has been considerable recent interest in the design of new organic chromophores, oligomers and polymers with potentially large two-photon cross-sections for a variety of applications that span such diverse areas as photo-dynamic therapy to optical power limiting of nanosecond and picosecond laser pulses. One particularly attractive system is based on poly[p-phenylene vinylene] (PPV) oligomers containing electron-donating substituents. We have recently designed and synthesized several PPV dimers with bis- diphenylamino) donor groups attached to the terminal phenyl rings, and have demonstrated that these materials have very large two-photon cross-sections for nanosecond pulses. It is probable that these enhanced cross-sections are due to excited state absorption following the initial two-photon absorption. We have also examined bis- (diphenylamino)diphenylpolyenes, and more recently extended our design concept to dendrimer structures based on bis- (diphenylamino)stilbene repeat units. Initial studies on the dendrimer structures and bis-(diphenylamino)-PPV dimer reveal extremely large two-photon cross-sections which we have also ascribed to probable excited-state absorption. The efficacy of this design approach will be discussed, as well as projected future design paradigms for even greater TPA enhancement.

  5. Two-photon double ionization of H2 using exterior complex scaling

    SciTech Connect

    Horner, Daniel A; Morales, F; Martin, F; Rescigno, T N; Mccurdy, C W

    2009-03-09

    We report converged calculations of fully, singly differential and total cross sections for two-photon double ionization of the hydrogen molecule in the range of 26-30 eV. These results have been obtained by using the method of exterior complex scaling combined with the use of DVR basis set.

  6. Probing carrier lifetimes in photovoltaic materials using subsurface two-photon microscopy

    PubMed Central

    Barnard, Edward S.; Hoke, Eric T.; Connor, Stephen T.; Groves, James R.; Kuykendall, Tevye; Yan, Zewu; Samulon, Eric C.; Bourret-Courchesne, Edith D.; Aloni, Shaul; Schuck, P. James; Peters, Craig H.; Hardin, Brian E.

    2013-01-01

    Accurately measuring the bulk minority carrier lifetime is one of the greatest challenges in evaluating photoactive materials used in photovoltaic cells. One-photon time-resolved photoluminescence decay measurements are commonly used to measure lifetimes of direct bandgap materials. However, because the incident photons have energies higher than the bandgap of the semiconductor, most carriers are generated close to the surface, where surface defects cause inaccurate lifetime measurements. Here we show that two-photon absorption permits sub-surface optical excitation, which allows us to decouple surface and bulk recombination processes even in unpassivated samples. Thus with two-photon microscopy we probe the bulk minority carrier lifetime of photovoltaic semiconductors. We demonstrate how the traditional one-photon technique can underestimate the bulk lifetime in a CdTe crystal by 10× and show that two-photon excitation more accurately measures the bulk lifetime. Finally, we generate multi-dimensional spatial maps of optoelectronic properties in the bulk of these materials using two-photon excitation. PMID:23807197

  7. Inclusive D*-meson production in two-photon collisions at LEP

    NASA Astrophysics Data System (ADS)

    Sokolov, A. A.

    2002-06-01

    The inclusive production of D*+ is measured by DELPHI in photon-photon collisions at LEP-II energies. The measured cross sections are compatible with the QCD calculations having the contributions from the resolved processes sensitive to the gluon density in photon. The total cross section of the charm quark production in two-photon collisions at LEP-II energies is estimated.

  8. Gold Nanocluster Embedded Albumin Nanoparticles for Two-Photon Imaging of Cancer Cells Accompanying Drug Delivery.

    PubMed

    Khandelia, Rumi; Bhandari, Satyapriya; Pan, Uday Narayan; Ghosh, Siddhartha Sankar; Chattopadhyay, Arun

    2015-09-01

    Gold nanoclusters in albumin nanoparticles (nanovehicles) are used for single-photon and two-photon imaging of cancer cells following the delivery of doxorubicin through the nanovehicle. NIR excitation and emission wavelengths in the biological window (650-900 nm) make the nanovehicle an ideal potential platform for imaging guided drug delivery. PMID:25939342

  9. Simultaneous Two-Photon Absorption to Gerade Excited Singlet States of Diphenylacetylene and Diphenylbutadiyne Using Optical-Probing Photoacoustic Spectroscopy.

    PubMed

    Isozaki, Tasuku; Oba, Hikari; Ikoma, Tadaaki; Suzuki, Tadashi

    2016-08-11

    Simultaneous two-photon absorption to one-photon forbidden electronically excited states of diphenylacetylene (DPA) and diphenylbutadiyne (DPB) was investigated by means of highly sensitive optical-probing photoacoustic spectroscopy. The incident laser power dependencies on photoacoustic signal intensity indicate that the signals are dominated by the two-photon absorption regime. Two-photon absorption is responsible for transitions to gerade excited states based on the selection rule. The two-photon absorption bands observed in the heat action spectra were assigned with the aid of quantum chemical calculations. The relative magnitude of the two-photon absorption cross sections of DPA and DPB was estimated, and the larger two-photon absorption cross section of DPB was related to the resonance effect with the red-shifted one-photon allowed 1(1)B1u ← 1(1)Ag transition of DPB. PMID:27410388

  10. Two-Photon Autofluorescence Imaging Reveals Cellular Structures Throughout the Retina of the Living Primate Eye

    PubMed Central

    Sharma, Robin; Williams, David R.; Palczewska, Grazyna; Palczewski, Krzysztof; Hunter, Jennifer J.

    2016-01-01

    Purpose Although extrinsic fluorophores can be introduced to label specific cell types in the retina, endogenous fluorophores, such as NAD(P)H, FAD, collagen, and others, are present in all retinal layers. These molecules are a potential source of optical contrast and can enable noninvasive visualization of all cellular layers. We used a two-photon fluorescence adaptive optics scanning light ophthalmoscope (TPF-AOSLO) to explore the native autofluorescence of various cell classes spanning several layers in the unlabeled retina of a living primate eye. Methods Three macaques were imaged on separate occasions using a custom TPF-AOSLO. Two-photon fluorescence was evoked by pulsed light at 730 and 920 nm excitation wavelengths, while fluorescence emission was collected in the visible range from several retinal layers and different locations. Backscattered light was recorded simultaneously in confocal modality and images were postprocessed to remove eye motion. Results All retinal layers yielded two-photon signals and the heterogeneous distribution of fluorophores provided optical contrast. Several structural features were observed, such as autofluorescence from vessel walls, Müller cell processes in the nerve fibers, mosaics of cells in the ganglion cell and other nuclear layers of the inner retina, as well as photoreceptor and RPE layers in the outer retina. Conclusions This in vivo survey of two-photon autofluorescence throughout the primate retina demonstrates a wider variety of structural detail in the living eye than is available through conventional imaging methods, and broadens the use of two-photon imaging of normal and diseased eyes. PMID:26903224

  11. 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.

  12. Two-photon photoacoustics ultrasound measurement by a loss modulation technique

    NASA Astrophysics Data System (ADS)

    Lai, Yu-Hung; Chang, Chieh-Feng; Cheng, Yu-Hsiang; Sun, Chi-Kuang

    2013-03-01

    In this work, we investigated the principle of the two-photon absorption (TPA) detection with a loss modulation technique, and first demonstrated the existence of two-photon photoacoustics ultrasound excited by a femtosecond high repetition rate laser. By using the AO modulation with different modulation frequencies, we successfully create the beating of the light signal when the two arms of the beams are both spatial and temporal overlapping. The pulse train of the femtosecond laser causes the narrow band excitation, providing the frequency selectivity and sensitivity. Moreover, the pulse energy is no more than 15nJ/pulse, which is at least 3 orders of magnitude smaller than that of the nanosecond laser, and therefore prevents the thermal damage of the sample. With the help of lock-in detection and a low noise amplifier, we can separate the signal of two-photon absorption from one-photon absorption. We used an ultrasonic transducer to detect the response of the sample, and verified the existence of the two-photon photoacoustics ultrasound generating by the femtosecond laser. Several contrast agents, such as the black carbon solution, the fluorescence dye and the nano-particles, were used in the experiment. In the end, we demonstrated the application, two photo-acoustic imaging, which provides the high spatial resolution (<10μm) and large penetration depth (~1mm), to the simulated biological tissue. This is a milestone to develop the two-photon photoacoustics microscopy, which, in principle, has the great potential to achieve the in vitro and in vivo high resolution deep tissue imaging.

  13. Study of the Effect of the Pulse Width of the Excitation Source on the Two-Photon Absorption and Two-Photon Circular Dichroism Spectra of Biaryl Derivatives.

    PubMed

    Vesga, Yuly; Hernandez, Florencio E

    2016-09-01

    Herein we report on the expanded theoretical calculations and the experimental measurements of the two-photon absorption (TPA) and two-photon circular dichroism (TPCD) spectra of a series of optically active biaryl derivatives (R-BINOL, R-VANOL, and R-VAPOL) using femtosecond pulses. The comparative analysis of the experimental TPCD spectra obtained with our tunable amplified femtosecond system with those previously measured in our group on the same series of compounds in the picosecond regime reveals a decrease in the amplitude of the signal and an improvement in matching with the theory in the former. These results can be explained based on the negligible contribution of excited state absorption (ESA) using femtosecond pulses compared to the picosecond regime. We show how ESA affects both the strength of the signal and the shape of the TPA and TPCD spectra. TPA and TPCD spectra were obtained using the double L-scan technique over a broad spectral range (450-750 nm) using 90 fs pulses at 50 Hz repetition rate produced by an amplified femtosecond system. The theoretical calculations were performed using modern analytical response theory within the time-dependent density functional theory (TD-DFT) approach using CAM-B3LYP and 6-311++G(d,p) basis sets. PMID:27525702

  14. The nonresonant two-photon zero kinetic energy photoelectron spectrum from the electronic ground state of H2S

    NASA Astrophysics Data System (ADS)

    Fischer, Ingo; Lochschmidt, Andreas; Strobel, Andreas; Niedner-Schatteburg, Gereon; Mueller-Dethlefs, Klaus; Bondybey, Vladimir E.

    1993-03-01

    Zero kinetic energy photoelectron spectra from the electronic ground state of hydrogen sulfide are obtained via nonresonant two-photon ionization with complete rotational resolution in the ion. The two-photon spectra are compared with those recently obtained via one-photon VUV photoionization. The spectra show a close similarity, but type a transitions in the two-photon spectra are twice as intense.

  15. A note on approximate teleportation of an unknown atomic state in the two-photon Jaynes-Cummings model

    NASA Astrophysics Data System (ADS)

    dSouza, A. D.; Cardoso, W. B.; Avelar, A. T.; Baseia, B.

    2009-04-01

    We consider recent schemes [J.M. Liu, B. Weng, Physica A 367 (2006) 215] to teleport unknown atomic states and superposition of zero- and two-photon states using the two-photon Jaynes-Cummings model. Here we do the same using the “full two-photon Jaynes-Cumming”, valid for arbitrary average number of photons. The success probability and fidelity of this teleportation are also considered.

  16. 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.

  17. Laser optogalvanic spectroscopy of neon in a discharge plasma and modeling and analysis of rocket plume RF-line emissions

    NASA Astrophysics Data System (ADS)

    Ogungbemi, Kayode I.

    The Optogalvanic Effect (OGE) of neon in a hollow cathode discharge lamp has been investigated both experimentally and theoretically. A tunable dye laser was tuned to several 1si -- 2pj neon transitions and the associated time--resolved optogalvanic (OG) spectral waveforms recorded corresponding to the DeltaJ = DeltaK = 0, +/-1 selection rules and modeled using a semi-empirical model. Decay rate constants, amplitudes and the instrumentation time constants were recorded following a good least-squares fit (between the experimental and the theoretical OG data) using the Monte Carlo technique and utilizing both the search and random walk methods. Dominant physical processes responsible for the optogalvanic effect have been analyzed, and the corresponding populations of the laser-excited level and collisional excited levels determined. The behavior of the optogalvanic signal waveform as a function of time, together with the decay rate constants as a function of the discharge current and the instrumentation time constant as a function of current have been studied in detail. The decay times of the OG signals and the population redistributions were also determined. Fairly linear relationships between the decay rate constant and the discharge current, as well as between the instrumental time constant and the discharge current, have been observed. The decay times and the electron collisional rate parameters of the 1s levels involved in the OG transitions have been obtained with accuracy. The excitation temperature of the discharge for neon transitions grouped with the same 1s level have been determined and found to be fairly constant for the neon transitions studied. The experimental optogalvanic effort in the visible region of the electromagnetic spectrum has been complemented by a computation-intensive modeling investigation of rocket plumes in the microwave region. Radio frequency lines of each of the plume species identified were archived utilizing the HITRAN and other

  18. Two-photon excitation spectrum of light-harvesting complex II and fluorescence upconversion after one- and two-photon excitation of the carotenoids

    SciTech Connect

    Walla, P.J.; Yom, J.; Krueger, B.P.; Fleming, G.R.

    2000-05-18

    The two-photon excitation (TPE) spectrum of light-harvesting complex II (LHC II) has been measured in the spectral region of 1,000--1,600 nm, corresponding to one-photon wavelengths of 500--800 nm. The authors observed a band with an origin at {approximately}2 x 660 nm (ca. 15,100 {+-} 300 cm{sup {minus}1}) and a maximum at {approximately}2 x 600 nm. The line shape and origin of this band strongly suggest that the observed signal is due to the two-photon-allowed S{sub 1} state of the energy-transferring carotenoids (Car ) in LHC II. The authors also report the time dependence of the upconverted chlorophyll (Chl) fluorescence after TPE at the maximum of the observed band. Surprisingly, a fast rise of 250 {+-} 50 fs followed by a multiexponential decay on the picosecond time scale was observed. This result provides strong indication that there is a fast energy transfer even from the dipole-forbidden Car S{sub 1} state to the Chl's. The sub picosecond energy transfer from the Car S{sub 1} state is likely a consequence of the large number of energy-accepting Chls in van der Waals contact with the central Car's in LHC II. They also present upconversion data of the Car S{sub 2}, Chl a, and Chl b fluorescence observed after one-photon excitation into the dipole-allowed Car S{sub 2} state. The lifetime of the Car S{sub 2} state is {approximately}120 {+-} 30 fs. With the observed time constants they are able to calculate quantum yields for the different possible pathways contributing to the overall Car to Chl energy transfer in LHC II.

  19. Two-photon excited fluorescence microendoscopic imaging using a GRIN lens

    NASA Astrophysics Data System (ADS)

    Yan, Wei; Peng, Xiao; Lin, Danying; Wang, Qi; Gao, Jian; Zhou, Jie; Ye, Tong; Qu, Junle; Niu, Hanben

    2015-03-01

    With the rapid development of life sciences, there is an increasing demand for intravital fluorescence imaging of small animals. However, large dimensions and limited working distances of objective lenses in traditional fluorescence microscopes have limited the imaging applications mostly to superficial tissues. To overcome this disadvantage, researchers have developed the graded-index (GRIN) probes with small diameters for imaging internal organs of small animals in a minimally invasive fashion. Here, we present the development of a fluorescence endoscopic imaging system based on a GRIN lens using two-photon excitation. Experimental results showed that this system could perform dynamic fluorescence microendoscopic imaging and monitor the blood flow in anesthetized living mice using two-photon excitation.

  20. Two-photon-induced x-ray emission in neon atoms

    SciTech Connect

    Sun Yuping; Wang Chuankui; Rinkevicius, Zilvinas; Gel'mukhanov, Faris; Carniato, Stephane; Simon, Marc; Taieeb, Richard

    2010-10-15

    We investigated the resonant x-ray emission from a neon atom induced by the two-photon population of a double-core-hole excited state. Two qualitatively different schemes of this process are studied: The first one involves an off-resonant intermediate single-core-hole state; the second scheme passes through a resonant core-ionized intermediate state. The numerical simulations of the resonant x-ray emission performed for different peak intensities and pulse durations show significant population of the double-core-hole final states. Therefore, rather strong two-photon absorption-induced x-ray emission is predicted for both studied schemes. Thus, high counting rates in experimental measurements are expected.

  1. Spin dynamics in nonsequential two-photon double ionization of helium in an intense laser field

    SciTech Connect

    Bhattacharyya, S.; Mazumder, Mina; Chakrabarti, J.; Faisal, F. H. M.

    2011-04-15

    Nonsequential two-photon double ionization of a two-electron system (He and He-like ions) in a circularly polarized intense laser field is developed in a relativistic field theoretic way. Antisymmetry is maintained in the correlated wave functions of He in the initial state after modification to include Dirac spinor, and in the Volkov wave functions of the two electrons in the final free state. The present theory endeavors to provide an estimate of the helicity-dependent angular asymmetry in spin-current generation in nonsequential two-photon double ionization. Angular dependence of circular dichroism obtained in this paper, in coplanar and orthogonal geometries, is compared with the only existing nonrelativistic result obtained using lowest-order perturbation theory. Present result for dichroism underestimates the nonrelativistic result. Entanglement in the spins of the ejected electrons is concluded.

  2. Single- and Two-Photon-Induced Processes at the B Factories

    SciTech Connect

    Li, Selina Z.; /SLAC

    2012-06-15

    We discuss single- and two-photon-induced processes in e{sup +}e{sup -} annihilations with center-of-mass energy near 10.58 GeV from the BaBar and Belle experiments. In particular, we present experimental results from two-photon physics of {gamma}{gamma} {yields} {pi}{sup 0}{pi}{sup 0} and {gamma}{gamma}* {yields} {pi}{sup 0}. We also review the observation of the Two-Virtual-Photon-Annihilation process (e{sup +}e{sup -} {yields} {rho}{sup 0}{rho}{sup 0} and e{sup +}e{sup -} {yields} {phi}{rho}{sup 0}) and the observation of e{sup +}e{sup -} {yields} {rho}{sup +}{rho}{sup -}, which should be primarily a one virtual photon process, but whose angular distributions may imply potential interference effects.

  3. Additive controlled synthesis of gold nanorods (GNRs) for two-photon luminescence imaging of cancer cells

    NASA Astrophysics Data System (ADS)

    Zhu, Jing; Yong, Ken-Tye; Roy, Indrajit; Hu, Rui; Ding, Hong; Zhao, Lingling; Swihart, Mark T.; He, Guang S.; Cui, Yiping; Prasad, Paras N.

    2010-07-01

    Gold nanorods (GNRs) with a longitudinal surface plasmon resonance peak that is tunable from 600 to 1100 nm have been fabricated in a cetyl trimethylammoniumbromide (CTAB) micellar medium using hydrochloric acid and silver nitrate as additives to control their shape and size. By manipulating the concentrations of silver nitrate and hydrochloric acid, the aspect ratio of the GNRs was reliably and reproducibly tuned from 2.5 to 8. The GNRs were first coated with polyelectrolyte multilayers and then bioconjugated to transferrin (Tf) to target pancreatic cancer cells. Two-photon imaging excited from the bioconjugated GNRs demonstrated receptor-mediated uptake of the bioconjugates into Panc-1 cells, overexpressing the transferrin receptor (TfR). The bioconjugated GNR formulation exhibited very low toxicity, suggesting that it is biocompatible and potentially suitable for targeted two-photon bioimaging.

  4. Dynamic behavior, electrochromism, and two-photon absorption of dicyanomethylenated quinacridone.

    PubMed

    Takeda, Takashi; Sugihara, Hiroyuki; Suzuki, Yasutaka; Kawamata, Jun; Akutagawa, Tomoyuki

    2014-10-17

    Molecular structures of dicyanomethylenated quinacridone (1) as a solid and in solution were examined on the basis of single-crystal X-ray structural analysis, temperature-dependent (1)H NMR in CD2Cl2, and theoretical calculations. Crystal 1 had a curved, butterfly-shaped molecular structure. Thermally activated flipping between the curved, butterfly-shaped structure and an armchair structure occurred in solution. Electrochemical reduction triggered a dynamic change from the curved, butterfly-shaped conformation in the neutral state to a planar conformation in the dianion state, which represented electrochromic behavior with electrochemical bistability. A large two-photon absorption cross section of compound 1 was observed in the resonance-enhancement region of 423 GM (1 GM = 1 × 10(-50) cm(4) s photon(-1) molecule(-1)) at 710 nm. Multiple donor-acceptor charge-transfer pathways of molecule 1 enhanced two-photon absorption. PMID:25254634

  5. Lifetimes of two-photon-emitting states in heliumlike and hydrogenlike nickel

    SciTech Connect

    Dunford, R. W.; Hass, M.; Bakke, E.; Berry, H. G.; Liu, C. J.; Raphaelian, M. L. A.; Curtis, L. J.

    1989-06-12

    We report measurements of the lifetimes of the 2/sup 1/S/sub 0/ state of heliumlike Ni/sup 26 +/ and the 2/sup 2/S/sub 1/2/ state of hydrogenlike Ni/sup 27 +/, both of which decay predominantly by two-photon emission. Our method differs from previous measurements of the lifetimes of similar states in that we require a coincidence between the two photons. Our lifetime of 217.1(1.8) ps for the hydrogenlike decay is in agreement with the theoretical value of 215.45 ps. The heliumlike decay lifetime of 156.1(1.6) ps is in fair agreement with the theoretical value of 154.3(0.5) ps.

  6. Performance comparison of acrylic and thiol-acrylic resins in two-photon polymerization.

    PubMed

    Jiang, Lijia; Xiong, Wei; Zhou, Yushen; Liu, Ying; Huang, Xi; Li, Dawei; Baldacchini, Tommaso; Jiang, Lan; Lu, Yongfeng

    2016-06-13

    Microfabrication by two-photon polymerization is investigated using resins based on thiol-ene chemistry. In particular, resins containing different amounts of a tetrafunctional acrylic monomer and a tetrafunctional thiol molecule are used to create complex microstructures. We observe the enhancement of several characteristics of two-photon polymerization when using thiol-acrylic resins. Specifically, microfabrication is carried out using higher writing velocities and it produces stronger polymeric microstructures. Furthermore, the amount of shrinkage typically observed in the production of three-dimensional microstructures is reduced also. By means of microspectrometry, we confirm that the thiol-acrylate mixture in TPP resins promote monomer conversion inducing a higher degree of cross-linked network formation. PMID:27410383

  7. Two-photon or higher-order absorbing optical materials for generation of reactive species

    NASA Technical Reports Server (NTRS)

    Cumpston, Brian (Inventor); Lipson, Matthew (Inventor); Marder, Seth R. (Inventor); Perry, Joseph W. (Inventor)

    2003-01-01

    Disclosed are highly efficient multiphoton absorbing compounds and methods of their use. The compounds generally include a bridge of pi-conjugated bonds connecting electron donating groups or electron accepting groups. The bridge may be substituted with a variety of substituents as well. Solubility, lipophilicity, absorption maxima and other characteristics of the compounds may be tailored by changing the electron donating groups or electron accepting groups, the substituents attached to or the length of the pi-conjugated bridge. Numerous photophysical and photochemical methods are enabled by converting these compounds to electronically excited states upon simultaneous absorption of at least two photons of radiation. The compounds have large two-photon or higher-order absorptivities such that upon absorption, one or more Lewis acidic species, Lewis basic species, radical species or ionic species are formed.

  8. Two-photon or higher-order absorbing optical materials for generation of reactive species

    NASA Technical Reports Server (NTRS)

    Cumpston, Brian (Inventor); Lipson, Matthew (Inventor); Marder, Seth R (Inventor); Perry, Joseph W (Inventor)

    2007-01-01

    Disclosed are highly efficient multiphoton absorbing compounds and methods of their use. The compounds generally include a bridge of pi-conjugated bonds connecting electron donating groups or electron accepting groups. The bridge may be substituted with a variety of substituents as well. Solubility, lipophilicity, absorption maxima and other characteristics of the compounds may be tailored by changing the electron donating groups or electron accepting groups, the substituents attached to or the length of the pi-conjugated bridge. Numerous photophysical and photochemical methods are enabled by converting these compounds to electronically excited states upon simultaneous absorption of at least two photons of radiation. The compounds have large two-photon or higher-order absorptivities such that upon absorption, one or more Lewis acidic species, Lewis basic species, radical species or ionic species are formed.

  9. Mitochondrial Dynamics Tracking with Two-Photon Phosphorescent Terpyridyl Iridium(III) Complexes

    NASA Astrophysics Data System (ADS)

    Huang, Huaiyi; Zhang, Pingyu; Qiu, Kangqiang; Huang, Juanjuan; Chen, Yu; Ji, Liangnian; Chao, Hui

    2016-02-01

    Mitochondrial dynamics, including fission and fusion, control the morphology and function of mitochondria, and disruption of mitochondrial dynamics leads to Parkinson’s disease, Alzheimer’s disease, metabolic diseases, and cancers. Currently, many types of commercial mitochondria probes are available, but high excitation energy and low photo-stability render them unsuitable for tracking mitochondrial dynamics in living cells. Therefore, mitochondrial targeting agents that exhibit superior anti-photo-bleaching ability, deep tissue penetration and intrinsically high three-dimensional resolutions are urgently needed. Two-photon-excited compounds that use low-energy near-infrared excitation lasers have emerged as non-invasive tools for cell imaging. In this work, terpyridyl cyclometalated Ir(III) complexes (Ir1-Ir3) are demonstrated as one- and two-photon phosphorescent probes for real-time imaging and tracking of mitochondrial morphology changes in living cells.

  10. Coherence gated wavefront sensorless adaptive optics for two photon excited fluorescence retinal imaging (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Jian, Yifan; Cua, Michelle; Bonora, Stefano; Pugh, Edward N.; Zawadzki, Robert J.; Sarunic, Marinko V.

    2016-03-01

    We present a novel system for adaptive optics two photon imaging. We utilize the bandwidth of the femtosecond excitation beam to perform coherence gated imaging (OCT) of the sample. The location of the focus is directly observable in the cross sectional OCT images, and adjusted to the desired depth plane. Next, using real time volumetric OCT, we perform Wavefront Sensorless Adaptive Optics (WSAO) aberration correction using a multi-element adaptive lens capable of correcting up to 4th order Zernike polynomials. The aberration correction is performed based on an image quality metric, for example intensity. The optimization time is limited only by the OCT acquisition rate, and takes ~30s. Following aberration correction, two photon fluorescence images are acquired, and compared to results without adaptive optics correction. This technique is promising for multiphoton imaging in multi-layered, scattering samples such as eye and brain, in which traditional wavefront sensing and guide-star sensorless adaptive optics approaches may not be suitable.

  11. Two-photon excitation in living cells induced by low-power cw laser beams

    NASA Astrophysics Data System (ADS)

    Koenig, Karsten; Krasieva, Tatiana B.; Liu, Yagang; Berns, Michael W.; Tromberg, Bruce J.

    1996-05-01

    We demonstrate multi-photon excitation in optically-trapped living cells. Intracellular non- resonant two-photon excitation of endogenous and exogenous chromophores was induced by CW near infrared (NIR) trapping beams of 105 mW power. In the case of fluorescent chromophores, detection of NIR-excited visible fluorescence was achieved by imaging and spectroscopy methods. Trap-induced, two-photon excited fluorescence was employed as a novel diagnostic method to monitor intracellular redox state and cell vitality of single motile spermatozoa and Chinese hamster ovary cells. We found, that nonlinear absorption of NIR photons < 800 nm may lead to oxidative stress and severe cell damage. Biological response was amplified in multimode CW lasers due to longitudinal mode-beating and partial mode- locking. As a result, we recommend the use of longwavelength-NIR, single-frequency traps (`optical tweezers') for micromanipulation of vital cells.

  12. Synthesis, crystal structures, and two-photon absorption of a series of cyanoacetic acid triphenylamine derivatives.

    PubMed

    Hao, Fuying; Li, Dandan; Zhang, Qiong; Li, Shengli; Zhang, Shengyi; Zhou, Hongping; Wu, Jieying; Tian, Yupeng

    2015-11-01

    A specific series of chromophores (CN1, CN2, CN3, and CN4) have been synthesized, in which contained a triphenylamine moiety as the electron donor (D), a cyanoacetic acid moiety as the electron acceptor (A), vinylene or phenylethyne as the π-bridge, and ethyoxyl groups as auxiliary electron donor (D') to construct the D-π-A or D'-D-π-A molecular configuration. Photophysical properties of them were systematically investigated. These results show that the chromophores display a solvatochromism (blue shift) and large Stokes shifts for their absorption bands with increasing polarity of the solvent. Furthermore, the chromophore CN4 shows the strongest intensity of two-photon excited fluorescence and largest two-photon absorption cross section (2783 GM) in the near infrared region. Finally, the connections between the structures and properties are systematically investigated relying on the information from linear and nonlinear optical properties, crytsal structures and quantum chemical calculation. PMID:26119354

  13. In vivo reactive neural plasticity investigation by means of correlative two photon: electron microscopy

    NASA Astrophysics Data System (ADS)

    Allegra Mascaro, A. L.; Cesare, P.; Sacconi, L.; Grasselli, G.; Mandolesi, G.; Maco, B.; Knott, G.; Huang, L.; De Paola, V.; Strata, P.; Pavone, F. S.

    2013-02-01

    In the adult nervous system, different populations of neurons correspond to different regenerative behavior. Although previous works showed that olivocerebellar fibers are capable of axonal regeneration in a suitable environment as a response to injury1, we have hitherto no details about the real dynamics of fiber regeneration. We set up a model of singularly axotomized climbing fibers (CF) to investigate their reparative properties in the adult central nervous system (CNS) in vivo. Time lapse two-photon imaging has been combined to laser nanosurgery2, 3 to define a temporal pattern of the degenerative event and to follow the structural rearrangement after injury. To characterize the damage and to elucidate the possible formation of new synaptic contacts on the sprouted branches of the lesioned CF, we combined two-photon in vivo imaging with block face scanning electron microscopy (FIB-SEM). Here we describe the approach followed to characterize the reactive plasticity after injury.

  14. Non-resonant below-bandgap two-photon absorption in quantum dot solar cells

    SciTech Connect

    Li, Tian; Dagenais, Mario

    2015-04-27

    We study the optically nonlinear sub-bandgap photocurrent generation facilitated by an extended tailing distribution of states in an InAs/GaAs quantum dots (QDs) solar cell. The tailing states function as both the energy states for low energy photon absorption and the photocarriers extraction pathway. One of the biggest advantages of our method is that it can clearly differentiate the photocurrent due to one-photon absorption (1PA) process and two-photon absorption (2PA) process. Both 1PA and 2PA photocurrent generation efficiency in an InAs/GaAs QD device operated at 1550 nm have been quantitatively evaluated. A two-photon absorption coefficient β = 5.7 cm/GW is extracted.

  15. Two-Photon-Induced Selective Decarboxylation of Aspartic Acids D85 and D212 in Bacteriorhodopsin.

    PubMed

    Imhof, Martin; Rhinow, Daniel; Linne, Uwe; Hampp, Norbert

    2012-10-18

    The interest in microbial opsins stems from their photophysical properties, which are superior to most organic dyes. Microbial rhodopsins like bacteriorhodopsin (BR) from Halobacterium salinarum have an astonishingly high cross-section for two-photon-absorption (TPA), which is of great interest for technological applications such as data storage. Irradiation of BR with intense laser pulses at 532 nm leads to formation of a bathochromic photoproduct, which is further converted to a photochemical species absorbing in the UV range. As demonstrated earlier, the photochemical conversions are induced by resonant TPA. However, the molecular basis of these conversions remained unresolved. In this work we use mass spectroscopy to demonstrate that TPA of BR leads to selective decarboxylation of two aspartic acids in the vicinity of the retinal chromphore. These photochemical conversions are the basis of permanent two-photon data storage in BR and are of critical importance for application of microbial opsins in optogenetics. PMID:26292239

  16. 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

  17. Rapid imaging of surgical breast excisions using direct temporal sampling two photon fluorescent lifetime imaging

    PubMed Central

    Giacomelli, Michael G.; Sheikine, Yuri; Vardeh, Hilde; Connolly, James L.; Fujimoto, James G.

    2015-01-01

    Two photon fluorescent lifetime imaging is a modality that enables depth-sectioned, molecularly-specific imaging of cells and tissue using intrinsic contrast. However, clinical applications have not been well explored due to low imaging speed and limited field of view, which make evaluating large pathology samples extremely challenging. To address these limitations, we have developed direct temporal sampling two photon fluorescent lifetime imaging (DTS-FLIM), a method which enables a several order of magnitude increase in imaging speed by capturing an entire lifetime decay in a single fluorescent excitation. We use this greatly increased speed to perform a preliminary study using gigapixel-scale imaging of human breast pathology surgical specimens. PMID:26600997

  18. Phonon-assisted robust and deterministic two-photon biexciton preparation in a quantum dot

    NASA Astrophysics Data System (ADS)

    Bounouar, S.; Müller, M.; Barth, A. M.; Glässl, M.; Axt, V. M.; Michler, P.

    2015-04-01

    We investigate both experimentally and theoretically a simple yet more robust and flexible alternative to Rabi oscillation-type biexciton preparation protocols traditionally used for semiconductor quantum dots. The quantum dot is excited by a strong laser pulse positively detuned from the two-photon resonance yielding an on demand initialization of the biexciton state by making use of the phonon-induced thermalization of the photon dressed states. It is shown that for excitation pulses in the picosecond range, a stable and high occupation of up to CX X=0.95 ±0.02 is reached. Notably, the generated photons show similar coherence properties as measured in the resonant two-photon scheme. This protocol is a powerful tool for the control of complex solid state systems combining radiative cascades, entanglement, and resonant cavity modes.

  19. Mitochondrial Dynamics Tracking with Two-Photon Phosphorescent Terpyridyl Iridium(III) Complexes.

    PubMed

    Huang, Huaiyi; Zhang, Pingyu; Qiu, Kangqiang; Huang, Juanjuan; Chen, Yu; Ji, Liangnian; Chao, Hui

    2016-01-01

    Mitochondrial dynamics, including fission and fusion, control the morphology and function of mitochondria, and disruption of mitochondrial dynamics leads to Parkinson's disease, Alzheimer's disease, metabolic diseases, and cancers. Currently, many types of commercial mitochondria probes are available, but high excitation energy and low photo-stability render them unsuitable for tracking mitochondrial dynamics in living cells. Therefore, mitochondrial targeting agents that exhibit superior anti-photo-bleaching ability, deep tissue penetration and intrinsically high three-dimensional resolutions are urgently needed. Two-photon-excited compounds that use low-energy near-infrared excitation lasers have emerged as non-invasive tools for cell imaging. In this work, terpyridyl cyclometalated Ir(III) complexes (Ir1-Ir3) are demonstrated as one- and two-photon phosphorescent probes for real-time imaging and tracking of mitochondrial morphology changes in living cells. PMID:26864567

  20. Selective two-photon absorptive resonance femtosecond-laser electronic-excitation tagging velocimetry.

    PubMed

    Jiang, Naibo; Halls, Benjamin R; Stauffer, Hans U; Danehy, Paul M; Gord, James R; Roy, Sukesh

    2016-05-15

    Selective two-photon absorptive resonance femtosecond-laser electronic-excitation tagging (STARFLEET), a nonseeded ultrafast-laser-based velocimetry technique, is demonstrated in reactive and nonreactive flows. STARFLEET is pumped via a two-photon resonance in N2 using 202.25 nm 100 fs light. STARFLEET greatly reduces the per-pulse energy required (30 μJ/pulse) to generate the signature FLEET emission compared to the conventional FLEET technique (1.1 mJ/pulse). This reduction in laser energy results in less energy deposited in the flow, which allows for reduced flow perturbations (reactive and nonreactive), increased thermometric accuracy, and less severe damage to materials. Velocity measurements conducted in a free jet of N2 and in a premixed flame show good agreement with theoretical velocities, and further demonstrate the significantly less intrusive nature of STARFLEET. PMID:27176968

  1. Two-photon excited autofluorescence imaging of human retinal pigment epithelial cells.

    PubMed

    Han, Meng; Bindewald-Wittich, Almut; Holz, Frank G; Giese, Guenter; Niemz, Markolf H; Snyder, Sarah; Sun, Hui; Yu, Jiayi; Agopov, Michael; La Schiazza, Olivier; Bille, Josef F

    2006-01-01

    Degeneration of retinal pigment epithelial (RPE) cells severely impairs the visual function of retina photoreceptors. However, little is known about the events that trigger the death of RPE cells at the subcellular level. Two-photon excited autofluorescence (TPEF) imaging of RPE cells proves to be well suited to investigate both the morphological and the spectral characteristics of the human RPE cells. The dominant fluorophores of autofluorescence derive from lipofuscin (LF) granules that accumulate in the cytoplasm of the RPE cells with increasing age. Spectral TPEF imaging reveals the existence of abnormal LF granules with blue shifted autofluorescence in RPE cells of aging patients and brings new insights into the complicated composition of the LF granules. Based on a proposed two-photon laser scanning ophthalmoscope, TPEF imaging of the living retina may be valuable for diagnostic and pathological studies of age related eye diseases. PMID:16526877

  2. Two-photon optical pumping of NH/sub 3/ in a multipass cell

    SciTech Connect

    Bobrovskii, A.N.; Kiselev, V.P.; Kozhevnikov, A.V.; Likhanskii, V.V.; Mishchenko, V.A.; Myl'nikov, G.D.

    1983-11-01

    A multipass cell was used in optical pumping of ammonia molecules by CO/sub 2/ laser radiation. Several new lasing lines were observed in the case of two-photon optical pumping of the NH/sub 3/ molecule at wavelengths in the range 16--35 ..mu... The output power of the various lines was in the range 10--50 kW. The divergence of the resultant radiation was diffraction-limited. A theoretical study was made of the two-photon pumping process. A stable (on the frequency scale) maximum was found in the gain profile of the output radiation. It was concluded that it should be possible to increase the energy and extend the emission spectrum of an ammonia laser pumped by double-photon absorption.

  3. In Vivo Monitoring of Multiple Circulating Cell Populations Using Two-photon Flow Cytometry

    PubMed Central

    Tkaczyk, Eric R.; Zhong, Cheng Frank; Ye, Jing Yong; Myc, Andrzej; Thomas, Thommey; Cao, Zhengyi; Duran-Struuck, Raimon; Luker, Kathryn E.; Luker, Gary D.; Norris, Theodore B.; Baker, James R.

    2008-01-01

    To detect and quantify multiple distinct populations of cells circulating simultaneously in the blood of living animals, we developed a novel optical system for two-channel, two-photon flow cytometry in vivo. We used this system to investigate the circulation dynamics in live animals of breast cancer cells with low (MCF-7) and high (MDA-MB-435) metastatic potential, showing for the first time that two different populations of circulating cells can be quantified simultaneously in the vasculature of a single live mouse. We also non-invasively monitored a population of labeled, circulating red blood cells for more than two weeks, demonstrating that this technique can also quantify the dynamics of abundant cells in the vascular system for prolonged periods of time. These data are the first in vivo application of multichannel flow cytometry utilizing two-photon excitation, which will greatly enhance our capability to study circulating cells in cancer and other disease processes. PMID:19221581

  4. Measurement of electron beam polarization from unstrained GaAs via two-photon photoemission

    SciTech Connect

    McCarter, James L.; Afanasev, A.; Gay, T. J.; Hansknecht, John C.; Kechiantz, A.; Poelker, B. Matthew

    2014-02-01

    Two-photon absorption of 1560 nm light was used to generate polarized electron beams from unstrained GaAs photocathodes of varying thickness: 625 {mu}m, 0.32 {mu}m, and 0.18 {mu}m. For each photocathode, the degree of spin polarization of the photoemitted beam was less than 50%, contradicting earlier predictions based on simple quantum mechanical selection rules for spherically-symmetric systems but consistent with the more sophisticated model of Bhat et al. (Phys. Rev. B 71 (2005) 035209). Polarization via two-photon absorption was the highest from the thinnest photocathode sample and comparable to that obtained via one-photon absorption (using 778 nm light), with values 40.3 +- 1.0% and 42.6 +- 1.0%, respectively.

  5. One- and two-photon photocurrents from tunable organic microcavity photodiodes

    NASA Astrophysics Data System (ADS)

    Koeppe, R.; Müller, J. G.; Lupton, J. M.; Feldmann, J.; Scherf, U.; Lemmer, U.

    2003-04-01

    We have constructed multilayer thin-film organic microcavity photodiodes with the photoactive layer comprised of a spin-coated conjugated polymer and an evaporated C60 layer. The electrodes are designed as semitransparent mirrors which form a resonant cavity structure. The photocurrent spectra show distinct maxima at the optical resonances of the cavities, which are located up to 200 nm below the fundamental optical transition of the polymer. The design allows a simple tuning of the spectral response by varying the layer thickness. Microcavity photodiodes are also shown to be highly sensitive two-photon detectors, which exhibit a factor 500 improvement in the two-photon response compared to devices without photonic confinement.

  6. Mitochondrial Dynamics Tracking with Two-Photon Phosphorescent Terpyridyl Iridium(III) Complexes

    PubMed Central

    Huang, Huaiyi; Zhang, Pingyu; Qiu, Kangqiang; Huang, Juanjuan; Chen, Yu; Ji, Liangnian; Chao, Hui

    2016-01-01

    Mitochondrial dynamics, including fission and fusion, control the morphology and function of mitochondria, and disruption of mitochondrial dynamics leads to Parkinson’s disease, Alzheimer’s disease, metabolic diseases, and cancers. Currently, many types of commercial mitochondria probes are available, but high excitation energy and low photo-stability render them unsuitable for tracking mitochondrial dynamics in living cells. Therefore, mitochondrial targeting agents that exhibit superior anti-photo-bleaching ability, deep tissue penetration and intrinsically high three-dimensional resolutions are urgently needed. Two-photon-excited compounds that use low-energy near-infrared excitation lasers have emerged as non-invasive tools for cell imaging. In this work, terpyridyl cyclometalated Ir(III) complexes (Ir1-Ir3) are demonstrated as one- and two-photon phosphorescent probes for real-time imaging and tracking of mitochondrial morphology changes in living cells. PMID:26864567

  7. 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.

  8. Control of the two-Photon Double Ionization of Helium with Intense Chirped Attosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Barmaki, Samira; Laulan, Stephane

    2014-05-01

    We study the two-photon double ionization process of the helium atom by solving numerically the nonrelativistic time-dependent Schrödinger equation in its full dimensionality. We investigate with an intense chirped attosecond laser pulse of central carrier frequency that corresponds to the 29th harmonic of a Ti-sapphire laser the direct and sequential processes in helium. We show how it is possible by adjusting the chirp parameter to control the dominance of one process over the other within the atom. Attosecond chirped laser pulses offer a promising way to probe and control the two-photon double ionization of helium when compared with attosecond transform-limited pulses.

  9. Cationic Two-Photon Lanthanide Bioprobes Able to Accumulate in Live Cells.

    PubMed

    Bui, Anh Thy; Beyler, Maryline; Liao, Yuan-Yuan; Grichine, Alexei; Duperray, Alain; Mulatier, Jean-Christophe; Guennic, Boris Le; Andraud, Chantal; Maury, Olivier; Tripier, Raphaël

    2016-07-18

    An original cationic water-soluble cyclen-based Eu(III) complex [EuL(1)](+) featuring a chromophore-functionalized antenna to increase the two-photon (2P) absorption properties was synthesized. The photophysical properties were thoroughly studied in various solvents and rationalized with the help of theoretical calculations. The complex exhibits an optimized 2P absorption cross section. Finally, 2P microscopy imaging experiments on living T24 human cancer cells highlighted the spontaneous internalization and the biological stability of this 2P bioprobe in vitro. Macrocyclic-based antennas open new perspectives for future optimization of the photophysical properties and allows envisaging the design of Eu, Tb, Yb, and Sm bioprobes. This result also opens the way for the design of functional two-photon Ln complexes able to monitor intracellular physicochemical parameters. PMID:27367598

  10. Deep vascular imaging in wounds by two-photon fluorescence microscopy.

    PubMed

    Yanez, Ciceron O; Morales, Alma R; Yue, Xiling; Urakami, Takeo; Komatsu, Masanobu; Järvinen, Tero A H; Belfield, Kevin D

    2013-01-01

    Deep imaging within tissue (over 300 μm) at micrometer resolution has become possible with the advent of two-photon fluorescence microscopy (2PFM). The advantages of 2PFM have been used to interrogate endogenous and exogenous fluorophores in the skin. Herein, we employed the integrin (cell-adhesion proteins expressed by invading angiogenic blood vessels) targeting characteristics of a two-photon absorbing fluorescent probe to image new vasculature and fibroblasts up to ≈ 1600 μm within wound (neodermis)/granulation tissue in lesions made on the skin of mice. Reconstruction revealed three dimensional (3D) architecture of the vascular plexus forming at the regenerating wound tissue and the presence of a fibroblast bed surrounding the capillaries. Biologically crucial events, such as angiogenesis for wound healing, may be illustrated and analyzed in 3D on the whole organ level, providing novel tools for biomedical applications. PMID:23844028

  11. 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.

  12. Search for SM Higgs decaying to two photons via ATLAS detector

    NASA Astrophysics Data System (ADS)

    Fang, Yaquan

    This dissertation reports the discovery potential of the Standard Model Higgs boson with the di-photon decay using the ATLAS detector. First, photon calibration techiques is studied and a likelihood method for photon identification and jet rejection is developed. A method to evaluate photon identification and fake photon backgrounds with data was also discussed. The potential of an inclusive SM Higgs decaying to two photons search and Higgs boson searches in association with one or two high PT jets is evaluated. Finally an extended maximum likelihood fit together with event classifications was performed to estimate the sensitivity of the search. With 30 1/fb data, the expected sensitivity for the channel Higgs decaying to two photons is above 5 sigma for Higgs masses between 120 and 140 GeV.

  13. [Frontiers in Live Bone Imaging Researches. Two-Photon Excitation Microscopy, principles and technologies].

    PubMed

    Oikawa, Yoshiro

    2015-06-01

    The "two photon absorption" phenomenon had been predicted by the American Physicist, Maria Ghöppert-Mayer in 1931. Denk and Webb group had proved it in 1990 and the first product had been launched in the market in 1996. But ever since the product became available, the number of users are not increased. Moreover, the system had been too difficult to use and the system sometimes stay not working in labs. But recently, the new easier-to-use products are released and the ultra short pulse IR laser became stable. And its applications are extending from neuro-science to oncology or immunology fields. Due to these reasons, the shipment of multi-photon microscope in Japan in 2013 is approximately 40 units which is 3 times bigger than in 2010. In this paper, I would like to discuss the principles of two-photon microscopy and some of the new technologies for the higher signal capture efficiency. PMID:26017864

  14. 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

  15. Synthesis of Photoresponsive Dual NIR Two-Photon Absorptive [60]Fullerene Triads and Tetrads

    PubMed Central

    Jeon, Seaho; Wang, Min; Tan, Loon-Seng; Cooper, Thomas; Hamblin, Michael R.; Chiang, Long Y.

    2013-01-01

    Broadband nonlinear optical (NLO) organic nanostructures exhibiting both ultrafast photoresponse and a large cross-section of two-photon absorption throughout a wide NIR spectrum may make them suitable for use as nonlinear biophotonic materials. We report here the synthesis and characterization of two C60-(antenna)x analogous compounds as branched triad C60(>DPAF-C18)(>CPAF-C2M) and tetrad C60(>DPAF-C18)(>CPAF-C2M)2 nanostructures. These compounds showed approximately equal extinction coefficients of optical absorption over 400–550 nm that corresponds to near-IR two-photon based excitation wavelengths at 780–1,100 nm. Accordingly, they may be utilized as potential precursor candidates to the active-core structures of photosensitizing nanodrugs for 2γ-PDT in the biological optical window of 800–1,050 nm. PMID:23941881

  16. Cascaded two-photon spectroscopy of Yb atoms with a transportable effusive atomic beam apparatus.

    PubMed

    Song, Minsoo; Yoon, Tai Hyun

    2013-02-01

    We present a transportable effusive atomic beam apparatus for cascaded two-photon spectroscopy of the dipole-forbidden transition (6s(2)(1)S0↔ 6s7s (1)S0) of Yb atoms. An ohmic-heating effusive oven is designed to have a reservoir volume of 1.6 cm(3) and a high degree of atomic beam collimation angle of 30 mrad. The new atomic beam apparatus allows us to detect the spontaneously cascaded two-photons from the 6s7s(1)S0 state via the intercombination 6s6p(3)P1 state with a high signal-to-noise ratio even at the temperature of 340 °C. This is made possible in our apparatus because of the enhanced atomic beam flux and superior detection solid angle. PMID:23464193

  17. Two-Photon Imaging of Lymphocyte Motility and Antigen Response in Intact Lymph Node

    NASA Astrophysics Data System (ADS)

    Miller, Mark J.; Wei, Sindy H.; Parker, Ian; Cahalan, Michael D.

    2002-06-01

    Lymphocyte motility is vital for trafficking within lymphoid organs and for initiating contact with antigen-presenting cells. Visualization of these processes has previously been limited to in vitro systems. We describe the use of two-photon laser microscopy to image the dynamic behavior of individual living lymphocytes deep within intact lymph nodes. In their native environment, T cells achieved peak velocities of more than 25 micrometers per minute, displaying a motility coefficient that is five to six times that of B cells. Antigenic challenge changed T cell trajectories from random walks to ``swarms'' and stable clusters. Real-time two-photon imaging reveals lymphocyte behaviors that are fundamental to the initiation of the immune response.

  18. Two-photon triggered drug delivery system: a new way to prevent posterior capsule opacification

    NASA Astrophysics Data System (ADS)

    Kim, H.-C.; Härtner, S.; Hampp, N.

    2006-02-01

    One of the major complications of cataract surgery is posterior capsule opacification caused by proliferation and migration of residual lens epithelial cells into the visual axis. In this study we present a novel approach to treat posterior capsule opacification in a non-invasive manner. A polymer-drug conjugate has been developed which is suitable for manufacturing functional intraocular lenses equipped with a drug delivery system. The therapeutic molecules, 5-fluorouracil, were attached through a photolabile linkage to the acrylic polymer backbone of the intraocular lens material. The controlled release of 5-fluorouracil is accomplished by two-photon induced cleavage of the linkage which is stable in ordinary conditions. The properties of the therapeutic system are characterized and the function is demonstrated in in vitro tests. The utilization of two-photon-absorption processes in drug delivery may provide a powerful tool to prevent posterior capsule opacification.

  19. Confocal, two-photon laser-induced fluorescence technique for the detection of nitric oxide.

    PubMed

    Reeves, M; Musculus, M; Farrell, P

    1998-10-01

    We describe a confocal two-photon laser-induced fluorescence scheme for the detection of gaseous NO. Excitation from a simple YAG-pumped Coumarin 450 dye system near 452.6 nm was used to promote the two-photon NO(A (2)?(+), nu? = 0 ? X (2)?, nu? = 0) transition in the gamma(0, 0) band. Subsequent fluorescence detection in the range 200-300 nm permitted almost total rejection of elastic and geometric scatter of laser radiation for excellent signal/noise ratio characteristics. The goal of the research was to apply NO fluorescence to a relatively realistic limited optical access combustion environment. A confocal optical arrangement was demonstrated for single-point measurements of NO concentration in gas samples and in atmospheric-pressure flames. The technique is suitable for applications that offer only a single direction for optical access and when significant elastic scatter is present. PMID:18301470

  20. Two-Photon or Higher-Order Absorbing Optical Materials for Generation of Reactive Species

    NASA Technical Reports Server (NTRS)

    Cumpston, Brian (Inventor); Lipson, Matthew (Inventor); Marder, Seth R. (Inventor); Perry, Joseph W. (Inventor)

    2013-01-01

    Disclosed are highly efficient multiphoton absorbing compounds and methods of their use. The compounds generally include a bridge of pi-conjugated bonds connecting electron donating groups or electron accepting groups. The bridge may be substituted with a variety of substituents as well. Solubility, lipophilicity, absorption maxima and other characteristics of the compounds may be tailored by changing the electron donating groups or electron accepting groups, the substituents attached to or the length of the pi-conjugated bridge. Numerous photophysical and photochemical methods are enabled by converting these compounds to electronically excited states upon simultaneous absorption of at least two photons of radiation. The compounds have large two-photon or higher-order absorptivities such that upon absorption, one or more Lewis acidic species, Lewis basic species, radical species or ionic species are formed.

  1. 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).

  2. Two-photon excited fluorescence lifetime imaging microscopy for FRET study on protein interactions

    NASA Astrophysics Data System (ADS)

    Qu, Junle; Lin, Ziyang; Liu, Lixin; Guo, Xuan; Chen, Danni; Niu, Hanben

    2005-01-01

    Two-photon excited fluorescence lifetime imaging (2P-FLIM) provides a more direct and precise approach to fluorescence resonance energy transfer (FRET), which allows studying the dynamic behavior of protein-protein interactions in living cells. In this paper, we describe the combination of a Leica TCS SP2 laser scanning microscope and a time-correlated single photon counting (TCSPC) lifetime imaging module developed by Becker & Hickl for two-photon excited fluorescence lifetime imaging. This 2P-FLIM system was used for FRET study on the interaction of heat shock protein hsp27 with p38 MAP kinase in the single living cell. Results show that the reduction in donor (CFP) lifetime in the presence of acceptor (YFP) reveals interactions between the two proteins.

  3. Evaluation of human sclera after femtosecond laser ablation using two photon and confocal microscopy

    NASA Astrophysics Data System (ADS)

    Sun, Hui; Kurtz, Ronald; Juhasz, Tibor

    2012-08-01

    Glaucoma is the second-leading cause of blindness worldwide and is often associated with elevated intraocular pressure (IOP). Partial thickness intrascleral channels can be created with a femtosecond laser operating at a wavelength of 1700 nm. Such channels have the potential to increase outflow facility and reduce elevated IOP. Analysis of the dimensions and location of these channels is important in understanding their effects. We describe the application of two-photon microscopy and confocal microscopy for noninvasive imaging of the femtosecond laser created partial-thickness scleral channels in human cadaver eyes. High-resolution images, hundreds of microns deep in the sclera, were obtained to allow determination of the shape and dimension of such channels. This demonstrates that concept of integrating femtosecond laser surgery, and two-photon and confocal imaging has the future potential for image-guided high-precision surgery in transparent and translucent tissue.

  4. Coherent phase control of resonance-mediated two-photon absorption in rare-earth ions

    SciTech Connect

    Zhang, Shian Lu, Chenhui; Jia, Tianqing; Sun, Zhenrong; Qiu, Jianrong

    2013-11-04

    We theoretically and experimentally demonstrate the quantum coherent control of the resonance-mediated two-photon absorption in rare-earth ions by the phase-shaped femtosecond laser pulse. Our theoretical results show that the resonance-mediated two-photon absorption can be effectively controlled, but the control efficiency depends on the laser repetition rate in real experiment due to the long lifetime and the short decoherence time of the excited state, and the larger laser repetition rate yields the lower control efficiency. These theoretical results are experimentally confirmed in glass sample doped with Er{sup 3+} by utilizing the femtosecond lasers with low repetition rate of 1 kHz and high repetition rate of 80 MHz.

  5. Two-photon microscopy of oxygen: polymersomes as probe carrier vehicles

    PubMed Central

    Sinks, Louise E.; Robbins, Gregory P.; Roussakis, Emmanuel; Troxler, Thomas; Hammer, Daniel A.; Vinogradov, Sergei A.

    2010-01-01

    Oxygen concentration distributions in biological systems can be imaged by the phosphorescence quenching method in combination with two-photon laser scanning microscopy. In this paper we identified the excitation regime in which the signal of a two-photon-enhanced phosphorescent probe1 is dependent quadratically on the excitation power (quadratic regime), and performed simulations that relate the photophysical properties of the probe to the imaging resolution. Further, we characterized polymersomes as a method of probe encapsulation and delivery. Photo-physical and oxygen sensing properties of the probe were found unchanged when the probe is encapsulated in polymersomes. Polymersomes were found capable of sustaining high probe concentrations, thereby serving to improve the signal-to-noise ratios for oxygen detection compared to the previously employed probe delivery methods. Imaging of polymersomes loaded with the probe was used as a test-bed for a new method. PMID:20462225

  6. Synthesis of photoresponsive dual NIR two-photon absorptive [60]fullerene triads and tetrads.

    PubMed

    Jeon, Seaho; Wang, Min; Tan, Loon-Seng; Cooper, Thomas; Hamblin, Michael R; Chiang, Long Y

    2013-01-01

    Broadband nonlinear optical (NLO) organic nanostructures exhibiting both ultrafast photoresponse and a large cross-section of two-photon absorption throughout a wide NIR spectrum may make them suitable for use as nonlinear biophotonic materials. We report here the synthesis and characterization of two C₆₀-(antenna)(x) analogous compounds as branched triad C₆₀(>DPAF-C₁₈)(>CPAF-C(2M)) and tetrad C₆₀(>DPAF-C₁₈)(>CPAF-C(2M))₂ nanostructures. These compounds showed approximately equal extinction coefficients of optical absorption over 400-550 nm that corresponds to near-IR two-photon based excitation wavelengths at 780-1,100 nm. Accordingly, they may be utilized as potential precursor candidates to the active-core structures of photosensitizing nanodrugs for 2γ-PDT in the biological optical window of 800-1,050 nm. PMID:23941881

  7. Two-photon-induced excited-state absorption in high-index fibers

    NASA Astrophysics Data System (ADS)

    Shensky, William M., III; Cohanoschi, Ion; Sevian, Armen; Hagan, David J.; Van Stryland, Eric W.

    2004-06-01

    We have studied the nonlinear optical properties of a high-index (n = 1.82) glass that is used as the core material in a commercially available fiber optic inverter, which is a coherent fiber bundle twisted 180 degrees to produce an inverted image. We have determined through open aperture Z-scan the two-photon absorption coefficient of the glass to be 0.8 cm/GW using 23 ps pulses (FWHM) at 532 nm, far from the linear absorption edge of 320 nm. For 5 ns (FWHM) pulses the nonlinear absorption is much larger, and is dominated by two-photon induced excited-state absorption. These effects contribute to the nanosecond optical limiting response that we have observed for the inverter using an F/5 focusing geometry.

  8. 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.

  9. Two-Photon Excitation STED Microscopy in Two Colors in Acute Brain Slices

    PubMed Central

    Bethge, Philipp; Chéreau, Ronan; Avignone, Elena; Marsicano, Giovanni; Nägerl, U. Valentin

    2013-01-01

    Many cellular structures and organelles are too small to be properly resolved by conventional light microscopy. This is particularly true for dendritic spines and glial processes, which are very small, dynamic, and embedded in dense tissue, making it difficult to image them under realistic experimental conditions. Two-photon microscopy is currently the method of choice for imaging in thick living tissue preparations, both in acute brain slices and in vivo. However, the spatial resolution of a two-photon microscope, which is limited to ∼350 nm by the diffraction of light, is not sufficient for resolving many important details of neural morphology, such as the width of spine necks or thin glial processes. Recently developed superresolution approaches, such as stimulated emission depletion microscopy, have set new standards of optical resolution in imaging living tissue. However, the important goal of superresolution imaging with significant subdiffraction resolution has not yet been accomplished in acute brain slices. To overcome this limitation, we have developed a new microscope based on two-photon excitation and pulsed stimulated emission depletion microscopy, which provides unprecedented spatial resolution and excellent experimental access in acute brain slices using a long-working distance objective. The new microscope improves on the spatial resolution of a regular two-photon microscope by a factor of four to six, and it is compatible with time-lapse and simultaneous two-color superresolution imaging in living cells. We demonstrate the potential of this nanoscopy approach for brain slice physiology by imaging the morphology of dendritic spines and microglial cells well below the surface of acute brain slices. PMID:23442956

  10. Realization of binary radial diffractive optical elements by two-photon polymerization technique.

    PubMed

    Osipov, Vladimir; Pavelyev, Vladimir; Kachalov, Denis; Zukauskas, Albertas; Chichkov, Boris

    2010-12-01

    Application of the two-photon polymerization (2PP) technique for the fabrication of submicron-size relief of radial binary diffractive optical elements (DOE's) is studied. Binary DOE's for the formation of special longitudinal intensity distribution (axial light segment) are realized. Interferometric investigations of the diffractive relief produced by the 2PP-technique and investigations of optical properties of the formed elements are presented. Results of computer simulations are in good agreement with the experimental observations. PMID:21164925

  11. Recent Results on Two-Photon Physics at BaBar

    SciTech Connect

    Druzhinin, Vladimir P.; /Novosibirsk, IYF

    2011-12-02

    The authors present measurements of the {gamma}{gamma}* {yields} {pi}{sup 0} transition form factor for the momentum transfer range Q{sup 2} = 4-40 GeV{sup 2} and the {gamma}{gamma}* {yields} {eta}{sub c} transition form factor for the range Q{sup 2} = 2-50 GeV{sup 2}. The results of the measurement of the {eta}{sub c} mass, total and two-photon widths are also presented.

  12. 910nm femtosecond Nd-doped fiber laser for in vivo two-photon microscopic imaging.

    PubMed

    Chen, Bingying; Jiang, Tongxiao; Zong, Weijian; Chen, Liangyi; Zhang, Zhigang; Wang, Aimin

    2016-07-25

    Pre-chirp technique was used in an Nd-doped fiber amplifier to optimize high-quality 910 nm pulses with the pulses width of 114 fs and pulse energy of 4.4 nJ. The in vivo zebrafish imaging results from our totally home-made microscopy proves our femtosecond Nd fiber laser an ideal source in two-photon microscopic imaging. PMID:27464109

  13. Near-threshold photoelectron spectrum in resonant two-photon ionization of atoms

    SciTech Connect

    Raczyn-acute-accentski, A.; Zaremba, J.

    1987-11-15

    The near-threshold photoelectron spectrum in a resonant two-photon ionization process is investigated using a nonperturbative method. The hydrogen atom is represented by a realistic model including an infinite number of Rydberg states converging at the threshold. When the threshold is crossed a typical two-peak structure of the spectrum is modified by cutting off part of the spectrum which may include one or even two peaks.

  14. Time-resolved two-photon excitation of dark states in quantum dots

    SciTech Connect

    Gautham, C. Snoke, D. W.; Rastelli, A.; Schmidt, O. G.

    2014-04-07

    We have performed time-resolved measurements of the time scale for conversion of excitons in dark states to bright (light-emitting) states in GaAs quantum dots. The dark states are pumped using two-photon absorption, while the bright state emission is observed in single-photon emission. This conversion time is connected to the spin flip time for carriers in the quantum dots. The time scale is found to be of the order of several hundred picoseconds.

  15. Endogenous Fluorophores Enable Two-Photon Imaging of the Primate Eye

    PubMed Central

    Palczewska, Grazyna; Golczak, Marcin; Williams, David R.; Hunter, Jennifer J.; Palczewski, Krzysztof

    2014-01-01

    Purpose. Noninvasive two-photon imaging of a living mammalian eye can reveal details of molecular processes in the retina and RPE. Retinyl esters and all-trans-retinal condensation products are two types of retinoid fluorophores present in these tissues. We measured the content of these two types of retinoids in monkey and human eyes to validate the potential of two-photon imaging for monitoring retinoid changes in human eyes. Methods. Two-photon microscopy (TPM) was used to visualize excised retina from monkey eyes. Retinoid composition and content in human and monkey eyes were quantified by HPLC and mass spectrometry (MS). Results. Clear images of inner and outer segments of rods and cones were obtained in primate eyes at different eccentricities. Fluorescence spectra from outer segments revealed a maximum emission at 480 nm indicative of retinols and their esters. In cynomolgus monkey and human retinal extracts, retinyl esters existed predominantly in the 11-cis configuration along with notable levels of 11-cis-retinol, a characteristic of cone-enriched retinas. Average amounts of di-retinoid-pyridinium-ethanolamine (A2E) in primate and human eyes were 160 and 225 pmol/eye, respectively. Conclusions. These data show that human retina contains sufficient amounts of retinoids for two-photon excitation imaging. Greater amounts of 11-cis-retinyl esters relative to rodent retinas contribute to the fluorescence signal from both monkey and human eyes. These observations indicate that TPM imaging found effective in mice could detect early age- and disease-related changes in human retina. PMID:24970255

  16. A rapid two-photon fabrication of tube array using an annular Fresnel lens.

    PubMed

    Zhang, Chenchu; Hu, Yanlei; Li, Jiawen; Li, Guoqiang; Chu, Jiaru; Huang, Wenhao

    2014-02-24

    A rapid method of fabricating microscopic tubular structures via two-photon polymerization is presented. Novel Fresnel lens is designed and applied to modulate the light field into a uniform ring pattern with controllable diameters. Comparing with the conventional holographic processing method, Fresnel lens shows higher uniformity and better flexibility, while easier to generate. This versatile method provides a powerful solution to produce tube structure array within several seconds. PMID:24663719

  17. Tailored probes for atomic force microscopy fabricated by two-photon polymerization

    NASA Astrophysics Data System (ADS)

    Göring, Gerald; Dietrich, Philipp-Immanuel; Blaicher, Matthias; Sharma, Swati; Korvink, Jan G.; Schimmel, Thomas; Koos, Christian; Hölscher, Hendrik

    2016-08-01

    3D direct laser writing based on two-photon polymerization is considered as a tool to fabricate tailored probes for atomic force microscopy. Tips with radii of 25 nm and arbitrary shape are attached to conventionally shaped micro-machined cantilevers. Long-term scanning measurements reveal low wear rates and demonstrate the reliability of such tips. Furthermore, we show that the resonance spectrum of the probe can be tuned for multi-frequency applications by adding rebar structures to the cantilever.

  18. Biocompatible and Photostable AIE Dots with Red Emission for In Vivo Two-Photon Bioimaging

    NASA Astrophysics Data System (ADS)

    Wang, Dan; Qian, Jun; Qin, Wei; Qin, Anjun; Tang, Ben Zhong; He, Sailing

    2014-03-01

    Bioimaging systems with cytocompatibility, photostability, red fluorescence, and optical nonlinearity are in great demand. Herein we report such a bioimaging system. Integration of tetraphenylethene (T), triphenylamine (T), and fumaronitrile (F) units yielded adduct TTF with aggregation-induced emission (AIE). Nanodots of the AIE fluorogen with efficient red emission were fabricated by encapsulating TTF with phospholipid. The AIE dots enabled three-dimensional dynamic imaging with high resolution in blood vessels of mouse brain under two-photon excitation.

  19. Electron angular distributions of noble gases in sequential two-photon double ionization

    NASA Astrophysics Data System (ADS)

    Braune, M.; Hartmann, G.; Ilchen, M.; Knie, A.; Lischke, T.; Reinköster, A.; Meissner, A.; Deinert, S.; Glaser, L.; Al-Dossary, O.; Ehresmann, A.; Kheifets, A. S.; Viefhaus, J.

    2016-02-01

    We present an angle resolved study of photoelectrons emitted from ions of the noble gases neon, argon and krypton by means of time-of-flight spectroscopy. The ionic targets are generated in a sequential two-photon process induced by the free-electron laser FLASH. Values of the anisotropy parameters ? and ? are derived from electron angular distribution measurements in the photon energy range from 38 to 91 eV and compared with recent theoretical calculations.

  20. Three dimensional silicon photonic crystals fabricated by two photon phase mask lithography.

    SciTech Connect

    Wiltzius, P.; Braun, P. V.; Liao, H.; Brzezinski, A.; Chen, Y. C.; Nelson, E.; Shir, D.; Rogers, J. A.; Bogart, Katherine Huderle Andersen

    2008-08-01

    We describe the fabrication of silicon three dimensional photonic crystals using polymer templates defined by a single step, two-photon exposure through a layer of photopolymer with relief molded on its surface. The resulting crystals exhibit high structural quality over large areas, displaying geometries consistent with calculation. Spectroscopic measurements of transmission and reflection through the silicon and polymer structures reveal excellent optical properties, approaching properties predicted by simulations that assume ideal layouts.

  1. Simultaneous imaging of multiple focal planes using a two-photon scanning microscope

    NASA Astrophysics Data System (ADS)

    Amir, W.; Carriles, R.; Hoover, E. E.; Planchon, T. A.; Durfee, C. G.; Squier, J. A.

    2007-06-01

    Despite all the advances in nonlinear microscopy, all existing instruments are constrained to obtain images of one focal plane at a time. In this Letter we demonstrate a two-photon absorption fluorescence scanning microscope capable of imaging two focal planes simultaneously. This is accomplished by temporally demultiplexing the signal coming from two focal volumes at different sample depths. The scheme can be extended to three or more focal planes.

  2. Two-photon photoemission and the dynamics of electrons at interfaces

    SciTech Connect

    Padowitz, D.F.; Harris, C.B.; Jordan, R.E.; Lingle, R.L. Jr.; McNeill, J.D.; Merry, W.R.

    1994-01-01

    A new instrument for angle-resolved two-photon photoemission with exceptional sensitivity and energy resolution has allowed a detailed examination of the interaction of image-state electrons with adsorbates. In addition to measuring the electrostatic properties of molecular-thickness films, the technique serves as a probe of adsorbate growth modes, and provides new opportunities to explore the dynamics of electrons in well-controlled two-dimensional systems.

  3. Single-spin asymmetries from two-photon exchange in elastic electron proton scattering

    SciTech Connect

    A.V. Afanasev; N.P. Merenkov

    2005-02-01

    The parity-conserving single-spin beam asymmetry of elastic electron-proton scattering is induced by an absorptive part of the two-photon exchange amplitude. We demonstrate that this asymmetry has logarithmic and double-logarithmic enhancement due to contributions of hard collinear quasi-real photons. An optical theorem is used to evaluate the asymmetry in terms of the total photoproduction cross section on the proton.

  4. Polarization dependence of the phase of interference between single- and two-photon ionization.

    PubMed

    Baranova, N B; Chudinov, A N; Shulginov, A A; Zel'dovich, B Y

    1991-09-01

    The interference between single-photon and two-photon ionization has been observed for electrons ejected in the direction n from the photomultiplier cathode exposed simultaneously to the picosecond pulse of a Nd laser E(omega) and its second harmonic E(2omega). The change of the phase difference of such interference was measured for the switch of the polarizations from E(omega) ||n, E(2omega) ||n to E(omega) ? n, E(2omega) || n. PMID:19776966

  5. A Highly Selective Ratiometric Two-Photon Fluorescent Probe for Human Cytochrome P450 1A.

    PubMed

    Dai, Zi-Ru; Ge, Guang-Bo; Feng, Lei; Ning, Jing; Hu, Liang-Hai; Jin, Qiang; Wang, Dan-Dan; Lv, Xia; Dou, Tong-Yi; Cui, Jing-Nan; Yang, Ling

    2015-11-18

    Cytochrome P450 1A (CYP1A), one of the most important phase I drug-metabolizing enzymes in humans, plays a crucial role in the metabolic activation of procarcinogenic compounds to their ultimate carcinogens. Herein, we reported the development of a ratiometric two-photon fluorescent probe NCMN that allowed for selective and sensitive detection of CYP1A for the first time. The probe was designed on the basis of substrate preference of CYP1A and its high capacity for O-dealkylation, while 1,8-naphthalimide was selected as fluorophore because of its two-photon absorption properties. To achieve a highly selective probe for CYP1A, a series of 1,8-naphthalimide derivatives were synthesized and used to explore the potential structure-selectivity relationship, by using a panel of human CYP isoforms for selectivity screening. After screening and optimization, NCMN displayed the best combination of selectivity, sensitivity and ratiometric fluorescence response following CYP1A-catalyzed O-demetylation. Furthermore, the probe can be used to real-time monitor the enzyme activity of CYP1A in complex biological systems, and it has the potential for rapid screening of CYP1A modulators using tissue preparation as enzyme sources. NCMN has also been successfully used for two-photon imaging of intracellular CYP1A in living cells and tissues, and showed high ratiometric imaging resolution and deep-tissue imaging depth. In summary, a two-photon excited ratiometric fluorescent probe NCMN has been developed and well-characterized for sensitive and selective detection of CYP1A, which holds great promise for bioimaging of endogenous CYP1A in living cells and for further investigation on CYP1A associated biological functions in complex biological systems. PMID:26488456

  6. 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.

  7. Perturbative calculation of two-photon double electron ionization of helium

    NASA Astrophysics Data System (ADS)

    Ivanov, I. A.; Kheifets, A. S.

    2008-05-01

    We report the total integrated cross-section (TICS) of two-photon double ionization of helium in the photon energy range from 40 to 54 eV. We compute the TICS in the lowest order perturbation theory (LOPT) using the length and Kramers-Henneberger gauges of the electromagnetic interaction. Our findings indicate that the LOPT gives results for the TICS in agreement with our earlier non-perturbative calculations.

  8. Quantum teleportation of a generic two-photon state with weak cross-Kerr nonlinearities

    NASA Astrophysics Data System (ADS)

    Wang, Meiyu; Yan, Fengli

    2016-05-01

    We present a scheme for teleporting a generic two-photon polarization state by using two EPR states as quantum channel based on weak cross-Kerr nonlinearities. As the core component of the present framework, the quantum nondemolition detector based on the weak cross-Kerr nonlinearity acts as an EPR entangler as well as the Bell-state analyzer. This makes the teleportation protocol be achieved near deterministically and be feasible in the current experimental technology.

  9. Acute two-photon imaging of the neurovascular unit in the cortex of active mice

    PubMed Central

    Tran, Cam Ha T.; Gordon, Grant R.

    2015-01-01

    In vivo two-photon scanning fluorescence imaging is a powerful technique to observe physiological processes from the millimeter to the micron scale in the intact animal. In neuroscience research, a common approach is to install an acute cranial window and head bar to explore neocortical function under anesthesia before inflammation peaks from the surgery. However, there are few detailed acute protocols for head-restrained and fully awake animal imaging of the neurovascular unit during activity. This is because acutely performed awake experiments are typically untenable when the animal is naïve to the imaging apparatus. Here we detail a method that achieves acute, deep-tissue two-photon imaging of neocortical astrocytes and microvasculature in behaving mice. A week prior to experimentation, implantation of the head bar alone allows mice to train for head-immobilization on an easy-to-learn air-supported ball treadmill. Following just two brief familiarization sessions to the treadmill on separate days, an acute cranial window can subsequently be installed for immediate imaging. We demonstrate how running and whisking data can be captured simultaneously with two-photon fluorescence signals with acceptable movement artifacts during active motion. We also show possible applications of this technique by (1) monitoring dynamic changes to microvascular diameter and red blood cells in response to vibrissa sensory stimulation, (2) examining responses of the cerebral microcirculation to the systemic delivery of pharmacological agents using a tail artery cannula during awake imaging, and (3) measuring Ca2+ signals from synthetic and genetically encoded Ca2+ indicators in astrocytes. This method will facilitate acute two-photon fluorescence imaging in awake, active mice and help link cellular events within the neurovascular unit to behavior. PMID:25698926

  10. Quantum teleportation of a generic two-photon state with weak cross-Kerr nonlinearities

    NASA Astrophysics Data System (ADS)

    Wang, Meiyu; Yan, Fengli

    2016-08-01

    We present a scheme for teleporting a generic two-photon polarization state by using two EPR states as quantum channel based on weak cross-Kerr nonlinearities. As the core component of the present framework, the quantum nondemolition detector based on the weak cross-Kerr nonlinearity acts as an EPR entangler as well as the Bell-state analyzer. This makes the teleportation protocol be achieved near deterministically and be feasible in the current experimental technology.

  11. Doppler-free approach to optical pumping dynamics in the 6S1/2-5D5/2 electric quadrupole transition of cesium vapor.

    PubMed

    Chan, Eng Aik; Aljunid, Syed Abdullah; Zheludev, Nikolay I; Wilkowski, David; Ducloy, Martial

    2016-05-01

    The 6S1/2-5D5/2 electric quadrupole transition is investigated in cesium vapor at room temperature via nonlinear Doppler-free 6P-6S-5D three-level spectroscopy. Frequency-resolved studies of individual E2 hyperfine lines allow one to analyze the optical pumping dynamics, polarization selection rules, and line intensities. It opens the way to studies of transfer of light orbital angular momentum to atoms and the influence of metamaterials on E2 line spectra. PMID:27128060

  12. Polarization and spectral characteristics of the two-photon luminescence from colloidal gold nanoparticles excited by tunable laser radiation

    SciTech Connect

    Yashunin, D. A. Korytin, A. I.; Stepanov, A. N.

    2015-12-15

    We have experimentally studied two-photon luminescence from a colloidal solution of spherical gold nanoparticles by tuning the wavelength of the exciting radiation. The measured polarization and spectral characteristics of the two-photon luminescence signal show that the observed nonlinear optical response is determined by the dimers present in the solution with a concentration of a few percent of total nanoparticle number.

  13. Spectroscopy of α,ω-dithienyl polyenes: evidence for two-photon absorption states from fluorescence studies

    NASA Astrophysics Data System (ADS)

    Natarajan, Lalgudi V.; Kirkpatrick, Sean M.; Sutherland, Richard L.; Sowards, Laura A.; Spangler, Charles W.; Fleitz, Paul A.; Cooper, Thomas M.

    1998-10-01

    The photophysics of a series (alpha) ,(omega) -dithienyl polyenes was studied. Both one photon excited fluorescence and fluorescence originating from two photon absorption states were investigated. There is strong evidence of two photon absorption from fluorescence studies in agreement with our earlier studies involving nonlinear absorption.

  14. Two-Photon Activation of p-Hydroxyphenacyl Phototriggers: Toward Spatially Controlled Release of Diethyl Phosphate and ATP.

    PubMed

    Houk, Amanda L; Givens, Richard S; Elles, Christopher G

    2016-03-31

    Two-photon activation of the p-hydroxyphenacyl (pHP) photoactivated protecting group is demonstrated for the first time using visible light at 550 nm from a pulsed laser. Broadband two-photon absorption measurements reveal a strong two-photon transition (>10 GM) near 4.5 eV that closely resembles the lowest-energy band at the same total excitation energy in the one-photon absorption spectrum of the pHP chromophore. The polarization dependence of the two-photon absorption band is consistent with excitation to the same S3 ((1)ππ*) excited state for both one- and two-photon activation. Monitoring the progress of the uncaging reaction under nonresonant excitation at 550 nm confirms a quadratic intensity dependence and that two-photon activation of the uncaging reaction is possible using visible light in the range 500-620 nm. Deprotonation of the pHP chromophore under mildly basic conditions shifts the absorption band to lower energy (3.8 eV) in both the one- and two-photon absorption spectra, suggesting that two-photon activation of the pHP chromophore may be possible using light in the range 550-720 nm. The results of these measurements open the possibility of spatially and temporally selective release of biologically active compounds from the pHP protecting group using visible light from a pulsed laser. PMID:26962676

  15. On the Theory of the Shift Linear Photovoltaic Effect in Semiconductors of Tetrahedral Symmetry Under Two-Photon Absorption

    NASA Astrophysics Data System (ADS)

    Rasulov, R. Ya.; Rasulov, V. R.; Eshboltaev, I.

    2016-05-01

    An occurrence of the current of the shift linear photovoltaic effect under two-photon absorption of light in semiconductors without a center of symmetry with a complex band structure is theoretically analyzed. The contributions both from the simultaneous absorption of two photons and successive absorption of two single photons to the photocurrent are taken into account.

  16. 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.

  17. Two-photon fluorescence and fluorescence imaging of two styryl heterocyclic dyes combined with DNA

    NASA Astrophysics Data System (ADS)

    Gao, Chao; Liu, Shu-yao; Zhang, Xian; Liu, Ying-kai; Qiao, Cong-de; Liu, Zhao-e.

    2016-03-01

    Two new styryl heterocyclic two-photon (TP) materials, 4-[4-(N-methyl)styrene]-imidazo [4,5-f][1,10] phenanthroline-benzene iodated salt (probe-1) and 4,4- [4-(N-methyl)styrene] -benzene iodated salt (probe-2) were successfully synthesized and studied as potential fluorescent probes of DNA detection. The linear and nonlinear photophysical properties of two compounds in different solvents were investigated. The absorption, one- and two-photon fluorescent spectra of the free dye and dye-DNA complex were also examined to evaluate their photophysical properties. The binding constants of dye-DNA were obtained according to Scatchard equation with good values. The results showed that two probes could be used as fluorescent DNA probes by two-photon excitation, and TP fluorescent properties of probe-1 are superior to that of probe-2. The fluorescent method date indicated that the mechanisms of dye-DNA complex interaction may be groove binding for probe-1 and electrostatic interaction for probe-2, respectively. The MTT assay experiments showed two probes are low toxicity. Moreover, the TP fluorescence imaging of DNA detection in living cells at 800 nm indicated that the ability to locate in cell nuclei of probe-1 is better than that of probe-2.

  18. Video-rate scanning two-photon excitation fluorescence microscopy and ratio imaging with cameleons.

    PubMed

    Fan, G Y; Fujisaki, H; Miyawaki, A; Tsay, R K; Tsien, R Y; Ellisman, M H

    1999-05-01

    A video-rate (30 frames/s) scanning two-photon excitation microscope has been successfully tested. The microscope, based on a Nikon RCM 8000, incorporates a femtosecond pulsed laser with wavelength tunable from 690 to 1050 nm, prechirper optics for laser pulse-width compression, resonant galvanometer for video-rate point scanning, and a pair of nonconfocal detectors for fast emission ratioing. An increase in fluorescent emission of 1.75-fold is consistently obtained with the use of the prechirper optics. The nonconfocal detectors provide another 2.25-fold increase in detection efficiency. Ratio imaging and optical sectioning can therefore be performed more efficiently without confocal optics. Faster frame rates, at 60, 120, and 240 frames/s, can be achieved with proportionally reduced scan lines per frame. Useful two-photon images can be acquired at video rate with a laser power as low as 2.7 mW at specimen with the genetically modified green fluorescent proteins. Preliminary results obtained using this system confirm that the yellow "cameleons" exhibit similar optical properties as under one-photon excitation conditions. Dynamic two-photon images of cardiac myocytes and ratio images of yellow cameleon-2.1, -3.1, and -3.1nu are also presented. PMID:10233058

  19. A Series of Imidazole Derivatives: Synthesis, Two-Photon Absorption, and Application for Bioimaging

    PubMed Central

    Zhu, Yingzhong; Xiao, Lufei; Zhao, Meng; Zhou, Jiazheng; Zhang, Qiong; Wang, Hui; Li, Shengli; Zhou, Hongping; Wu, Jieying; Tian, Yupeng

    2015-01-01

    A new series of D-π-A type imidazole derivatives have been synthesized and characterized. Two corresponding imidazolium salts (iodine and hexafluorophosphate) were prepared from the imidazole compound. Their electron-withdrawing ability can be largely tunable by salt formation reaction or ion exchange. UV-vis absorption and single-photon fluorescence spectra have been systematically investigated in different solvents. The two-photon cross sections (δ2PA) of the imidazole derivatives are measured by two-photon excited fluorescence (2PEF) method. Compared with those of T-1 (107 GM) and T-3 (96 GM), T-2 (imidazolium iodine salt) has a large two-photon absorption (2PA) cross section value of 276 GM. Furthermore, the cytotoxicity and applications in bioimaging for the imidazole derivatives were carried out. The results showed that T-1 can be used as a lysosomal tracker with high stability and water solubility within pHs of 4–6, while T-2 and T-3 can be used as probes for cell cytoplasm. PMID:26579544

  20. Detection of TNT using a sensitive two-photon organic dendrimer for remote sensing

    NASA Astrophysics Data System (ADS)

    Narayanan, Aditya; Varnavski, Oleg; Mongin, Oliver; Majoral, Jean-Pierre; Blanchard-Desce, Mireille; Goodson, Theodore, III

    2008-03-01

    There is currently a need for superior stand-off detection schemes for protection against explosive weapons of mass destruction. Fluorescence detection at small distances from the target has proven to be attractive. A novel unexplored route in fluorescence chemical sensing that utilizes the exceptional spectroscopic capabilities of nonlinear optical methods is two-photon excited fluorescence. This approach utilizes infra-red light for excitation of remote sensors. Infra-red light suffers less scattering in porous materials which is beneficial for vapor sensing and has greater depth of penetration through the atmosphere, and there are fewer concerns regarding eye safety in remote detection schemes. We demonstrate this method using a novel dendritic system which possesses both excellent fluorescence sensitivity to the presence of TNT with infra-red pulses of light and high two-photon absorption (TPA) response. This illustrates the use of TPA for potential stand-off detection of energetic materials in the infra-red spectral regions in a highly two-photon responsive dendrimer.

  1. 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.

  2. Beyond the Born Approximation: Two Photon Exchange in Nucleon Structure Studies

    NASA Astrophysics Data System (ADS)

    Averett, Todd

    2013-10-01

    Precision measurements of the electric form factor of the proton at Jefferson Lab have revealed a striking difference between Rosenbluth separation and polarization transfer data. Much of this discrepancy has been attributed to two-photon exchange, previously ignored in nucleon structure studies due to lack of precision in the data. Recently, experiments were conducted at Jefferson Lab where unpolarized electrons were scattered from neutrons polarized normal to the electron scattering plane. The polarized neutrons were produced by polarizing 3He nuclei using spin-exchange optical pumping. The single spin asymmetry for inclusive scattering, formed by flipping the target spin direction, is predicted to be exactly zero in the Born approximation by the Christ-Lee theorem. A non-zero asymmetry is an indication of contributions from two-photon exchange. This asymmetry provides a new tool to study the structure of the nucleon and to directly test models of two-photon exchange contributions. Results will be presented from measurements in the quasi-elastic and deep-inelastic regions.

  3. A biphenyl type two-photon fluorescence probe for monitoring the mitochondrial membrane potential.

    PubMed

    Moritomo, Hiroki; Yamada, Kengo; Kojima, Yuki; Suzuki, Yasutaka; Tani, Seiji; Kinoshita, Hazuki; Sasaki, Akira; Mikuni, Shintaro; Kinjo, Masataka; Kawamata, Jun

    2014-01-01

    Here we describe the design and synthesis of a bifunctional two-photon fluorescence probe, N,N'-‍dimethyl-4,4'-(biphenyl-2,1-ethenediyl)dipyridinium hexafluorophosphate (BP6). HeLa, Hek293, and Paramecium caudatum cells were stained with BP6. BP6 accumulated on the mitochondria of all three cell types when the mitochondrial membrane potential was high. As the mitochondrial membrane potential decreased following the addition of carbonyl cyanide m-chlorophenyl hydrazine, BP6 moved from the mitochondria to the nucleus in a reversible manner, depending on the mitochondrial membrane potential status. The maximum value of the two-photon absorption cross-section of BP6 is 250 GM (1 GM=1×10(-50) cm(4) s molecules(-1) photon(-1)). This value is 3 and 30 times larger, respectively, than that of the conventional mitochondria selective probes, rhodamine 123 and green fluorescence protein. These results suggest that BP6 should be useful for monitoring mitochondrial membrane potential by two-photon excitation. PMID:25319070

  4. 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.

  5. Two-photon fluorescent sensor for K+ imaging in live cells (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Sui, Binglin; Yue, Xiling; Kim, Bosung; Belfield, Kevin D.

    2016-03-01

    It is difficult to overstate the physiological importance of potassium for life as its indispensable roles in a variety of biological processes are widely known. As a result, efficient methods for determining physiological levels of potassium are of paramount importance. Despite this, relatively few K+ fluorescence sensors have been reported, with only one being commercially available. A new two-photon excited fluorescent K+ sensor is reported. The sensor is comprised of three moieties, a highly selective K+ chelator as the K+ recognition unit, a boron-dipyrromethene (BODIPY) derivative modified with phenylethynyl groups as the fluorophore, and two polyethylene glycol chains to afford water solubility. The sensor displays very high selectivity (<52-fold) in detecting K+ over other physiological metal cations. Upon binding K+, the sensor switches from non-fluorescent to highly fluorescent, emitting red to near-IR (NIR) fluorescence. The sensor exhibited a good two-photon absorption cross section, 500 GM at 940 nm. Moreover, it is not sensitive to pH in the physiological pH range. Time-dependent cell imaging studies via both one- and two-photon fluorescence microscopy demonstrate that the sensor is suitable for dynamic K+ sensing in living cells.

  6. Combined two-photon imaging, electrophysiological, and anatomical investigation of the human neocortex in vitro.

    PubMed

    Kerekes, Bálint Péter; Tóth, Kinga; Kaszás, Attila; Chiovini, Balázs; Szadai, Zoltán; Szalay, Gergely; Pálfi, Dénes; Bagó, Attila; Spitzer, Klaudia; Rózsa, Balázs; Ulbert, István; Wittner, Lucia

    2014-07-01

    Spontaneous synchronous population activity (SPA) can be detected by electrophysiological methods in cortical slices of epileptic patients, maintained in a physiological medium in vitro. In order to gain additional spatial information about the network mechanisms involved in the SPA generation, we combined electrophysiological studies with two-photon imaging. Neocortical slices prepared from postoperative tissue of epileptic and tumor patients were maintained in a dual perfusion chamber in a physiological incubation medium. SPA was recorded with a 24-channel extracellular linear microelectrode covering all neocortical layers. After identifying the electrophysiologically active regions of the slice, bolus loading of neuronal and glial markers was applied on the tissue. SPA-related [Formula: see text] transients were detected in a large population of neighboring neurons with two-photon microscopy, simultaneous with extracellular SPA and intracellular whole-cell patch-clamp recordings. The intracellularly recorded cells were filled for subsequent anatomy. The cells were reconstructed in three dimensions and examined with light- and transmission electron microscopy. Combining high spatial resolution two-photon [Formula: see text] imaging techniques and high temporal resolution extra- and intracellular electrophysiology with cellular anatomy may permit a deeper understanding of the structural and functional properties of the human neocortex. PMID:26157969

  7. High-throughput spatial light modulation two-photon microscopy for fast functional imaging.

    PubMed

    Pozzi, Paolo; Gandolfi, Daniela; Tognolina, Marialuisa; Chirico, Giuseppe; Mapelli, Jonathan; D'Angelo, Egidio

    2015-01-01

    The optical monitoring of multiple single neuron activities requires high-throughput parallel acquisition of signals at millisecond temporal resolution. To this aim, holographic two-photon microscopy (2PM) based on spatial light modulators (SLMs) has been developed in combination with standard laser scanning microscopes. This requires complex coordinate transformations for the generation of holographic patterns illuminating the points of interest. We present a simpler and fully digital setup (SLM-2PM) which collects three-dimensional two-photon images by only exploiting the SLM. This configuration leads to an accurate placement of laser beamlets over small focal volumes, eliminating mechanically moving parts and making the system stable over long acquisition times. Fluorescence signals are diffraction limited and are acquired through a pixelated detector, setting the actual limit to the acquisition rate. High-resolution structural images were acquired by raster-scanning the sample with a regular grid of excitation focal volumes. These images allowed the selection of the structures to be further investigated through an interactive operator-guided selection process. Functional signals were collected by illuminating all the preselected points with a single hologram. This process is exemplified for high-speed (up to 1 kHz) two-photon calcium imaging on acute cerebellar slices. PMID:26157984

  8. Diagnosis of basal cell carcinoma by two photon excited fluorescence combined with lifetime imaging

    NASA Astrophysics Data System (ADS)

    Fan, Shunping; Peng, Xiao; Liu, Lixin; Liu, Shaoxiong; Lu, Yuan; Qu, Junle

    2014-02-01

    Basal cell carcinoma (BCC) is the most common type of human skin cancer. The traditional diagnostic procedure of BCC is histological examination with haematoxylin and eosin staining of the tissue biopsy. In order to reduce complexity of the diagnosis procedure, a number of noninvasive optical methods have been applied in skin examination, for example, multiphoton tomography (MPT) and fluorescence lifetime imaging microscopy (FLIM). In this study, we explored two-photon optical tomography of human skin specimens using two-photon excited autofluorescence imaging and FLIM. There are a number of naturally endogenous fluorophores in skin sample, such as keratin, melanin, collagen, elastin, flavin and porphyrin. Confocal microscopy was used to obtain structures of the sample. Properties of epidermic and cancer cells were characterized by fluorescence emission spectra, as well as fluorescence lifetime imaging. Our results show that two-photon autofluorescence lifetime imaging can provide accurate optical biopsies with subcellular resolution and is potentially a quantitative optical diagnostic method in skin cancer diagnosis.

  9. 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.

  10. Wide field of view two-photon excited fluorescence imaging, theory and applications

    NASA Astrophysics Data System (ADS)

    Stoltzfus, Caleb Ray

    Two-photon excited fluorescence (2PEF) is a unique photophysical process that has benefited many diverse areas of science. Imaging the 2PEF signal offers numerous intrinsic benefits, including low background scattering, high sample photo-stability, and high excitation selectivity. The 2PEF signal has a nonlinear dependence on excitation intensity, which has proven to be extremely useful for high resolution, three dimensional microscopy. This same nonlinear dependence, in conjunction with the typically low probability of two-photons being simultaneously absorbed, also makes 2PEF imaging difficult to scale, leaving most two-photon microscopes with a field of view (FOV) limited to less than a few mm2. This effectively limits the benefits of the unique properties of 2PEF imaging to microscopic applications. This dissertation explores the development and application of a wide FOV 2PEF imaging technique, where a FOV as large as 10 cm2 is achieved by increasing the peak photon flux of the excitation source, and expanding the illumination region. The use of this imaging technique for the in depth characterization and optimization of fluorescent proteins (FPs), as well as taking high contrast images of fingermarks is described. This new wide FOV 2PEF imaging technique greatly expands the usefulness of the unique photophysical properties of 2PEF and allows for sensitive, high contrast 2PEF imaging on a much larger scale than was previously possible.

  11. 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

  12. 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.

  13. 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

  14. Virtual Sequential Picture for Nonsequential Two-Photon Double Ionization of Helium

    NASA Astrophysics Data System (ADS)

    Jiang, Wei-Chao; Shan, Jun-Yi; Gong, Qihuang; Peng, Liang-You

    2015-10-01

    By using a model based on the second-order time-dependent perturbation theory, we show that the nonsequential two-photon double ionization of He can be understood in a virtual sequential picture: to excite the final double continuum state |k1,k2 ⟩ by absorbing two photons from the ground state |1 s2,1S0 ⟩ , the single continuum states |1 s ,k1 ⟩ and |1 s ,k2 ⟩ serve as the dominant intermediate states. This virtual sequential picture is verified by the perfect agreement of the total ionization cross section, respectively, calculated by this model and by the sophisticated numerical solution to the full-dimensional time-dependent Schrödinger equation. This model, without the consideration of the electron correlation in the final double continuum state, works well for a wide range of laser parameters extending from the nonsequential to the sequential regime. The present Letter demonstrates that the electron correlation in the final double continuum state is not important in evaluating the total cross section, while it is indispensable for an accurate computation of a triply differential cross section. In addition, the virtual sequential picture bridges the sequential and nonsequential two-photon double ionization and reveals connections and distinctions between them.

  15. Photochemical effects in 243-nm two-photon excitation of atomic hydrogen in flames.

    PubMed

    Goldsmith, J E

    1989-03-15

    This paper describes photochemical effects observed during two-photon 1S-2S excitation of atomic hydrogen in flames using 243-nm laser radiation. An I(4) intensity dependence is observed in regions of the flame where the natural atomic concentration is low, suggesting an I(2) photochemical production mechanism, which we believe is due to two-photon excitation of water molecules, which then predissociate to form H and OH fragments. In a measurement of OH created in the flame by the 243-nm beam, we observe the same I(2) intensity dependence with the laser detuned from the atomic hydrogen 1S-2S resonance, but an apparent I(3.4) dependence is observed when the laser is tuned to the resonance. We believe that a second photochemical mechanism contributes at the resonance, namely, two-photon excitation of H, followed by collisional energy transfer to water molecules, which then fall apart into H and OH fragments. We model this process and show that a combination of I(2) and I(4) dependences can lead to an intensity dependence that mimics a single I(3.4) dependence over a limited range of intensities. PMID:20548641

  16. Research of the new optical diffractive super-resolution element of the two-photon microfabrication

    NASA Astrophysics Data System (ADS)

    Wei, Peng; Zhu, Yu; Duan, Guanghong

    2006-11-01

    The new optical diffractive superresolution element (DSE) is being applied to improve the microfabrication radial superresolution in the two-photon three-dimension (3D) microfabrication system, which appeared only a few years ago and can provide the ability to confine photochemical and physical reactions to the order of laser wavelength in three dimensions. The design method of the DSE is that minimizing M if the lowest limit S l of the S and the highest limit G u of the G is set, where Liu [1] explained the definition of the S, M and G. Simulation test result proved that the microfabrication radial superresolution can be improved by the new optical DSE. The phenomenon can only be interpreted as the intensity of high-order and side of the zero-order diffraction peaks have been clapped under the twophoton absorption (TPA) polymerization threshold. In a word the polymerized volume can be chosen because the S l and the G u is correspondingly adjustable, even if the laser wavelength, objective lens and the photosensitive resin is fixed for a given two-photon microfabrication system. That means the radial superresolution of the two-photon microfabrication can be chosen.

  17. Two-photon absorption in gapped bilayer graphene with a tunable chemical potential.

    PubMed

    Brinkley, M K; Abergel, D S L; Clader, B D

    2016-09-14

    Despite the now vast body of two-dimensional materials under study, bilayer graphene remains unique in two ways: it hosts a simultaneously tunable band gap and electron density; and stems from simple fabrication methods. These two advantages underscore why bilayer graphene is critical as a material for optoelectronic applications. In the work that follows, we calculate the one- and two-photon absorption coefficients for degenerate interband absorption in a graphene bilayer hosting an asymmetry gap and adjustable chemical potential-all at finite temperature. Our analysis is comprehensive, characterizing one- and two-photon absorptive behavior over wide ranges of photon energy, gap, chemical potential, and thermal broadening. The two-photon absorption coefficient for bilayer graphene displays a rich structure as a function of photon energy and band gap due to the existence of multiple absorption pathways and the nontrivial dispersion of the low energy bands. This systematic work will prove integral to the design of bilayer-graphene-based nonlinear optical devices. PMID:27392275

  18. 3D Image Processing of Two-Photon Microscopy Images Depicting Nanoprobes in Skin

    NASA Astrophysics Data System (ADS)

    Bongo, Andrew E.

    Choosing a deconvolution algorithm can be beneficial when imaging nanoprobes in skin by means of two-photon microscopy. By design, deconvolution algorithms can increase the signal to noise ratio of the raw images and thus make it easier to identify discrete, subresolution nanoprobes from blurry two-photon image data. This poses the favorable benefit of knowing more precise locations of nanoprobes inside skin. This thesis demonstrates how the Expectation-Maximization deconvolution algorithm (EM algorithm) can be applied to three-dimensional, two-photon images depicting quantum dot nanoprobes inside human skin. This was accomplished in part by devising a way to deliver nanoprobes inside skin by means of low frequency ultrasound. Many nanoprobes become sparsely scattered inside skin when using this nanoprobe delivery methodology. The scattered nanoprobes resulting from the nanoprobe delivery pose a unique benefit in acquiring an experimental point spread function of the imaging system. This in turn gives an accurate representation of the point spread function that can be used as an input to the EM algorithm. The methodology of utilizing the EM algorithm in this manner is presented.

  19. SLM Microscopy: Scanless Two-Photon Imaging and Photostimulation with Spatial Light Modulators

    PubMed Central

    Nikolenko, Volodymyr; Watson, Brendon O.; Araya, Roberto; Woodruff, Alan; Peterka, Darcy S.; Yuste, Rafael

    2008-01-01

    Laser microscopy has generally poor temporal resolution, caused by the serial scanning of each pixel. This is a significant problem for imaging or optically manipulating neural circuits, since neuronal activity is fast. To help surmount this limitation, we have developed a “scanless” microscope that does not contain mechanically moving parts. This microscope uses a diffractive spatial light modulator (SLM) to shape an incoming two-photon laser beam into any arbitrary light pattern. This allows the simultaneous imaging or photostimulation of different regions of a sample with three-dimensional precision. To demonstrate the usefulness of this microscope, we perform two-photon uncaging of glutamate to activate dendritic spines and cortical neurons in brain slices. We also use it to carry out fast (60 Hz) two-photon calcium imaging of action potentials in neuronal populations. Thus, SLM microscopy appears to be a powerful tool for imaging and optically manipulating neurons and neuronal circuits. Moreover, the use of SLMs expands the flexibility of laser microscopy, as it can substitute traditional simple fixed lenses with any calculated lens function. PMID:19129923

  20. Ultrashort coherence times in partially polarized stationary optical beams measured by two-photon absorption.

    PubMed

    Shevchenko, Andriy; Roussey, Matthieu; Friberg, Ari T; Setälä, Tero

    2015-11-30

    We measure the recently introduced electromagnetic temporal degree of coherence of a stationary, partially polarized, classical optical beam. Instead of recording the visibility of intensity fringes, the spectrum, or the polarization characteristics, we introduce a novel technique based on two-photon absorption. Using a Michelson interferometer equipped with polarizers and a specific GaAs photocount tube, we obtain the two fundamental quantities pertaining to the fluctuations of light: the degree of coherence and the degree of polarization. We also show that the electromagnetic intensity-correlation measurements with two-photon absorption require that the polarization dynamics, i.e., the time evolution of the instantaneous polarization state, is properly taken into account. We apply the technique to unpolarized and polarized sources of amplified spontaneous emission (Gaussian statistics) and to a superposition of two independent, narrow-band laser beams of different mid frequencies (non-Gaussian statistics). For these two sources femtosecond-range coherence times are found that are in good agreement with the traditional spectral measurements. Although previously employed for laser pulses, two-photon absorption provides a new physical principle to study electromagnetic coherence phenomena in classical and quantum continuous-wave light at extremely short time scales. PMID:26698754