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We demonstrate a simple and efficient method for producing ultrathin Bessel ('non-diffracting') light sheets of any color using a line-shaped beam and an annulus filter. With this robust and cost-effective technology, we obtained two-color, 3D images of biological samples with lateral/axial resolution of 250 nm/400 nm, and high-speed, 4D volume imaging of 20 mu m sized live sample at 1 Hz temporal resolution.

An unusual mass tansport behavior has been observed in the dense Pb wetting layer on the Si(111) surface. Mass transport is studied by observing non-equilibrium coverage profile evolution with low energy electron microscopy and micro-low energy electron diffraction (m-LEED). The strong sensitivity of diffraction features to Pb coverage in this system allows the Pb coverage profile to be determined precisely with high spatial resolution using m-LEED. Equilibration of an initial coverage step profile produced by laser induced thermal desorption proceeds by the exchange of mass between two steep coverage gradients that travel in opposite directions with invariant shapes. The coverage profile between these two moving edges unexpectedly exhibits a concave shape that apparently contradicts local mass conservation given by the continuity equation. The equilibration time is independent of Pb coverage above a critical coverage, 1.24 ML, but diverges sharply below. The observed spatio-temporal characteristics and lower cutoff for fast dynamics may signal a very unusual coverage dependence of diffusion or might suggest an exceptional collective super-diffusive mechanism by which diffusion is not driven by the local coverage gradient in the usual way.

We report the piezotionic effects on the photoluminescence (PL) properties of bent ZnO nanowires We find that the piezoelectric field largely modifies, the spatial distribution of the photoexcited carriers in a bent ZnO NW. This effect together with it rain-induced, changes in the energy band structure due to the piezoresistive effects, results in a net redshift of free excitone PL emission from a bent ZnO NW. At the large-size limit this net redshift depends only on the strain parameter, but it is size-dependent if the diameter. of the NW is comparable to that Of the depletion layer. The experimental data obtained using the near-field scanning optical microscopy technique at low temperatures support our theoretical model.

We generate narrowband hyperentangled nondegenerate paired photons using spontaneous four-wave mixing in cold atoms. The entanglement in both time-frequency and polarization is confirmed by correlation measurements and quantum state tomography. © 2011 Optical Society of America.

Spatially resolved photoluminescence (PL) investigations were carried out on ZnO single nanowires, tetrapods, and nanocrystals. The fractional intensity for bound exciton (BX) transitions was shown to be correlated with the size in all these ZnO nanostructures. This size dependency is attributed to the inhomogeneous density distribution of the defects as binding sites for BX in the ZnO nanostructures, in good agreement with a simple model calculation.

We have experimentally determined that a Pb wetting layer grown on Si(111)-7 x 7 is conductive, while In and Ag wetting layers are not, despite the fact that they are all made of metallic atoms. We have further demonstrated that the conduction of the Pb wetting layer at low temperatures plays an important role for the study of low temperature tunneling spectroscopy of metal nanostructures formed on Si(111) substrates. (c) 2008 Elsevier B.V. All rights reserved.

ZnO tetrapods and nanowires were fabricated by a simple method of thermal evaporation of pure Zn powder in the air. These nanostructures, formed in different temperature regions of the same apparatus, displayed distinct photoluminescence (PL) characteristics. Spatially resolved PL measurements on legs of individual tetrapods show that the green luminescence (GL) decreases with decreasing leg diameter, and there was no detectable GL from nanowires grown simultaneously. These PL properties suggest that the green luminescence may not come from surface states, but rather from bulk defects.

THz time-domain spectroscopy is applied to probe the transient conductivity single-walled carbon nanotubes (SWNTs). The ultrafast transport properties and carrier dynamics are examined for different levels of laser excitation. © 2005 Optical Society of America.

Using scanning tunneling microscopy, we have studied the adsorption and intra-half-unit-cell diffusion of a single Ag atom on a Si(111)7x7 surface over a large range of temperatures. Strong asymmetric behaviors in terms of adsorption sites, intra-diffusion barrier and electric field effect for a single Ag atom in the faulted and unfaulted half unit cells were observed, in contrast to many other species on this surface for which negligible asymmetry have been seen. While Ag adsorbs at the corner Si-adatom sites on the faulted half, it finds the center Si-adatom sites more stable for adsorption. The diffusion pathways and barriers for the two halves are thus found very different. Furthermore, it was observed that the diffusion in the unfaulted half unit cell is very susceptible to electric field applied by the STM tips. Our results clearly indicate the importance of the stacking fault in affecting the interaction between a Ag atom and a Si(111)7x7 surface.

The up-conversion processes were investigated in highly doped Er3+-Yb3+ silica fiber pumped by CW or mode-locked Ti:Sapphire laser at 800 nm band. The mechanism is different from that at 980 nm pumped band. The pumping wavelength and power dependence of green, blue and red fluorescence emission were obtained. The up-conversion efficiencies of different doped concentration were investigated. The strong infrared emissions, which limit the efficiency of up-conversion were observed.

We report the first study of femtosecond desorption of CO from Pt(111), using 800 nm laser pulses with durations from 125 fs to 1.5 ps. The results for the CO/Pt system are qualitatively similar to other diatomic molecule systems previously studied and can be understood using the electronic friction model. We also studied the CO desorption yield using frequency-chirped laser pulses of the same pulse duration. With the chirping magnitude of ca. 1.5% in our experiment we did not observe any difference between positive and negative chirping.

The frequency upconversion of Tm-doped fiber pumped by Ti:sapphire tunable laser from 760 nm to 810 nm operating at the wavelength of commercial available laser diode was presented. The efficiencies of 460 nm, 680 nm and 370 nm upconversion emission are charged with different pumping wavelengths at 760-810 nm range. The optimum pumping wavelengths for 460 nm and 370 nm upconversion emission are 765 nm, while for the red upconversion emission of 680 nm, the pumping wavelength is optimized at 791 nm.

Ionization probabilities of NO molecules electronically excited in the A 2∑+ and B 2∏ states have been determined by (1+1) resonance-enhanced, two-photon ionization. Various vibrational levels within these states have been excited prior to ionization. Measurements of the unsaturated ionization signal yields accurate values for the relative detection probabilities of NO of 1:(0.70±0.07): (0.67±0.11) for excitation via the γ(0-0), γ(1-1), and γ(2-2) bands, respectively, and (3.7±0.36)×10-7 and (5.8±0.65)×10-4 for ionization through β(0-0) and β(2-1) bands, respectively. Applying published data for the γ- and β-band transition probabilities allows the deduction of the ionization cross section of A 2∑+ and B 2∏ vibrational states. The respective ionization cross sections are (7.0±0.9)×10-19 cm2, (8.5±0.8)×10-19 cm2, (6.0±1.0)×10-19 cm2 for A 2∑+(v′=0, 1, and 2) and (5.0±0.5)×10-21 cm2 and (1.7±0.2)×10-20 cm2 for B 2∏(v′=0 and 2). These values are based on the experimentally determined cross section for A 2∑+(v′=0). Using a larger theoretical cross section for this state the other cross sections scale accordingly, within the experimental uncertainties. © 1996 American Institute of Physics.

This study used 80-fs pulses of a Ti:sapphire-laser with a repetition rate of 1 kHz to investigate the generation of the second and third harmonics in a plasma of self-induced breakdown in atmospheric air. The performed investigations demonstrated a high efficiency of high-repetition-rate harmonic generation in a plasma of self-induced optical breakdown. The maximum conversion efficiency of the power of fundamental laser radiation to the third harmonic achieved in our experiments was as high as 0.17%. Harmonic generation in the field of strong ultrashort laser pulses is accompanied by the spatial self-action and spectral broadening of both fundamental and harmonic radiation.

The process of desorption for the system of O2/Pd(111) under excitation by 100 fs pulses of visible light has been examined. Molecular desorption is found to occur with high efficiency and a nonlinear dependence on laser fluence. Direct time-domain measurements using a two-pulse correlation scheme reveal a dominant subpicosecond response together with a weaker, but significant correlation persisting for tens of picoseconds. These results imply a desorption pro-cess driven by the high electron temperatures produced by the femtosecond laser radiation. The slower component of the correlation response is interpreted as an enhancement of the desorption rate by adsorbate vibrational excitation. © 1994 American Institute of Physics.

Quantum-state distributions are reported for nitric oxide (NO) molecules desorbed from a Pd(111) surface at a base temperature of 140 K by laser pulses of 400 fs duration. Significant vibrational populations are observed in the V; = 0, 1, and 2 levels. For a femtosecond laser fluence capable of producing substrate electronic temperatures of ∼ 4500 K, the vibrational distribution of the desorbed NO molecules is roughly thermal with an average degree of vibrational excitation corresponding to a temperature of 2900 K. These measurements can be regarded as the reverse of the usual vibrational relaxation measurement in that here energy flows from the substrate to the adsorbate vibration. The high degree of excitation of the NO intramolecular vibration can be attributed directly to efficient coupling to the electron-hole pairs generated in the Pd substrate by the femtosecond laser pulse. The process is modeled by calculating electronic and lattice temperatures for the Pd substrate and then incorporating the electron temperature profile into a master equation for the NO vibrational populations. The analysis permits an effective coupling constant of ∼ 15 cm-1 to be inferred for the interaction between the substrate electronic excitation and the intramolecular vibration. © 1993.

The rotational energy distribution of nitric oxide desorbed from a Pd(111) surface has been determined directly at high surface temperature by means of laser heating of the substrate. For a surface temperature of Ts = 1100 ± 100 K, the rotational energy distribution of the desorbed NO could be described as thermal, but with a significantly lower temperature of Tr = 640 ± 40 K. © 1990.

A pulsed, narrow-band FA (II) color center laser is described which provides peak powers up to 20 kW with a band-width below 0.3 cm-1 in the wavelength range from 2.4 μm to 2.9 μm. A frequency-doubled Nd: YAG laser is used as a pump source. The high peak power and short pulse length makes this layer system very attractive for time-resolved infrared spectroscopy on a nonosecond timescale. © 1981.

The CO 2 laser-induced dissociation of nitromethane (CH 3NO 2) is investigated through luminescence and laser-induced flourescence studies. The main reaction channel is found to involve fission of the CN bond. Both ground state and electronically excited NO 2 molecules are produced. Emission from electronically excited diatomic fragments is also observed. Interesingly, at pressures below 0.5 Torr the CN * (B 2Σ + radical is produced unimolecularly. The mechanism of the fragmentation is discussed. © 1980.

Two-photon resonantly enhanced parametric generation processes have generally been described using time-dependent perturbation theory. In this paper we show that a theory of two-photon coherent effects can be used to derive and explain these nonlinear mixing processes. Our technique makes use of the adiabatic following (AF) approximation to obtain solutions to a vector model describing the two-photon resonance. We show that the usual results for the nonlinear susceptibilities correspond to the r → vector of Feynman, Vernon, and Hellwarth adiabatically following the γ→ vector in the small-angle limit. Consequently, the theory allows a natural extension to large angles, and power-dependent nonlinear susceptibilities are obtained. We then use these AF results for the polarization to study the propagation of pulses nearly resonant with a two-photon transition, and we demonstrate that the pulse reshaping is due to the two related effects of a nonlinear pulse velocity and self-phase modulation.

A 16-μm source based upon the combined effects of stimulated rotational Raman scattering and four-wave mixing in gaseous para-hydrogen has been experimentally demonstrated. The input beams were synchronized pulses from a ruby laser and a CO2 TEA laser. Pulses with ∼2 μJ of energy were generated at 627.8 cm-1.

Amplitude modulation and temporal compression of 10-μ light at a frequency up to 80 MHz were demonstrated using a dispersive molulator - a NH3 vapor cell with a near-resonant time-dependent transition frequency controlled externally via the Stark effect. The peak output intensity was observed to be higher than the input intensity, showing that compression effects due to the time-dependent dispersion are essential in determining the output waveform.

Using a pulsed, time resolved IR-UV double resonance technique, we have measured initial and final state specific rates for collision-induced rotational and spin-orbit transitions in NO in its (X 2Π, v=2) vibronic state. A systematic study of the rates was done for initial and final rotational states with J between 1/2 and 35/2, for both Ω=1/2 and the Ω=3/2 spin-orbit components of the X 2Π state. Collision partners were room temperature NO, He, Ar, N2, CO and SF6. No propensity rules favoring ΔΩ=0 or ΔJ=0, ±1 were observed, except in NO-He collisions, where ΔΩ=0 was favored. The state-to-state rates do not vary much with initial state and fall off slowly with increasing ΔJ. Total cross sections for collision-induced rotational transitions were found to be tens of Å2, insensitive to initial state, and correlated with the size of the collision partner. © 1982 American Institute of Physics.

The authors report relative ionization probabilities as a function of vibrational excitation for v′= 0, 1, 2 in the A2 Σ+ states of NO. The measurements have been performed by means of (and at wavelengths appropriate for) the single-color (1 + 1) REMPI process. The experimental procedure is described, and the results are analyzed. These findings are the results required to infer accurate vibrational population distributions for NO in its ground electronic state from (1 + 1) REMPI spectra.

Gaseous chlorine perchlorate, ClOClO3, is found to be a major photolysis product of chlorine dioxide (OClO). Experiments were performed at room temperature with both continuous wave (mercury lamp) and pulsed (XeCl UV laser) light sources. The technique of time-resolved IR spectral photography (TRISP) was used to monitor the growth of the strong 1282-cm-1 ClOClO3 IR band following the application of a single ∼35 ns long, ∼70 mJ/cm2, XeCl laser pulse to a mixture of ∼30 torr of OClO and ∼700 torr of N2. It was found that under these conditions this band forms with a time constant of ∼1 μs. A transient IR band of unknown origin at ∼1232 cm-1 was also observed to develop on the same time scale. © 1982 American Chemical Society.

Resonantly enhanced two-photon ionization has been used to obtain detailed information about the rotational and electronic relaxation in pulsed supersonic expansions of nitric oxide seeded in helium and argon. Due to the sensitivity of the method we were able to measure rotational distributions up to high quantum numbers J″ > 24.5. Measurements were made for stagnation pressures (p0) and nozzle diameters (d) in the range 0.44≤p 0d≤22 [Torr cm] for NO/Ar beams, and 0.88≤p0d≤36 [Torr cm] for NO/He beams. In general non-Boltzmann rotational population distributions were observed. Furthermore, we found that for NO/He beams, the two electronic substates 2Π1/2 and 2Π 3/2 of NO were not in local equihbrium. These observations can be understood in terms of a simple model using state-to-state collision cross sections combined with the empirical hydrodynamic equations to describe the isentropic expansions. © 1984 American Institute of Physics.

Application of laser excitation and detection techniques has allowed us to perform state-specific studies of the scattering of a molecular beam of vibrationally excited NO molecules from a Ag(111) surface. State-specific angular and velocity distributions have been obtained which indicate a direct-inelastic type of scattering mechanism. This information is combined with rotational and electronic (spin-orbit) distributions to determine the probability for survival of vibrational excitation, SP = 0.9. © 1986.

Summary form only given. The surface optical second harmonic generation (SHG) technique has been applied to study clean crystalline Si(111) surfaces. Analysis of the polarization dependences of the SHG process has yielded information on the symmetry of the reconstructed surfaces. A method for identifying mirror symmetry was developed and utilized in precise measurements on the reconstructed surfaces as well as in monitoring the creation of additional mirror planes during the 2 multiplied by 1 yields 7 multiplied by 7 surface phase transformation.

Summary form only given. The authors report here the survival probability for the scattering of a well-characterized molecular beam of vibrationally excited NO from a LiF(100) surface. Laser spectroscopic techniques are combined with molecular beam techniques to perform state-to-state scattering experiments. In these experiments, two laser beams intersect a supersonic molecular beam of NO. The state-to-state scattering experiments reported here give details of the scattering from an initial single electronic, vibrational, and rotational state with a narrow velocity distribution into specific final channels on collision with a clean well-defined surface and permit a more careful comparison with theoretical calculations than is possible with static gas sample techniques.

Summary form only given. The authors report that the optical probe of second-harmonic generation (SHG) can be used to monitor the change in structure of the silicon (Si) surfaces induced by ion bombardment and the deposition of Si atoms. By relating the surface nonlinear susceptibility to the degree of disordering of the surface, the area of the surface disrupted by each incoming ion or atom was inferred.

Results are presented on the desorption of nitric oxide (NO) from a Pd(111) surface under exposure to visible laser radiation in a 200-fs pulse. The desorption process for this prototype system of a diatomic molecule chemisorbed on a nonreactive metal surface has been investigated by measuring the yield and energy distribution of the desorbed molecules. The salient features of the experiment are described, with emphasis on the internal energy distributions of the desorbed NO molecules. A rotational energy distribution for desorbed NO molecules in the ground vibrational and electronic states is shown and discussed.

We report a nondestructive optical probing technique for superconducting films, by which a cross-sectional gradient of the local transition temperature Tc and a two-dimensional map of the local critical current I c of an Al film were obtained. The two-dimensional map clearly shows a variety of defects of the Al film. Some of them can be correlated to visible pinholes.

We show that, by virtue of the linewidth reduction provided by counter-propagating beams, it is possible to use the optical Stark shift to sweep a two-photon resonance through the sum frequency of the applied light while simultaneously satisfying the conditions required for optical adiabatic rapid passage. Consequently, the application of a near-resonant pulse of light can result in complete population inversion of a two-photon transition.

The authors observed voltage pulses having half-widths of less than 500 ps generated by constant-current-biased superconducting Pb variable thickness microbridges driven normal by short (3 - 5 ps) light pulses. This represents a step to generate even shorter pulses, which according to an analysis of the Rothwarf-Taylor equations should be possible. The ultimate width should be equal to the phonon pair-breaking time which, for materials such as Nb, can be a few picoseconds. In addition to monitoring the voltage pulses directly use was made of a novel adoption of the optical autocorrelation technique having a time resolution limited only by the laser pulse width. It is pointed out that even shorter voltage pulses, and therefore greater potential for device applications, can be achieved by direct injection of quasiparticles.