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Coupling between two microcavity plasmas in a symmetric, microfabricated dielectric barrier structure has been observed by injecting charge from one of the plasmas into an intervening microchannel. Periodic modulation of the electric field strength in the injector (or electron "donor") cavity has the effect of deforming the acceptor microplasma which exhibits two distinct and stable spatiotemporal modes. Throughout the time interval in which the two microplasmas are coupled electrostatically, the acceptor plasma is elongated and displaced by 75-100 μm (~30% of its diameter) in the direction of the microchannel. The depletion of charge in the microchannel results in an immediate transition of the second (acceptor) microplasma to an equilibrium state in which the plasma is azimuthally symmetric and centered within its microcavity. Switching between these two spatial modes requires a shift (in the plasma centroid) of ~80 μm in <50 ns which corresponds to a velocity of 1.6 km/s. Precise control of this plasma phase transition through device fabrication, and modulation of the donor plasma electric field, suggest applications of this plasma coupling and charge transport mechanism to signal processing, photonics, and electromagnetics. [ABSTRACT FROM AUTHOR]

The diatomic collisional intermediate responsible for the formation of an electronically excited molecule by teratomic recombination has been observed in both the spectral and temporal domains by laser spectroscopy. We report experiments demonstrating thermal Xe(6s[3/2]2)-Xe(5p6 1S0) atomic collision pairs to be the immediate precursor to the formation of Xe*2(a³Σ+u, A¹Σ+u) by the three body process: Xe*(6s)+2Xe → Xe*2 + Xe, where the asterisk denotes an excited electronic state. Photoassociating Xe(6s)-Xe atomic pairs by free ← free transitions of the collision complex interrupts the production of the electronically excited Xe dimer, thereby suppressing Xe2 spontaneous emission in the vacuum ultraviolet (VUV, λ ~ 172 nm, A¹Σ+u → X¹Σ+g). Intercepting Xe(6s)-Xe pairs before the complex is stabilized by the arrival of the third atom in the teratomic collision process selectively depletes the pair population in a specific Franck-Condon region determined by the probe laser wavelength (λ). Measurements of the variation of VUV emission suppression with λ provide a spectral signature of the [Xe(6s[3/2]2) - Xe(¹S0)]* complex and map the probe laser wavelength onto the thermal energy (∊″) of the incoming collision pairs. [ABSTRACT FROM AUTHOR]

Coupled oscillators are prevalent in nature and fundamental to fields as disparate as astrophysics, photonics, the mechanical sciences, and geophysics. Theory has identified singularities in the response of coupled oscillators, known as exceptional points (EPs), that are associated with non-Hermitian operators and lie at the transition between weak and strong coupling of the oscillator. Although several EPs have been reported or predicted to exist in nanophotonic resonators and Feshbach resonances, for example, tuning the phase of two interfering atomic or molecular coherences near an EP has not been demonstrated previously. We report the observation of an EP associated with a pair of interfering atomic coherences in Rb, oscillating at 386.3 and 384.2 THz, and confirm the theoretical prediction of an abrupt phase shift of ∼π/4 as the EP is traversed by independently varying two experimental parameters. Pairs (and trios) of coupled coherences in thermal Rb atoms are established among the 7s1/2, 5d5/2, 5p3/2, and 5s1/2 states in pump–probe experiments with <200 fs laser pulses, and observed directly in the temporal and spectral domains through the ensuing quantum beating in the ∼2–36 THz interval. Interference between the (5d5/2–5p3/2) and (5p3/2–5s1/2) coherences is mediated by the 5p3/2 state and detected through quantum beating in the vicinity of the (5d5/2–5p3/2)–(5p3/2–5s1/2) difference frequency of 2.11 THz which is monitored by a parametric four-wave mixing process. Phase of this composite atomic oscillator is first controlled by varying the mean Rb–Rb nearest neighbor distance (⟨R⟩) in a thermalized vapor. A discontinuous transition of (0.8 ± 0.2) ∼ π/4 radians in the phase of the coupled oscillator occurs when ⟨R⟩ is varied over the ∼80–90 nm interval, a phase shift associated with the transformation of a broadband, dissipative oscillator (characterized by a Fano interference window) into a strongly-coupled system resonant at 2.1 THz. [ABSTRACT FROM AUTHOR]

Bound←bound transitions of the Xe dimer at small internuclear separation (R < 4.0 Å) have been observed in the 545-555 nm and 675-800 nm spectral regions by laser spectroscopy in the afterglow of a pulsed Xe microplasma with a volume of ∼160 nl. Transient suppression of Xe2 A¹Σu+ (Ou+) → X¹Σg+ (Og+) emission in the vacuum ultraviolet (∼172 nm), induced by laser excitation of Ωg ← a³Σu+ (1u,Ou-) [Rydberg←Rydberg] transitions of the molecule, has confirmed the existence of structure between 720 and 770 nm (reported by Killeen and Eden [J. Chem. Phys. 84, 6048 (1986)]) but also reveals red-degraded vibrational bands extending to wavelengths beyond 800 nm. Spectral simulations based on calculations of Franck-Condon factors for assumed Ωg ← a³Σu+ transitions involving Ω = 0±,1 gerade Rydberg states suggest that the upper level primarily responsible for the observed spectrum is an Ω = 1 state correlated, in the separated atom limit, with Xe(5p6 ¹S0) + Xe(5p5 6p) and built on a predominantly A²Π3/2g molecular ion core. Specifically, the spectroscopic constants for the upper state of the 1g ← 1u,Ou± absorptive transitions are determined to be Te = 13 000 ± 150 cm-1, ωe′ = 120 ± 10 cm-1, ωexe′ = 1.1 ± 0.4 cm-1, De = 3300 ± 300 cm-1, and ΔRe = Re′- Re″ = 0.3 ± 0.1 Å which are in general agreement with the theoretical predictions of the pseudopotential hole-particle formalism, developed by Jonin and Spiegelmann [J. Chem. Phys. 117, 3059 (2002)], for both the (5)1g and (3)Og+ states of Xe2. These spectra exhibit the most extensive vibrational development, and provide evidence for the first molecular coreswitching transition, observed to date for any of the rare gas dimers at small R (<4 Å). Experiments in the green (545-555 nm) also provide improved absorption spectra, relative to data reported in 1986 and 1999, associated with Xe2 Rydberg states derived from the Xe(7p) orbital. [ABSTRACT FROM AUTHOR]

An analytic expression for the electromagnetic enhancement of the spontaneous emission rate and Raman scattering cross-section for an excited atom or molecule in close proximity to a metal nanocylinder has been derived by quantum theory. Coupling of the atomic or molecular optical radiation into the TM0 surface plasmon mode of the nanocylinder results in reradiation by the cylinder, a process that is most efficient when the incident radiation is linearly polarized, with the electric field oriented parallel to the axis of the nanocylinder. For a silver cylinder having a radius and length of 5 and 20 nm, respectively, the enhancement in the spontaneous emission rate is >107 for hω0≃2.4 eV (λ=514 nm), which corresponds to an increase of ≈1014 in the Raman scattering cross section. This result, as well as the prediction that the atomic dipole generates broadband, femtosecond pulses, are in qualitative agreement with previously reported experiments involving metal nanoparticle aggregates. The theoretical results described here are expected to be of value in guiding future nonlinear optical experiments in which carbon nanotubes or metal nanowires with controllable physical and electrical characteristics are patterned onto a substrate and coupled with emitting atoms or molecules. [ABSTRACT FROM AUTHOR]

Two well-developed Rydberg series of atomic iodine, built on the ...5s[sup 2]5p[sup 4] [sup 3]P[sub 1] ion core and assigned to nd[2][sub 5/2] and ns[1][sub 3/2] states with principal quantum numbers as high as n=47, have been observed by two photon (566≤λ≤600 nm) ionization of I(6s [sup 2]P[sub 3/2]), and time-of-flight photoelectron spectroscopy and mass spectrometry. The data reported here extend the nd[2][sub 5/2] and ns[1][sub 3/2] series by 27 and 23 terms, respectively. The limit for both series, 91 387.9±1.3 cm-1, revises upwards by 5.8 cm-1 the value for the I[sup +]([sup 3]P[sub 1]) state energy suggested by Minnhagen in 1962 [Ark. Fys. 21, 415 (1962)]. The quantum defects for the nd[2][sub 5/2] and ns[1][sub 3/2] series were determined to be 2.44±0.03 and 4.03±0.02, respectively. Several terms of a third, weaker series were also detected and tentatively assigned to nd[2][sub 3/2] states, also having the [sup 3]P[sub 1] ion core. Photoelectron peaks associated with direct, five photon ionization of I[sub 2] have been observed and are attributed to electronic autoionization of A [sup 2]Π[sub (3/2)u] ion core Rydberg states into the X [sup 2]Π[sub (1/2)g,(3/2)g] ionization continua. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the growth of gallium arsenide irradiated with ultraviolet laser light in a metalorganic chemical vapor deposition reactor. Information on laser photochemical vapor deposition; Methodology of the study; Results and discussion.

The B 1Σ+u←a 3Πg transition of Cd2 (natural abundance) and 114Cd2 has been observed by laser excitation spectroscopy and analyzed. By exciting the Cd2 B←a transition in the visible (560≤λ≤730 nm) while monitoring B 1Σ+u→X 1Σ+g (bound→free) emission in the ultraviolet (∼270–310 nm), more than 40 red-degraded vibrational bands were recorded. Analysis of the spectrum has yielded vibrational constants for both the a 3Πg and B 1Σ+u states: ωe″=153.6±4.0 cm-1, ωe″xe″=0.52±0.06 cm-1, ωe′=105.3±1.0 cm-1, and ωe′xe′=0.44±0.03 cm-1. In addition, ΔRe≡ReB-Rea was determined to be 0.31±0.03 Å. Rotational structure has been partially resolved for 114Cd2 bands in the 620–655 nm and 719–723 nm regions, and the spontaneous emission lifetime of the a 3Πg state and the rate constant for quenching of Cd2 (a 3Πg) by collisions with background Cd atoms have been determined to be 8.6±2.5 μs and (2.2±0.3)×10-13 cm3 s-1, respectively. Also, analysis of the B→X emission (Condon internal diffraction) spectra produced when specific B 1Σ+u vibrational levels are populated has yielded ReX-ReB=0.95±0.02 Å. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Inter-Rydberg transitions of Ar2 in the green (∼460–530 nm) have been studied by intracavity, laser absorption spectroscopy. All five Hund’s case (c) members of the Aπu5p manifold, predicted by the guidelines established by Mulliken [J. Chem. Phys. 52, 5170 (1970)] for Xe2 and later adapted by Chang and Setser [J. Chem. Phys. 69, 3885 (1978)] for Ar2, have been observed. The molecular transitions originate from Aσg4s(1u,0-u) and terminate on the A2 Σ+ 1/2 u ion core, 3Πg on the A2 Σ+ 1/2 u ion co-derived (5p Rydberg electron 0-g, 0+g, 2g, 1g, and 1g. Transitions involving three of these are strongly red degraded [revealing that Re4s(1u, 0-u)

Absolute photoabsorption cross sections for the lowest excited state (4 2Γ) of Kr2F and the ground state (1( 1/2 )u) of Kr+2 have been measured in the visible and ultraviolet (Kr2F: 248, 308, 335–600 nm; Kr+2 : 360–500 nm). As predicted by theory, the Kr2F spectrum is dominated by the 9 2Γ←4 2Γ band which peaks below 340 nm and correlates with the Kr+2 2( 1/2 )g ←1( 1/2 )u transition. However, Kr2F(4 2Γ) and Kr+2 (1( 1/2 )u) both absorb more strongly for wavelengths beyond ∼450 nm than expected, apparently owing to a nonthermalized Kr+2 vibrational distribution. Despite interference from Kr2F stimulated emission between ∼350 and 460 nm, the experimental results show the Kr2F(4 2Γ) and Kr+2 absorption profiles to be similar for λ≥460 nm but diverging rapidly as λ increases from 335 to 360 nm. At 360 nm, the absorption cross sections differ by a factor of 3. Contrary to theoretical expectations, the Kr2F absolute absorption cross section is consistently smaller (typically <40%) than that for Kr+2 which suggests that the impact of F- on the Kr+2 oscillator strengths is significant. [ABSTRACT FROM AUTHOR]

Excitation spectra of the 5s 3Σ+u(1u,0-u) state of the Kr2 molecule have been obtained in the wavelength interval 335≼λ≲545 nm by monitoring atomic Kr emission at 758.7 nm (5p[1/2]0→5s[3/2]1) that accompanies dye laser excitation of the neutral excited molecule. The dominant peaks in the spectrum are identified as arising from np 3Πg←5s 3Σ+u Rydberg transitions where 7≤n≤18. The series limit and quantum defect δ for this series have been determined to be 28 471.9±3.9 cm-1 (351.12±0.05 nm) and 2.629±0.004, respectively, and the vibrational frequency ωe of the 5s 3Σ+u(1u,0-u) excimer has been estimated to be ∼195 cm-1. All of the observed Rydberg states have an A 2Σ+1/2u[1(1/2)u] ion core. Comparison of the np 3Πg←5s 3Σ+u series limit and the ionization potential of Kr* 5s[3/2]2 shows that the A 2Σ+1/2u ground state dimer ion is ∼0.55 eV more deeply bound than is the Kr2 5s 3Σ+u neutral species. Also, dissociation energies of the np 3ΠgRydbergs are shown to be nearly identical to that of the A 2Σ+1/2u dimer ion state. A second series of spectral peaks has also been identified and assigned to n′p 3Σ+g ←5s 3Σ+u transitions. Analysis of the series yielded a limit of 28 424±120 cm-1 and a quantum defect of 3.39±0.04. Two members of a third, unidentified series having a quantum defect of 3.24±0.01 and also converging to A 2Σ+1/2u (v′=0) have been observed. Absolute photoabsorption cross sections for the np 3Πg←5s 3Σ+u (7≤n≤18) transitions have also been determined. [ABSTRACT FROM AUTHOR]

Transient absorption spectra of rare gas dimer Rydberg transitions in the ultraviolet, visible, and near infrared (220≤λ≤900 nm) spectral regions have been observed in electron beam excited rare gases. The most prominent molecular bands for He2, Ne2, Ar2, Kr2, and Xe2 are assigned to the mp 3Πg←ns 3Σ+u (He[ATOTHER]@B:[/ATOTHER]n=2, 3≤m≤10; Ne[ATOTHER]@B:[/ATOTHER]n=3, 4≤m≤10; Ar[ATOTHER]@B:[/ATOTHER]n=4, 5≤m≤15; Kr[ATOTHER]@B:[/ATOTHER]n=5, 6≤m≤16; Xe:n=6, 8≤m≤11) Rydberg series of the dimer. Adiabatic ionization potentials, relative to the ns 3Σ+u state, are determined by extrapolation of the series to their limits (m→∞) to be 34 361.4±30 cm-1 (4.260±0.004 eV) for He2, 34 396.3±25 cm-1 (4.265±0.003 eV) for Ne2, 29 351.9±15 cm-1 (3.639±0.002 eV) for Ar2, 28 428.5±10 cm-1 (3.525±0.001 eV) for Kr2, and 26 664.5±250 cm-1 (3.306±0.031 eV) for Xe2. Absorption bands which are ascribed to m’p 3Σ+g←ns 3Σ+u Rydberg series of Ne2(m’=4,6,8), Ar2(5≤m’≤10), Kr2(6≤m’≤10), and Xe2(m’=8,9) are also reported, and the ns 3Σ+u ionization potentials found to be identical to the respective values quoted above. All of the observed molecular Rydberg states have an A 2Σ+1/2u ion core. The lowest vibrational quanta (ΔG1/2) for the ns 3Σ+u states are determined from vibronic structure in the Rydberg transitions to be 1723 cm-1 for He2, 539 cm-1 for Ne2, 302 cm-1 for Ar2, 172 cm-1 for Kr2, and 135 cm-1 for Xe2, and are consistent with previously reported values. The instability of the ns 3Σ+u metastable state with respect to the dimer ion core potential [D0(A 2Σ+1/2u)-D0(ns 3Σ+u)] is calculated to be 0.508±0.004 eV for He2, 0.681±0.003 eV for Ne2, 0.572±0.002 eV for Ar2, 0... [ABSTRACT FROM AUTHOR]

Rydberg series of Ar2 and Kr2 have been observed in the visible and ultraviolet (350≤λ≤560 nm) absorption spectra of the lowest-lying metastable states of the dimer (ns 3Σ+u(1u, 0-u); Ar: n=4, Kr: n=5). The most prominent series for Ar2 and Kr2 are assigned to ns 3Σ+u → mp 3Πg (Ar: 5≤m≤15; Kr: 6≤m≤16) Rydberg transitions of the diatomic molecule and adiabatic ionization potentials are determined from an extrapolation of the series to their limits (m → ∞) to be 116 356±340 cm-1 (14.43±0.04 eV) for Ar2 and 104 616±150 cm-1 (12.97±0.02 eV) for Kr2. The dissociation energies of the A2Σ+u[1( (1)/(2) )u] dimer ion states of Ar2 and Kr2 are, therefore, 1.33±0.04 and 1.03±0.02 eV, respectively. All of the observed Rydberg states have an A2 Σ+u ion core. Binding energies of the lowest observed 3Πg states, were determined to be (1.331±0.005) eV for Ar2 and (1.030±0.001) eV for Kr2. The quantum defects for the Ar2 and Kr2 series (1.656±0.006 and 2.621±0.004, respectively) and ωe-2ωexe for the ns 3Σ+u metastable state of Ar2 (303±20 cm-1) and Kr2 (172±10 cm-1) were also measured and the vibrational frequencies are consistent with previously reported values. Absorption peaks which are attributed to ns 3Σ+u→m’p 3Σ+g Rydberg transitions of Ar2 (6≤m’≤10) and Kr2 (7≤m’≤10) are also reported. [ABSTRACT FROM AUTHOR]

The ultraviolet and visible absorption spectra of potassium vapor–xenon mixtures have been studied for [K] and [Xe] as large as 7×1017 and 4×1019 cm-3, respectively. Collision-induced absorption is observed in the ultraviolet (285≤λ≾370 nm) for the 4s → nf, nd (4≤n≤8) transitions but peak absorption lies an average of ∼0.6 nm to the red side of the position of the electric dipole forbidden line. The 4s → 4f, 5f transitions, in particular, are quite strong, having peak reduced absorption coefficients measured to be 1.1×10-39 and 2.6×10-40 cm5, respectively. Also, the KXe (C 2Σ) excimer has been observed in absorption for the first time. Absorption at the band peak (reduced absorption coefficient of ∼2×10-40 cm5 at λ=507 nm) is roughly two orders of magnitude weaker than that for the analogous bands of CsXe and RbXe and is displaced at least 5 nm to the blue side of the peak (∼520 nm) in the emission spectrum. Six reproducible undulations to the blue side of the absorption maximum display a periodicity of 111±17 cm-1. [ABSTRACT FROM AUTHOR]

The bound→free absorption band recently observed in a 114CdI laser discharge [Greene and Eden, Opt. Comm. (1985)] is shown to arise from absorption by the B 2Σ excited state of 114CdI to a previously unobserved level lying ∼4.3×104 cm-1 above ground. Pumping of the absorptive transition with a pulsed blue dye laser strongly suppresses gain (and, hence, laser output power) on the B→X band in the red (657 nm). Therefore, this constitutes the first known report of an ionic excited state→covalent absorption band [i.e., (M+X-)+hω→M*+X; M, X=metal and halogen atoms, respectively] for any of the group IIB metal halides or rare gas–halide laser molecules. Also, ωe for the B 2Σ state of 114CdI is >=110 cm-1 (considerably larger than an existing value in the literature) and the terminal level for this blue absorption band is tentatively assigned to a dissociative 2Σ state correlated with the Cd(5p 3PJ)+I separated atom limit. [ABSTRACT FROM AUTHOR]

The emission spectrum of Br2 in the ultraviolet (180≤λ≤400nm) has been examined in electron beam pumped rare gas–hydrogen bromide (HBr) gas mixtures. Temporally resolved and rare gas pressure-dependent studies of the Br2 fluorescence at 292 (D’→A’), 312, 334, and 358 nm indicate that the formation processes for Br2 ion pair states differ for Ne and Ar diluents. Experimental evidence suggests that Br2 excited states in the first tier [correlated with Br-(1S0)+Br+(3P2)] in Ar/HBr mixtures are formed by ion–ion recombination in which Br+(3P2) is produced by charge transfer between Ar+(2P) and HBr, followed by predissociation of HBr+(A 2Σ+). In Ne buffer, Br2 states well above D’ are apparently produced by Penning ionization of HBr by Ne 3s 3P followed by recombination of Br+(3P0,1,2 ) ions with Br-(1S0). Also, Ar is effective in collisionally relaxing the lowest manifold of six Br2 ion pair states but both Ne and Ar are poor quenchers of the D’(2g) level. [ABSTRACT FROM AUTHOR]

Absolute cross sections for the photoionization of Kr (5s) and Kr2 5s 3Σ+u (1u, 0-u ) at 248 nm have been measured to be (5.7±1.1)×10-19 and (1.4±0.3)×10-18 cm2, respectively. In these experiments, absolute photoelectron densities were measured in real time with a microwave absorption apparatus, and the excited atomic and molecular species were produced and subsequently photoionized by excimer lasers. The measured Kr (5s) cross section is consistent with the upper limit experimentally determined by Dunning and Stebbings [Phys. Rev. A 9, 2378 (1974)] and is close to the theoretical value calculated by Hartquist [J. Phys. B 11, 2101 (1978)]. For Kr2 5s 3Σ+u (1u, 0-u) , the cross section reported here is intermediate to those measured previously for the lowest 3Σ+u states of Ar2 and Xe2. [ABSTRACT FROM AUTHOR]

Absorption from the lowest-lying ion pair state of HgBr (i.e., Hg+–Br-: B 2∑+1/2 ) has been observed by transient absorption spectroscopy in a pulsed, transverse discharge containing a mixture of Ne, N2, and HgBr2 vapor. A highly structured band peaking at ∼447 nm is shown to be associated with charge–transfer transitions from the B 2∑+1/2 state to a higher-lying, covalently bonded (Hg*–Br) state. By pumping the 447 nm transition with a pulsed dye laser while simultaneously monitoring gain on the HgBr (B 2∑+1/2 →X 2∑+1/2 ) band at 502 nm, the absorption cross section for the blue band was measured to be (3.0±1.5)×10-17 cm2 and the saturation intensity for the transition at 447 nm was determined to be 710±50 kW cm-2. [ABSTRACT FROM AUTHOR]

The absorption cross section for the lowest-lying, bound excited state (4 2Γ) of Xe2Cl has been measured at several wavelengths in the ultraviolet (UV). Temporally isolating the excited Xe2Cl species in Xe/Cl2 gas mixtures has been accomplished by producing XeCl molecules in the B state by photoassociation [Xe+Cl+hω → XeCl(B)] at λ=308 nm. Collisional mixing of the lowest lying ion pair states of the excimer subsequently forms the XeCl species in its C state. Following the formation of Xe2Cl* from XeCl(B,C) by a three-body collision, the long radiative lifetime of the trimer (>200 ns) relative to those for the XeCl B and C levels is exploited to ensure that the triatomic molecule is the predominant species when the experiments are performed. A second UV laser pulse depletes the Xe2Cl(4 2Γ) population by photoexcitation [as evidenced by the sudden suppression of the 4 2Γ → 1 2Γ blue-green (λ∼485 nm) fluorescence] and the absorption cross section is determined from the dependence of the degree of fluorescence suppression on the laser intensity. Contrary to the known Xe+21(1/2)u → 2(1/2)gUV absorption profile, Xe2Cl(4 2Γ) exhibits significant absorption at wavelengths as low as 193 nm, whereas the dimer ion absorption at 248 nm is only a fraction of its peak (λ∼340 nm) value. Photoionization of excited Xe2Cl at wavelengths below ∼275 nm may be responsible for the cross sections measured for photon energies as large as 6.4 eV. [ABSTRACT FROM AUTHOR]