Cs-Ar optical amplifier with a saturation intensity of 10†kW-cm-2 and single-pass extraction efficiency of 28% at 852.2†nm.

Optical amplification by the stimulated emission of Cs(6p2P3/2)-Ar atomic pairs, observed in pump-probe experiments over a ∼290 GHz-wide spectral region lying to the red of the Cs D2 line (852.1 nm), has been realized by photoexciting thermalized, ground state Cs-Ar atoms in the 834-849 nm wavelength interval. When the gain medium is pumped at the peak of the CsAr B2Σ1/2+←X2Σ1/2+ transition at 836.7 nm, maximum gain occurs between 852.2 nm and 852.3 nm and >28% of the energy stored in the upper laser level is extracted with 8 ns (FWHM) probe pulses in a single pass. From the measured rate of saturation of the extracted pulse energy with increasing probe intensity, the product of γ0L and Esat, the saturation pulse energy, is measured directly to be 400 ± 20 µJ and the lower limit for the saturation intensity (Isat) of this amplifier is estimated to be 10 kW-cm-2 at 852.2 nm. Circularly polarizing the optical pump beam increases the optical-to-optical conversion efficiency by 20%, and the storage lifetime of the upper laser level is observed from temporally-resolved gain spectra to be 5 ± 1 ns. Pump excitation spectra also reveal a significant contribution from Ar-Cs-Ar (3-body) photoassociation and suprathermal Ar atoms generated by the dissociation of the CsAr B2Σ1/2+ complex. Multipass-amplifier geometries with broad-bandwidth probe signals are expected to yield upper state energy extraction efficiencies above 50%. This alkali-rare gas amplifier demonstrates the efficiencies available with the storage of energy in, and optical extraction from, excited atomic collision pairs.

Markov-Airy description of optical scattering, waveguides, and resonators.

Representing the reflection and transmission of light by multilayer dielectric structures in terms of Markov chains provides an intuitive, precise, and computationally efficient framework for calculating the dispersive properties (group delay, group delay dispersion, and higher order phase derivatives) of ultrafast laser mirrors and other broadband optical components. The theoretical basis for the Markov-Airy formalism is described, and its ability to precisely determine the dispersive characteristics of multilayer dielectric structures is demonstrated here. Exact expressions for the three lowest order phase derivatives for a dielectric mirror and waveguide are derived, and Markov-Airy-based numerical simulations of specific mirror designs are compared with results obtained with the conventional transition matrix formalism.

Manipulating excited state hyperfine level populations in an atomic laser through electronic spin polarization: controlling upper laser level degeneracy and small Signal Gain.

Anisotropic coherent radiation has been generated from an isotropic medium, in the absence of an external magnetic field, by the spin polarization of an atomic excited state. Lasing on specific hyperfine lines of the 6p2P32→6s2S12 (D2) transition of Cs at 852.1 nm has been realized by photoexciting Cs-rare gas thermal collision pairs with a circularly-polarized (σ+) optical field. Subsequent dissociation of the transient Cs-rare gas B2Σ12+ diatomic molecule selectively populates the F = 4, 5 hyperfine levels of the Cs 6p2P32 state. Not only does electronic spin polarization of the upper laser level yield circularly-polarized coherent emission, but the effective degeneracy (g2) of the 6p2P32 state is altered by the non-statistical hyperfine state population distribution, thereby permitting control of the laser small signal gain with an elliptically-polarized pump optical field. The D2 laser efficiency and output power correlate directly with the molecular orbital structure of the Cs-rare gas B2Σ+ state in the region of internuclear separation at which the diatomic complex is born.

Mode suppression of 53 dB and pulse repetition rates of 2.87 and 36.4 GHz in a compact, mode-locked fiber laser comprising coupled Fabry-Perot cavities of low finesse (F = 2).

Multiplication of the pulse repetition frequency (PRF) of a compact, mode-locked fiber laser by a factor as large as 25 has been achieved with two coupled Fabry-Perot (FP) resonators of low finesse (F = 2). Reducing the FP finesse by at least two orders of magnitude, relative to previous pulse frequency multiplication architectures, has the effect of stabilizing the oscillator with respect to pulse-to-pulse amplitude, dropped pulses, and other effects of cavity detuning. Coupling two Fabry-Perot cavities, each encompassing a 3.3-3.6 cm length of fiber, in a hybrid geometry resembling that of the coupled-cavity laser interferometer has yielded side mode suppressions ≥ 50 dB while simultaneously doubling the laser PRF to 2.87 GHz. Pulses approximately 3.9 ps in duration (FWHM) are emitted at intervals of 27.5 ps, and in groups (bursts) of pulses separated by 350 ps. Thus, the PRF within the pulse bursts is 36 GHz, a factor of 25 greater than the free spectral range for a conventional mode-locked cavity having a length of 6.9 cm. Experimental data are in accord with simulations of the phase coherence and temporal behavior of the mode-locked pulses.

Spin Polarization of Rb and Cs np

We report the selective population of Rb or Cs np ^{2}P_{3/2} (n=5, 6; F=4, 5) hyperfine states by the photodissociation of a transient, alkali-rare gas diatomic molecule. Circularly polarized (σ^{-}), amplified spontaneous emission (ASE) on the D_{2} line of Rb or Cs (780.0 and 852.1 nm, respectively) is generated when Rb-Xe or Cs-Xe ground state collision pairs are photoexcited by a σ^{+}-polarized optical field having a wavelength within the D_{2} blue satellite continuum, associated with the B^{2}Σ_{1/2}^{+}←X^{2}Σ_{1/2}^{+} (free←free) transition of the diatomic molecule. The degree of spin polarization of Cs (6p ^{2}P_{3/2}), specifically, is found to be dependent on the interatomic distance (R) at which the excited complex is born, a result attributed to the structure of the B^{2}Σ_{1/2}^{+} state. For Cs-Xe atomic pairs, tuning the wavelength of the optical field from 843 to 848 nm varies the degree of circular polarization of the ASE from 63% to almost unity because of the perturbation, in the 5≤R≤6 Å interval, of the ^{2}Σ_{1/2}^{+} potential by a dσ molecular orbital associated with a higher ^{2}Λ electronic state. Monitoring only the Cs 6p ^{2}P_{3/2} spin polarization reveals a previously unobserved interaction of CsXe (B^{2}Σ_{1/2}^{+}) with the lowest vibrational levels of a ^{2}Λ state derived from Cs (5d)+Xe. By inserting a molecular intermediate into the alkali atom excitation mechanism, these experiments realize electronic spin polarization through populating no more than two np ^{2}P_{3/2} hyperfine states, and demonstrate a sensitive spectroscopic probe of R-dependent state-state interactions and their impact on interatomic potentials.

Interruption of electronically excited Xe dimer formation by the photoassociation of Xe(6s[3/2]2)-Xe(5p(6) (1)S0) thermal collision pairs.

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(5p(6) (1)S0) atomic collision pairs to be the immediate precursor to the formation of Xe2 (∗)(a(3)Σu (+),A(1)Σu (+)) by the three body process: Xe(∗)(6s) + 2Xe ⟶ Xe2 (∗) + 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, A(1)Σu (+)→X(1)Σg (+)). 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((1)S0)](∗) complex and map the probe laser wavelength onto the thermal energy (ϵ″) of the incoming collision pairs.

Xe2 gerade Rydberg states observed in the afterglow of a microplasma by laser spectroscopy of a(3)Σ(+)(u)(1(u), O(-)(u)) absorption in the green (545-555 nm) and near-infrared (675-800 nm).

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 A(1)Σ(+)(u)(O(+)(u)) --> X(1)Σ(+)(g)(O(+)(g)) emission in the vacuum ultraviolet (∼172 nm), induced by laser excitation of Ω(g) ← a(3)Σ(+)(u)(1(u), O(-)(u)) [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 Ω(g) ← a(3)Σ(+)(u) 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(5p(6) (1)S0) + Xe(5p(5) 6p) and built on a predominantly A(2)Π3/2g molecular ion core. Specifically, the spectroscopic constants for the upper state of the 1(g) ← 1(u), O(±)(u) absorptive transitions are determined to be Te = 13,000 ± 150 cm(-1), ω'(e) = 120 ± 10 cm(-1), ω'(e)x'(e) = 1.1 ± 0.4 cm(-1), De = 3300 ± 300 cm(-1), and ΔR(e) = R'(e) = R''(e) = 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)O(+)(g) states of Xe2. These spectra exhibit the most extensive vibrational development, and provide evidence for the first molecular core-switching transition, observed to date for any of the rare gas dimers at small R (<4 Ǻ). 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.

Integration of microplasma with transmission electron microscopy: Real-time observation of gold sputtering and island formation.

An in situ platform for characterizing plasma-materials interactions at the nanoscale in the transmission electron microscope (TEM) has been demonstrated. Integrating a DC microplasma device, having plane-parallel electrodes with a 25 nm thick Au film on both the cathode and anode and operating in 760 Torr of Ar, within a TEM provides real-time observation of Au sputtering and island formation with a spatial resolution of < 100 nm. Analyses of TEM and atomic force microscopy images show the growth of Au islands to proceed by a Stranski-Krastanov process at a rate that varies linearly with the discharge power and is approximately a factor of 3 larger than the predictions of a DC plasma sputtering model. The experiments reported here extend in situ TEM diagnostics to plasma-solid and plasma-liquid interactions.

Linkage of oxygen deficiency defects and rare earth concentrations in silica glass optical fiber probed by ultraviolet absorption and laser excitation spectroscopy.

Ultraviolet absorption measurements and laser excitation spectroscopy in the vicinity of 248 nm provide compelling evidence for linkages between the oxygen deficiency center (ODC) and rare earth concentrations in Yb and Er-doped glass optical fibers. Investigations of YAG-derived and solution-doped glass fibers are described. For both Yb and Er-doped fibers, the dependence of Type II ODC absorption on the rare earth number density is approximately linear, but the magnitude of the effect is greater for Yb-doped fibers. Furthermore, laser excitation spectra demonstrate unambiguously the existence of an energy transfer mechanism coupling an ODC with Yb(3+). Photopumping glass fibers with a Ti:sapphire laser/optical parametric amplifier system, tunable over the 225-265 nm region, or with a KrF laser at 248.4 nm show: 1) emission features in the 200-1100 nm interval attributable only to the ODC (Type II) defect or Yb(3+), and 2) the excitation spectra for ODC (II) emission at ~280 nm and Yb(3+) fluorescence (λ ~1.03 µm) to be, within experimental uncertainty, identical. The latter demonstrates that, when irradiating Yb-doped silica fibers between ~240 and 255 nm, the ODC (II) defect is at least the primary precursor to Yb(3+) emission. Consistent with previous reports in the literature, the data show the ODC (II) absorption spectrum to have a peak wavelength and breadth of ~246 nm and ~19 nm (FWHM). Experiments also reveal that, in the absence of Yb, incorporating either Al(2)O(3) or Y(2)O(3) into glass fibers has a negligible impact on the ODC concentration. Not only do the data reported here demonstrate the relationship between the ODC (II) number density and the Yb doping concentration, but they also suggest that the appearance of ODC defects in the fiber is associated with the introduction of Yb and the process by which the fiber is formed.

Cs 894.3 nm laser pumped by photoassociation of Cs-Kr pairs: excitation of the Cs D(2) blue and red satellites.

Lasing on the D(1) transition (6P1/22-->6S1/22) of Cs has been observed by photoassociating Cs-Kr atomic pairs with a tunable, pulsed dye laser. Pumping of the blue or red satellites of the Cs D(2) line (62P3/2<==>62S1/2), peaking at approximately 841.1 nm and approximately 853 nm (respectively) in Cs/Kr/C(2)H(6) gas mixtures, provides a photodissociation laser in which the CsKr excimer parent molecule is not, at any point in the pumping process, in a bound electronic state. Relative to the absorbed pump pulse energy, laser slope efficiencies greater than or approximately 5% have been measured when the Cs number density is in the range of 5x10(14)-1.5x10(15) cm(-3) and the pump wavelength is 841.1 nm. Direct photoexcitation of the Cs 6P3/22 state at 852.1 nm under these conditions is a less efficient pathway for pumping the 894.3 nm laser, presumably as a result of competing nonlinear optical processes such as 1+2 resonantly enhanced multiphoton ionization of the alkali atom.

Many-body dipole-dipole interactions between excited Rb atoms probed by wave packets and parametric four-wave mixing.

Dipole-dipole interactions between excited Rb atoms at long range (approximately 300a0-2150a0) have been observed with molecular wave packets and a coherent nonlinear optical process. Fourier analysis of the parametric four-wave mixing (PFWM) signal wave intensity produced in femtosecond pump-probe experiments demonstrates the appearance of sidebands associated with the Rb 7s-5d(5/2) quantum beating frequency of approximately 18.3 THz. Calculations show that the observed sideband splittings and Fourier domain profiles result from multiple atom, dipole-dipole interactions, and ensembles comprising five or fewer Rb (7s, 6p) atoms account for virtually all of the data.

Enhancement of Raman scattering for an atom or molecule near a metal nanocylinder: quantum theory of spontaneous emission and coupling to surface plasmon modes.

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 >10(7) for variant Planck's over 2pi omega0 approximately 2.4 eV (lambda=514 nm), which corresponds to an increase of approximately 10(14) 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.

Arrays of silicon microdischarge devices with multicomponent dielectrics.

Arrays as large as 15x15 of microdischarge devices having inverted pyramidal silicon cathodes (50mumx50mum) and SiO(2)- Si(3)N(4)- polymer composite dielectrics have been fabricated and characterized with Ne gas. The lifetimes, reliability, and ignition characteristics of the arrays are superior to those of earlier designs having a single polymer dielectric. Operating voltages as low as 150 V for a 10x10 pixel array and 1000 Torr of Ne have been measured. Single (50mumx50mum) pyramidal cathode devices operate at voltages as low as 113 V when the Ne pressure is 900 Torr.

Interaction of atomic wave packets with four-wave mixing: detection of rubidium and potassium wave packets by coherent ultraviolet emission.

The observation of an atomic wave packet by use of a coherent, nonlinear-optical process is reported. Wave packets formed in K or Rb vapor by two-photon excitation of ns and (n-2)dstates (n=8 for K; n=11 , 12 for Rb) with red (~620-nm) , 80-100-fs pulses were detected by four-wave mixing in pump-probe experiments. The temporal behavior of the wave packet is observed by monitoring the coherent UV radiation generated near the alkali mp(2)P? (2)S(1/2) (7

Room-temperature fluorozirconate glass fiber laser in the violet (412 nm).

Continuous oscillation on the (2)P(3/2) ? (4)I(11/2) transition of Nd(3+) in a f luorozirconate glass (ZBLAN) fiber at room temperature has been observed. When pumped at ~590 nm, a Nd:ZBLAN f iber 39 cm in length lases in the violet at 412 nm and produces ~0.5 mW of power for 320 mW of pump power and a cavity output coupling of 0.4%. The breadth of the laser's excitation spectrum is ~12 nm (581-593 nm).

Injection locking and saturation intensity of a cadmium iodide laser.

A discharge-pumped cadmium monoiodide (CdI) laser utilizing isotopically pure CdI(2) ((114)CdI(2)) has been injection locked with a flashlamp-pumped dye laser having a linewidth of 0.3 cm(-1). Complete locking of the slave oscillator occurs for wavelengths between 655 and 660 nm and for injection intensities of ~5 W cm(-2). The saturation intensity for the B ? X band of CdI has been directly measured with an excimer-pumped dye laser to be (125 +/- 60) kW cm(-2).

Iodine monofluoride 140-kW laser: small signal gain and operating parameters.

Output energies in excess of 4 mJ in a ~30-nsec FWHM pulse (~140-kW peak power) have been obtained from a discharge-pumped IF laser for a cavity output coupling of 35%. In addition, oscillation on a new transition of the IF (E ? A) band at 472.7 nm has been observed. By measurement of the output power of the laser for various values of output mirror transmission, the small signal gain and loss coefficients were found to be (3.1 +/- 0.7)%-cm(-1) and ~0.3%-cm(-1), respectively.

Lifetime and collisional quenching measurements of XeF*(B) by photolysis of XeF2.

By photolyzing XeF 2 using ArCl* 175-nm radiation, the spontaneous radiative lifetime of the XeF(B --> X) band has been measured to be 14.25 + 0.2 nsec. Also, the rates of two-body collisional deactivation of the XeF(B) state by Ne, Ar, and XeF 2 have been determined to be 7.7 X 10(-13) cm3 sec(-1), 4.9 X 10(-12) cm3 sec(-1), and 2.6 X 10(-10) cm3 sec(-1), respectively. A three-body quenching rate of 7.2 X 10(-32) cm6 sec(-1) was found for Ar. The large two- and three-body quenching rates of XeF* by Ar suggest that Ne may be preferable to Ar as a diluent in high-pressure XeF (350-nm) laser mixtures.