Higher-order fractal transverse modes observed in microlasers.

Two classes of higher-order, fractal spatial eigenmodes have been predicted computationally and observed experimentally in microlasers. The equatorial plane of a close-packed array of microspheres, lying on one mirror within a Fabry-Pérot resonator and immersed in the laser gain medium, acts as a refractive slit array in a plane transverse to the optical axis. Edge diffraction from the slit array generates the high spatial frequencies (>10cm) required for the formation of high-order laser fractal modes, and fractal transverse modes are generated, amplified, and evolve within the active medium.

Micro mercury trapped ion clock prototypes with 10[Formula: see text] frequency stability in 1-liter packages.

Modern communication and navigation systems are increasingly relying on atomic clocks. As timing precision requirements increase, demands for lower SWaP (size, weight, and power) clocks rise. However, it has been challenging to break through the general trade-off trend between the clock stability performance and SWaP.

Ultrasound harmonic generation and atomic layer deposition of multilayer, deep-UV mirrors and filters with microcavity plasma arrays.

Abstract: In honor of Professor Kurt Becker's pioneering contributions to microplasma physics and applications, we report the capabilities of arrays of microcavity plasmas in two emerging and disparate applications. The first of these is the generation of ultrasound radiation in the 20-240 kHz spectral range with microplasmas in either a static or jet configuration. When a array of microplasma jets is driven by a 20-kHz sinusoidal voltage, for example, harmonics as high as  = 12 are detected and are produced by controlling the spatial symmetry of the emitter array.

CsAr, CsXe, and RbXe BΣ Interatomic Potentials Determined from Absorption Spectra and Calculations of Franck-Condon Factors for Free-Free Optical Transitions of Atomic Collision Pairs.

Interatomic potentials for the BΣ states of CsAr, CsXe, and RbXe have been determined through comparisons of experimental B ← X absorption spectra for alkali vapor-rare gas mixtures with calculations of the Franck-Condon factors (FCFs) associated with free-free transitions of thermal atomic pairs. Simulations of optical transitions of alkali-rare gas atomic pairs between the thermal and vibrational continua of the XΣ and BΣ states of the molecule, responsible for the blue satellites of the Cs and Rb D resonance lines in a rare gas background, require the incorporation of ground-state values above ∼400 into the FCF calculations and proper normalization of the free-particle wave functions. Absorption spectra computed on the basis of several X and B state interatomic potentials available in the literature were found to be sensitive to the height of the BΣ state barrier, as well as the XΣ state repulsive wall contour and the location of the van der Waals minimum.

Treatment of Fungal-Infected Diabetic Wounds with Low Temperature Plasma.

Diabetes mellitus renders patients susceptible to chronic wounds and various infections. Regarding the latter, fungal infections are of particular concern since, although they are the source of significant morbidity and mortality in immunocompromised patients, they are generally resistant to conventional treatment and a definite treatment strategy has not yet been established. Herein, we report the treatment of skin wounds in a diabetic rat model, infected by , with low temperature helium plasma generated in a hand-held atmospheric jet device.

Inactivation and sensitization of Pseudomonas aeruginosa by microplasma jet array for treating otitis media.

Otitis media (OM), known as a middle ear infection, is the leading cause of antibiotic prescriptions for children. With wide-spread use of antibiotics in OM, resistance to antibiotics continues to decrease the efficacy of the treatment. Furthermore, as the presence of a middle ear biofilm has contributed to this reduced susceptibility to antimicrobials, effective interventions are necessary.

Photolithography in the vacuum ultraviolet (172 nm) with sub-400 nm resolution: photoablative patterning of nanostructures and optical components in bulk polymers and thin films on semiconductors.

Precision photoablation of bulk polymers or films with incoherent vacuum ultraviolet (VUV) radiation from flat, microplasma array-powered lamps has led to the realization of a photolithographic process in which an acrylic, polycarbonate, or other polymer serves as a dry photoresist. Patterning of the surface of commercial-grade, bulk polymers (or films spun onto Si substrates) such as poly-methyl methacrylate (PMMA) and acrylonitrile butadiene styrene (ABS) with 172 nm lamp intensities as low as ∼10 mW cm and a fused silica contact mask yields trenches, as well as arbitrarily-complex 3D structures, with depths reproducible to ∼10 nm. For 172 nm intensities of 10 mW cm at the substrate, linearized PMMA photoablation rates of ∼4 nm s are measured for exposure times t≤ 70 s but a gradual decline is observed thereafter.

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

Optical amplification by the stimulated emission of Cs(6pP)-Ar atomic pairs, observed in pump-probe experiments over a ∼290 GHz-wide spectral region lying to the red of the Cs D 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 BΣ←XΣ transition at 836.

Monolithic mtesla-level magnetic induction by self-rolled-up membrane technology.

Monolithic strong magnetic induction at the mtesla to tesla level provides essential functionalities to physical, chemical, and medical systems. Current design options are constrained by existing capabilities in three-dimensional (3D) structure construction, current handling, and magnetic material integration. We report here geometric transformation of large-area and relatively thick (~100 to 250 nm) 2D nanomembranes into multiturn 3D air-core microtubes by a vapor-phase self-rolled-up membrane (S-RuM) nanotechnology, combined with postrolling integration of ferrofluid magnetic materials by capillary force.

Microplasmas for Advanced Materials and Devices.

Microplasmas are low-temperature plasmas that feature microscale dimensions and a unique high-energy-density and a nonequilibrium reactive environment, which makes them promising for the fabrication of advanced nanomaterials and devices for diverse applications. Here, recent microplasma applications are examined, spanning from high-throughput, printing-technology-compatible synthesis of nanocrystalline particles of common materials types, to water purification and optoelectronic devices. Microplasmas combined with gaseous and/or liquid media at low temperatures and atmospheric pressure open new ways to form advanced functional materials and devices.

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.

Disintegration of simulated drinking water biofilms with arrays of microchannel plasma jets.

Biofilms exist and thrive within drinking water distribution networks, and can present human health concerns. Exposure of simulated drinking water biofilms, grown from groundwater, to a 9 × 9 array of microchannel plasma jets has the effect of severely eroding the biofilm and deactivating the organisms they harbor. measurements of biofilm structure and thickness with an optical coherence tomography (OCT) system show the biofilm thickness to fall from 122 ± 17 µm to 55 ± 13 µm after 15 min.

Fractal modes and multi-beam generation from hybrid microlaser resonators.

Fractals are ubiquitous in nature, and prominent examples include snowflakes and neurons. Although it has long been known that intricate optical fractal patterns can be realized with components such as gratings and reflecting spheres, generating fractal transverse modes from a laser has proven to be elusive. By introducing a 2D network of microspheres into a Fabry-Pérot cavity bounding a gain medium, we demonstrate a hybrid optical resonator in which the spheres enable the simultaneous generation of arrays of conventional (Gaussian) and fractal laser modes.

Microplasma Jet Arrays as a Therapeutic Choice for Fungal Keratitis.

The clinical impact of microplasma jets on rabbit eyes infected by Candida albicans has been investigated. Arrays of such jets produce low-temperature plasma micro-columns suitable for ophthalmic therapeutics and fungal infections, in particular, and the technology is capable of being scaled to surface areas of at least 10 cm. Keratitis was induced in the right central corneas of rabbits, whereas the left eyes served as a normal group.

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 6pP→6sS (D) 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.

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.

Spin Polarization of Rb and Cs np ^{2}P_{3/2} (n=5, 6) Atoms by Circularly Polarized Photoexcitation of a Transient Diatomic Molecule.

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.

Flavin mononucleotide biomolecular laser: longitudinal mode structure, polarization, and temporal characteristics as probes of local chemical environment.

A detailed characterization of the flavin mononucleotide (FMN) biomolecular laser, optically pumped in a stable resonator, is reported here. Photoexcitation of the molecule at 355 nm results in lasing over the ~566.5-573.

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 (+)).

An experimental burn wound-healing study of non-thermal atmospheric pressure microplasma jet arrays.

In contrast with a thermal plasma surgical instrument based on coagulative and ablative properties, low-temperature (non-thermal) non-equilibrium plasmas are known for novel medicinal effects on exposed tissue while minimizing undesirable tissue damage. In this study we demonstrated that arrays of non-thermal microplasma jet devices fabricated from a transparent polymer can efficiently inactivate fungi (Candida albicans) as well as bacteria (Escherichia coli), both in vitro and in vivo, and that this leads to a significant wound-healing effect. Microplasma jet arrays offer several advantages over conventional single-jet devices, including superior packing density, inherent scalability for larger treatment areas, unprecedented material flexibility in a plasma jet device, and the selective generation of medically relevant reactive species at higher plasma densities.

Injection-seeded optoplasmonic amplifier in the visible.

A hybrid optoplasmonic amplifier, injection-seeded by an internally-generated Raman signal and operating in the visible (563-675 nm), is proposed and evidence for amplification is presented. Comprising a gain medium tethered to a whispering gallery mode (WGM) resonator with a protein, and a plasmonic surface, the optical system described here selectively amplifies a single (or a few) Raman line(s) produced within the WGM resonator and is well-suited for routing narrowband optical power on-a-chip. Over the past five decades, optical oscillators and amplifiers have typically been based on the buildup of the field from the spontaneous emission background.

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.

External cavity laser biosensor.

Utilizing a tunable photonic crystal resonant reflector as a mirror of an external cavity laser cavity, we demonstrate a new type of label-free optical biosensor that achieves a high quality factor through the process of stimulated emission, while at the same time providing high sensitivity and large dynamic range. The photonic crystal is fabricated inexpensively from plastic materials, and its resonant wavelength is tuned by adsorption of biomolecules on its surface. Gain for the lasing process is provided by a semiconductor optical amplifier, resulting in a simple detection instrument that operates by normally incident noncontact illumination of the photonic crystal and direct back-reflection into the amplifier.

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.

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.