W.S. Brocklesby

Fabrication and optical properties of lead‐germanate glasses and a new class of optical fibers doped with Tm3+

In this article we present a study of a new class of optical fibers based on lead germanate glass. The maximum vibrational frequency of this glass is intermediate between silica and zirconium barium lanthanum aluminum fluoride glass, causing a beneficial change in nonradiative decay and therefore quantum efficiency for particular laser transitions. Fabrication of high-strength, low-loss fibers of this glass has been achieved by modification of the composition to produce optimal physical properties for fiber drawing, while retaining the useful vibrational properties of the original PbGeO2 glass. Measurements of both the thermal and optical properties are described. The fibers produced are ideal for many applications in fiber devices.

Infrared emission from holmium doped gallium lanthanum sulphide glass

Infrared emission at 1.2, 1.25, 1.67, 2.0, 2.2, 2.9, 3.9, and 4.9µm is measured in holmium (Ho3+) doped gallium lanthanum sulphide (GLS) glass. Branching ratios, radiative quantum efficiencies, and emission cross sections are calculated from lifetime, absorption, and emission measurements using Judd-Ofelt analysis and the Fuchtbauer-Ladenburg equation. The fluorescence band at 3.9µm coincides with an atmospheric transmission window and the fluorescence band at 4.9µm overlaps with the fundamental absorption of carbon monoxide, making the glass a potential fibre laser source for remote sensing and gas sensing applications. This is the first time this latter transition has been reported in any holmium doped host.

Crystallisation effects on rare earth dopants in oxyfluoride glass ceramics

Transparent oxyfluoride glass-ceramic materials are of significant interest for the production of new optoelectronic devices. In this paper we report measurements of the detailed spectroscopy of rare earth dopants in both an oxyfluoride transparent glass ceramic and its glass precursor. We show that several spectroscopically different sites exist for the rare earth even in the glass precursor material, where a significant amount of the rare earth is already coordinated with fluorine. In the glass-ceramic material, these glassy fluorine-coordinated sites are replaced with crystalline sites, but a significant fraction of the rare earth ions are still within the glass phase. The fraction of rare earth ion that is incorporated into the crystalline phase is estimated from the rare earth spectroscopy, and the role of the rare earth coordination in the precursor glass is discussed.

Imaging of free-space interference patterns used to manufacture fiber Bragg gratings

A technologically important use of the free-space interference patterns formed by phase gratings is in the creation of the refractive-index variation along optical fiber Bragg gratings. The patterns can be imaged directly by use of a tapered optical fiber tip, which acts as a local probe of the optical field. We present measurements of these patterns under varying conditions and compare them with theoretical predictions. In discussing the results within the context of fiber grating manufacture, we also demonstrate the effects of incident-beam misalignment and wave-front curvature.

Soft-x-ray wavelength shift induced by ionization effects in a capillary

Coherent soft x rays are produced by high-harmonic generation in a capillary filled with Ar gas. We demonstrate that the tuning of the harmonic wavelengths with intensity and chirp arises from changes in the Ar ionization level. Control over the tuning can be achieved either by changing the average intensity of the laser pulse or by varying the quadratic spectral phase of the laser pulse. We observe an ionization-dependent blueshift of the fundamental wavelength that is directly imprinted on the harmonic wavelengths. The harmonic tuning is shown to depend on nonlinear spectral shifts of the fundamental laser pulse that are due to the plasma created by ionization, rather than directly on any chirp imposed on the fundamental wavelength.

Spectroscopic properties of Nd3+ and Pr3+ in gallate glasses with low phonon energies

Absorption and fluorescence spectra of Nd3 +were measured in potassium tantalum gallate, lead bismuth gallate (PBG), fluorozirconate (ZBLAN), and Ge-Ga-S glasses. A Judd -Ofelt analysis was performed to determine the spontaneous emission probability and stimulated emission cross section of the4 F3/2 ?4 I11/2 transition of Nd3 +. Raman spectra were studied to clarify the maximum phonon energies of the glasses. The fluorescence of the1 G4?3 H5 transition of Pr3 + in a dehydrated PBG glass was observed for the first time to our knowledge. The PBG glass has a higher quantum efficiency than that of ZBLAN glass based on the Judd -Ofelt analysis.

Time resolved and site selective spectroscopy of thulium doped into germano- and alumino-silicate optical fibres and preforms

Abstract Optical properties of thulium ions doped in varying concentrations into germano- and alumino-silicate glass fibres and their preforms are studied. Absorption and fluorescence spectra are shown to vary little with thulium concentrations up to 12 000 ppm, but vary drastically with germanium or aluminium codopant. Resonant fluorescence studies of Tm3+ show correlations in the movements of the Stark levels of the ground state, indicating systematic correlations between the ion site and Stark level position. An upper limit of 10 cm-1 for the homogeneous line width of thulium in alumino-silicate glass is established at 9 K. The lifetimes of the 1G4 and 3F4 levels are studied and are related to codopant influence and cross-relaxation which are linked to fibre drawing and Tm3+ concentration. A significant lifetime shortening is observed on drawing preform to fibre. A model is presented for non-exponential decay of the 3F4 level. Three- and four-level rate equations have been successfully used to simulate the observed rise of the 3F4 fluorescence and decay of the 1D2 fluorescence, excited resonantly and by up-conversion processes, respectively. These models yield both the excitation pump rate and cross-relaxation rates.

Optical control of gallium nanoparticle growth

The study of metallic nanoparticles has a long tradition in linear and nonlinear optics [1], with current emphasis on the ultrafast dynamics, size, shape and collective effects in their optical response [2-6]. Nanoparticles also represent the ultimate confined geometry:high surface-to-volume ratios lead to local field enhancements and a range of dramatic modifications of the materials properties and phase diagram [7-9]. Confined gallium has become a subject of special interest as the light-induced structural phase transition recently observed in gallium films [10, 11] has allowed for the demonstration of all-optical switching devices that operate at low laser power [12]. Spontaneous self-assembly has been the main approach to the preparation of nanoparticles (for a review see 13). Here we report that light can dramatically influence the nanoparticle self-assembly process: illumination of a substrate exposed to a beam of gallium atoms results in the formation of nanoparticles with a relatively narrow size distribution. Very low light intensities, below the threshold for thermally-induced evaporation, exert considerable control over nanoparticle formation through non-thermal atomic desorption induced by electronic excitation.We report that low-intensity light can dramatically influence and regulate the nanoparticle self-assembly process: Illumination of a substrate exposed to a beam of gallium atoms results in the formation of gallium nanoparticles with a relatively narrow size distribution. Very low light intensities, below the threshold for thermally induced evaporation, exert considerable control over nanoparticle formation.

Spectroscopy of yttria-alumina-silica glass doped with thulium and erbium

Yttria-alumina-silica (YAS) glasses doped with Er/sup 3+/ and Tm/sup 3+/ have been examined spectroscopically for their potential as fiber amplifier gain media for optical telecommunication systems. Absorption and emission spectra as well as emission lifetime measurements and Judd-Ofelt calculations are reported. Tm/sup 3+/: YAS glass exhibits an emission bandwidth of 122 nm around 1470 nm, making it promising for S/sup +/-band amplification.

Photosensitivity of lead germanate glass waveguides grown by pulsed laser deposition.

We report very large photoinduced refractive-index changes Dn, of the order of ~10(2), in lead germanate glass waveguides grown by pulsed-laser deposition. The magnitude of Dn was derived from measurements of diffraction efficiency for gratings written by exposure to 244-nm light through a phase mask, whereas the sign of Dn was determined from ellipsometric data. Results are shown for films grown under oxygen pressures ranging from 1 chi 10(-2) to 6 chi 10(-2)mbars (1.33mbars=1 Torr).