Mira Naftaly

Terahertz Time-Domain Spectroscopy for Material Characterization

Terahertz time-domain spectroscopy is used to study properties of nonpolar amorphous materials. Terahertz absorption spectra and refractive indices were measured in a number of glasses, lubricating oils, and polymers, and the results were correlated with material properties.

Tm 3+ -doped tellurite glass for a broadband amplifier at 1.47 µm

Tm(3+)-doped tellurite glass is investigated as a host for a broadband amplifier at 1.47 mum. The Tm(3+) fluorescence spectrum, lifetime, and cross section in tellurite glass are compared with those in fluorozirconate glasses. The advantages of a Tm(3+)-tellurite amplifier, especially when it is employed in combination with an Er(3+)-tellurite 1.55-mum amplifier, are discussed.

Nd3+-doped fluoroaluminate glasses for a 1.3 μm amplifier

A Nd3+-doped 1.3 μm fiber amplifier has the potential to be an efficient, high-gain device. A major problem to overcome is the long wavelength of the gain spectrum. In the majority of Nd3+-doped glasses the gain is shifted out of the second telecom window as a result of long-wavelength emission and signal excited-state absorption (ESA). In this article we present new fluoroaluminate glasses developed as hosts for the 1.3 μm Nd3+-doped fiber amplifier. Nd3+ emission peaks below 1320 nm were demonstrated in bulk glasses. Gain in the 1310–1320 nm region was measured in unclad fibers, with evidence of significantly reduced ESA. Another serious problem in amplifier design lies in overcoming the competing amplified spontaneous emission (ASE) at 1050 nm. We discuss ASE filtering using in-fiber Bragg gratings and present results supporting its feasibility. The article also examines thermal and viscous properties of matched core and cladding glasses in relation to preform and fiber fabrication.

Tungsten–tellurite—a host glass for broadband EDFA

Abstract Tungsten–tellurite glass is proposed as a host for broadband erbium-doped fibre amplifiers (EDFA). The spectroscopic properties of Er 3+ -doped tungsten–tellurite glass are described, and a broad 1.5 μm emission spectrum of 85 nm FWHM is demonstrated. The suitability of tungsten–tellurite glass as a host for EDFA and its advantages over tellurite are discussed.

Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties

Terahertz (THz) time-domain transmission spectroscopy was used to obtain the absorption coefficients and refractive indices of silica, Pyrex, and seven different Schott glasses. The refractive indices were analyzed using the Clausius–Mossotti equation, and the absorption coefficients in terms of the power-law model of far-infrared absorption. Relationships were observed between THz absorption and refractive indices on the one hand, and glass properties on the other. THz transmission data have been shown to provide a useful insight into glass structure.

Electrical and radiation characteristics of semilarge photoconductive terahertz emitters

We present experimental characterization of semilarge photoconductive emitters, including their electrical/photoconductive parameters and terahertz spectra. A range of emitters were studied and fabricated on both LT-GaAs and SI-GaAs, having a variety of electrode geometries. The spatial cone of terahertz radiation was defined. The dependencies of the photocurrent and the terahertz power on the bias voltage and the laser power were determined. A Fourier-transform interferometer is used to determine the terahertz spectra and to clarify the effects of the substrate and electrode geometry.

Tm3+- and Er3+- doped tellurite glass fibers for a broadband amplifier at 1430 to 1600 nm

Tellurite glasses doped with Er3+ and Tm3+ are investigated for broadband amplifiers in the third telecommunications window. Fluorescence spectra and lifetimes of Er3+ and Tm3+ in tellurite glass were measured. Stimulated emission cross-sections were calculated using the McCumber method for Er3+ and the Judd-Ofelt analysis for Tm3+. The obtained emission parameters are compared with those in other glass hosts. The potential advantages of tellurite glass as amplifier host are discussed.

Effects of the site symmetry and host polarizability on the hypersensitive transition 3P0→3F2 of Pr3+ in fluoride glasses

Observations and analysis of hypersensitive 3P0→3F2 transition of Pr3+ ion are reported in a series of fluoride (fluoroindate, fluoroaluminate, and fluorozirconate) glasses. The data in fluoride families are also compared with the data on the selected tellurite and sulfide glasses. The structure of dopant sites in fluoride glasses and the mechanism of hypersensitivity are discussed in relation to the symmetry of dopant sites and host polarizability. The possibilities of quenching, or alternatively, of magnification of the hypersensitive transitions of rare-earth ions in the glassy hosts and their applications are discussed.

Characterization of Terahertz Beam Profile and Propagation

Two techniques for imaging a terahertz (THz) beam profile are described and employed in characterizing the THz beam propagation in a time-domain spectrometer. Aperture scanning yields a 2-D cross-sectional map of field amplitude at selected frequencies that is used to track beam evolution along its path. The Hartmann test produces a 2-D topographical image of the wavefront, also at selected frequencies. The results are compared with theory, and the respective advantages of the two methods are discussed.

1.3 μm Fluorescence quenching in Pr-doped glasses

Short fluorescence lifetime is the main problem encountered in designing an efficient Pr3+-doped amplifier at 1.3 μm. Lifetimes observed in low phonon energy glasses are far shorter than those indicated by calculations. We examine 1.3 μm fluorescence quenching in Pr3+-doped glasses via concentration and impurity quenching in order to estimate the limits on metastable lifetimes achievable in low-doped, low-impurity glasses. The optimum doping level and the requirements for impurity content are assessed. Three glass hosts are studied in detail; cadmium-halide, gallium-indium-fluoride, and germanium-gallium-sulphide. The prospects for extending the Pr3+ metastable lifetime in these glasses are considered.