Ivan S. Ruddock

Optical spectroscopy of , and single crystals

The optical absorption and photoluminescence properties of , and crystals grown by laser-heated pedestal growth (LHPG) have been measured at T = 14 K, 77 K and 300 K. These spectra show very high absorption coefficients for the three rare-earth (RE) ions and strong luminescence signals characteristic of ions at high concentration in distorted symmetry sites. The rare-earth ions in these compounds are shown to occupy single sites only. The strong luminescence output at 300 K makes these crystals potential hosts for diode-pumped laser gain media.

Graded-index characteristics in single-crystal fibers.

Single-crystal fibers of Ti(3+):Al(2)O (3)have been grown by the laser-heated pedestal growth technique and shown to exhibit radial refractive-index gradients. A refractive-index increase of approximately 12% in the fiber core with respect to the fiber sidewalls has been measured. The index profile can be fitted with a parabolic model. Postgrowth treatment of Cr(3+):Gd(3)Sc (2)Al (3)O(12)fibers has been shown to produce a uniform cladding region with a graded-index core. The core index is some 12.5% larger than the cladding region, with an index profile shape that is approximately parabolic in nature.

Report and recommendations on multimedia materials for teaching and learning electricity and magnetism

This paper presents the results of a peer review of multimedia materials for teaching and learning electricity and magnetism prepared as a part of the annual activities undertaken by an international group of scientists associated with Multimedia Physics in Teaching and Learning. The work promotes the use of valuable and freely accessible information technology materials for different levels of teaching, mostly higher education. The authors discuss the process of selecting resources and the rubrics used in the rating process. The reviews of high-quality learning resources are presented along with descriptions of valuable didactical features.

Dopant incorporation in single-crystal fibre growth by the laser-heated miniature pedestal growth technique

Abstract A theoretical model of single-crystal fibre growth by laser-heated miniature pedestal growth has been developed to account for the transfer of dopant from the source rod to the growing fibre. This model predicts the time evolution of the melt dopant concentration when the source rod dopant concentration is axially non-uniform. From this the axial distribution of dopant in the final grown fibre may be predicted. This model has been experimentally confirmed and an estimate of the evaporation time constant of Ti in the growth of Ti:Al2O3 fibres made.

The imaging properties of gradient index optical fibres

The optical properties of gradient index optical fibre are described as the basis for an undergraduate experiment. Its imaging ability is demonstrated by results obtained by two of the authors during their final year undergraduate research projects.

Interferometric measurement of refractive index

In this paper a simple method is described for measuring the principal refractive indices of crystals using a Michelson interferometer and a single principal section of the material. This work formed the basis of the final year BSc project in laser physics and optoelectronics for one of the authors. The refractive indices of a sapphire crystal obtained by this technique are accurate to the third decimal place. The procedure is then used to obtain the three principal refractive indices of a new biaxial crystal, potassium niobium borate, whose refractive indices were previously unknown.

Nonlinear optical second harmonic generation

The generation of the second harmonic of the 632.8 nm light from an He-Ne laser is described as the basis of an undergraduate experiment. The dependence of the signal on phase-matching angle and intensity of the fundamental beam is discussed.

Light by light modulation in semiconductor doped glass

Fifty percent modulation was observed in Schott Glass OG530 semiconductor doped filter glass with a c.w. argon-ion laser. Laser-induced clearing and darkening were also detected, the balance between them being dependent on sample temperature, modulation frequency and light intensity.

Potential of two-photon-excited fluorescence for distributed fiber sensing

The design and operating parameters of a new class of continuously distributed optical fiber sensor are described. By use of counterpropagating pulses, two-photon excitation of fluorescence from ions doped into the fiber enables any position to be monitored. By this means temperature and also strain may be sensed with high spatial and temporal resolution. As the doped fiber is transparent for single-photon absorption at the wavelength of the light pulses, attenuation does not set an upper limit to its length.

Laser heated pedestal growth and spectroscopic properties of K2NdNb5O15 and Ba2NdNbO6 crystals

Abstract Single crystals of mixed niobastes K2NdNb5O15 and Ba2NdNbO6 have been grown by the laser heated pedestal growth (LHPG) technique. The mini-crystals grown by this method were characterized by X-ray diffraction, optical absorption and photoluminescence techniques. The optical absorption spectra (400–950 nm) and emission spectra 4 P F 3 2 → 4 I 9 2 (∼ 900 nm), 4 I 11 2 (∼1070 nm) are strongly broadened by intrinsic crystalline disorder in both materials.