Preparation and characterization of highly thulium- and alumina-doped optical fibers for single-frequency fiber lasers

Thulium-doped fibers suitable for core-pumped single-frequency lasers were fabricated by the modified chemical vapor deposition (MCVD) method. Refractive index profile, doping profile and spectral absorption was measured. High doping concentration of thulium ions should be achieved to allow for high absorption of light at a pump wavelength while the thulium ions clustering should be avoided to prevent the cooperative upconversion and quenching processes. The fabricated fibers featured pump absorption up to 70dB/m at a pump wavelength of 1611nm. The single-frequency master oscillator with a resonator composed of a pair of fiber Bragg gratings and a thulium-doped fiber was demonstrated with predominantly single ended operation. We achieved a slope efficiency of 22% and a threshold of 22mW at a lasing wavelength of 1944nm

Preparation and Properties of Er-Doped ZrO2 Nanocrystalline Phase-Separated Preforms of Optical Fibers by MCVD Process

The fabrication of Er-doped ZrO2-based nanocrystalline phase-separated silica optical preforms by the MCVD and solution doping techniques is presented. Fabricated preform cores are nearly transparent and contain phase-separated rare-earth doped nanocrystalline particles with diameters mainly in a range from 20 to 80 nm. High concentrations of erbium and aluminium in preform cores of about 0.3 and 14 mol%, respectively have been achieved without defects on the core-cladding interface. Spectral losses in a range 800-1600 nm and fluorescence spectra of erbium ions around 1550 nm measured on a fibre drawn from the preform are reported

Use of two-dimensional fluorescence spectroscopy for monitoring of the effect of dimethyl sulfoxide on the growth and viability of immobilized plant cells

The growth and viability of tobacco cells (Nicotiana tabacum L) immobilized in alginate or pectate were monitored during their cultivation by using two-dimensional fluorescence spectroscopy (2-D FS). The cell growth was followed via the fluorescence of amino acids in proteins. The correlation between the tryptophan fluorescence and the cell biomass inside the alginate beads was verified by comparison with the dry weight of the cells. The determination of biomass content or cell viability by measurement of the intensity of NAD(P)H fluorescence was found unsuitable. Cell viability was estimated by determination of cell esterase activity using fluorescein diacetate as a fluorogenic substrate. The fluorescence intensities of both fluorophores, tryptophan and fluorescein, were determined by scanning a 2-D FS spectrum of intact beads in front face cuvette. Using this technique the effect of organic solvent, dimethyl sulfoxide, on the growth and metabolic activities of cells within the beads was evaluated. While 4% DMSO was tolerated by cells, 6% DMSO led to the cell destruction

Wideband and high-power light sources for in-line interferometric diagnostics of laser structur-ing systems

Laser structuring is rapidly developing manufacturing technique for broad spectrum of industrial branches, e.g. aerospace, power engineering, tool- and mould making, and automotive. It enables to prepare work pieces and products with very fine micro structures achieving a far better degree of details than conventional structuring techniques like etching or eroding. However, the state of art in laser structuring shows a crucial deficit. Used systems contain no metrology setup to detect the shape geometry (depth and length) and contour accuracy during the process. Therefore, an innovative in-line metrology technique based on low coherence interferometry for laser structuring systems has been investigated and described in the paper. In this contribution we present our results in the research of wideband and highpower light sources for the proposed low-coherence interferometric measurement system. The system can be incorporated into a structuring workplace equipped with a Q -switched ytterbium-doped fiber laser at 1064 nm for material processing. In the paper we focus on two wideband sources for such a measurement system. The first source is based on a superluminescent diode and the second one is based on an amplified spontaneous emission in a double-clad ytterbium-doped fiber. An example of results measured with the proposed in-line metrology system is presented