M. A. Illarramendi

An Optical Fiber Bundle Sensor for Tip Clearance and Tip Timing Measurements in a Turbine Rig

When it comes to measuring blade-tip clearance or blade-tip timing in turbines, reflective intensity-modulated optical fiber sensors overcome several traditional limitations of capacitive, inductive or discharging probe sensors. This paper presents the signals and results corresponding to the third stage of a multistage turbine rig, obtained from a transonic wind-tunnel test. The probe is based on a trifurcated bundle of optical fibers that is mounted on the turbine casing. To eliminate the influence of light source intensity variations and blade surface reflectivity, the sensing principle is based on the quotient of the voltages obtained from the two receiving bundle legs. A discrepancy lower than 3% with respect to a commercial sensor was observed in tip clearance measurements. Regarding tip timing measurements, the travel wave spectrum was obtained, which provides the average vibration amplitude for all blades at a particular nodal diameter. With this approach, both blade-tip timing and tip clearance measurements can be carried out simultaneously. The results obtained on the test turbine rig demonstrate the suitability and reliability of the type of sensor used, and suggest the possibility of performing these measurements in real turbines under real working conditions.

Ultrafast random laser emission in a dye-doped silica gel powder

We report efficient random lasing in a ground powder of a novel solid-state material based on silica gel containing SiO(2) nanoparticles embedding rhodamine 6G (Rh6G) dye. Basic properties of random lasing such as emission kinetics, emission spectrum, and threshold of stimulated emission are investigated by using real-time spectroscopy. The laser-like emission dynamics can be accurately described by a light diffusive propagation model. The device behavior is close to a conventional ultrafast Q-switched laser, which is an interesting fact aimed to further applications.

Optical Fiber Sensors for Aircraft Structural Health Monitoring

Aircraft structures require periodic and scheduled inspection and maintenance operations due to their special operating conditions and the principles of design employed to develop them. Therefore, structural health monitoring has a great potential to reduce the costs related to these operations. Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors. Several practical applications for structures and engines we have been working on are reported in this article. Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described. With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

Spectroscopic Characterization of Plastic Optical Fibers Doped With Fluorene Oligomers

The optical properties of four fluorene oligomers embedded in plastic optical fiber have been investigated by using steady-state luminescence technique. In particular, we study the dependence of the optical spectra with dopant oligofluorene, emission wavelength, excitation wavelength, and light propagation distance through the fiber. Using this information, we have characterized the optical loss in these doped optical fibers.

Light propagation in optical crystal powders: effects of particle size and volume filling factor

In this work, we analyse the light propagation in some laser and nonlinear crystal powders. In particular, we study the dependence of the diffusive absorption lengths and the transport lengths on particle size and volume filling factor. The theoretical calculations have been made by assuming a diffusive propagation of light in these materials.

Luminescence study of chromium (III) in Zirconium Barium Fluoride glass (ZBLA)

The optical properties of trivalent chromium ions in ZBLA glass have been studied for different concentrations of Cr 3+ . Optical absorption, luminescence and lifetimes were investigated in a wide temperature range. Analysis of lifetime data, emission and time resolved spectra have yielded the following results. There are two kinds of metal sites characterized by two gaussian emissions and two lifetimes, the higher energy gaussian being associated with the long emission lifetime. The two sites have the same thermal quenching mechanism independent of concentration

Computational Analysis of the Power Spectral Shifts and Widths Along Dye-Doped Polymer Optical Fibers

Polymer optical fibers doped with organic dyes can be used as efficient optical amplifiers and lasers in the visible region. We computationally analyze the spectral features of both their fluorescence and their amplified emission for different amounts of overlap between the emission and absorption spectra of the dyes employed. Representative cases are compared by calculating the respective evolutions along the doped fiber of the average wavelength, peak wavelength, and full-width at half-maximum of the output power obtained.

Characterization of light scattering in translucent ceramics

We have obtained expressions for the reflectance and transmittance of a scattering medium with weak absorption in terms of a diffusion model, where the source is an incoming beam, whose intensity exponentially decays along the propagation path. We have applied three experimental techniques, one of which is based on the developed model, to determine the transport mean-free-path in translucent samples of Nd:YAG ceramics.

Steady-state and time resolved laser spectroscopy of Cr3+ in lead-based fluoride glasses

The optical properties of Cr3+ ions in lead-based fluoride glasses (PBI, PZG) have been investigated. Optical absorption, emission, lifetimes, and time resolved spectra were measured. The thermal quenching of the broadband emission is discussed in terms of the quantum mechanical single configurational coordinate (QMSCC) model using the Struck and Fonger method, and a good agreement with the experimental results is obtained. In order to correlate glass matrix composition with emission spectral properties, detailed time-resolved measurements have been performed. The obtained results provide a first insight into a possible site distribution of Cr3+ in these glasses.

Optical spectroscopy of Cr3+ doped fluoride BIGaZYT glass

Abstract A detailed spectroscopic study on Cr3+ in BIGaZYT (30BaF2-18InF3-20ZnF3-10YF3-10ThF4-12GaF3) fluoride glass is presented. Optical absorption, emission, lifetimes, and time resolved spectra were measured. The thermal quenching of the Cr3+ broad band luminescence is discussed in terms of the quantum mechanical single configurational coordinate (QMSCC) model using the Struck and Fonger method. A reasonably good agreement with experimental data is achieved. Finally, the time evolution of excitation and emission spectra is analyzed in order to give a first insight into a possible site distribution of Cr3+ in this glass.