Biomedical subjects

Gonzalo Paez

Publications and source records attributed to Gonzalo Paez.

4 recordsLinked to original sources

PubMed2006

Characterization of upconversion coefficient in erbium-doped materials.

We describe a new method for determining the homogeneous upconversion coefficient by using only three measurements: two fluorescence decays as a function of time and the relationship of normalized fluorescence with excitation power. This technique results in increased accuracy upon employment of a smaller number of measurements. Specifically, the intermediate steps of finding the absorption cross section of the doped material, the emission spectrum of the pumping source, and its spatial power distribution are not necessary. Our technique employs only one experimental setup: changing the pumping conditions. Furthermore, it incorporates dual-function fitting to reduce the uncertainty and error propagation. This method will find ample applications in the study and characterization of erbium-doped materials used in lasers and optical amplifiers, where precise knowledge of efficiency and losses is of uppermost importance.

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PubMed2003

Comparison of linear and rotationally shearing interferometric layouts for extrasolar planet detection from space.

We use the point spread function and the modulation transfer function (MTF) as two figures-of-merit to evaluate the performance of the multiaperture interferometric configurations for the detection of a faint planet in the vicinity of its bright star. We design nonredundant interferometric layouts that provide satisfactory coverage of the spatial frequencies of interest. We propose a design incorporating a rotating, rotationally shearing interferometer in a gravity-free environment and compare its performance with the Earth-based, fixed, linear configurations. The side peak of its MTF may be centered on the coordinate associated with a likely planet spatial frequency, resulting in planet signal enhancement and isolation.

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PubMed2003

Dove prism with increased throughput for implementation in a rotational-shearing interferometer.

An analytical expression is derived for the tilt introduced into a wave front by a Dove prism with manufacturing errors in the prism's base angles and pyramidal angle. We found that the tilt decreases when the base angles are increased above the values of traditional design. The increase in the length-aperture ratio of a prism is detrimental to the prism's performance. However, a Dove prism with a widened aperture increases throughput and maintains a manageable prism weight for implementation in a rotational shearing interferometer. Thus we propose a Dove prism designed with a widened aperture to increase throughput in a rotational shearing interferometer and with larger base angles to minimize the wave-front tilt introduced by manufacturing errors. Experimental results implemented in a rotational shearing interferometer demonstrate the feasibility of this design.

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PubMed2003

Erbium-doped optical fiber fluorescence temperature sensor with enhanced sensitivity, a high signal-to-noise ratio, and a power ratio in the 520-530- and 550-560-nm bands.

We analyze and predict the performance of a fiber-optic temperature sensor from the measured fluorescence spectrum to optimize its design. We apply this analysis to an erbium-doped silica fiber by employing the power-ratio technique. We develop expressions for the signal-to-noise ratio in a band to optimize sensor performance in each spectral channel. We improve the signal-to-noise ratio by a factor of 5 for each channel, compared with earlier results. We evaluate the analytical expression for the sensor sensitivity and predict it to be approximately 0.02 degrees C(-1) for the temperature interval from room temperature to above 200 degrees C, increasing from 0.01 degrees C(-1) at the edges of the interval to 0.03 degrees C(-1) at the center, at 100-130 degrees C. The sensitivity again increases at temperatures higher than 300 degrees C, delineating its useful temperature intervals.

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