Biomedical subjects

Elsa Garmire

Publications and source records attributed to Elsa Garmire.

3 recordsLinked to original sources

PubMed2005

Low-power optical vibration detection by photoconductance monitoring with a laser speckle pattern.

We present a quantitative evaluation of the performance of a photoconductance-monitoring sensor array in a speckle-based vibration detection configuration. The device is found to be capable of detecting nanometer-amplitude vibrations in a single shot with incident intensities of only a few microwatts per square centimeter at kilohertz frequencies. This performance indicates that the photoconductance-monitoring array requires approximately 3 orders of magnitude lower intensity to achieve the same displacement sensitivity as competing technologies, such as photo-electromotive-force detectors.

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PubMed2003

Theory of quarter-wave-stack dielectric mirrors used in a thin fabry-perot filter.

I present a new derivation of the analytic form for the phase shift near resonance and the optical penetration length upon reflection from a distributed dielectric mirror consisting of a quarter-wave stack. The requirement of proper termination to achieve high reflectivity is suspended to investigate large optical penetration depths. Separate equations, derived for N and N + 1/2 layer pairs, are convenient for the design of tunable Fabry-Perot filters with a specified tuning range. The analysis is also applicable to distributed Bragg reflectors, vertical-cavity surface-emitting lasers, and resonant photodiodes. I show that the penetration length can sharply reduce the overly broad free spectral range of an ultrathin Fabry-Perot filter that might be useful in applications such as tunable wavelength filters for wavelength division multiplexing applications. The results also demonstrate regimes of zero dispersion and of superluminal reflection in the dielectric mirrors, which are of particular interest in photonic bandgap structures.

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PubMed2002

Analytic performance analysis based on material properties for electroabsorptive asymmetric Fabry-Perot reflection modulators.

Simple and accurate analytic expressions are provided for the maximum reflectivity and tolerances of an impedance-matched asymmetric Fabry-Perot used as a high-contrast spatial light modulator when electroabsorptive quantum wells provide loss modulation. When the device geometry is optimized, these expressions depend only on material properties. The maximum reflectivity depends only on the fractional absorption change and is independent of the front-mirror reflectivity. The most important tolerance is on the flatness of crystal growth; the fractional-length tolerance is proportional to the absorption coefficient. These formulas agree with experimentally reported results from multiple-quantum-well modulators and previous numerical analyses; they are useful for quickly predicting optimized performance of possible new materials. The normally on and normally off geometries are compared. The effect of finite back-mirror reflectivity is clarified. Deviations from impedance match enable increased reflectance difference at the expense of contrast ratio, an approach which is evaluated as a function of material parameters.

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