Robert Frey | PubMed Health

PubMed2007

Intracavity gain gratings.

Intracavity gain gratings are theoretically demonstrated to exhibit diffraction efficiencies that are 100 times larger than unity at pump powers substantially below the lasing threshold. Experiments performed using a Nd:YVO4 microlaser pumped below threshold by two interfering Ti:sapphire laser beams are described. Huge enhancement of the diffraction efficiency (5000X) and a large increase of the angular selectivity (10X) are demonstrated despite the angular reduction of the Fabry-Perot cavity finesse. Much better results are expected using gain gratings with larger areas or thinner cavities such as vertical cavity surface-emitting lasers. Such large fan-out values could be very interesting for applications to optical signal processing.

Journal Article↗

PubMed2006

Band-edge-induced Bragg diffraction in two-dimensional photonic crystals.

Two-dimensional photonic crystals composed of two orthogonal volume diffraction gratings have been photogenerated in photopolymers. When the read beam is set at the Bragg angle, the diffraction efficiency of the transmission grating is strongly enhanced at the band edge of the reflection grating recorded in the material. Such a device provides Bragg operation and enhancement of the diffraction efficiency of the thin diffraction grating together with good wavelength selectivity. Such advantages could be interesting for optical signal processing.

Journal Article↗

PubMed2005

Uncertainties associated with incidence estimates of HIV/AIDS diagnoses adjusted for reporting delay and risk redistribution.

Reporting delay occurs frequently in the case surveillance of a disease such as HIV/AIDS. To evaluate the current trend of incidence, it is important to consider incidence estimates adjusted for reporting delays and the uncertainty associated with this adjustment. For a surveillance system in which cases are reported monthly, there is no straightforward method for constructing the confidence interval estimators for annual incidence or incidence for a period longer than a month. This is because the monthly incidence estimators are not independent and the correlations among them are not available. Furthermore, to estimate the incidence for a specific risk, or exposure, group (e.g. men who have sex with men), we also have to consider the uncertainty associated with the counts from cases reported without an identified risk. Cases with no reported risk are assigned proportionally to each risk group on the basis of experience with cases reported initially with no reported risk but reported later with an identified risk. In this article, we introduce a method for combining the uncertainties associated with both reporting delay and risk redistribution. An estimator for the covariance between two incidence estimators is also provided so that we can make pairwise comparisons and discover any significant changes in incidence over time. Results are applied to evaluating the current trends in AIDS incidence among men who have sex with men in the United States.

Acquired Immunodeficiency Syndrome↗