Investigation of autofluorescence in zooplankton for use in classification of larval salmon lice.

We present autofluorescence of six zooplankton species, including salmon lice (Lepeophtheirus salmonis), for the purpose of classification in marine environments. Using a 410 nm excitation wavelength, we find that all measured zooplankton species exhibit broad cyan fluorescence centered around 510-520 nm. Furthermore, salmon lice show an absence of red fluorescence from undigested chlorophyll, which is measured from the gut of the herbivorous zooplankton species. We show the capability to distinguish noneating species, including salmon lice, from algae-eating species using a dual-band analysis of the fluorescence spectra. This shows the potential of autofluorescence as an important signature in real-time monitoring and classification of salmon lice.

SHG (532 nm)-induced spontaneous parametric downconversion noise in 1064-nm-pumped IR upconversion detectors.

As a novel technique for infrared detection, frequency upconversion has been successfully deployed in many applications. However, investigations into the noise properties of upconversion detectors (UCDs) have also received considerable attention. In this Letter, to the best of our knowledge, we present a new noise source-second-harmonic generation (SHG)-induced spontaneous parametric downconversion-experimentally and theoretically shown to exist in short-wavelength-pumped UCDs. We investigate the noise properties of two UCDs based on single-pass 1064-nm-pumped periodically poled LiNbO3 bulk crystals. One UCD is designed to detect signals in the telecom band and the other in the mid-infrared regime. Our experimental demonstration and theoretical analysis reveal the basic properties of this newly discovered UCD noise source, including its dependence on crystal temperature and pump power. Furthermore, the principle behind the generation of this noise source can also be applied to other UCDs, which utilize nonlinear crystals either in waveguide form or with different bulk materials. This study may also aid in developing methods to suppress the newly identified noise in future UCD designs.

Optical-feedback semiconductor laser Michelson interferometer for displacement measurements with directional discrimination.

An optical-feedback semiconductor laser Michelson interferometer (OSMI) is presented for measuring microscopic linear displacements without ambiguity in the direction of motion. The two waves from the interferometer arms, one from the reference mirror and the other from the reflecting moving target, are fed back into the lasing medium (lambda = 830 nm), causing variations in the laser output power. We model the OSMI into an equivalent Fabry-Perot resonator and derive the dependence of the output power (and the junction voltage) on the path difference between the two interferometer arms. Numerical and experimental results consistently show that the laser output power varies periodically (period, lambda/2) with path difference. The output power variation exhibits an asymmetric behavior with the direction of motion, which is used to measure, at subwavelength resolution, the displacement vector (both amplitude and direction) of the moving sample. Two samples are considered in the experiments: (i) a piezoelectric transducer and (ii) an audio speaker.