Cavity-enhanced direct frequency comb spectroscopy

Cavity-enhanced direct frequency comb spectroscopy combines broad spectral bandwidth, high spectral resolution, precise frequency calibration, and ultrahigh detection sensitivity, all in one experimental platform based on an optical frequency comb interacting with a high-finesse optical cavity. Precise control of the optical frequency comb allows highly efficient, coherent coupling of individual comb components with corresponding resonant modes of the high-finesse cavity. The long cavity lifetime dramatically enhances the effective interaction between the light field and intracavity matter, increasing the sensitivity for measurement of optical losses by a factor that is on the order of the cavity finesse. The use of low-dispersion mirrors permits almost the entire spectral bandwidth of the frequency comb to be employed for detection, covering a range of ~10% of the actual optical frequency. The light transmitted from the cavity is spectrally resolved to provide a multitude of detection channels with spectral resolutions ranging from a several gigahertz to hundreds of kilohertz. In this review we will discuss the principle of cavity-enhanced direct frequency comb spectroscopy and the various implementations of such systems. In particular, we discuss several types of UV, optical, and IR frequency comb sources and optical cavity designs that can be used for specific spectroscopic applications. We present several cavity-comb coupling methods to take advantage of the broad spectral bandwidth and narrow spectral components of a frequency comb. Finally, we present a series of experimental measurements on trace gas detections, human breath analysis, and characterization of cold molecular beams.Comment: 36 pages, 27 figure

Differentiation and gene flow among island and mainland populations of the true armyworm, Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae)

Copyright © 2003, NRC Canada. Reproduced by permission.The genetic structure of populations of the true armyworm, Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae), in the Azores archipelago was studied using polyacrylamide-gel electrophoresis. Four enzyme systems (aldehyde oxidase, esterase, phosphoglucomutase, and phosphoglucose isomerase) were examined in six populations from islands in the Azores (Santa Maria, São Miguel, Terceira, Pico, Faial, Flores) and compared with those from populations from mainland Portugal and Canada. The North American and European populations are not clearly separated from the Azorean ones. Similarly, studies of different enzyme systems (aldehyde oxidase, esterase, malic enzyme, sorbitol dehydrogenase, manose-6-phosphate isomerase, and phosphoglucomutase) over 2 years (1997 and 1998) at different times of the year (spring, summer, and autumn) and at three different altitudes (0, 250, and 500 m above sea level) on three different islands (Santa Maria, São Miguel, and Faial) uncovered no distinct differences. These results, obtained from classically used loci, suggest that there is still some gene flow between sites or that island populations have not been isolated for sufficient time to have diverged from founder populations.RÉSUMÉ: La structure génétique des populations açoriennes de la légionnaire uniponctuée Pseudaletia unipuncta (Haworth) (Lepidoptera : Noctuidae), a été étudiée à l'aide d'enzymes séparées par électrophorèse sur gel de polyacrylamide. Quatre systèmes enzymatiques (aldéhyde oxydase, estérase, phosphoglucomutase et phosphoglucose isomerase) ont été analyses chez six populations des Açores (îles de Santa Maria, São Miguel, Terceira, Pico, Faial et Flores) et chez des populations portugaise et canadienne. Les populations européenne et américaine ne sont pas nettement séparées des populations açoriennes. De la même manière, l'étude de six systèmes enzymatiques (aldéhyde oxydases, estérase, enzymes maliques, sorbitol déshydrogénases, manose-6-phosphate isomérases et phosphoglucomutases) durant deux années (1997 et 1998), à différentes périodes de l'année (printemps, été et automne) et à trois altitudes différentes (0, 250 et 500 m) sur trois lies (Santa Maria, São Miguel et Faial) n'a pas dévoilé de divergences évidentes, Ces résultats obtenu à partir de locus classiquement utilisés et en nombre suffisant, suggèrent qu' il subsiste un certain flux génique entre les populations étudiées, et (ou) que les populations insulaires sont isolées depuis trop peu de temps pour avoir pu diverger des populations fondatrices