Science.gov

Sample records for sex combs asx

  1. Drosophila Sex Combs as a Model of Evolutionary Innovations

    PubMed Central

    Kopp, Artyom

    2011-01-01

    The diversity of animal and plant forms is shaped by nested evolutionary innovations. Understanding the genetic and molecular changes responsible for these innovations is therefore one of the key goals of evolutionary biology. From the genetic point of view, the origin of novel traits implies the origin of new regulatory pathways to control their development. To understand how these new pathways are assembled in the course of evolution, we need model systems that combine relatively recent innovations with a powerful set of genetic and molecular tools. One such model is provided by the Drosophila sex comb a male-specific morphological structure that evolved in a relatively small lineage related to the model species D. melanogaster. Our extensive knowledge of sex comb development in D. melanogaster provides the basis for investigating the genetic changes responsible for sex comb origin and diversification. At the same time, sex combs can change on microevolutionary timescales and differ spectacularly among closely related species, providing opportunities for direct genetic analysis and for integrating developmental and population-genetic approaches. Sex comb evolution is associated with the origin of novel interactions between HOX and sex determination genes. Activity of the sex determination pathway was brought under the control of the HOX code to become segment-specific, while HOX gene expression became sexually dimorphic. At the same time, both HOX and sex determination genes were integrated into the intrasegmental spatial patterning network, and acquired new joint downstream targets. Phylogenetic analysis shows that similar sex comb morphologies evolved independently in different lineages. Convergent evolution at the phenotypic level reflects convergent changes in the expression of HOX and sex determination genes, involving both independent gains and losses of regulatory interactions. However, the downstream cell differentiation programs have diverged between species, and in some lineages similar adult morphologies are produced by different morphogenetic mechanisms. These features make the sex comb an excellent model for examining not only the genetic changes responsible for its evolution, but also the cellular processes that translate DNA sequence changes into morphological diversity. The origin and diversification of sex combs provides insights into the roles of modularity, cooption, and regulatory changes in evolutionary innovations, and can serve as a model for understanding the origin of the more drastic novelties that define higher-order taxa. PMID:23016935

  2. Evolution of Drosophila sex comb length illustrates the inextricable interplay between selection and variation.

    PubMed

    Malagn, Juan N; Ahuja, Abha; Sivapatham, Gabilan; Hung, Julian; Lee, Jiwon; Muoz-Gmez, Sergio A; Atallah, Joel; Singh, Rama S; Larsen, Ellen

    2014-09-30

    In spite of the diversity of possible biological forms observed in nature, a limited range of morphospace is frequently occupied for a given trait. Several mechanisms have been proposed to explain this bias in the distribution of phenotypes including selection, drift, and developmental constraints. Despite extensive work on phenotypic bias, the underlying developmental mechanisms explaining why particular regions of morphological space remain unoccupied are poorly understood. To address this issue, we studied the sex comb, a group of modified bristles used in courtship that shows marked morphological diversity among Drosophila species. In many Drosophila species including Drosophila melanogaster, the sex comb rotates 90 to a vertical position during development. Here we analyze the effect of changing D. melanogaster sex comb length on the process of rotation. We find that artificial selection changes the number of bristles per comb without a proportional change in the space available for rotation. As a result, when increasing sex comb length, rather than displaying a similar straight vertical shape observed in other Drosophila species, long sex combs bend because rotation is blocked by a neighboring row of bristles. Our results show ways in which morphologies that would be favored by natural selection are apparently impossible to achieve developmentally. These findings highlight the potential role of development in modifying selectable variation in the evolution of Drosophila sex comb length. PMID:25197080

  3. Wing Defects in Drosophila xenicid Mutant Clones Are Caused by C-Terminal Deletion of Additional Sex Combs (Asx)

    PubMed Central

    Bischoff, Kara; Ballew, Anna C.; Simon, Michael A.; O'Reilly, Alana M.

    2009-01-01

    Background The coordinated action of genes that control patterning, cell fate determination, cell size, and cell adhesion is required for proper wing formation in Drosophila. Defects in any of these basic processes can lead to wing aberrations, including blisters. The xenicid mutation was originally identified in a screen designed to uncover regulators of adhesion between wing surfaces [1]. Principal Findings Here, we demonstrate that expression of the βPS integrin or the patterning protein Engrailed are not affected in developing wing imaginal discs in xenicid mutants. Instead, expression of the homeotic protein Ultrabithorax (Ubx) is strongly increased in xenicid mutant cells. Conclusion Our results suggest that upregulation of Ubx transforms cells from a wing blade fate to a haltere fate, and that the presence of haltere cells within the wing blade is the primary defect leading to the adult wing phenotypes observed. PMID:19956620

  4. Genetic Basis of a Violation of Dollos Law: Re-Evolution of Rotating Sex Combs in Drosophila bipectinata

    PubMed Central

    Seher, Thaddeus D.; Ng, Chen Siang; Signor, Sarah A.; Podlaha, Ondrej; Barmina, Olga; Kopp, Artyom

    2012-01-01

    Phylogenetic analyses suggest that violations of Dollos lawthat is, re-evolution of lost complex structuresdo occur, albeit infrequently. However, the genetic basis of such reversals has not been examined. Here, we address this question using the Drosophila sex comb, a recently evolved, male-specific morphological structure composed of modified bristles. In some species, sex comb development involves only the modification of individual bristles, while other species have more complex rotated sex combs that are shaped by coordinated migration of epithelial tissues. Rotated sex combs were lost in the ananassae species subgroup and subsequently re-evolved, ?12 million years later, in Drosophila bipectinata and its sibling species. We examine the genetic basis of the differences in sex comb morphology between D. bipectinata and D. malerkotliana, a closely related species with a much simpler sex comb representing the ancestral condition. QTL mapping reveals that >50% of this difference is controlled by one chromosomal inversion that covers ?5% of the genome. Several other, larger inversions do not contribute appreciably to the phenotype. This genetic architecture suggests that rotating sex combs may have re-evolved through changes in relatively few genes. We discuss potential developmental mechanisms that may allow lost complex structures to be regained. PMID:23086218

  5. Characterization of the Cis-Regulatory Region of the Drosophila Homeotic Gene Sex Combs Reduced

    PubMed Central

    Gindhart-Jr., J. G.; King, A. N.; Kaufman, T. C.

    1995-01-01

    The Drosophila homeotic gene Sex combs reduced (Scr) controls the segmental identity of the labial and prothoracic segments in the embryo and adult. It encodes a sequence-specific transcription factor that controls, in concert with other gene products, differentiative pathways of tissues in which Scr is expressed. During embryogenesis, Scr accumulation is observed in a discrete spatiotemporal pattern that includes the labial and prothoracic ectoderm, the subesophageal ganglion of the ventral nerve cord and the visceral mesoderm of the anterior and posterior midgut. Previous analyses have demonstrated that breakpoint mutations located in a 75-kb interval, including the Scr transcription unit and 50 kb of upstream DNA, cause Scr misexpression during development, presumably because these mutations remove Scr cis-regulatory sequences from the proximity of the Scr promoter. To gain a better understanding of the regulatory interactions necessary for the control of Scr transcription during embryogenesis, we have begun a molecular analysis of the Scr regulatory interval. DNA fragments from this 75-kb region were subcloned into P-element vectors containing either an Scr-lacZ or hsp70-lacZ fusion gene, and patterns of reporter gene expression were assayed in transgenic embryos. Several fragments appear to contain Scr regulatory sequences, as they direct reporter gene expression in patterns similar to those normally observed for Scr, whereas other DNA fragments direct Scr reporter gene expression in developmentally interesting but non-Scr-like patterns during embryogenesis. Scr expression in some tissues appears to be controlled by multiple regulatory elements that are separated, in some cases, by more than 20 kb of intervening DNA. Interestingly, regulatory sequences that direct reporter gene expression in an Scr-like pattern in the anterior and posterior midgut are imbedded in the regulatory region of the segmentation gene fushi tarazu (ftz), which is normally located between 10 and 20 kb 5' of the Scr transcription start site. This analysis provides an entry point for the study of how Scr transcription is regulated at the molecular level. PMID:7713432

  6. The Polycomb-group gene, extra sex combs, encodes a nuclear member of the WD-40 repeat family.

    PubMed Central

    Gutjahr, T; Frei, E; Spicer, C; Baumgartner, S; White, R A; Noll, M

    1995-01-01

    We have delimited the extra sex combs (esc) gene to < 4 kb that include a single transcript and are able to rescue both the maternal and zygotic esc phenotypes. Several mutations have been identified within the esc transcript. In agreement with earlier genetic studies, esc is expressed maternally and its product is most abundant during the early embryonic stages. It encodes a protein of the WD-40 repeat family, which localizes predominantly to the nucleus. During germ band extension, it is expressed in a stereotypic pattern of neuroblasts. We propose a model in which Esc is recruited by gap proteins both to act as a corepressor that competes with the TAFII80 coactivator to block transcription and also to mediate the transition to permanent repression by Polycomb-group proteins. Images PMID:7556071

  7. A Logical OR Redundancy Within the Asx-Pro-Asx-Gly Type I beta-Turn Motif

    SciTech Connect

    Lee,J.; Dubey, V.; Longo, L.; Blaber, M.

    2008-01-01

    Turn secondary structure is essential to the formation of globular protein architecture. Turn structures are, however, much more complex than either ?-helix or ?-sheet, and the thermodynamics and folding kinetics are poorly understood. Type I ?-turns are the most common type of reverse turn, and they exhibit a statistical consensus sequence of Asx-Pro-Asx-Gly (where Asx is Asp or Asn). A comprehensive series of individual and combined Asx mutations has been constructed within three separate type I 3:5 G1 bulge ?-turns in human fibroblast growth factor-1, and their effects on structure, stability, and folding have been determined. The results show a fundamental logical OR relationship between the Asx residues in the motif, involving H-bond interactions with main-chain amides within the turn. These interactions can be modulated by additional interactions with residues adjacent to the turn at positions i + 4 and i + 6. The results show that the Asx residues in the turn motif make a substantial contribution to the overall stability of the protein, and the Asx logical OR relationship defines a redundant system that can compensate for deleterious point mutations. The results also show that the stability of the turn is unlikely to be the prime determinant of formation of turn structure in the folding transition state.

  8. A Logical OR Redundancy within the Asx-Pro-Asx-Gly Type 1 {Beta}-Turn Motif

    SciTech Connect

    Lee, Jihun; Dubey, Vikash Kumar; Longo, Lian M.; Blaber, Michael

    2008-04-19

    Turn secondary structure is essential to the formation of globular protein architecture. Turn structures are, however, much more complex than either {alpha}-helix or {beta}-sheet, and the thermodynamics and folding kinetics are poorly understood. Type I {beta}-turns are the most common type of reverse turn, and they exhibit a statistical consensus sequence of Asx-Pro-Asx-Gly (where Asx is Asp or Asn). A comprehensive series of individual and combined Asx mutations has been constructed within three separate type I 3:5 G1 bulge {beta}-turns in human fibroblast growth factor-1, and their effects on structure, stability, and folding have been determined. The results show a fundamental logical OR relationship between the Asx residues in the motif, involving H-bond interactions with main-chain amides within the turn. These interactions can be modulated by additional interactions with residues adjacent to the turn at positions i + 4 and i + 6. The results show that the Asx residues in the turn motif make a substantial contribution to the overall stability of the protein, and the Asx logical OR relationship defines a redundant system that can compensate for deleterious point mutations. The results also show that the stability of the turn is unlikely to be the prime determinant of formation of turn structure in the folding transition state.

  9. Expression and properties of wild-type and mutant forms of the Drosophila sex comb on midleg (SCM) repressor protein.

    PubMed Central

    Bornemann, D; Miller, E; Simon, J

    1998-01-01

    The Sex comb on midleg (Scm) gene encodes a transcriptional repressor of the Polycomb group (PcG). Here we show that SCM protein is nuclear and that its expression is widespread during fly development. SCM protein contains a C-terminal domain, termed the SPM domain, which mediates protein-protein interactions. The biochemical function of another domain consisting of two 100-amino-acid-long repeats, termed "mbt" repeats, is unknown. We have determined the molecular lesions of nine Scm mutant alleles, which identify functional requirements for specific domains. The Scm alleles were tested for genetic interactions with mutations in other PcG genes. Intriguingly, three hypomorphic Scm mutations, which map within an mbt repeat, interact with PcG mutations more strongly than do Scm null alleles. The strongest interactions produce partial synthetic lethality that affects doubly heterozygous females more severely than males. We show that mbt repeat alleles produce stable SCM proteins that associate with normal sites in polytene chromosomes. We also analyzed progeny from Scm mutant germline clones to compare the effects of an mbt repeat mutation during embryonic vs. pupal development. We suggest that the mbt repeat alleles produce altered SCM proteins that incorporate into and impair function of PcG protein complexes. PMID:9755199

  10. Distinct self-interaction domains promote Multi Sex Combs accumulation in and formation of the Drosophila histone locus body

    PubMed Central

    Terzo, Esteban A.; Lyons, Shawn M.; Poulton, John S.; Temple, Brenda R. S.; Marzluff, William F.; Duronio, Robert J.

    2015-01-01

    Nuclear bodies (NBs) are structures that concentrate proteins, RNAs, and ribonucleoproteins that perform functions essential to gene expression. How NBs assemble is not well understood. We studied the Drosophila histone locus body (HLB), a NB that concentrates factors required for histone mRNA biosynthesis at the replication-dependent histone gene locus. We coupled biochemical analysis with confocal imaging of both fixed and live tissues to demonstrate that the Drosophila Multi Sex Combs (Mxc) protein contains multiple domains necessary for HLB assembly. An important feature of this assembly process is the self-interaction of Mxc via two conserved N-terminal domains: a LisH domain and a novel self-interaction facilitator (SIF) domain immediately downstream of the LisH domain. Molecular modeling suggests that the LisH and SIF domains directly interact, and mutation of either the LisH or the SIF domain severely impairs Mxc function in vivo, resulting in reduced histone mRNA accumulation. A region of Mxc between amino acids 721 and 1481 is also necessary for HLB assembly independent of the LisH and SIF domains. Finally, the C-terminal 195 amino acids of Mxc are required for recruiting FLASH, an essential histone mRNA-processing factor, to the HLB. We conclude that multiple domains of the Mxc protein promote HLB assembly in order to concentrate factors required for histone mRNA biosynthesis. PMID:25694448

  11. Setting limits on homeotic gene function: restraint of Sex combs reduced activity by teashirt and other homeotic genes.

    PubMed Central

    Andrew, D J; Horner, M A; Petitt, M G; Smolik, S M; Scott, M P

    1994-01-01

    Each of the homeotic genes of the HOM or HOX complexes is expressed in a limited domain along the anterior-posterior axis. Each homeotic protein directs the formation of characteristic structures, such as wings or ribs. In flies, when a heat shock-inducible homeotic gene is used to produce a homeotic protein in all cells of the embryo, only some cells respond by altering their fates. We have identified genes that limit where the homeotic gene Sex combs reduced (Scr) can affect cell fates in the Drosophila embryo. In the abdominal cuticle Scr is prevented from inducing prothoracic structures by the three bithorax complex (BX-C) homeotic genes. However, two of the BX-C homeotic genes, Ultrabithorax (Ubx) and abdominal-A (abd-A), have no effect on the ability of Scr to direct the formation of salivary glands. Instead, salivary gland induction by Scr is limited in the trunk by the homeotic gene teashirt (tsh) and in the last abdominal segment by the third BX-C gene, Abdominal-B (AbdB). Therefore, spatial restrictions on homeotic gene activity differ between tissues and result both from the regulation of homeotic gene transcription and from restraints on where homeotic proteins can function. Images PMID:7907545

  12. Sex comb on midleg (Scm) is a functional link between PcG-repressive complexes in Drosophila

    PubMed Central

    Kang, Hyuckjoon; McElroy, Kyle A.; Jung, Youngsook Lucy; Alekseyenko, Artyom A.; Zee, Barry M.; Park, Peter J.

    2015-01-01

    The Polycomb group (PcG) proteins are key regulators of development in Drosophila and are strongly implicated in human health and disease. How PcG complexes form repressive chromatin domains remains unclear. Using cross-linked affinity purifications of BioTAP-Polycomb (Pc) or BioTAP-Enhancer of zeste [E(z)], we captured all PcG-repressive complex 1 (PRC1) or PRC2 core components and Sex comb on midleg (Scm) as the only protein strongly enriched with both complexes. Although previously not linked to PRC2, we confirmed direct binding of Scm and PRC2 using recombinant protein expression and colocalization of Scm with PRC1, PRC2, and H3K27me3 in embryos and cultured cells using ChIP-seq (chromatin immunoprecipitation [ChIP] combined with deep sequencing). Furthermore, we found that RNAi knockdown of Scm and overexpression of the dominant-negative Scm-SAM (sterile ? motif) domain both affected the binding pattern of E(z) on polytene chromosomes. Aberrant localization of the Scm-SAM domain in long contiguous regions on polytene chromosomes revealed its independent ability to spread on chromatin, consistent with its previously described ability to oligomerize in vitro. Pull-downs of BioTAP-Scm captured PRC1 and PRC2 and additional repressive complexes, including PhoRC, LINT, and CtBP. We propose that Scm is a key mediator connecting PRC1, PRC2, and transcriptional silencing. Combined with previous structural and genetic analyses, our results strongly suggest that Scm coordinates PcG complexes and polymerizes to produce broad domains of PcG silencing. PMID:26063573

  13. Identification of polycomb and trithorax group responsive elements in the regulatory region of the Drosophila homeotic gene Sex combs reduced

    SciTech Connect

    Gindhart, J.G. Jr.; Kaufman, T.C.

    1995-02-01

    The Drosophilia homeotic gene Sex combs reduced (Scr) is necessary for the establishment and maintenance of the morphological identity of the labial and prothoracic segments. In the early embryo, its expression pattern is established through the activity of several gap and segmentation gene products, as well as other transcription factors. Once established, the Polycomb group (Pc-G) and trithorax group (trx-G) gene products maintain the spatial pattern of Scr expression for the remainder of development. We report the identification of DNA fragments in the Scr regulatory region that may be important for its regulation by Polycomb and trithorax group gene products. When DNA fragments containing these regulatory sequences are subcloned into P-element vectors containing a white minigene, transformants containing these constructs exhibit mosaic patterns of pigmentation in the adult eye, indicating that white minigene expression is repressed in a clonally heritable manner. The size of pigmented and nonpigmented clones in the adult eye suggests that the event determining whether a cell in the eye anlagen will express white occurs at least as early as the first larval instar. The amount of white minigene repression is reduced in some Polycomb group mutants, whereas repression is enhanced in flies mutant for a subset of trithorax group loci. The repressor activity of one fragment, normally located in Scr Intron 2, is increased when it is able to homologously pair, a property consistent with genetic data suggesting that Scr exhibits transvection. Another Scr regulatory fragment, normally located 40 kb upstream of the Scr promoter, silences ectopic expression of an Scr-lacZ fusion gene in the embryo and does so in a Polycomb-dependent manner. We propose that the regulatory sequences located within these DNA fragments may normally mediate the regulation of Scr by proteins encoded by members of Polycomb and trithorax group loci. 98 refs., 6 figs., 4 tabs.

  14. The gap gene Krppel of Rhodnius prolixus is required for segmentation and for repression of the homeotic gene sex comb-reduced.

    PubMed

    Lavore, Andrs; Esponda-Behrens, Natalia; Pagola, Luca; Rivera-Pomar, Rolando

    2014-03-01

    The establishment of the anterior-posterior segmentation in insects requires the concerted action of a hierarchical gene network. Here, we study the orthologue of Krppel gap gene in the hemipteran Rhodnius prolixus (Rp-Kr). We characterized its structure, expression pattern and function. The genomic sequence upstream of the Rp-Kr transcriptional unit shows a putative regulatory region conserved in the orthologue genes from Drosophila melanogaster and Tribolium castaneum. Rp-Kr expression is zygotic and it is expressed in the anterior half of the embryo (the posterior half of the egg) during the blastoderm stage and germ band formation; later, during germ band extension, it is expressed in a central domain, from T2 to A3. The Rp-Kr loss of function phenotypes shows disrupted thoracic and abdominal segmentation. Embryos with weak segmentation phenotypes show homeotic transformations, in which an ectopic tibial comb, typical of T1 leg, appears in T2, which correlates with the ectopic expression of Rp-sex-comb reduced in this leg. PMID:24406318

  15. Compact electrostatic comb actuator

    DOEpatents

    Rodgers, M. Steven (Albuquerque, NM); Burg, Michael S. (Albuquerque, NM); Jensen, Brian D. (Albuquerque, NM); Miller, Samuel L. (Albuquerque, NM); Barnes, Stephen M. (Albuquerque, NM)

    2000-01-01

    A compact electrostatic comb actuator is disclosed for microelectromechanical (MEM) applications. The actuator is based upon a plurality of meshed electrostatic combs, some of which are stationary and others of which are moveable. One or more restoring springs are fabricated within an outline of the electrostatic combs (i.e. superposed with the moveable electrostatic combs) to considerably reduce the space required for the actuator. Additionally, a truss structure is provided to support the moveable electrostatic combs and prevent bending or distortion of these combs due to unbalanced electrostatic forces or external loading. The truss structure formed about the moveable electrostatic combs allows the spacing between the interdigitated fingers of the combs to be reduced to about one micron or less, thereby substantially increasing the number of active fingers which can be provided in a given area. Finally, electrostatic shields can be used in the actuator to substantially reduce unwanted electrostatic fields to further improve performance of the device. As a result, the compact electrostatic comb actuator of the present invention occupies only a fraction of the space required for conventional electrostatic comb actuators, while providing a substantial increase in the available drive force (up to one-hundred times).

  16. Tuneable electromechanical comb generation

    NASA Astrophysics Data System (ADS)

    Mahboob, I.; Wilmart, Q.; Nishiguchi, K.; Fujiwara, A.; Yamaguchi, H.

    2012-03-01

    An array of equally spaced oscillations or a comb is created within the bandwidth of the fundamental mode of an electromechanical resonator. This phenomenon utilises 2 continuous-wave (CW) pump excitations that piezoelectrically modulate the tension in the mechanical element and is seeded by a CW harmonic excitation of the first mode i.e., the signal. The resultant comb can be dynamically manipulated via the pumps and signal where the teeth separation can be tuned over 3 orders of magnitude and the comb density can be increased from just 2 teeth to nearly 102.

  17. Dynamics of comb-of-comb networks

    NASA Astrophysics Data System (ADS)

    Liu, Hongxiao; Lin, Yuan; Dolgushev, Maxim; Zhang, Zhongzhi

    2016-03-01

    The dynamics of complex networks, a current hot topic in many scientific fields, is often coded through the corresponding Laplacian matrix. The spectrum of this matrix carries the main features of the networks' dynamics. Here we consider the deterministic networks which can be viewed as "comb-of-comb" iterative structures. For their Laplacian spectra we find analytical equations involving Chebyshev polynomials whose properties allow one to analyze the spectra in deep. Here, in particular, we find that in the infinite size limit the corresponding spectral dimension goes as ds→2 . The ds leaves its fingerprint on many dynamical processes, as we exemplarily show by considering the dynamical properties of polymer networks, including single monomer displacement under a constant force, mechanical relaxation, and fluorescence depolarization.

  18. Frequency comb swept lasers

    PubMed Central

    Tsai, Tsung-Han; Zhou, Chao; Adler, Desmond C.; Fujimoto, James G.

    2010-01-01

    We demonstrate a frequency comb (FC) swept laser and a frequency comb Fourier domain mode locked (FC-FDML) laser for applications in optical coherence tomography (OCT). The fiber-based FC swept lasers operate at a sweep rate of 1kHz and 120kHz, respectively over a 135nm tuning range centered at 1310nm with average output powers of 50mW. A 25GHz free spectral range frequency comb filter in the swept lasers causes the lasers to generate a series of well defined frequency steps. The narrow bandwidth (0.015nm) of the frequency comb filter enables a ~?1.2dB sensitivity roll off over ~3mm range, compared to conventional swept source and FDML lasers which have ?10dB and ?5dB roll offs, respectively. Measurements at very long ranges are possible with minimal sensitivity loss, however reflections from outside the principal measurement range of 03mm appear aliased back into the principal range. In addition, the frequency comb output from the lasers are equally spaced in frequency (linear in k-space). The filtered laser output can be used to self-clock the OCT interference signal sampling, enabling direct fast Fourier transformation of the fringe signals, without the need for fringe recalibration procedures. The design and operation principles of FC swept lasers are discussed and designs for short cavity lasers for OCT and interferometric measurement applications are proposed. PMID:19997365

  19. Tellurium n-type doping of highly mismatched amorphous GaN1-xAsx alloys in plasma-assisted molecular beam epitaxy

    DOE PAGESBeta

    Novikov, S. V.; Ting, M.; Yu, K. M.; Sarney, W. L.; Martin, R. W.; Svensson, S. P.; Walukiewicz, W.; Foxon, C. T.

    2014-10-01

    In this paper we report our study on n-type Te doping of amorphous GaN1-xAsx layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN1-xAsx layers has been successfully achieved with a maximum Te concentration of 9×10²⁰ cm⁻³. Tellurium incorporation resulted in n-doping of GaN1-xAsx layers with Hall carrier concentrations up to 3×10¹⁹ cm⁻³ and mobilities of ~1 cm²/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN1-xAsx layers has been determined.

  20. Tellurium n-type doping of highly mismatched amorphous GaN1-xAsx alloys in plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Ting, M.; Yu, K. M.; Sarney, W. L.; Martin, R. W.; Svensson, S. P.; Walukiewicz, W.; Foxon, C. T.

    2014-10-01

    In this paper we report our study on n-type Te doping of amorphous GaN1-xAsx layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN1-xAsx layers has been successfully achieved with a maximum Te concentration of 91020 cm-3. Tellurium incorporation resulted in n-doping of GaN1-xAsx layers with Hall carrier concentrations up to 31019 cm-3 and mobilities of ~1 cm2/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN1-xAsx layers has been determined.

  1. Butelase 1 is an Asx-specific ligase enabling peptide macrocyclization and synthesis.

    PubMed

    Nguyen, Giang K T; Wang, Shujing; Qiu, Yibo; Hemu, Xinya; Lian, Yilong; Tam, James P

    2014-09-01

    Proteases are ubiquitous in nature, whereas naturally occurring peptide ligases, enzymes catalyzing the reverse reactions of proteases, are rare occurrences. Here we describe the discovery of butelase 1, to our knowledge the first asparagine/aspartate (Asx) peptide ligase to be reported. This highly efficient enzyme was isolated from Clitoria ternatea, a cyclic peptide-producing medicinal plant. Butelase 1 shares 71% sequence identity and the same catalytic triad with legumain proteases but does not hydrolyze the protease substrate of legumain. Instead, butelase 1 cyclizes various peptides of plant and animal origin with yields greater than 95%. With Kcat values of up to 17 s(-1) and catalytic efficiencies as high as 542,000 M(-1) s(-1), butelase 1 is the fastest peptide ligase known. Notably, butelase 1 also displays broad specificity for the N-terminal amino acids of the peptide substrate, thus providing a new tool for C terminus-specific intermolecular peptide ligations. PMID:25038786

  2. Dual-comb MIXSEL

    NASA Astrophysics Data System (ADS)

    Link, S. M.; Zaugg, C. A.; Klenner, A.; Mangold, M.; Golling, M.; Tilma, B. W.; Keller, U.

    2015-03-01

    We present a single semiconductor disk laser simultaneously emitting two different gigahertz modelocked pulse trains. A birefringent crystal inside a modelocked integrated external-cavity surface-emitting laser (MIXSEL) separates the cavity beam into two spatially separated beams with perpendicular polarizations on the MIXSEL chip. This MIXSEL then generates two orthogonally polarized collinear modelocked pulse trains from one simple straight cavity. Superimposing the beams on a photo detector creates a microwave beat signal, representing a strikingly simple setup to down-convert the terahertz optical frequencies into the electronically accessible microwave regime. This makes the dual-comb MIXSEL scheme an ultra-compact and cost-efficient candidate for dual-comb spectroscopy applications.

  3. Structural investigations of Ge5AsxSe95-x and Ge15AsxSe85-x glasses using x-ray diffraction and extended x-ray fine structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Kaban, I.; Jvri, P.; Wang, R.-P.; Luther-Davies, B.; Mattern, N.; Eckert, J.

    2012-09-01

    The structure of Ge5AsxSe95-x (x = 10, 20, 30, 38 at.%) and Ge15AsxSe85-x (x = 10, 25, 34 at.%) glasses has been investigated by high-energy x-ray diffraction and extended x-ray absorption fine structure measurements. The experimental datasets have been modelled using the reverse Monte Carlo simulation technique. The model atomic configurations have been analysed in detail. It has been found that the homonuclear Ge-Ge, As-As, Se-Se and heteronuclear Ge-As bonds play an important role in the structure formation of the Ge-As-Se glasses. The total number of these bonds decreases quite slowly with the mean coordination number similarly to the nonlinear refractive index.

  4. Spectrally resolved frequency comb interferometry

    NASA Astrophysics Data System (ADS)

    van den Berg, S.

    2014-04-01

    In this contribution a novel method for interferometric distance measurement is presented, that is based on unraveling the spectrum of a femtosecond frequency comb. The light of a frequency comb is sent into a Michelson interferometer. The output of the interferometer is analyzed by a high-resolution spectrometer, resolving the individual comb modes. The path-length difference between the two arms is determined on the level of tens of nm, by utilizing the wealth of information present in the unraveled spectrum, showing homodyne interference for each individual frequency comb mode. The measurement method allows for high-accuracy measurements in combination with a large range of non-ambiguity.

  5. The gap structure of BaFe2(AsxP1-x)2 determined from specific heat measurements

    NASA Astrophysics Data System (ADS)

    Malone, L.; Mizukami, Y.; Walmsley, P.; Putzke, C.; Kasahara, S.; Terashima, T.; Shibauchi, T.; Matsuda, Y.; Carrington, A.

    2014-03-01

    The structure of the superconducting gap of the pncitide superconductors is an unresolved but crucial issue to understanding their mechanism of superconductivity. While some experiments and theories support a fully gapped s+/s- state, several experiments have revealed evidence for nodes in some families of pnictides. Detailed knowledge of the superconducting gap structure and how it varies as a function of material properties can be useful in helping to decide between microscopic theories. BaFe2(AsxP1-x)2 is a pnictide family with a nodal gap structure and evidence for quantum critical behavior. We have measured the specific heat of several samples of BaFe2(AsxP1-x)2 in a range of x values. We examine the temperature, field and field angle dependence of the specific heat to deduce the changes in the superconducting gap structure as the material is tuned to the quantum critical point.

  6. Molecular Spectroscopy with Frequency Combs

    NASA Astrophysics Data System (ADS)

    Coddington, Ian

    2010-03-01

    Pulsed femtosecond frequency combs are rapidly developing as a powerful spectroscopic tool. As a spectroscopic source stabilized frequency combs potentially offer broad spectral coverage, near perfect frequency accuracy, low timing jitter and broadband compatibility with resonant cavities. This talk will focus on the first three advantages in a dual comb spectroscopic technique that is highly analogous to traditional Fourier transform spectroscopy. In the dual comb approach, (pioneered in the THz by Keilmann, Van der Weide and coworkers under the name multi-heterodyne spectroscopy), one comb is used to sample a gas and a second frequency comb serves as a local oscillator (LO) that samples the first comb. The LO is held at a slightly different repetition rate than the first comb. When viewed in the time domain, the comb sources each emit a train of pulses. With the difference in repetition rates, for each successive pair of pulses, the timing between the sample and LO laser pulses shifts slightly. Through successive measurements, the LO pulses read out the entire time domain structure of the transmitted sample pulse. Through a Fourier transform, we recover the broadband, complex, absorption profile of the sample gas. In analogy to a Fourier transform spectrometer the LO serves as a scanning interferometer arm. The removal of moving parts from the system along with the addition of high brightness collimated sources brings new flexibility to FTIR spectroscopy. This talk will focus on strengths and limitations of the dual comb technique. Specifically we focus on comb stabilization techniques that allow for long averaging periods, firmware based averaging techniques that keep data sizes manageable and allow for realtime data processing, time domain multiplexing of signal and reference data for continuous removal of system drift, and difference frequency generation techniques to extend this system into the mid IR. We will also discuss methods to improve the sensitivity of this technique as well as tradeoffs between sensitivity and resolution, while maintaining the inherent frequency accuracy of this system.

  7. Molecular Comb Development

    SciTech Connect

    Ferrell, T.L.; Thundat, G.T.; Witkowski, C.E., III

    2007-07-17

    This CRADA was developed to enable ORNL to assist Protein Discovery, Inc. to develop a novel biomolecular separation system based on an ORNL patent application 'Photoelectrochemical Molecular Comb' by Thundat, Ferrell, and Brown. The Molecular Comb concept is based on creating light-induced charge carriers at a semiconductor-liquid interface, which is kept at a potential control such that a depletion layer is formed in the semiconductor. Focusing light from a low-power illumination source creates electron-hole pairs, which get separated in the depletion layer. The light-induced charge carriers reaching the surface attract oppositely charged biomolecules present in the solution. The solution is a buffer solution with very small concentrations of biomolecules. As the focused light is moved across the surface of the semiconductor-liquid interface, the accumulated biomolecules follow the light beam. A thin layer of gel or other similar material on the surface of the semiconductor can act as a sieving medium for separating the biomolecules according to their sizes.

  8. Material properties and modeling characteristics for MnFeP1-xAsx materials for application in magnetic refrigeration

    NASA Astrophysics Data System (ADS)

    Engelbrecht, K.; Nielsen, K. K.; Bahl, C. R. H.; Carroll, C. P.; van Asten, D.

    2013-05-01

    Compounds of MnFeP1-xAsx have received attention recently for their use in active magnetic regenerators (AMR) because of their relatively high isothermal entropy change and adiabatic temperature change with magnetization. However, the materials also generally exhibit a significant magnetic and thermal hysteresis, and it is not well understood how the hysteresis will affect performance in a practical AMR device. The amount of hysteresis shown by a material can be controlled to an extent by tuning the processing conditions used during material synthesis; therefore, knowledge of the practical impact of hysteresis is a key element to guide successful material development and synthesis. The properties of a magnetocaloric MnFeP1-xAsx compound are characterized as a function of temperature and applied magnetic field, and the results are used to assess the effects of hysteresis on magnetocaloric properties. Different methods of building property functions from the measured specific heat, magnetization, and adiabatic temperature change are presented. It is shown that model predictions can be highly dependent on how the properties that are used by the AMR model are calculated.

  9. Tensile-strained GaAs quantum wells and quantum dots in a GaAsxSb1-x matrix

    NASA Astrophysics Data System (ADS)

    Toropov, A. A.; Lyublinskaya, O. G.; Meltser, B. Ya.; Solov'Ev, V. A.; Sitnikova, A. A.; Nestoklon, M. O.; Rykhova, O. V.; Ivanov, S. V.; Thonke, K.; Sauer, R.

    2004-11-01

    We report on the fabrication and analysis of tensily strained thin GaAs layers (insertion layers) in a GaAsxSb1-x matrix (x<0.05) . The GaAs insertion layers vary in nominal thickness in the range of 0.6-2 monolayers. They were grown by molecular beam epitaxy on GaSb substrates. Transmission electron microscopy studies indicated either growth of ultra-thin quantum wells (QWs) or self-organized formation of quantum dots (QDs), depending on the nominal thickness of the insertion layers. Two photoluminescence (PL) peaks are observed at photon energies below the GaAsxSb1-x band edge. One of them, detected near 0.7eV for any insertion layer thickness, is attributed to the emission of a type II QW. The second peak shifted toward smaller energies in the thicker insertion layers is assigned to the PL of type II QDs. This assignment is supported by microscopic tight-binding calculations of the QW electron states.

  10. Lossless equalization of frequency combs.

    PubMed

    Torres-Company, Vctor; Lancis, Jess; Andrs, Pedro

    2008-08-15

    Frequency combs obtained by sinusoidal phase modulation of narrowband cw lasers are widely used in the field of optical communications. However, the resulting spectral envelope of the comb is not flat. We propose a general and efficient approach to achieve flat frequency combs with tunable bandwidth. The idea is based on a two-step process. First, efficient generation of a train with a temporal flat-top-pulse profile is required. Second, we use large parabolic phase modulation in every train period to map the temporal intensity shape into the spectral domain. In this way the resulting spectral envelope is flat, and the size is tunable with the chirping rate. Two different schemes are proposed and verified through numerical simulations. PMID:18709099

  11. Broadband midinfrared frequency comb with tooth scanning

    NASA Astrophysics Data System (ADS)

    Lee, Kevin F.; Mas?owski, P.; Mills, A.; Mohr, C.; Jiang, Jie; Schunemann, Peter G.; Fermann, M. E.

    2015-03-01

    Frequency combs are a massively parallel source of extremely accurate optical frequencies. Frequency combs generally operate at the visible or near-infrared wavelengths, but fundamental molecular vibrations occur at midinfrared wavelengths. We demonstrate an optically-referenced, broadband midinfrared frequency comb based on a doublyresonant optical parametric oscillator (OPO). By tuning the wavelength of the reference laser, the comb line frequencies are tuned as well. By scanning the reference wavelength, any frequency can be accessed, not just the frequencies of the base comb. Combined with our comb-resolving Fourier transform spectrometer, we can measure 200 wavenumber wide broadband absorption spectra with 200 kHz linewidth comb teeth. Our OPO is pumped by an amplified Tm fiber frequency comb, with phase-locked carrier envelope offset frequency, and repetition rate fixed by phase-locking a frequency comb line to a narrow linewidth diode laser at a telecom channel. The frequency comb is referenced to GPS by long-term stabilization of the repetition rate to a selected value using the temperature of the reference laser as the control. The resulting pump comb is about 3W of 100 fs pulses at 418 MHz repetition rate at 1950 nm. Part of the comb is used for supercontinuum generation for frequency stabilization, and the rest pumps an orientation-patterned gallium arsenide (OP-GaAs) crystal in a doubly-resonant optical parametric oscillator cavity, yielding collinear signal and idler beams from about 3 to 5.5 ?m. We verify comb scanning by resolving the 200 MHz wide absorption lines of the entire fundamental CO vibrational manifold at 11 Torr pressure.

  12. On-chip dual-comb based on quantum cascade laser frequency combs

    NASA Astrophysics Data System (ADS)

    Villares, G.; Wolf, J.; Kazakov, D.; Süess, M. J.; Hugi, A.; Beck, M.; Faist, J.

    2015-12-01

    Dual-comb spectroscopy is emerging as an appealing application of mid-infrared frequency combs for high-resolution molecular spectroscopy, as it leverages on the unique coherence properties of frequency combs. Here, we present an on-chip dual-comb source based on mid-infrared quantum cascade laser frequency combs. Control of the combs repetition and offset frequencies is obtained by integrating micro-heaters next to each laser. We show that a full control of the dual-comb system is possible, by measuring a multi-heterodyne beating corresponding to an optical bandwidth of 32 cm-1 centered at 1330 cm-1 (7.52 μm), demonstrating that this device represents a critical step towards compact dual-comb systems.

  13. Visible wavelength astro-comb.

    PubMed

    Benedick, Andrew J; Chang, Guoqing; Birge, Jonathan R; Chen, Li-Jin; Glenday, Alexander G; Li, Chih-Hao; Phillips, David F; Szentgyorgyi, Andrew; Korzennik, Sylvain; Furesz, Gabor; Walsworth, Ronald L; Krtner, Franz X

    2010-08-30

    We demonstrate a tunable laser frequency comb operating near 420 nm with mode spacing of 20-50 GHz, usable bandwidth of 15 nm and output power per line of ~20 nW. Using the TRES spectrograph at the Fred Lawrence Whipple Observatory, we characterize this system to an accuracy below 1m/s, suitable for calibrating high-resolution astrophysical spectrographs used, e.g., in exoplanet studies. PMID:20940813

  14. Sequence analysis of a pea comb locus on chicken chromosome 1.

    PubMed

    Sato, S; Sato, S; Otake, T; Suzuki, C; Uemoto, Y; Saburi, J; Hashimoto, H; Kobayashi, E

    2010-12-01

    To facilitate gene identification, this study aimed to narrow the scope of the genome region affecting chicken comb type by using two bird populations. First, an F2 resource population was generated by crossing Japanese game fowl (Shamo; pea comb, P/p and P/P) with White Plymouth Rock (single comb, p/p). Comb types of the 240 F2 offspring produced by an F1 intercross between eight males and 57 females were segregated at a ratio of 3:1 (pea:single). The pea comb locus was mapped to a chromosomal region on Gallus gallus chromosome 1 that was flanked by microsatellite markers MCW0112, MCW0019 and ABR521. The second population (five-generation, n=1300 animals) was derived from a cross between Shamo and Rhode Island Red (single comb, p/p) that had been genotyped for additional polymorphic single nucleotide polymorphisms and microsatellite markers within this region through development of chicken draft sequences. To close some gaps in these draft sequences, we constructed a bacterial artificial chromosome contig and sequenced it using the shotgun sequencing technique. Chickens selected from pedigrees in these populations were grouped by inheritance of a P or p haplotype at the locus constructed by the additional markers. Finally, this locus was fine-mapped to roughly 60 kb based on the association of haplotypes and comb types. Chicken genome sequences suggest that the most likely polymorphism responsible for the pea comb locus is a duplicated sequence and that the sex determining region Y-box 5 gene, one predicted gene and one expressed sequence tag in a critical region may be associated with the duplicated sequence. PMID:20412124

  15. Charge carrier localization effects on the quantum efficiency and operating temperature range of InAsxP1-x/InP quantum well detectors

    NASA Astrophysics Data System (ADS)

    Vashisht, Geetanjali; Dixit, V. K.; Porwal, S.; Kumar, R.; Sharma, T. K.; Oak, S. M.

    2016-03-01

    The effect of charge carrier localization resulting in "S-shaped" temperature dependence of the photoluminescence peak energy of InAsxP1-x/InP quantum wells (QWs) is distinctly revealed by the temperature dependent surface photo voltage (SPV) and photoconductivity (PC) processes. It is observed that the escape efficiency of carriers from QWs depends on the localization energy, where the carriers are unable to contribute in SPV/PC signal below a critical temperature. Below the critical temperature, carriers are strongly trapped in the localized states and are therefore unable to escape from the QW. Further, the critical temperature increases with the magnitude of localization energy of carriers. Carrier localization thus plays a pivotal role in defining the operating temperature range of InAsxP1-x/InP QW detectors.

  16. Ultrafast electrooptic dual-comb interferometry.

    PubMed

    Durn, Vicente; Tainta, Santiago; Torres-Company, Victor

    2015-11-16

    Dual-comb interferometry is a particularly compelling technique that relies on the phase coherence of two laser frequency combs for measuring broadband complex spectra. This method is rapidly advancing the field of optical spectroscopy and empowering new applications, from nonlinear microscopy to laser ranging. Up to now, most dual-comb interferometers were based on modelocked lasers, whose repetition rates have restricted the measurement speed to ~kHz. Here we demonstrate a dual-comb interferometer that is based on electrooptic frequency combs and measures consecutive complex spectra at an ultra-high refresh rate of 25 MHz. These results pave the way for novel scientific and metrology applications of frequency comb generators beyond the realm of molecular spectroscopy, where the measurement of ultrabroadband waveforms is of paramount relevance. PMID:26698533

  17. A Josephson radiation comb generator.

    PubMed

    Solinas, P; Gasparinetti, S; Golubev, D; Giazotto, F

    2015-01-01

    We propose the implementation of a Josephson Radiation Comb Generator (JRCG) based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. When the magnetic flux crosses a diffraction node of the critical current interference pattern, the superconducting phase undergoes a jump of π and a voltage pulse is generated at the extremes of the SQUID. Under periodic drive this allows one to generate a sequence of sharp, evenly spaced voltage pulses. In the frequency domain, this corresponds to a comb-like structure similar to the one exploited in optics and metrology. With this device it is possible to generate up to several hundreds of harmonics of the driving frequency. For example, a chain of 50 identical high-critical-temperature SQUIDs driven at 1 GHz can deliver up to a 0.5 nW at 200 GHz. The availability of a fully solid-state radiation comb generator such as the JRCG, easily integrable on chip, may pave the way to a number of technological applications, from metrology to sub-millimeter wave generation. PMID:26193628

  18. A Josephson radiation comb generator

    PubMed Central

    Solinas, P.; Gasparinetti, S.; Golubev, D.; Giazotto, F.

    2015-01-01

    We propose the implementation of a Josephson Radiation Comb Generator (JRCG) based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. When the magnetic flux crosses a diffraction node of the critical current interference pattern, the superconducting phase undergoes a jump of π and a voltage pulse is generated at the extremes of the SQUID. Under periodic drive this allows one to generate a sequence of sharp, evenly spaced voltage pulses. In the frequency domain, this corresponds to a comb-like structure similar to the one exploited in optics and metrology. With this device it is possible to generate up to several hundreds of harmonics of the driving frequency. For example, a chain of 50 identical high-critical-temperature SQUIDs driven at 1 GHz can deliver up to a 0.5 nW at 200 GHz. The availability of a fully solid-state radiation comb generator such as the JRCG, easily integrable on chip, may pave the way to a number of technological applications, from metrology to sub-millimeter wave generation. PMID:26193628

  19. A Josephson radiation comb generator

    NASA Astrophysics Data System (ADS)

    Solinas, P.; Gasparinetti, S.; Golubev, D.; Giazotto, F.

    2015-07-01

    We propose the implementation of a Josephson Radiation Comb Generator (JRCG) based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. When the magnetic flux crosses a diffraction node of the critical current interference pattern, the superconducting phase undergoes a jump of π and a voltage pulse is generated at the extremes of the SQUID. Under periodic drive this allows one to generate a sequence of sharp, evenly spaced voltage pulses. In the frequency domain, this corresponds to a comb-like structure similar to the one exploited in optics and metrology. With this device it is possible to generate up to several hundreds of harmonics of the driving frequency. For example, a chain of 50 identical high-critical-temperature SQUIDs driven at 1 GHz can deliver up to a 0.5 nW at 200 GHz. The availability of a fully solid-state radiation comb generator such as the JRCG, easily integrable on chip, may pave the way to a number of technological applications, from metrology to sub-millimeter wave generation.

  20. Femtosecond laser comb based subterahertz synthesizer

    NASA Astrophysics Data System (ADS)

    Makarov, D. S.; Tretyakov, M. Yu.; Shkaev, A. P.; Kiselev, A. M.; Stepanov, A. N.; Parshin, V. V.

    2014-08-01

    Functioning layout of a frequency comb-based subterahertz synthesizer is demonstrated. A primary subterahertz oscillator was phase-locked against the Ti:Sapphire femtosecond laser frequency comb down-converted to the subterahertz range by the semiconductor mixer. Synthesizer operation is demonstrated through Fabri-Perot resonator response curve recording experiment. Spectral purity of the synthesizer was estimated. The advantage of the comb-based synthesizer over the synthesizer based on the Agilent E8257D device was shown.

  1. Stabilization of a Kerr frequency comb oscillator.

    PubMed

    Savchenkov, A A; Eliyahu, D; Liang, W; Ilchenko, V S; Byrd, J; Matsko, A B; Seidel, D; Maleki, L

    2013-08-01

    We study stability and spectral purity of a microresonator-based Kerr frequency comb oscillator experimentally and observe a correlation between the frequency of the continuous wave laser pumping the nonlinear resonator and the repetition frequency of the comb. This correlation is used in a proof-of-principle demonstration of a Kerr frequency comb stabilized with an optical transition of 87Rb. PMID:23903097

  2. Scaling of Yb-Fiber Frequency Combs

    NASA Astrophysics Data System (ADS)

    Ruehl, Axel; Marcinkevicius, Andrius; Fermann, Martin E.; Hartl, Ingmar

    2010-06-01

    Immediately after their introduction in 1999, femtosecond laser frequency combs revolutionized the field of precision optical frequency metrology and are key elements in many experiments. Frequency combs based on femtosecond Er-fiber lasers based were demonstrated in 2005, allowing additionally rugged, compact set-ups and reliable unattended long-term operation. The introduction of Yb-fiber technology led to an dramatic improvement in fiber-comb performance in various aspects. Low-noise Yb-fiber femtosecond oscillators enabled a reduction of relative comb tooth linewidth to the sub-Hz level as well as scaling of the fundamental comb spacings up to 1 GHz. This is beneficial for any frequency-domain comb application due to the higher power per comb-mode. Many spectroscopic applications require, however, frequency combs way beyond the wavelength range accessible with broad band laser materials, so nonlinear conversion and hence higher peak intensity is required. We demonstrated power scaling of Yb-fiber frequency combs up to 80 W average power in a strictly linear chirped-pulse amplification schemes compatible with low-noise phase control. These high-power Yb-fiber-frequency combs facilitated not only the extension to the mid-IR spectral region. When coupled to a passive enhancement cavity, the average power can be further scaled to the kW-level opening new capabilities for XUV frequency combs via high-harmonic generation. All these advances of fiber-based frequency combs will trigger many novel applications both in fundamental and applied sciences. Schibli et al., Nature Photonics 2 355 (2008). Hartl et al., MF9 in Advanced Solid-State Photonics. 2009, Optical Society of America. Ruehl et al., AWC7 in Advanced Solid-State Photonics. 2010, Optical Society of America. Adler et al., Optics Letters 34 1330 (2009). Yost et al., Nature Physics 5 815 (2009).

  3. Phononic Frequency Combs through Nonlinear Resonances

    NASA Astrophysics Data System (ADS)

    Cao, L. S.; Qi, D. X.; Peng, R. W.; Wang, Mu; Schmelcher, P.

    2014-02-01

    We explore an analogue of optical frequency combs in driven nonlinear phononic systems, and present a mechanism for generating phononic frequency combs through nonlinear resonances. In the underlying process, a set of phonon modes is simultaneously excited by the external driving which yields frequency combs with an array of discrete and equidistant spectral lines of each nonlinearly excited phonon mode. Frequency combs through nonlinear resonance of different orders are investigated, and in particular the possibility of correlation tailoring in higher-order cases is revealed. We suggest that our results can be applied in various nonlinear acoustic processes, such as phonon harvesting, and can also be generalized to other nonlinear systems.

  4. Bichromatically pumped microresonator frequency combs

    NASA Astrophysics Data System (ADS)

    Hansson, T.; Wabnitz, S.

    2014-07-01

    A study is made of the nonlinear dynamics of bichromatically pumped microresonator Kerr frequency combs described by a driven and damped nonlinear Schrdinger equation, with an additional degree of freedom in the form of the modulation frequency. A truncated four-wave model is derived for the pump modes and the dominant sideband pair, which is found to be able to describe much of the essential dynamical behavior of the full equation. The stability of stationary states within the four-wave model is investigated, and numerical simulations are made to demonstrate that a large range of solutions, including cavity solitons, are possible beyond previously considered low-intensity patterns.

  5. Arthur Wright Combs: A Humanistic Pioneer

    ERIC Educational Resources Information Center

    Magnuson, Sandy

    2012-01-01

    Arthur Wright Combs (1912-1999) championed humanistic counseling and education. He proposed a theory that incorporated humanistic values and cognitive factors. This article features a review of his contributions, an overview of his theory, a synthesis of stories about Combs that were acquired during research interviews, and my commentary on his

  6. Phononic frequency combs through nonlinear resonances

    NASA Astrophysics Data System (ADS)

    Peng, Ru-Wen; Cao, Lu-Shuai; Qi, Dong-Xiang; Wang, Mu; Schmelcher, Peter

    2015-03-01

    It is well known that optical frequency combs have become important coherent optical sources with diverging applications, ranging from optical frequency metrology to ultracold gases. In this work, we explore an analogue of optical frequency combs in driven nonlinear phononic systems, and present a mechanism for generating phononic frequency combs through nonlinear resonances. In the underlying process, a set of phonon modes is simultaneously excited by the external driving which yields frequency combs with an array of discrete and equidistant spectral lines of each nonlinearly excited phonon mode. Frequency combs through nonlinear resonance of different orders are investigated, and in particular the possibility of correlation tailoring in higher-order cases is revealed. We suggest that our results can be applied in various nonlinear acoustic processes, such as phonon harvesting, and can also be generalized to other nonlinear systems. Supported by NSF and MOST of China.

  7. Dual-comb modelocked laser.

    PubMed

    Link, Sandro M; Klenner, Alexander; Mangold, Mario; Zaugg, Christian A; Golling, Matthias; Tilma, Bauke W; Keller, Ursula

    2015-03-01

    In this paper we present the first semiconductor disk laser (SDL) emitting simultaneously two collinearly overlapping cross-polarized gigahertz modelocked pulse trains with different pulse repetition rates. Using only a simple photo detector and a microwave spectrum analyzer directly down-converts the frequency comb difference from the optical to the microwave frequency domain. With this setup, the relative carrier-envelope-offset (CEO) frequency can be accessed directly without an f-to2f interferometer. A very compact design is obtained using the modelocked integrated external-cavity surface emitting laser (MIXSEL) which is part of the family of optically pumped SDLs and similar to a vertical external cavity surface emitting laser (VECSEL) but with both gain and saturable absorber integrated into the same semiconductor wafer (i.e. MIXSEL chip). We then simply added an additional intracavity birefringent crystal inside the linear straight cavity between the output coupler and the MIXSEL chip which splits the cavity beam into two collinear but spatially separated cross-polarized beams on the MIXSEL chip. This results in two modelocked collinear and fully overlapping cross-polarized output beams with adjustable pulse repetition frequencies with excellent noise performance. We stabilized both pulse repetition rates of the dual comb MIXSEL. PMID:25836785

  8. Femtosecond optical parametric oscillator frequency combs

    NASA Astrophysics Data System (ADS)

    Kobayashi, Yohei; Torizuka, Kenji; Marandi, Alireza; Byer, Robert L.; McCracken, Richard A.; Zhang, Zhaowei; Reid, Derryck T.

    2015-09-01

    Techniques to measure and manipulate the carrier-envelope phase within femtosecond optical parametric oscillators (OPOs) allow their outputs to be stabilized in a way that produces a frequency comb structure, potentially tunable throughout the transparency band of the gain material. In this review we describe the fundamental principles of phase control, on which the development of singly- and doubly-resonant OPO frequency combs is based. We give examples of practical embodiments of such combs, and discuss in detail several applications, including spectroscopy, metrology, quantum computation and astrophotonics.

  9. Frequency Comb Generation in Superconducting Resonators

    NASA Astrophysics Data System (ADS)

    Erickson, R. P.; Vissers, M. R.; Sandberg, M.; Jefferts, S. R.; Pappas, D. P.

    2014-10-01

    We have generated frequency combs spanning 0.5 to 20 GHz in superconducting ? /2 resonators at T =3 K . Thin films of niobium-titanium nitride enabled this development due to their low loss, high nonlinearity, low frequency dispersion, and high critical temperature. The combs nucleate as sidebands around multiples of the pump frequency. Selection rules for the allowed frequency emission are calculated using perturbation theory, and the measured spectrum is shown to agree with the theory. Sideband spacing is measured to be accurate to 1 part in 1 08. The sidebands coalesce into a continuous comb structure observed to cover at least several frequency octaves.

  10. Fractional diffusion on a fractal grid comb

    NASA Astrophysics Data System (ADS)

    Sandev, Trifce; Iomin, Alexander; Kantz, Holger

    2015-03-01

    A grid comb model is a generalization of the well known comb model, and it consists of N backbones. For N =1 the system reduces to the comb model where subdiffusion takes place with the transport exponent 1 /2 . We present an exact analytical evaluation of the transport exponent of anomalous diffusion for finite and infinite number of backbones. We show that for an arbitrarily large but finite number of backbones the transport exponent does not change. Contrary to that, for an infinite number of backbones, the transport exponent depends on the fractal dimension of the backbone structure.

  11. Light beam frequency comb generator

    DOEpatents

    Priatko, G.J.; Kaskey, J.A.

    1992-11-24

    A light beam frequency comb generator uses an acousto-optic modulator to generate a plurality of light beams with frequencies which are uniformly separated and possess common noise and drift characteristics. A well collimated monochromatic input light beam is passed through this modulator to produce a set of both frequency shifted and unshifted optical beams. An optical system directs one or more frequency shifted beams along a path which is parallel to the path of the input light beam such that the frequency shifted beams are made incident on the modulator proximate to but separated from the point of incidence of the input light beam. After the beam is thus returned to and passed through the modulator repeatedly, a plurality of mutually parallel beams are generated which are frequency-shifted different numbers of times and possess common noise and drift characteristics. 2 figs.

  12. Light beam frequency comb generator

    DOEpatents

    Priatko, Gordon J.; Kaskey, Jeffrey A.

    1992-01-01

    A light beam frequency comb generator uses an acousto-optic modulator to generate a plurality of light beams with frequencies which are uniformly separated and possess common noise and drift characteristics. A well collimated monochromatic input light beam is passed through this modulator to produce a set of both frequency shifted and unshifted optical beams. An optical system directs one or more frequency shifted beams along a path which is parallel to the path of the input light beam such that the frequency shifted beams are made incident on the modulator proximate to but separated from the point of incidence of the input light beam. After the beam is thus returned to and passed through the modulator repeatedly, a plurality of mutually parallel beams are generated which are frequency-shifted different numbers of times and possess common noise and drift characteristics.

  13. Calculation of tunable type-II band alignments in InAsxSbyP1‑x‑y/InAs heterojunctions

    NASA Astrophysics Data System (ADS)

    Shim, Kyurhee

    2016-01-01

    The energy band gaps of the alloy InAsxSbyP1‑x‑y are calculated using the correlated function expansion (CFE) technique over the entire composition space x and y, for which the CFE band gap composition contour for the mid-infrared (MIR) spectral region of 2 (0.62)–5 µm (0.25 eV) is presented. The composition dependence of the valence-band maximum (VBM) is obtained using the universal tight binding (UTB) method, and the corresponding conduction-band minimum (CBM) can be computed from the difference between the band gap and the VBM. By organizing the relative positions of the VBM and CBM between the quaternary alloy InAsSbP and the binary compound InAs, the band alignments and band types of InAsSbP/InAs heterojunctions (HJs) along the lattice-matching conditions x and y [i.e., y = 0.311(1 ‑ x)] are determined. It is found that the VBMs of the alloy InAsxSbyP1‑x‑y are located within the band gap of InAs, whereas the CBMs of the alloy lie outside the band gap of InAs over the entire composition range. This implies that the InAsxSbyP1‑x‑y/InAs HJs exhibit composition-tunable, type-II (staggered) band alignments. In addition, the conduction-band offset (CBO) and valence-band offset (VBO) of InAsSbP/InAs HJs both present the upward bowing trend, with the CBO curves appearing sharp and the VBO curves appearing smooth.

  14. Femtosecond Comb Coherent Accumulation and Spectroscopy

    NASA Astrophysics Data System (ADS)

    Stowe, Matthew; Lawall, John; Felinto, Daniel; Cruz, Flavio; Ye, Jun

    2005-05-01

    The development of phase stabilized modelocked lasers has enabled a revolution in the field of high precision spectroscopy. The light produced by such a broadband laser typically consists of millions of equally spaced modes spanning many tens of nanometers. Once the comb is referenced to a frequency standard the optical frequencies of the laser modes are known with excellent precision. Current applications of femtosecond frequency combs range from atomic clocks and molecular spectroscopy to frequency transfer and high field physics. The technique of multiple pulse coherent accumulation is used to conduct direct frequency comb spectroscopy via one and two photon absorption in cold Rubidium atoms. Femtosecond pulses allow more efficient frequency mixing than with comparable power cw lasers. This fact combined with the narrow comb mode linewidth enables spectroscopy and perhaps cooling of atoms on transitions at traditionally hard to reach wavelengths.

  15. Frequency Comb Generation in Superconducting Resonators

    NASA Astrophysics Data System (ADS)

    Pappas, David; Erickson, Robert; Vissers, Michael; Ku, Hsiang-Sheng

    2015-03-01

    We have generated frequency combs spanning 0.5 to 20 GHz in superconducting ? = 2 resonators at T =3 K. Thin films of niobium-titanium nitride enabled this development due to their low loss, high nonlinearity, low frequency dispersion, and high critical temperature. The combs nucleate as sidebands around multiples of the pump frequency. Selection rules for the allowed frequency emission are calculated using perturbation theory, and the measured spectrum is shown to agree with the theory. Sideband spacing is measured to be accurate to 1 part in 108 The sidebands coalesce into a continuous comb structure observed to cover at least several frequency octaves. Generation of combs in this frequency range allows for unprecedented analysis of this non-linear phenomena in the time domain. We acknowledge DARPA and the NIST Quantum Information program.

  16. Frequency comb transferred by surface plasmon resonance

    PubMed Central

    Geng, Xiao Tao; Chun, Byung Jae; Seo, Ji Hoon; Seo, Kwanyong; Yoon, Hana; Kim, Dong-Eon; Kim, Young-Jin; Kim, Seungchul

    2016-01-01

    Frequency combs, millions of narrow-linewidth optical modes referenced to an atomic clock, have shown remarkable potential in time/frequency metrology, atomic/molecular spectroscopy and precision LIDARs. Applications have extended to coherent nonlinear Raman spectroscopy of molecules and quantum metrology for entangled atomic qubits. Frequency combs will create novel possibilities in nano-photonics and plasmonics; however, its interrelation with surface plasmons is unexplored despite the important role that plasmonics plays in nonlinear spectroscopy and quantum optics through the manipulation of light on a subwavelength scale. Here, we demonstrate that a frequency comb can be transformed to a plasmonic comb in plasmonic nanostructures and reverted to the original frequency comb without noticeable degradation of <6.51 × 10−19 in absolute position, 2.92 × 10−19 in stability and 1 Hz in linewidth. The results indicate that the superior performance of a well-defined frequency comb can be applied to nanoplasmonic spectroscopy, quantum metrology and subwavelength photonic circuits. PMID:26898307

  17. Wideband RF channelizer based on parametric combs

    NASA Astrophysics Data System (ADS)

    Zlatanovic, S.; Adleman, J. R.; Huynh, C. K.; Jester, S. B.; Lin, C.; Wiberg, A. O...; Myslivets, E.; Radic, S.; Jacobs, E. W.

    2015-05-01

    RF photonic channelizers can overcome limitations of conventional electronic methods for analysis of wideband RF spectral content. Here, we will present a recent progress on the RF photonic channelizer systems that are based on optical parametric combs. These systems can analyze very wide RF bandwidths exceeding 100GHz, therefore providing essential capability for the applications demanding a wide-bandwidth spectral analysis. The RF channelizers being presented utilize parametric processes in the highly non-linear fiber mixers to generate a large number of RF signal copies in the optical domain. Two different implementations for generation of RF signal copies will be presented and compared: one using a parametric multicasting and another utilizing a direct comb modulation. Generation of optical combs spanning more than 10THz will be shown. We will also present two distinct system architectures for RF photonic channelizer system: one employing a periodic optical filter such as Fabry-Perot etalon to select channels from the signal comb, and another one utilizing a coherent detection between a frequency-locked signal comb and a parametrically generated local oscillator (LO) comb. The second scheme gives benefit of providing both in-phase and quadrature (I/Q) information on channelized intermediate frequency (IF) signals. We will present a system with 32 implemented channels using a filtered scheme and a 32-channel coherent system with a full-field detection implemented on one tunable channel. Sensitivity and dynamic range as well as benefits of both system architectures will be discussed.

  18. Frequency comb transferred by surface plasmon resonance.

    PubMed

    Geng, Xiao Tao; Chun, Byung Jae; Seo, Ji Hoon; Seo, Kwanyong; Yoon, Hana; Kim, Dong-Eon; Kim, Young-Jin; Kim, Seungchul

    2016-01-01

    Frequency combs, millions of narrow-linewidth optical modes referenced to an atomic clock, have shown remarkable potential in time/frequency metrology, atomic/molecular spectroscopy and precision LIDARs. Applications have extended to coherent nonlinear Raman spectroscopy of molecules and quantum metrology for entangled atomic qubits. Frequency combs will create novel possibilities in nano-photonics and plasmonics; however, its interrelation with surface plasmons is unexplored despite the important role that plasmonics plays in nonlinear spectroscopy and quantum optics through the manipulation of light on a subwavelength scale. Here, we demonstrate that a frequency comb can be transformed to a plasmonic comb in plasmonic nanostructures and reverted to the original frequency comb without noticeable degradation of <6.51 × 10(-19) in absolute position, 2.92 × 10(-19) in stability and 1 Hz in linewidth. The results indicate that the superior performance of a well-defined frequency comb can be applied to nanoplasmonic spectroscopy, quantum metrology and subwavelength photonic circuits. PMID:26898307

  19. Phase steps and resonator detuning measurements in microresonator frequency combs

    NASA Astrophysics Data System (ADS)

    Del'Haye, Pascal; Coillet, Aurlien; Loh, William; Beha, Katja; Papp, Scott B.; Diddams, Scott A.

    2015-01-01

    Experiments and theoretical modelling yielded significant progress toward understanding of Kerr-effect induced optical frequency comb generation in microresonators. However, the simultaneous Kerr-mediated interaction of hundreds or thousands of optical comb frequencies with the same number of resonator modes leads to complicated nonlinear dynamics that are far from fully understood. An important prerequisite for modelling the comb formation process is the knowledge of phase and amplitude of the comb modes as well as the detuning from their respective microresonator modes. Here, we present comprehensive measurements that fully characterize optical microcomb states. We introduce a way of measuring resonator dispersion and detuning of comb modes in a hot resonator while generating an optical frequency comb. The presented phase measurements show unpredicted comb states with discrete ? and ?/2 steps in the comb phases that are not observed in conventional optical frequency combs.

  20. Phase steps and resonator detuning measurements in microresonator frequency combs.

    PubMed

    Del'Haye, Pascal; Coillet, Aurlien; Loh, William; Beha, Katja; Papp, Scott B; Diddams, Scott A

    2015-01-01

    Experiments and theoretical modelling yielded significant progress toward understanding of Kerr-effect induced optical frequency comb generation in microresonators. However, the simultaneous Kerr-mediated interaction of hundreds or thousands of optical comb frequencies with the same number of resonator modes leads to complicated nonlinear dynamics that are far from fully understood. An important prerequisite for modelling the comb formation process is the knowledge of phase and amplitude of the comb modes as well as the detuning from their respective microresonator modes. Here, we present comprehensive measurements that fully characterize optical microcomb states. We introduce a way of measuring resonator dispersion and detuning of comb modes in a hot resonator while generating an optical frequency comb. The presented phase measurements show unpredicted comb states with discrete ? and ?/2 steps in the comb phases that are not observed in conventional optical frequency combs. PMID:25565467

  1. Frequency Comb Velocity Modulation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Cossel, Kevin C.; Sinclair, Laura C.; Coffey, Tyler; Cornell, Eric; Ye, Jun

    2011-06-01

    We have developed a novel technique for rapid ion-sensitive spectroscopy over a broad spectral bandwidth by combining the high sensitivity of velocity modulation spectroscopy (VMS) with the parallel nature and high frequency accuracy of cavity-enhanced direct frequency comb spectroscopy. Prior to this research, no techniques have been capable of high sensitivity velocity modulation spectroscopy on every parallel detection channel over such a broad spectral range. We have demonstrated the power of this technique by measuring the A^2?_u - X^2?_g^+ (4,2) band of N_2^+ at 830 nm with an absorption sensitivity of 110-6 for each of 1500 simultaneous measurement channels spanning 150 Cm-1. A densely sampled spectrum consisting of interleaved measurements to achieve 75 MHz spacing is acquired in under an hour. This technique is ideally suited for high resolution survey spectroscopy of molecular ions with applications including chemical physics, astrochemistry, and precision measurement. Currently, this system is being used to map the electronic transitions of HfF^+ for the JILA electron electric dipole moment (eEDM) experiment. The JILA eEDM experiment uses trapped molecular ions to significantly increase the coherence time of the measurement in addition to utilizing the strong electric field enhancement available from molecules. Previous theoretical work has shown that the metastable ^3?_1 state in HfF^+ and ThF^+ provides high sensitivity to the eEDM and good cancellation of systematic effects; however, the electronic level structure of these species have not previously been measured, and the theoretical uncertainties are hundreds to thousands of wavenumbers. This necessitates broad-bandwidth, high-resolution survey spectroscopy provided by frequency comb VMS in the 700-900 nm spectral window. F. Adler, M. J. Thorpe, K. C. Cossel, and J. Ye. Annu. Rev. Anal. Chem. 3, 175-205 (2010) A. E. Leanhardt, et. al. arXiv:1008.2997v2 E. Meyer, J. L. Bohn, and M. P. Deskevich. Phys. Rev. A 73, 062108 (2006) A. N. Petrov, N. S. Mosyagin, T. A. Isaev, and A. V. Titov Phys. Rev. A 76, 030501 (2007)

  2. Kinetics of phase transitions in vitreous chalcogenide semiconductors AsxSe100m-x-yBiy as studied by the differential thermal analysis and exoelectron emission methods

    NASA Astrophysics Data System (ADS)

    Grecki, Cz; Grecki, T.

    2011-04-01

    Kinetics of glass transition (retrification) in chalcogenide semiconductors AsxSe100-x-yBy (x = 20 or 30, and y = 0 and 1) has been investigated by parallel differential thermal analysis (DTA) and exoelectron emission (EEE) measurements. EEE is a surface effect accompanying the structural transformations in the surface layer, whereas the DTA technique gives information about the transformations occurring in the volume of the sample. Temperature dependencies of the DTA signal and of the EEE intensity have been determined and the values of the activation energy for both the volume and the surface retrification have been determined by the Ozawa method for each of the four investigated materials. It has been found that addition of Bi into the vitreous AsxSe100-x glass changes distinctly the kinetics of both the surface and volume retrification. Addition of Bi causes a distinct decrease in the value of the activation energy for retrification process in both the surface layer and in the volume, i.e. reduces the thermal stability of investigated materials.

  3. Laboratory duplication of comb layering in the Rhum pluton. [igneous rocks with comb layered texture

    NASA Technical Reports Server (NTRS)

    Donaldson, C. H.

    1977-01-01

    A description is provided of the texture of harrisite comb layers, taking into account the results of crystallization experiments at controlled cooling rates, which have reproduced the textural change from 'cumulate' to comb-layered harrisite. Melted samples of harrisite were used in the dynamic crystallization experiments considered. The differentiation of a cooling rate run with respect to olivine grain size and shape is shown and three possible origins of hopper olivine in differentiated crystallization runs are considered. It is found that olivine nucleation occurred throughout cooling, except for the incubation period during early cooling. The elongate combed olivines in harrisite apparently grew as the magma locally supercooled to at least 30 C. It is suggested that the branching crystals in most comb layers, including comb-layered harrisite, probably grew along thermal gradients.

  4. George Combe and common sense.

    PubMed

    Dyde, Sean

    2015-06-01

    This article examines the history of two fields of enquiry in late eighteenth- and early nineteenth-century Scotland: the rise and fall of the common sense school of philosophy and phrenology as presented in the works of George Combe. Although many previous historians have construed these histories as separate, indeed sometimes incommensurate, I propose that their paths were intertwined to a greater extent than has previously been given credit. The philosophy of common sense was a response to problems raised by Enlightenment thinkers, particularly David Hume, and spurred a theory of the mind and its mode of study. In order to succeed, or even to be considered a rival of these established understandings, phrenologists adapted their arguments for the sake of engaging in philosophical dispute. I argue that this debate contributed to the relative success of these groups: phrenology as a well-known historical subject, common sense now largely forgotten. Moreover, this history seeks to question the place of phrenology within the sciences of mind in nineteenth-century Britain. PMID:25921681

  5. Electrostatic comb drive for vertical actuation

    SciTech Connect

    Lee, A. P., LLNL

    1997-07-10

    The electrostatic comb finger drive has become an integral design for microsensor and microactuator applications. This paper reports on utilizing the levitation effect of comb fingers to design vertical-to-the-substrate actuation for interferometric applications. For typical polysilicon comb drives with 2 {micro}m gaps between the stationary and moving fingers, as well as between the microstructures and the substrate, the equilibrium position is nominally 1-2 {micro}m above the stationary comb fingers. This distance is ideal for many phase shifting interferometric applications. Theoretical calculations of the vertical actuation characteristics are compared with the experimental results, and a general design guideline is derived from these results. The suspension flexure stiffnesses, gravity forces, squeeze film damping, and comb finger thicknesses are parameters investigated which affect the displacement curve of the vertical microactuator. By designing a parallel plate capacitor between the suspended mass and the substrate, in situ position sensing can be used to control the vertical movement, providing a total feedback-controlled system. Fundamentals of various capacitive position sensing techniques are discussed. Experimental verification is carried out by a Zygo distance measurement interferometer.

  6. Frequency comb generation in quadratic nonlinear media

    NASA Astrophysics Data System (ADS)

    Ricciardi, Iolanda; Mosca, Simona; Parisi, Maria; Maddaloni, Pasquale; Santamaria, Luigi; De Natale, Paolo; De Rosa, Maurizio

    2015-06-01

    We experimentally demonstrate and theoretically explain the onset of optical frequency combs in a simple cavity-enhanced second-harmonic-generation system, exploiting second-order nonlinear interactions. Two combs are simultaneously generated around the fundamental pump frequency, with a spectral bandwidth up to about 10 nm, and its second harmonic. We observe different regimes of generation, depending on the phase-matching condition for second-harmonic generation. Moreover, we develop an elemental model which provides a deep physical insight into the observed dynamics. Despite the different underlying physical mechanism, the proposed model is remarkably similar to the description of third-order effects in microresonators, revealing a potential variety of new effects to be explored and laying the groundwork for a novel class of highly efficient and versatile frequency comb synthesizers based on second-order nonlinear materials.

  7. Nonlinear transmission spectroscopy with dual frequency combs

    NASA Astrophysics Data System (ADS)

    Glenn, Rachel; Mukamel, Shaul

    2014-08-01

    We show how two frequency combs E1, E2 can be used to measure single-photon, two-photon absorption (TPA), and Raman resonances in a molecule with three electronic bands, by detecting the radio frequency modulation of the nonlinear transmission signal. Some peaks are independent of the carrier frequency of the comb and others shift with that frequency and have a width close to the comb width. TPA and Raman resonances independent of the carrier frequency are selected by measuring the transmission signal E12E22 and the single-photon resonances are selected by measuring the transmission signal E13E2. Sinusoidal spectral phase shaping strongly affects the TPA, but not the Raman resonances.

  8. Radiation comb generation with extended Josephson junctions

    NASA Astrophysics Data System (ADS)

    Solinas, P.; Bosisio, R.; Giazotto, F.

    2015-09-01

    We propose the implementation of a Josephson radiation comb generator based on an extended Josephson junction subject to a time dependent magnetic field. The junction critical current shows known diffraction patterns and determines the position of the critical nodes when it vanishes. When the magnetic flux passes through one of such critical nodes, the superconducting phase must undergo a ?-jump to minimize the Josephson energy. Correspondingly, a voltage pulse is generated at the extremes of the junction. Under periodic driving, this allows us to produce a comb-like voltage pulses sequence. In the frequency domain, it is possible to generate up to hundreds of harmonics of the fundamental driving frequency, thus mimicking the frequency comb used in optics and metrology. We discuss several implementations through a rectangular, cylindrical, and annular junction geometries, allowing us to generate different radiation spectra and to produce an output power up to 10 pW at 50 GHz for a driving frequency of 100 MHz.

  9. Microresonator-based optical frequency combs.

    PubMed

    Kippenberg, T J; Holzwarth, R; Diddams, S A

    2011-04-29

    The series of precisely spaced, sharp spectral lines that form an optical frequency comb is enabling unprecedented measurement capabilities and new applications in a wide range of topics that include precision spectroscopy, atomic clocks, ultracold gases, and molecular fingerprinting. A new optical frequency comb generation principle has emerged that uses parametric frequency conversion in high resonance quality factor (Q) microresonators. This approach provides access to high repetition rates in the range of 10 to 1000 gigahertz through compact, chip-scale integration, permitting an increased number of comb applications, such as in astronomy, microwave photonics, or telecommunications. We review this emerging area and discuss opportunities that it presents for novel technologies as well as for fundamental science. PMID:21527707

  10. Kerr frequency comb generation in overmoded resonators.

    PubMed

    Savchenkov, A A; Matsko, A B; Liang, W; Ilchenko, V S; Seidel, D; Maleki, L

    2012-11-19

    We show that scattering-based interaction among nearly degenerate optical modes is the key factor in low threshold generation of Kerr frequency combs in nonlinear optical resonators with small group velocity dispersion (GVD). Mode interaction is capable of producing drastic changes in the local GVD, resulting in either a significant reduction, or an increase, in the oscillation threshold. Furthermore, we show that mode interaction is also responsible for majority of observed optical frequency combs in resonators characterized with large normal GVD. We present results of our numerical simulations together with supporting experimental data. PMID:23187584

  11. Relationship between transport properties and band diagrams in InAsxSb1-x/Al0.1In0.9Sb quantum wells

    NASA Astrophysics Data System (ADS)

    Manago, Takashi; Ishida, Shuichi; Geka, Hirotaka; Shibasaki, Ichiro

    2015-06-01

    The resistivity of InAs0.1Sb0.9/Al0.1In0.9Sb quantum wells (QWs) is much lower than that of InSb/Al0.1In0.9Sb QWs, staying low resistivity even at low temperature. Fundamental difference in low temperature transport properties between InSb/Al0.1In0.9Sb and InAs0.1Sb0.9/Al0.1In0.9Sb QWs was revealed, based on the band diagram calculations of these QWs. Band diagrams of InAsxSb1-x/Al0.1In0.9Sb QWs showed that the energy band of the InAsxSb1-x layer moves downward with increasing As content x. The QW is type I at x equal to 0, becomes type II at x equal to 0.1. The Fermi level (EF) of the InSb QWs lies in the band gap and below apart from the bottom of the conduction band, while EF of the InAs0.1Sb0.9 QWs is above the bottom of the conduction band of the well. The calculated sheet carrier densities are in good agreement with the experimental results. It well explains that the sheet carrier density difference between InSb and InAs0.1Sb0.9 QWs mainly originates from this band diagram difference and the position of EF.

  12. Time sequence photography of Roosters Comb

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The importance of understanding natural landscape changes is key in properly determining rangeland ecology. Time sequence photography allows a landscape snapshot to be documented and enables the ability to compare natural changes overtime. Photographs of Roosters Comb were taken from the same vantag...

  13. Coherence and Incoherence in an Optical Comb

    NASA Astrophysics Data System (ADS)

    Viktorov, Evgeny A.; Habruseva, Tatiana; Hegarty, Stephen P.; Huyet, Guillaume; Kelleher, Bryan

    2014-06-01

    We demonstrate a coexistence of coherent and incoherent modes in the optical comb generated by a passively mode-locked quantum dot laser. This is experimentally achieved by means of optical linewidth, radio frequency spectrum, and optical spectrum measurements and confirmed numerically by a delay-differential equation model showing excellent agreement with the experiment. We interpret the state as a chimera state.

  14. Phase separation of comb polymer nanocomposite melts.

    PubMed

    Xu, Qinzhi; Feng, Yancong; Chen, Lan

    2016-02-01

    In this work, the spinodal phase demixing of branched comb polymer nanocomposite (PNC) melts is systematically investigated using the polymer reference interaction site model (PRISM) theory. To verify the reliability of the present method in characterizing the phase behavior of comb PNCs, the intermolecular correlation functions of the system for nonzero particle volume fractions are compared with our molecular dynamics simulation data. After verifying the model and discussing the structure of the comb PNCs in the dilute nanoparticle limit, the interference among the side chain number, side chain length, nanoparticle-monomer size ratio and attractive interactions between the comb polymer and nanoparticles in spinodal demixing curves is analyzed and discussed in detail. The results predict two kinds of distinct phase separation behaviors. One is called classic fluid phase boundary, which is mediated by the entropic depletion attraction and contact aggregation of nanoparticles at relatively low nanoparticle-monomer attraction strength. The second demixing transition occurs at relatively high attraction strength and involves the formation of an equilibrium physical network phase with local bridging of nanoparticles. The phase boundaries are found to be sensitive to the side chain number, side chain length, nanoparticle-monomer size ratio and attractive interactions. As the side chain length is fixed, the side chain number has a large effect on the phase behavior of comb PNCs; with increasing side chain number, the miscibility window first widens and then shrinks. When the side chain number is lower than a threshold value, the phase boundaries undergo a process from enlarging the miscibility window to narrowing as side chain length increases. Once the side chain number overtakes this threshold value, the phase boundary shifts towards less miscibility. With increasing nanoparticle-monomer size ratio, a crossover of particle size occurs, above which the phase separation is consistent with that of chain PNCs. The miscibility window for this condition gradually narrows while the other parameters of the PNCs system are held constant. These results indicate that the present PRISM theory can give molecular-level details of the underlying mechanisms of the comb PNCs. It is hoped that the results can be used to provide useful guidance for the future design control of novel, thermodynamically stable comb PNCs. PMID:26754414

  15. The Rose-comb Mutation in Chickens Constitutes a Structural Rearrangement Causing Both Altered Comb Morphology and Defective Sperm Motility

    PubMed Central

    Boije, Henrik; Bed'hom, Bertrand; Fillon, Valrie; Dorshorst, Ben; Rubin, Carl-Johan; Liu, Ranran; Gao, Yu; Gu, Xiaorong; Wang, Yanqiang; Gourichon, David; Zody, Michael C.; Zecchin, William; Vieaud, Agathe; Tixier-Boichard, Michle; Hu, Xiaoxiang; Hallbk, Finn; Li, Ning; Andersson, Leif

    2012-01-01

    Rose-comb, a classical monogenic trait of chickens, is characterized by a drastically altered comb morphology compared to the single-combed wild-type. Here we show that Rose-comb is caused by a 7.4 Mb inversion on chromosome 7 and that a second Rose-comb allele arose by unequal crossing over between a Rose-comb and wild-type chromosome. The comb phenotype is caused by the relocalization of the MNR2 homeodomain protein gene leading to transient ectopic expression of MNR2 during comb development. We also provide a molecular explanation for the first example of epistatic interaction reported by Bateson and Punnett 104 years ago, namely that walnut-comb is caused by the combined effects of the Rose-comb and Pea-comb alleles. Transient ectopic expression of MNR2 and SOX5 (causing the Pea-comb phenotype) occurs in the same population of mesenchymal cells and with at least partially overlapping expression in individual cells in the comb primordium. Rose-comb has pleiotropic effects, as homozygosity in males has been associated with poor sperm motility. We postulate that this is caused by the disruption of the CCDC108 gene located at one of the inversion breakpoints. CCDC108 is a poorly characterized protein, but it contains a MSP (major sperm protein) domain and is expressed in testis. The study illustrates several characteristic features of the genetic diversity present in domestic animals, including the evolution of alleles by two or more consecutive mutations and the fact that structural changes have contributed to fast phenotypic evolution. PMID:22761584

  16. Broadband 2.5-6?m frequency comb source for dual-comb molecular spectroscopy

    NASA Astrophysics Data System (ADS)

    Smolski, V. O.; Vodopyanov, K. L.

    2015-02-01

    Absorption spectroscopy with frequency combs in the molecular fingerprint portion of the spectrum (2-10 ?m) has great potential for trace molecular detection and in particular for such applications as monitoring of the atmosphere and medical breath analysis. Especially attractive is dual-comb Fourier transform spectroscopy where full advantage is taken of temporal and spatial coherence of frequency combs as well as of their broadband nature. The promise is high speed, broad spectral coverage, superior sensitivity, high spectral resolution, and the possibility of absolute frequency calibration of molecular resonances. Here we report a system suitable for performing dual-comb spectroscopy in the range of 2.5-6 ?m and beyond. Broadband mid-IR frequency combs are obtained via a doubly-resonant near-degenerate synchronously pumped optical parametric oscillator (OPO) based on orientation-patterned GaAs (OP-GaAs) pumped by a femtosecond Tm-fiber laser at 2-?m wavelength. Low pump threshold (7 mW), high coherence, and broad instantaneous spectral coverage make this system extremely promising for spectroscopic studies.

  17. Mesoscopic description of random walks on combs

    NASA Astrophysics Data System (ADS)

    Méndez, Vicenç; Iomin, Alexander; Campos, Daniel; Horsthemke, Werner

    2015-12-01

    Combs are a simple caricature of various types of natural branched structures, which belong to the category of loopless graphs and consist of a backbone and branches. We study continuous time random walks on combs and present a generic method to obtain their transport properties. The random walk along the branches may be biased, and we account for the effect of the branches by renormalizing the waiting time probability distribution function for the motion along the backbone. We analyze the overall diffusion properties along the backbone and find normal diffusion, anomalous diffusion, and stochastic localization (diffusion failure), respectively, depending on the characteristics of the continuous time random walk along the branches, and compare our analytical results with stochastic simulations.

  18. Laser Frequency Combs for Astronomical Observations

    NASA Astrophysics Data System (ADS)

    Steinmetz, Tilo; Wilken, Tobias; Araujo-Hauck, Constanza; Holzwarth, Ronald; Hnsch, Theodor W.; Pasquini, Luca; Manescau, Antonio; D'Odorico, Sandro; Murphy, Michael T.; Kentischer, Thomas; Schmidt, Wolfgang; Udem, Thomas

    2008-09-01

    A direct measurement of the universes expansion history could be made by observing in real time the evolution of the cosmological redshift of distant objects. However, this would require measurements of Doppler velocity drifts of ~1 centimeter per second per year, and astronomical spectrographs have not yet been calibrated to this tolerance. We demonstrated the first use of a laser frequency comb for wavelength calibration of an astronomical telescope. Even with a simple analysis, absolute calibration is achieved with an equivalent Doppler precision of ~9 meters per second at ~1.5 micrometersbeyond state-of-the-art accuracy. We show that tracking complex, time-varying systematic effects in the spectrograph and detector system is a particular advantage of laser frequency comb calibration. This technique promises an effective means for modeling and removal of such systematic effects to the accuracy required by future experiments to see direct evidence of the universes putative acceleration.

  19. Coherence and incoherence in an optical comb.

    PubMed

    Viktorov, Evgeny A; Habruseva, Tatiana; Hegarty, Stephen P; Huyet, Guillaume; Kelleher, Bryan

    2014-06-01

    We demonstrate a coexistence of coherent and incoherent modes in the optical comb generated by a passively mode-locked quantum dot laser. This is experimentally achieved by means of optical linewidth, radio frequency spectrum, and optical spectrum measurements and confirmed numerically by a delay-differential equation model showing excellent agreement with the experiment. We interpret the state as a chimera state. PMID:24949771

  20. Frequency-agile dual-comb spectroscopy

    NASA Astrophysics Data System (ADS)

    Millot, Guy; Pitois, Stéphane; Yan, Ming; Hovhannisyan, Tatevik; Bendahmane, Abdelkrim; Hänsch, Theodor W.; Picqué, Nathalie

    2016-01-01

    Spectroscopic gas sensing and its applications to, for example, trace detection or chemical kinetics, require ever more demanding measurement times, acquisition rates, sensitivities, precisions and broad tuning ranges. Here, we propose a new approach to near-infrared molecular spectroscopy, utilizing advanced concepts of optical telecommunications and supercontinuum photonics. We generate, without mode-locked lasers, two frequency combs of slightly different repetition frequencies and moderate, but rapidly tunable, spectral span. The output of a frequency-agile continuous-wave laser is split and sent into two electro-optic intensity modulators. Flat-top low-noise frequency combs are produced by wave-breaking in a nonlinear optical fibre of normal dispersion. With a dual-comb spectrometer, we record Doppler-limited spectra spanning 60 GHz within 13 μs and an 80 kHz refresh rate, at a tuning speed of 10 nm s‑1. The sensitivity for weak absorption is enhanced by a long gas-filled hollow-core fibre. New opportunities for real-time diagnostics may be opened up, even outside the laboratory.

  1. Endless frequency shifting of optical frequency comb lines.

    PubMed

    Benkler, Erik; Rohde, Felix; Telle, Harald R

    2013-03-11

    The functional principle of a novel technique for frequency shifting lines of an optical frequency comb is demonstrated. The underlying principle is to shift the carrier frequency by changing the carrier phase within the time span between subsequent pulses of a mode-locked laser used as comb generator. This universal frequency shifter does not require intrusion into the comb generator and provides high agility for arbitrary temporal frequency evolutions. PMID:23482149

  2. Recent advances in ultrafast optical parametric oscillator frequency combs

    NASA Astrophysics Data System (ADS)

    McCracken, Richard A.; Zhang, Zhaowei; Reid, Derryck T.

    2014-12-01

    We discuss recent advances in the stabilization and application of femtosecond frequency combs based on optical parametric oscillators (OPOs) pumped by femtosecond lasers at 800 and 1060 nm. A method for locking to zero the carrier-envelope-offset of a Ti:sapphire-pumped OPO comb is described. The application of Yb:KYW-laser-pumped dual-combs for mid-infrared spectroscopy is detailed, specifically methane spectroscopy at approximately a 0.7% concentration at 1 atm.

  3. Optimization of filtering schemes for broadband astro-combs.

    PubMed

    Chang, Guoqing; Li, Chih-Hao; Phillips, David F; Szentgyorgyi, Andrew; Walsworth, Ronald L; Krtner, Franz X

    2012-10-22

    To realize a broadband, large-line-spacing astro-comb, suitable for wavelength calibration of astrophysical spectrographs, from a narrowband, femtosecond laser frequency comb ("source-comb"), one must integrate the source-comb with three additional components: (1) one or more filter cavities to multiply the source-comb's repetition rate and thus line spacing; (2) power amplifiers to boost the power of pulses from the filtered comb; and (3) highly nonlinear optical fiber to spectrally broaden the filtered and amplified narrowband frequency comb. In this paper we analyze the interplay of Fabry-Perot (FP) filter cavities with power amplifiers and nonlinear broadening fiber in the design of astro-combs optimized for radial-velocity (RV) calibration accuracy. We present analytic and numeric models and use them to evaluate a variety of FP filtering schemes (labeled as identical, co-prime, fraction-prime, and conjugate cavities), coupled to chirped-pulse amplification (CPA). We find that even a small nonlinear phase can reduce suppression of filtered comb lines, and increase RV error for spectrograph calibration. In general, filtering with two cavities prior to the CPA fiber amplifier outperforms an amplifier placed between the two cavities. In particular, filtering with conjugate cavities is able to provide <1 cm/s RV calibration error with >300 nm wavelength coverage. Such superior performance will facilitate the search for and characterization of Earth-like exoplanets, which requires <10 cm/s RV calibration error. PMID:23187265

  4. Wet combing for the eradication of head lice.

    PubMed

    2013-03-01

    Manual removal (using conditioner and comb or a wet comb) can be used in the treatment of head lice. Head lice infestation (Pediculosis humanus capitis) is a common problem. It is diagnosed by visualising the lice. As half of people infested with head lice will not scratch, all people in contact with a person affected with head lice should be manually checked for infestations. Wet combing is easily and safely performed at home, but persistence is needed. This article describes the process of head lice removal using a wet comb. It has NHMRC Level 2 evidence of efficacy and no serious adverse effects have been reported. PMID:23529522

  5. Frequency comb from a microresonator with engineered spectrum.

    PubMed

    Grudinin, Ivan S; Baumgartel, Lukas; Yu, Nan

    2012-03-12

    We demonstrate that by varying the ratio between the linewidth and dispersion of a whispering gallery mode resonator we are able to control the number N of free spectral ranges separating the first generated comb sidebands from the pump. We observed combs with N = 19 and N = 1. For the comb with N = 1 we have achieved a span of over 200 nm using a 0.4 mm MgF? resonator pumped with 50 mW at 1560 nm. This pump power is a factor of 10 lower than previously reported for combs with comparable bandwidth. PMID:22418543

  6. High-Temperature Thermoelectric Properties of the Solid–Solution Zintl Phase Eu11Cd6Sb12–xAsx (x < 3)

    SciTech Connect

    Kazem, Nasrin; Xie, Weiwei; Ohno, Saneyuki; Zevalkink, Alexandra; Miller, Gordon J; Snyder, G Jeffrey; Kauzlarich, Susan M

    2014-02-11

    Zintl phases are compounds that have shown promise for thermoelectric applications. The title solid–solution Zintl compounds were prepared from the elements as single crystals using a tin flux for compositions x = 0, 1, 2, and 3. Eu11Cd6Sb12–xAsx (x < 3) crystallize isostructurally in the centrosymmetric monoclinic space group C2/m (no. 12, Z = 2) as the Sr11Cd6Sb12 structure type (Pearson symbol mC58). Efforts to make the As compositions for x exceeding ~3 resulted in structures other than the Sr11Cd6Sb12 structure type. Single-crystal X-ray diffraction indicates that As does not randomly substitute for Sb in the structure but is site specific for each composition. The amount of As determined by structural refinement was verified by electron microprobe analysis. Electronic structures and energies calculated for various model structures of Eu11Cd6Sb10As2 (x = 2) indicated that the preferred As substitution pattern involves a mixture of three of the six pnicogen sites in the asymmetric unit. In addition, As substitution at the Pn4 site opens an energy gap at the Fermi level, whereas substitution at the other five pnicogen sites remains semimetallic with a pseudo gap. Thermoelectric properties of these compounds were measured on hot-pressed, fully densified pellets. Samples show exceptionally low lattice thermal conductivities from room temperature to 775 K: 0.78–0.49 W/mK for x = 0; 0.72–0.53 W/mK for x = 1; and 0.70–0.56 W/mK for x = 2. Eu11Cd6Sb12 shows a high p-type Seebeck coefficient (from +118 to 153 μ V/K) but also high electrical resistivity (6.8 to 12.8 mΩ·cm). The value of zT reaches 0.23 at 774 K. The properties of Eu11Cd6Sb12–xAsx are interpreted in discussion with the As site substitution.

  7. Spectrally interleaved, comb-mode-resolved spectroscopy using swept dual terahertz combs

    PubMed Central

    Hsieh, Yi-Da; Iyonaga, Yuki; Sakaguchi, Yoshiyuki; Yokoyama, Shuko; Inaba, Hajime; Minoshima, Kaoru; Hindle, Francis; Araki, Tsutomu; Yasui, Takeshi

    2014-01-01

    Optical frequency combs are innovative tools for broadband spectroscopy because a series of comb modes can serve as frequency markers that are traceable to a microwave frequency standard. However, a mode distribution that is too discrete limits the spectral sampling interval to the mode frequency spacing even though individual mode linewidth is sufficiently narrow. Here, using a combination of a spectral interleaving and dual-comb spectroscopy in the terahertz (THz) region, we achieved a spectral sampling interval equal to the mode linewidth rather than the mode spacing. The spectrally interleaved THz comb was realized by sweeping the laser repetition frequency and interleaving additional frequency marks. In low-pressure gas spectroscopy, we achieved an improved spectral sampling density of 2.5 MHz and enhanced spectral accuracy of 8.39 × 10−7 in the THz region. The proposed method is a powerful tool for simultaneously achieving high resolution, high accuracy, and broad spectral coverage in THz spectroscopy. PMID:24448604

  8. High temperature and composition induced phase transitions in LiZnV?-xAsxO? phenacites: Crystal structure and Raman spectroscopy studies.

    PubMed

    Manoun, B; Azrour, M; Lazor, P; Azdouz, M; Bih, L; Benmokhtar, S; Essehli, R; El Ammari, L

    2015-12-01

    In this work, using techniques of X-ray diffraction and Raman spectroscopy, we report the composition and high-temperature induced phase transition in the system LiZnV1-xAsxO4 (0?x?1). Both techniques showed that the increase of arsenic amount induced a structural transition from R-3 LiZnVO4 type to LiZnAsO4 type belonging to R3 space group, the transition occurring between x=0.7 and x=0.8. Furthermore, increasing temperature for the compositions (0.8?x?1) manifests a transition from the LiZnAsO4 structural type with R3 space group to the R-3 LiZnVO4 structural type. For this series, the transition from the space group R3 to the centro-symmetric space group R-3 shows considerable changes in the compositional and temperature dependencies of the bands: spectral positions of all the observed Raman bands exhibit shifts linearly proportional to the temperature increase, with points of shift-rate changes revealing a symmetry change. The Raman-spectra based temperature-composition phase diagram confirms the results obtained using the method of Rietveld refinements, thus showing the R-3 to R3 transition occurring between x=0.7 and 0.8. PMID:26186614

  9. Efficiency optimization for atomic frequency comb storage

    SciTech Connect

    Bonarota, M.; Ruggiero, J.; Le Goueet, J.-L.; Chaneliere, T.

    2010-03-15

    We study the efficiency of the atomic frequency comb storage protocol. We show that for a given optical depth, the preparation procedure can be optimize to significantly improve the retrieval. Our prediction is well supported by the experimental implementation of the protocol in a Tm{sup 3+}:YAG crystal. We observe a net gain in efficiency from 10 to 17% by applying the optimized preparation procedure. In the perspective of high bandwidth storage, we investigate the protocol under different magnetic fields. We analyze the effect of the Zeeman and superhyperfine interaction.

  10. Feshbach resonances in Kerr frequency combs

    NASA Astrophysics Data System (ADS)

    Matsko, Andrey B.; Maleki, Lute

    2015-01-01

    We show that both the power and repetition rate of a frequency comb generated in a nonlinear ring resonator, pumped with continuous-wave (cw) coherent light, are modulated. The modulation is brought about by the interaction of the cw background with optical pulses excited in the resonator, and occurs in resonators with nonzero high-order chromatic dispersion and wavelength-dependent quality factor. The modulation frequency corresponds to the detuning of the pump frequency from the eigenfrequency of the pumped mode in the resonator.

  11. Dual-Comb Spectroscopy in the Open Air

    NASA Astrophysics Data System (ADS)

    Rieker, Greg B.; Klose, Andrew; Diddams, Scott; Coddington, Ian; Giorgetta, Fabrizio; Sinclair, Laura; Baumann, Esther; Truong, Gar-Wing; Ycas, Gabriel; Swann, William C.; Newbury, Nathan R.

    2015-06-01

    Dual-comb spectroscopy is arguably the natural successor to FTIR. Based on the interference between two frequency combs, this technique can record broadband spectra with a resolution better than 0.0003 wn. Like FTIR, dual-comb spectroscopy measures an entire spectrum simultaneously, allowing for suppression of systematic errors related to temporal dynamics of the sample. Unlike FTIR it records the entire spectrum with virtually no instrument lineshape or error in the frequency axis. The lack of moving parts in dual-comb spectroscopy means that spectra can be recorded in milliseconds to microseconds with the desired signal-to-noise being the only real constrain on the minimum recording time. Finally the high spacial beam quality of the frequency combs allows for increased sensitivity through long interaction paths either in free-space, multi-pass cells or enhancement cavities. This talk will explore the recent use of dual-comb spectroscopy in the near-infrared to measure atmospheric carbon dioxide, methane and water concentrations over a 2-km outdoor open-air path. Due to many of the strengths just mentioned, precisions of <1 ppm for CO_2 and <3 ppb for CH_4 in 5 min are achieved making this system very attractive for carbon monitoring at length scales relevant to carbon transport models. Additionally this presentation will address recent work on robust, compact, and portable dual-comb spectrometers as well as dual-comb spectroscopy further into the IR.

  12. On timing jitter of mode locked Kerr frequency combs.

    PubMed

    Matsko, Andrey B; Maleki, Lute

    2013-11-18

    We study fundamental timing jitter in repetition rate of a mode locked Kerr frequency comb generated in an externally pumped nonlinear ring resonator. We show that the increase in the integrated power of the comb harmonics, and the corresponding decrease of the duration of the associated pulse, results in the increase of low frequency noise, and a decrease in high frequency noise. PMID:24514400

  13. Normal group-velocity dispersion Kerr frequency comb.

    PubMed

    Matsko, A B; Savchenkov, A A; Maleki, L

    2012-01-01

    We show via numerical simulation that Kerr frequency combs can be generated in a nonlinear resonator characterized with normal group-velocity dispersion. We find the spectral shape of the comb and temporal envelope of the corresponding optical pulses formed in the resonator. PMID:22212785

  14. Coherent Raman dual-comb spectroscopy and imaging

    NASA Astrophysics Data System (ADS)

    Ideguchi, Takuro; Holzner, Simon; Bernhardt, Birgitta; Guelachvili, Guy; Hänsch, Theodor W.; Picqué, Nathalie

    2014-11-01

    The invention of the optical frequency comb technique has revolutionized the field of precision spectroscopy, providing a way to measure the absolute frequency of any optical transition. Since, frequency combs have become common equipment for frequency metrology. In the last decade, novel applications for the optical frequency comb have been demonstrated beyond its original purpose. Broadband molecular spectroscopy is one of those. One such technique of molecular spectroscopy with frequency combs, dual-comb Fourier transform spectroscopy provides short measurement times with resolution and accuracy. Two laser frequency combs with slightly different repetition frequencies generate pairs of pulses with a linearly-scanned delay between pulses in a pair. The system without moving parts mimics a fast scanning Fourier transform interferometer. The measurement speed may be several orders of magnitude faster than that of a Michelson-based Fourier transform spectrometer, which opens up new opportunities for broadband molecular spectroscopy. Recently, dual-comb spectroscopy has been extended to nonlinear phenomena. A broadband Raman spectrum of molecular fingerprints may be measured within a few tens of microseconds with coherent Raman dual-comb spectroscopy. Raster scanning the sample leads to hyperspectral images. This rapid and broadband label-free vibrational spectroscopy and imaging technique might provide new diagnostic methods in a variety of scientific and industrial fields.

  15. Theory and applications of sampled analog recursive CTD comb filters

    NASA Technical Reports Server (NTRS)

    Tao, T. F.; Holmes, S. V.; Ejaz, A.; Piazza, F.; Saetre, L. T.; Freund, B.

    1976-01-01

    Sampled analog comb filter using a recursive filter implementation was studied. Charge transfer device delay lines were used as the delay elements. The similarities and differences between sampled analog recursive filter and digital recursive filter were pointed out. Both canceller type and integrator type comb filter using the first order or the second order canonical circuits were studied. Experimental results of frequency response are presented to show their difference from that of digital filters. A theoretical analysis was presented based essentially on the digital filter theory but modified to take into account the differences described above. The usefulness of this theory in analyzing the comb filter characteristics was discussed. Several applications of both the canceller type comb filter and the integrator type comb filter were demonstrated.

  16. Comparative analysis of spectral coherence in microresonator frequency combs.

    PubMed

    Torres-Company, Victor; Castell-Lurbe, David; Silvestre, Enrique

    2014-02-24

    Microresonator combs exploit parametric oscillation and nonlinear mixing in an ultrahigh-Q cavity. This new comb generator offers unique potential for chip integration and access to high repetition rates. However, time-domain studies reveal an intricate spectral coherence behavior in this type of platform. In particular, coherent, partially coherent or incoherent combs have been observed using the same microresonator under different pumping conditions. In this work, we provide a numerical analysis of the coherence dynamics that supports the above experimental findings and verify particular design rules to achieve spectrally coherent microresonator combs. A particular emphasis is placed in understanding the differences between so-called Type I and Type II combs. PMID:24663786

  17. Does combing the scalp reduce scalp electrode impedances?

    PubMed

    Mahajan, Yatin; McArthur, Genevieve

    2010-05-15

    Electrical activity from the human brain can be recorded via electrodes on the scalp. It is important to reduce the impedance of each electrode to minimize unwanted noise in the recording. Electrode impedance can be improved by abrading the skin to remove dead skin cells. In this experiment, we tested if abrading the skin by combing the scalp leads to a significant reduction in electrode impedance. We compared the mean electrode impedance values of 20 subjects whose scalps were combed prior to electrode cap placement, with 20 subjects whose scalps were not combed. Combing significantly reduced the impedances at central, right, and left areas of the scalp. This finding supports the use of scalp combing to reduce the time and subject discomfort that can be associated with placing scalp electrodes. This is particularly important for experiments testing children. PMID:20211649

  18. Spectral noise correlations of an ultrafast frequency comb.

    PubMed

    Schmeissner, Roman; Roslund, Jonathan; Fabre, Claude; Treps, Nicolas

    2014-12-31

    Cavity-based noise detection schemes are combined with ultrafast pulse shaping as a means to diagnose the spectral correlations of both the amplitude and phase noise of an ultrafast frequency comb. The comb is divided into ten spectral regions, and the distribution of noise as well as the correlations between all pairs of spectral regions are measured against the quantum limit. These correlations are then represented in the form of classical noise matrices, which furnish a complete description of the underlying comb dynamics. Their eigendecomposition reveals a set of theoretically predicted, decoupled noise modes that govern the dynamics of the comb. These matrices also contain the information necessary to deduce macroscopic noise properties of the comb. PMID:25615340

  19. Tunable Surface Properties from Bioinspired Comb Copolymers

    NASA Astrophysics Data System (ADS)

    van Zoelen, Wendy; Buss, Hilda; Ellebracht, Nathan; Zuckermann, Ronald; Segalman, Rachel

    2013-03-01

    A modular polymer system which incorporates multiple functionalities simultaneously while keeping an identical backbone chemistry is a useful tool in determining necessary functionalities for marine antifouling properties. We have investigated the surface properties and antifouling behavior of polypeptoids, a class of non-natural biomimetic polymers based on an N-substituted glycine backbone, that combine many of the advantageous properties of bulk polymers with those of synthetically produced proteins, including controllable chain shape, sequence, and self-assembled structure. Using thiol-ene click chemistry, thiol functionalized amphiphilic peptoid sequences consisting of hydrophilic methoxyethyl and hydrophobic heptafluorobutyl side chains were attached to polystyrene-block-poly(ethylene oxide-stat-allyl glycidyl ether), creating comb-shaped molecules. Near edge X-ray absorption fine structure spectroscopy (NEXAFS) was used to study the surface characteristics as a function of peptoid length and composition. Only 20% of fluorinated groups in the peptoid were sufficient for promoting surface display of the otherwise hydrophilic PEO/peptoid comb block. Antifouling experiments with spores of the green algae Ulva indicated an influence of sequence.

  20. Theory for direct frequency-comb spectroscopy

    SciTech Connect

    Felinto, Daniel; Lopez, Carlos E. E.

    2009-07-15

    Direct frequency-comb spectroscopy is a technique that employs a train of well-stabilized ultrashort pulses to study the spectral properties of atomic or molecular systems. In this way, it opens the possibility of incorporating various coherent-control techniques for such spectral investigations. Here we introduce a theory for the interaction of a multilevel atom with such pulse trains, which is general enough to take into account an arbitrarily shaped frequency comb. We illustrate its application by studying the interaction of {sup 87}Rb atoms with trains of pulses of various shapes, resonant with the 5S-5D two-photon transition of rubidium. More specifically, we treat the interaction with hyperbolic-secant pulses, chirped pulses, and 0-{pi} pulses, respectively. The theory is designed to work at an arbitrary perturbation order. For the results presented here, we mostly used a 12th-order perturbation series at the pulse's electric field. Due to the large number of levels involved, such modeling may be quite complex computationally, and an important point of the present work is then to introduce the required numerical approach to treat this problem efficiently.

  1. Cavity-Enhanced Optical Frequency Comb Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ye, Jun; Thorpe, Michael J.; Adler, Florian; Cossel, Kevin C.

    2009-06-01

    Cavity-enhanced optical frequency comb spectroscopy is a new technique that realizes simultaneously broad spectral coverage and high spectral resolution provided by an optical frequency comb as well as ultrahigh detection sensitivities enabled with a high-finesse optical cavity [1]. These powerful capabilities have been demonstrated in a series of experiments where real-time detection and identification of many different molecular states or species are achieved in a massively parallel fashion [2,3]. We will discuss the principle, technical requirements, and various implementations for this spectroscopic approach, as well as applications that include trace gas detections, human breath analysis, and characterization of cold and ultracold molecules [4,5,6]. References: [1] M. J. Thorpe, K. D. Moll, B. Safdi, and J. Ye, Science 311, 1595 (2006). [2] M. J. Thorpe, D. D. Hudson, K. D. Moll, J. Lasri, and J. Ye, Opt. Lett. 32, 307 (2007). [3] C. Gohle, B. Stein, A. Schliesser, T. Udem, and T. W. Hnsch, Phys. Rev. Lett. 99, 263902 (2007). [4] M. J. Thorpe, D. Balslev-Clausen, M. Kirchner, and J. Ye, Opt. Express. 16, 2387 (2008). [5] M. J. Thorpe and J. Ye, Appl. Phys. B 91, 397 (2008). [6] M. J. Thorpe, F. Adler, K. C. Cossel, M. H. G. de Miranda, and J. Ye, Chem. Phys. Lett. 468, 1 (2009).

  2. Coherent terabit communications with microresonator Kerr frequency combs

    PubMed Central

    Pfeifle, Joerg; Brasch, Victor; Lauermann, Matthias; Yu, Yimin; Wegner, Daniel; Herr, Tobias; Hartinger, Klaus; Schindler, Philipp; Li, Jingshi; Hillerkuss, David; Schmogrow, Rene; Weimann, Claudius; Holzwarth, Ronald; Freude, Wolfgang; Leuthold, Juerg; Kippenberg, Tobias J.; Koos, Christian

    2014-01-01

    Optical frequency combs have the potential to revolutionize terabit communications1. Generation of Kerr combs in nonlinear microresonators2 represents a particularly promising option3 enabling line spacings of tens of GHz. However, such combs may exhibit strong phase noise4-6, which has made high-speed data transmission impossible up to now. Here we demonstrate that systematic adjustment of pump conditions for low phase noise4,7-9 enables coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the comb. In a first experiment, we encode a data stream of 392 Gbit/s on a Kerr comb using quadrature phase shift keying (QPSK) and 16-state quadrature amplitude modulation (16QAM). A second experiment demonstrates feedback-stabilization of the comb and transmission of a 1.44 Tbit/s data stream over up to 300 km. The results show that Kerr combs meet the highly demanding requirements of coherent communications and thus offer an attractive solution towards chip-scale terabit/s transceivers. PMID:24860615

  3. Analysis of Replicating Yeast Chromosomes by DNA Combing.

    PubMed

    Gallo, David; Wang, Gang; Yip, Christopher M; Brown, Grant W

    2016-01-01

    Molecular combing of DNA fibers is a powerful technique to monitor origin usage and DNA replication fork progression in the budding yeast Saccharomyces cerevisiae. In contrast to traditional flow cytometry, microarray, or sequencing techniques, which provide population-level data, DNA combing provides DNA replication profiles of individual molecules. DNA combing uses yeast strains that express human thymidine kinase, which facilitates the incorporation of thymidine analogs into nascent DNA. First, DNA is isolated and stretched uniformly onto silanized glass coverslips. Following immunodetection with antibodies that recognize the thymidine analog and the DNA, the DNA fibers are imaged using a fluorescence microscope. Finally, the lengths of newly replicated DNA tracks are measured and converted to base pairs, allowing calculations of the speed of the replication fork and of interorigin distances. DNA combing can be applied to monitor replication defects caused by gene mutations or by chemical agents that induce replication stress. Here, we present a methodology for studying replicating yeast chromosomes by molecular DNA combing. We begin with procedures for the preparation of silanized coverslips and for assembly of a DNA combing machine (DCM) and conclude by presenting a detailed protocol for molecular DNA combing in yeast. PMID:26832684

  4. Silicon-chip mid-infrared frequency comb generation

    NASA Astrophysics Data System (ADS)

    Griffith, Austin G.; Lau, Ryan K. W.; Cardenas, Jaime; Okawachi, Yoshitomo; Mohanty, Aseema; Fain, Romy; Lee, Yoon Ho Daniel; Yu, Mengjie; Phare, Christopher T.; Poitras, Carl B.; Gaeta, Alexander L.; Lipson, Michal

    2015-02-01

    Optical frequency combs are a revolutionary light source for high-precision spectroscopy because of their narrow linewidths and precise frequency spacing. Generation of such combs in the mid-infrared spectral region (2-20 μm) is important for molecular gas detection owing to the presence of a large number of absorption lines in this wavelength regime. Microresonator-based frequency comb sources can provide a compact and robust platform for comb generation that can operate with relatively low optical powers. However, material and dispersion engineering limitations have prevented the realization of an on-chip integrated mid-infrared microresonator comb source. Here we demonstrate a complementary metal-oxide-semiconductor compatible platform for on-chip comb generation using silicon microresonators, and realize a broadband frequency comb spanning from 2.1 to 3.5 μm. This platform is compact and robust and offers the potential to be versatile for use outside the laboratory environment for applications such as real-time monitoring of atmospheric gas conditions.

  5. Coherent terabit communications with microresonator Kerr frequency combs.

    PubMed

    Pfeifle, Joerg; Brasch, Victor; Lauermann, Matthias; Yu, Yimin; Wegner, Daniel; Herr, Tobias; Hartinger, Klaus; Schindler, Philipp; Li, Jingshi; Hillerkuss, David; Schmogrow, Rene; Weimann, Claudius; Holzwarth, Ronald; Freude, Wolfgang; Leuthold, Juerg; Kippenberg, Tobias J; Koos, Christian

    2014-05-01

    Optical frequency combs have the potential to revolutionize terabit communications(1). Generation of Kerr combs in nonlinear microresonators(2) represents a particularly promising option(3) enabling line spacings of tens of GHz. However, such combs may exhibit strong phase noise(4-6), which has made high-speed data transmission impossible up to now. Here we demonstrate that systematic adjustment of pump conditions for low phase noise(4,7-9) enables coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the comb. In a first experiment, we encode a data stream of 392 Gbit/s on a Kerr comb using quadrature phase shift keying (QPSK) and 16-state quadrature amplitude modulation (16QAM). A second experiment demonstrates feedback-stabilization of the comb and transmission of a 1.44 Tbit/s data stream over up to 300 km. The results show that Kerr combs meet the highly demanding requirements of coherent communications and thus offer an attractive solution towards chip-scale terabit/s transceivers. PMID:24860615

  6. XUV frequency combs based on intracavity high harmonic generation

    NASA Astrophysics Data System (ADS)

    Jones, R. Jason

    2014-05-01

    Intracavity high harmonic generation utilizing femtosecond enhancement cavities (fsEC's) has been established as an efficient route for the generation of femtosecond frequency combs in the vacuum-ultraviolet (VUV) to the extreme-ultraviolet (XUV) spectral regions. Such VUV/XUV frequency combs enable precision spectroscopy of atomic and potentially molecular spectra in an otherwise difficult to access spectral region. An improved understanding of the intracavity ionization dynamics that currently limit pulse enhancement has enabled a new generation of XUV frequency comb sources with significantly higher powers, at the >10 microwatt level per harmonic order extending below 50nm. We have developed a novel time-resolved pump-probe measurement technique to monitor and characterize the intracavity ionization dynamics by utilizing the sensitive response of the fsEC resonance itself to plasma induced nonlinear phase shifts. In recent work, we have developed a high power dual-frequency comb system based on Yb-fiber laser technology. The two phase-coherent frequency combs can be up-converted to the VUV/XUV using the fsEC. Dual-comb spectroscopy has already been established as a powerful spectroscopic method in the infrared. It's extension to the VUV/XUV spectral region will enable robust and high precision direct frequency comb spectroscopy of complex atomic and molecular structure in this spectral region.

  7. Digital processing of RF signals from optical frequency combs

    NASA Astrophysics Data System (ADS)

    Cizek, Martin; Smid, Radek; Buchta, Zden?k.; Mikel, B?etislav; Lazar, Josef; Cip, Ond?ej

    2013-01-01

    The presented work is focused on digital processing of beat note signals from a femtosecond optical frequency comb. The levels of mixing products of single spectral components of the comb with CW laser sources are usually very low compared to products of mixing all the comb components together. RF counters are more likely to measure the frequency of the strongest spectral component rather than a weak beat note. Proposed experimental digital signal processing system solves this problem by analyzing the whole spectrum of the output RF signal and using software defined radio (SDR) algorithms. Our efforts concentrate in two main areas: Firstly, using digital servo-loop techniques for locking free running continuous laser sources on single components of the fs comb spectrum. Secondly, we are experimenting with digital signal processing of the RF beat note spectrum produced by f-2f 1 technique used for assessing the offset and repetition frequencies of the comb, resulting in digital servo-loop stabilization of the fs comb. Software capable of computing and analyzing the beat-note RF spectrums using FFT and peak detection was developed. A SDR algorithm performing phase demodulation on the f- 2f signal is used as a regulation error signal source for a digital phase-locked loop stabilizing the offset frequency of the fs comb.

  8. Coherent terabit communications with microresonator Kerr frequency combs

    NASA Astrophysics Data System (ADS)

    Pfeifle, Joerg; Brasch, Victor; Lauermann, Matthias; Yu, Yimin; Wegner, Daniel; Herr, Tobias; Hartinger, Klaus; Schindler, Philipp; Li, Jingshi; Hillerkuss, David; Schmogrow, Rene; Weimann, Claudius; Holzwarth, Ronald; Freude, Wolfgang; Leuthold, Juerg; Kippenberg, Tobias J.; Koos, Christian

    2014-05-01

    Optical frequency combs have the potential to revolutionize terabit communications. The generation of Kerr combs in nonlinear microresonators is particularly promising, enabling line spacings of tens of gigahertz. However, such combs may exhibit strong phase noise, which has made high-speed data transmission impossible up to now. Here, we demonstrate that systematic adjustment of the pump conditions for low phase noise enables coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the comb. In a first experiment, we encode a data stream of 392 Gbit s-1 on a Kerr comb using quadrature phase-shift keying and 16-state quadrature amplitude modulation. A second experiment demonstrates feedback stabilization of the comb and transmission of a 1.44 Tbit s-1 data stream over up to 300 km. The results show that Kerr combs meet the highly demanding requirements of coherent communications and thus offer an attractive route towards chip-scale terabit-per-second transceivers.

  9. Dual-comb spectroscopy using frequency-doubled combs around 775 nm.

    PubMed

    Potvin, Simon; Genest, Jrme

    2013-12-16

    Two frequency-doubled combs are generated by nonlinear frequency conversion to realize spectroscopic measurements around 775 nm. Frequency-doubled interferograms are corrected in real-time by monitoring the relative instabilities between the combs at their fundamental frequency. Rubidium absorption lines are used to demonstrate the technique's accuracy and serve as absolute references to calibrate the frequency grid of computed spectra. The method allows frequency-doubled interferograms to be averaged without distortion during long periods of time. The calibrated frequency grid is validated by the measurement of the oxygen A-band. Moreover, the measurement analysis of the acetylene ?(1) + 3?(3) overtone band has revealed some discrepancies with previous publications. PMID:24514646

  10. Nonlinear conversion efficiency in Kerr frequency comb generation.

    PubMed

    Bao, Changjing; Zhang, Lin; Matsko, Andrey; Yan, Yan; Zhao, Zhe; Xie, Guodong; Agarwal, Anuradha M; Kimerling, Lionel C; Michel, Jurgen; Maleki, Lute; Willner, Alan E

    2014-11-01

    We analytically and numerically investigate the nonlinear conversion efficiency in ring microresonator-based mode-locked frequency combs under different dispersion conditions. Efficiency is defined as the ratio of the average round trip energy values for the generated pulse(s) to the input pump light. We find that the efficiency degrades with growth of the comb spectral width and is inversely proportional to the number of comb lines. It depends on the cold-cavity properties of a microresonator only and can be improved by increasing the coupling coefficient. Also, it can be increased in the multi-soliton state. PMID:25361295

  11. Precision spectroscopy using a partially stabilized frequency comb.

    PubMed

    Lyon, M; Bergeson, S D

    2014-08-10

    We present a simple method for precision spectroscopy using an optical frequency comb. One mode of a 1GHz repetition rate mode-locked Ti:sapphire laser is offset-locked to an Rb-stabilized diode laser. This partially stabilized frequency comb stays locked, unattended, for hours at a time. Using the measured offset frequency and repetition rate, we calculate the frequency of each comb mode with absolute uncertainty of about 10kHz in a 10s measurement window. We demonstrate the capabilities and limitations of this approach with measurements in Rb, Cs, and Ca. PMID:25320925

  12. All-optically stabilized frequency comb

    NASA Astrophysics Data System (ADS)

    Okubo, Sho; Gunji, Kenta; Onae, Atsushi; Schramm, Malte; Nakamura, Keisuke; Hong, Feng-Lei; Hattori, Toshiaki; Hosaka, Kazumoto; Inaba, Hajime

    2015-12-01

    We present an all-optically stabilized, erbium-doped mode-locked fiber laser with an optically pumped ytterbium-doped fiber. The mode-locked fiber laser has two frequency-control actuators that are pump laser powers for erbium-doped and ytterbium-doped fibers. We investigate the frequency-control characteristics of the mode-locked laser and find that the fixed points for the two actuators are sufficiently apart from each other, realizing the simultaneous phase locking of the repetition and carrier envelope offset frequencies. We describe a long-term frequency measurement of an acetylene-stabilized laser at 1542 nm using an all-optically stabilized frequency comb.

  13. Safe sex

    MedlinePLUS

    Safe sex means taking steps before and during sex that can prevent you from getting an infection, or from ... the skin around the genital area. Before having sex: Get to know your partner and discuss your ...

  14. Combing gravitational hair in 2 + 1 dimensions

    NASA Astrophysics Data System (ADS)

    Donnelly, William; Marolf, Donald; Mintun, Eric

    2016-01-01

    The gravitational Gauss law requires any addition of energy to be accompanied by the addition of gravitational flux. The possible configurations of this flux for a given source may be called gravitational hair, and several recent works discuss gravitational observables (‘gravitational Wilson lines’) which create this hair in highly collimated ‘combed’ configurations. We construct and analyze time-symmetric classical solutions of 2 + 1 Einstein-Hilbert gravity such as might be created by smeared versions of such operators. We focus on the AdS3 case, where this hair is characterized by the profile of the boundary stress tensor; the desired solutions are those where the boundary stress tensor at initial time t = 0 agrees precisely with its vacuum value outside an angular interval [-α ,α ]. At linear order in source strength the energy is independent of the combing parameter α, but nonlinearities cause the full energy to diverge as α \\to 0. In general, solutions with combed gravitational flux also suffer from what we call displacement from their naive location. For weak sources and large α one may set the displacement to zero by further increasing the energy, though for strong sources and small α we find no preferred notion of a zero-displacement solution. In the latter case we conclude that naively expected gravitational Wilson lines do not exist. In the zero-displacement case, taking the AdS scale ℓ to infinity gives finite-energy flux-directed solutions that may be called asymptotically flat.

  15. A genomic duplication is associated with ectopic eomesodermin expression in the embryonic chicken comb and two duplex-comb phenotypes.

    PubMed

    Dorshorst, Ben; Harun-Or-Rashid, Mohammad; Bagherpoor, Alireza Jian; Rubin, Carl-Johan; Ashwell, Chris; Gourichon, David; Tixier-Boichard, Michle; Hallbk, Finn; Andersson, Leif

    2015-03-01

    Duplex-comb (D) is one of three major loci affecting comb morphology in the domestic chicken. Here we show that the two Duplex-comb alleles, V-shaped (D*V) and Buttercup (D*C), are both associated with a 20 Kb tandem duplication containing several conserved putative regulatory elements located 200 Kb upstream of the eomesodermin gene (EOMES). EOMES is a T-box transcription factor that is involved in mesoderm specification during gastrulation. In D*V and D*C chicken embryos we find that EOMES is ectopically expressed in the ectoderm of the comb-developing region as compared to wild-type embryos. The confinement of the ectopic expression of EOMES to the ectoderm is in stark contrast to the causal mechanisms underlying the two other major comb loci in the chicken (Rose-comb and Pea-comb) in which the transcription factors MNR2 and SOX5 are ectopically expressed strictly in the mesenchyme. Interestingly, the causal mutations of all three major comb loci in the chicken are now known to be composed of large-scale structural genomic variants that each result in ectopic expression of transcription factors. The Duplex-comb locus also illustrates the evolution of alleles in domestic animals, which means that alleles evolve by the accumulation of two or more consecutive mutations affecting the phenotype. We do not yet know whether the V-shaped or Buttercup allele correspond to the second mutation that occurred on the haplotype of the original duplication event. PMID:25789773

  16. A Genomic Duplication is Associated with Ectopic Eomesodermin Expression in the Embryonic Chicken Comb and Two Duplex-comb Phenotypes

    PubMed Central

    Dorshorst, Ben; Rubin, Carl-Johan; Ashwell, Chris; Gourichon, David; Tixier-Boichard, Michle; Hallbk, Finn; Andersson, Leif

    2015-01-01

    Duplex-comb (D) is one of three major loci affecting comb morphology in the domestic chicken. Here we show that the two Duplex-comb alleles, V-shaped (D*V) and Buttercup (D*C), are both associated with a 20 Kb tandem duplication containing several conserved putative regulatory elements located 200 Kb upstream of the eomesodermin gene (EOMES). EOMES is a T-box transcription factor that is involved in mesoderm specification during gastrulation. In D*V and D*C chicken embryos we find that EOMES is ectopically expressed in the ectoderm of the comb-developing region as compared to wild-type embryos. The confinement of the ectopic expression of EOMES to the ectoderm is in stark contrast to the causal mechanisms underlying the two other major comb loci in the chicken (Rose-comb and Pea-comb) in which the transcription factors MNR2 and SOX5 are ectopically expressed strictly in the mesenchyme. Interestingly, the causal mutations of all three major comb loci in the chicken are now known to be composed of large-scale structural genomic variants that each result in ectopic expression of transcription factors. The Duplex-comb locus also illustrates the evolution of alleles in domestic animals, which means that alleles evolve by the accumulation of two or more consecutive mutations affecting the phenotype. We do not yet know whether the V-shaped or Buttercup allele correspond to the second mutation that occurred on the haplotype of the original duplication event. PMID:25789773

  17. Radiative properties tailoring of grating by comb-drive microactuator

    NASA Astrophysics Data System (ADS)

    Jiao, Y.; Liu, L. H.; Liu, L. J.; Hsu, P.-f.

    2014-08-01

    Micro-scale grating structures are widely researched in recent years. Although micro-scale fabrication technology is highly advanced today, with grating aspect ratio greater than 25:1 being achievable some fabrication requirements, such as fine groove processing, are still challenging. Comb-drive microactuator is proposed in this paper to be utilized on simple binary grating structures for tailoring or modulating spectral radiation properties by active adjustment. The rigorous coupled-wave analysis (RCWA) is used to calculate the absorptance of proposed structures and to investigate the impacts brought by the geometry and displacement of comb-drive microactuator. The results show that the utilization of comb-drive microactuator on grating improves the absorptance of simple binary grating while avoiding the difficulty fine groove processing. Spectral radiation property tailoring after gratings are fabricated becomes possible with the comb-drive microactuator structure.

  18. Doppler Cooling Trapped Ions with a UV Frequency Comb.

    PubMed

    Davila-Rodriguez, Josue; Ozawa, Akira; Hnsch, Theodor W; Udem, Thomas

    2016-01-29

    We demonstrate Doppler cooling of trapped magnesium ions using a frequency comb at 280nm obtained from a frequency tripled Ti:sapphire laser. A comb line cools on the 3s_{1/2}-3p_{3/2} transition, while the nearest blue-detuned comb line contributes negligible heating. We observe the cooling-heating transition and long-term cooling of ion chains with several sympathetically cooled ions. Spatial thermometry shows that the ion is cooled to near the Doppler limit. Doppler cooling with frequency combs has the potential to open many additional atomic species to laser cooling by reaching further into the vacuum and extreme ultraviolet via high-harmonic generation and by providing a broad bandwidth from which multiple excitation sidebands can be obtained. PMID:26871326

  19. Doppler Cooling Trapped Ions with a UV Frequency Comb

    NASA Astrophysics Data System (ADS)

    Davila-Rodriguez, Josue; Ozawa, Akira; Hänsch, Theodor W.; Udem, Thomas

    2016-01-01

    We demonstrate Doppler cooling of trapped magnesium ions using a frequency comb at 280 nm obtained from a frequency tripled Ti:sapphire laser. A comb line cools on the 3 s1 /2-3 p3 /2 transition, while the nearest blue-detuned comb line contributes negligible heating. We observe the cooling-heating transition and long-term cooling of ion chains with several sympathetically cooled ions. Spatial thermometry shows that the ion is cooled to near the Doppler limit. Doppler cooling with frequency combs has the potential to open many additional atomic species to laser cooling by reaching further into the vacuum and extreme ultraviolet via high-harmonic generation and by providing a broad bandwidth from which multiple excitation sidebands can be obtained.

  20. Frequency stabilisation of femtosecond frequency combs with a reference laser

    SciTech Connect

    Bagayev, S N; Pivtsov, V S; Zheltikov, Aleksei M

    2002-04-30

    A solution to the key problem of femtosecond metrology - elimination of the frequency offset related to the intracavity dispersion of a femtosecond laser - is proposed. The proposed method involves stabilisation of the intermode interval between equidistant spectral components in a frequency comb produced by a mode-locked femtosecond laser by phase-locking the frequency difference between a pair of discrete spectral components in this comb to the frequency of a reference laser. An introduction of a nonlinear-optical crystal for frequency doubling into the scheme for frequency-comb stabilisation allows the frequency offset related to the intracavity dispersion of the femtosecond laser to be eliminated, thus suggesting the way for absolute stabilisation of frequency combs generated by femtosecond mode-locked lasers. Radiation of a reference laser with such an approach plays the role of an anchor in the femtosecond clockwork. (control of laser radiation parameters)

  1. Spectro-temporal dynamics of Kerr combs with parametric seeding.

    PubMed

    Lin, Guoping; Martinenghi, Romain; Diallo, Souleymane; Saleh, Khaldoun; Coillet, Aurlien; Chembo, Yanne K

    2015-03-20

    We report a joint theoretical and experimental investigation of the parametric seeding of a primary Kerr optical frequency comb. Electro-optic modulation sidebands matching multiple free-spectral ranges of an ultrahigh-Q millimeter-size magnesium fluoride disk resonator are used as seed signals. These seed signals interact through four-wave mixing with the spectral components of a stable primary comb and give rise to complex spectro-temporal patterns. We show that the new frequency combs feature multiscale frequency spacing, with major frequency gaps in the order of a few hundred gigahertz, and minor frequency spacing in the order of a few tens of gigahertz. The experimental results are in agreement with numerical simulations using the Lugiato-Lefever equation. We expect such versatile and coherent optical frequency combs to have potential applications in optical communications systems where frequency management assigns predefined spectral windows at the emitter stage. PMID:25968529

  2. Material candidates for optical frequency comb generation in microspheres.

    PubMed

    Riesen, Nicolas; Afshar V, Shahraam; Franois, Alexandre; Monro, Tanya M

    2015-06-01

    This paper evaluates the opportunities for using materials other than silica for optical frequency comb generation in whispering gallery mode microsphere resonators. Different materials are shown to satisfy the requirement of dispersion compensation in interesting spectral regions such as the visible or mid-infrared and for smaller microspheres. This paper also analyses the prospects of comb generation in microspheres within aqueous solution for potential use in applications such as biosensing. It is predicted that to achieve comb generation with microspheres in aqueous solution the visible low-loss wavelength window of water needs to be exploited. This is because efficient comb generation necessitates ultra-high Q-factors, which are only possible for cavities with low absorption of the evanescent field outside the cavity. This paper explores the figure of merit for nonlinear interaction efficiency and the potential for dispersion compensation at unique wavelengths for a host of microsphere materials and dimensions and in different surroundings. PMID:26072837

  3. Raman-induced Kerr-effect dual-comb spectroscopy.

    PubMed

    Ideguchi, T; Bernhardt, B; Guelachvili, G; Hnsch, T W; Picqu, N

    2012-11-01

    We report on the first (to our knowledge) demonstration of nonlinear dual-frequency-comb spectroscopy. In multi-heterodyne femtosecond Raman-induced Kerr-effect spectroscopy, the Raman gain resulting from the coherent excitation of molecular vibrations by a spectrally narrow pump is imprinted onto the femtosecond laser frequency comb probe spectrum. The birefringence signal induced by the nonlinear interaction of these beams and the sample is heterodyned against a frequency comb local oscillator with a repetition frequency slightly different from that of the comb probe. Such time-domain interference provides multiplex access to the phase and amplitude Raman spectra over a broad spectral bandwidth within a short measurement time. PMID:23114342

  4. High density terahertz frequency comb produced by coherent synchrotron radiation.

    PubMed

    Tammaro, S; Pirali, O; Roy, P; Lampin, J-F; Ducournau, G; Cuisset, A; Hindle, F; Mouret, G

    2015-01-01

    Frequency combs have enabled significant progress in frequency metrology and high-resolution spectroscopy extending the achievable resolution while increasing the signal-to-noise ratio. In its coherent mode, synchrotron radiation is accepted to provide an intense terahertz continuum covering a wide spectral range from about 0.1 to 1 THz. Using a dedicated heterodyne receiver, we reveal the purely discrete nature of this emission. A phase relationship between the light pulses leads to a powerful frequency comb spanning over one decade in frequency. The comb has a mode spacing of 846 kHz, a linewidth of about 200 Hz, a fractional precision of about 2 × 10(-10) and no frequency offset. The unprecedented potential of the comb for high-resolution spectroscopy is demonstrated by the accurate determination of pure rotation transitions of acetonitrile. PMID:26190043

  5. High density terahertz frequency comb produced by coherent synchrotron radiation

    PubMed Central

    Tammaro, S.; Pirali, O.; Roy, P.; Lampin, J.-F.; Ducournau, G.; Cuisset, A.; Hindle, F.; Mouret, G.

    2015-01-01

    Frequency combs have enabled significant progress in frequency metrology and high-resolution spectroscopy extending the achievable resolution while increasing the signal-to-noise ratio. In its coherent mode, synchrotron radiation is accepted to provide an intense terahertz continuum covering a wide spectral range from about 0.1 to 1 THz. Using a dedicated heterodyne receiver, we reveal the purely discrete nature of this emission. A phase relationship between the light pulses leads to a powerful frequency comb spanning over one decade in frequency. The comb has a mode spacing of 846 kHz, a linewidth of about 200 Hz, a fractional precision of about 2 × 10−10 and no frequency offset. The unprecedented potential of the comb for high-resolution spectroscopy is demonstrated by the accurate determination of pure rotation transitions of acetonitrile. PMID:26190043

  6. Frequency comb selection enabled flexible all optical Nyquist pulse generation

    NASA Astrophysics Data System (ADS)

    Fang, Yuan; Yu, Jianjun; Zhang, Junwen; Li, Xinying; Chi, Nan; Xiao, Jiangnan

    2015-08-01

    In this paper, we propose and experimentally demonstrate flexible all optical Nyquist pulse generation enabled by frequency comb selection with cascaded intensity modulators and tunable optical band-pass filters. Cascaded intensity modulators are used to generate frequency-locked optical comb with flat amplitude and linear phase with up to 15 tones. Arbitrary frequency comb selection based on tunable optical band-pass filters allows the control of the pulse width and repetitive period of the high quality sinc-shaped Nyquist pulse. The optical spectra of the selected 3 and 7 tones frequency comb and the corresponding time-domain waveforms are measured in experiment and simulated by software, respectively. Experimental results conform well to the simulation results which verifies the feasibility of our scheme. The scheme we propose is with excellent flexibility in Nyquist pulse generation and is suitable for high capacity optical transmission system.

  7. Optimal Sharpening of Compensated Comb Decimation Filters: Analysis and Design

    PubMed Central

    Troncoso Romero, David Ernesto

    2014-01-01

    Comb filters are a class of low-complexity filters especially useful for multistage decimation processes. However, the magnitude response of comb filters presents a droop in the passband region and low stopband attenuation, which is undesirable in many applications. In this work, it is shown that, for stringent magnitude specifications, sharpening compensated comb filters requires a lower-degree sharpening polynomial compared to sharpening comb filters without compensation, resulting in a solution with lower computational complexity. Using a simple three-addition compensator and an optimization-based derivation of sharpening polynomials, we introduce an effective low-complexity filtering scheme. Design examples are presented in order to show the performance improvement in terms of passband distortion and selectivity compared to other methods based on the traditional Kaiser-Hamming sharpening and the Chebyshev sharpening techniques recently introduced in the literature. PMID:24578674

  8. Universality of comb structures in strong-field quantum electrodynamics

    NASA Astrophysics Data System (ADS)

    Krajewska, Katarzyna; Kami?ski, Jerzy

    2015-05-01

    We demonstrate a new mechanism for coherent comb generation in both radiation and matter domains, which is by using strong-field quantum electrodynamics processes. Specifically, we demonstrate this for nonlinear Compton scattering which has the potential to generate frequency combs extending towards the ?-ray spectral region and combs of ultra-relativistic electrons extending towards the MeV regime. Moreover, we show that coherent energy combs of positrons (electrons) emerge in laser-induced pair creation processes such as the Breit-Wheeler process, proving the universality of the proposed mechanism. We acknowledge the support from the Kosciuszko Foundation (KK) and from the Polish National Science Center (NCN), under Grant No. 2012/05/B/ST2/02547 (JZK).

  9. CombFunc: predicting protein function using heterogeneous data sources

    PubMed Central

    Wass, Mark N.; Barton, Geraint; Sternberg, Michael J. E.

    2012-01-01

    Only a small fraction of known proteins have been functionally characterized, making protein function prediction essential to propose annotations for uncharacterized proteins. In recent years many function prediction methods have been developed using various sources of biological data from protein sequence and structure to gene expression data. Here we present the CombFunc web server, which makes Gene Ontology (GO)-based protein function predictions. CombFunc incorporates ConFunc, our existing function prediction method, with other approaches for function prediction that use protein sequence, gene expression and proteinprotein interaction data. In benchmarking on a set of 1686 proteins CombFunc obtains precision and recall of 0.71 and 0.64 respectively for gene ontology molecular function terms. For biological process GO terms precision of 0.74 and recall of 0.41 is obtained. CombFunc is available at http://www.sbg.bio.ic.ac.uk/combfunc. PMID:22641853

  10. Direct frequency comb spectroscopy in the extreme ultraviolet.

    PubMed

    Cingz, Arman; Yost, Dylan C; Allison, Thomas K; Ruehl, Axel; Fermann, Martin E; Hartl, Ingmar; Ye, Jun

    2012-02-01

    The development of the optical frequency comb (a spectrum consisting of a series of evenly spaced lines) has revolutionized metrology and precision spectroscopy owing to its ability to provide a precise and direct link between microwave and optical frequencies. A further advance in frequency comb technology is the generation of frequency combs in the extreme-ultraviolet spectral range by means of high-harmonic generation in a femtosecond enhancement cavity. Until now, combs produced by this method have lacked sufficient power for applications, a drawback that has also hampered efforts to observe phase coherence of the high-repetition-rate pulse train produced by high-harmonic generation, which is an extremely nonlinear process. Here we report the generation of extreme-ultraviolet frequency combs, reaching wavelengths of 40?nanometres, by coupling a high-power near-infrared frequency comb to a robust femtosecond enhancement cavity. These combs are powerful enough for us to observe single-photon spectroscopy signals for both an argon transition at 82?nanometres and a neon transition at 63?nanometres, thus confirming the combs' coherence in the extreme ultraviolet. The absolute frequency of the argon transition has been determined by direct frequency comb spectroscopy. The resolved ten-megahertz linewidth of the transition, which is limited by the temperature of the argon atoms, is unprecedented in this spectral region and places a stringent upper limit on the linewidth of individual comb teeth. Owing to the lack of continuous-wave lasers, extreme-ultraviolet frequency combs are at present the only promising route to extending ultrahigh-precision spectroscopy to the spectral region below 100?nanometres. At such wavelengths there is a wide range of applications, including the spectroscopy of electronic transitions in molecules, experimental tests of bound-state and many-body quantum electrodynamics in singly ionized helium and neutral helium, the development of next-generation 'nuclear' clocks and searches for variation of fundamental constants using the enhanced sensitivity of highly charged ions. PMID:22297971

  11. Adaptive real-time dual-comb spectroscopy

    PubMed Central

    Ideguchi, Takuro; Poisson, Antonin; Guelachvili, Guy; Picqué, Nathalie; Hänsch, Theodor W.

    2014-01-01

    The spectrum of a laser frequency comb consists of several hundred thousand equally spaced lines over a broad spectral bandwidth. Such frequency combs have revolutionized optical frequency metrology and they now hold much promise for significant advances in a growing number of applications including molecular spectroscopy. Despite an intriguing potential for the measurement of molecular spectra spanning tens of nanometres within tens of microseconds at Doppler-limited resolution, the development of dual-comb spectroscopy is hindered by the demanding stability requirements of the laser combs. Here we overcome this difficulty and experimentally demonstrate a concept of real-time dual-comb spectroscopy, which compensates for laser instabilities by electronic signal processing. It only uses free-running mode-locked lasers without any phase-lock electronics. We record spectra spanning the full bandwidth of near-infrared fibre lasers with Doppler-limited line profiles highly suitable for measurements of concentrations or line intensities. Our new technique of adaptive dual-comb spectroscopy offers a powerful transdisciplinary instrument for analytical sciences. PMID:24572636

  12. Parentage and relatedness in polyandrous comb-crested jacanas using ISSRs

    USGS Publications Warehouse

    Haig, Susan M.; Mace, Terrence R.; Mullins, Thomas D.

    2003-01-01

    In this article we present the first analysis of parentage and relatedness in a natural vertebrate population, using Intersimple Sequence Repeat (ISSR) markers. Thus, 28 ISSR markers were used in a study of a sex-role reversed, simultaneously polyandrous shorebird from northeastern Australia, the comb-crested jacana (Irediparra gallinacea). Assessment of parentage was based on comparison of field observations, novel bands, individual-specific bands found in 7/9 males and 4/6 females, and a 99% CI exclusion criteria. Integrating results from these approaches resulted in confirmation of paternity in all 36 chicks. In only one case (2.8% of chicks) was a co-mate assigned paternity. Thus, comb-crested jacanas appear to be genetically monogamous. These results showed resemblance to sequentially polyandrous birds but differed from the simultaneously polyandrous wattled jacana ( Jacana jacana; Emlen et al. 1998). A significant relationship between relatedness and ISSR similarity resulted in recognition that 14/15 adults sampled may be related to at least one other adult by 0.25 or more. Lack of dispersal may be explained by physical limitations and adequate regional habitat. ISSRs proved to be simple and helpful in resolving these issues.

  13. Treatment of head lice (Pediculus humanus capitis) infestation: is regular combing alone with a special detection comb effective at all levels?

    PubMed

    Kurt, zgr; Balc?o?lu, I Cneyt; Limoncu, M Emin; Girginkarde?ler, Nogay; Arserim, Sha K; Grgn, Serhan; Oyur, Tuba; Karaku?, Mehmet; Dzyol, Didem; Gkmen, Aysegl Aksoy; Kitap?o?lu, Gl; zbel, Yusuf

    2015-04-01

    Head lice infestation (HLI) caused by Pediculus humanus capitis has been a public health problem worldwide. Specially designed combs are used to identify head lice, while anti-lice products are applied on the scalp for treatment. In the present study, we aimed to test whether combing only by precision detection comb (PDC) or metal pin comb (MPC) could be effective alternatives to the use of anti-lice products in children. A total of 560 children from two rural schools in Turkey were screened. In the PDC trial, children were combed every second day for 14 days, while in the MPC trial, combing was performed once in every four days for 15 days. Children were divided into two groups (dry combing and wet combing) for both trials and results were compared. The results showed no significant differences between dry and wet combing strategies for both combs for the removal of head lice (p?>?0.05). The number of adult head lice declined significantly on each subsequent combing day in both approaches, except on day 15 in the MPC trial. In the end, no louse was found in 54.1 and 48.9% of children in the PDC and MPC trials, respectively. Since family members of infested children were not available, they were not checked for HLI. Four times combing within 2 weeks with MPC combs was found effective for both treatment of low HLI and prevention of heavy HLI. In conclusion, regular combing by special combs decreases HLI level in children and is safely applicable as long-term treatment. PMID:25604670

  14. Effect of Isovalent Substitution on the Structure and Properties of the Zintl Phase Solid Solution Eu7Cd4Sb8-xAsx (2 ? x ? 5).

    PubMed

    Cooley, Joya; Kazem, Nasrin; Zaikina, Julia V; Fettinger, James C; Kauzlarich, Susan M

    2015-12-21

    A novel Zintl phase structure type, Eu7Cd4Sb8-xAsx (x = 2, 3, 4, and 5), with the general formula Eu7Cd4Pn8 (Pn = mixed occupancy Sb and As), was synthesized by molten tin flux reaction. Its structure was determined using single-crystal X-ray diffraction methods. This structure type is only preserved for 2 ? x ? 5 under our experimental conditions, and efforts to synthesize samples with x < 2 or x > 5 resulted in other structure types. The mixed occupancy Sb and As can be thought of as a pseudoatom whose ideal size, in this range of Sb/As ratios, fits the structure. The title phase crystallizes in the I-centered monoclinic space group I2/m (No. 12, Z = 4) with unit cell parameters ranging as follows: a = 19.7116(17)-19.4546(13) , b = 4.6751(4)-4.6149(3) , c = 24.157(2)-23.871(15) , and ? = 95.8798(1)-96.016(5), depending on the Sb/As ratio. The structure can be described as parallel double pentagonal tubes resulting from Cd-Pn and Pn-Pn bonding. These double pentagons are formed through corner sharing of the Cd-centered CdPn4 tetrahedra and a Pn-Pn interaction from two adjacent CdPn4 tetrahedra. This structure type is closely related to the Sr11Cd6Sb12 structure type as both share the same bonding features of Pn-Pn bonding and double pentagonal tubes. Electron microprobe analysis confirms the composition of these new Zintl solid solution phases. The As exhibits preferential substitution on specific sites, and site specificity trends are supported by lowest energy models from theoretical calculations. Theoretical calculations also predict that Sb-rich compounds should be metallic or semimetallic and that they should become more insulating as As content increases. Members of the solid-solution order ferromagnetically between 5 and 6 K and exhibit relatively low electrical resistivity between 50 and 300 K, ranging from ?0.57 to ?26 m?cm, increasing with increasing As content. PMID:26605859

  15. Broadband Comb-Resolved Cavity Enhanced Spectrometer with Graphene Modulator

    NASA Astrophysics Data System (ADS)

    Lee, Kevin; Mohr, Christian; Jiang, Jie; Fermann, Martin; Lee, Chien-Chung; Schibli, Thomas R.; Kowzan, Grzegorz; Maslowski, Piotr

    2015-06-01

    Optical cavities enhance sensitivity in absorption spectroscopy. While this is commonly done with single wavelengths, broad bandwidths can be coupled into the cavity using frequency combs. The combination of cavity enhancement and broad bandwidth allows simultaneous measurement of tens of transitions with high signal-to-noise for even weak near-infrared transitions. This removes the need for time-consuming sequencing acquisition or long-term averaging, so any systematic errors from long-term drifts of the experimental setup or slow changes of sample composition are minimized. Resolving comb lines provides a high accuracy, absolute frequency axis. This is of great importance for gas metrology and data acquisition for future molecular lines databases, and can be applied to simultaneous trace-gas detection of gas mixtures. Coupling of a frequency comb into a cavity can be complex, so we introduce and demonstrate a simplification. The Pound-Drever-Hall method for locking a cavity and a frequency comb together requires a phase modulation of the laser output. We use the graphene modulator that is already in the Tm fiber laser cavity for controlling the carrier envelope offset of the frequency comb, rather than adding a lossy external modulator. The graphene modulator can operate at frequencies of over 1~ MHz, which is sufficient for controlling the laser cavity length actuator which operates below 100~kHz. We match the laser cavity length to fast variations of the enhancement cavity length. Slow variations are stabilized by comparison of the pulse repetition rate to a GPS reference. The carrier envelope offset is locked to a constant value chosen to optimize the transmitted spectrum. The transmitted pulse train is a stable frequency comb suitable for long measurements, including the acquisition of comb-resolved Fourier transform spectra with a minimum absorption coefficient of about 210-7 wn. For our 38 cm long enhancement cavity, the comb spacing is 394~MHz. With our 300 wn bandwidth at 2 ?m, we simultaneously measure the full comb line resolved CO_2 vibrational manifold at 4850 wn. Other spectral ranges can be accessed by using graphene with different gain fibers or nonlinear frequency conversion.

  16. Structure and effective interactions of comb polymer nanocomposite melts

    NASA Astrophysics Data System (ADS)

    Xu, Qinzhi; Xu, Mengjin; Feng, Yancong; Chen, Lan

    2014-11-01

    In this work, the structure and effective interactions of branched comb polymer nanocomposite (PNC) melts are investigated by using the polymer reference interaction site model (PRISM) integral equation theory. It is observed that the nanoparticle contact (bridging) aggregation is formed when the nanoparticle-monomer attraction strength is relatively weak (large) in comb PNCs. The organization states of aggregation for the moderate nanoparticle-monomer attraction strength can be well suppressed by the comb polymer architecture, while the bridging structure for relatively large attraction is obviously promoted. With the increase of the particle volume fraction, the organization states of bridging-type structure become stronger and tighter; however, this effect is weaker than that of the nanoparticle-monomer attraction strength. When the particle volume fraction and moderate nanoparticle-monomer attraction strength are fixed, the effects of degree of polymerization, side chain number, side chain length, and nanoparticle-monomer size ratio on the organization states of PNC melts are not prominent and the nanoparticles can well disperse in comb polymer. All the observations indicate that the present PRISM theory can give a detailed description of the comb PNC melts and assist in future design control of new nanomaterials.

  17. Optimizing intracavity high harmonic generation for XUV fs frequency combs.

    PubMed

    Lee, Jane; Carlson, David R; Jones, R Jason

    2011-11-01

    Previous work has shown that use of a passive enhancement cavity designed for ultrashort pulses can enable the up-conversion of the fs frequency comb into the extreme ultraviolet (XUV) spectral region utilizing the highly nonlinear process of high harmonic generation. This promising approach for an efficient source of highly coherent light in this difficult to reach spectral region promises to be a unique tool for precision spectroscopy and temporally resolved measurements. Yet to date, this approach has not been extensively utilized due in part to the low powers so far achieved and in part due to the challenges in directly probing electronic transitions with the frequency comb itself. We report on a dramatically improved XUV frequency comb producing record power levels to date in the 50-150 nm spectral region based on intracavity high harmonic generation. We measure up to 77 ?W at the 11th harmonic of the fundamental (72 nm) with ?W levels down to the 15th harmonic (53nm). Phase-matching and related design considerations unique to intracavity high harmonic generation are discussed, guided by numerical simulations which provide insight into the role played by intracavity ionization dynamics. We further propose and analyze dual-comb spectroscopy in the XUV and show that the power levels reported here permit this approach for the first time. Dual-comb spectroscopy in this physically rich spectral region promises to enable the study of a significantly broader range of atomic and molecular spectra with unprecedented precision and accuracy. PMID:22109209

  18. Laser cooling and trapping with optical frequency combs

    NASA Astrophysics Data System (ADS)

    Long, Xueping; Jayich, Andrew; Ransford, Anthony; Wang, Anna; Campbell, Wesley

    2015-05-01

    A large number of atoms and molecules are difficult to control with continuous wave lasers because generating sufficient power at all of the necessary wavelengths is technologically challenging. Mode-locked lasers, through their enhanced efficiency of nonlinear frequency conversion, provide some of these hard to access wavelengths. As a step towards control of exotic atoms and molecules we report on laser cooling and trapping of atoms using an optical frequency comb in two different regimes. Using a single comb, we have created a simultaneous dual-species (isotopes) MOT, demonstrating that multiple comb teeth can be used in parallel to cool and confine species requiring many cw lasers. Separately, we demonstrate comb-based laser cooling on a two-photon transition, which efficiently uses the full time-averaged optical power of the entire comb. Our progress toward extending this to include trapping by making a MOT using this two-photon transition is presented. This work is supported by the National Science Foundation.

  19. Tunable frequency combs based on dual microring resonators.

    PubMed

    Miller, Steven A; Okawachi, Yoshitomo; Ramelow, Sven; Luke, Kevin; Dutt, Avik; Farsi, Alessandro; Gaeta, Alexander L; Lipson, Michal

    2015-08-10

    In order to achieve efficient parametric frequency comb generation in microresonators, external control of coupling between the cavity and the bus waveguide is necessary. However, for passive monolithically integrated structures, the coupling gap is fixed and cannot be externally controlled, making tuning the coupling inherently challenging. We design a dual-cavity coupled microresonator structure in which tuning one ring resonance frequency induces a change in the overall cavity coupling condition. We demonstrate wide extinction tunability with high efficiency by engineering the ring coupling conditions. Additionally, we note a distinct dispersion tunability resulting from coupling two cavities of slightly different path lengths, and present a new method of modal dispersion engineering. Our fabricated devices consist of two coupled high quality factor silicon nitride microresonators, where the extinction ratio of the resonances can be controlled using integrated microheaters. Using this extinction tunability, we optimize comb generation efficiency as well as provide tunability for avoiding higher-order mode-crossings, known for degrading comb generation. The device is able to provide a 110-fold improvement in the comb generation efficiency. Finally, we demonstrate open eye diagrams using low-noise phase-locked comb lines as a wavelength-division multiplexing channel. PMID:26367998

  20. A quantitative mode-resolved frequency comb spectrometer.

    PubMed

    Hbert, Nicolas Bourbeau; Scholten, Sarah K; White, Richard T; Genest, Jrme; Luiten, Andre N; Anstie, James D

    2015-06-01

    We have developed a frequency-comb spectrometer that records 35-nm (4 THz) spectra with 2-pm (250 MHz) spectral sampling and an absolute frequency accuracy of 2 kHz. We achieve a signal-to-noise ratio of ~400 in a measurement time of 8.2 s. The spectrometer is based on a commercial frequency comb decimated by a variable-length, low-finesse Fabry Prot filter cavity to fully resolve the comb modes as imaged by a virtually imaged phased array (VIPA), diffraction grating and near-IR camera. By tuning the cavity length, spectra derived from all unique decimated combs are acquired and then interleaved to achieve frequency sampling at the comb repetition rate of 250 MHz. We have validated the performance of the spectrometer by comparison with a previous high-precision absorption measurement of H13C14N near 1543 nm. We find excellent agreement, with deviations from the expected line centers and widths of, at most, 1 pm (125 MHz) and 3 pm (360 MHz), respectively. PMID:26072768

  1. 1-GHz harmonically pumped femtosecond optical parametric oscillator frequency comb.

    PubMed

    Balskus, K; Leitch, S M; Zhang, Z; McCracken, R A; Reid, D T

    2015-01-26

    We present the first example of a femtosecond optical parametric oscillator frequency comb harmonically-pumped by a 333-MHz Ti:sapphire laser to achieve a stabilized signal comb at 1-GHz mode spacing in the 1.1-1.6-m wavelength band. Simultaneous locking of the comb carrier-envelope-offset and repetition frequencies is achieved with uncertainties over 1 s of 0.27 Hz and 5 mHz respectively, which are comparable with those of 0.27 Hz and 1.5 mHz achieved for 333-MHz fundamental pumping. The phase-noise power-spectral density of the CEO frequency integrated from 1 Hz-64 kHz was 2.8 rad for the harmonic comb, 1.0 rad greater than for fundamental pumping. The results show that harmonic operation does not substantially compromise the frequency-stability of the comb, which is shown to be limited only by the Rb atomic frequency reference used. PMID:25835887

  2. Single DNA molecule analysis: applications of molecular combing.

    PubMed

    Lebofsky, Ronald; Bensimon, Aaron

    2003-01-01

    Dynamic changes to the genomic structure and to the DNA replication programme are important determinants of normal and abnormal cell development. To understand these changes and how they vary from cell to cell, single DNA molecules from both normal and abnormal cell populations must be examined and compared. Physical characterisation of single genomes at the kilobase level of resolution over large genomic regions is possible with molecular combing technology. An array of combed single DNA molecules is prepared by stretching molecules attached by their extremities to a silanised glass surface with a receding air-water meniscus. By performing fluorescent hybridisation on combed DNA, genomic probe position can be directly visualised, providing a means to construct physical maps and detect micro-rearrangements. Single-molecule DNA replication can also be monitored through fluorescent detection of incorporated nucleotide analogues on combed DNA molecules. These and other single-molecule applications of molecular combing are discussed in this paper and future developments of the technology are considered. PMID:15239885

  3. Phrenology, heredity and progress in George Combe's Constitution of Man.

    PubMed

    Jenkins, Bill

    2015-09-01

    The Constitution of Man by George Combe (1828) was probably the most influential phrenological work of the nineteenth century. It not only offered an exposition of the phrenological theory of the mind, but also presented Combe's vision of universal human progress through the inheritance of acquired mental attributes. In the decades before the publication of Darwin's Origin of Species, the Constitution was probably the single most important vehicle for the dissemination of naturalistic progressivism in the English-speaking world. Although there is a significant literature on the social and cultural context of phrenology, the role of heredity in Combe's thought has been less thoroughly explored, although both John van Wyhe and Victor L. Hilts have linked Combe's views on heredity with the transformist theories of Jean-Baptiste Lamarck. In this paper I examine the origin, nature and significance of his ideas and argue that Combe's hereditarianism was not directly related to Lamarckian transformism but formed part of a wider discourse on heredity in the early nineteenth century. PMID:25998794

  4. X-ray frequency combs from optically controlled resonance fluorescence

    NASA Astrophysics Data System (ADS)

    Cavaletto, Stefano M.; Harman, Zoltán; Buth, Christian; Keitel, Christoph H.

    2013-12-01

    An x-ray pulse-shaping scheme is put forward for imprinting an optical frequency comb onto the radiation emitted on a driven x-ray transition, thus producing an x-ray frequency comb. A four-level system is used to describe the level structure of N ions driven by narrow-bandwidth x rays, an optical auxiliary laser, and an optical frequency comb. By including many-particle enhancement of the emitted resonance fluorescence, a spectrum is predicted consisting of equally spaced narrow lines which are centered on an x-ray transition energy and separated by the same tooth spacing as the driving optical frequency comb. Given an x-ray reference frequency, our comb could be employed to determine an unknown x-ray frequency. While relying on the quality of the light fields used to drive the ensemble of ions, the model has validity at energies from the 100 eV to the keV range.

  5. Microresonator-based comb generation without an external laser source

    NASA Astrophysics Data System (ADS)

    Johnson, Adrea R.; Okawachi, Yoshitomo; Lamont, Michael R. E.; Levy, Jacob S.; Lipson, Michal; Gaeta, Alexander L.

    2014-01-01

    Recent developments demonstrate that parametric four-wave mixing (FWM) in high-Q microresonators is a highly promising and effective approach for optical frequency comb generation, with applications including spectroscopy, optical clocks, arbitrary waveform generation, frequency metrology, and astronomical spectrograph calibration. Each of these microresonator platforms utilizes a scheme in which the system is pumped by a single-frequency laser at a cavity resonance. This scheme requires tuning of the pump wavelength into resonance and the generated comb is susceptible to fluctuations in pump power or frequency which can disrupt the soft thermal lock and comb generation. We demonstrate a novel fiber-microresonator dual-cavity architecture that preferentially oscillates at modes of the microresonator due to its high density of states and generates robust and broadband combs (> 900 nm) without an external pump laser. Such a scheme could greatly simplify the comb generation process and allow for a fully-integrated chip-scale source with an on-chip amplifier.

  6. Tunable frequency combs based on dual microring resonators

    NASA Astrophysics Data System (ADS)

    Miller, Steven A.; Okawachi, Yoshitomo; Ramelow, Sven; Luke, Kevin; Dutt, Avik; Farsi, Alessandro; Gaeta, Alexander L.; Lipson, Michal

    2015-08-01

    In order to achieve efficient parametric frequency comb generation in microresonators, external control of coupling between the cavity and the bus waveguide is necessary. However, for passive monolithically integrated structures, the coupling gap is fixed and cannot be externally controlled, making tuning the coupling inherently challenging. We design a dual-cavity coupled microresonator structure in which tuning one ring resonance frequency induces a change in the overall cavity coupling condition. We demonstrate wide extinction tunability with high efficiency by engineering the ring coupling conditions. Additionally, we note a distinct dispersion tunability resulting from coupling two cavities of slightly different path lengths, and present a new method of modal dispersion engineering. Our fabricated devices consist of two coupled high quality factor silicon nitride microresonators, where the extinction ratio of the resonances can be controlled using integrated microheaters. Using this extinction tunability, we optimize comb generation efficiency as well as provide tunability for avoiding higher-order mode-crossings, known for degrading comb generation. The device is able to provide a 110-fold improvement in the comb generation efficiency. Finally, we demonstrate open eye diagrams using low-noise phase-locked comb lines as a wavelength-division multiplexing channel.

  7. Brood comb as a humidity buffer in honeybee nests

    NASA Astrophysics Data System (ADS)

    Ellis, Michael B.; Nicolson, Sue W.; Crewe, Robin M.; Dietemann, Vincent

    2010-04-01

    Adverse environmental conditions can be evaded, tolerated or modified in order for an organism to survive. During their development, some insect larvae spin cocoons which, in addition to protecting their occupants against predators, modify microclimatic conditions, thus facilitating thermoregulation or reducing evaporative water loss. Silk cocoons are spun by honeybee ( Apis mellifera) larvae and subsequently incorporated into the cell walls of the wax combs in which they develop. The accumulation of this hygroscopic silk in the thousands of cells used for brood rearing may significantly affect nest homeostasis by buffering humidity fluctuations. This study investigates the extent to which the comb may influence homeostasis by quantifying the hygroscopic capacity of the cocoons spun by honeybee larvae. When comb containing cocoons was placed at high humidity, it absorbed 11% of its own mass in water within 4 days. Newly drawn comb composed of hydrophobic wax and devoid of cocoons absorbed only 3% of its own mass. Therefore, the accumulation of cocoons in the comb may increase brood survivorship by maintaining a high and stable humidity in the cells.

  8. Honeybee combs: construction through a liquid equilibrium process?

    PubMed

    Pirk, C W W; Hepburn, H R; Radloff, S E; Tautz, J

    2004-07-01

    Geometrical investigations of honeycombs and speculations on how honeybees measure and construct the hexagons and rhombi of their cells are centuries old. Here we show that honeybees neither have to measure nor construct the highly regular structures of a honeycomb, and that the observed pattern of combs can be parsimoniously explained by wax flowing in liquid equilibrium. The structure of the combs of honeybees results from wax as a thermoplastic building medium, which softens and hardens as a result of increasing and decreasing temperatures. It flows among an array of transient, close-packed cylinders which are actually the self-heated honeybees themselves. The three apparent rhomboids forming the base of each cell do not exist but arise as optical artefacts from looking through semi-transparent combs. PMID:15257392

  9. Broadband degenerate OPO for mid-infrared frequency comb generation.

    PubMed

    Leindecker, Nick; Marandi, Alireza; Byer, Robert L; Vodopyanov, Konstantin L

    2011-03-28

    We present a new technique suitable for generating broadband phase- and frequency-locked frequency combs in the mid-infrared. Our source is based on a degenerate optical parametric oscillator (OPO) which rigorously both down-converts and augments the spectrum of a pump frequency comb provided by a commercial mode-locked near-IR laser. Low intracavity dispersion, combined with extensive cross-mixing of comb components, results in extremely broad instantaneous mid-IR bandwidths. We achieve an output power of 60 mW and 20 dB bandwidth extending from 2500 to 3800 nm. Among other applications, such a source is well-suited for coherent Fourier-transform spectroscopy in the absorption-rich mid-IR 'molecular fingerprint' region. PMID:21451655

  10. Quantum cascade laser combs: effects of modulation and dispersion.

    PubMed

    Villares, Gustavo; Faist, Jrme

    2015-01-26

    Frequency comb formation in quantum cascade lasers is studied theoretically using a Maxwell-Bloch formalism based on a modal decomposition, where dispersion is considered. In the mid-infrared, comb formation persists in the presence of weak cavity dispersion (500 fs2 mm-1) but disappears when much larger values are used (30'000 fs2 mm-1). Active modulation at the round-trip frequency is found to induce mode-locking in THz devices, where the upper state lifetime is in the tens of picoseconds. Our results show that mode-locking based on four-wave mixing in broadband gain, low dispersion cavities is the most promising way of achieving broadband quantum cascade laser frequency combs. PMID:25835922

  11. Methods and apparatus for broadband frequency comb stabilization

    DOEpatents

    Cox, Jonathan A; Kaertner, Franz X

    2015-03-17

    Feedback loops can be used to shift and stabilize the carrier-envelope phase of a frequency comb from a mode-locked fibers laser or other optical source. Compared to other frequency shifting and stabilization techniques, feedback-based techniques provide a wideband closed-loop servo bandwidth without optical filtering, beam pointing errors, or group velocity dispersion. It also enables phase locking to a stable reference, such as a Ti:Sapphire laser, continuous-wave microwave or optical source, or self-referencing interferometer, e.g., to within 200 mrad rms from DC to 5 MHz. In addition, stabilized frequency combs can be coherently combined with other stable signals, including other stabilized frequency combs, to synthesize optical pulse trains with pulse durations of as little as a single optical cycle. Such a coherent combination can be achieved via orthogonal control, using balanced optical cross-correlation for timing stabilization and balanced homodyne detection for phase stabilization.

  12. A deep-UV optical frequency comb at 205 nm.

    PubMed

    Peters, E; Diddams, S A; Fendel, P; Reinhardt, S; Hnsch, T W; Udem, Th

    2009-05-25

    By frequency quadrupling a picosecond pulse train from a Ti:sapphire laser at 820 nm we generate a frequency comb at 205 nm with nearly bandwidth-limited pulses. The nonlinear frequency conversion is accomplished by two successive frequency doubling stages that take place in resonant cavities that are matched to the pulse repetition rate of 82 MHz. This allows for an overall efficiency of 4.5 % and produces an output power of up to 70 mW for a few minutes and 25 mW with continuous operation for hours. Such a deep UV frequency comb may be employed for direct frequency comb spectroscopy in cases where it is less efficient to convert to these short wavelengths with continuous wave lasers. PMID:19466167

  13. Nonlinear amplification of side-modes in frequency combs.

    PubMed

    Probst, R A; Steinmetz, T; Wilken, T; Hundertmark, H; Stark, S P; Wong, G K L; Russell, P St J; Hnsch, T W; Holzwarth, R; Udem, Th

    2013-05-20

    We investigate how suppressed modes in frequency combs are modified upon frequency doubling and self-phase modulation. We find, both experimentally and by using a simplified model, that these side-modes are amplified relative to the principal comb modes. Whereas frequency doubling increases their relative strength by 6 dB, the growth due to self-phase modulation can be much stronger and generally increases with nonlinear propagation length. Upper limits for this effect are derived in this work. This behavior has implications for high-precision calibration of spectrographs with frequency combs used for example in astronomy. For this application, Fabry-Prot filter cavities are used to increase the mode spacing to exceed the resolution of the spectrograph. Frequency conversion and/or spectral broadening after non-perfect filtering reamplify the suppressed modes, which can lead to calibration errors. PMID:23736390

  14. Decade-Spanning High-Precision Terahertz Frequency Comb

    NASA Astrophysics Data System (ADS)

    Finneran, Ian A.; Good, Jacob T.; Holland, Daniel B.; Carroll, P. Brandon; Allodi, Marco A.; Blake, Geoffrey A.

    2015-04-01

    The generation and detection of a decade-spanning terahertz (THz) frequency comb is reported using two Ti:sapphire femtosecond laser oscillators and asynchronous optical sampling THz time-domain spectroscopy. The comb extends from 0.15 to 2.4 THz, with a tooth spacing of 80 MHz, a linewidth of 3.7 kHz, and a fractional precision of 1.8 10-9 . With time-domain detection of the comb, we measure three transitions of water vapor at 10 mTorr between 1-2 THz with an average Doppler-limited fractional accuracy of 6.1 10-8 . Significant improvements in bandwidth, resolution, and sensitivity are possible with existing technologies.

  15. Characterization of a partially-stabilized frequency comb

    NASA Astrophysics Data System (ADS)

    Gold Dahl, M. E.; Erikson, Alex; Woodbury, Daniel; Bergeson, Scott

    2015-05-01

    We present measurements of well-known frequency intervals in Cs, Rb, and Ca. These measurements are used to determine the accuracy of a partially-stabilized ti:sapphire frequency comb. One mode of our frequency comb is offset-locked to a Rb-stabilized diode laser. The comb's repetition rate is counted but not locked. A second laser is used to probe well-known atomic transitions in Cs, Rb, and Ca. We describe our offset locking and scanning techniques and demonstrate a frequency precision of 10 kHz in a 30 second measurement time. The accuracy of our laser frequency interval measurements is approximately 40 kHz. However, cell-based frequency references can be off by several hundred kHz. Research supported by the National Science Foundation (Grant No. PHY-0969856) and the Air Force (Grant No. FA9950-12-1-0308).

  16. Software reconfigurable highly flexible gain switched optical frequency comb source.

    PubMed

    Pascual, M Deseada Gutierrez; Zhou, Rui; Smyth, Frank; Anandarajah, Prince M; Barry, Liam P

    2015-09-01

    The authors present the performance and noise properties of a software reconfigurable, FSR and wavelength tunable gain switched optical frequency comb source. This source, based on the external injection of a temperature tuned Fabry-Pérot laser diode, offers quasi-continuous wavelength tunability over the C-band (30nm) and FSR tunability ranging from 6 to 14GHz. The results achieved demonstrate the excellent spectral quality of the comb tones (RIN ~-130dB/Hz and low phase noise of 300kHz) and its outstanding stability (with fluctuations of the individual comb tones of less than 0.5dB in power and 5pm in wavelength, characterized over 24hours) highlighting its suitability for employment in next generation flexible optical transmission networks. PMID:26368425

  17. Comparative reproduction of Varroa destructor in different types of Russian and Italian honey bee combs

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We studied whether or not older comb supported less varroa reproduction in both Russian and Italian honey bees, whether Russian bees produced comb which inhibited varroa reproduction and whether comb foundation contained enough acaricides to influence varroa reproduction. The major differences foun...

  18. Frequency comb laser spectroscopy in the vacuum-ultraviolet region

    SciTech Connect

    Zinkstok, Roel Th.; Witte, Stefan; Ubachs, Wim; Hogervorst, Wim; Eikema, Kjeld S.E.

    2006-06-15

    We demonstrate that the output of a frequency comb laser can be amplified and upconverted to the vacuum ultraviolet (vuv) in a gaseous medium while its phase coherence is maintained to a high degree (<(1/30) of a vuv cycle). The produced vuv pulses are well suited to perform frequency comb spectroscopy with sub-MHz accuracy, which is experimentally verified using a Ramsey-type quantum interference scheme to excite a transition in xenon at 125 nm. The achieved resolution constitutes an improvement of six orders of magnitude compared to previous demonstrations of frequency domain quantum interference in this wavelength range.

  19. Fourier domain optical coherence tomography using optical frequency comb

    NASA Astrophysics Data System (ADS)

    Bajraszewski, T.; Wojtkowski, M.; Szkulmowska, A.; Fojt, W.; Szkulmowski, M.; Kowalczyk, A.

    2007-02-01

    Novel Fourier domain OCT method and instrumentation using Optical Frequency Comb (OFC) is demonstrated. This technique can overcome some limitations of Spectral OCT and Optical Frequency domain Imaging (Swept Source OCT) and enables ultrahigh resolution imaging in 800 nm range. In the novel method external OFC generator placed after the broad band light source is used. We will demonstrate preliminary data showing the general performance, advantages and limitations of the Fourier domain OCT method using Optical Frequency Comb generator based on Fabry-Perot interferometer (F-P). High quality, high resolution cross-sectional images of biological samples obtained with the presented technique are shown.

  20. Frequency-Comb-Assisted Terahertz Quantum Cascade Laser Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bartalini, S.; Consolino, L.; Cancio, P.; De Natale, P.; Bartolini, P.; Taschin, A.; De Pas, M.; Beere, H.; Ritchie, D.; Vitiello, M. S.; Torre, R.

    2014-04-01

    We report a metrological-grade THz spectroscopy based on the combination of a THz frequency-comb synthesizer (FCS) and a THz quantum cascade laser (QCL). The QCL, emitting at 2.5 THz, is phase locked to the free-space THz FCS, and its frequency is swept across a methanol transition by tuning the comb-repetition rate, which is ultimately disciplined by the Cs primary frequency standard. The absolute frequency scale provides an uncertainty of a few parts in 10-11 on the laser frequency and 10-9 on the line-center determination, ranking this technique among the most precise ever developed in the THz range.

  1. Optical frequency comb generation from aluminum nitride microring resonator.

    PubMed

    Jung, Hojoong; Xiong, Chi; Fong, King Y; Zhang, Xufeng; Tang, Hong X

    2013-08-01

    Aluminum nitride (AlN) is an appealing nonlinear optical material for on-chip wavelength conversion. Here we report optical frequency comb generation from high-quality-factor AlN microring resonators integrated on silicon substrates. By engineering the waveguide structure to achieve near-zero dispersion at telecommunication wavelengths and optimizing the phase matching for four-wave mixing, frequency combs are generated with a single-wavelength continuous-wave pump laser. Further, the Kerr coefficient (n?) of AlN is extracted from our experimental results. PMID:23903149

  2. The generation of Continuous-Variable Entanglement Frequency Comb

    NASA Astrophysics Data System (ADS)

    Yu, Youbin; Cheng, Xiaomin; Wang, Huaijun; Shi, Zhongtao; Zhao, Junwei; Ji, Fengmin; Yin, Zhi; Wang, Yajuan

    2015-01-01

    Continuous-variable (CV) entanglement frequency comb can be produced by enhanced Raman scattering in an above-threshold optical oscillator cavity in which a hexagonally-poled LiTaO3 crystal resides as a Raman gain medium. The Stokes and anti-Stokes Raman signals are enhanced by a coupled quasi-phase-matching optical parametric process and the entanglement natures among these Raman signals and pump are demonstrated by applying a sufficient inseparability criterion for CV entanglement. Such entanglement frequency comb source with different frequencies and continuously tunable frequency interval may be very significant for the applications in quantum communication and networks.

  3. Spatiotemporal dynamics of Kerr-Raman optical frequency combs

    NASA Astrophysics Data System (ADS)

    Chembo, Yanne K.; Grudinin, Ivan S.; Yu, Nan

    2015-10-01

    Optical frequency combs generated with ultrahigh-Q whispering-gallery-mode resonators are expected to provide a compact, versatile, and energy-efficient source for the generation of coherent lightwave and microwave signals. So far, Kerr and Raman nonlinearities in these resonators have predominantly been investigated separately, even though both effects originate from the same third-order susceptibility. We present a spatiotemporal formalism for the theoretical understanding of these Kerr-Raman combs, which allows us to describe the complex interplay between both nonlinearities and all-order dispersion. These theoretical findings are successfully compared with experiments performed with ultrahigh-Q calcium and magnesium fluoride resonators.

  4. Routes to spatiotemporal chaos in Kerr optical frequency combs

    SciTech Connect

    Coillet, Aurlien; Chembo, Yanne K.

    2014-03-15

    We investigate the various routes to spatiotemporal chaos in Kerr optical frequency combs, obtained through pumping an ultra-high Q-factor whispering-gallery mode resonator with a continuous-wave laser. The LugiatoLefever model is used to build bifurcation diagrams with regards to the parameters that are externally controllable, namely, the frequency and the power of the pumping laser. We show that the spatiotemporal chaos emerging from Turing patterns and solitons display distinctive dynamical features. Experimental spectra of chaotic Kerr combs are also presented for both cases, in excellent agreement with theoretical spectra.

  5. Routes to spatiotemporal chaos in Kerr optical frequency combs

    SciTech Connect

    Coillet, Aurélien; Chembo, Yanne K.

    2014-03-15

    We investigate the various routes to spatiotemporal chaos in Kerr optical frequency combs, obtained through pumping an ultra-high Q-factor whispering-gallery mode resonator with a continuous-wave laser. The Lugiato–Lefever model is used to build bifurcation diagrams with regards to the parameters that are externally controllable, namely, the frequency and the power of the pumping laser. We show that the spatiotemporal chaos emerging from Turing patterns and solitons display distinctive dynamical features. Experimental spectra of chaotic Kerr combs are also presented for both cases, in excellent agreement with theoretical spectra.

  6. Coherent combs in ionization by intense and short laser pulses

    NASA Astrophysics Data System (ADS)

    Krajewska, K.; Kamiński, J. Z.

    2016-03-01

    Photoionization of positive ions by a train of intense, short laser pulses is investigated within the relativistic strong field approximation, using the velocity gauge. The formation of broad peak structures in the high-energy domain of photoelectrons is observed and interpreted. The emergence of coherent photoelectron energy combs within these structures is demonstrated, and it is interpreted as the consequence of the Fraunhofer-type interference/diffraction of probability amplitudes of ionization from individual pulses comprising the train. Extensions to the coherent angular combs are also studied, and effects related to the radiation pressure are presented.

  7. Coherent multiheterodyne spectroscopy using stabilized optical frequency combs.

    PubMed

    Coddington, Ian; Swann, William C; Newbury, Nathan R

    2008-01-11

    The broadband, coherent nature of narrow-linewidth fiber frequency combs is exploited to measure the full complex spectrum of a molecular gas through multiheterodyne spectroscopy. We measure the absorption and phase shift experienced by each of 155 000 individual frequency-comb lines, spaced by 100 MHz and spanning from 1495 to 1620 nm, after passing through hydrogen cyanide gas. The measured phase spectrum agrees with the Kramers-Kronig transformation of the absorption spectrum. This technique can provide a full complex spectrum rapidly, over wide bandwidths, and with hertz-level accuracy. PMID:18232764

  8. The generation of Continuous-Variable Entanglement Frequency Comb

    PubMed Central

    Yu, Youbin; Cheng, Xiaomin; Wang, Huaijun; Shi, Zhongtao; Zhao, Junwei; Ji, Fengmin; Yin, Zhi; Wang, Yajuan

    2015-01-01

    Continuous-variable (CV) entanglement frequency comb can be produced by enhanced Raman scattering in an above-threshold optical oscillator cavity in which a hexagonally-poled LiTaO3 crystal resides as a Raman gain medium. The Stokes and anti-Stokes Raman signals are enhanced by a coupled quasi-phase-matching optical parametric process and the entanglement natures among these Raman signals and pump are demonstrated by applying a sufficient inseparability criterion for CV entanglement. Such entanglement frequency comb source with different frequencies and continuously tunable frequency interval may be very significant for the applications in quantum communication and networks. PMID:25600617

  9. Low loss silicon microring resonator as comb filter

    NASA Astrophysics Data System (ADS)

    Deng, Qingzhong; Yi, Huaxiang; Long, Qifeng; Wang, Xingjun; Zhou, Zhiping

    2015-11-01

    Scattering loss caused by roughness of waveguide sidewalls is a key problem for long circumference microring based applications, such as comb filters. This paper presents a Si microring resonator incorporated with the multimode waveguide and single-mode waveguide, which suppresses the unwanted resonance of high-order modes while allowing the fundamental mode resonance with low loss. Both numerical and experimental results proved that the proposed solution is capable to achieve ~88.5% scattering loss reduction which is promising for narrow channel spacing comb filters.

  10. Honeybee combs: how the circular cells transform into rounded hexagons

    PubMed Central

    Karihaloo, B. L.; Zhang, K.; Wang, J.

    2013-01-01

    We report that the cells in a natural honeybee comb have a circular shape at birth but quickly transform into the familiar rounded hexagonal shape, while the comb is being built. The mechanism for this transformation is the flow of molten visco-elastic wax near the triple junction between the neighbouring circular cells. The flow may be unconstrained or constrained by the unmolten wax away from the junction. The heat for melting the wax is provided by the hot worker bees. PMID:23864500

  11. A "comb" structure measurement of a micrometer displacement in laser plasma propulsion

    NASA Astrophysics Data System (ADS)

    Zheng, Z. Y.; Gao, L.; Gao, H.; Xing, J.; Wu, X. W.

    2014-08-01

    A "comb" structure of beam intensity distribution is achieved to measure target displacements at the micrometer level in laser plasma propulsion experiments. Compared with single-beam and double-beam detection, the "comb" structure is more suitable for a thin film targets with a velocity lower than 10-2 m/s. Combined with a light-electric monitor, the "comb" structure can be used to measure a velocity range from 10-3 to 1 m/s. Using this "comb" structure, the coupling coefficient of aluminum ablated by nanosecond pulse laser in air is determined and compared. The results indicate that this "comb" structure is an effective experimental approach.

  12. Target micro-displacement measurement by a "comb" structure of intensity distribution in laser plasma propulsion

    NASA Astrophysics Data System (ADS)

    Zheng, Z. Y.; Zhang, S. Q.; Gao, L.; Gao, H.

    2015-05-01

    A "comb" structure of beam intensity distribution is designed and achieved to measure a target displacement of micrometer level in laser plasma propulsion. Base on the "comb" structure, the target displacement generated by nanosecond laser ablation solid target is measured and discussed. It is found that the "comb" structure is more suitable for a thin film target with a velocity lower than tens of millimeters per second. Combing with a light-electric monitor, the `comb' structure can be used to measure a large range velocity.

  13. Mid-infrared frequency comb for broadband high precision and sensitivity molecular spectroscopy.

    PubMed

    Galli, I; Bartalini, S; Cancio, P; Cappelli, F; Giusfredi, G; Mazzotti, D; Akikusa, N; Yamanishi, M; De Natale, P

    2014-09-01

    We report on the experimental demonstration of the metrological and spectroscopic performances of a mid-infrared comb generated by a nonlinear downconversion process from a Ti:sapphire-based near-infrared comb. A quantum cascade laser at 4330 nm was phase-locked to a single tooth of this mid-infrared comb and its frequency-noise power spectral density was measured. The mid-infrared comb itself was also used as a multifrequency highly coherent source to perform ambient air direct comb spectroscopy with the Vernier technique, by demultiplexing it with a high-finesse Fabry-Perot cavity. PMID:25166071

  14. Spectral characterization of a frequency comb based on cascaded quadratic nonlinearities inside an optical parametric oscillator

    NASA Astrophysics Data System (ADS)

    Ulvila, Ville; Phillips, C. R.; Halonen, Lauri; Vainio, Markku

    2015-09-01

    We present an experimental study of optical frequency comb generation based on cascaded quadratic nonlinearities inside a continuous-wave-pumped optical parametric oscillator. We demonstrate comb states which produce narrow-linewidth intermode beat note signals, and we verify the mode-spacing uniformity of the comb at the Hertz level. We also show that the spectral quality of the comb can be improved by modulating the parametric gain at a frequency that corresponds to the comb mode spacing. We have reached a high average output power of over 4 W in the near-infrared region, at 2 ? m .

  15. A stable frequency comb directly referenced to rubidium electromagnetically induced transparency and two-photon transitions

    SciTech Connect

    Hou, Dong; Wu, Jiutao; Zhang, Shuangyou; Ren, Quansheng; Zhang, Zhigang; Zhao, Jianye

    2014-03-17

    We demonstrate an approach to create a stable erbium-fiber-based frequency comb at communication band by directly locking the combs to two rubidium atomic transitions resonances (electromagnetically induced transparency absorption and two-photon absorption), respectively. This approach directly transfers the precision and stability of the atomic transitions to the comb. With its distinguishing feature of compactness by removing the conventional octave-spanning spectrum and f-to-2f beating facilities and the ability to directly control the comb's frequency at the atomic transition frequency, this stable optical comb can be widely used in optical communication, frequency standard, and optical spectroscopy and microscopy.

  16. Spectral and temporal characterization of a fused-quartz-microresonator optical frequency comb

    SciTech Connect

    Papp, Scott B.; Diddams, Scott A.

    2011-11-15

    We report on the fabrication of high-Q, fused-quartz microresonators and the parametric generation of a frequency comb with 36-GHz line spacing using them. We have characterized the intrinsic stability of the comb in both the time and frequency domains to assess its suitability for future precision metrology applications. Intensity autocorrelation measurements and line-by-line comb control reveal near-transform-limited picosecond pulse trains that are associated with good relative phase and amplitude stability of the comb lines. The comb's 36-GHz line spacing can be readily photodetected, which enables measurements of its intrinsic and absolute phase fluctuations.

  17. Spectrum and dynamics of optical frequency combs generated with monolithic whispering gallery mode resonators.

    PubMed

    Chembo, Yanne K; Strekalov, Dmitry V; Yu, Nan

    2010-03-12

    Optical frequency comb generation in whispering gallery mode resonators has been demonstrated in several experiments. The spectra of the combs exhibit a wide variety of complex profiles that are not fully understood. We report a detailed study on frequency comb generation in whispering gallery mode resonators including a complete stability analysis and numerical simulations. We show that the interaction of dispersion and nonlinearity is the key in determining the stability of the comb, the complex characteristics of its spectral profile, and its frequency span. The results will be important for understanding the essential physical processes leading to efficient comb generation. PMID:20366426

  18. Astro-Comb Revolutionizing Precision Spectroscopy in Astrophysics

    NASA Astrophysics Data System (ADS)

    Cramer, C. E.; Li, C.-H.; Glenday, A. G.; Phillips, D. F.; Furesz, G.; Sasselov, D.; Szentgyorgyi, A.; Walsworth, R. L.; Benedick, A.; Kärtner, F. X.

    2009-04-01

    Precision Doppler spectroscopy in astrophysics is limited by the stability of calibration sources, as well as the number, width and distribution of available calibration lines. Broadband frequency combs generated from mode-locked femtosecond lasers have revolutionized precision laboratory spectroscopy. We present a laser comb with up to 40 GHz line-spacing, generated from a 1 GHz repetition-rate "source comb" and a Fabry-Perot filtering cavity. The line spacing can be optimized for use with any high-resolution astronomical spectrograph. Our prototype, which we have recently tested with the Tillinghast Reflector Echelle Spectrograph on Mt. Hopkins, provides a 100-nm band of calibration light centered on 850 nm, in the center of the a region difficult to calibrate with atomic sources. The astro-comb should allow more than an order-of-magnitude improvement in sensitivity to changes in Doppler-shifts and cosmological redshifts, with significant impact on many fields, including stellar seismology, cosmology, and the search for extrasolar earths.

  19. Progress with a green astro-comb for exoplanet searches

    NASA Astrophysics Data System (ADS)

    Li, Chih-Hao; Glenday, Alexander G.; Phillips, David F.; Langellier, Nicholas; Chang, Guoqing; Furesz, Gabor; Kaertner, Franz X.; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L.

    2015-05-01

    Searches for extrasolar planets using the precision stellar radial velocity (RV) measurement technique are approaching Earth-like planet sensitivity. Astro-combs, which consist of a laser frequency comb, coherent wavelength shifting mechanism (such as a doubling crystal and photonic crystal fiber), and a mode-filtering Fabry-Perot cavity (FPC), provide a promising route to increased accuracy and long-term stability on the astrophysical spectrograph calibration. We first present the design of a green astro-comb from an octave spanning Ti:Sapphire laser, spectrally broadened by custom tapered PCF to the visible band via fiber-optic Cherenkov radiation for frequency shifting, and filtered by a broadband FPC, constructed by a pair of complementary chirped mirrors. We also present results from two years of operation of the astro-comb calibrating the HARPS-N spectrograph at the Italian National Telescope on La Palma, Canary Islands, including its use in measurements of solar radial velocities as well as its use in searches for extrasolar planets.

  20. Invited Article: A compact optically coherent fiber frequency comb.

    PubMed

    Sinclair, L C; Deschnes, J-D; Sonderhouse, L; Swann, W C; Khader, I H; Baumann, E; Newbury, N R; Coddington, I

    2015-08-01

    We describe the design, fabrication, and performance of a self-referenced, optically coherent frequency comb. The system robustness is derived from a combination of an optics package based on polarization-maintaining fiber, saturable absorbers for mode-locking, high signal-to-noise ratio (SNR) detection of the control signals, and digital feedback control for frequency stabilization. The output is phase-coherent over a 1-2 ?m octave-spanning spectrum with a pulse repetition rate of ?200 MHz and a residual pulse-to-pulse timing jitter <3 fs well within the requirements of most frequency-comb applications. Digital control enables phase coherent operation for over 90 h, critical for phase-sensitive applications such as timekeeping. We show that this phase-slip free operation follows the fundamental limit set by the SNR of the control signals. Performance metrics from three nearly identical combs are presented. This laptop-sized comb should enable a wide-range of applications beyond the laboratory. PMID:26329167

  1. Invited Article: A compact optically coherent fiber frequency comb

    NASA Astrophysics Data System (ADS)

    Sinclair, L. C.; Deschênes, J.-D.; Sonderhouse, L.; Swann, W. C.; Khader, I. H.; Baumann, E.; Newbury, N. R.; Coddington, I.

    2015-08-01

    We describe the design, fabrication, and performance of a self-referenced, optically coherent frequency comb. The system robustness is derived from a combination of an optics package based on polarization-maintaining fiber, saturable absorbers for mode-locking, high signal-to-noise ratio (SNR) detection of the control signals, and digital feedback control for frequency stabilization. The output is phase-coherent over a 1-2 μm octave-spanning spectrum with a pulse repetition rate of ˜200 MHz and a residual pulse-to-pulse timing jitter <3 fs well within the requirements of most frequency-comb applications. Digital control enables phase coherent operation for over 90 h, critical for phase-sensitive applications such as timekeeping. We show that this phase-slip free operation follows the fundamental limit set by the SNR of the control signals. Performance metrics from three nearly identical combs are presented. This laptop-sized comb should enable a wide-range of applications beyond the laboratory.

  2. Comparative efficacy of commercial combs in removing head lice (Pediculus humanus capitis) (Phthiraptera: Pediculidae).

    PubMed

    Gallardo, Anabella; Toloza, Ariel; Vassena, Claudia; Picollo, Mara Ins; Mougabure-Cueto, Gastn

    2013-03-01

    The use of a fine comb for removing lice from the head of the human host is a relevant tool both in the diagnosis of infestations and as part of an integrated control strategy of head lice. The effectiveness of a fine comb depends, in part, on the design and material they are built. The aim of this study was to compare in vivo the efficacy of metal and plastic combs that are currently used in the removal of head lice and eggs worldwide. The space between comb teeth and the length was 0.23 and 13mm in KSL plastic, 0.3 and 10.7mm in NOPUCID plastic, 0.15 and 31mm in KSL metal and 0.09 and 37mm in ASSY metal. The assays were performed comparing the combs in pairs: (a) KSL vs. NOPUCID plastic combs, (b) KSL vs. ASSY metal combs and (c) KSL plastic comb vs. ASSY metal comb. The most effective plastic comb was KSL, removing a higher number of individuals of all stages. The most effective metal comb was ASSY, removing more insects of all stages (except adults). The comparative test between KSL plastic and ASSY metal showed that ASSY was the most effective in removing head lice and their eggs. PMID:23212391

  3. A frequency comb calibrated solar atlas

    NASA Astrophysics Data System (ADS)

    Molaro, P.; Esposito, M.; Monai, S.; Lo Curto, G.; Gonzlez Hernndez, J. I.; Hnsch, T. W.; Holzwarth, R.; Manescau, A.; Pasquini, L.; Probst, R. A.; Rebolo, R.; Steinmetz, T.; Udem, Th.; Wilken, T.

    2013-12-01

    Context. The solar spectrum is a primary reference for the study of physical processes in stars and their variation during activity cycles. High resolution spectra of the Sun are easily obtained from spatially selected regions of the solar disk, while those taken over the integrated disk are more problematic. However, a proxy can be obtained by using solar light reflected by small bodies of the solar system. Aims: In November 2010 an experiment with a prototype of a laser frequency comb (LFC) calibration system was performed with the HARPS spectrograph of the 3.6m ESO telescope at La Silla during which high signal-to-noise spectra of the Moon were obtained. We exploit those Echelle spectra to study a portion of the optical integrated solar spectrum and in particular to determine the solar photospheric line positions. Methods: The DAOSPEC program is used to measure solar line positions through Gaussian fitting in an automatic way. The solar spectra are calibrated both with an LFC and a Th-Ar. Results: We first apply the LFC solar spectrum to characterize the CCDs of the HARPS spectrograph. The comparison of the LFC and Th-Ar calibrated spectra reveals S-type distortions on each order along the whole spectral range with an amplitude of 40 m s-1 . This confirms the pattern found in the first LFC experiment on a single order and extends the detection of the distortions to the whole analyzed region revealing that the precise shape varies with wavelength. A new data reduction is implemented to deal with CCD pixel inequalities to obtain a wavelength corrected solar spectrum. By using this spectrum we provide a new LFC calibrated solar atlas with 400 line positions in the range of 476-530, and 175 lines in the 534-585 nm range corresponding to the LFC bandwidth. The new LFC atlas is consistent on average with that based on FTS solar spectra, but it improves the accuracy of individual lines by a significant factor reaching a mean value of ?10 m s-1 . Conclusions: The LFC-based solar line wavelengths are essentially free of major instrumental effects and provide a reference for absolute solar line positions at the date of Nov. 2010, i.e. an epoch of low solar activity. We suggest that future LFC observations could be used to trace small radial velocity changes of the whole solar photospheric spectrum in connection with the solar cycle and for direct comparison with the predicted line positions of 3D radiative hydrodynamical models of the solar photosphere. The LFC calibrated solar atlas can be also used to verify the accuracy of ground or space spectrographs by means of the solar spectrum. Observations based on the ESO 3.6 m telescope at La Silla, Chile.Full Table 3 and a solar spectrum are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A61

  4. Sex Offenders.

    ERIC Educational Resources Information Center

    Hayes, Susan

    1991-01-01

    This paper on the problem of sex offending among individuals with intellectual disabilities examines the incidence of this problem, characteristics of intellectually disabled sex offenders, determination of whether the behavior is a paraphilia or functional age-related behavior, and treatment options, with emphasis on the situation in New South

  5. Sex Stereotyping.

    ERIC Educational Resources Information Center

    Rivas, Richard G.

    This article uses findings from several previous studies to define the kinds of sex stereotyping present in our society. The author considers sex roles as dealt with in children's literature, public schools, advertising, and vocational counseling. He describes, in particular, the situation at an unnamed state university, and cites the woman's

  6. Direct frequency comb spectroscopy and high-resolution coherent control

    NASA Astrophysics Data System (ADS)

    Stowe, Matthew C.

    We present the first experiments demonstrating absolute frequency measurements of one- and two-photon transitions using direct frequency comb spectroscopy (DFCS). In particular we phase stabilized the inter-pulse period and optical phases of the pulses emitted from a mode-locked Ti:Sapphire laser, creating a broad-bandwidth optical frequency comb. By referencing the optical comb directly to the cesium microwave frequency standard, we were able to measure absolute transition frequencies over greater than a 50 nm bandwidth, utilizing the phase coherence between wavelengths spanning from 741 nm to 795 nm. As an initial demonstration of DFCS we studied transitions from the 5S to 5P, 5D, and 7S states in Rb. To reduce Doppler broadening the atoms were laser cooled in a magneto-optical trap. We present an overview of several systematic error sources that perturb the natural transition frequencies, magnitudes, and linewidths. These include radiation pressure from the probe beam, AC-Stark shifts, Zeeman shifts, power-broadening, and incoherent optical pumping. After careful study and suppression of these systematic error sources, we measured transition linewidths as narrow as 1.1 MHz FWHM and 10 kHz linecenter uncertainties. Our measurements of the 5S to 7S two-photon transition frequency demonstrated the ability to determine the comb mode order numbers when the initial transition frequency is not known to better than the comb mode frequency spacing. By modifying the spectral phase of the pulses we demonstrated high-resolution coherent control. Our first coherent control experiment utilized a grating based pulse stretcher/compressor to apply a large chirp to the pulses. We measured the two-photon transition rate as a function of linear frequency chirp. The results illustrate the differences between similar classic coherent experiments done with a single femtosecond pulse and ours conducted with multiple pulses. Furthermore, we show that it is possible to reduce the two-photon transition rate by tuning the comb such that the two-photon amplitudes from all comb mode pairs destructively interfere. One of the unique features of DFCS is the large bandwidth over which atomic coherence may be established. We tuned the comb frequencies to not only be two-photon resonant, but also resonant with two different intermediate states separated by 7 THz. In this experiment we demonstrate the phase sensitive excitation of a closed-loop four-level system in a diamond configuration. Using a spatial light modulator based pulse shaper, we adjusted the relative phase of the two different two-photon transition pathways. We measured a sinusoidally varying two-photon transition rate as a function of the pulse shaper phase, with a fringe visibility of up to 69%. As a final example of high-resolution coherent control, we adjusted the spectral phase of the pulses to force constructive interference between the two-photon amplitudes that arise from the many thousands of mode pairs detuned from an intermediate state. This resulted in an increase of the two-photon transition rate by approximately 250%.

  7. Sex Stereotyping.

    ERIC Educational Resources Information Center

    Western European Education, 1982

    1982-01-01

    Presents the Norwegian Ministry of Education's recommendations to the Council of Europe for reforming European education to prevent sex discrimination against women at the elementary and secondary levels. (AM)

  8. Generation of a frequency comb and applications thereof

    SciTech Connect

    Hagmann, Mark J; Yarotski, Dmitry A

    2013-12-03

    Apparatus for generating a microwave frequency comb (MFC) in the DC tunneling current of a scanning tunneling microscope (STM) by fast optical rectification, cause by nonlinearity of the DC current vs. voltage curve for the tunneling junction, of regularly-spaced, short pulses of optical radiation from a focused mode-locked, ultrafast laser, directed onto the tunneling junction, is described. Application of the MFC to high resolution dopant profiling in semiconductors is simulated. Application of the MFC to other measurements is described.

  9. A Novel Nit Comb Concept Using Ultrasound Actuation: Preclinical Evaluation.

    PubMed

    Burgess, Mark N; Brunton, Elizabeth R; Burgess, Ian F

    2016-01-01

    Nit combing and removal of head louse, Pediculus humanus capitis De Geer (Anoplura: Pediculidae), eggs is a task made more difficult because "nit combs" vary in efficiency. There is currently no evidence that the binding of the eggshell to the hair can be loosened chemically and few hair treatments improve the slip of the louse eggs along the hair. Ultrasound, applied through the teeth of a nit comb, may facilitate the flow of fluids into the gap between the hair shaft and the tube of fixative holding louse eggs in place to improve lubrication. Ultrasound alone had little effect to initiate sliding, requiring a force of 121.5??23.8 millinewtons (mN) compared with 125.8??18.0?mN without ultrasound, but once the egg started to move it made the process easier. In the presence of a conditioner-like creamy lotion, ultrasound reduced the Peak force required to start movement to 24.3??8.8?mN from 50.4??13.0?mN without ultrasound. In contrast, some head louse treatments made removal of eggs more difficult, requiring approximately twice the Peak force to initiate movement compared with dry hair in the absence of ultrasound. However, following application of ultrasound, the forces required to initiate movement increased for an essential oil product, remained the same for isopropyl myristate and cyclomethicone, and halved for 4% dimeticone lotion. Fixing the nit comb at an estimated angle of 16.5 to the direction of pull gave an optimum effect to improve the removal process when a suitable lubricant was used. PMID:26545717

  10. Chemical detection with hyperspectral lidar using dual frequency combs.

    PubMed

    Boudreau, Sylvain; Levasseur, Simon; Perilla, Carlos; Roy, Simon; Genest, Jrme

    2013-03-25

    High-resolution spectral lidar measurements using dual frequency combs as a source is presented. The technique enables the range-resolved measurement of fine spectral features, such as gas absorption lines, provided that a suitable scatterer is present in the scene. Measurements of HCN absorption lines at 20 meters are presented, with a water droplet cloud and a diffusely reflective surface as scatterers. PMID:23546124

  11. Direct fiber comb stabilization to a gas-filled hollow-core photonic crystal fiber.

    PubMed

    Wu, Shun; Wang, Chenchen; Fourcade-Dutin, Coralie; Washburn, Brian R; Benabid, Fetah; Corwin, Kristan L

    2014-09-22

    We have isolated a single tooth from a fiber laser-based optical frequency comb for nonlinear spectroscopy and thereby directly referenced the comb. An 89 MHz erbium fiber laser frequency comb is directly stabilized to the P(23) (1539.43 nm) overtone transition of (12)C(2)H(2) inside a hollow-core photonic crystal fiber. To do this, a single comb tooth is isolated and amplified from 20 nW to 40 mW with sufficient fidelity to perform saturated absorption spectroscopy. The fractional stability of the comb, ~7 nm away from the stabilized tooth, is shown to be 6 × 10(-12) at 100 ms gate time, which is over an order of magnitude better than that of a comb referenced to a GPS-disciplined Rb oscillator. PMID:25321837

  12. [Gender, medicine and consumer culture: the cultural history of comb in the Ming and Qing Dynasties].

    PubMed

    Chen, Siyan

    2014-09-01

    In the Ming and Qing Dynasties, in addition to combing the hair, the comb also gradually played a role in people's daily life for disease treatment and keeping people's health. In short, during this period, the characteristic of comb reveal, as a whole, its reinforcing practicability and weakening of its ornamentality. During its application, people's behavioral activities endowed the comb with definite cultural connotation, which, thanks to the presence of gender and personality, became the symbol for expressing love between man and woman. By analogizing people's thought, since the comb could dredge something. Therefore, it can be used to cure diseases. Thus, it could be seen that, based on consumer's cultural description, the comb, tiny as it may be, did reflect the aesthetic ideas and interests and daily life-preservation habit of the literati due to the flourishing of book market in the Ming and Qing Dynasties. PMID:25579212

  13. Mode-resolved 10-GHz frequency comb from a femtosecond optical parametric oscillator.

    PubMed

    Zhang, Zhaowei; Balskus, Karolis; McCracken, Richard A; Reid, Derryck T

    2015-06-15

    We report a 10-GHz frequency comb generated by filtering a 333.3-MHz OPO frequency comb with a Fabry-Perot (FP) cavity, which was directly stabilized to the incident fundamental comb. This result is supported by a detailed analysis of the Vernier-effect-induced multiple peaks in the transmitted comb power as the FP cavity spacing is detuned. Modes of the generated 10-GHz comb were clearly resolved by a Fourier transform spectrometer with a spectral resolution of 830MHz, considerably better than the Nyquist sampling limit. The potentially broad tuning range of this mode-resolved OPO frequency comb opens unique opportunities for precise frequency metrology and high-precision spectroscopy. PMID:26076238

  14. Solar oscillations and the search for Venus enabled by a laser frequency comb

    NASA Astrophysics Data System (ADS)

    Phillips, David F.; Glenday, Alexander G.; Li, Chih-Hao; Langellier, Nicholas; Chang, Guoqing; Furesz, Gabor; Kaertner, Franz X.; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L.

    2015-05-01

    We have recently demonstrated sub-m/s sensitivity in measuring the radial velocity (RV) between the Earth and Sun using a simple, home-built solar telescope feeding the HARPS-N spectrograph at the Italian National Telescope calibrated with our green astro-comb. The green astro-comb is a laser frequency comb optimized for calibrating astrophysical spectrographs. We plan, in the coming year, to use the astro-comb calibrated spectrograph and solar telescope to detect the solar RV signal induced by Venus and thus demonstrate sensitivity of these instruments to detect terrestrial exoplanets. Here, we will present the astro-comb, results from the astro-comb calibrating the HARPS-N exoplanet searcher spectrograph, solar RV stability and plans for observing the signature of Venus.

  15. Introduction to molecular combing: genomics, DNA replication, and cancer.

    PubMed

    Herrick, John; Bensimon, Aaron

    2009-01-01

    The sequencing of the human genome inaugurated a new era in both fundamental and applied genetics. At the same time, the emergence of new technologies for probing the genome has transformed the field of pharmaco-genetics and made personalized genomic profiling and high-throughput screening of new therapeutic agents all but a matter of routine. One of these technologies, molecular combing, has served to bridge the technical gap between the examination of gross chromosomal abnormalities and sequence-specific alterations. Molecular combing provides a new perspective on the structure and dynamics of the human genome at the whole genome and sub-chromosomal levels with a resolution ranging from a few kilobases up to a megabase and more. Originally developed to study genetic rearrangements and to map genes for positional cloning, recent advances have extended the spectrum of its applications to studying the real-time dynamics of the replication of the genome. Understanding how the genome is replicated is essential for elucidating the mechanisms that both maintain genome integrity and result in the instabilities leading to human genetic disease and cancer. In the following, we will examine recent discoveries and advances due to the application of molecular combing to new areas of research in the fields of molecular cytogenetics and cancer genomics. PMID:19563102

  16. Applications of Cavity-Enhanced Direct Frequency Comb Spectroscopy

    NASA Astrophysics Data System (ADS)

    Cossel, Kevin C.; Adler, Florian; Maslowski, Piotr; Ye, Jun

    2010-06-01

    Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) is a unique technique that provides broad bandwidth, high resolution, and ultra-high detection sensitivities. This is accomplished by combining a femtosecond laser based optical frequency comb with an enhancement cavity and a broadband, multichannel imaging system. These systems are capable of simultaneously recording many terahertz of spectral bandwidth with sub-gigahertz resolution and absorption sensitivities of 110-7 cm-1 Hz-1/2. In addition, the ultrashort pulses enable efficient nonlinear processes, which makes it possible to reach spectral regions that are difficult to access with conventional laser sources. We will present an application of CE-DFCS for trace impurity detection in the semiconductor processing gas arsine near 1.8 ?m and the development of a high-power, mid-infrared frequency comb for breath analysis in the 2.8-4.8 ?m region. M. J. Thorpe, K. D. Moll, R. J. Jones, B. Safdi, and J. Ye. Science 311, 1595-1599 (2006) F. Adler, M. J. Thorpe, K. C. Cossel, and J. Ye. Annu. Rev. Anal. Chem. 3, 175-205 (2010) F. Adler, K. C. Cossel, M. J. Thorpe, I. Hartl, M. E. Fermann, and J. Ye. Opt. Lett. 34, 1330-1332 (2009)

  17. Dual-Colored DNA Comb Polymers for Single Molecule Rheology

    NASA Astrophysics Data System (ADS)

    Mai, Danielle; Marciel, Amanda; Schroeder, Charles

    2014-03-01

    We report the synthesis and characterization of branched biopolymers for single molecule rheology. In our work, we utilize a hybrid enzymatic-synthetic approach to graft ``short'' DNA branches to ``long'' DNA backbones, thereby producing macromolecular DNA comb polymers. The branches and backbones are synthesized via polymerase chain reaction with chemically modified deoxyribonucleotides (dNTPs): ``short'' branches consist of Cy5-labeled dNTPs and a terminal azide group, and ``long'' backbones contain dibenzylcyclooctyne-modified (DBCO) dNTPs. In this way, we utilize strain-promoted, copper-free cycloaddition ``click'' reactions for facile grafting of azide-terminated branches at DBCO sites along backbones. Copper-free click reactions are bio-orthogonal and nearly quantitative when carried out under mild conditions. Moreover, comb polymers can be labeled with an intercalating dye (e.g., YOYO) for dual-color fluorescence imaging. We characterized these materials using gel electrophoresis, HPLC, and optical microscopy, with atomic force microscopy in progress. Overall, DNA combs are suitable for single molecule dynamics, and in this way, our work holds the potential to improve our understanding of topologically complex polymer melts and solutions.

  18. Control of Cell Behavior Using Comb Polymer Surfaces

    NASA Astrophysics Data System (ADS)

    Irvine, D. J.; Mayes, Anne M.; Griffith, Linda G.

    1998-03-01

    The successful development of a tissue engineering paradigm for the growth of a few cells in vitro into a functional organ will be a many step process due to the complexity of interactions between cells and their environment. We are focusing on one particular aspect of this paradigm: manipulation of cellular interactions with a substrate. The approach we are investigating for substrate design employs a protein-resistant comb copolymer which can be surface-functionalized with peptide cell adhesion ligands. Such a surface allows the controlled investigation of ligand spatial distribution on cell behavior. Our aim is to develop a system which utilizes surface segregation of a comb copolymer from a homopolymer matrix to create the necessary surface structure on bulk FDA-approved, mechanically stable materials. Self-organization of the comb copolymer at the surface of a blend provides the desired cell-signaling surface structure on an otherwise hydrophobic, protein-adsorbing material. The design of three-dimensional objects such as a tissue engineering scaffold from such blends will be discussed.

  19. Coherent Raman spectro-imaging with laser frequency combs.

    PubMed

    Ideguchi, Takuro; Holzner, Simon; Bernhardt, Birgitta; Guelachvili, Guy; Picqu, Nathalie; Hnsch, Theodor W

    2013-10-17

    Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection or frequency-swept laser beams. Laser frequency combs are finding increasing use for broadband molecular linear absorption spectroscopy. Here we show, by exploring their potential for nonlinear spectroscopy, that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques. PMID:24132293

  20. Coherent Raman spectro-imaging with laser frequency combs

    NASA Astrophysics Data System (ADS)

    Ideguchi, Takuro; Holzner, Simon; Bernhardt, Birgitta; Guelachvili, Guy; Picqu, Nathalie; Hnsch, Theodor W.

    2013-10-01

    Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection or frequency-swept laser beams. Laser frequency combs are finding increasing use for broadband molecular linear absorption spectroscopy. Here we show, by exploring their potential for nonlinear spectroscopy, that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques.

  1. Mid-infrared soliton and Raman frequency comb generation in silicon microrings.

    PubMed

    Hansson, Tobias; Modotto, Daniele; Wabnitz, Stefan

    2014-12-01

    We numerically study the mechanisms of frequency comb generation in the mid-infrared spectral region from cw-pumped silicon microring resonators. Coherent soliton comb generation may be obtained even for a pump with zero linear cavity detuning, through suitable control of the effective lifetime of free carriers from multiphoton absorption, which introduces a nonlinear cavity detuning via free-carrier dispersion. Conditions for optimal octave spanning Raman comb generation are also described. PMID:25490668

  2. Redescription of Synthesium pontoporiae n. comb. with notes on S. tursionis and S. seymouri n. comb. (Digenea: Brachycladiidae Odhner, 1905).

    PubMed

    Marigo, Juliana; Vicente, Ana Carolina Paulo; Valente, Ana Luisa Schifino; Measures, Lena; Santos, Cludia Portes

    2008-04-01

    Synthesium pontoporiae n. comb. is redescribed, together with Synthesium tursionis and Synthesium seymouri n. comb.; the parasites were obtained from stranded and accidentally caught cetaceans. The sucker ratio (ratio between widths of the oral and ventral suckers) in S. pontoporiae was 1:1.8-3.0 (mean 1:2.2); in S. tursionis was 1:0.8-1.2; and in S. seymouri was 1:0.5-0.7. Synthesium pontoporiae differed from its congeners by additional diagnostic characters, including: oval to lobed testes; small cirrus with pyriform proximal region and flexible, tubular distal region formed by evagination of ejaculatory duct; and vitellarium in small follicles extending from the level of the seminal vesicle to the posterior extremity of the body and not forming dendritic radial bunches. Data on the morphology of adult S. pontoporiae and S. tursionis were inferred from confocal laser microscopical observations. PMID:18564752

  3. Broadband Mid-Infrared Comb-Resolved Fourier Transform Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Kevin; Mills, Andrew; Mohr, Christian; Jiang, Jie; Fermann, Martin; Maslowski, Piotr

    2014-06-01

    We report on a comb-resolved, broadband, direct-comb spectroscopy system in the mid-IR and its application to the detection of trace gases and molecular line shape analysis. By coupling an optical parametric oscillator (OPO), a 100 m multipass cell, and a high-resolution Fourier transform spectrometer (FTS), sensitive, comb-resolved broadband spectroscopy of dilute gases is possible. The OPO has radiation output at 3.1-3.7 and 4.5-5.5 μm. The laser repetition rate is scanned to arbitrary values with 1 Hz accuracy around 417 MHz. The comb-resolved spectrum is produced with an absolute frequency axis depending only on the RF reference (in this case a GPS disciplined oscillator), stable to 1 part in 10^9. The minimum detectable absorption is 1.6x10-6 wn Hz-1/2. The operating range of the experimental setup enables access to strong fundamental transitions of numerous molecular species for applications based on trace gas detection such as environmental monitoring, industrial gas calibration or medical application of human breath analysis. In addition to these capabilities, we show the application for careful line shape analysis of argon-broadened CO band spectra around 4.7 μm. Fits of the obtained spectra clearly illustrate the discrepancy between the measured spectra and the Voigt profile (VP), indicating the need to include effects such as Dicke narrowing and the speed-dependence of the collisional width and shift in the line shape model, as was shown in previous cw-laser studies. In contrast to cw-laser based experiments, in this case the entire spectrum (˜ 250 wn) covering the whole P and R branches can be measured in 16 s with 417 MHz resolution, decreasing the acquisition time by orders of magnitude. The parallel acquisition allows collection of multiple lines simultaneously, removing the correlation of possible temperature and pressure drifts. While cw-systems are capable of measuring spectra with higher precision, this demonstration opens the door for fast, massively parallel line shape parameters retrieval combined with analysis reaching beyond the VP and with absolute frequency calibration delivered by frequency combs. R. Wehr et al. J. Mol. Spec. 235 54-68 (2003) A. Cygan, et al. Eur. Phys. J. Special Topics 222 2119-2142 (2013)

  4. Spectral linewidth preservation in parametric frequency combs seeded by dual pumps.

    PubMed

    Tong, Zhi; Wiberg, Andreas O J; Myslivets, Evgeny; Kuo, Bill P P; Alic, Nikola; Radic, Stojan

    2012-07-30

    We demonstrate new technique for generation of programmable-pitch, wideband frequency combs with low phase noise. The comb generation was achieved using cavity-less, multistage mixer driven by two tunable continuous-wave pump seeds. The approach relies on phase-correlated continuous-wave pumps in order to cancel spectral linewidth broadening inherent to parametric comb generation. Parametric combs with over 200-nm bandwidth were obtained and characterized with respect to phase noise scaling to demonstrate linewidth preservation over 100 generated tones. PMID:23038314

  5. Wide-range tunability, thermal locking, and mode-crossing effects in Kerr optical frequency combs

    NASA Astrophysics Data System (ADS)

    Lin, Guoping; Saleh, Khaldoun; Henriet, Rmi; Diallo, Souleymane; Martinenghi, Romain; Coillet, Aurlien; Chembo, Yanne K.

    2014-12-01

    We theoretically and experimentally investigate some effects related to the Kerr optical frequency comb generation, using a millimeter-size magnesium fluoride ultrahigh quality disk resonator. We show that the Kerr comb tunability can be extremely wide in the Turing pattern (or primary comb) regime, with an intermodal frequency that can be tuned from 4 to 229 multiple free spectral ranges (corresponding to a frequency spacing ranging from 24 GHz to 1.35 THz). We also discuss the role played by thermal locking while pumping the resonator, as well as the effect of modal crossing when broadband combs are generated.

  6. Erbium fiber laser-based direct frequency comb spectroscopy of Rb two-photon transitions.

    PubMed

    Wu, Jiutao; Hou, Dong; Qin, Zhengyu; Dai, Xiaoliang; Zhang, Zhigang; Zhao, Jianye

    2013-12-01

    We demonstrate the direct frequency comb spectroscopy of Rb 5S?5D two-photon transitions directly excited by an optical frequency comb (OFC) in 1.5 ?m fiber communication bands. A chain of comb spectral manipulation and quantum coherence control is implemented to enhance the efficiency of second harmonic OFC generation and eliminate the Doppler-broadening background. The direct frequency comb spectroscopy with clearly resolved transition lines is obtained. Our scheme provides a potential approach to realize the OFC at ~1.5 ?m with high stability and accuracy. PMID:24281501

  7. The Tribolium castaneum ortholog of Sex combs reduced controls dorsal ridge development

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In insects, the boundary between the embryonic head and thorax is formed by the dorsal ridge, a fused structure composed of portions of the maxillary and labial segments. However, the mechanisms that promote development of this unusual structure remain a mystery. In Drosophila, mutations in the Hox ...

  8. A Frequency-stabilized, Diode-pumped Ytterbium:KYW Optical Frequency Comb for Metrology

    NASA Astrophysics Data System (ADS)

    Meyer, Stephanie A.

    2011-12-01

    There has been a wealth of research into applying optical frequency combs to a variety of scientific and technological problems in the last decade. Thus there is much interest in the development of new frequency comb sources to fulfill the requirements of these applications. In this thesis I will present the first frequency-stabilized, diode-pumped Yb3+-crystal frequency comb. The comb is based on a 180 MHz mode-locked Yb:Tungstate (Yb:KYW) fs-laser. The fs-laser output was amplified, temporally compressed and broadened to an octave-spanning spectrum in microstructured fiber. The offset frequency was then detected using an f--2f interferometer and locked using a phase-locked loop. The repetition rate was locked to a cavity-stabilized laser. The frequency-locked Yb:KYW comb was compared to a Ti:Sapphire comb locked to a different CW reference laser. Each comb was photodetected and the resulting microwave harmonics of the repetition rates were mixed. The phase noise of the mixed-down signal was measured to verify the generation of very stable microwave signals from the Yb:KYW comb. This result demonstrated the potential of Yb:KYW combs for low noise applications. With that established, routes towards the GHz repetition rates that are desirable for many comb applications will be presented. These include a Kerr-lens mode-locked 800 MHz Yb:KYW fs-laser and a combination of amplification and cavity filtration. My results demonstrate that such a Yb-doped tungstate laser can provide an efficient, compact, high-repetition-rate optical frequency comb with coverage from 650-1450 nm. Finally, in the process of the laser development, the pump-dependent Yb:KYW resonant dispersion was measured, which will also be presented.

  9. Sex Education.

    ERIC Educational Resources Information Center

    Williams, Sue

    1991-01-01

    This discussion of sex education for individuals with intellectual disabilities outlines Delys Sergeant's "coat hanger theory," which involves three coats or phases of sexuality: a physiological stimulus response coat; a reproductive coat; and a coat of attitudes, values, and self-esteem. Influences acting on individuals' sexuality include family,

  10. Comb-Referenced Sub-Doppler Resolution Infrared Spectrometer

    NASA Astrophysics Data System (ADS)

    Sasada, Hiroyuki

    2015-06-01

    We have developed a sub-Doppler resolution spectrometer. A difference frequency generation source, which consists of a pump source of a Nd:YAG laser, a signal source of an extended-cavity laser diode, and a waveguide-type PPLN, covers from 87 to 93 THz (2900 to 3100 wn). An enhanced-cavity absorption cell remarkably improves the sensitivity of Lamb dips. An optical frequency comb controls the central frequency of the source with an uncertainty of a few kilohertz. Because the idler frequency is swept based on absolute frequency through the comb, recorded spectra can be repeatedly accumulated without any frequency drift. We have applied the spectrometer to resolve the hyperfine structure of the fundamental band of HCl with a spectral resolution of about 250 kHz. To reduce the transit-time broadening, a novel enhanced-cavity absorption cell coupled with an idler wave of 1.9-mm beam radius at the beam waist has been introduced. The A1-A2 splitting of the ?b{1} and ?b{4} bands of CH3D is resolved for a few tens low-J transitions with the Lamb-dip linewidth of 60 to 100 kHz. Very recently, the source linewidth has reduced to 3 kHz using a linewidth transfer technique from the Nd:YAG laser to the extended-cavity laser diode through a novel optical frequency comb with a fast servo control. When methane sample is cooled with liquid-nitrogen, and the beam radius is expanded to 3 mm, the observed Lamb dip is 20 kHz wide without any enhanced-cavity absorption cell.

  11. Sub-Lethal Effects of Pesticide Residues in Brood Comb on Worker Honey Bee (Apis mellifera) Development and Longevity

    PubMed Central

    Wu, Judy Y.; Anelli, Carol M.; Sheppard, Walter S.

    2011-01-01

    Background Numerous surveys reveal high levels of pesticide residue contamination in honey bee comb. We conducted studies to examine possible direct and indirect effects of pesticide exposure from contaminated brood comb on developing worker bees and adult worker lifespan. Methodology/Principal Findings Worker bees were reared in brood comb containing high levels of known pesticide residues (treatment) or in relatively uncontaminated brood comb (control). Delayed development was observed in bees reared in treatment combs containing high levels of pesticides particularly in the early stages (day 4 and 8) of worker bee development. Adult longevity was reduced by 4 days in bees exposed to pesticide residues in contaminated brood comb during development. Pesticide residue migration from comb containing high pesticide residues caused contamination of control comb after multiple brood cycles and provided insight on how quickly residues move through wax. Higher brood mortality and delayed adult emergence occurred after multiple brood cycles in contaminated control combs. In contrast, survivability increased in bees reared in treatment comb after multiple brood cycles when pesticide residues had been reduced in treatment combs due to residue migration into uncontaminated control combs, supporting comb replacement efforts. Chemical analysis after the experiment confirmed the migration of pesticide residues from treatment combs into previously uncontaminated control comb. Conclusions/Significance This study is the first to demonstrate sub-lethal effects on worker honey bees from pesticide residue exposure from contaminated brood comb. Sub-lethal effects, including delayed larval development and adult emergence or shortened adult longevity, can have indirect effects on the colony such as premature shifts in hive roles and foraging activity. In addition, longer development time for bees may provide a reproductive advantage for parasitic Varroa destructor mites. The impact of delayed development in bees on Varroa mite fecundity should be examined further. PMID:21373182

  12. Microwave photonic comb filter with ultra-fast tunability.

    PubMed

    Jiang, H Y; Yan, L S; Pan, Y; Pan, W; Luo, B; Zou, X H; Eggleton, B J

    2015-11-01

    A microwave comb filter with ultra-fast tunability is proposed based on the fundamental delay-line microwave photonic filter. The central frequency of the passband or stopband in such a filter can be rapidly adjusted, along with the independent tunability of the free spectral range (FSR). Experimental results show that the central frequency of the transfer function is electronically tuned with a frequency difference of half of the FSR at a speed of <100??ps. Such high-speed tunability is vital for high-speed microwave switching, frequency hopping, cognitive radio, and next-generation radar systems. PMID:26512477

  13. Highly non-linear optical microresonators for frequency combs generation

    NASA Astrophysics Data System (ADS)

    Zhivotkov, Daniil S.; Romanova, Elena A.; Vukovic, Ana; Phang, Sendy

    2015-03-01

    Highly non-linear chalcogenide glasses are considered as a prospective material for frequency comb generation in optical microresonators. Using of a 2D microresonator for tailoring the normal material dispersion of chalcogenide glass is analyzed by evaluation of the group velocity dispersion coefficient in near- and mid- infrared. This is done for both approximate and accurate modal resonances of the whispering gallery modes of a 2D circular chalcogenide resonators. The results show that the using of a chalcogenide resonator extends the spectral range of normal dispersion regime to longer wavelengths.

  14. Adaptive dual-comb spectroscopy in the green region.

    PubMed

    Ideguchi, T; Poisson, A; Guelachvili, G; Hnsch, T W; Picqu, N

    2012-12-01

    Dual-comb spectroscopy is extended to the visible spectral range with two short-pulse frequency-doubled free-running ytterbium-doped fiber lasers. When the spectrum is shifted to other domains by nonlinear frequency conversion, tracking the relative fluctuations of the femtosecond oscillators at their fundamental wavelength automatically produces the correction signal needed for the recording of distortion-free spectra. The dense rovibronic spectrum of iodine around 19,240 cm(-1) is recorded within 12 ms at Doppler-limited resolution. PMID:23202066

  15. Frequency Combs with Weakly Lasing Exciton-Polariton Condensates

    NASA Astrophysics Data System (ADS)

    Rayanov, K.; Altshuler, B. L.; Rubo, Y. G.; Flach, S.

    2015-05-01

    We predict the spontaneous modulated emission from a pair of exciton-polariton condensates due to coherent (Josephson) and dissipative coupling. We show that strong polariton-polariton interaction generates complex dynamics in the weak-lasing domain way beyond Hopf bifurcations. As a result, the exciton-polariton condensates exhibit self-induced oscillations and emit an equidistant frequency comb light spectrum. A plethora of possible emission spectra with asymmetric peak distributions appears due to spontaneously broken time-reversal symmetry. The lasing dynamics is affected by the shot noise arising from the influx of polaritons. That results in a complex inhomogeneous line broadening.

  16. Precise Control of Molecular Dynamics with a Femtosecond Frequency Comb

    NASA Astrophysics Data System (ADS)

    Pe'Er, Avi; Shapiro, Evgeny A.; Stowe, Matthew C.; Shapiro, Moshe; Ye, Jun

    2007-03-01

    We present a general and highly efficient scheme for performing narrow-band Raman transitions between molecular vibrational levels using a coherent train of weak pump-dump pairs of shaped ultrashort pulses. The use of weak pulses permits an analytic description within the framework of coherent control in the perturbative regime, while coherent accumulation of many pulse pairs enables near unity transfer efficiency with a high spectral selectivity, thus forming a powerful combination of pump-dump control schemes and the precision of the frequency comb. Simulations verify the feasibility and robustness of this concept, with the aim to form deeply bound, ultracold molecules.

  17. Frequency combs with weakly lasing exciton-polariton condensates.

    PubMed

    Rayanov, K; Altshuler, B L; Rubo, Y G; Flach, S

    2015-05-15

    We predict the spontaneous modulated emission from a pair of exciton-polariton condensates due to coherent (Josephson) and dissipative coupling. We show that strong polariton-polariton interaction generates complex dynamics in the weak-lasing domain way beyond Hopf bifurcations. As a result, the exciton-polariton condensates exhibit self-induced oscillations and emit an equidistant frequency comb light spectrum. A plethora of possible emission spectra with asymmetric peak distributions appears due to spontaneously broken time-reversal symmetry. The lasing dynamics is affected by the shot noise arising from the influx of polaritons. That results in a complex inhomogeneous line broadening. PMID:26024173

  18. Entanglement of Atomic Qubits Using an Optical Frequency Comb

    SciTech Connect

    Hayes, D.; Matsukevich, D. N.; Maunz, P.; Hucul, D.; Quraishi, Q.; Olmschenk, S.; Campbell, W.; Mizrahi, J.; Senko, C.; Monroe, C.

    2010-04-09

    We demonstrate the use of an optical frequency comb to coherently control and entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used to efficiently and coherently transfer population between electronic and vibrational states of trapped atomic ions and implement an entangling quantum logic gate with high fidelity. This technique can be extended to the high field regime where operations can be performed faster than the trap frequency. This general approach can be applied to more complex quantum systems, such as large collections of interacting atoms or molecules.

  19. Frequency comb formation and transition to chaos in microresonators with near-zero dispersion.

    PubMed

    Rogov, Andrei S; Narimanov, Evgenii E

    2014-08-01

    We investigate the frequency comb formation in microresonators with near-zero dispersion, study the route from integrability to chaos in the corresponding nonlinear system, and demonstrate the key role of nonlinear dynamics of such a system for frequency comb generation and stability. PMID:25078163

  20. Astronomical optical frequency comb generation and test in a fiber-fed MUSE spectrograph

    NASA Astrophysics Data System (ADS)

    Chavez Boggio, J. M.; Fremberg, T.; Moralejo, B.; Rutowska, M.; Hernandez, E.; Zajnulina, M.; Kelz, A.; Bodenmller, D.; Sandin, C.; Wysmolek, M.; Sayinc, H.; Neumann, J.; Haynes, R.; Roth, M. M.

    2014-07-01

    We here report on recent progress on astronomical optical frequency comb generation at innoFSPEC-Potsdam and present preliminary test results using the fiber-fed Multi Unit Spectroscopic Explorer (MUSE) spectrograph. The frequency comb is generated by propagating two free-running lasers at 1554.3 and 1558.9 nm through two dispersionoptimized nonlinear fibers. The generated comb is centered at 1590 nm and comprises more than one hundred lines with an optical-signal-to-noise ratio larger than 30 dB. A nonlinear crystal is used to frequency double the whole comb spectrum, which is efficiently converted into the 800 nm spectral band. We evaluate first the wavelength stability using an optical spectrum analyzer with 0.02 nm resolution and wavelength grid of 0.01 nm. After confirming the stability within 0.01 nm, we compare the spectra of the astro-comb and the Ne and Hg calibration lamps: the astro-comb exhibits a much larger number of lines than lamp calibration sources. A series of preliminary tests using a fiber-fed MUSE spectrograph are subsequently carried out with the main goal of assessing the equidistancy of the comb lines. Using a P3d data reduction software we determine the centroid and the width of each comb line (for each of the 400 fibers feeding the spectrograph): equidistancy is confirmed with an absolute accuracy of 0.4 pm.

  1. Thermal tuning of Kerr frequency combs in silicon nitride microring resonators.

    PubMed

    Xue, Xiaoxiao; Xuan, Yi; Wang, Cong; Wang, Pei-Hsun; Liu, Yang; Niu, Ben; Leaird, Daniel E; Qi, Minghao; Weiner, Andrew M

    2016-01-11

    Microresonator based Kerr frequency comb generation has many attractive features, including ultrabroad spectra, chip-level integration, and low power consumption. Achieving precise tuning control over the comb frequencies will be important for a number of practical applications, but has been little explored for microresonator combs. In this paper, we characterize the thermal tuning of a coherent Kerr frequency comb generated from an on-chip silicon nitride microring. When the microring temperature is changed by ~70 C with an integrated microheater, the line spacing and center frequency of the comb are tuned respectively by -253 MHz (-3.57 MHz/C) and by -175 GHz (-2.63 GHz/C); the latter constitutes 75% of the comb line spacing. From these results we obtain a shift of 25 GHz (362.07 MHz/C) in the comb carrier-envelope offset frequency. Numerical simulations are performed by taking into account the thermo-optic effects in the waveguide core and cladding. The temperature variation of the comb line spacing predicted from simulations is close to that observed in experiments. The time-dependent thermal response of the microheater based tuning scheme is characterized; time constants of 30.9 ?s and 0.71ms are observed. PMID:26832298

  2. High Resolution Atomic Coherent Control via Spectral Phase Manipulation of an Optical Frequency Comb

    NASA Astrophysics Data System (ADS)

    Stowe, Matthew C.; Cruz, Flavio C.; Marian, Adela; Ye, Jun

    2006-04-01

    We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.

  3. High Resolution Atomic Coherent Control via Spectral Phase Manipulation of an Optical Frequency Comb

    SciTech Connect

    Stowe, Matthew C.; Cruz, Flavio C.; Marian, Adela; Ye Jun

    2006-04-21

    We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.

  4. Design and Fabrication of Polymer Electrostatic Comb-Drive Actuators for Micro Conveyer Systems

    NASA Astrophysics Data System (ADS)

    Pham, Phuc Hong; Dao, Dzung Viet; Amaya, Satoshi; Kitada, Ryoji; Li, Yigui; Sugiyama, Susumu

    We propose the design, simulation and preliminary fabrication of Micro Conveyer Systems (MCS) based on polymer electrostatic comb-drive actuators using polymethylmethacrylate (PMMA). This MCS consists of linear comb actuators, rotational comb actuators, micro containers, and a ratchet mechanism. Micro containers, used for carrying micro and nano samples such as protein, cells, are moved by comb-actuators through the ratchet mechanism. The silicon MCS was fabricated and checked to confirm characteristics and working principles. Each PMMA MCS, which has dimension of 1x1cm2, will be fabricated by using hot embossing technique or X-ray lithography. A silicon mold has to be fabricated first by using silicon wafer and ICP-RIE process. Salient advantages of PMMA comb-drive actuators are low cost, high throughput and consuming less energy compared with the counterpart using silicon because PMMA has a lower Young's modulus.

  5. Mid-infrared optical frequency combs at 2.5??m based on crystalline microresonators

    NASA Astrophysics Data System (ADS)

    Wang, C. Y.; Herr, T.; Del'Haye, P.; Schliesser, A.; Hofer, J.; Holzwarth, R.; Hnsch, T. W.; Picqu, N.; Kippenberg, T. J.

    2013-01-01

    The mid-infrared spectral range (?~2-20??m) is of particular importance as many molecules exhibit strong vibrational fingerprints in this region. Optical frequency combsbroadband optical sources consisting of equally spaced and mutually coherent sharp linesare creating new opportunities for advanced spectroscopy. Here we demonstrate a novel approach to create mid-infrared optical frequency combs via four-wave mixing in a continuous-wave pumped ultra-high Q crystalline microresonator made of magnesium fluoride. Careful choice of the resonator material and design made it possible to generate a broadband, low-phase noise Kerr comb at ?=2.5??m spanning 200?nm (?10?THz) with a line spacing of 100?GHz. With its distinguishing features of compactness, efficient conversion, large mode spacing and high power per comb line, this novel frequency comb source holds promise for new approaches to molecular spectroscopy and is suitable to be extended further into the mid-infrared.

  6. Photothermally driven fast responding photo-actuators fabricated with comb-type hydrogels and magnetite nanoparticles

    PubMed Central

    Lee, Eunsu; Kim, Dowan; Kim, Haneul; Yoon, Jinhwan

    2015-01-01

    To overcome the slow kinetics of the volume phase transition of stimuli-responsive hydrogels as platforms for soft actuators, thermally responsive comb-type hydrogels were prepared using synthesized poly(N-isopropylacrylamide) macromonomers bearing graft chains. Fast responding light-responsive hydrogels were fabricated by combining a comb-type hydrogel matrix with photothermal magnetite nanoparticles (MNP). The MNPs dispersed in the matrix provide heat to stimulate the volume change of the hydrogel matrix by converting absorbed visible light to thermal energy. In this process, the comb-type hydrogel matrix exhibited a rapid response due to the free, mobile grafted chains. The comb-type hydrogel exhibited significantly enhanced light-induced volume shrinkage and rapid recovery. The comb-type hydrogels containing MNP were successfully used to fabricate a bilayer-type photo-actuator with fast bending motion. PMID:26459918

  7. Frequency-comb-referenced tunable diode laser spectroscopy and laser stabilization applied to laser cooling.

    PubMed

    Fordell, Thomas; Wallin, Anders E; Lindvall, Thomas; Vainio, Markku; Merimaa, Mikko

    2014-11-01

    Laser cooling of trapped atoms and ions in optical clocks demands stable light sources with precisely known absolute frequencies. Since a frequency comb is a vital part of any optical clock, the comb lines can be used for stabilizing tunable, user-friendly diode lasers. Here, a light source for laser cooling of trapped strontium ions is described. The megahertz-level stability and absolute frequency required are realized by stabilizing a distributed-feedback semiconductor laser to a frequency comb. Simple electronics is used to lock and scan the laser across the comb lines, and comb mode number ambiguities are resolved by using a separate, saturated absorption cell that exhibits easily distinguishable hyperfine absorption lines with known frequencies. Due to the simplicity, speed, and wide tuning range it offers, the employed technique could find wider use in precision spectroscopy. PMID:25402914

  8. Photothermally driven fast responding photo-actuators fabricated with comb-type hydrogels and magnetite nanoparticles.

    PubMed

    Lee, Eunsu; Kim, Dowan; Kim, Haneul; Yoon, Jinhwan

    2015-01-01

    To overcome the slow kinetics of the volume phase transition of stimuli-responsive hydrogels as platforms for soft actuators, thermally responsive comb-type hydrogels were prepared using synthesized poly(N-isopropylacrylamide) macromonomers bearing graft chains. Fast responding light-responsive hydrogels were fabricated by combining a comb-type hydrogel matrix with photothermal magnetite nanoparticles (MNP). The MNPs dispersed in the matrix provide heat to stimulate the volume change of the hydrogel matrix by converting absorbed visible light to thermal energy. In this process, the comb-type hydrogel matrix exhibited a rapid response due to the free, mobile grafted chains. The comb-type hydrogel exhibited significantly enhanced light-induced volume shrinkage and rapid recovery. The comb-type hydrogels containing MNP were successfully used to fabricate a bilayer-type photo-actuator with fast bending motion. PMID:26459918

  9. Photothermally driven fast responding photo-actuators fabricated with comb-type hydrogels and magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Lee, Eunsu; Kim, Dowan; Kim, Haneul; Yoon, Jinhwan

    2015-10-01

    To overcome the slow kinetics of the volume phase transition of stimuli-responsive hydrogels as platforms for soft actuators, thermally responsive comb-type hydrogels were prepared using synthesized poly(N-isopropylacrylamide) macromonomers bearing graft chains. Fast responding light-responsive hydrogels were fabricated by combining a comb-type hydrogel matrix with photothermal magnetite nanoparticles (MNP). The MNPs dispersed in the matrix provide heat to stimulate the volume change of the hydrogel matrix by converting absorbed visible light to thermal energy. In this process, the comb-type hydrogel matrix exhibited a rapid response due to the free, mobile grafted chains. The comb-type hydrogel exhibited significantly enhanced light-induced volume shrinkage and rapid recovery. The comb-type hydrogels containing MNP were successfully used to fabricate a bilayer-type photo-actuator with fast bending motion.

  10. Molecular combing compared to Southern blot for measuring D4Z4 contractions in FSHD.

    PubMed

    Vasale, Jessica; Boyar, Fatih; Jocson, Michael; Sulcova, Vladimira; Chan, Patricia; Liaquat, Khalida; Hoffman, Carol; Meservey, Marc; Chang, Isabell; Tsao, David; Hensley, Kerri; Liu, Yan; Owen, Renius; Braastad, Corey; Sun, Weimin; Walrafen, Pierre; Komatsu, Jun; Wang, Jia-Chi; Bensimon, Aaron; Anguiano, Arturo; Jaremko, Malgorzata; Wang, Zhenyuan; Batish, Sat; Strom, Charles; Higgins, Joseph

    2015-12-01

    We compare molecular combing to Southern blot in the analysis of the facioscapulohumeral muscular dystrophy type 1 locus (FSHD1) on chromosome 4q35-qter (chr 4q) in genomic DNA specimens sent to a clinical laboratory for FSHD testing. A de-identified set of 87 genomic DNA specimens determined by Southern blot as normal (n = 71), abnormal with D4Z4 macrosatellite repeat array contractions (n = 7), indeterminate (n = 6), borderline (n = 2), or mosaic (n = 1) was independently re-analyzed by molecular combing in a blinded fashion. The molecular combing results were identical to the Southern blot results in 75 (86%) of cases. All contractions (n = 7) and mosaics (n = 1) detected by Southern blot were confirmed by molecular combing. Of the 71 samples with normal Southern blot results, 67 (94%) had concordant molecular combing results. The four discrepancies were either mosaic (n = 2), rearranged (n = 1), or borderline by molecular combing (n = 1). All indeterminate Southern blot results (n = 6) were resolved by molecular combing as either normal (n = 4), borderline (n = 1), or rearranged (n = 1). The two borderline Southern blot results showed a D4Z4 contraction on the chr 4qA allele and a normal result by molecular combing. Molecular combing overcomes a number of technical limitations of Southern blot by providing direct visualization of D4Z4 macrosatellite repeat arrays on specific chr 4q and chr 10q alleles and more precise D4Z4 repeat sizing. This study suggests that molecular combing has superior analytical validity compared to Southern blot for determining D4Z4 contraction size, detecting mosaicism, and resolving borderline and indeterminate Southern blot results. Further studies are needed to establish the clinical validity and diagnostic accuracy of these findings in FSHD. PMID:26420234

  11. [Lethal sex].

    PubMed

    Rabinerson, David; Ben-Shitrit, Gadi; Glezerman, Marek

    2011-03-01

    Asphyxiophilic sex is a form of autoerotic activity, in which the user creates mechanical means (such as hanging or bondage) in order to achieve cerebral hypoxia, which, in turn, enhances sexual, as well as orgasmic, stimulus. Failure of safety mechanisms, created by the user, may lead to instant death as a result of asphyxiation or strangulation. This kind of sexual practice is more prevalent among men than in women. In cases of death, it is difficult to relate it to the sexual practice itself. Suicide and homicide are the main differential diagnoses. Closely related derivatives of asphyxiophilic sex are anesthesiophilia (inhalation of variable volatile substances) and electrophilia (use of electric current during sexual activity)--both also intended to enhance the sexual stimulation. These forms of sexual practice are less prevalent than asphyxiophilia. PMID:21574359

  12. Sex during Pregnancy

    MedlinePLUS

    ... Caring for Your Child All About Food Allergies Sex During Pregnancy KidsHealth > For Parents > Sex During Pregnancy ... satisfying and safe sexual relationship during pregnancy. Is Sex During Pregnancy Safe? Sex is considered safe during ...

  13. Sex during Pregnancy

    MedlinePLUS

    ... Allergy Emergency Cerebral Palsy: Caring for Your Child Sex During Pregnancy KidsHealth > For Parents > Sex During Pregnancy ... satisfying and safe sexual relationship during pregnancy. Is Sex During Pregnancy Safe? Sex is considered safe during ...

  14. When Sex Is Painful

    MedlinePLUS

    ... AQ FREQUENTLY ASKED QUESTIONS GYNECOLOGIC PROBLEMS FAQ020 When Sex Is Painful • How common is painful sex? • What causes pain during sex? • Where is pain during sex felt? • When should ...

  15. Harnessing high-dimensional hyperentanglement through a biphoton frequency comb

    NASA Astrophysics Data System (ADS)

    Xie, Zhenda; Zhong, Tian; Shrestha, Sajan; Xu, Xinan; Liang, Junlin; Gong, Yan-Xiao; Bienfang, Joshua C.; Restelli, Alessandro; Shapiro, Jeffrey H.; Wong, Franco N. C.; Wei Wong, Chee

    2015-08-01

    Quantum entanglement is a fundamental resource for secure information processing and communications, and hyperentanglement or high-dimensional entanglement has been separately proposed for its high data capacity and error resilience. The continuous-variable nature of the energy-time entanglement makes it an ideal candidate for efficient high-dimensional coding with minimal limitations. Here, we demonstrate the first simultaneous high-dimensional hyperentanglement using a biphoton frequency comb to harness the full potential in both the energy and time domain. Long-postulated Hong-Ou-Mandel quantum revival is exhibited, with up to 19 time-bins and 96.5% visibilities. We further witness the high-dimensional energy-time entanglement through Franson revivals, observed periodically at integer time-bins, with 97.8% visibility. This qudit state is observed to simultaneously violate the generalized Bell inequality by up to 10.95 standard deviations while observing recurrent Clauser-Horne-Shimony-Holt S-parameters up to 2.76. Our biphoton frequency comb provides a platform for photon-efficient quantum communications towards the ultimate channel capacity through energy-time-polarization high-dimensional encoding.

  16. Geotropism of hornet comb construction under persistent acceleration.

    PubMed

    Ishay, J; Sadeh, D

    1978-01-01

    Social wasps (Vespinae) are insects which build in a precise geotactical orientation. The effect of persistent acceleration on comb construction by Oriental hornet (Vespa orientalis) workers was assessed experimentally within breeding boxes of various size and shape. Groups of hornets at the building phase were subjected to a centrifugal and gravitational force with a resultant ranging between 26 degrees and 45 degrees. The comb construction within such boxes was compared to that within control boxes under ordinary gravitational pull. It was found that: a) juvenile hornets (1-2 days of age) placed in quasi-rectangular boxes built in the direction of the resultant force; b) juvenile and adult hornets (3-7 days of age) placed in spherical shaped containers also built in the direction of the resultant force; c) adult hornets who had spent their first days of life in a stationary rectangular box, apparently learned the direction of the gravitational force and "tried" to build in this direction when exposed to a centrifugal force; d) adult hornets made to spin in quasi-rectangular boxes tilted in the direction of the calculated resultant force built in the direction of the resultant. These results suggest that hornets learn the direction of the gravitational force during the first days of life and that geometrical cues within the breeding box enable them to build in the direction of the force to which they have become habituated. From the standpoint of geometric cues, only the roof of the breeding box is of critical importance. PMID:11965666

  17. A Fine-Tooth Comb to Measure the Accelerating Universe

    NASA Astrophysics Data System (ADS)

    2008-09-01

    Astronomical instruments needed to answer crucial questions, such as the search for Earth-like planets or the way the Universe expands, have come a step closer with the first demonstration at the telescope of a new calibration system for precise spectrographs. The method uses a Nobel Prize-winning technology called a 'laser frequency comb', and is published in this week's issue of Science. Uncovering the disc ESO PR Photo 26a/08 A Laser Comb for Astronomy "It looks as if we are on the way to fulfil one of astronomers' dreams," says team member Theodor Hnsch, director at the Max Planck Institute for Quantum Optics (MPQ) in Germany. Hnsch, together with John Hall, was awarded the 2005 Nobel Prize in Physics for work including the frequency comb technique. Astronomers use instruments called spectrographs to spread the light from celestial objects into its component colours, or frequencies, in the same way water droplets create a rainbow from sunlight. They can then measure the velocities of stars, galaxies and quasars, search for planets around other stars, or study the expansion of the Universe. A spectrograph must be accurately calibrated so that the frequencies of light can be correctly measured. This is similar to how we need accurate rulers to measure lengths correctly. In the present case, a laser provides a sort of ruler, for measuring colours rather than distances, with an extremely accurate and fine grid. New, extremely precise spectrographs will be needed in experiments planned for the future European Extremely Large Telescope (E-ELT), which is being designed by ESO, the European Southern Observatory. These new spectrographs will need to be calibrated with even more accurate 'rulers'. In fact, they must be accurate to about one part in 30 billions - a feat equivalent to measuring the circumference of the Earth to about a millimetre! "We'll need something beyond what current technology can offer, and that's where the laser frequency comb comes in. It is worth recalling that the kind of precision required, 1 cm/s, corresponds, on the focal plane of a typical high-resolution spectrograph, to a shift of a few tenths of a nanometre, that is, the size of some molecules," explains PhD student and team member Constanza Araujo-Hauck from ESO. The new calibration technique comes from the combination of astronomy and quantum optics, in a collaboration between researchers at ESO and the Max Planck Institute for Quantum Optics. It uses ultra-short pulses of laser light to create a 'frequency comb' - light at many frequencies separated by a constant interval - to create just the kind of precise 'ruler' needed to calibrate a spectrograph. After successful tests in the MPQ laboratory in 2007, the team have successfully tested a prototype device using the laser comb at the VTT (Vacuum Tower Telescope) solar telescope in Tenerife, on 8 March 2008, measuring the spectrum of the Sun in infrared light. The results are already impressive, and the technique promises to achieve the accuracy needed to study these big astronomical questions. "In our tests in Tenerife, we have already achieved beyond state-of-the-art accuracy. Now we are going to make the system more versatile, and develop it even further," says team member Tilo Steinmetz, from Menlo Systems GmbH, a spin-off company from the Max Planck Institute, which was founded to commercialise the frequency comb technique. Having tested the technique on a solar telescope, a new version of the system is now being built for the HARPS planet-finder instrument on ESO's 3.6-metre telescope at La Silla in Chile, before being considered for future generations of instruments. One of the ambitious project to be realised with the E-ELT, called CODEX, aims to measure the recently discovered acceleration of the universe directly, by following the velocities of distant galaxies and quasars over a 20-year period. This would let astronomers test Einstein's general relativity and the nature of the recently discovered, and mysterious, dark energy. "We have to measu

  18. Doppler-Free Two-Photon Absorption Spectroscopy of Naphthalene Assisted by AN Optical Frequency Comb

    NASA Astrophysics Data System (ADS)

    Nishiyama, Akiko; Matsuba, Ayumi; Misono, Masatoshi

    2014-06-01

    Optical frequency combs are powerful tools for precise frequency measurements in various wavelength regions. The combs have been applied not only to metrology, but also to molecular spectroscopy. Recently, we studied high resolution spectroscopy of iodine molecule assisted by an optical frequency comb. In the study, the comb was used for frequency calibration of a scanning dye laser. In this study, we developed a frequency calibration scheme with a comb and an acousto-optic modulator to realize more precise frequency measurement in a wide frequency range. And the frequency calibration scheme was applied to Doppler-free two-photon absorption (DFTPA) spectroscopy of naphthalene. Naphthalene is one of the prototypical aromatic molecules, and its detailed structure and dynamics in excited states have been reported. We measured DFTPA spectra of A^1B1u(v4=1) ? X^1A_g(v=0) transition around 298 nm. A part of obtained spectra is shown in the figure. The spectral lines are rotationally resolved and the resolution is about 100 kHz. The horizontal axis was calibrated by the developed frequency calibration system employing the comb. The uncertainties of the calibrated frequencies were determined by the fluctuations of the comb modes which were stabilized to a GPS-disciplined clock. A. Nishiyama, D. Ishikawa, and M. Misono, J. Opt. Soc. Am. B 30, 2107 (2013).

  19. Terabit/s communications using chip-scale frequency comb sources

    NASA Astrophysics Data System (ADS)

    Koos, Christian; Kippenberg, Tobias J.; Barry, Liam P.; Dalton, Larry; Freude, Wolfgang; Leuthold, Juerg; Pfeifle, Joerg; Weimann, Claudius; Lauermann, Matthias; Kemal, Juned N.; Palmer, Robert; Koeber, Sebastian; Schindler, Philipp C.; Herr, Tobias; Brasch, Victor; Watts, Regan T.; Elder, Delwin

    2015-03-01

    High-speed optical interconnects rely on advanced wavelength-division multiplexing (WDM) schemes. However, while photonic-electronic interfaces can be efficiently realized on silicon-on-insulator chips, dense integration of the necessary light sources still represents a major challenge. Chip-scale frequency comb sources present an attractive alternative for providing a multitude of optical carriers for WDM transmission. In this paper, we give an overview of our recent progress towards terabit communications with chip-scale frequency comb sources. In a first set of experiments, we demonstrate frequency comb generation based on silicon-organic hybrid (SOH) electro-optic modulators, enabling line rates up to 1.152 Tbit/s. In a second set of experiments, we use injection locking of a gain-switched laser diode to enerate frequency combs. This approach leads to line rates of more than 2 Tbit/s. A third set of experiments is finally dedicated to using Kerr nonlinearities in integrated nonlinear microcavities for frequency comb generation. We demonstrate coherent communication using Kerr frequency comb sources, thereby achieving line rates up to 1.44 Tbit/s. Our experiments show that frequency comb generation in chip-scale devices represents a viable approach to terabit communications.

  20. Broadband mid-IR frequency comb source for standoff chemical detection

    NASA Astrophysics Data System (ADS)

    Vodopyanov, Konstantin L.

    2015-05-01

    Frequency-comb-based absorption spectroscopy in the molecular fingerprint part of the spectrum 2-12 ?m has great potential for standoff chemical sensing because of massive parallelism of data acquisition. Especially attractive is the dual-comb Fourier transform spectroscopy, with two phase-locked sources, where full advantage is taken of temporal and spatial coherence of frequency combs as well as of their broadband nature. The promise is high speed (up to 1M spectral points in less than a second), broad spectral coverage (> one octave), superior sensitivity (< 1 part per billion in gas phase), high spectral resolution (~100 MHz), and the possibility of absolute frequency calibration of molecular resonances. Here we report a broadband frequency comb source based on a degenerate optical parametric oscillator (OPO) that allows extending frequency comb technology to the mid-IR range. The OPO uses, as gain element an orientation-patterned GaAs crystal (OP-GaAs), is pumped by a femtosecond Tm-fiber lasers at 2-?m wavelength, and is suitable for performing broadband dual-comb spectroscopy. High temporal coherence and broad instantaneous spectral coverage of 2.5 - 7.5 ?m make this system promising for chemical detection and trace molecular sensing. Few examples of single- and dual-comb spectroscopic sensing are presented.

  1. Noise-Immune Cavity-Enhanced Optical Frequency Comb Spectroscopy

    NASA Astrophysics Data System (ADS)

    Rutkowski, Lucile; Khodabakhsh, Amir; Johanssson, Alexandra C.; Foltynowicz, Aleksandra

    2015-06-01

    We present noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS), a recently developed technique for sensitive, broadband, and high resolution spectroscopy. In NICE-OFCS an optical frequency comb (OFC) is locked to a high finesse cavity and phase-modulated at a frequency precisely equal to (a multiple of) the cavity free spectral range. Since each comb line and sideband is transmitted through a separate cavity mode in exactly the same way, any residual frequency noise on the OFC relative to the cavity affects each component in an identical manner. The transmitted intensity contains a beat signal at the modulation frequency that is immune to frequency-to-amplitude noise conversion by the cavity, in a way similar to continuous wave noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS). The light transmitted through the cavity is detected with a fast-scanning Fourier-transform spectrometer (FTS) and the NICE-OFCS signal is obtained by fast Fourier transform of the synchronously demodulated interferogram. Our NICE-OFCS system is based on an Er:fiber femtosecond laser locked to a cavity with a finesse of 9000 and a fast-scanning FTS equipped with a high-bandwidth commercial detector. We measured NICE-OFCS signals from the 3?b{1}+?b{3} overtone band of CO_2 around 1.57 ?m and achieved absorption sensitivity 6.410-11cm-1 Hz-1/2 per spectral element, corresponding to a minimum detectable CO_2 concentration of 25 ppb after 330 s integration time. We will describe the principles of the technique and its technical implementation, and discuss the spectral lineshapes of the NICE-OFCS signals. A. Khodabakhsh, C. Abd Alrahman, and A. Foltynowicz, Opt. Lett. 39, 5034-5037 (2014). J. Ye, L. S. Ma, and J. L. Hall, J. Opt. Soc. Am. B 15, 6-15 (1998). A. Khodabakhsh, A. C. Johansson, and A. Foltynowicz, Appl. Phys. B (2015) doi:10.1007/s00340-015-6010-7.

  2. Towards efficient octave-spanning comb with micro-structured crystalline resonator

    NASA Astrophysics Data System (ADS)

    Grudinin, Ivan S.; Yu, Nan

    2015-03-01

    Optical frequency combs, typically produced by mode locked lasers, have revolutionized many applications in science and technology. Frequency combs were recently generated by micro resonators through nonlinear Kerr processes. However, the comb span from micro resonators was found to be limited by resonator dispersion and mode spectrum. While dispersion engineering has been reported in on-chip devices, monolithic crystalline resonators offer an advantage of high optical quality factor. Moreover, most resonators used for comb generation support many mode families, leading to unavoidable crossings in resonator spectrum. Such crossings strongly influence comb dynamics and may prevent stable coherent mode-locking and soliton states. We report a new crystalline resonator approach supporting dispersion control and single mode spectrum while maintaining high quality factor. Dispersion engineering by waveguide micro-structuring is used to flatten the dispersion in our MgF2 resonator. Both absolute magnitude of dispersion and its slopes can be altered over a wavelength span exceeding an octave. Dispersion flattening leads to generation of an octave-spanning frequency comb with repetition rate of 46 GHz and coupled pump power below 100 mW. We also demonstrate that the micro- structuring dispersion engineering approach can be used to achieve flattened and anomalous dispersion in a CaF2 resonator near 1550 nm wavelength. In addition, we describe observation of discrete steps between the modulation instability states of the primary comb and on the three-stage comb unfolding dynamics. The micro-structured resonators may enable efficient low repetition rate coherent octave spanning frequency combs without external broadening, ideal for applications in optical frequency synthesis, metrology, spectroscopy, and communications.

  3. Ornamental comb colour predicts T-cell-mediated immunity in male red grouse Lagopus lagopus scoticus.

    PubMed

    Mougeot, Francois

    2008-02-01

    Sexual ornaments might reliably indicate the ability to cope with parasites and diseases, and a better ability to mount a primary inflammatory response to a novel challenge. Carotenoid-based ornaments are amongst the commonest sexual signals of birds and often influence mate choice. Because carotenoids are immuno-stimulants, signallers may trade-off allocating these to ornamental colouration or using them for immune responses, so carotenoid-based ornaments might be particularly useful as honest indicators of immuno-compentence. Tetraonid birds, such as the red grouse Lagopus lagopus scoticus, exhibit supra-orbital yellow-red combs, a conspicuous ornament which functions in intra- and inter-sexual selection. The colour of combs is due to epidermal pigmentation by carotenoids, while their size is testosterone-dependent. In this study, I investigated whether comb characteristics, and in particular, comb colour, indicated immuno-competence in free-living male red grouse. I assessed T-cell-mediated immunity using a standardised challenge with phytohaemagglutinin. Red grouse combs reflect in the red and in the ultraviolet spectrum of light, which is not visible to humans but that grouse most likely see, so I measured comb colour across the whole bird visible spectrum (300-700 nm) using a reflectance spectrometer. I found that males with bigger and redder combs, but with less ultraviolet reflectance, had greater T-cell-mediated immune response. Comb colour predicted T-cell-mediated immune response better than comb size, indicating that the carotenoid-based colouration of this ornament might reliably signal this aspect of male quality. PMID:17898979

  4. Ornamental comb colour predicts T-cell-mediated immunity in male red grouse Lagopus lagopus scoticus

    NASA Astrophysics Data System (ADS)

    Mougeot, Francois

    2008-02-01

    Sexual ornaments might reliably indicate the ability to cope with parasites and diseases, and a better ability to mount a primary inflammatory response to a novel challenge. Carotenoid-based ornaments are amongst the commonest sexual signals of birds and often influence mate choice. Because carotenoids are immuno-stimulants, signallers may trade-off allocating these to ornamental colouration or using them for immune responses, so carotenoid-based ornaments might be particularly useful as honest indicators of immuno-compentence. Tetraonid birds, such as the red grouse Lagopus lagopus scoticus, exhibit supra-orbital yellow red combs, a conspicuous ornament which functions in intra- and inter-sexual selection. The colour of combs is due to epidermal pigmentation by carotenoids, while their size is testosterone-dependent. In this study, I investigated whether comb characteristics, and in particular, comb colour, indicated immuno-competence in free-living male red grouse. I assessed T-cell-mediated immunity using a standardised challenge with phytohaemagglutinin. Red grouse combs reflect in the red and in the ultraviolet spectrum of light, which is not visible to humans but that grouse most likely see, so I measured comb colour across the whole bird visible spectrum (300 700 nm) using a reflectance spectrometer. I found that males with bigger and redder combs, but with less ultraviolet reflectance, had greater T-cell-mediated immune response. Comb colour predicted T-cell-mediated immune response better than comb size, indicating that the carotenoid-based colouration of this ornament might reliably signal this aspect of male quality.

  5. Mid-infrared optical frequency combs based on difference frequency generation for molecular spectroscopy

    NASA Astrophysics Data System (ADS)

    Cruz, Flavio C.; Maser, Daniel L.; Johnson, Todd; Ycas, Gabriel; Klose, Andrew; Giorgetta, Fabrizio R.; Coddington, Ian; Diddams, Scott A.

    2015-10-01

    Mid-infrared femtosecond optical frequency combs were produced by difference frequency generation of the spectral components of a near-infrared comb in a 3-mm-long MgO:PPLN crystal. We observe strong pump depletion and 9.3 dB parametric gain in the 1.5 \\mu m signal, which yields powers above 500 mW (3 \\mu W/mode) in the idler with spectra covering 2.8 \\mu m to 3.5 \\mu m. Potential for broadband, high-resolution molecular spectroscopy is demonstrated by absorption spectra and interferograms obtained by heterodyning two combs.

  6. All-optical stabilization of a soliton frequency comb in a crystalline microresonator.

    PubMed

    Jost, J D; Lucas, E; Herr, T; Lecaplain, C; Brasch, V; Pfeiffer, M H P; Kippenberg, T J

    2015-10-15

    We demonstrate the all-optical stabilization of a low-noise temporal soliton based microresonator based optical frequency comb in a crystalline resonator via a new technique to control the repetition rate. This is accomplished by thermally heating the microresonator with an additional probe laser coupled to an auxiliary optical resonator mode. The carrier-envelope offset frequency is controlled by stabilizing the pump laser frequency to a reference optical frequency comb. We analyze the stabilization by performing an out-of-loop comparison and measure the overlapping Allan deviation. This all-optical stabilization technique can prove useful as an actuator for self-referenced microresonator frequency combs. PMID:26469604

  7. Evaluating the coherence and time-domain profile of quantum cascade laser frequency combs.

    PubMed

    Burghoff, David; Yang, Yang; Hayton, Darren J; Gao, Jian-Rong; Reno, John L; Hu, Qing

    2015-01-26

    Recently, much attention has been focused on the generation of optical frequency combs from quantum cascade lasers. We discuss how fast detectors can be used to demonstrate the mutual coherence of such combs, and present an inequality that can be used to quantitatively evaluate their performance. We discuss several technical issues related to shifted wave interference Fourier Transform spectroscopy (SWIFTS), and show how such measurements can be used to elucidate the time-domain properties of such combs, showing that they can possess signatures of both frequency-modulation and amplitude-modulation. PMID:25835878

  8. Chaotic dynamics of frequency combs generated with continuously pumped nonlinear microresonators.

    PubMed

    Matsko, A B; Liang, W; Savchenkov, A A; Maleki, L

    2013-02-15

    We theoretically and experimentally investigate the chaotic regime of optical frequency combs generated in nonlinear ring microresonators pumped with continuous wave light. We show that the chaotic regime reveals itself by a flat top symmetric envelope of the frequency spectrum, when observed by means of an optical spectrum analyzer. The comb, demodulated on a fast photodiode, produces a noisy radio frequency signal with spectral width significantly exceeding the linear bandwidth of the microresonator mode. We discuss practical ways of excitation of a coherent frequency comb and avoiding the chaotic regime. PMID:23455124

  9. Quantum-Fluctuation-Initiated Coherence in Multioctave Raman Optical Frequency Combs

    NASA Astrophysics Data System (ADS)

    Wang, Y. Y.; Wu, Chunbai; Couny, F.; Raymer, M. G.; Benabid, F.

    2010-09-01

    We show experimentally and theoretically that the spectral components of a multioctave frequency comb spontaneously created by stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber exhibit strong self-coherence and mutual coherence within each 12 ns driving laser pulse. This coherence arises in spite of the fields initiation being from quantum zero-point fluctuations, which causes each spectral component to show large phase and energy fluctuations. This points to the possibility of an optical frequency comb with nonclassical correlations between all comb lines.

  10. Broadband parametric frequency comb generation with a 1-?m pump source.

    PubMed

    Saha, Kasturi; Okawachi, Yoshitomo; Levy, Jacob S; Lau, Ryan K W; Luke, Kevin; Foster, Mark A; Lipson, Michal; Gaeta, Alexander L

    2012-11-19

    We report the first experimental demonstration of broadband frequency comb generation from a single-frequency pump laser at 1-?m using parametric oscillation in a high-Q silicon-nitride ring resonator. The resonator dispersion is engineered to have a broad anomalous group velocity dispersion region near the pump wavelength for efficient parametric four-wave mixing. The comb spans 55 THz with a 230-GHz free spectral range. These results demonstrate the powerful advantage of dispersion engineering in chip-based devices for producing combs with a wide range of pump wavelengths. PMID:23187548

  11. Quantum-fluctuation-initiated coherence in multioctave Raman optical frequency combs.

    PubMed

    Wang, Y Y; Wu, Chunbai; Couny, F; Raymer, M G; Benabid, F

    2010-09-17

    We show experimentally and theoretically that the spectral components of a multioctave frequency comb spontaneously created by stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber exhibit strong self-coherence and mutual coherence within each 12 ns driving laser pulse. This coherence arises in spite of the field's initiation being from quantum zero-point fluctuations, which causes each spectral component to show large phase and energy fluctuations. This points to the possibility of an optical frequency comb with nonclassical correlations between all comb lines. PMID:20867639

  12. Complex direct comb spectroscopy with a virtually imaged phased array.

    PubMed

    Scholten, Sarah K; Anstie, James D; Hébert, Nicolas Bourbeau; White, Richard T; Genest, Jérôme; Luiten, Andre N

    2016-03-15

    We demonstrate a simple interferometric technique to directly measure the complex optical transmittance over a large spectral range using a frequency-comb spectrometer based on a virtually imaged phased array. A Michelson interferometer encodes the phase deviations induced by a sample contained in one of its arms into an interferogram image. When combined with an additional image taken from each arm separately, along with a frequency-calibration image, this allows full reconstruction of the sample's optical transfer function. We demonstrate the technique with a vapor cell containing H13C14N, producing transmittance and phase spectra spanning 2.9 THz (∼23  nm) with ∼1  GHz resolution. PMID:26977688

  13. A novel, multichannel, comb-frequency Doppler backscatter system

    SciTech Connect

    Peebles, W. A.; Rhodes, T. L.; Hillesheim, J. C.; Zeng, L.; Wannberg, C.

    2010-10-15

    Doppler backscattering has emerged in recent years as a powerful diagnostic tool in high temperature fusion plasmas. The technique is sensitive to plasma turbulence flow and has been utilized to determine radial electric field and to study geodesic acoustic modes, zonal flows, and intermediate scale density turbulence. The current manuscript describes a novel technique for creating a stable, multichannel system covering the V-band frequency range (50-75 GHz) which enables simultaneous monitoring of turbulent flows and fluctuation levels at eight distinct spatial locations. The system is based on a high-frequency, low phase noise comb-frequency generator combined with a filter bank and quadrature detection system. The system is now in operation on DIII-D and has allowed monitoring of the flow and turbulence levels across the plasma radius during events such as the L-H transition.

  14. High spectral purity Kerr frequency comb radio frequency photonic oscillator.

    PubMed

    Liang, W; Eliyahu, D; Ilchenko, V S; Savchenkov, A A; Matsko, A B; Seidel, D; Maleki, L

    2015-01-01

    Femtosecond laser-based generation of radio frequency signals has produced astonishing improvements in achievable spectral purity, one of the basic features characterizing the performance of an radio frequency oscillator. Kerr frequency combs hold promise for transforming these lab-scale oscillators to chip-scale level. In this work we demonstrate a miniature 10?GHz radio frequency photonic oscillator characterized with phase noise better than -60?dBc?Hz(-1) at 10?Hz, -90?dBc?Hz(-1) at 100?Hz and -170?dBc?Hz(-1) at 10?MHz. The frequency stability of this device, as represented by Allan deviation measurements, is at the level of 10(-10) at 1-100?s integration time-orders of magnitude better than existing radio frequency photonic devices of similar size, weight and power consumption. PMID:26260955

  15. Acoustic frequency combs for carrier-envelope phase stabilization.

    PubMed

    Borchers, Bastian; Lücking, Fabian; Steinmeyer, Günter

    2014-02-01

    A method for improved performance of feed-forward carrier-envelope phase stabilization in amplified laser sources is presented and experimentally demonstrated. The phase stabilization scheme is applicable for a broad range of repetition rates spanning from subhertz to 100 kHz. The method relies on driving an acousto-optic frequency shifter by few-cycle transients. The phase of these transients suitably controls the grating phase of the generated index grating inside the shifter material. This approach removes beam pointing as well as amplitude noise issues observed in continuously driven feed-forward schemes. The synthesis of these gratings can be understood as the acoustic equivalent of mode-locking or acoustic frequency combs. PMID:24487861

  16. High performance tunnel injection quantum dot comb laser

    SciTech Connect

    Lee, C.-S.; Guo Wei; Basu, Debashish; Bhattacharya, Pallab

    2010-03-08

    A high-speed multiwavelength quantum dot comb laser, grown by molecular beam epitaxy, is demonstrated. The device is characterized with a 75.9 nm (full width at half maximum) and a 91.4 nm (DELTA{sub -15dB}) wide lasing spectrum. There are 105 and 185 simultaneously emitted longitudinal modes with a maximum channel intensity nonuniformity of less than 3 dB in the spectral range of 1231-1252 nm and 1274-1311 nm, respectively, for a laser with 1040 mum cavity length. The channel spacing can be tuned with cavity length and remains invariant in the temperature range of 300-323 K. The small signal modulation bandwidth is 7.5 GHz.

  17. The shapes of simple three and four junction comb polymers

    NASA Astrophysics Data System (ADS)

    von Ferber, Christian; Bishop, Marvin; Forzaglia, Thomas; Reid, Cooper; Zajac, Gregory

    2015-01-01

    A scheme originally proposed by G. Wei [Physica A 222, 152 (1995); Physica A 222, 155 (1995)] is redesigned to produce numerical shape parameters of arbitrary tree-branched polymers based on the Kirchhoff matrix eigenvalue spectrum. This method and two different Monte Carlo techniques (pivot and growth) are employed to investigate the asphericity of three and four junction comb polymers in both the ideal and excluded volume regimes. It is found that the extrapolated g-ratio and asphericity values obtained by all of these methods are in excellent agreement with each other and the available theory in the ideal regime and that polymers with a complete set of interior branches display a more sphere-like shape.

  18. Characterizing a fiber-based frequency comb with electro-optic modulator.

    PubMed

    Zhang, Wei; Lours, Michel; Fischer, Marc; Holzwarth, Ronald; Santarelli, Giorgio; Coq, Yann

    2012-03-01

    We report on the characterization of a commercial- core fiber-based frequency comb equipped with an intracavity free-space electro-optic modulator (EOM). We investigate the relationship between the noise of the pump diode and the laser relative intensity noise (RIN) and demonstrate the use of a low-noise current supply to substantially reduce the laser RIN. By measuring several critical transfer functions, we evaluate the potential of the EOM for comb repetition rate stabilization. We also evaluate the coupling to other relevant parameters of the comb. From these measurements, we infer the capabilities of the femtosecond laser comb to generate very-low-phase-noise microwave signals when phase-locked to a high-spectral-purity ultra-stable laser. PMID:22481776

  19. Inhibition of bacterial adhesion on well ordered comb-like polymer surfaces.

    PubMed

    Sohn, Eun-Ho; Kim, Jaeeun; Kim, Byoung Gak; Kang, Jun Il; Chung, Jae-Seung; Ahn, Jooyeon; Yoon, Jeyong; Lee, Jong-Chan

    2010-06-01

    The surfaces of comb-like poly(oxyethylene) derivatives with n-alkylsulfonyl side groups were more effective at reducing Pseudomonas aeruginosa adhesion than the surfaces of common materials such as polystyrene, poly(methyl methacrylate), poly(dimethylsiloxane), fluorinated polyacrylate, and glass. When the comb-like poly(oxyethylene) was mixed with polystyrene and poly(methyl methacrylate), the topology and roughness of the surfaces varied according to the mixture compositions. However the surface energies of the mixtures were close to that of the comb-like poly(oxyethylene) in the range of 21-23 mN/m and bacterial adhesion resistances of the mixture surfaces were also comparable to that of the pure comb-like poly(oxyethylene) surface. PMID:20185280

  20. Tracing part-per-billion line shifts with direct-frequency-comb Vernier spectroscopy

    NASA Astrophysics Data System (ADS)

    Siciliani de Cumis, M.; Eramo, R.; Coluccelli, N.; Cassinerio, M.; Galzerano, G.; Laporta, P.; De Natale, P.; Cancio Pastor, P.

    2015-01-01

    Accurate frequency measurements of molecular transitions around 2 μ m are performed by using a direct-frequency-comb spectroscopy approach that combines an Er+ frequency-comb oscillator at 1.5 μ m , a Tm-Ho fiber amplifier, and a Fabry-Perot-filter, high-resolution dispersive spectrometer optical multiplex-detection system. This apparatus has unique performances in terms of a wide dynamic range to integrate the intensity per comb mode, which allows one to measure molecular absorption profiles with high precision. Spectroscopic information about transition frequencies and linewidths is very accurately determined. Relative frequency uncertainties of the order of a few parts in 10-9 are achieved for rovibrational transitions of the CO2 molecule around 5100 cm-1. Moreover, tiny frequency shifts due to molecular collisions and interacting laser power using direct comb spectroscopy are investigated in a systematic way.

  1. Mode-resolved frequency comb interferometry for high-accuracy long distance measurement.

    PubMed

    van den Berg, Steven A; van Eldik, Sjoerd; Bhattacharya, Nandini

    2015-01-01

    Optical frequency combs have developed into powerful tools for distance metrology. In this paper we demonstrate absolute long distance measurement using a single femtosecond frequency comb laser as a multi-wavelength source. By applying a high-resolution spectrometer based on a virtually imaged phased array, the frequency comb modes are resolved spectrally to the level of an individual mode. Having the frequency comb stabilized against an atomic clock, thousands of accurately known wavelengths are available for interferometry. From the spectrally resolved output of a Michelson interferometer a distance is derived. The presented measurement method combines spectral interferometry, white light interferometry and multi-wavelength interferometry in a single scheme. Comparison with a fringe counting laser interferometer shows an agreement within <10(-8) for a distance of 50?m. PMID:26419282

  2. Mode-resolved frequency comb interferometry for high-accuracy long distance measurement

    NASA Astrophysics Data System (ADS)

    van den Berg, Steven. A.; van Eldik, Sjoerd; Bhattacharya, Nandini

    2015-09-01

    Optical frequency combs have developed into powerful tools for distance metrology. In this paper we demonstrate absolute long distance measurement using a single femtosecond frequency comb laser as a multi-wavelength source. By applying a high-resolution spectrometer based on a virtually imaged phased array, the frequency comb modes are resolved spectrally to the level of an individual mode. Having the frequency comb stabilized against an atomic clock, thousands of accurately known wavelengths are available for interferometry. From the spectrally resolved output of a Michelson interferometer a distance is derived. The presented measurement method combines spectral interferometry, white light interferometry and multi-wavelength interferometry in a single scheme. Comparison with a fringe counting laser interferometer shows an agreement within <10-8 for a distance of 50?m.

  3. Mode-resolved frequency comb interferometry for high-accuracy long distance measurement

    PubMed Central

    van den Berg, Steven. A.; van Eldik, Sjoerd; Bhattacharya, Nandini

    2015-01-01

    Optical frequency combs have developed into powerful tools for distance metrology. In this paper we demonstrate absolute long distance measurement using a single femtosecond frequency comb laser as a multi-wavelength source. By applying a high-resolution spectrometer based on a virtually imaged phased array, the frequency comb modes are resolved spectrally to the level of an individual mode. Having the frequency comb stabilized against an atomic clock, thousands of accurately known wavelengths are available for interferometry. From the spectrally resolved output of a Michelson interferometer a distance is derived. The presented measurement method combines spectral interferometry, white light interferometry and multi-wavelength interferometry in a single scheme. Comparison with a fringe counting laser interferometer shows an agreement within <10?8 for a distance of 50?m. PMID:26419282

  4. An octave-spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide.

    PubMed

    Kuyken, Bart; Ideguchi, Takuro; Holzner, Simon; Yan, Ming; Hnsch, Theodor W; Van Campenhout, Joris; Verheyen, Peter; Coen, Stphane; Leo, Francois; Baets, Roel; Roelkens, Gunther; Picqu, Nathalie

    2015-01-01

    Laser frequency combs, sources with a spectrum consisting of hundred thousands evenly spaced narrow lines, have an exhilarating potential for new approaches to molecular spectroscopy and sensing in the mid-infrared region. The generation of such broadband coherent sources is presently under active exploration. Technical challenges have slowed down such developments. Identifying a versatile highly nonlinear medium for significantly broadening a mid-infrared comb spectrum remains challenging. Here we take a different approach to spectral broadening of mid-infrared frequency combs and investigate CMOS-compatible highly nonlinear dispersion-engineered silicon nanophotonic waveguides on a silicon-on-insulator chip. We record octave-spanning (1,500-3,300 nm) spectra with a coupled input pulse energy as low as 16 pJ. We demonstrate phase-coherent comb spectra broadened on a room-temperature-operating CMOS-compatible chip. PMID:25697764

  5. An octave-spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide

    NASA Astrophysics Data System (ADS)

    Kuyken, Bart; Ideguchi, Takuro; Holzner, Simon; Yan, Ming; Hnsch, Theodor W.; van Campenhout, Joris; Verheyen, Peter; Coen, Stphane; Leo, Francois; Baets, Roel; Roelkens, Gunther; Picqu, Nathalie

    2015-02-01

    Laser frequency combs, sources with a spectrum consisting of hundred thousands evenly spaced narrow lines, have an exhilarating potential for new approaches to molecular spectroscopy and sensing in the mid-infrared region. The generation of such broadband coherent sources is presently under active exploration. Technical challenges have slowed down such developments. Identifying a versatile highly nonlinear medium for significantly broadening a mid-infrared comb spectrum remains challenging. Here we take a different approach to spectral broadening of mid-infrared frequency combs and investigate CMOS-compatible highly nonlinear dispersion-engineered silicon nanophotonic waveguides on a silicon-on-insulator chip. We record octave-spanning (1,500-3,300?nm) spectra with a coupled input pulse energy as low as 16?pJ. We demonstrate phase-coherent comb spectra broadened on a room-temperature-operating CMOS-compatible chip.

  6. An octave-spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide

    PubMed Central

    Kuyken, Bart; Ideguchi, Takuro; Holzner, Simon; Yan, Ming; Hnsch, Theodor W.; Van Campenhout, Joris; Verheyen, Peter; Coen, Stphane; Leo, Francois; Baets, Roel; Roelkens, Gunther; Picqu, Nathalie

    2015-01-01

    Laser frequency combs, sources with a spectrum consisting of hundred thousands evenly spaced narrow lines, have an exhilarating potential for new approaches to molecular spectroscopy and sensing in the mid-infrared region. The generation of such broadband coherent sources is presently under active exploration. Technical challenges have slowed down such developments. Identifying a versatile highly nonlinear medium for significantly broadening a mid-infrared comb spectrum remains challenging. Here we take a different approach to spectral broadening of mid-infrared frequency combs and investigate CMOS-compatible highly nonlinear dispersion-engineered silicon nanophotonic waveguides on a silicon-on-insulator chip. We record octave-spanning (1,5003,300?nm) spectra with a coupled input pulse energy as low as 16?pJ. We demonstrate phase-coherent comb spectra broadened on a room-temperature-operating CMOS-compatible chip. PMID:25697764

  7. Characteristics of distributed-type inorganic electroluminescence panels with comb-shaped electrodes

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shin-Ichi; Uraoka, Yukiharu; Taguchi, Nobuyoshi; Nonaka, Toshihiro

    2013-09-01

    We deposited comb electrodes with narrow gaps between the teeth on a glass substrate, thus realizing a high electric field intensity that cannot be achieved with conventional structures. Au electrodes are deposited to form a comb shape and then spin-coated with a phosphor layer obtained by mixing ZnS phosphor particles with resins in a certain ratio. An AC voltage was applied to the gaps between the teeth of the comb electrode to emit light, from which the luminance was measured for different electric field intensities. The luminance was not affected by the transmittance of the electrodes themselves when measured from the phosphor layer side. Therefore, it may be possible to produce a display that does not require transparent electrodes by using the phosphor layer side of a device with comb electrodes made of metals, such as Au, for the display.

  8. Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel

    NASA Astrophysics Data System (ADS)

    Probst, R. A.; Wang, L.; Doerr, H.-P.; Steinmetz, T.; Kentischer, T. J.; Zhao, G.; Hnsch, T. W.; Udem, Th; Holzwarth, R.; Schmidt, W.

    2015-02-01

    We investigate a new scheme for astronomical spectrograph calibration using the laser frequency comb at the Solar Vacuum Tower Telescope on Tenerife. Our concept is based upon a single-mode fiber channel, that simultaneously feeds the spectrograph with comb light and sunlight. This yields nearly perfect spatial mode matching between the two sources. In combination with the absolute calibration provided by the frequency comb, this method enables extremely robust and accurate spectroscopic measurements. The performance of this scheme is compared to a sequence of alternating comb and sunlight, and to absorption lines from Earths atmosphere. We also show how the method can be used for radial-velocity detection by measuring the well-explored 5 min oscillations averaged over the full solar disk. Our method is currently restricted to solar spectroscopy, but with further evolving fiber-injection techniques it could become an option even for faint astronomical targets.

  9. Improvement of rotated comb decimation filter magnitude characteristic using sharpening technique

    NASA Astrophysics Data System (ADS)

    Jovanovic Dolecek, Gordana

    2015-09-01

    Decreasing of sampling rate in a digital form is called decimation. This process may introduce aliasing, i.e. non desired replicas of the main spectrum of the decimated signal. That is why we need the filter before decimation. This filter is called the decimation or antialiasing filter. The most popular decimation filter is comb filter which is usually used in the first stage of decimation. However it has a high passband droop and low attenuations in the folding bands. Different methods have been proposed to improve comb magnitude characteristic. The methods based on simple zero rotations have been proposed recently. In this paper we use the sharpening technique to improve both the passband and the stopband of comb filter with the rotated zeros. The method is compared with methods based on the rotation of zeros of comb filter.

  10. Offset-free broadband Yb:fiber optical frequency comb for optical clocks.

    PubMed

    Nakamura, Takuma; Ito, Isao; Kobayashi, Yohei

    2015-07-27

    We demonstrate a passively offset-frequency stabilized optical frequency comb centered at 1060 nm. The offset-free comb was achieved through difference frequency generation (DFG) between two portions of a supercontinuum based on a Yb:fiber laser. As the DFG comb had only one degree of freedom, repetition frequency, full stabilization was achieved via locking one of the modes to an ultra-stable continuous wave (CW) laser. The DFG comb provided sufficient average power to enable further amplification, using Yb-doped fiber amplifier, and spectral broadening. The spectrum spanned from 690 nm to 1300 nm and the average power was of several hundred mW, which could be ideal for the comparison of optical clocks, such as optical lattice clocks operated with Sr (698 nm) and Hg (1063 nm) reference atoms. PMID:26367597

  11. Optimally coherent Kerr combs generated with crystalline whispering gallery mode resonators for ultrahigh capacity fiber communications.

    PubMed

    Pfeifle, Joerg; Coillet, Aurlien; Henriet, Rmi; Saleh, Khaldoun; Schindler, Philipp; Weimann, Claudius; Freude, Wolfgang; Balakireva, Irina V; Larger, Laurent; Koos, Christian; Chembo, Yanne K

    2015-03-01

    Optical Kerr frequency combs are known to be effective coherent multiwavelength sources for ultrahigh capacity fiber communications. These combs are the frequency-domain counterparts of a wide variety of spatiotemporal dissipative structures, such as cavity solitons, chaos, or Turing patterns (rolls). In this Letter, we demonstrate that Turing patterns, which correspond to the so-called primary combs in the spectral domain, are optimally coherent in the sense that for the same pump power they provide the most robust carriers for coherent data transmission in fiber communications using advanced modulation formats. Our model is based on a stochastic Lugiato-Lefever equation which accounts for laser pump frequency jitter and amplified spontaneous emission noise induced by the erbium-doped fiber amplifier. Using crystalline whispering-gallery-mode resonators with quality factor Q?10^{9} for the comb generation, we show that when the noise is accounted for, the coherence of a primary comb is significantly higher than the coherence of their solitonic or chaotic counterparts for the same pump power. In order to confirm this theoretical finding, we perform an optical fiber transmission experiment using advanced modulation formats, and we show that the coherence of the primary comb is high enough to enable data transmission of up to 144??Gbit/s per comb line, the highest value achieved with a Kerr comb so far. This performance evidences that compact crystalline photonic systems have the potential to play a key role in a new generation of coherent fiber communication networks, alongside fully integrated systems. PMID:25793816

  12. Generation of wideband frequency combs by continuous-wave seeding of multistage mixers with synthesized dispersion.

    PubMed

    Myslivets, Evgeny; Kuo, Bill P P; Alic, Nikola; Radic, Stojan

    2012-01-30

    We numerically and experimentally demonstrate efficient generation of an equalized optical comb with 150-nm bandwidth. The comb was generated by low-power, continuous-wave seeds, eliminating the need for pulsed laser sources. The new architecture relies on efficient creation of higher-order mixing tones in phase-matched nonlinear fiber stages separated by a linear compressor. Wideband generation was enabled by precise dispersion engineering of multiple-stage parametric mixers. PMID:22330571

  13. Fiber comb filters based on UV-writing Bragg gratings in graded-index multimode fibers

    NASA Astrophysics Data System (ADS)

    Liu, Yu; Lit, John; Gu, Xijia; Wei, Li

    2005-10-01

    We report a new kind of comb filters based on fiber Bragg gratings in graded-index multimode fibers. It produces two groups of spectra with a total of 36 reflection peaks that correspond to 18 principal modes and cross coupled modes. The mode indices and wavelength spacings have been investigated theoretically and experimentally. This kind of comb filters may be used to construct multi-wavelength light sources for sensing, optical communications, and instrumentations

  14. A new method for determining the plasma electron density using optical frequency comb interferometer

    SciTech Connect

    Arakawa, Hiroyuki Tojo, Hiroshi; Sasao, Hajime; Kawano, Yasunori; Itami, Kiyoshi

    2014-04-15

    A new method of plasma electron density measurement using interferometric phases (fractional fringes) of an optical frequency comb interferometer is proposed. Using the characteristics of the optical frequency comb laser, high density measurement can be achieved without fringe counting errors. Simulations show that the short wavelength and wide wavelength range of the laser source and low noise in interferometric phases measurements are effective to reduce ambiguity of measured density.

  15. Analysis of microwave frequency combs generated by semiconductor lasers under hybrid optical injections

    NASA Astrophysics Data System (ADS)

    Lin, Cheng-Ting; Wu, Yi-Hua; Juan, Yu-Shan

    2015-03-01

    Microwave frequency combs utilizing hybrid optical injections schemes by varying the operational parameters, injection strength, repetition frequency, and detuning frequency are demonstrated and characterized. The dynamical hybrid optical injections are realized by both optical pulse injection and optical cw injection to the slave laser simultaneously under the condition of zero detuning frequency between two injecting source lasers. For pure pulse injection case, the amplitude variation of ±27.3 dB in a 30 GHz range is obtained. By further applying the injection strength of the cw injection to the pulses injected semiconductor laser, the amplitude variation of ±3.3 dB in a 30 GHz range in microwave frequency combs are observed when operating the cw injection system in a stable locking state. In order to examine the microwave frequency comb precisely, each operational parameters of the hybrid optical injections schemes are analyzed. The amplitude variation of microwave frequency combs is also strongly influenced by operating the cw injection system in different states. Comparing to the cw injection system operated in period-one states, the amplitude variation is reduced when operated in the stable locking states. Moreover, the bandwidth broadening in microwave frequency comb is expected when the cw injection system operating in a stable locking state. In this paper, strongly improve the amplitude variation of the microwave frequency combs generated utilizing hybrid injections scheme compared to single injection case are obtained and compared.

  16. Modeling of a High Force Density Fishbone Shaped Electrostatic Comb Drive Microactuator

    PubMed Central

    Megat Hasnan, Megat Muhammad Ikhsan; Mohd Sabri, Mohd Faizul; Mohd Said, Suhana; Nik Ghazali, Nik Nazri

    2014-01-01

    This paper presents the design and evaluation of a high force density fishbone shaped electrostatic comb drive actuator. This comb drive actuator has a branched structure similar to a fishbone, which is intended to increase the capacitance of the electrodes and hence increase the electrostatic actuation force. Two-dimensional finite element analysis was used to simulate the motion of the fishbone shaped electrostatic comb drive actuator and compared against the performance of a straight sided electrostatic comb drive actuator. Performances of both designs are evaluated by comparison of displacement and electrostatic force. For both cases, the active area and the minimum gap distance between the two electrodes were constant. An active area of 800 300??m, which contained 16 fingers of fishbone shaped actuators and 40 fingers of straight sided actuators, respectively, was used. Through simulation, improvement of drive force of the fishbone shaped electrostatic comb driver is approximately 485% higher than conventional electrostatic comb driver. These results indicate that the fishbone actuator design provides good potential for applications as high force density electrostatic microactuator in MEMS systems. PMID:25165751

  17. Modeling of a high force density fishbone shaped electrostatic comb drive microactuator.

    PubMed

    Megat Hasnan, Megat Muhammad Ikhsan; Mohd Sabri, Mohd Faizul; Mohd Said, Suhana; Nik Ghazali, Nik Nazri

    2014-01-01

    This paper presents the design and evaluation of a high force density fishbone shaped electrostatic comb drive actuator. This comb drive actuator has a branched structure similar to a fishbone, which is intended to increase the capacitance of the electrodes and hence increase the electrostatic actuation force. Two-dimensional finite element analysis was used to simulate the motion of the fishbone shaped electrostatic comb drive actuator and compared against the performance of a straight sided electrostatic comb drive actuator. Performances of both designs are evaluated by comparison of displacement and electrostatic force. For both cases, the active area and the minimum gap distance between the two electrodes were constant. An active area of 800 300 ?m, which contained 16 fingers of fishbone shaped actuators and 40 fingers of straight sided actuators, respectively, was used. Through simulation, improvement of drive force of the fishbone shaped electrostatic comb driver is approximately 485% higher than conventional electrostatic comb driver. These results indicate that the fishbone actuator design provides good potential for applications as high force density electrostatic microactuator in MEMS systems. PMID:25165751

  18. Supercontinuum-based 10-GHz flat-topped optical frequency comb generation.

    PubMed

    Wu, Rui; Torres-Company, Victor; Leaird, Daniel E; Weiner, Andrew M

    2013-03-11

    The generation of high-repetition-rate optical frequency combs with an ultra-broad, coherent and smooth spectrum is important for many applications in optical communications, radio-frequency photonics and optical arbitrary waveform generation. Usually, nonlinear broadening techniques of comb-based sources do not provide the required flatness over the whole available bandwidth. Here we present a 10-GHz ultra-broadband flat-topped optical frequency comb (> 3.64-THz or 28 nm bandwidth with ~365 spectral lines within 3.5-dB power variation) covering the entire C-band. The key enabling point is the development of a pre-shaping-free directly generated Gaussian comb-based 10-GHz pulse train to seed a highly nonlinear fiber with normal dispersion profile. The combination of the temporal characteristics of the seed pulses with the nonlinear device allows the pulses to enter into the optical wave-breaking regime, thus achieving a smooth flat-topped comb spectral envelope. To further illustrate the high spectral coherence of the comb, we demonstrate high-quality pedestal-free short pulse compression to the transform-limited duration. PMID:23482172

  19. Thermoresponsive comb-shaped copolymer-Si(100) hybrids for accelerated temperature-dependent cell detachment.

    PubMed

    Xu, F J; Zhong, S P; Yung, L Y L; Tong, Y W; Kang, En-Tang; Neoh, K G

    2006-03-01

    Well-defined comb-shaped copolymer-Si(100) hybrids were prepared, via successive surface-initiated atom transfer radical polymerizations (ATRPs) of glycidyl methacrylate (GMA) and N-isopropylacrylamide (NIPAAm), for accelerated cell detachment at a lower temperature. The Si-C bonded comb copolymer consisted of a well-defined (nearly monodispersed) poly(glycidyl methacrylate) (P(GMA)) main chain, a well-defined NIPAAm polymer (P(NIPAAm) block, and well-defined P(NIPAAm) side chains. The ring opening reaction of epoxy groups of the P(GMA) main chain with 2-chloropropionic acid resulted in the immobilization of the alpha-chloroester groups (the ATRP initiators for the NIPAAm side chains) and the concomitant formation of hydroxyl groups. P(NIPAAm) acted as the thermoresponsive side chains of the comb copolymer for control of cell adhesion and detachment, while the P(GMA) main chain with hydroxyl groups provided a local hydrophilic microenvironment. The unique microstructure of the comb copolymer brushes facilitated cell recovery at 20 degrees C (below the lower critical solution temperature (LCST) of P(NIPAAm)) without restraining cell attachments and growth at 37 degrees C. The accelerated detachment of cells indicated that the underlying hydrophilic environment of the comb copolymer brushes contributed to speedy hydration of the P(NIPAAm) segments below the LCST. The thermoresponsive comb copolymer-Si(100) hybrids are potentially useful as adhesion modifiers for cells in silicon-based biomedical devices. PMID:16182362

  20. Frequency-noise measurements of optical frequency combs by multiple fringe-side discriminator

    PubMed Central

    Coluccelli, Nicola; Cassinerio, Marco; Gambetta, Alessio; Laporta, Paolo; Galzerano, Gianluca

    2015-01-01

    The frequency noise of an optical frequency comb is routinely measured through the hetherodyne beat of one comb tooth against a stable continuous-wave laser. After frequency-to-voltage conversion, the beatnote is sent to a spectrum analyzer to retrive the power spectral density of the frequency noise. Because narrow-linewidth continuous-wave lasers are available only at certain wavelengths, heterodyning the comb tooth can be challenging. We present a new technique for direct characterization of the frequency noise of an optical frequency comb, requiring no supplementary reference lasers and easily applicable in all spectral regions from the terahertz to the ultraviolet. The technique is based on the combination of a low finesse Fabry-Perot resonator and the so-called “fringe-side locking” method, usually adopted to characterize the spectral purity of single-frequency lasers, here generalized to optical frequency combs. The effectiveness of this technique is demonstrated with an Er-fiber comb source across the wavelength range from 1 to 2 μm. PMID:26548900

  1. Coherent dual-comb spectroscopy at high signal-to-noise ratio

    SciTech Connect

    Coddington, I.; Swann, W. C.; Newbury, N. R.

    2010-10-15

    Two coherent frequency combs are used to measure the full complex response of a sample in a configuration analogous to a dispersive Fourier transform spectrometer, infrared time domain spectrometer, or a multiheterodyne laser spectrometer. This dual-comb spectrometer retains the frequency accuracy and resolution of the reference underlying the stabilized combs. We discuss the specific design of our coherent dual-comb spectrometer and demonstrate the potential of this technique by measuring the overtone vibration of hydrogen cyanide, centered at 194 THz (1545 nm). We measure the fully normalized, complex response of the gas over a 9 THz bandwidth at 220 MHz frequency resolution yielding 41,000 resolution elements. The average spectral signal-to-noise ratio (SNR) over the 9 THz bandwidth is 2500 for both the magnitude and phase of the measured spectral response and the peak SNR is 4000. This peak SNR corresponds to a fractional absorption sensitivity of 0.05% and a phase sensitivity of 250 microradians. As the spectral coverage of combs expands, coherent dual-comb spectroscopy could provide high-frequency accuracy and resolution measurements of a complex sample response across a range of spectral regions. Work of U. S. government, not subject to copyright.

  2. Dispersing Zwitterions into Comb Polymers for Nonviral Transfection: Experiments and Molecular Simulation.

    PubMed

    Ghobadi, Ahmadreza F; Letteri, Rachel; Parelkar, Sangram S; Zhao, Yue; Chan-Seng, Delphine; Emrick, Todd; Jayaraman, Arthi

    2016-02-01

    Polymer-based gene delivery vehicles benefit from the presence of hydrophilic groups that mitigate the inherent toxicity of polycations and that provide tunable polymer-DNA binding strength and stable complexes (polyplexes). However, hydrophilic groups screen charge, and as such can reduce cell uptake and transfection efficiency. We report the effect of embedding zwitterionic sulfobetaine (SB) groups in cationic comb polymers, using a combination of experiments and molecular simulations. Ring-opening metathesis polymerization (ROMP) produced comb polymers with tetralysine (K4) and SB pendent groups. Dynamic light scattering, zeta potential measurements, and fluorescence-based experiments, together with coarse-grained molecular dynamics simulations, described the effect of SB groups on the size, shape, surface charge, composition, and DNA binding strength of polyplexes formed using these comb polymers. Experiments and simulations showed that increasing SB composition in the comb polymers decreased polymer-DNA binding strength, while simulations indicated that the SB groups distributed throughout the polyplex. This allows polyplexes to maintain a positive surface charge and provide high levels of gene expression in live cells. Notably, comb polymers with nearly 50 mol % SB form polyplexes that exhibit positive surface charge similarly as polyplexes formed from purely cationic comb polymers, indicating the ability to introduce an appreciable amount of SB functionality without screening surface charge. This integrated simulation-experimental study demonstrates the effectiveness of incorporating zwitterions in polyplexes, while guiding the design of new and effective gene delivery vectors. PMID:26741292

  3. Occurrence of fungi in combs of fungus-growing termites (Isoptera: Termitidae, Macrotermitinae).

    PubMed

    Guedegbe, Herbert J; Miambi, Edouard; Pando, Anne; Roman, Jocelyne; Houngnandan, Pascal; Rouland-Lefevre, Corinne

    2009-10-01

    Fungus-growing termites cultivate their mutualistic basidiomycete Termitomyces species on a substrate called a fungal comb. Here, the Suicide Polymerase Endonuclease Restriction (SuPER) method was adapted for the first time to a fungal study to determine the entire fungal community of fungal combs and to test whether fungi other than the symbiotic cultivar interact with termite hosts. Our molecular analyses show that although active combs are dominated by Termitomyces fungi isolated with direct Polymerase Endonuclease Restriction - Denaturing Gradient Gel Electrophoresis (PCR-DGGE), they can also harbor some filamentous fungi and yeasts only revealed by SuPER PCR-DGGE. This is the first molecular evidence of the presence of non-Termitomyces species in active combs. However, because there is no evidence for a species-specific relationship between these fungi and termites, they are mere transient guests with no specialization in the symbiosis. It is however surprising to notice that termite-associated Xylaria strains were not isolated from active combs even though they are frequently retrieved when nests are abandoned by termites. This finding highlights the implication of fungus-growing termites in the regulation of fungi occurring within the combs and also suggests that they might not have any particular evolutionary-based association with Xylaria species. PMID:19576985

  4. Femtosecond optical parametric oscillators toward real-time dual-comb spectroscopy

    NASA Astrophysics Data System (ADS)

    Jin, Yuwei; Cristescu, Simona M.; Harren, Frans J. M.; Mandon, Julien

    2015-04-01

    We demonstrate mid-infrared dual-comb spectroscopy with an optical parametric oscillator (OPO) toward real-time field measurement. A singly resonant OPO based on a MgO-doped periodically poled lithium niobate (PPLN) crystal is demonstrated. Chirped mirrors are used to compensate the dispersion caused by the optical cavity and the crystal. A low threshold of 17 mW has been achieved. The OPO source generates a tunable idler frequency comb between 2.7 and 4.7 ?m. Dual-comb spectroscopy is achieved by coupling two identical Yb-fiber mode-locked lasers to this OPO with slightly different repetition frequencies. A measured absorption spectrum of methane is presented with a spectral bandwidth of , giving an instrumental resolution of . In addition, a second OPO containing two MgO-doped PPLN crystals in a singly resonant ring cavity is demonstrated. As such, this OPO generates two idler combs (average power up to 220 mW), covering a wavelength range between 2.7 and 4.2 ?m, from which a mid-infrared dual-comb Fourier transform spectrometer is constructed. By detecting the heterodyned signal between the two idler combs, broadband spectra of molecular gases can be observed over a spectral bandwidth of more than . This special cavity design allows the spectral resolution to be improved to without locking the OPO cavity, indicating that this OPO represents an ideal high-power broadband mid-infrared source for real-time gas sensing.

  5. Frequency-noise measurements of optical frequency combs by multiple fringe-side discriminator

    NASA Astrophysics Data System (ADS)

    Coluccelli, Nicola; Cassinerio, Marco; Gambetta, Alessio; Laporta, Paolo; Galzerano, Gianluca

    2015-11-01

    The frequency noise of an optical frequency comb is routinely measured through the hetherodyne beat of one comb tooth against a stable continuous-wave laser. After frequency-to-voltage conversion, the beatnote is sent to a spectrum analyzer to retrive the power spectral density of the frequency noise. Because narrow-linewidth continuous-wave lasers are available only at certain wavelengths, heterodyning the comb tooth can be challenging. We present a new technique for direct characterization of the frequency noise of an optical frequency comb, requiring no supplementary reference lasers and easily applicable in all spectral regions from the terahertz to the ultraviolet. The technique is based on the combination of a low finesse Fabry-Perot resonator and the so-called “fringe-side locking” method, usually adopted to characterize the spectral purity of single-frequency lasers, here generalized to optical frequency combs. The effectiveness of this technique is demonstrated with an Er-fiber comb source across the wavelength range from 1 to 2 μm.

  6. Frequency-noise measurements of optical frequency combs by multiple fringe-side discriminator.

    PubMed

    Coluccelli, Nicola; Cassinerio, Marco; Gambetta, Alessio; Laporta, Paolo; Galzerano, Gianluca

    2015-01-01

    The frequency noise of an optical frequency comb is routinely measured through the hetherodyne beat of one comb tooth against a stable continuous-wave laser. After frequency-to-voltage conversion, the beatnote is sent to a spectrum analyzer to retrive the power spectral density of the frequency noise. Because narrow-linewidth continuous-wave lasers are available only at certain wavelengths, heterodyning the comb tooth can be challenging. We present a new technique for direct characterization of the frequency noise of an optical frequency comb, requiring no supplementary reference lasers and easily applicable in all spectral regions from the terahertz to the ultraviolet. The technique is based on the combination of a low finesse Fabry-Perot resonator and the so-called "fringe-side locking" method, usually adopted to characterize the spectral purity of single-frequency lasers, here generalized to optical frequency combs. The effectiveness of this technique is demonstrated with an Er-fiber comb source across the wavelength range from 1 to 2 μm. PMID:26548900

  7. Genomics of Sex and Sex Chromosomes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sex chromosomes are distinctive, not only because of their gender determining role, but also for genomic features that reflect their evolutionary history. The genomic sequences in the ancient sex chromosomes of humans and in the incipient sex chromosomes of medaka, stickleback, and papaya exhibit u...

  8. Mid-infrared frequency comb based on a quantum cascade laser.

    PubMed

    Hugi, Andreas; Villares, Gustavo; Blaser, Stphane; Liu, H C; Faist, Jrme

    2012-12-13

    Optical frequency combs act as rulers in the frequency domain and have opened new avenues in many fields such as fundamental time metrology, spectroscopy and frequency synthesis. In particular, spectroscopy by means of optical frequency combs has surpassed the precision and speed of Fourier spectrometers. Such a spectroscopy technique is especially relevant for the mid-infrared range, where the fundamental rotational-vibrational bands of most light molecules are found. Most mid-infrared comb sources are based on down-conversion of near-infrared, mode-locked, ultrafast lasers using nonlinear crystals. Their use in frequency comb spectroscopy applications has resulted in an unequalled combination of spectral coverage, resolution and sensitivity. Another means of comb generation is pumping an ultrahigh-quality factor microresonator with a continuous-wave laser. However, these combs depend on a chain of optical components, which limits their use. Therefore, to widen the spectroscopic applications of such mid-infrared combs, a more direct and compact generation scheme, using electrical injection, is preferable. Here we present a compact, broadband, semiconductor frequency comb generator that operates in the mid-infrared. We demonstrate that the modes of a continuous-wave, free-running, broadband quantum cascade laser are phase-locked. Combining mode proliferation based on four-wave mixing with gain provided by the quantum cascade laser leads to a phase relation similar to that of a frequency-modulated laser. The comb centre carrier wavelength is 7?micrometres. We identify a narrow drive current range with intermode beat linewidths narrower than 10?hertz. We find comb bandwidths of 4.4 per cent with an intermode stability of less than or equal to 200?hertz. The intermode beat can be varied over a frequency range of 65?kilohertz by radio-frequency injection. The large gain bandwidth and independent control over the carrier frequency offset and the mode spacing open the way to broadband, compact, all-solid-state mid-infrared spectrometers. PMID:23235876

  9. On the generation of octave-spanning optical frequency combs using monolithic whispering-gallery-mode microresonators.

    PubMed

    Chembo, Yanne K; Yu, Nan

    2010-08-15

    Octave-spanning optical frequency combs are especially interesting in optical metrology owing to the ability of self-referencing. We report a theoretical study on the generation of octave-spanning combs in the whispering gallery modes of a microresonator. Through a modal expansion model simulation in a calcium fluoride microcavity, we show that a combination of suitable pump power, Kerr nonlinearity, and dispersion profile can lead to stable and robust octave-spanning optical frequency combs. PMID:20717427

  10. Sex ratio evolution under probabilistic sex determination.

    PubMed

    Paixo, Tiago; Phadke, Sujal S; Azevedo, Ricardo B R; Zufall, Rebecca A

    2011-07-01

    Sex allocation theory has been remarkably successful at explaining the prevalence of even sex ratios in natural populations and at identifying specific conditions that can result in biased sex ratios. Much of this theory focuses on parental sex determination (SD) strategies. Here, we consider instead the evolutionary causes and consequences of mixed offspring SD strategies, in which the genotype of an individual determines not its sex, but the probability of developing one of multiple sexes. We find that alleles specifying mixed offspring SD strategies can generally outcompete alleles that specify pure strategies, but generate constraints that may prevent a population from reaching an even sex ratio. We use our model to analyze sex ratios in natural populations of Tetrahymena thermophila, a ciliate with seven sexes determined by mixed SD alleles. We show that probabilistic SD is sufficient to account for the occurrence of skewed sex ratios in natural populations of T. thermophila, provided that their effective population sizes are small. Our results highlight the importance of genetic drift in sex ratio evolution and suggest that mixed offspring SD strategies should be more common than currently thought. PMID:21729059

  11. Ultra-low noise all polarization-maintaining Er fiber-based optical frequency combs facilitated with a graphene modulator.

    PubMed

    Kuse, N; Lee, C-C; Jiang, J; Mohr, C; Schibli, T R; Fermann, M E

    2015-09-21

    High bandwidth carrier phase and repetition rate control are critical for the construction of low phase noise optical frequency combs. Here we demonstrate the use of a graphene modulator for the former and a bulk electro-optic modulator for the latter enabling record low phase noise operation of an Er fiber frequency comb. For applications that do not require carrier phase control, we show that the form factor of a fiber comb can be reduced by adapting a graphene modulator for rapid repetition rate control. Moreover, the whole system demonstration is performed with all-polarization maintaining Er fiber frequency combs, highly suitable for applications in the field. PMID:26406639

  12. Generation of a coherent near-infrared Kerr frequency comb in a monolithic microresonator with normal GVD.

    PubMed

    Liang, Wei; Savchenkov, Anatoliy A; Ilchenko, Vladimir S; Eliyahu, Danny; Seidel, David; Matsko, Andrey B; Maleki, Lute

    2014-05-15

    We demonstrate experimentally, and describe theoretically, generation of a wide, fundamentally phase-locked Kerr frequency comb in a nonlinear resonator with a normal group velocity dispersion (GVD). A magnesium fluoride whispering-gallery mode resonator characterized with 10GHz free spectral range and pumped either at 780 or 795nm is used in the experiment. The envelope of the observed frequency comb differs significantly from the Kerr frequency comb spectra reported previously. We show via numerical simulation that, while the frequency comb does not correspond to generation of short optical pulses, the relative phase of the generated harmonics are fixed. PMID:24978237

  13. Reclassification of Acetomicrobium faecale as Caldicoprobacter faecalis comb. nov.

    PubMed

    Bouanane-Darenfed, Amel; Ben Hania, Wajdi; Cayol, Jean-Luc; Ollivier, Bernard; Fardeau, Marie-Laure

    2015-10-01

    Taking into account its phenotypical and genetic characteristics, Acetomicrobium faecale was first recognized as a member of the genus Acetomicrobium, family Bacteroidaceae, order Bacteroidales, phylum Bacteroidetes, with Acetomicrobium flavidum the type species of the genus. However, it was found that A. faecale had 95.8 %, 97.6 % and 98.4 % similarity, respectively, with Caldicoprobacter guelmensis, Caldicoprobacter algeriensis and Caldicoprobacter oshimai and only 82 % similarity with A. flavidum. The DNA G+C content of A. faecale is 45 mol , which is of the same order as the DNA G+C content of the three strains of species of the genus Caldicoprobacter and its main fatty acid is C16 : 0, with its second most prominent fatty acid, iso-C17 : 0, also common to strains of species of the genus Caldicoprobacter. On the basis of further phylogenetic, genetic and chemotaxonomic studies, we propose that A. faecale (type strain DSM 20678T = JCM 30420T) be reclassified as Caldicoprobacter faecalis comb. nov. PMID:26297233

  14. Cationic comb-type copolymers for DNA analysis

    NASA Astrophysics Data System (ADS)

    Kim, Won Jong; Sato, Yuichi; Akaike, Toshihiro; Maruyama, Atsushi

    2003-12-01

    Genetic diagnoses, such as single nucleotide polymorphism (SNP) typing, allow elucidation of gene-based physiological differences, such as susceptibility to diseases and response to drugs, among individuals. Many detection technologies, including allele-specific hybridization, allele-specific primer extension and oligonucleotide ligation, are being used to discriminate SNP alleles. These methods still have many unsolved practical issues. In general they require adequate and specific hybridizations of primer or probe DNAs with target DNAs. This frequently needs optimization of the probe/primer structures and operating conditions. In nature, highly homology-sensitive hybridization is assisted by a nucleic acid chaperone that reduces the energy barrier associated with breakage and reassociation of nucleic base pairs. Here we report a simple, quick, precise but enzyme-free method for SNP analysis. The method uses cationic comb-type copolymers (CCCs) producing high nucleic acid chaperone activities. A single-base mismatch in 20-mer DNA can be detected within a few minutes at ambient temperatures (25-37 C). Even without careful optimization processes, the method has the sensitivity to detect the mismatches causing subtle changes (?Tm ~ 1 C) in duplex thermal stability. CCCs may have various bioanalytical applications where precise hybridization of nucleic acids is needed.

  15. Impulse response of microresonators with a dual frequency comb probe

    NASA Astrophysics Data System (ADS)

    Michaud-Belleau, Vincent; Bergeron, Hugo; Carrier, Jean-Raphal; Roy, Julien; Genest, Jrme; Allen, Claudine

    2013-05-01

    Label-free microsphere were shown to be sensitive optical biosensors thanks to the very high quality factor up to Q ~109 of their whispering gallery modes (WGMs). Several resonances are available to probe the frequency response in polarizability, but the spectrum of WGMs for an elliptical resonator is more complicated, warranting further measures of light propagation. Our high resolution interferometric studies of a silica microresonator with a dual frequency comb provide both its impulse response in the time domain with 80 fs resolution and its transmission spectrum in the frequency domain with 125 MHz resolution, i.e. at the picometer level. We observe that a light pulse is periodically outcoupling from a ~ 156 ?m microsphere after round trips of ~ 2 ps as can be expected from the group velocity. However, the structure of the full impulse response is more rich, for example showing clusters of pulses separated by roughly ~ 50 ps. This reveals the light pulse is not outcoupling from the slightly elliptical microresonator at each round trip because its trajectory is precessing. Finally, we see that a refractive index change at the resonator surface causes a phase delay in the impulse response corresponding to the WGM frequency shifts in the spectrum.

  16. The Comb Jelly Opsins and the Origins of Animal Phototransduction

    PubMed Central

    Feuda, Roberto; Rota-Stabelli, Omar; Oakley, Todd H.; Pisani, Davide

    2014-01-01

    Opsins mediate light detection in most animals, and understanding their evolution is key to clarify the origin of vision. Despite the public availability of a substantial collection of well-characterized opsins, early opsin evolution has yet to be fully understood, in large part because of the high level of divergence observed among opsins belonging to different subfamilies. As a result, different studies have investigated deep opsin evolution using alternative data sets and reached contradictory results. Here, we integrated the data and methods of three, key, recent studies to further clarify opsin evolution. We show that the opsin relationships are sensitive to outgroup choice; we generate new support for the existence of Rhabdomeric opsins in Cnidaria (e.g., corals and jellyfishes) and show that all comb jelly opsins belong to well-recognized opsin groups (the Go-coupled opsins or the Ciliary opsins), which are also known in Bilateria (e.g., humans, fruit flies, snails, and their allies) and Cnidaria. Our results are most parsimoniously interpreted assuming a traditional animal phylogeny where Ctenophora are not the sister group of all the other animals. PMID:25062921

  17. The comb jelly opsins and the origins of animal phototransduction.

    PubMed

    Feuda, Roberto; Rota-Stabelli, Omar; Oakley, Todd H; Pisani, Davide

    2014-08-01

    Opsins mediate light detection in most animals, and understanding their evolution is key to clarify the origin of vision. Despite the public availability of a substantial collection of well-characterized opsins, early opsin evolution has yet to be fully understood, in large part because of the high level of divergence observed among opsins belonging to different subfamilies. As a result, different studies have investigated deep opsin evolution using alternative data sets and reached contradictory results. Here, we integrated the data and methods of three, key, recent studies to further clarify opsin evolution. We show that the opsin relationships are sensitive to outgroup choice; we generate new support for the existence of Rhabdomeric opsins in Cnidaria (e.g., corals and jellyfishes) and show that all comb jelly opsins belong to well-recognized opsin groups (the Go-coupled opsins or the Ciliary opsins), which are also known in Bilateria (e.g., humans, fruit flies, snails, and their allies) and Cnidaria. Our results are most parsimoniously interpreted assuming a traditional animal phylogeny where Ctenophora are not the sister group of all the other animals. PMID:25062921

  18. Dual-etalon, cavity-ring-down, frequency comb spectroscopy.

    SciTech Connect

    Strecker, Kevin E.; Chandler, David W.

    2010-10-01

    The 'dual etalon frequency comb spectrometer' is a novel low cost spectometer with limited moving parts. A broad band light source (pulsed laser, LED, lamp ...) is split into two beam paths. One travels through an etalon and a sample gas, while the second arm is just an etalon cavity, and the two beams are recombined onto a single detector. If the free spectral ranges (FSR) of the two cavities are not identical, the intensity pattern at the detector with consist of a series of heterodyne frequencies. Each mode out of the sample arm etalon with have a unique frequency in RF (radio-frequency) range, where modern electronics can easily record the signals. By monitoring these RF beat frequencies we can then determine when an optical frequencies is absorbed. The resolution is set by the FSR of the cavity, typically 10 MHz, with a bandwidth up to 100s of cm{sup -1}. In this report, the new spectrometer is described in detail and demonstration experiments on Iodine absorption are carried out. Further we discuss powerful potential next generation steps to developing this into a point sensor for monitoring combustion by-products, environmental pollutants, and warfare agents.

  19. Regeneration of ciliary comb plates in the ctenophore Mnemiopsis leidyi. i. morphology.

    PubMed

    Tamm, Sidney L

    2012-01-01

    Regeneration of missing body parts in model organisms provides information on the mechanisms underlying the regeneration process. The aim here is to use ctenophores to investigate regeneration of their giant ciliary swimming plates. When part of a row of comb plates on Mnemiopsis is excised, the wound closes and heals, greatly increasing the distance between comb plates near the former cut edges. Video differential interference contrast (DIC) microscopy of the regeneration of new comb plates between widely separated plates shows localized widenings of the interplate ciliated groove (ICG) first, followed by growth of two opposing groups of comb plate cilia on either side. The split parts of a new plate elongate as their bases extend laterally away from the ICG widening and continue ciliogenesis at both ends. The split parts of a new plate grow longer and move closer together into the ICG widening until they merge into a single plate that interrupts the ICG in a normal manner. Video DIC snapshots of dissected gap preparations 1.5-3-day postoperation show that ICG widenings and/or new plates do not all appear at the same time or with uniform spacing within a gap: the lengths and distances between young plates in a gap are quite variable. Video stereo microscopy of intact animals 3-4 days after the operation show that all the new plates that will form in a gap are present, fairly evenly spaced and similar in length, but smaller and closer together than normal. Normal development of comb plates in embryos and growing animals is compared to the pattern of comb plate regeneration in adults. Comb plate regeneration differs in the cydippid Pleurobrachia that lacks ICGs and has a firmer mesoglea than Mnemiopsis. This study provides a morphological foundation for histological, cellular, and molecular analysis of ciliary regeneration in ctenophores. PMID:21987455

  20. The Riddle of Sex.

    ERIC Educational Resources Information Center

    Sagan, Dorion; Margulis, Lynn

    1985-01-01

    Discusses the work of evolutionary biologists in determining how sexual reproduction arose. Topics explored include the nature of sex, bacterial sex, meiotic sex, and asexual reproduction. A diagram (which can be used as a duplicating master) illustrating types of bacterial sex is included. (DH)

  1. Modal expansion approach to optical-frequency-comb generation with monolithic whispering-gallery-mode resonators

    SciTech Connect

    Chembo, Yanne K.; Yu, Nan

    2010-09-15

    We describe a general framework based on modal expansion for the study of optical-frequency combs generated with monolithic whispering-gallery-mode resonators. We obtain a set of time-domain rate equations describing the dynamics of each mode as a function of the main characteristics of the cavity, namely, Kerr nonlinearity, absorption, coupling losses, and cavity dispersion (geometrical and material). A stability analysis of the various side modes is performed, which finds analytically the threshold power needed for comb generation. We show that the various whispering gallery modes are excited in a nontrivial way, strongly dependent on the value of the overall cavity dispersion. We demonstrate that the combs are not simply generated through a direct transfer of energy from the pumped mode to all their neighbors but rather through complex intermediate interactions. Anomalous cavity dispersion is also demonstrated to be critical for these cascading processes, and comb generation is thereby unambiguously linked to modulational instability. This theory accurately describes the emergence of spectral modulation and free spectral-range tunability in the comb. It also enables a clear understanding of the various phenomena responsible for the spectral span limitation. Our theoretical predictions are in excellent agreement with the numerical simulations, and they successfully explain the internal mechanisms responsible for the generation of hundreds of Kerr modes in monolithic whispering-gallery-mode resonators.

  2. Highly Stable, Anion Conductive, Comb-Shaped Copolymers for Alkaline Fuel Cells

    SciTech Connect

    Li, NW; Leng, YJ; Hickner, MA; Wang, CY

    2013-07-10

    To produce an anion-conductive and durable polymer electrolyte for alkaline fuel cell applications, a series of quaternized poly(2,6-dimethyl phenylene oxide)s containing long alkyl side chains pendant to the nitrogen-centered cation were synthesized using a Menshutkin reaction to form comb-shaped structures. The pendant alkyl chains were responsible for the development of highly conductive ionic domains, as confirmed by small-angle X-ray scattering (SAXS). The comb-shaped polymers having one alkyl side chain showed higher hydroxide conductivities than those with benzyltrimethyl ammonium moieties or structures with more than one alkyl side chain per cationic site. The highest conductivity was observed for comb-shaped polymers with benzyldimethylhexadecyl ammonium cations. The chemical stabilities of the comb-shaped membranes were evaluated under severe, accelerated-aging conditions, and degradation was observed by measuring IEC and ion conductivity changes during aging. The comb-shaped membranes retained their high ion conductivity in 1 M NaOH at 80 degrees C for 2000 h. These cationic polymers were employed as ionomers in catalyst layers for alkaline fuel cells. The results indicated that the C-16 alkyl side chain ionomer had a slightly better initial performance, despite its low IEC value, but very poor durability in the fuel cell. In contrast, 90% of the initial performance was retained for the alkaline fuel cell with electrodes containing the C-6 side chain after 60 h of fuel cell operation.

  3. Generation of a green astro-comb using tapered photonic crystal fibers

    NASA Astrophysics Data System (ADS)

    Phillips, David; Glenday, Alexander; Li, Chih-Hao; Furesz, Gabor; Langellier, Nicholas; Webber, Matthew; Chang, Guoqing; Chen, Li-Jin; Chen, Hung-Wen; Lim, Jinkang; Kaertner, Franz; Szentgyorgyi, Andrew; Walsworth, Ronald

    2012-06-01

    Searches for exoplanets using precision stellar radial velocity (PRV) measurements are approaching Earth-like planet sensitivity. Astro-combs, which consist of a laser frequency comb, coherent wavelength shifting mechanism (such as a doubling crystal or photonic crystal fiber), and a mode-filtering Fabry-Perot cavity, provide a promising route to increased accuracy and long-term stability of the astrophysical spectrograph wavelength calibration. To find an Earth-like exoplanet around a Sun-like star requires astro-combs that cover the visible spectral bands in which there is maximal stellar photon flux and rich high-quality spectral features for high-sensitivity PRV measurements. However, currently no comb lines are available directly from mode-lock lasers in the visible band. Here, we report generation of a green astro-comb from an octave spanning Ti:Sapphire laser, spectrally broadened by a custom tapered PCF to the visible band via fiber-optic Cherenkov radiation for frequency shifting, and filtered by a broadband Fabry-Perot cavity constructed by a pair of complementary chirped mirrors.

  4. Mechanisms behind the metabolic flexibility of an invasive comb jelly

    NASA Astrophysics Data System (ADS)

    Augustine, Starrlight; Jaspers, Cornelia; Kooijman, Sebastiaan A. L. M.; Carlotti, François; Poggiale, Jean-Christophe; Freitas, Vânia; van der Veer, Henk; van Walraven, Lodewijk

    2014-11-01

    Mnemiopsis leidyi is an invasive comb jelly which has successfully established itself in European seas. The species is known to produce spectacular blooms yet it is holoplanktonic and not much is known about its population dynamics in between. One way to gain insight on how M. leidyi might survive between blooms and how it can bloom so fast is to study how the metabolism of this species actually responds to environmental changes in food and temperature over its different life-stages. To this end we combined modelling and data analysis to study the energy budget of M. leidyi over its full life-cycle using Dynamic Energy Budget (DEB) theory and literature data. An analysis of data obtained at temperatures ranging from 8 to 30 °C suggests that the optimum thermal tolerance range of M. leidyi is higher than 12 °C. Furthermore M. leidyi seems to undergo a so-called metabolic acceleration after hatching. Intriguingly, the onset of the acceleration appears to be delayed and the data do not yet exist which allows determining what actually triggers it. It is hypothesised that this delay confers a lot of metabolic flexibility by controlling generation time. We compared the DEB model parameters for this species with those of another holoplanktonic gelatinous zooplankton species (Pelagia noctiluca). After accounting for differences in water content, the comparison shows just how fundamentally different the two energy allocation strategies are. P. noctiluca has an extremely high reserve capacity, low turnover times of reserve compounds and high resistance to shrinking. M. leidyi adopts the opposite strategy: it has a low reserve capacity, high turnover rates of reserve compounds and fast shrinking.

  5. Brillouin-enhanced hyperparametric generation of an optical frequency comb in a monolithic highly nonlinear fiber cavity pumped by a cw laser.

    PubMed

    Braje, Danielle; Hollberg, Leo; Diddams, Scott

    2009-05-15

    We demonstrate self-seeded generation of a broadband comb in a highly nonlinear fiber resonator. When pumped with a cw laser, the fiber cavity generates a comb with two characteristic spacings. Hyperparametric modes spaced by approximately 2 THz create the base structure of the comb, while commensurate Brillouin modes spaced by approximately 10 GHz populate the intermediate frequency gaps. The frequency modes are coherent, and the repetition rate of the comb has been locked to a microwave standard. PMID:19518952

  6. Mode-locked dark pulse Kerr combs in normal-dispersion microresonators

    NASA Astrophysics Data System (ADS)

    Xue, Xiaoxiao; Xuan, Yi; Liu, Yang; Wang, Pei-Hsun; Chen, Steven; Wang, Jian; Leaird, Dan E.; Qi, Minghao; Weiner, Andrew M.

    2015-09-01

    The generation of Kerr frequency combs in a coherently driven nonlinear microresonator is now extensively investigated more generally by the research community as a potentially portable technology for a variety of applications. Here, we report experiments in which dark pulse combs are formed in normal-dispersion microresonators with mode-interaction-assisted excitation, and mode-locking transitions are observed in the normal-dispersion regime. The mode-interaction-aided excitation of dark pulses appears to occur through a deterministic pathway, in sharp contrast to the situation for bright pulses in the anomalous dispersion region. The ability to mode-lock in the normal-dispersion regime increases the freedom in the microresonator design and may make it possible to extend Kerr comb generation into the visible, where material dispersion is likely to dominate.

  7. Molecular Combing of Single DNA Molecules on the 10 Megabase Scale

    PubMed Central

    Kaykov, Atanas; Taillefumier, Thibaud; Bensimon, Aaron; Nurse, Paul

    2016-01-01

    DNA combing allows the investigation of DNA replication on genomic single DNA molecules, but the lengths that can be analysed have been restricted to molecules of 200–500 kb. We have improved the DNA combing procedure so that DNA molecules can be analysed up to the length of entire chromosomes in fission yeast and up to 12 Mb fragments in human cells. Combing multi-Mb-scale DNA molecules revealed previously undetected origin clusters in fission yeast and shows that in human cells replication origins fire stochastically forming clusters of fired origins with an average size of 370 kb. We estimate that a single human cell forms around 3200 clusters at mid S-phase and fires approximately 100,000 origins to complete genome duplication. The procedure presented here will be adaptable to other organisms and experimental conditions. PMID:26781994

  8. Fast wavelength calibration method for spectrometers based on waveguide comb optical filter

    SciTech Connect

    Yu, Zhengang; Huang, Meizhen Zou, Ye; Wang, Yang; Sun, Zhenhua; Cao, Zhuangqi

    2015-04-15

    A novel fast wavelength calibration method for spectrometers based on a standard spectrometer and a double metal-cladding waveguide comb optical filter (WCOF) is proposed and demonstrated. By using the WCOF device, a wide-spectrum beam is comb-filtered, which is very suitable for spectrometer wavelength calibration. The influence of waveguide filters structural parameters and the beam incident angle on the comb absorption peaks wavelength and its bandwidth are also discussed. The verification experiments were carried out in the wavelength range of 2001100 nm with satisfactory results. Comparing with the traditional wavelength calibration method based on discrete sparse atomic emission or absorption lines, the new method has some advantages: sufficient calibration data, high accuracy, short calibration time, fit for produce process, stability, etc.

  9. Evaluating the performance of the NPL femtosecond frequency combs: agreement at the 10-21 level

    NASA Astrophysics Data System (ADS)

    Johnson, L. A. M.; Gill, P.; Margolis, H. S.

    2015-02-01

    Results are presented from a series of comparisons between two independent femtosecond frequency comb systems at NPL, which were carried out in order to assess their systematic uncertainty. Simultaneous measurements with the two systems demonstrate agreement at the level of 5 10-18 when measuring an optical frequency against a common microwave reference. When simultaneously measuring the ratio of two optical frequencies, agreement at the 3 10-21 level is observed. The results represent the highest reported level of agreement to date between Ti:Sapphire and Er-doped femtosecond combs. The limitations of the combs when operating in these two different manners are discussed, including traceability to the SI second, which can be achieved with an uncertainty below 1 10-16. The technical details presented underpin recent absolute frequency measurements of the 88Sr+ and 171Yb+ optical clock transitions at NPL, as well as a frequency ratio measurement between the two optical clock transitions in 171Yb+.

  10. Parameter optimization of a dual-comb ranging system by using a numerical simulation method.

    PubMed

    Wu, Guanhao; Xiong, Shilin; Ni, Kai; Zhu, Zebin; Zhou, Qian

    2015-12-14

    Dual-comb system parameters have significant impacts on the ranging accuracy. We present a theoretical model and a numerical simulation method for the parameter optimization of a dual-comb ranging system. With this method we investigate the impacts of repetition rate difference, repetition rate, and carrier-envelope-offset frequency on the ranging accuracy. Firstly, the simulation results suggest a series of discrete zones of repetition rate difference in an optimal range, which are consistent with the experimental results. Secondly, the simulation results of the repetition rate indicate that a higher repetition rate is very favorable to improve the ranging accuracy. Finally, the simulation results suggest a series of discrete optimal ranges of the carrier-envelope-offset frequency for the dual-comb system. The simulated results were verified by our experiments. PMID:26698995

  11. Molecular Combing of Single DNA Molecules on the 10 Megabase Scale.

    PubMed

    Kaykov, Atanas; Taillefumier, Thibaud; Bensimon, Aaron; Nurse, Paul

    2016-01-01

    DNA combing allows the investigation of DNA replication on genomic single DNA molecules, but the lengths that can be analysed have been restricted to molecules of 200-500?kb. We have improved the DNA combing procedure so that DNA molecules can be analysed up to the length of entire chromosomes in fission yeast and up to 12?Mb fragments in human cells. Combing multi-Mb-scale DNA molecules revealed previously undetected origin clusters in fission yeast and shows that in human cells replication origins fire stochastically forming clusters of fired origins with an average size of 370?kb. We estimate that a single human cell forms around 3200 clusters at mid S-phase and fires approximately 100,000 origins to complete genome duplication. The procedure presented here will be adaptable to other organisms and experimental conditions. PMID:26781994

  12. Dual electro-optic optical frequency combs for multiheterodyne molecular dispersion spectroscopy.

    PubMed

    Martn-Mateos, Pedro; Jerez, Borja; Acedo, Pablo

    2015-08-10

    In this paper, a multiheterodyne architecture for molecular dispersion spectroscopy based on a coherent dual-comb source generated using a single continuous wave laser and electro-optic modulators is presented and validated. The phase-sensitive scheme greatly simplifies previous dual-comb implementations by the use of an electro-optic dual comb and by phase-locking all the signal generators of the setup eliminating, in this way, the necessity of any reference optical path currently mandatory in absorption-based instruments. The architecture is immune to the classical baseline and normalization problems of absorption-based analyzers and provides an output linearly dependent on the gas concentration. In addition, the simultaneous parallel multi-wavelength measurement approach has the ability to deliver an improved output bandwidth (measurement speed) over gas analyzers based on tunable lasers. PMID:26367964

  13. Comparison analysis of optical frequency comb generation with nonlinear effects in highly nonlinear fibers.

    PubMed

    Yang, Ting; Dong, Jianji; Liao, Shasha; Huang, Dexiu; Zhang, Xinliang

    2013-04-01

    We compare several schemes for broadband optical frequency comb (OFC) generation based on several nonlinear effects in highly nonlinear fiber (HNLF). Cascaded four wave mixing (CFWM) and self-phase modulation (SPM) processes in HNLF are proved to be effective ways for spectrum broadening. We investigate some parameters affecting the performance of the output OFC in detail. When only CFWM occurs in the HNLF, broadband OFC can be generated with poor power flatness. When only SPM occurs in the HNLF, we obtain a 10 GHz OFC of 103 comb lines within 5-dB power deviation. When both CFWM and SPM simultaneously occur in the HNLF, we obtain a 10 GHz OFC of 143 comb lines within 4.5-dB power deviation. All the OFC generation schemes have the advantages of tunability of central wavelength and repetition frequency. PMID:23571940

  14. Generation of a 660-2100 nm laser frequency comb based on an erbium fiber laser.

    PubMed

    Ycas, Gabriel; Osterman, Steve; Diddams, Scott A

    2012-06-15

    We present a multibranch laser frequency comb based upon a 250 MHz mode-locked erbium-doped fiber laser that spans more than 300 THz of bandwidth, from 660 nm to 2100 nm. Light from a mode-locked Er:fiber laser is amplified and then broadened in highly-nonlinear fiber to produce substantial power at ?1050??nm. This light is subsequently amplified in Yb:fiber to produce 1.2 nJ, 73 fs pulses at 1040 nm. Extension of the frequency comb into the visible is achieved by supercontinuum generation from the 1040 nm light. Comb coherence is verified with cascaded f-2f interferometry and comparison to a frequency stabilized laser. PMID:22739854

  15. Recent developments in fiber-based optical frequency comb and its applications

    NASA Astrophysics Data System (ADS)

    Xia, Wei; Chen, Xuzong

    2016-04-01

    Fiber-based optical frequency combs, characterized by compact configuration and outstanding optical properties, have been developed into state-of-the-art precision instruments which are no longer used just for optical frequency metrology, but for a number of applications, including optical clocks, attosecond science, exoplanet searches, medical diagnostics, physicochemical processes control and advanced manufacturing. This short perspective presents some of the milestones and highlights in the evolution of fiber-based optical frequency combs and the technical revolution that are brought by them for a wide range of applications. Along the way, both the challenges and opportunities in the future development of the fiber-based optical frequency comb technology have been described as well.

  16. A novel frequency control scheme for comb-referenced sensitive difference-frequency-generation spectroscopy.

    PubMed

    Iwakuni, Kana; Okubo, Sho; Sasada, Hiroyuki

    2013-06-17

    We present a novel scheme of frequency scan and wavelength modulation of a difference-frequency-generation source for comb-referenced sensitive spectroscopy. While the pump and signal frequencies are phase-locked to an optical frequency comb (OFC), the offset frequency between the signal wave and the nearest comb tooth is modulated to apply a wavelength-modulation technique, and the idler wave frequency is repeatedly swept for signal accumulation by changing the repetition frequency of the OFC. The spectrometer is applied to absolute frequency measurement of weak hyperfine-resolved rovibration transitions of the ?(1) band of CH(3)I, and the uncertainty in frequency determination is reduced by one order of magnitude in compared with that of the previous work published in Optics Express 20, 9178-9186 (2012). PMID:23787670

  17. Mach-zehnder based optical marker/comb generator for streak camera calibration

    SciTech Connect

    Miller, Edward Kirk

    2015-03-03

    This disclosure is directed to a method and apparatus for generating marker and comb indicia in an optical environment using a Mach-Zehnder (M-Z) modulator. High speed recording devices are configured to record image or other data defining a high speed event. To calibrate and establish time reference, the markers or combs are indicia which serve as timing pulses (markers) or a constant-frequency train of optical pulses (comb) to be imaged on a streak camera for accurate time based calibration and time reference. The system includes a camera, an optic signal generator which provides an optic signal to an M-Z modulator and biasing and modulation signal generators configured to provide input to the M-Z modulator. An optical reference signal is provided to the M-Z modulator. The M-Z modulator modulates the reference signal to a higher frequency optical signal which is output through a fiber coupled link to the streak camera.

  18. A Novel Comb Architecture for Enhancing the Sensitivity of Bulk Mode Gyroscopes

    PubMed Central

    Elsayed, Mohannad Y.; Nabki, Frederic; El-Gamal, Mourad N.

    2013-01-01

    This work introduces a novel architecture for increasing the sensitivity of bulk mode gyroscopes. It is based on adding parallel plate comb drives to the points of maximum vibration amplitude, and tuning the stiffness of the combs. This increases the drive strength and results in a significant sensitivity improvement. The architecture is targeted for technologies with ?100 nm transducer gaps in order to achieve very high performance devices. In this work, this sensitivity enhancement concept was implemented in SOIMUMPs, a commercial relatively large gap technology. Prototypes were measured to operate at frequencies of ?1.5 MHz, with quality factors of ?33,000, at a 10 mTorr vacuum level. Measurements using discrete electronics show a rate sensitivity of 0.31 ?V//s, corresponding to a capacitance sensitivity of 0.43 aF//s/electrode, two orders of magnitude higher than a similar design without combs, fabricated in the same technology.

  19. Mid-infrared frequency comb generation in coupled silicon microring resonators

    NASA Astrophysics Data System (ADS)

    Zhang, Xuezhi; Liu, Tiegen; Jiang, Junfeng; Feng, Ming; Liu, Kun

    2014-12-01

    We propose and simulate an on-chip mid-IR frequency comb generator based on the four-wave mixing (FWM) effect in a coupled silicon microring resonator. The resonator is formed by suspended ridge waveguides that are designed to have low group-velocity dispersion. A continuous-wave pump laser coupled into the resonator excites other longitudinal modes of the resonator through FWM-based parametric oscillations. In comparison with the device based on a single-ring resonator, we numerically demonstrate that the pump threshold can be dramatically reduced by introducing an auxiliary ring resonator to compensate the phase mismatch between the pump and the generated comb components. The proposed frequency comb generator has a low pump threshold of ~40 mW and a high efficiency of ~25% at the pump power of 100 mW.

  20. Doppler cooling with coherent trains of laser pulses and a tunable velocity comb

    SciTech Connect

    Ilinova, Ekaterina; Ahmad, Mahmoud; Derevianko, Andrei

    2011-09-15

    We explore the possibility of decelerating and Doppler cooling an ensemble of two-level atoms by a coherent train of short, nonoverlapping laser pulses. We derive analytical expressions for mechanical force exerted by the train. In frequency space the force pattern reflects the underlying frequency comb structure. The pattern depends strongly on the ratio of the atomic lifetime to the repetition time between the pulses and pulse area. For example, in the limit of short lifetimes, the frequency-space peaks of the optical force wash out. We propose to tune the carrier-envelope offset frequency to follow the Doppler-shifted detuning as atoms decelerate; this leads to compression of atomic velocity distribution about comb teeth and results in a ''velocity comb''--a series of narrow equidistant peaks in the velocity space.

  1. Doppler-Limited Spectroscopy with a Decade-Spanning Terahertz Frequency Comb

    NASA Astrophysics Data System (ADS)

    Finneran, Ian A.; Good, Jacob T.; Holland, Daniel; Carroll, Brandon; Allodi, Marco A.; Blake, Geoffrey

    2015-06-01

    We report the generation and detection of a decade-spanning TeraHertz (THz) frequency comb (0.15-2.4 THz) using two Ti:Sapphire femtosecond laser oscillators and ASynchronous OPtical Sampling THz Time-Domain Spectroscopy (ASOPS-THz-TDS). The measured linewidth of the comb at 1.5 THz is 3 kHz over a 60 second acquisition. With time-domain detection of the comb, we measure three transitions of water vapor at 10 mTorr between 1-2 THz with an average Doppler-limited fractional uncertainty of 5.910-8. Significant improvements in bandwidth, resolution, and sensitivity are possible with existing technologies and will enable future studies of jet-cooled hydrogen-bonded clusters.

  2. 75 FR 11559 - Certain Combed Cotton Yarns: Effect of Modification of U.S.-Bahrain FTA Rules of Origin

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-11

    ... COMMISSION Certain Combed Cotton Yarns: Effect of Modification of U.S.- Bahrain FTA Rules of Origin AGENCY...-103-025, Certain Combed Cotton Yarns: Effect of Modification of U.S.-Bahrain FTA Rules Of Origin... effect of the proposed modifications on U.S. trade under the U.S.-Bahrain FTA, total U.S. trade, and...

  3. Draft Genome Sequence of Empedobacter (Formerly Wautersiella) falsenii comb. nov. Wf282, a Strain Isolated from a Cervical Neck Abscess.

    PubMed

    Traglia, German Matías; Dixon, Chelsea; Chiem, Kevin; Almuzara, Marisa; Barberis, Claudia; Montaña, Sabrina; Merino, Cindy; Mussi, María Alejandra; Tolmasky, Marcelo E; Iriarte, Andres; Vay, Carlos; Ramírez, María Soledad

    2015-01-01

    Empedobacter (formerly Wautersiella) falsenii comb. nov. strain Wf282 was isolated from a cervical neck abscess sample from an 18-year-old female patient. The isolate was resistant to many antibiotics, including meropenem and colistin. The total DNA from the multidrug-resistant E. falsenii comb. nov. Wf282 clinical isolate was sequenced. PMID:25838490

  4. Draft Genome Sequence of Empedobacter (Formerly Wautersiella) falsenii comb. nov. Wf282, a Strain Isolated from a Cervical Neck Abscess

    PubMed Central

    Traglia, German Matías; Dixon, Chelsea; Chiem, Kevin; Almuzara, Marisa; Barberis, Claudia; Montaña, Sabrina; Merino, Cindy; Mussi, María Alejandra; Tolmasky, Marcelo E.; Iriarte, Andres; Vay, Carlos

    2015-01-01

    Empedobacter (formerly Wautersiella) falsenii comb. nov. strain Wf282 was isolated from a cervical neck abscess sample from an 18-year-old female patient. The isolate was resistant to many antibiotics, including meropenem and colistin. The total DNA from the multidrug-resistant E. falsenii comb. nov. Wf282 clinical isolate was sequenced. PMID:25838490

  5. Phylogenetic analyses of the genus Glaciecola: emended description of the genus Glaciecola, transfer of Glaciecola mesophila, G. agarilytica, G. aquimarina, G. arctica, G. chathamensis, G. polaris and G. psychrophila to the genus Paraglaciecola gen. nov. as Paraglaciecola mesophila comb. nov., P. agarilytica comb. nov., P. aquimarina comb. nov., P. arctica comb. nov., P. chathamensis comb. nov., P. polaris comb. nov. and P. psychrophila comb. nov., and description of Paraglaciecola oceanifecundans sp. nov., isolated from the Southern Ocean.

    PubMed

    Shivaji, Sisinthy; Reddy, Gundlapally Sathyanarayana

    2014-09-01

    Phylogenetic analyses of the genus Glaciecola were performed using the sequences of the 16S rRNA gene and the GyrB protein to establish its taxonomic status. The results indicated a consistent clustering of the genus Glaciecola into two clades, with significant bootstrap values, with all the phylogenetic methods employed. Clade 1 was represented by seven species, Glaciecola agarilytica, G. aquimarina, G. arctica, G. chathamensis, G. mesophila, G. polaris and G. psychrophila, while clade 2 consisted of only three species, Glaciecola nitratireducens, G. pallidula and G. punicea. Evolutionary distances between species of clades 1 and 2, based on 16S rRNA gene and GyrB protein sequences, ranged from 93.0 to 95.0?% and 69.0 to 73.0?%, respectively. In addition, clades 1 and 2 possessed 18 unique signature nucleotides, at positions 132, 184?:?193, 185?:?192, 230, 616?:?624, 631, 632, 633, 738, 829, 1257, 1265, 1281, 1356 and 1366, in the 16S rRNA gene sequence and can be differentiated by the occurrence of a 15 nt signature motif 5'-CAAATCAGAATGTTG at positions 1354-1368 in members of clade 2. Robust clustering of the genus Glaciecola into two clades based on analysis of 16S rRNA gene and GyrB protein sequences, 16S rRNA gene sequence similarity of ?95.0?% and the occurrence of signature nucleotides and signature motifs in the 16S rRNA gene suggested that the genus should be split into two genera. The genus Paraglaciecola gen. nov. is therefore created to accommodate the seven species of clade 1, while the name Glaciecola sensu stricto is retained to represent species of clade 2. The species of clade 1 are transferred to the genus Paraglaciecola as Paraglaciecola mesophila comb. nov. (type strain DSM 15026(T)?=?KMM 241(T)), P. agarilytica comb. nov. (type strain NO2(T)?=?KCTC 12755(T)?=?LMG 23762(T)), P. aquimarina comb. nov. (type strain GGW-M5(T)?=?KCTC 32108(T)?=?CCUG 62918(T)), P. arctica comb. nov. (type strain BSs20135(T)?=?CCTCC AB 209161(T)?=?KACC 14537(T)), P. chathamensis comb. nov. (type strain E3(T)?=?CGMCC 1.7001(T)?=?JCM 15139(T)), P. polaris comb. nov. (type strain ARK 150(T)?=?CIP 108324(T)?=?LMG 21857(T)) and P. psychrophila comb. nov. (type strain 170(T)?=?CGMCC1.6130(T)?=?JCM 13954(T)). The type species of the genus Paraglaciecola is Paraglaciecola mesophila. An emended description of the genus Glaciecola is provided. In addition, a novel strain, 162Z-12(T), was isolated from seawater collected as part of an iron fertilization experiment (LOHAFEX) conducted in the Southern Ocean in 2009 and was subjected to polyphasic taxonomic characterization. Cells of 162Z-12(T) were Gram-negative, aerobic, motile, ovoid to short rod-shaped, obligatorily halophilic and possessed all the characteristics of the genus Paraglaciecola. Strain 162Z-12(T) shared the highest 16S rRNA gene sequence similarity with the type strains of P. agarilytica (99.7?%), P. chathamensis (99.7?%), P. mesophila (98.5?%) and P. polaris (98.3?%). However, it exhibited DNA-DNA relatedness of less than 70.0?% with its nearest phylogenetic relatives, well below the threshold value for species delineation. Further, strain 162Z-12(T) differed from the nearest species in several phenotypic characteristics, in addition to the occurrence of unique nucleotides G, T, T and T at positions 1194, 1269, 1270 and 1271 of the 16S rRNA gene. Based on the cumulative differences it exhibited from its nearest phylogenetic neighbours, strain 162Z-12(T) was identified as a novel member of the genus Paraglaciecola and assigned to the novel species Paraglaciecola oceanifecundans sp. nov. The type strain of Paraglaciecola oceanifecundans is 162Z-12(T) (?=?KCTC 32337(T)?=?LMG 27453(T)). PMID:24981324

  6. Use of DNA combing to study DNA replication in Xenopus and human cell-free systems.

    PubMed

    Marheineke, Kathrin; Goldar, Arach; Krude, Torsten; Hyrien, Olivier

    2009-01-01

    The Xenopus egg extract has become the gold standard for in vitro studies of metazoan DNA replication. We have used this system to study the mechanisms that ensure rapid and complete DNA replication despite random initiation during Xenopus early development. To this end we adapted the DNA combing technique to investigate the distribution of replication bubbles along single DNA molecules. DNA replicating in egg extracts is labelled by addition of digoxigenin-11-dUTP and/or biotin-16-dUTP at precise times. These two dTTP analogues are efficiently incorporated into DNA during replication in the extract. After DNA purification and combing the DNA is visualized with appropriate fluorescent antibody/streptavidin molecules. Replicated DNA appears as green or red tracts whose pattern reveals how each molecule was replicated, allowing to follow the dynamics of DNA replication through S phase. We describe (a) the preparation and use of egg extracts and demembranated sperm chromatin templates; (b) a simple method for preparing silanized glass coverslips suitable for DNA combing and fluorescence detection; (c) two alternative replicative DNA labelling schemes and their respective advantages; and (d) a protocol for combining replicative labelling with detection of specific DNA sequences by fluorescent in situ hybridization (FISH). Although most observations made in Xenopus egg extracts are applicable to other eukaryotes, there are differences in cell-cycle regulation between mammalian somatic cells and embryonic amphibian cells, which led to the development of human cell-free systems that can initiate semi-conservative chromosomal DNA replication under cell-cycle control. We have employed the knowledge gained with Xenopus extracts to characterize DNA replication intermediates generated in human cell-free systems using DNA combing. We describe here (a) the preparation and use of human cell-free extracts and initiation-competent template nuclei for DNA combing studies; (b) an optimized labelling scheme for DNA replication intermediates by molecular combing and fluorescence microscopy. PMID:19563130

  7. Near infrared standard sources, generated by electro-optic frequency comb, using injection-locked DFB laser

    NASA Astrophysics Data System (ADS)

    Lee, Sung Hun; Suh, Ho Suhng

    2014-02-01

    Stable, near-infrared laser sources were generated by an electro-optic modulator with selected comb-mode seeding. The single comb mode was selected from the fiber laser comb using a Fabry-Prot cavity (FPC) of 1.25 GHz spacing, and injection locking technique. An electro-optic frequency comb (EOFC) with spacing of 25 GHz was generated as the side mode of the injection-locked comb mode. Using a single mode of the EOFC, we measured the frequency of the acetylene stabilized laser used as the calibration reference frequency light source for optical communication. The absolute frequency and estimated stability of the acetylene stabilized laser were 194 369 569 384.6 kHz and 2.310-12 (average time 1 s), respectively.

  8. Numerical investigation into the injection-locking phenomena of gain switched lasers for optical frequency comb generation

    SciTech Connect

    Dill, Sean P. Anandarajah, Prince M.; Zhou, Rui; Barry, Liam P.

    2015-05-25

    We present detailed numerical simulations of the laser dynamics that describe optical frequency comb formation by injection-locking a gain-switched laser. The typical rate equations for semiconductor lasers including stochastic carrier recombination and spontaneous emission suffice to show the injection-locking behavior of gain switched lasers, and we show how the optical frequency comb evolves starting from the free-running state, right through the final injection-locked state. Unlike the locking of continuous wave lasers, we show that the locking range for gain switched lasers is considerably greater because injection locking can be achieved by injecting at frequencies close to one of the comb lines. The quality of the comb lines is formally assessed by calculating the frequency modulation (FM)-noise spectral density and we show that under injection-locking conditions the FM-noise spectral density of the comb lines tend to that of the maser laser.

  9. Integrated frequency comb source based Hilbert transformer for wideband microwave photonic phase analysis.

    PubMed

    Nguyen, Thach G; Shoeiby, Mehrdad; Chu, Sai T; Little, Brent E; Morandotti, Roberto; Mitchell, Arnan; Moss, David J

    2015-08-24

    We demonstrate a photonic RF Hilbert transformer for broadband microwave in-phase and quadrature-phase generation based on an integrated frequency optical comb, generated using a nonlinear microring resonator based on a CMOS compatible, high-index contrast, doped-silica glass platform. The high quality and large frequency spacing of the comb enables filters with up to 20 taps, allowing us to demonstrate a quadrature filter with more than a 5-octave (3 dB) bandwidth and an almost uniform phase response. PMID:26368182

  10. Application of Laser Frequency Combs and Nitrogen Vacancy Diamond Magnetometers to Searches for New Physics

    NASA Astrophysics Data System (ADS)

    Phillips, D. F.; Walsworth, R. L.

    2014-01-01

    Searches for new physics often benefit from improved technologies. Here we discuss possible applications of two emerging technologies to searches for physics beyond the Standard Model. First, laser frequency combs enable broad spectral coverage and coherent conversion between optical and RF signals. We are investigating tests of the nonminimal Standard-Model Extension using frequency combs coupled to broadband optical cavities. Second, nitrogen vacancy centers in diamond enable precision nanoscale magnetometry with applications from imaging to quantum science. We are investigating their use in searches for short-range spin-spin couplings.

  11. High order SSB modulation and its application for advanced optical comb generation based on RFS

    NASA Astrophysics Data System (ADS)

    Sun, Lin; Du, Jiangbing; Li, Lu; He, Zuyuan

    2015-11-01

    In this work, a method for high-order single sideband (SSB) modulation is demonstrated. Extended frequency shifting can be obtained based on the high-order SSB modulator. The design of the 2nd and 3rd order SSB modulators are presented and investigated based on simulations. The demonstrated high-order SSB modulators can be used for advanced optical comb generation when they are configured in recirculating frequency shifter (RFS). Optical comb with significantly enlarged carrier-to-carrier spacing can be obtained and thus applications including wavelength division multiplexing (WDM) communication, optical frequency domain reflectometry (OFDR) and so on can be benefited.

  12. Analysis of the second harmonic generation of a femtosecond optical frequency comb

    NASA Astrophysics Data System (ADS)

    Wei, Dong; Aketagawa, Masato

    2014-12-01

    The second harmonic generation (SHG) of a femtosecond optical frequency comb (FOFC) has been studied. This work focuses on the SHG frequencies that are generated by the mixing of even-numbered frequency components from the original comb with odd-numbered components. It is observed that the generation of those frequencies is the reason the original FOFC and FOFC-based SHG signal have the same repetition frequency. The theoretical derivation agrees with the result of an optical experiment. Our results may be of use with the high-harmonic-generation process and FOFC-based SHG applications, including high-resolution spectroscopy, attosecond pulse generation, and precision length measurement.

  13. Evidence for frequency comb emission from a Fabry-Prot terahertz quantum-cascade laser.

    PubMed

    Wienold, M; Rben, B; Schrottke, L; Grahn, H T

    2014-12-15

    We report on a broad-band terahertz quantum-cascade laser (QCL) with a long Fabry-Prot ridge cavity, for which the tuning range of the individual laser modes exceeds the mode spacing. While a spectral range of approximately 60 GHz (2 cm(-1)) is continuously covered by current and temperature tuning, the total emission range spans more than 270 GHz (9 cm(-1)). Within certain operating ranges, we found evidence for stable frequency comb operation of the QCL. An experimental technique is presented to characterize frequency comb operation, which is based on the self-mixing effect. PMID:25606987

  14. Effects of multiphoton absorption on parametric comb generation in silicon microresonators.

    PubMed

    Lau, Ryan K W; Lamont, Michael R E; Okawachi, Yoshitomo; Gaeta, Alexander L

    2015-06-15

    We investigate theoretically the parametric frequency comb generation in silicon microresonators at telecom and mid-infrared (MIR) wavelengths in the presence of multiphoton absorption and free-carrier effects using a modified Lugiato-Lefever model. We show that parametric oscillation may occur at MIR wavelengths, provided that the free-carrier lifetime is sufficiently short or the optical pump power is sufficiently low, but is inhibited at telecom wavelengths. In addition, we propose an etchless, air-clad silicon microresonator that enables an octave-spanning frequency comb in a completely passive device. PMID:26076260

  15. Flat frequency comb generation based on efficiently multiple four-wave mixing without polarization control

    NASA Astrophysics Data System (ADS)

    Dong, Qimeng; Sun, Bao; Chen, Fushen; Jiang, Jun

    2015-09-01

    This paper presents a new technique for flat optical frequency comb (OFC) generation, which is based on the nonlinear process of multiple four-wave mixing (FWM) effects. The nonlinear effects are significantly enhanced by using the proposed optical feedback scheme consisting of a single mode fiber (SMF), two highly nonlinear fibers (HNLFs) with different zero dispersion wavelengths (ZDWs) and polarization beam splitters (PBSs). Simulation results illustrate its efficiency and applicability of expanding a comb to 128 coherent lines spaced by only 20 GHz within 6-dB power deviation.

  16. Optical Nyquist channel generation using a comb-based tunable optical tapped-delay-line.

    PubMed

    Ziyadi, Morteza; Chitgarha, Mohammad Reza; Mohajerin-Ariaei, Amirhossein; Khaleghi, Salman; Almaiman, Ahmed; Cao, Yinwen; Willner, Moshe J; Tur, Moshe; Paraschis, Loukas; Langrock, Carsten; Fejer, Martin M; Touch, Joseph D; Willner, Alan E

    2014-12-01

    We demonstrate optical Nyquist channel generation based on a comb-based optical tapped-delay-line. The frequency lines of an optical frequency comb are used as the taps of the optical tapped-delay-line to perform a finite-impulse response (FIR) filter function. A single optical nonlinear element is utilized to multiplex the taps and form the Nyquist signal. The tunablity of the approach over the baud rate and modulation format is shown. Optical signal-to-noise ratio penalty of 2.8 dB is measured for the 11-tap Nyquist filtering of 32-Gbaud QPSK signal. PMID:25490627

  17. Radiative effects driven by shock waves in cavity-less four-wave mixing combs.

    PubMed

    Conforti, Matteo; Trillo, Stefano

    2014-10-01

    We investigate the frequency comb spectrum produced in an optical fiber via multiple four-wave mixing pumped in the normal group-velocity region close to the zero-dispersion wavelength. We show that the dynamics are strongly affected by shock formation. In this regime, the resonant radiation emitted by the shock waves correctly explains the enhanced spectral peaks in the comb. The resonant frequencies found by means of perturbation theory accurately fit those observed from the numerical simulation based on the generalized nonlinear Schrdinger equation. PMID:25360978

  18. Improvement of flatness of optical frequency comb based on nonlinear effect of intensity modulator.

    PubMed

    Dou, Yujie; Zhang, Hongming; Yao, Minyu

    2011-07-15

    Optical frequency comb (OFC) generated using cascaded intensity and phase modulators was experimentally demonstrated. Very flat OFC can be achieved by cascading intensity and phase modulators driven directly by sinusoidal waveform, where chirped fiber Bragg grating or specially tailored radio frequency waveforms are not required. It is found that the spectral flatness of OFC is related to direct current (DC) bias of intensity modulator and the optimum ratio of DC bias to half-wave voltage is 0.35. In the experiment, 15 comb lines within 1 dB spectral power variation are obtained at 10 GHz microwave frequency. The experimental results agree well with the simulation. PMID:21765530

  19. Surface acoustic wave opto-mechanical oscillator and frequency comb generator.

    PubMed

    Savchenkov, A A; Matsko, A B; Ilchenko, V S; Seidel, D; Maleki, L

    2011-09-01

    We report on realization of an efficient triply resonant coupling between two long lived optical modes and a high frequency surface acoustic wave (SAW) mode of the same monolithic crystalline whispering gallery mode resonator. The coupling results in an opto-mechanical oscillation and generation of a monochromatic SAW. A strong nonlinear interaction of this mechanical mode with other equidistant SAW modes leads to mechanical hyperparametric oscillation and generation of a SAW pulse train and associated frequency comb in the resonator. We visualized the comb by observing the modulation of the light escaping the resonator. PMID:21886203

  20. Er-doped fiber frequency comb with mHz relative linewidth.

    PubMed

    Kim, Yunseok; Kim, Seungman; Kim, Young-Jin; Hussein, Hatem; Kim, Seung-Woo

    2009-07-01

    A low-noise fiber frequency comb is demonstrated to improve the frequency accuracy and linewidth by suppressing the phase noise caused by the nonlinear self-phase modulation as well as the amplified spontaneous emission within the Er-doped fiber amplifier. The linewidth of the carrier-envelop- offset signal measures less than 1.9 mHz and the frequency stability well follows the reference Rb clock. This achievement will facilitate the use of the fiber frequency comb for industrial applications to precision near-infrared spectroscopy, frequency calibration, optical clocks and length metrology. PMID:19582112

  1. Widely-tunable mid-infrared frequency comb source based on difference frequency generation.

    PubMed

    Ruehl, Axel; Gambetta, Alessio; Hartl, Ingmar; Fermann, Martin E; Eikema, Kjeld S E; Marangoni, Marco

    2012-06-15

    We report on a mid-IR frequency comb source of unprecedented tunability covering the entire 3-10 ?m molecular fingerprint region. The system is based on difference frequency generation in a GaSe crystal pumped by a 151 MHz Yb:fiber frequency comb. The process was seeded with Raman-shifted solitons generated in a highly nonlinear suspended-core fiber with the same source. Average powers up to 1.5 mW were achieved at the 4.7 ?m wavelength. PMID:22739865

  2. Spatial frequency combs and supercontinuum generation in one-dimensional photonic lattices.

    PubMed

    Dong, Rong; Rter, Christian E; Kip, Detlef; Manela, Ofer; Segev, Mordechai; Yang, Chengliang; Xu, Jingjun

    2008-10-31

    We experimentally demonstrate the formation of spatial supercontinuum and of spatial frequency combs in nonlinear photonic lattices. This process results from multiple four-wave mixing initiated by launching two Floquet-Bloch modes into a one-dimensional lattice. The dynamics of the waves is sensitively dependent on the transverse momentum difference between the two initial modes: when this momentum difference is commensurable with the lattice momentum the waves evolve into a frequency comb, whereas when it is incommensurable the waves evolve into a supercontinuum of spatial frequencies. PMID:18999833

  3. Direct link of a mid-infrared QCL to a frequency comb by optical injection.

    PubMed

    Borri, S; Galli, I; Cappelli, F; Bismuto, A; Bartalini, S; Cancio, P; Giusfredi, G; Mazzotti, D; Faist, J; De Natale, P

    2012-03-15

    A narrow-linewidth comb-linked nonlinear source is used as master radiation to injection lock a room-temperature mid-infrared quantum cascade laser (QCL). This process leads to a direct lock of the QCL to the optical frequency comb, providing the unique features of narrow linewidth, absolute frequency, higher output power, and wide mode-hop-free tunability. The QCL reproduces the injected radiation within more than 94%, with a reduction of the frequency-noise spectral density by 3 to 4 orders of magnitude up to about 100 kHz, and a linewidth narrowing from a few MHz to 20 kHz. PMID:22446207

  4. High-resolution terahertz spectroscopy with a single tunable frequency comb.

    PubMed

    Skryl, A S; Pavelyev, D G; Tretyakov, M Y; Bakunov, M I

    2014-12-29

    We report an improvement of three orders of magnitude in the spectral resolution of a recently proposed single-comb terahertz spectroscopy [Opt. Lett.39, 5669 (2014)]. The improvement is achieved by using a femtosecond optical pulse train with a tunable repetition rate. Terahertz comb with tunable spectral line spacing generated by the train is detected via nonlinear mixing with a harmonic of a CW signal from a microwave frequency synthesizer. By applying this technique to the low-pressure gas spectroscopy, we achieved a 100 kHz spectral resolution in measuring separate absorption lines of the rotational manifold of fluoroform (CF3H). PMID:25607192

  5. Control of Four-Level Quantum Coherence via Discrete Spectral Shaping of an Optical Frequency Comb

    SciTech Connect

    Stowe, Matthew C.; Peer, Avi; Ye Jun

    2008-05-23

    We present experiments demonstrating high-resolution and wide-bandwidth coherent control of a four-level atomic system in a diamond configuration. A femtosecond frequency comb is used to excite a specific pair of two-photon transitions in cold {sup 87}Rb. The optical-phase-sensitive response of the closed-loop diamond system is studied by controlling the phase of the comb modes with a pulse shaper. Finally, the pulse shape is optimized resulting in a 256% increase in the two-photon transition rate by forcing constructive interference between the mode pairs detuned from an intermediate resonance.

  6. Investigation of frictional properties on wire combed PCC (Portland Cement Concrete) pavement surfaces

    NASA Astrophysics Data System (ADS)

    1982-09-01

    This report involves PCC Pavements constructed with surface textures produced by a wide variety of wire combs. A small amount of testing was also performed on PCCP with other textures as a follow up of previous research on frictional properties. A limited amount of noise evaluation by rating panels and sound level (dbA) meters was conducted to assist in selection of an optimum the spacing for wire combs on future PCC Pavement projects. Included in this report is a brief description of each major project with summaries of friction number tests, standpatch texture depth tests, and sound level measurements.

  7. Control of Four-Level Quantum Coherence via Discrete Spectral Shaping of an Optical Frequency Comb

    NASA Astrophysics Data System (ADS)

    Stowe, Matthew C.; Pe'Er, Avi; Ye, Jun

    2008-05-01

    We present experiments demonstrating high-resolution and wide-bandwidth coherent control of a four-level atomic system in a diamond configuration. A femtosecond frequency comb is used to excite a specific pair of two-photon transitions in cold Rb87. The optical-phase-sensitive response of the closed-loop diamond system is studied by controlling the phase of the comb modes with a pulse shaper. Finally, the pulse shape is optimized resulting in a 256% increase in the two-photon transition rate by forcing constructive interference between the mode pairs detuned from an intermediate resonance.

  8. Pair-by-pair pulse shaping for optical arbitrary waveform generation by dual-comb heterodyne.

    PubMed

    Zhou, Xin; Zheng, Xiaoping; Wen, He; Zhang, Hanyi; Zhou, Bingkun

    2013-12-15

    We present a novel optical arbitrary waveform generation approach based on pair-by-pair pulse shaping. Based on the heterodyne between a pair of optical frequency combs with different repetition rates, the repetition rate of the generated signals can be flexibly tuned from MHz to GHz without changing the setup. The restriction of the spectral resolution of the optical spectrum processor is overcome by the pair-by-pair approach while the spectral resolution of the system can be improved to MHz by dual-comb heterodyne. Hyperfine control of a higher resolution spectrum at MHz is achieved, which benefits the generation of the ultrawideband signals. PMID:24322250

  9. Broadly tunable, low timing jitter, high repetition rate optoelectronic comb generator

    PubMed Central

    Metcalf, A. J.; Quinlan, F.; Fortier, T. M.; Diddams, S. A.; Weiner, A. M.

    2016-01-01

    We investigate the low timing jitter properties of a tunable single-pass optoelectronic frequency comb generator. The scheme is flexible in that both the repetition rate and center frequency can be continuously tuned. When operated with 10 GHz comb spacing, the integrated residual pulse-to-pulse timing jitter is 11.35 fs (1 Hz to 10 MHz) with no feedback stabilization. The corresponding phase noise at 1 Hz offset from the photodetected 10 GHz carrier is −100 dBc/Hz. PMID:26865734

  10. Comb-based radio-frequency photonic filtering with 20 ns bandwidth reconfiguration.

    PubMed

    Wu, Rui; Song, Minhyup; Leaird, Daniel E; Weiner, Andrew M

    2013-08-01

    We present a scheme to generate a 10 GHz optical frequency comb that is bandwidth reconfigurable on a time scale of tens of nanoseconds via electronic control of the drive signal to a phase modulator. When such a comb is used as the source for a radio-frequency (RF) photonic filter employing dispersive propagation, the RF filter bandwidth varies in inverse proportion to the optical bandwidth. As a result we are able to demonstrate, for the first time to our knowledge, bandwidth-reconfigurable RF filtering with transition times under 20 ns. The reconfiguration speed is determined by the response time of a programmable RF variable attenuator. PMID:23903127

  11. Coherent frequency combs produced by self frequency modulation in quantum cascade lasers

    SciTech Connect

    Khurgin, J. B.; Dikmelik, Y.; Hugi, A.; Faist, J.

    2014-02-24

    One salient characteristic of Quantum Cascade Laser (QCL) is its very short ????1?ps gain recovery time that so far thwarted the attempts to achieve self-mode locking of the device into a train of single pulses. We show theoretically that four wave mixing, combined with the short gain recovery time causes QCL to operate in the self-frequency-modulated regime characterized by a constant power in time domain and stable coherent comb in the frequency domain. Coherent frequency comb may enable many potential applications of QCL's in sensing and measurement.

  12. Flat frequency comb generation based on efficiently multiple four-wave mixing without polarization control

    NASA Astrophysics Data System (ADS)

    Dong, Qimeng; Sun, Bao; Chen, Fushen; Jiang, Jun

    2016-03-01

    This paper presents a new technique for flat optical frequency comb (OFC) generation, which is based on the nonlinear process of multiple four-wave mixing (FWM) effects. The nonlinear effects are significantly enhanced by using the proposed optical feedback scheme consisting of a single mode fiber (SMF), two highly nonlinear fibers (HNLFs) with different zero dispersion wavelengths (ZDWs) and polarization beam splitters (PBSs). Simulation results illustrate its efficiency and applicability of expanding a comb to 128 coherent lines spaced by only 20 GHz within 6-dB power deviation.

  13. Comb/serpentine/cross-bridge test structure for fabrication process evaluation

    NASA Technical Reports Server (NTRS)

    Sayah, Hoshyar R.; Buehler, Martin G.

    1988-01-01

    The comb/serpentine/cross-bridge structure was developed to monitor and evaluate same layer shorts and step coverage problems (open and high-resistance wire over steps) for integrated circuit fabrication processes. The cross-bridge provides local measurements of wire sheet resistance and wirewidth. These local parametric measurements are used in the analysis of the serpentine wire, which identifies step coverage problems. The comb/serpentine/cross-bridge structure was fabricated with 3 microns CMOS/bulk p-well process and tested using a computer-controlled parametric test system.

  14. High-bandwidth transfer of phase stability through a fiber frequency comb.

    PubMed

    Scharnhorst, Nils; Wbbena, Jannes B; Hannig, Stephan; Jakobsen, Kornelius; Kramer, Johannes; Leroux, Ian D; Schmidt, Piet O

    2015-07-27

    We demonstrate phase locking of a 729 nm diode laser to a 1542 nm master laser via an erbium-doped-fiber frequency comb, using a transfer-oscillator feedforward scheme which suppresses the effect of comb noise in an unprecedented 1.8 MHz bandwidth. We illustrate its performance by carrying out coherent manipulations of a trapped calcium ion with 99 % fidelity even at few-?s timescales. We thus demonstrate that transfer-oscillator locking can provide sufficient phase stability for high-fidelity quantum logic manipulation even without pre-stabilization of the slave diode laser. PMID:26367634

  15. Optical properties of the iridescent organ of the comb-jellyfish Bero cucumis (Ctenophora)

    NASA Astrophysics Data System (ADS)

    Welch, Victoria; Vigneron, Jean Pol; Lousse, Virginie; Parker, Andrew

    2006-04-01

    Using transmission electron microscopy, analytical modeling, and detailed numerical simulations, the iridescence observed from the comb rows of the ctenophore Bero cucumis was investigated. It is shown that the changing coloration which accompanies the beating of comb rows as the animal swims can be explained by the weakly-contrasted structure of the refractive index induced by the very coherent packing of locomotory cilia. The colors arising from the narrow band-gap reflection are shown to be highly saturated and, as a function of the incidence angle, cover a wide range of the visible and ultraviolet spectrum. The high transparency of the structure at the maximal bioluminescence wavelength is also explained.

  16. Electromagnetically induced transparency in rubidium vapor prepared by a comb of short optical pulses

    SciTech Connect

    Sautenkov, Vladimir A.; Rostovtsev, Yuri V.; Ye, C.Y.; Welch, George R.; Kocharovskaya, Olga; Scully, Marlan O.

    2005-06-15

    It was shown by Kocharovskaya and Khanin [Sov. Phys. JETP 63, 945 (1986)] that a comb of optical pulses can induce a ground-state atomic coherence and change the optical response of an atomic medium. In our experiment, we studied the propagation of a comb of optical pulses produced by a mode-locked diode laser in rubidium atomic vapor. Electromagnetically induced transparency (EIT) was observed when the pulse repetition rate is a subharmonic of the hyperfine splitting of the ground state. The width of the EIT resonance is determined by the relaxation rate of the ground-state coherence. Possible applications to magnetometery, atomic clocks, and frequency chains are discussed.

  17. Bacterial communities in termite fungus combs are comprised of consistent gut deposits and contributions from the environment.

    PubMed

    Otani, Saria; Hansen, Lars H; Sørensen, Søren J; Poulsen, Michael

    2016-01-01

    Fungus-growing termites (subfamily Macrotermitinae) mix plant forage with asexual spores of their plant-degrading fungal symbiont Termitomyces in their guts and deposit this blend in fungus comb structures, within which the plant matter is degraded. As Termitomyces grows, it produces nodules with asexual spores, which the termites feed on. Since all comb material passes through termite guts, it is inevitable that gut bacteria are also deposited in the comb, but it has remained unknown which bacteria are deposited and whether distinct comb bacterial communities are sustained. Using high-throughput sequencing of the 16S rRNA gene, we explored the bacterial community compositions of 33 fungus comb samples from four termite species (three genera) collected at four South African geographic locations in 2011 and 2013. We identified 33 bacterial phyla, with Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, and Candidate division TM7 jointly accounting for 92 % of the reads. Analyses of gut microbiotas from 25 of the 33 colonies showed that dominant fungus comb taxa originate from the termite gut. While gut communities were consistent between 2011 and 2013, comb community compositions shifted over time. These shifts did not appear to be due to changes in the taxa present, but rather due to differences in the relative abundances of primarily gut-derived bacteria within fungus combs. This indicates that fungus comb microbiotas are largely termite species-specific due to major contributions from gut deposits and also that environment affects which gut bacteria dominate comb communities at a given point in time. PMID:26518432

  18. Symbiotic Fungi Produce Laccases Potentially Involved in Phenol Degradation in Fungus Combs of Fungus-Growing Termites in Thailand

    PubMed Central

    Taprab, Yaovapa; Johjima, Toru; Maeda, Yoshimasa; Moriya, Shigeharu; Trakulnaleamsai, Savitr; Noparatnaraporn, Napavarn; Ohkuma, Moriya; Kudo, Toshiaki

    2005-01-01

    Fungus-growing termites efficiently decompose plant litter through their symbiotic relationship with basidiomycete fungi of the genus Termitomyces. Here, we investigated phenol-oxidizing enzymes in symbiotic fungi and fungus combs (a substrate used to cultivate symbiotic fungi) from termites belonging to the genera Macrotermes, Odontotermes, and Microtermes in Thailand, because these enzymes are potentially involved in the degradation of phenolic compounds during fungus comb aging. Laccase activity was detected in all the fungus combs examined as well as in the culture supernatants of isolated symbiotic fungi. Conversely, no peroxidase activity was detected in any of the fungus combs or the symbiotic fungal cultures. The laccase cDNA fragments were amplified directly from RNA extracted from fungus combs of five termite species and a fungal isolate using degenerate primers targeting conserved copper binding domains of basidiomycete laccases, resulting in a total of 13 putative laccase cDNA sequences being identified. The full-length sequences of the laccase cDNA and the corresponding gene, lcc1-2, were identified from the fungus comb of Macrotermes gilvus and a Termitomyces strain isolated from the same fungus comb, respectively. Partial purification of laccase from the fungus comb showed that the lcc1-2 gene product was a dominant laccase in the fungus comb. These findings indicate that the symbiotic fungus secretes laccase to the fungus comb. In addition to laccase, we report novel genes that showed a significant similarity with fungal laccases, but the gene product lacked laccase activity. Interestingly, these genes were highly expressed in symbiotic fungi of all the termite hosts examined. PMID:16332742

  19. Same sex, no sex, and unaware sex in neurotoxicology.

    PubMed

    Weiss, Bernard

    2011-10-01

    Males and females of virtually all species differ in how they respond to their environment. Because such differences exist in almost all biological realms, including disease patterns and therapeutic outcomes, they have evoked calls by various bodies to incorporate their assessment in research. Neurobehavioral indices pose special questions because, unlike outwardly visible markers, they are described by complex functional outcomes or subtle alterations in brain structure. These divergent responses arise because they are inscribed in the genome itself and then by endocrine mechanisms that govern sexual differentiation of the brain during development and operate throughout life. Other organ systems that exhibit sex differences include the liver, an important consideration for neurotoxicology because it may process many toxic chemicals differentially in males and females. Despite the scope and pervasiveness of sex differences, however, they are disregarded by much of neurotoxicology research. Males predominate in behavioral experiments, few such experiments study both sexes, some investigators fail to even describe the sex of their subjects, and in vitro studies tend to wholly ignore sex, even for model systems aimed at neurological disorders that display marked sex differences. The public is acutely aware of sex differences in behavior, as attested by its appetite for books on the topic. It closely follows debates about the proportion of women in professions that feature science and mathematics. Neurotoxicology, especially in the domain of laboratory research, will be hindered in its ability to translate its findings into human health measures if it assigns sex differences to a minor role. It must also be sensitive to how such debates are framed. Often, the differences evoking the most discussion are subtle in scope. They do not lend themselves to the typical analyses conducted by experimenters; that is, reliance on mean differences and null hypothesis testing. PMID:20875453

  20. Answering Questions About Sex

    ERIC Educational Resources Information Center

    Yarber, William L.

    1977-01-01

    Lists suggestions for aiding teachers in answering student questions about sex, including hints for classroom discussions, questioning and answering techniques, and appropriate role for the teacher. Also lists resources (textbooks, filmstrips, pamphlets and reports) for answering questions about sex. (CS)

  1. Sex-linked recessive

    MedlinePLUS

    Inheritance - sex-linked recessive; Genetics - sex-linked recessive; X-linked recessive ... X-linked recessive diseases usually occur in males. Males have only one X chromosome. A single recessive ...

  2. Practice Safer Sex

    MedlinePLUS

    ... This information in Spanish ( en español ) Practice safer sex Related information Men's health Screening tests and vaccines ... Return to top More information on Practice safer sex Explore other publications and websites Addressing HIV, Other ...

  3. Sex Education: Another View

    ERIC Educational Resources Information Center

    Hamilton, Jennifer

    1977-01-01

    The mother of a 14-year-old mentally retarded boy comments on the viewpoints of Dr. Sol Gordon (a sex education columnist) regarding masturbation, questions on sex, marriage, and the parents' role. (SBH)

  4. Hexagonal comb cells of honeybees are not produced via a liquid equilibrium process.

    PubMed

    Bauer, Daniel; Bienefeld, Kaspar

    2013-01-01

    The nests of European honeybees (Apis mellifera) are organised into wax combs that contain many cells with a hexagonal structure. Many previous studies on comb-building behaviour have been made in order to understand how bees produce this geometrical structure; however, it still remains a mystery. Direct construction of hexagons by bees was suggested previously, while a recent hypothesis postulated the self-organised construction of hexagonal comb cell arrays; however, infrared and thermographic video observations of comb building in the present study failed to support the self-organisation hypothesis because bees were shown to be engaged in direct construction. Bees used their antennae, mandibles and legs in a regular sequence to manipulate the wax, while some bees supported their work by actively warming the wax. During the construction of hexagonal cells, the wax temperature was between 33.6 and 37.6C. This is well below 40C, i.e. the temperature at which wax is assumed to exist in the liquid equilibrium that is essential for self-organised building. PMID:23149932

  5. A calcium regenerative potential controlling ciliary reversal is propagated along the length of ctenophore comb plates.

    PubMed Central

    Moss, A G; Tamm, S L

    1987-01-01

    We have used the giant ciliary comb plates of ctenophores to record electrical activity directly from cilia. A compound action potential was recorded extracellularly over most of the length of the comb plate cilia in response to electrical stimulation of the ectodermal nerve net. The ciliary action potential was correlated with intracellularly recorded action potentials, selectively blocked by Ca2+-channel antagonists, and correlated with ciliary reorientation and reversed beating. Dual-electrode recording from different sites on the same comb plate showed that, unlike protistan cilia, the approximately 1-mm-long cilia of comb plates are not isopotential. Rather, action potentials are generated 150-200 microns from the base and propagate to the tip of the cilia. These results indicate that voltage-dependent channels that mediate increases in intraciliary Ca2+ concentration are distributed over most of the length of the cilia. Consequently, the Ca2+-sensitive machinery controlling ciliary motor responses is also likely to be located along the length of the axoneme. Images PMID:2442759

  6. Effect of partial comb and wattle trim on pullet behavior and thermoregulation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The wattles and comb of chickens are important for thermoregulation allowing for heat exchange during high temperatures. These integumentary tissues are sometimes trimmed to prevent tears if caught on cage equipment and to also improve feed efficiency; however, the procedure itself could be painful ...

  7. Absolute distance measurement based on femtosecond frequency comb with wavelet transform

    NASA Astrophysics Data System (ADS)

    Li, Yao; Hu, Kun; Ji, Rongyi; Liu, Deming; Zhou, Weihu

    2014-12-01

    Spectrally resolved interferometry based on optical frequency comb is an effective way for absolute distance measurement. We introduce wavelet transform to spectrally resolve interferometry as an effective data analysis tool. A comparison has been presented between wavelet transform and conventional algorithm. The results demonstrate that the wavelet transform is a reliable technique and provides good performance over noise resistance for spectrally resolved interferometry measurement.

  8. Probing Buffer-Gas Cooled Molecules with Direct Frequency Comb Spectroscopy in the Mid-Infrrared

    NASA Astrophysics Data System (ADS)

    Spaun, Ben; Changala, Bryan; Bjork, Bryce J.; Heckl, Oliver H.; Patterson, David; Doyle, John M.; Ye, Jun

    2015-06-01

    We present the first demonstration of cavity-enhanced direct frequency comb spectroscopy on buffer-gas cooled molecules.By coupling a mid-infrared frequency comb to a high-finesse cavity surrounding a helium buffer-gas chamber, we can gather rotationally resolved absorption spectra with high sensitivity over a broad wavelength region. The measured 10 K rotational and translational temperatures of buffer-gas cooled molecules drastically simplify the observed spectra, compared to those of room temperature molecules, and allow for high spectral resolution limited only by Doppler broadening (10-100 MHz). Our system allows for the extension of high-resolution spectroscopy to larger molecules, enabling detailed analysis of molecular structure and dynamics, while taking full advantage of the powerful optical properties of frequency combs. A. Foltynowicz et al. Cavity-enhanced optical frequency comb spectroscopy in the mid-infrared application to trace detection of hydrogen peroxide. Applied Physics B, vol. 110, pp. 163-175, 2013. {D. Patterson and J. M. Doyle. Cooling molecules in a cell for FTMW spectroscopy. Molecular Physics 110, 1757-1766, 2012

  9. Hexagonal comb cells of honeybees are not produced via a liquid equilibrium process

    NASA Astrophysics Data System (ADS)

    Bauer, Daniel; Bienefeld, Kaspar

    2013-01-01

    The nests of European honeybees ( Apis mellifera) are organised into wax combs that contain many cells with a hexagonal structure. Many previous studies on comb-building behaviour have been made in order to understand how bees produce this geometrical structure; however, it still remains a mystery. Direct construction of hexagons by bees was suggested previously, while a recent hypothesis postulated the self-organised construction of hexagonal comb cell arrays; however, infrared and thermographic video observations of comb building in the present study failed to support the self-organisation hypothesis because bees were shown to be engaged in direct construction. Bees used their antennae, mandibles and legs in a regular sequence to manipulate the wax, while some bees supported their work by actively warming the wax. During the construction of hexagonal cells, the wax temperature was between 33.6 and 37.6 °C. This is well below 40 °C, i.e. the temperature at which wax is assumed to exist in the liquid equilibrium that is essential for self-organised building.

  10. Look closer: Time sequence photography of Roosters Comb in the Sheep Creek Range, Nevada

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The importance of understanding natural landscape changes is key in properly determining rangeland ecology. Time sequence photography allows a snapshot of a landscape to be documented and enables the ability to compare natural changes overtime. Photographs of Roosters Comb were taken from the same v...

  11. Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers.

    PubMed

    Consolino, L; Taschin, A; Bartolini, P; Bartalini, S; Cancio, P; Tredicucci, A; Beere, H E; Ritchie, D A; Torre, R; Vitiello, M S; De Natale, P

    2012-01-01

    Optical frequency comb synthesizers have represented a revolutionary approach to frequency metrology, providing a grid of frequency references for any laser emitting within their spectral coverage. Extending the metrological features of optical frequency comb synthesizers to the terahertz domain would be a major breakthrough, due to the widespread range of accessible strategic applications and the availability of stable, high-power and widely tunable sources such as quantum cascade lasers. Here we demonstrate phase-locking of a 2.5 THz quantum cascade laser to a free-space comb, generated in a LiNbO(3) waveguide and covering the 0.1-6 THz frequency range. We show that even a small fraction (<100 nW) of the radiation emitted from the quantum cascade laser is sufficient to generate a beat note suitable for phase-locking to the comb, paving the way to novel metrological-grade terahertz applications, including high-resolution spectroscopy, manipulation of cold molecules, astronomy and telecommunications. PMID:22948822

  12. Tunable optical correlator using an optical frequency comb and a nonlinear multiplexer.

    PubMed

    Ziyadi, Morteza; Chitgarha, Mohammad Reza; Khaleghi, Salman; Mohajerin-Ariaei, Amirhossein; Almaiman, Ahmed; Touch, Joe; Tur, Moshe; Langrock, Carsten; Fejer, Martin M; Willner, Alan E

    2014-01-13

    We experimentally demonstrate a tunable optical correlator to search for multiple patterns among QPSK symbols. We utilize an optical frequency comb to generate the coherent signals and multiplex them coherently in a single PPLN waveguide. Multiple patterns with different lengths are successfully searched within QPSK symbols in a 40-Gb/s signal. PMID:24514968

  13. Straining graphene with low-temperature compatible electrostatic comb-drive actuators

    NASA Astrophysics Data System (ADS)

    Khodkov, Tymofiy; Goldsche, Matthias; Reichardt, Sven; Stampfer, Christoph

    2015-03-01

    Graphene holds great promises as an active element in future nano electromechanical systems. Therefore, thorough study of electromechanical properties of this 2D material is a crucial step towards its applications in flexible electronics. We present the fabrication and characterization of silicon-based electrostatic comb-drive actuators made for integrating individual graphene sheets. The micromachined comb-drive actuators are designed such that they can induce significant mechanical forces for straining graphene allowing to systematically investigate mechanical and electromechanical properties of high-quality graphene. By using highly doped silicon the comb-drive actuators become compatible with low temperatures, i.e. cryogenic temperatures allowing for quantum electromechanical experiments. Further device functionality is introduced by a local gate that enables the tunability of the chemical potential of the graphene. This approach makes possible a detailed study of the graphene under controlled high strain allowing simultaneous and independent tuning of other external parameters, i.e temperature, charge density, magnetic field. With Raman spectroscopy we measure and characterize mono and bilayer graphene samples at room temperature under applied strains up to 1%. A detailed analysis of data allows clear separation of strain and doping. It is demonstrated that with this technique graphene sheet reproducibly experiences only strain while operating the comb-drive actuator.

  14. Digital approach to stabilizing optical frequency combs and beat notes of CW lasers

    NASA Astrophysics Data System (ADS)

    ?ek, Martin; ?p, Ond?ej; md, Radek; Hrabina, Jan; Mikel, B?etislav; Lazar, Josef

    2013-10-01

    In cases when it is necessary to lock optical frequencies generated by an optical frequency comb to a precise radio frequency (RF) standard (GPS-disciplined oscillator, H-maser, etc.) the usual practice is to implement phase and frequency-locked loops. Such system takes the signal generated by the RF standard (usually 10 MHz or 100 MHz) as a reference and stabilizes the repetition and offset frequencies of the comb contained in the RF output of the f-2f interferometer. These control loops are usually built around analog electronic circuits processing the output signals from photo detectors. This results in transferring the stability of the standard from RF to optical frequency domain. The presented work describes a different approach based on digital signal processing and software-defined radio algorithms used for processing the f-2f and beat-note signals. Several applications of digital phase and frequency locks to a RF standard are demonstrated: the repetition (frep) and offset frequency (fceo) of the comb, and the frequency of the beat note between a CW laser source and a single component of the optical frequency comb spectrum.

  15. Molecular fingerprinting with the resolved modes of a femtosecond laser frequency comb.

    PubMed

    Diddams, Scott A; Hollberg, Leo; Mbele, Vela

    2007-02-01

    The control of the broadband frequency comb emitted from a mode-locked femtosecond laser has permitted a wide range of scientific and technological advances--ranging from the counting of optical cycles for next-generation atomic clocks to measurements of phase-sensitive high-field processes. A unique advantage of the stabilized frequency comb is that it provides, in a single laser beam, about a million optical modes with very narrow linewidths and absolute frequency positions known to better than one part in 10(15) (ref. 5). One important application of this vast array of highly coherent optical fields is precision spectroscopy, in which a large number of modes can be used to map internal atomic energy structure and dynamics. However, an efficient means of simultaneously identifying, addressing and measuring the amplitude or relative phase of individual modes has not existed. Here we use a high-resolution disperser to separate the individual modes of a stabilized frequency comb into a two-dimensional array in the image plane of the spectrometer. We illustrate the power of this technique for high-resolution spectral fingerprinting of molecular iodine vapour, acquiring in a few milliseconds absorption images covering over 6 THz of bandwidth with high frequency resolution. Our technique for direct and parallel accessing of stabilized frequency comb modes could find application in high-bandwidth spread-spectrum communications with increased security, high-resolution coherent quantum control, and arbitrary optical waveform synthesis with control at the optical radian level. PMID:17287805

  16. Optical Comb Generation for Streak Camera Calibration for Inertial Confinement Fusion Experiments

    SciTech Connect

    Ronald Justin, Terence Davies, Frans Janson, Bruce Marshall, Perry Bell, Daniel Kalantar, Joseph Kimbrough, Stephen Vernon, Oliver Sweningsen

    2008-09-18

    The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) is coming on-line to support physics experimentation for the U.S. Department of Energy (DOE) programs in Inertial Confinement Fusion (ICF) and Stockpile Stewardship (SS). Optical streak cameras are an integral part of the experimental diagnostics instrumentation at NIF. To accurately reduce streak camera data a highly accurate temporal calibration is required. This article describes a technique for simultaneously generating a precise +/- 2 ps optical marker pulse (fiducial reference) and trains of precisely timed, short-duration optical pulses (so-called comb pulse trains) that are suitable for the timing calibrations. These optical pulse generators are used with the LLNL optical streak cameras. They are small, portable light sources that, in the comb mode, produce a series of temporally short, uniformly spaced optical pulses, using a laser diode source. Comb generators have been produced with pulse-train repetition rates up to 10 GHz at 780 nm, and somewhat lower frequencies at 664 nm. Individual pulses can be as short as 25-ps FWHM. Signal output is via a fiber-optic connector on the front panel of the generator box. The optical signal is transported from comb generator to streak camera through multi-mode, graded-index optical fiber.

  17. Optical zooming interferometer for subnanometer positioning using an optical frequency comb

    SciTech Connect

    Kajima, Mariko; Minoshima, Kaoru

    2010-10-20

    A high-precision positioning stage based on an optical zooming interferometer is proposed. Two external-cavity diode lasers, stabilized to a femtosecond optical frequency comb, are used as optical sources. The zooming principle is demonstrated, and the positioning resolution of 0.2 nm is achieved. The positioning accuracy was partly evaluated.

  18. Power, Prayers, and Protection: Comb Ridge as a Case Study in Navajo Thought

    ERIC Educational Resources Information Center

    McPherson, Robert S.

    2010-01-01

    Beginning in 2005, a five-year survey of cultural resources began to unfold in southeastern Utah along a prominent sandstone rock formation known as Comb Ridge. This visually dramatic monocline stretches a considerable distance from the southwestern corner of Blue Mountain (Abajos) in Utah to Kayenta, Arizona, approximately one hundred miles to…

  19. Quantum theory of phase correlations in optical frequency combs generated by stimulated Raman scattering

    SciTech Connect

    Wu Chunbai; Raymer, M. G.; Wang, Y. Y.; Benabid, F.

    2010-11-15

    We explore theoretically the phase correlation between multiple generated sidebands in a Raman optical frequency comb under conditions of spontaneous initiation from quantum zero-point noise. We show that there is a near-deterministic correlation between sideband phases in each laser shot which may lead to synthesis of attosecond pulse trains.

  20. Power, Prayers, and Protection: Comb Ridge as a Case Study in Navajo Thought

    ERIC Educational Resources Information Center

    McPherson, Robert S.

    2010-01-01

    Beginning in 2005, a five-year survey of cultural resources began to unfold in southeastern Utah along a prominent sandstone rock formation known as Comb Ridge. This visually dramatic monocline stretches a considerable distance from the southwestern corner of Blue Mountain (Abajos) in Utah to Kayenta, Arizona, approximately one hundred miles to

  1. Conformational Properties of Comb-Like Polyelectrolytes: A Coarse-Grained MD Study.

    PubMed

    Ghelichi, Mahdi; Eikerling, Michael H

    2016-03-17

    This article presents a coarse-grained molecular dynamics study of single comb-like polyelectrolyte or ionomer chains in aqueous solution. The model polymer is comprised of a hydrophobic backbone chain with grafted side chains that terminate in anionic headgroups. The comb-polymer is modeled at a coarse-grained level with implicit treatment of the solvent. The computational study rationalizes conformational properties of the backbone chain and localization of counterions as functions of side chain length, grafting density of side chains, backbone stiffness, and counterion valence. The main interplay that determines the ionomer properties unfolds between electrostatic interactions among charged groups, hydrophobic backbone interactions, and steric effects induced by the pendant side chains. Depending on the density of branching sites, we have found two opposing effects of side chain length on the backbone gyration radius and local persistence length. Variation in comb-polyelectrolyte architecture is shown to have nontrivial effects on the localization of mobile counterions. Changes in Bjerrum length and counterion valence are also shown to alter the strength of Coulomb interactions and emphasize the role of excluded-volume effects on controlling the backbone conformational behavior. The results of simulations are in qualitative agreement with existing experimental and theoretical studies. The comprehensive conformational picture provides a framework for future studies of comb-polyelectrolyte systems. PMID:26910617

  2. Gravity orientation in social wasp comb cells (Vespinae) and the possible role of embedded minerals

    NASA Astrophysics Data System (ADS)

    Ishay, Jacob S.; Barkay, Zahava; Eliaz, Noam; Plotkin, Marian; Volynchik, Stanislav; Bergman, David J.

    2008-04-01

    Social wasps and hornets maintain their nest in the dark. The building of the combs by all Vespinae is always in the direction of the gravitational force of Earth, and in each cell’s ceiling, at least one ‘keystone’ is embedded and fastened by saliva. The sensory mechanisms that enable both building of sizeable symmetrical combs and nursing of the brood in the darkness merit investigation, and the aim of the present study was to identify and characterize the ‘keystones’ that exist in the ceiling and in the walls of the social wasp comb cells. Bio-ferrography was used to isolate magnetic particles on slides. These slides, as well as original cells, were analyzed in an environmental scanning electron microscope by a variety of analytical tools. It was found that both the roof and the walls of each comb cell bear minerals, like ferrites, as well as Ti and Zr. The latter two elements are less abundant in the soil around the nest. Ti and Zr are known to reflect infrared (IR) light. IR imaging showed a thermoregulatory center in the dorsal thorax of the adult Oriental hornet. It is not known yet whether these insects can sense IR light.

  3. Adaptive sampling dual terahertz comb spectroscopy using dual free-running femtosecond lasers

    PubMed Central

    Yasui, Takeshi; Ichikawa, Ryuji; Hsieh, Yi-Da; Hayashi, Kenta; Cahyadi, Harsono; Hindle, Francis; Sakaguchi, Yoshiyuki; Iwata, Tetsuo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Minoshima, Kaoru; Inaba, Hajime

    2015-01-01

    Terahertz (THz) dual comb spectroscopy (DCS) is a promising method for high-accuracy, high-resolution, broadband THz spectroscopy because the mode-resolved THz comb spectrum includes both broadband THz radiation and narrow-line CW-THz radiation characteristics. In addition, all frequency modes of a THz comb can be phase-locked to a microwave frequency standard, providing excellent traceability. However, the need for stabilization of dual femtosecond lasers has often hindered its wide use. To overcome this limitation, here we have demonstrated adaptive-sampling THz-DCS, allowing the use of free-running femtosecond lasers. To correct the fluctuation of the time and frequency scales caused by the laser timing jitter, an adaptive sampling clock is generated by dual THz-comb-referenced spectrum analysers and is used for a timing clock signal in a data acquisition board. The results not only indicated the successful implementation of THz-DCS with free-running lasers but also showed that this configuration outperforms standard THz-DCS with stabilized lasers due to the slight jitter remained in the stabilized lasers. PMID:26035687

  4. Measuring the shift of a femtosecond laser frequency comb by the interference method

    SciTech Connect

    Basnak, Dmitriy V; Bikmukhametov, K A; Dmitriev, Aleksandr K; Dychkov, Aleksandr S; Kuznetsov, Sergei A; Lugovoy, A A; Mitsziti, P

    2012-01-31

    We have demonstrated the possibility of measuring the femtosecond laser frequency comb shift by the position of a Fabry - Perot interferometer's transmission bands with a statistical error of 10{sup -2} and a systematic shift of 10{sup -1}. (control of laser radiation parameters)

  5. Sexing young snowy owls

    USGS Publications Warehouse

    Seidensticker, M.T.; Holt, D.W.; Detienne, J.; Talbot, S.; Gray, K.

    2011-01-01

    We predicted sex of 140 Snowy Owl (Bubo scandiacus) nestlings out of 34 nests at our Barrow, Alaska, study area to develop a technique for sexing these owls in the field. We primarily sexed young, flightless owls (3844 d old) by quantifying plumage markings on the remiges and tail, predicting sex, and collecting blood samples to test our field predictions using molecular sexing techniques. We categorized and quantified three different plumage markings: two types of bars (defined as markings that touch the rachis) and spots (defined as markings that do not touch the rachis). We predicted sex in the field assuming that males had more spots than bars and females more bars than spots on the remiges and rectrices. Molecular data indicated that we correctly sexed 100% of the nestlings. We modeled the data using random forests and classification trees. Both models indicated that the number and type of markings on the secondary feathers were the most important in classifying nestling sex. The statistical models verified our initial qualitative prediction that males have more spots than bars and females more bars than spots on flight feathers P6P10 for both wings and tail feathers T1 and T2. This study provides researchers with an easily replicable and highly accurate method for sexing young Snowy Owls in the field, which should aid further studies of sex-ratios and sex-related variation in behavior and growth of this circumpolar owl species. ?? 2011 The Raptor Research Foundation, Inc.

  6. Osho - Insights on sex

    PubMed Central

    Nagaraj, Anil Kumar Mysore

    2013-01-01

    Sex is a mysterious phenomenon, which has puzzled even great sages. Human beings have researched and mastered the biology of sex. But that is not all. Sex needs to be understood from the spiritual perspective too. The vision of Osho is an enlightening experience in this regard. Out of the thousands of lectures, five lectures on sex made Osho most notorious. Born into a Jain family of Madhya Pradesh, Rajneesh, who later wanted himself to be called Osho, is a great master. He has spoken volumes on a wide range of topics ranging from sex to super-consciousness. His contributions in the area of sex are based on the principles of “Tantra” which has its origin from Buddhism. This article focuses on his life and insights on sex, which if understood properly, can be a stepping stone for enlightenment. PMID:23858266

  7. XUV frequency-comb metrology on the ground state of helium

    SciTech Connect

    Kandula, Dominik Z.; Gohle, Christoph; Pinkert, Tjeerd J.; Ubachs, Wim; Eikema, Kjeld S. E.

    2011-12-15

    The operation of a frequency comb at extreme ultraviolet (xuv) wavelengths based on pairwise amplification and nonlinear upconversion to the 15th harmonic of pulses from a frequency-comb laser in the near-infrared range is reported. It is experimentally demonstrated that the resulting spectrum at 51 nm is fully phase coherent and can be applied to precision metrology. The pulses are used in a scheme of direct-frequency-comb excitation of helium atoms from the ground state to the 1s4p and 1s5p {sup 1} P{sub 1} states. Laser ionization by auxiliary 1064 nm pulses is used to detect the excited-state population, resulting in a cosine-like signal as a function of the repetition rate of the frequency comb with a modulation contrast of up to 55%. Analysis of the visibility of this comb structure, thereby using the helium atom as a precision phase ruler, yields an estimated timing jitter between the two upconverted-comb laser pulses of 50 attoseconds, which is equivalent to a phase jitter of 0.38 (6) cycles in the xuv at 51 nm. This sets a quantitative figure of merit for the operation of the xuv comb and indicates that extension to even shorter wavelengths should be feasible. The helium metrology investigation results in transition frequencies of 5 740 806 993 (10) and 5 814 248 672 (6) MHz for excitation of the 1s4p and 1s5p {sup 1} P{sub 1} states, respectively. This constitutes an important frequency measurement in the xuv, attaining high accuracy in this windowless part of the electromagnetic spectrum. From the measured transition frequencies an eight-fold-improved {sup 4}He ionization energy of 5 945 204 212 (6) MHz is derived. Also, a new value for the {sup 4}He ground-state Lamb shift is found of 41 247 (6) MHz. This experimental value is in agreement with recent theoretical calculations up to order m{alpha}{sup 6} and m{sup 2}/M{alpha}{sup 5}, but with a six-times-higher precision, therewith providing a stringent test of quantum electrodynamics in bound two-electron systems.

  8. A 12.5 GHz-spaced optical frequency comb spanning >400 nm for near-infrared astronomical spectrograph calibration

    SciTech Connect

    Quinlan, F.; Diddams, S. A.; Ycas, G.; Osterman, S.

    2010-06-15

    A 12.5 GHz-spaced optical frequency comb locked to a global positioning system disciplined oscillator for near-infrared (IR) spectrograph calibration is presented. The comb is generated via filtering a 250 MHz-spaced comb. Subsequent nonlinear broadening of the 12.5 GHz comb extends the wavelength range to cover 1380-1820 nm, providing complete coverage over the H-band transmission window of earth's atmosphere. Finite suppression of spurious sidemodes, optical linewidth, and instability of the comb has been examined to estimate potential wavelength biases in spectrograph calibration. Sidemode suppression varies between 20 and 45 dB, and the optical linewidth is {approx}350 kHz at 1550 nm. The comb frequency uncertainty is bounded by {+-}30 kHz (corresponding to a radial velocity of {+-}5 cm/s), limited by the global positioning system disciplined oscillator reference. These results indicate that this comb can readily support radial velocity measurements below 1 m/s in the near IR.

  9. Spatiotemporal evolution of a cosine-modulated stationary field and Kerr frequency comb generation in a microresonator.

    PubMed

    Hu, Xiaohong; Liu, Yuanshan; Xu, Xin; Feng, Ye; Zhang, Wenfu; Wang, Weiqiang; Song, Jiazheng; Wang, Yishan; Zhao, Wei

    2015-10-10

    Based on the normalized spatiotemporal Lugiato-Lefever equation, the evolutions of cosine-modulated stationary fields relating to the generation of single-free spectral range (FSR) or multi-FSR Kerr frequency combs in a microresonator with anomalous dispersion are studied numerically. The research results show that a single-FSR comb arises when a dissipative soliton pulse or multiple nonequidistant soliton pulses form in the cavity. Compared with the smooth and regular spectral structure of a single soliton pulse, the comb corresponding to the uneven distribution of multiple soliton pulses exhibits a complex and irregular profile. When the stable intracavity field consists of a "roll" Turing pattern or N(N>1) evenly distributed soliton pulses separated by 2?/N, multi-FSR combs can be generated. In the case of the "roll" Turing pattern solution, it is found that third-order dispersion could modify the comb mode spacing and decrease the intensity of high-order comb modes. For the situation of multiple soliton pulse generation, the simulation results indicate that both the number and locations of the soliton pulses can be actively controlled through the careful selection of modulation frequency. In addition, for the selected cosine-modulated initial field profile, only those modes with the mode numbers being equal to an integer multiple of N can be greatly amplified by the parametric gain during propagation in the microresonator. This process eventually leads to the formation of a N-FSR frequency comb. PMID:26479815

  10. A 12.5 GHz-spaced optical frequency comb spanning >400 nm for near-infrared astronomical spectrograph calibration.

    PubMed

    Quinlan, F; Ycas, G; Osterman, S; Diddams, S A

    2010-06-01

    A 12.5 GHz-spaced optical frequency comb locked to a global positioning system disciplined oscillator for near-infrared (IR) spectrograph calibration is presented. The comb is generated via filtering a 250 MHz-spaced comb. Subsequent nonlinear broadening of the 12.5 GHz comb extends the wavelength range to cover 1380-1820 nm, providing complete coverage over the H-band transmission window of earth's atmosphere. Finite suppression of spurious sidemodes, optical linewidth, and instability of the comb has been examined to estimate potential wavelength biases in spectrograph calibration. Sidemode suppression varies between 20 and 45 dB, and the optical linewidth is approximately 350 kHz at 1550 nm. The comb frequency uncertainty is bounded by +/-30 kHz (corresponding to a radial velocity of +/-5 cm/s), limited by the global positioning system disciplined oscillator reference. These results indicate that this comb can readily support radial velocity measurements below 1 m/s in the near IR. PMID:20590223

  11. Threshold conditions, energy spectrum and bands generated by locally periodic Dirac comb potentials

    NASA Astrophysics Data System (ADS)

    Dharani, M.; Shastry, C. S.

    2016-01-01

    We derive expressions for polynomials governing the threshold conditions for different types of locally periodic Dirac comb potentials comprising of attractive and combination of attractive and repulsive delta potential terms confined symmetrically inside a one dimensional box of fixed length. The roots of these polynomials specify the conditions on the potential parameters in order to generate threshold energy bound states. The mathematical and numerical methods used by us were first formulated in our earlier works and it is also very briefly summarized in this paper. We report a number of mathematical results pertaining to the threshold conditions and these are useful in controlling the number of negative energy states as desired. We further demonstrate the correlation between the distribution of roots of these polynomials and negative energy eigenvalues. Using these results as basis, we investigate the energy bands in the positive energy spectrum for the above specified Dirac comb potentials and also for the corresponding repulsive case. In the case of attractive Dirac comb the base energy of the each band excluding the first band coincides with specific eigenvalue of the confining box whereas in the repulsive case it coincides with the band top. We deduce systematic correlation between band gaps, band spreads and box eigenvalues and explain the physical reason for the vanishing of band pattern at higher energies. In the case of Dirac comb comprising of orderly arranged attractive and repulsive delta potentials, specific box eigenvalues occur in the middle of each band excluding the first band. From our study we find that by controlling the number and strength parameters of delta terms in the Dirac comb and the size of confining box it is possible to generate desired types of band formations. We believe the results from our systematic analysis are useful and relevant in the study of various one dimensional systems of physical interest in areas like nanoscience.

  12. All solid state mid-infrared dual-comb spectroscopy platform based on QCL technology

    NASA Astrophysics Data System (ADS)

    Hugi, Andreas; Geiser, Markus; Villares, Gustavo; Cappelli, Francesco; Blaser, Stephane; Faist, Jrme

    2015-01-01

    We develop a spectroscopy platform for industrial applications based on semiconductor quantum cascade laser (QCL) frequency combs. The platform's key features will be an unmatched combination of bandwidth of 100 cm-1, resolution of 100 kHz, speed of ten to hundreds of ?s as well as size and robustness, opening doors to beforehand unreachable markets. The sensor can be built extremely compact and robust since the laser source is an all-electrically pumped semiconductor optical frequency comb and no mechanical elements are required. However, the parallel acquisition of dual-comb spectrometers comes at the price of enormous data-rates. For system scalability, robustness and optical simplicity we use free-running QCL combs. Therefore no complicated optical locking mechanisms are required. To reach high signal-to-noise ratios, we develop an algorithm, which is based on combination of coherent and non-coherent averaging. This algorithm is specifically optimized for free-running and small footprint, therefore high-repetition rate, comb sources. As a consequence, our system generates data-rates of up to 3.2 GB/sec. These data-rates need to be reduced by several orders of magnitude in real-time in order to be useful for spectral fitting algorithms. We present the development of a data-treatment solution, which reaches a single-channel throughput of 22% using a standard laptop-computer. Using a state-of-the art desktop computer, the throughput is increased to 43%. This is combined with a data-acquisition board to a stand-alone data processing unit, allowing real-time industrial process observation and continuous averaging to achieve highest signal fidelity.

  13. Effect of partial comb and wattle trim on pullet behavior and thermoregulation,1.

    PubMed

    Hester, P Y; Al-Ramamneh, D S; Makagon, M M; Cheng, H W

    2015-05-01

    The wattles and comb of chickens are important for thermoregulation allowing for heat exchange during high temperatures. These integumentary tissues are sometimes trimmed to prevent tears if caught on cage equipment and to also improve feed efficiency; however, the procedure itself could be painful to chicks. Our objective was to determine the effect of trimming the comb and wattles on behavior, BW, feed usage, and the surface temperature of pullets. The wattles and comb of Leghorns were partially trimmed at 21?d age (n = 6 cages, 13 chicks each) with another 6 cages serving as controls. Behaviors were recorded 3 times daily for 1?h starting at 0800, 1200, and 1500 using instantaneous scan sampling observations conducted every 5 min prior to, on the d of, and after the trim. Group BW at 21, 28, and 36?d age and the amount of feed used for 7?d beginning at 21 and 29?d age were measured per cage. At 1300?h on d before and after the trim, thermal images of the pullet's beak, comb, eye, wattle, and shank were randomly taken on 3 pullets/cage. Smaller proportions of trimmed chicks were eating and greater proportions were sitting on the d of the trim as compared to the controls with the opposite trend occurring on 4?d post-trim (treatment by age interaction, P = 0.03 and 0.0001, respectively). Standing behavior differed only on the d of the trim where smaller proportions of trimmed pullets stood as compared to intact controls (treatment by age interaction, P = 0.0002). Trimming the comb and wattles did not affect preening, running, BW, feed utilization, and the surface temperature of the pullet. The indices of behavior suggest that on the d of the trim, pullets may have experienced temporary distress, but they returned to normal behavior by 5?h post-trim with no long-term effect on BW, feed usage, or surface body temperature. PMID:25796274

  14. Generation of green frequency comb from chirped χ(2) nonlinear photonic crystals

    NASA Astrophysics Data System (ADS)

    Lai, C.-M.; Chang, K.-H.; Yang, Z.-Y.; Fu, S.-H.; Tsai, S.-T.; Hsu, C.-W.; Yu, N. E.; Boudrioua, A.; Kung, A. H.; Peng, L.-H.

    2014-12-01

    Spectrally broad frequency comb generation over 510-555 nm range was reported on chirped quasi-phase-matching (QPM) χ(2) nonlinear photonic crystals of 12 mm length with periodicity stepwise increased from 5.9 μm to 7.1 μm. When pumped with nanosecond infrared (IR) frequency comb derived from a QPM optical parametric oscillator (OPO) and spanned over 1040 nm to 1090 nm wavelength range, the 520 nm to 545 nm up-converted green spectra were shown to consist of contributions from (a) second-harmonic generation among the signal or the idler modes, and (b) sum-frequency generation (SFG) from the neighboring pairs of the signal or the idler modes. These mechanisms led the up-converted green frequency comb to have the same mode spacing of 450 GHz as that in the IR-OPO pump comb. As the pump was further detuned from the aforementioned near-degeneracy point and moved toward the signal (1020-1040 nm) and the idler (1090-1110 nm) spectral range, the above QPM parametric processes were preserved in the chirped QPM devices to support up-converted green generation in the 510-520 nm and the 545-555 nm spectral regime. Additional 530-535 nm green spectral generation was also observed due to concurrence of multi-wavelength SFG processes between the (signal, idler) mode pairs. These mechanisms facilitate the chirped QPM device to support a single-pass up-conversion efficiency ˜10% when subject to an IR-OPO pump comb with 200 mW average power operated near- or off- the degeneracy point.

  15. Generation of green frequency comb from chirped ?{sup (2)} nonlinear photonic crystals

    SciTech Connect

    Lai, C.-M.; Chang, K.-H.; Yang, Z.-Y.; Fu, S.-H.; Tsai, S.-T.; Hsu, C.-W.; Peng, L.-H.; Yu, N. E.; Boudrioua, A.; Kung, A. H.

    2014-12-01

    Spectrally broad frequency comb generation over 510555?nm range was reported on chirped quasi-phase-matching (QPM) ?{sup (2)} nonlinear photonic crystals of 12?mm length with periodicity stepwise increased from 5.9??m to 7.1??m. When pumped with nanosecond infrared (IR) frequency comb derived from a QPM optical parametric oscillator (OPO) and spanned over 1040?nm to 1090?nm wavelength range, the 520?nm to 545?nm up-converted green spectra were shown to consist of contributions from (a) second-harmonic generation among the signal or the idler modes, and (b) sum-frequency generation (SFG) from the neighboring pairs of the signal or the idler modes. These mechanisms led the up-converted green frequency comb to have the same mode spacing of 450?GHz as that in the IR-OPO pump comb. As the pump was further detuned from the aforementioned near-degeneracy point and moved toward the signal (10201040?nm) and the idler (10901110?nm) spectral range, the above QPM parametric processes were preserved in the chirped QPM devices to support up-converted green generation in the 510520?nm and the 545555?nm spectral regime. Additional 530535?nm green spectral generation was also observed due to concurrence of multi-wavelength SFG processes between the (signal, idler) mode pairs. These mechanisms facilitate the chirped QPM device to support a single-pass up-conversion efficiency ?10% when subject to an IR-OPO pump comb with 200 mW average power operated near- or off- the degeneracy point.

  16. The invariant-comb approach and its relation to the balancedness of multipartite entangled states

    NASA Astrophysics Data System (ADS)

    Osterloh, Andreas; Siewert, Jens

    2010-07-01

    The invariant-comb approach is a method to construct entanglement measures for multipartite systems of qubits. The essential step is the construction of an antilinear operator that we call comb in reference to the hairy-ball theorem. An appealing feature of this approach is that, for qubits (or spins 1/2), the combs are automatically invariant under SL(2,{\\rm\\kern.24em \\vrule width.04em height1.46ex depth-.07ex\\kern-.30em C}) , which implies that the obtained invariants are entanglement monotones by construction. By asking which property of a state determines whether or not it is detected by a polynomial SL(2,{\\rm\\kern.24em \\vrule width.04em height1.46ex depth-.07ex \\kern-.30em {C}}) invariant, we find that it is the presence of a balanced part that persists under local unitary transformations. We present a detailed analysis for the maximally entangled states detected by such polynomial invariants, which leads to the concept of irreducibly balanced states. The latter indicates a tight connection with stochastic local operations and classical communication (SLOCC) classifications of qubit entanglement. Combs may also help to define measures for multipartite entanglement of higher-dimensional subsystems. However, for higher spins there are many independent combs, such that it is nontrivial to find an invariant one. By restricting the allowed local operations to rotations of the coordinate system (i.e. again to the SL(2,{\\rm\\kern.24em \\vrule width.04em height1.46ex depth-.07ex \\kern-.30em C}) ), we manage to define a unique extension of the concurrence to general half-integer spin with an analytic convex-roof expression for mixed states.

  17. All-fiber frequency comb employing a single walled carbon nanotube saturable absorber for optical frequency metrology in near infrared

    NASA Astrophysics Data System (ADS)

    Lim, Jinkang

    2011-12-01

    Optical frequency combs produced by mode-locked fiber lasers are us eful tools for high precision frequency metrology and molecular spectroscopy in a robust and portable format. We have specifically investigated erbium doped fiber mode-locked lasers that use single-walled carbon nanotubes as a saturable absorber. We have, for the first time, developed and phase- stabilized a carbon nanotube fiber laser (CNFL) frequency comb. The carbon nanotube saturable absorber, which was fabricated using an optically driven deposition method, permits a high repetition frequency (>150 MHz) since an optical nonlinearity of fibers is not used for mode-locking. The CNFL comb combined with a parabolic pulse erbium doped fiber amplifier (EDFA) has shown a compact, robust, and cost-effective supercontinuum source. The amplified pulse from the parabolic pulse EDFA was compressed with a hollow-core photonic bandgap fiber, which produced a wave-breaking-free pulse with an all-fiber set-up. The stabilized comb has demonstrated a fractional instability of 1.2 x10-11 at 1 sec averaging time, the reference-limited instability. We have performed optical frequency metrology with the CNFL comb and have measured an optical frequency, P(13) which is a molecular overtone transition of C2H2. The measured frequency has shown a good agreement with the known value within an uncertainty of 10 kHz. In order to extend the application of the CNFL comb such as multi-heterodyne dual comb spectroscopy, we have investigated the noise of the CNFL comb and particularly, the broad carrier envelope offset frequency (f0) linewidth of the CNFL comb. The primary noise source is shown to be white amplitude noise on the oscillator pump laser combined with the sensitivity of the mode-locked laser to pump power fluctuations. The control bandwidth of f0 was limited by the response dynamics of the CNFL comb. The significant reduction of comb noise has been observed by implementing a phase-lead compensation to extend control bandwidth of the comb and by reducing the pump relative intensity noise simultaneously. Therefore the f0 linewidth has been narrower from 850 kHz to 220 kHz. The integrated phase noise for the f0 lock is 1.6 radians from 100 Hz to 102 kHz.

  18. Simultaneous low noise radio frequency tone and narrow linewidth optical comb generation from a regeneratively mode-locked laser

    NASA Astrophysics Data System (ADS)

    Ozdur, Ibrahim; Ozharar, Sarper; Delfyett, Peter J.

    2014-10-01

    A regeneratively mode-locked laser with simultaneous low noise radio frequency (RF) tone and optical comb generation is presented. The laser does not need any external RF signal and emits a pulse train at 10 GHz repetition rate with a 1.5-ps optical pulse width after compression. The generated RF tone has a signal-to-noise ratio of 121 dB/Hz and an RF fluctuation of 10-9 over 0.1 s. The optical frequency comb spacing is also at 10 GHz and the optical comb tooth has a linewidth of <1 kHz.

  19. Generation of Kerr combs centered at 4.5 ?m in crystalline microresonators pumped with quantum-cascade lasers.

    PubMed

    Savchenkov, Anatoliy A; Ilchenko, Vladimir S; Di Teodoro, Fabio; Belden, Paul M; Lotshaw, William T; Matsko, Andrey B; Maleki, Lute

    2015-08-01

    We report on the generation of mid-infrared Kerr frequency combs in high-finesse CaF2 and MgF2 whispering-gallery-mode resonators pumped with continuous-wave room-temperature quantum cascade lasers. The combs were centered at 4.5 ?m, the longest wavelength to date. A frequency comb wider than one half of an octave was demonstrated when approximately 20 mW of pump power was coupled to an MgF2 resonator characterized with quality factor exceeding 10(8). PMID:26258334

  20. Selection and amplification of modes of an optical frequency comb using a femtosecond laser injection-locking technique

    SciTech Connect

    Moon, H. S.; Kim, E. B.; Park, S. E.; Park, C. Y.

    2006-10-30

    The authors have demonstrated the selection and the amplification of the components of an optical frequency comb using a femtosecond laser injectionlocking technique. The author used a mode-locked femtosecond Ti:sapphire laser as the master laser and a single-mode diode laser as the slave laser. The femtosecond laser injection-locking technique was applied to a filter for mode selection of the optical frequency comb and an amplifier for amplification of the selected mode. The authors could obtain the laser source selected only the desired mode of the optical frequency comb and amplified the power of the selected modes several thousand times.

  1. Mutations in the extra sex combs and Enhancer of Polycomb Genes Increase Homologous Recombination in Somatic Cells of Drosophila melanogaster

    PubMed Central

    Holmes, Angela M.; Weedmark, Kelly A.; Gloor, Gregory B.

    2006-01-01

    We found that heterozygous mutant alleles of E(Pc) and esc increased homologous recombination from an allelic template in somatic cells in a P-element-induced double-strand break repair assay. Flies heterozygous for mutant alleles of these genes showed increased genome stability and decreased levels of apoptosis in imaginal discs and a concomitant increase in survival following ionizing radiation. We propose that this was caused by a genomewide increase in homologous recombination in somatic cells. A double mutant of E(Pc) and esc had no additive effect, showing that these genes act in the same pathway. Finally, we found that a heterozygous deficiency for the histone deacetylase, Rpd3, masked the radiation-resistant phenotype of both esc and E(Pc) mutants. These findings provide evidence for a gene dosage-dependent interaction between the esc/E(z) complex and the Tip60 histone acetyltransferase complex. We propose that esc and E(Pc) mutants enhance homologous recombination by modulating the histone acetylation status of histone H4 at the double-strand break. PMID:16452150

  2. Sex, epilepsy, and epigenetics

    PubMed Central

    Qureshi, Irfan A.; Mehler, Mark F.

    2014-01-01

    Epilepsy refers to a heterogeneous group of disorders that are associated with a wide range of pathogenic mechanisms, seizure manifestations, comorbidity profiles, and therapeutic responses. These characteristics are all influenced quite significantly by sex. As with other conditions exhibiting such patterns, sex differences in epilepsy are thought to arise—at the most fundamental level—from the “organizational” and “activational” effects of sex hormones as well as from the direct actions of the sex chromosomes. However, our understanding of the specific molecular, cellular, and network level processes responsible for mediating sex differences in epilepsy remains limited. Because increasing evidence suggests that epigenetic mechanisms are involved both in epilepsy and in brain sexual dimorphism, we make the case here that analyzing epigenetic regulation will provide novel insights into the basis for sex differences in epilepsy. PMID:24998474

  3. Generation of Optical Combs in a WGM Resonator from a Bichromatic Pump

    NASA Technical Reports Server (NTRS)

    Strekalov, Dmitry V.; Yu, Nan; Matsko, Andrey B.

    2010-01-01

    Optical combs generated by a monolithic resonator with Kerrmedium can be used in a number of applications, including orbital clocks and frequency standards of extremely high accuracy, such as astronomy, molecular spectroscopy, and the like. The main difficulty of this approach is the relatively high pump power that has to be used in such devices, causing undesired thermorefractive effects, as well as stimulated Raman scattering, and limiting the optical comb quality and utility. In order to overcome this problem, this innovation uses a different approach to excitation of the nonlinear oscillations in a Kerr-nonlinear whispering gallery mode (WGM) resonator and generation of the optical comb. By coupling to the resonator two optical pump frequencies instead of just one, the efficiency of the comb source can be increased considerably. It therefore can operate in a lowerpower regime where the undesirable effects are not present. This process does not have a power threshold; therefore, the new optical component can easily be made strong enough to generate further components, making the optical comb spread in a cascade fashion. Additionally, the comb spacing can be made in an arbitrary number of the resonator free spectral ranges (FSR). The experimental setup for this innovation used a fluorite resonator with OMEGA= 13.56 GHz. This material has very low dispersion at the wavelength of 1.5 microns, so the resonator spectrum around this wavelength is highly equidistant. Light was coupled in and out of the resonator using two optical fibers polished at the optimal coupling angle. The gap between the resonator and the fibers, affecting the light coupling and the resonator loading, was controlled by piezo positioners. The light from the input fiber that did not go into the resonator reflected off of its rim, and was collected by a photodetector. This enabled observation and measurement of the (absorption) spectrum of the resonator. The input fiber combined light from two lasers centered at around 1,560 nanometers. Both laser frequencies were simultaneously scanned around the selected WGMs of the same family. However, they were separated by one, two, three, or ten FSRs. This was achieved by fine-tuning each laser frequency offset until the selected resonances overlap on the oscilloscope screen. The resonator quality factor Q = 7 x 10(exp 7) was relatively low to increase the linewidth and, therefore, the duty cycle of both lasers simultaneously coupled into their WGMs. The optical spectrum analyzer (OSA) connected to the output fiber was continuously acquiring data, asynchronously with the laser scan. The instrument was set to retain the peak power values; therefore, a trace recorded for a sufficiently long period of time reflected the situation with both lasers maximally coupled to the WGMs.

  4. Wavelength and bandwidth-tunable silicon comb filter based on Sagnac loop mirrors with Mach-Zehnder interferometer couplers.

    PubMed

    Jiang, Xinhong; Wu, Jiayang; Yang, Yuxing; Pan, Ting; Mao, Junming; Liu, Boyu; Liu, Ruili; Zhang, Yong; Qiu, Ciyuan; Tremblay, Christine; Su, Yikai

    2016-02-01

    We propose and experimentally demonstrate a wavelength and bandwidth-tunable comb filter based on silicon Sagnac loop mirrors (SLMs) with Mach-Zehnder interferometer (MZI) couplers. By thermally tuning the MZI couplers in common and differential modes, the phase shift and reflectivity of the SLMs can be changed, respectively, leading to tunable wavelength and bandwidth of the comb filter. The fabricated comb filter has 93 comb lines in the wavelength range from 1535 nm to 1565 nm spaced by ~0.322 nm. The central wavelength can be red-shifted by ~0.462 nm with a tuning efficiency of ~0.019 nm/mW. A continuously tunable bandwidth from 5.88 GHz to 24.89 GHz is also achieved with a differential heating power ranging from 0.00 mW to 0.53 mW. PMID:26906794

  5. Spectral self-imaging of time-periodic coherent frequency combs by parabolic cross-phase modulation.

    PubMed

    Maram, Reza; Azaña, José

    2013-11-18

    Integer and fractional spectral self-imaging effects are induced on infinite-duration periodic frequency combs (probe signal) using cross-phase modulation (XPM) with a parabolic pulse train as pump signal. Free-spectral-range tuning (fractional effects) or wavelength-shifting (integer effects) of the frequency comb can be achieved by changing the parabolic pulse peak power or/and repetition rate without affecting the spectral envelope shape and bandwidth of the original comb. For design purposes, we derive the complete family of different pump signals that allow implementing a desired spectral self-imaging process. Numerical simulation results validate our theoretical analysis. We also investigate the detrimental influence of group-delay walk-off and deviations in the nominal temporal shape or power of the pump pulses on the generated output frequency combs. PMID:24514395

  6. Demonstration of on-sky calibration of astronomical spectra using a 25 GHz near-IR laser frequency comb.

    PubMed

    Ycas, Gabriel G; Quinlan, Franklyn; Diddams, Scott A; Osterman, Steve; Mahadevan, Suvrath; Redman, Stephen; Terrien, Ryan; Ramsey, Lawrence; Bender, Chad F; Botzer, Brandon; Sigurdsson, Steinn

    2012-03-12

    We describe and characterize a 25 GHz laser frequency comb based on a cavity-filtered erbium fiber mode-locked laser. The comb provides a uniform array of optical frequencies spanning 1450 nm to 1700 nm, and is stabilized by use of a global positioning system referenced atomic clock. This comb was deployed at the 9.2 m Hobby-Eberly telescope at the McDonald Observatory where it was used as a radial velocity calibration source for the fiber-fed Pathfinder near-infrared spectrograph. Stellar targets were observed in three echelle orders over four nights, and radial velocity precision of ?10 m/s (?6 MHz) was achieved from the comb-calibrated spectra. PMID:22418547

  7. Sandstone petrology and diagenesis of lower Tuscaloosa Formation reservoirs in McComb and Little Creek field areas, southwest Mississippi

    SciTech Connect

    Hamlin, K.H.; Cameron, C.P.

    1987-09-01

    Two major depositional facies characterize producing lower Tuscaloosa Formation (Upper Cretaceous) sandstone reservoirs in the McComb-Little Creek field areas: a lower fluvial sequence (Denkman sand) topped by nearshore marine deposits (McComb sand). Petrographic studies reveal that the sandstones of both fields were deposited as very fine to medium-grained quartzarenites and quartz litharenites. Petrographic and x-ray diffraction analyses of the clay mineral content of the sandstones indicate that most of the clays are authigenic and comprise a suite which includes chlorite, kaolinite, mixed-layer illite/smectite, and illite. Mixed-layer illite/smectite appears to be considerably more abundant in the McComb reservoir sandstones than at Little Creek. The reservoir sandstones in the McComb and Little Creek fields are highlighted by good secondary porosity (3-27%, average 19%) developed through dissolution of rock fragments and carbonate cements.

  8. High-power ultra-broadband frequency comb from ultraviolet to infrared by high-power fiber amplifiers.

    PubMed

    Yang, Kangwen; Li, Wenxue; Yan, Ming; Shen, Xuling; Zhao, Jian; Zeng, Heping

    2012-06-01

    A high-power ultra-broadband frequency comb covering the spectral range from ultraviolet to infrared was generated directly by nonlinear frequency conversion of a multi-stage high-power fiber comb amplifier. The 1030-nm infrared spectral fraction of a broadband Ti:sapphire femtosecond frequency comb was power-scaled up to 100 W average power by using a large-mode-area fiber chirped-pulse amplifier. We obtained a frequency-doubled green comb at 515 nm and frequency-quadrupled ultraviolet pulses at 258 nm with the average power of 12.8 and 1.62 W under the input infrared power of 42.2 W, respectively. The carrier envelope phase stabilization was accomplished with an ultra-narrow line-width of 1.86 mHz and a quite low accumulated phase jitter of 0.41 rad, corresponding to a timing jitter of 143 as. PMID:22714317

  9. Measurement of the carrier envelope offset frequency of a femtosecond frequency comb using a Fabry-Perot interferometer

    SciTech Connect

    Basnak, D V; Bikmukhametov, K A; Dmitrieva, N I; Dmitriev, Aleksandr K; Lugovoi, A A; Pokasov, P V; Chepurov, S V

    2010-10-15

    A method for measuring the carrier envelope offset (CEO) frequency of the femtosecond frequency comb with a bandwidth of less than one octave by using a Fabry-Perot interferometer is proposed and experimentally demonstrated. (laser components)

  10. Patterns of comb row development in young and adult stages of the ctenophores Mnemiopsis leidyi and Pleurobrachia pileus.

    PubMed

    Tamm, Sidney L

    2012-09-01

    The development of comb rows in larval and adult Mnemiopsis leidyi and adult Pleurobrachia pileus is compared to regeneration of comb plates in these ctenophores. Late gastrula embryos and recently hatched cydippid larvae of Mnemiopsis have five comb plates in subsagittal rows and six comb plates in subtentacular rows. Subsagittal rows develop a new (sixth) comb plate and both types of rows add plates at similar rates until larvae reach the transition to the lobate form at ?5 mm size. New plate formation then accelerates in subsagittal rows that later extend on the growing oral lobes to become twice the length of subtentacular rows. Interplate ciliated grooves (ICGs) develop in an aboral-oral direction along comb rows, but ICG formation itself proceeds from oral to aboral between plates. New comb plates in Mnemiopsis larvae are added at both aboral and oral ends of rows. At aboral ends, new plates arise as during regeneration: local widening of a ciliated groove followed by formation of a short split plate that grows longer and wider and joins into a common plate. At oral ends, new plates arise as a single tuft of cilia before an ICG appears. Adult Mnemiopsis continue to make new plates at both ends of rows. The frequency of new aboral plate formation varies in the eight rows of an animal and seems unrelated to body size. In Pleurobrachia that lack ICGs, new comb plates at aboral ends arise between the first and second plates as a single small nonsplit plate, located either on the row midline or off-axis toward the subtentacular plane. As the new (now second) plate grows larger, its distance from the first and third plates increases. Size of the new second plate varies within the eight rows of the same animal, indicating asynchronous formation of plates as in Mnemiopsis. New oral plates arise as in Mnemiopsis. The different modes of comb plate formation in Mnemiopsis versus Pleurobrachia are accounted for by differences in mesogleal firmness and mechanisms of ciliary coordination. In both cases, the body of a growing ctenophore is supplied with additional comb plates centripetally from opposite ends of the comb rows. PMID:22729952

  11. Sex tourism in Thailand.

    PubMed

    Van Kerkwijk, C

    1992-01-01

    Many foreigners visit Thailand in search of sex. While long-distance tourism was long enjoyed by members of more privileged social classes, even the lower economical classes of Japan, Malaysia, Europe, America, and Australia can now afford to travel over long distances. This relatively new breed of tourist is more likely to be of lower socioeconomic and educational status and less likely to use condoms when having sex. An estimated 30,000 sex workers are active in Bangkok, of whom 7000/10,000 are females who work specifically in the tourism sector. 1/2-1/3 of the 600 commercial sex establishments in the city are visited by foreigners. Phuket, Pattaya, Koh Samui, and Chiangmai are also well-frequented by sex tourists. Overall, a large, diverse, inexpensive, and accessible commercial sex market exists in Thailand. One may meet sex workers quasi-ubiquitously and be assured to find someone capable of meeting one's sexual needs. With these attributes, Thailand strongly attracts tourists in search of sex. A certain degree of recklessness also prevails among those on vacation. Away from the peers and social mores of their native lands, tourists may engage in sexually activities without criticism. Likewise, Thai sex workers who cater to foreigners, especially females, enjoy more freedom and control in sexual relations than their peers who work among nationals. Neither single nor married women in Thailand are allowed much sexual freedom and are traditionally expected to be obliging docile, and submissive. The greater than normal personal latitude enjoyed by both sex worker and foreigner lead to more negotiation on condom use and overall lower use. As such, Thailand's commercial sex market with foreigners' involvement therein threatens to spread HIV to many other countries throughout the world. PMID:12286018

  12. Generation of Flat Optical Frequency Comb based on Mach-Zehnder Modulator and Recirculating Frequency Shifter Loop

    NASA Astrophysics Data System (ADS)

    Wu, Shibao; Li, Yulong; Fei, Yue; Hu, Faze

    2014-06-01

    We propose a novel scheme to generate optical frequency comb by using Mach-Zehnder modulator and recirculating frequency shifter loop based on IQ modulator driven by radio frequency clock signals. A system of 4 flat and stable comb lines generation based on Mach-Zehnder modulator is set as the seed light source of the recirculating loop. Through theorical analysis and simulation it is shown that the proposed theoretical model is proved in good agreement with simulation results.

  13. Novel comb polymers from alternating N-acylated poly(aminoester)s obtained by spontaneous zwitterionic copolymerisation.

    PubMed

    Kempe, Kristian; de Jongh, Patrick A J M; Anastasaki, Athina; Wilson, Paul; Haddleton, David M

    2015-11-21

    N-Acylated poly(aminoester) (NPAE) macromonomers were synthesised via spontaneous copolymerisation of 2-oxazolines and acrylic acid. Inherent quantitative introduction of α-vinyl end-groups was observed, which enabled the preparation of a series of well-defined NPAE comb polymers through redox-initiated RAFT polymerisation. Investigations of the thermal properties of the comb polymers revealed similarities to poly(2-oxazoline) based systems. PMID:26400482

  14. [Laboratory medicine and sex differences].

    PubMed

    Nishimura, Motoi; Nomura, Fumio

    2015-04-01

    In the field of laboratory medicine, sex differences are found in many clinical tests. Human sex-determination system is at least doubly driven: by sex-chromosomes and by sex-hormones. Karyogram and sex-hormones are typical clinical tests that show sexual dimorphism. Cases of Androgen-Insensitive Syndromes imply sex hormones exert great influences on sex differences found in clinical tests. While childhood, sex steroids secretions from sex-specific organs are inhibited in both sexes. After puberty onset, differences in sex steroids enlarge. In case of females, estrogen secretion decreases in postmenopausal periods. In some of clinical tests, sex differences enlarge after puberty onset, and decrease in postmenopausal periods. Some clinical tests in the field of bone metabolism and lipid metabolism show this kind of sex difference, which seem to be influenced by estrogen. PMID:25936146

  15. Reclassification of Rhodospirillum photometricum Molisch 1907, Rhodospirillum sulfurexigens Anil Kumar et al. 2008 and Rhodospirillum oryzae Lakshmi et al. 2013 in a new genus, Pararhodospirillum gen. nov., as Pararhodospirillum photometricum comb. nov., Pararhodospirillum sulfurexigens comb. nov. and Pararhodospirillum oryzae comb. nov., respectively, and emended description of the genus Rhodospirillum.

    PubMed

    Lakshmi, K V N S; Divyasree, B; Ramprasad, E V V; Sasikala, Ch; Ramana, Ch V

    2014-04-01

    The genus Rhodospirillum is represented by four species, with three of them showing phylogenetic divergence compared to the type species, Rhodospirillum rubrum. Differences in the major diagnostic properties such as internal photosynthetic membranes, quinones, fatty acids, carotenoid composition and a few other phenotypic properties warrant the reclassification of members of this genus. Resultantly, a new genus, Pararhodospirillum gen. nov., is proposed based on the analysis of nine strains to accommodate Rhodospirillum photometricum, Rhodospirillum sulfurexigens and Rhodospirillum oryzae as Pararhodospirillum photometricum comb. nov., Pararhodospirillum sulfurexigens comb. nov. and Pararhodospirillum oryzae comb. nov., respectively. The type species of the genus is Pararhodospirillum photometricum comb. nov. An emended description of the genus Rhodospirillum is also proposed. PMID:24368693

  16. Sex: Making the Right Decision

    MedlinePLUS

    MENU Return to Web version Sex: Making the Right Decision Sex: Making the Right Decision What is sex? The word sex is used in several ways. It can refer ... by the penis. It also can mean what sex you were born (male or female) or physical ...

  17. Generation of optical frequency combs via four-wave mixing processes for low- and medium-resolution astronomy

    NASA Astrophysics Data System (ADS)

    Zajnulina, M.; Boggio, J. M. Chavez; Bhm, M.; Rieznik, A. A.; Fremberg, T.; Haynes, R.; Roth, M. M.

    2015-07-01

    We investigate the generation of optical frequency combs through a cascade of four-wave mixing processes in nonlinear fibres with optimised parameters. The initial optical field consists of two continuous-wave lasers with frequency separation larger than 40 GHz (312.7 pm at 1531 nm). It propagates through three nonlinear fibres. The first fibre serves to pulse shape the initial sinusoidal-square pulse, while a strong pulse compression down to sub-100 fs takes place in the second fibre which is an amplifying erbium-doped fibre. The last stage is a low-dispersion highly nonlinear fibre where the frequency comb bandwidth is increased and the line intensity is equalised. We model this system using the generalised nonlinear Schrdinger equation and investigate it in terms of fibre lengths, fibre dispersion, laser frequency separation and input powers with the aim to minimise the frequency comb noise. With the support of the numerical results, a frequency comb is experimentally generated, first in the near infra-red and then it is frequency-doubled into the visible spectral range. Using a MUSE-type spectrograph, we evaluate the comb performance for astronomical wavelength calibration in terms of equidistancy of the comb lines and their stability.

  18. A two-stage optical frequency comb generator based on polarization modulators and a Mach-Zehnder interferometer

    NASA Astrophysics Data System (ADS)

    Zhang, Fangzheng; Ge, Xiaozhong; Pan, Shilong

    2015-11-01

    A two-stage optical frequency comb (OFC) generator is proposed based on two polarization modulators (PolMs) and a Mach-Zehnder interferometer (MZI). In the first-stage OFC generator, a group of even-order sidebands and a group of odd-order sidebands are generated with similar powers, respectively, based on a single PolM. By tuning the power difference between the two sideband groups using an MZI, a flat OFC with increased comb-lines can be generated. In the experiment, OFCs with up to 11 comb-lines are generated with good flatness, which is better than most of the previous scheme based on a single modulator. To further increase the comb-line number, a second-stage OFC generator is followed using another PolM, which could increase the comb-line number by a factor of up to 5 theoretically. Performance of the proposed two-stage OFC generator is investigated through simulations and experiments. The results can verify the feasibility of the proposed OFC generator, which is a cost-effective way to generate flat OFCs with a large number of comb-lines.

  19. Optical-frequency-comb generation and entanglement with low-power optical input in a photonic molecule

    NASA Astrophysics Data System (ADS)

    Li, Jiahua; Yu, Rong; Ding, Chunling; Wang, Wei; Wu, Ying

    2014-09-01

    Optical-frequency combs consisting of equally spaced sharp lines in frequency space have triggered substantial advances in optical-frequency metrology and precision measurements and in applications such as laser-based gas sensing and molecular fingerprinting. Here, we propose a scheme to generate a type of optical-frequency combs and convert them from one cavity to the other in a hybrid optical system composed of a pair of coupled photonic crystal cavities called a photonic molecule (PM) and a single semiconductor quantum dot (QD) embedded in one cavity of the molecule. Optical-frequency combs are formed by the interaction between a cavity mode and a continuous-wave (CW) two-tone driving laser consisting of a pump field and a seed field via QD-induced strong nonlinearity. In this situation, the initial input pump and seed CW lasers can interact among each other and produce optical higher-order sidebands with equal spacing via parametric frequency conversion provided by QD-induced nonlinear optical effects. Using numerical simulations, it is clearly shown that the beat frequency of the two-tone components plays an important role in determining the comb spacing and matched frequency combs can be formed in the PM. We also demonstrate that the present interacting QD-PM system can serve as a platform to generate large-scale quantum entanglement between two comb modes. The results obtained here may be useful for real experiments in a photonic crystal platform.

  20. Coherent control of multiphoton resonance dynamics in high-order-harmonic generation driven by two frequency-comb fields

    NASA Astrophysics Data System (ADS)

    Zhao, Di; Jiang, Chen-Wei; Li, Fu-li

    2015-10-01

    We present a theoretical investigation of the multiphoton resonance dynamics in the high-order-harmonic generation (HHG) process driven by two frequency-comb fields with the carrier frequencies of fundamental and second harmonics, respectively. The many-mode Floquet theorem is employed to provide a nonperturbative and exact treatment of the interaction between a quantum system and frequency-comb laser fields. The coupling of the weak second-harmonic control frequency-comb laser field promises more routes to coherently optimize the multiphoton resonance dynamics and HHG power spectra. First, even-order harmonics are generated due to the coupling of the second-harmonic frequency-comb field. Second, the HHG power spectra can be greatly enhanced via multiphoton resonance, which can be achieved by tuning the carrier-envelope-phase (CEP) shifts and the peak intensities of both frequency-comb fields. Furthermore, besides the multiphoton transitions involving only fundamental-harmonic photons, additional multiphoton transitions involving both fundamental- and second-harmonic photons occur, resulting in the generation of combs with frequencies dependent on CEP shifts of both fields. Different multiphoton transition paths can interfere with each other when the two CEP shifts are matching, and the interference of paths allows one to coherently control the HHG power spectra by varying the relative phase between the fields.

  1. Sex Education. Kaleidoscope.

    ERIC Educational Resources Information Center

    Boderick, Carlfred; And Others

    This publication attempts to keep a portion of the educational community in touch with current topics and trends. The present focus is on sex education, a topic of growing concern in educational circles. The texts of three addresses are presented, with audience questions and speaker responses. Dr. Carlfred Broderick gives an overview of sex

  2. Sex differences in stroke

    PubMed Central

    Haast, Roy A M; Gustafson, Deborah R; Kiliaan, Amanda J

    2012-01-01

    Sex differences in stroke are observed across epidemiologic studies, pathophysiology, treatments, and outcomes. These sex differences have profound implications for effective prevention and treatment and are the focus of this review. Epidemiologic studies reveal a clear age-by-sex interaction in stroke prevalence, incidence, and mortality. While premenopausal women experience fewer strokes than men of comparable age, stroke rates increase among postmenopausal women compared with age-matched men. This postmenopausal phenomenon, in combination with living longer, are reasons for women being older at stroke onset and suffering more severe strokes. Thus, a primary focus of stroke prevention has been based on sex steroid hormone-dependent mechanisms. Sex hormones affect different (patho)physiologic functions of the cerebral circulation. Clarifying the impact of sex hormones on cerebral vasculature using suitable animal models is essential to elucidate male–female differences in stroke pathophysiology and development of sex-specific treatments. Much remains to be learned about sex differences in stroke as anatomic and genetic factors may also contribute, revealing its multifactorial nature. In addition, the aftermath of stroke appears to be more adverse in women than in men, again based on older age at stroke onset, longer prehospital delays, and potentially, differences in treatment. PMID:23032484

  3. Sex and America's Teenagers.

    ERIC Educational Resources Information Center

    Alan Guttmacher Inst., New York, NY.

    Although sexual activity is common among teenagers, it is not as widespread, and does not begin as early, as most adults believe. This report provides detailed data and analysis of sex among adolescents. Adolescent sexual activity is grouped in ten categories: (1) Rites of passage; (2) The context of adolescents' lives; (3) Sex among teenagers;…

  4. Advocating Elementary Sex Education.

    ERIC Educational Resources Information Center

    McNab, Warren L.

    1981-01-01

    Sex education is an important asset to personal growth during the elementary years. Though many parents are opposed to sex education during these early years, sexual knowledge acts as an antidote to fear and does not contribute to promiscuity. New programs in sexuality and family life are presently being developed. (JN)

  5. Sex Away from Home

    ERIC Educational Resources Information Center

    Greenwald, Harold

    1971-01-01

    The reasons why people who are normally truthful to their spouses engage in sex away from home are discussed. These reasons can include loneliness, ego building or the opportunity to have homosexual relations. Sex away from home is likely to increase since the number of people traveling is increasing. (Author/CG)

  6. Sex, Schools, and Socialization.

    ERIC Educational Resources Information Center

    Ornstein, Allan C.; Levine, Daniel U.

    1982-01-01

    Discusses various factors which affect sexual identity in boys and girls: orientation of curriculum and classroom activities; presence of competitive sports; and sex-role stereotypes in textbooks. Also discusses how societal changes, such as employment and educational attainment of women and decreased family size, are affecting former sex roles.

  7. Sex Roles within Marriage.

    ERIC Educational Resources Information Center

    Krausz, Susan Lavinsky

    1986-01-01

    Studied married couples' allocation of tasks within the household and found that role specialization existed in accordance with traditional sex role norms. Found that wives' self-esteem was not significant, but that the number of hours they were employed, their sex role orientation, and the attitudes of their significant others were significantly

  8. Sex: Who Cares? Introduction.

    ERIC Educational Resources Information Center

    Liben, Lynn S.

    2000-01-01

    Presents evidence supporting claim that sex and gender are important to the explanatory as well as the descriptive goals of developmental psychology. Maintains that studying psychosocial and biological components of gender and sex helps one to develop hypotheses about causal mechanisms for developmental outcomes more generally. Introduces the

  9. Single-Sex Classrooms

    ERIC Educational Resources Information Center

    Protheroe, Nancy

    2009-01-01

    Although single-sex education was once the norm in the U.S., the practice has largely been confined to private schools for more than a century. However, with the introduction of the final version of the U.S. Department of Education's so-called single-sex regulations in 2006, public schools were allowed greater flexibility to offer single-sex…

  10. Sex Determination in Papaya

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sex determination is an intriguing system in trioecious papaya. Over the past seven decades various hypotheses, based on the knowledge and information available at the time, have been proposed to explain the genetics of the papaya's sex determination. These include a single gene with three alleles...

  11. Sex: Who Cares? Introduction.

    ERIC Educational Resources Information Center

    Liben, Lynn S.

    2000-01-01

    Presents evidence supporting claim that sex and gender are important to the explanatory as well as the descriptive goals of developmental psychology. Maintains that studying psychosocial and biological components of gender and sex helps one to develop hypotheses about causal mechanisms for developmental outcomes more generally. Introduces the…

  12. Dimensional metrology using the optical comb of a mode-locked laser

    NASA Astrophysics Data System (ADS)

    Jin, Jonghan

    2016-02-01

    In the field of dimensional metrology, significant technical challenges have been encountered with regard to large-scale object assembly, satellite positioning, control of the long-distance precision stage, and inspections of large steps or deep holes on semiconductor devices and multi-layered display panels. The key elements required are high speeds, a long dynamic measurable range, and good precision of measurements, and conventional methods can scarcely meet such requirements simultaneously. Promisingly, the advent of the optical comb has opened up numerous possibilities to break through practical limits by exploiting several of its unique features. These include inter-mode interference, a wide spectral bandwidth with a long coherence length and well-defined longitudinal modes. In this review, various dimensional metrological methods using the optical comb are introduced, describing their basic principles and applications in scientific as well as industrial areas.

  13. Hierarchical, multilayered cell walls reinforced by recycled silk cocoons enhance the structural integrity of honeybee combs

    PubMed Central

    Zhang, Kai; Duan, Huiling; Karihaloo, Bhushan L.; Wang, Jianxiang

    2010-01-01

    We reveal the sophisticated and hierarchical structure of honeybee combs and measure the elastic properties of fresh and old natural honeycombs at different scales by optical microscope, environmental scanning electron microscope, nano/microindentation, and by tension and shear tests. We demonstrate that the comb walls are continuously strengthened and stiffened without becoming fragile by the addition of thin wax layers reinforced by recycled silk cocoons reminiscent of modern fiber-reinforced composite laminates. This is done to increase its margin of safety against collapse due to a temperature increase. Artificial engineering honeycombs mimic only the macroscopic geometry of natural honeycombs, but have yet to achieve the microstructural sophistication of their natural counterparts. The natural honeycombs serve as a prototype of truly biomimetic cellular materials with hitherto unattainable improvement in stiffness, strength, toughness, and thermal stability. PMID:20439765

  14. Implementation of a single femtosecond optical frequency comb for rovibrational cooling

    SciTech Connect

    Shi, W.; Malinovskaya, S.

    2010-07-15

    We show that a single femtosecond optical frequency comb may be used to induce two-photon transitions between molecular vibrational levels to form ultracold molecules (e.g., KRb). The phase across an individual pulse in the pulse train is sinusoidally modulated with a carefully chosen modulation amplitude and frequency. Piecewise adiabatic population transfer is fulfilled to the final state by each pulse in the applied pulse train, providing a controlled population accumulation in the final state. Detuning the pulse train carrier and modulation frequency from one-photon resonances changes the time scale of molecular dynamics but leads to the same complete population transfer to the ultracold state. A standard optical frequency comb with no modulation is shown to induce similar dynamics, leading to rovibrational cooling.

  15. A Laser Frequency Comb System for Absolute Calibration of the VTT Echelle Spectrograph

    NASA Astrophysics Data System (ADS)

    Doerr, H.-P.; Steinmetz, T.; Holzwarth, R.; Kentischer, T.; Schmidt, W.

    2012-10-01

    A wavelength calibration system based on a laser frequency comb (LFC) was developed in a co-operation between the Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut für Quantenoptik, Garching, Germany for permanent installation at the German Vacuum Tower Telescope (VTT) on Tenerife, Canary Islands. The system was installed successfully in October 2011. By simultaneously recording the spectra from the Sun and the LFC, for each exposure a calibration curve can be derived from the known frequencies of the comb modes that is suitable for absolute calibration at the meters per second level. We briefly summarize some topics in solar physics that benefit from absolute spectroscopy and point out the advantages of LFC compared to traditional calibration techniques. We also sketch the basic setup of the VTT calibration system and its integration with the existing echelle spectrograph.

  16. Performance of a laser frequency comb calibration system with a high-resolution solar echelle spectrograph

    NASA Astrophysics Data System (ADS)

    Doerr, H.-P.; Kentischer, T. J.; Steinmetz, T.; Probst, R. A.; Franz, M.; Holzwarth, R.; Udem, Th.; Hänsch, T. W.; Schmidt, W.

    2012-09-01

    Laser frequency combs (LFC) provide a direct link between the radio frequency (RF) and the optical frequency regime. The comb-like spectrum of an LFC is formed by exact equidistant laser modes, whose absolute optical frequencies are controlled by RF-references such as atomic clocks or GPS receivers. While nowadays LFCs are routinely used in metrological and spectroscopic fields, their application in astronomy was delayed until recently when systems became available with a mode spacing and wavelength coverage suitable for calibration of astronomical spectrographs. We developed a LFC based calibration system for the high-resolution echelle spectrograph at the German Vacuum Tower Telescope (VTT), located at the Teide observatory, Tenerife, Canary Islands. To characterize the calibration performance of the instrument, we use an all-fiber setup where sunlight and calibration light are fed to the spectrograph by the same single-mode fiber, eliminating systematic effects related to variable grating illumination.

  17. Resonant light scattering of a laser frequency comb by a quantum dot

    NASA Astrophysics Data System (ADS)

    Konthasinghe, K.; Peiris, M.; Muller, A.

    2014-08-01

    We investigate the spectral and temporal properties of light scattered near resonantly by a single quantum dot when the incident laser field is a frequency comb consisting of a superposition of monochromatic waves equidistant in frequency. Such fields encompass those generated by, e.g., a periodically pulsed laser. A general theoretical treatment for the calculation of first- and second-order correlation functions is given which takes account of spectral diffusion through a slowly varying detuning from resonance, permitting accurate comparison with experiments. We explore the two distinct regimes in which the frequency-comb separation is either larger or smaller than the radiative decay rate. We verify the validity of our calculations by a comparison with experimental data for the case of a bichromatic field and discuss the manifestation of phase coherence between the incoming field and the scattered single-photon wave packet.

  18. a New Broadband Cavity Enhanced Frequency Comb Spectroscopy Technique Using GHz Vernier Filtering.

    NASA Astrophysics Data System (ADS)

    Morville, Jrme; Rutkowski, Lucile; Dobrev, Georgi; Crozet, Patrick

    2015-06-01

    We present a new approach to Cavity Enhanced - Direct Frequency Comb Spectroscopy where the full emission bandwidth of a Titanium:Sapphire laser is exploited at GHz resolution. The technique is based on a low-resolution Vernier filtering obtained with an appreciable -actively stabilized- mismatch between the cavity Free Spectral Range and the laser repetition rate, using a diffraction grating and a split-photodiode. This particular approach provides an immunity to frequency-amplitude noise conversion, reaching an absorption baseline noise in the 10-9 cm-1 range with a cavity finesse of only 3000. Spectra covering 1800 cm-1 ( 55 THz) are acquired in recording times of about 1 second, providing an absorption figure of merit of a few 10-11 cm-1/?{Hz}. Initially tested with ambient air, we report progress in using the Vernier frequency comb method with a discharge source of small radicals. Rutkowski et al, Opt. Lett., 39(23)2014

  19. Transmission comb of a distributed Bragg reflector with two surface dielectric gratings

    PubMed Central

    Zhao, Xiaobo; Zhang, Yongyou; Zhang, Qingyun; Zou, Bingsuo; Schwingenschlogl, Udo

    2016-01-01

    The transmission behaviour of a distributed Bragg reector (DBR) with surface dielectric gratings on top and bottom is studied. The transmission shows a comb-like spectrum in the DBR band gap, which is explained in the Fano picture. The number density of the transmission peaks increases with increasing number of cells of the DBR, while the ratio of the average full width at half maximum to the corresponding average free spectral range, being only few percent for both transversal electric and magnetic waves, is almost invariant. The transmission peaks can be narrower than 0.1 nm and are fully separated from each other in certain wavebands. We further prove that the transmission combs are robust against randomness in the heights of the DBR layers. Therefore, the proposed structure is a candidate for an ultra-narrow-band multichannel filter or polarizer. PMID:26893069

  20. Frequency-comb-referenced multi-wavelength profilometry for largely stepped surfaces.

    PubMed

    Hyun, Sangwon; Choi, Minah; Chun, Byung Jae; Kim, Seungman; Kim, Seung-Woo; Kim, Young-Jin

    2013-04-22

    3-D profiles of discontinuous surfaces patterned with high step structures are measured using four wavelengths generated by phase-locking to the frequency comb of an Er-doped fiber femtosecond laser stabilized to the Rb atomic clock. This frequency-comb-referenced method of multi-wavelength interferometry permits extending the phase non-ambiguity range by a factor of 64,500 while maintaining the sub-wavelength measurement precision of single-wavelength interferometry. Experimental results show a repeatability of 3.13 nm (one-sigma) in measuring step heights of 1800, 500, and 70 ?m. The proposed method is accurate enough for the standard calibration of gauge blocks and also fast to be suited for the industrial inspection of microelectronics products. PMID:23609685

  1. A distance meter using a terahertz intermode beat in an optical frequency comb.

    PubMed

    Yokoyama, Shuko; Yokoyama, Toshiyuki; Hagihara, Yuki; Araki, Tsutomu; Yasui, Takeshi

    2009-09-28

    We propose a distance meter that utilizes an intermode beat of terahertz frequency in an optical frequency comb to perform high resolution and high dynamic range absolute distance measurements. The proposed system is based on a novel method, called multiheterodyne cross-correlation detection, in which intermode beat frequencies are scaled down to radio frequencies by optical mixing of two detuned optical frequency combs with a nonlinear optical crystal. Using this method, we obtained a 1.056 THz intermode beat and achieved a distance resolution of 0.820 microm from its phase measurement. Absolute distance measurement using 1.056 THz and 8.187 GHz intermode beats was also demonstrated in the range of 10 mm, resulting in a precision of 0.688 microm. PMID:19907518

  2. Frequency-comb-referenced singly-resonant OPO for sub-Doppler spectroscopy.

    PubMed

    Ricciardi, I; De Tommasi, E; Maddaloni, P; Mosca, S; Rocco, A; Zondy, J-J; De Rosa, M; De Natale, P

    2012-04-01

    We present a widely-tunable, singly-resonant optical parametric oscillator, emitting more than 1 W between 2.7 and 4.2 ?m, which is phase locked to a self-referenced frequency comb. Both pump and signal frequencies are directly phase-locked to the frequency comb of a NIR-emitting fs mode-locked fibre laser, linked, in turn, to the caesium primary standard. We estimate for the idler frequency a fractional Allan deviation of ? 3 10??? between 1 and 200 s. To test the spectroscopic performance of the OPO, we carried out saturation spectroscopy of several transitions belonging to the ?1 rovibrational band of CH?I, resolving their electronic quadrupole hyperfine structure, estimating a linewidth better than 200 kHz FWHM for the idler, and determining the absolute frequency of the hyperfine components with a 50-kHz-uncertainty. PMID:22513629

  3. Multi-delay, phase coherent pulse pair generation for precision Ramsey-frequency comb spectroscopy.

    PubMed

    Morgenweg, J; Eikema, K S E

    2013-03-11

    We demonstrate the generation of phase-stable mJ-pulse pairs at programmable inter-pulse delays up to hundreds of nanoseconds. A detailed investigation of potential sources for phase shifts during the parametric amplification of the selected pulses from a Ti:Sapphire frequency comb is presented, both numerically and experimentally. It is shown that within the statistical error of the phase measurement of 10 mrad, there is no dependence of the differential phase shift over the investigated inter-pulse delay range of more than 300 ns. In combination with nonlinear upconversion of the amplified pulses, the presented system will potentially enable short wavelength (<100 nm), multi-transition Ramsey-frequency comb spectroscopy at the kHz-level. PMID:23482099

  4. Transmission comb of a distributed Bragg reflector with two surface dielectric gratings.

    PubMed

    Zhao, Xiaobo; Zhang, Yongyou; Zhang, Qingyun; Zou, Bingsuo; Schwingenschlogl, Udo

    2016-01-01

    The transmission behaviour of a distributed Bragg reector (DBR) with surface dielectric gratings on top and bottom is studied. The transmission shows a comb-like spectrum in the DBR band gap, which is explained in the Fano picture. The number density of the transmission peaks increases with increasing number of cells of the DBR, while the ratio of the average full width at half maximum to the corresponding average free spectral range, being only few percent for both transversal electric and magnetic waves, is almost invariant. The transmission peaks can be narrower than 0.1?nm and are fully separated from each other in certain wavebands. We further prove that the transmission combs are robust against randomness in the heights of the DBR layers. Therefore, the proposed structure is a candidate for an ultra-narrow-band multichannel filter or polarizer. PMID:26893069

  5. Evanescent-wave comb spectroscopy of liquids with strongly dispersive optical fiber cavities

    NASA Astrophysics Data System (ADS)

    Avino, S.; Giorgini, A.; Salza, M.; Fabian, M.; Gagliardi, G.; De Natale, P.

    2013-05-01

    We demonstrate evanescent-wave fiber cavity-enhanced spectroscopy in the liquid phase using a near-infrared frequency comb. Exploiting strong fiber-dispersion effects, we show that liquid absorption spectra can be recorded without any external dispersive element. The fiber cavity is used both as sensor and spectrometer. The resonance modes are frequency locked to the comb teeth while the cavity photon lifetime is measured over 155 nm, from 1515 nm to 1670 nm, where absorption bands of liquid polyamines are detected as a proof of concept. Our fiber spectrometer lends itself to in situ, real-time chemical analysis in environmental monitoring, biomedical assays, and micro-opto-fluidic systems.

  6. Fast interrogation of fiber Bragg grating sensors using electro-optic dual optical frequency combs

    NASA Astrophysics Data System (ADS)

    Bonilla-Manrique, O. E.; Garcia-Souto, J. A.; Martin-Mateos, P.; Jerez-Gonzalez, B.; Acedo, P.

    2015-09-01

    In this document, a FBG interrogation system based on a multimode optical source and a direct read-out is proposed for measuring fast phenomena such as vibrations and ultrasounds. The system is based on an electro-optic dual optical frequency-comb. This architecture allows the configuration of the multimode optical source parameters such as the number of modes that are within the reflected spectrum (FWHM) of the FBG. Results are presented for the dual-comb operating under optimized control when mapping these optical modes onto detectable tones of multiples of 100 kHz around a centre radiofrequency tone (40 MHz). Dynamic strain is induced onto the fiber through an actuator, which generates changes in the reflected wavelength of the FBG and in turn the modes within the reflected spectrum. The electrical signals are analyzed using fast Fourier transform algorithms allowing identification of the vibrations.

  7. Frequency-comb-assisted precision laser spectroscopy of CHF3 around 8.6 ?m

    NASA Astrophysics Data System (ADS)

    Gambetta, Alessio; Coluccelli, Nicola; Cassinerio, Marco; Fernandez, Toney Teddy; Gatti, Davide; Castrillo, Antonio; Ceausu-Velcescu, Adina; Fasci, Eugenio; Gianfrani, Livio; Santamaria, Luigi; Di Sarno, Valentina; Maddaloni, Pasquale; De Natale, Paolo; Laporta, Paolo; Galzerano, Gianluca

    2015-12-01

    We report a high-precision spectroscopic study of room-temperature trifluoromethane around 8.6 ?m, using a CW quantum cascade laser phase-locked to a mid-infrared optical frequency comb. This latter is generated by a nonlinear down-conversion process starting from a dual-branch Er:fiber laser and is stabilized against a GPS-disciplined rubidium clock. By tuning the comb repetition frequency, several transitions falling in the ?5 vibrational band are recorded with a frequency resolution of 20 kHz. Due to the very dense spectra, a special multiple-line fitting code, involving a Voigt profile, is developed for data analysis. The combination of the adopted experimental approach and survey procedure leads to fractional accuracy levels in the determination of line center frequencies, down to 2 10-10. Line intensity factors, pressure broadening, and shifting parameters are also provided.

  8. Generation of multiphoton entangled quantum states by means of integrated frequency combs.

    PubMed

    Reimer, Christian; Kues, Michael; Roztocki, Piotr; Wetzel, Benjamin; Grazioso, Fabio; Little, Brent E; Chu, Sai T; Johnston, Tudor; Bromberg, Yaron; Caspani, Lucia; Moss, David J; Morandotti, Roberto

    2016-03-11

    Complex optical photon states with entanglement shared among several modes are critical to improving our fundamental understanding of quantum mechanics and have applications for quantum information processing, imaging, and microscopy. We demonstrate that optical integrated Kerr frequency combs can be used to generate several bi- and multiphoton entangled qubits, with direct applications for quantum communication and computation. Our method is compatible with contemporary fiber and quantum memory infrastructures and with chip-scale semiconductor technology, enabling compact, low-cost, and scalable implementations. The exploitation of integrated Kerr frequency combs, with their ability to generate multiple, customizable, and complex quantum states, can provide a scalable, practical, and compact platform for quantum technologies. PMID:26965623

  9. Novel active comb-shaped dry electrode for EEG measurement in hairy site.

    PubMed

    Huang, Yan-Jun; Wu, Chung-Yu; Wong, Alice May-Kuen; Lin, Bor-Shyh

    2015-01-01

    Electroencephalography (EEG) is an important biopotential, and has been widely applied in clinical applications. The conventional EEG electrode with conductive gels is usually used for measuring EEG. However, the use of conductive gel also encounters with the issue of drying and hardening. Recently, many dry EEG electrodes based on different conductive materials and techniques were proposed to solve the previous issue. However, measuring EEG in the hairy site is still a difficult challenge. In this study, a novel active comb-shaped dry electrode was proposed to measure EEG in hairy site. Different form other comb-shaped or spike-shaped dry electrodes, it can provide more excellent performance of avoiding the signal attenuation, phase distortion, and the reduction of common mode rejection ratio. Even under walking motion, it can effectively acquire EEG in hairy site. Finally, the experiments for alpha rhythm and steady-state visually evoked potential were also tested to validate the proposed electrode. PMID:25137719

  10. Tapered semiconductor amplifiers for optical frequency combs in the near infrared

    NASA Astrophysics Data System (ADS)

    Cruz, Flavio C.; Stowe, Matthew C.; Ye, Jun

    2006-05-01

    A tapered semiconductor amplifier is injection seeded by a femtosecond optical frequency comb at 780nm from a mode-locked Ti:sapphire laser. Energy gains of more than 17dB(12dB) are obtained for 1mW(20mW) of average input power when the input pulses are stretched into the picosecond range. A spectral window of supercontinuum light generated in a photonic fiber has also been amplified. Interferometric measurements show sub-Hertz linewidths for a heterodyne beat between the input and amplified comb components, yielding no detectable phase-noise degradation under amplication. These amplifiers can be used to boost the infrared power in f-to-2f interferometers used to determine the carrier-to-envelope offset frequency, with clear advantages for stabilization of octave-spanning femtosecond lasers and other supercontinuum light sources.

  11. Self referenced Yb-fiber-laser frequency comb using a dispersion micromanaged tapered holey fiber.

    PubMed

    Pal, Parama; Knox, Wayne H; Hartl, Ingmar; Fermann, Martin E

    2007-09-17

    We demonstrate a fully stabilized frequency comb in the 1mum spectral region based on an Yb-fiber oscillator and a cladding pumped chirped pulse Yb-fiber amplifier whose output is spectrally broadened in a dispersion micromanaged holey fiber. The dispersion micromanaged fiber is used to generate efficient, low noise spectral components at 523nm which are heterodyned with the second harmonic of the amplifier output for standard f-to-2f self-referenced carrier envelope offset frequency detection. For comb stabilization we phase-lock this offset frequency and the oscillator repetition frequency simultaneously to an RF reference by feedback controlling the oscillator pump diode current and the driving voltage of an intracavity piezo-electric fiber stretcher respectively. PMID:19547582

  12. Generation and photonic guidance of multi-octave optical-frequency combs.

    PubMed

    Couny, F; Benabid, F; Roberts, P J; Light, P S; Raymer, M G

    2007-11-16

    Ultrabroad coherent comb-like optical spectra spanning several octaves are a chief ingredient in the emerging field of attoscience. We demonstrate generation and guidance of a three-octave spectral comb, spanning wavelengths from 325 to 2300 nanometers, in a hydrogen-filled hollow-core photonic crystal fiber. The waveguidance results not from a photonic band gap but from the inhibited coupling between the core and cladding modes. The spectrum consists of up to 45 high-order Stokes and anti-Stokes lines and is generated by driving the confined gas with a single, moderately powerful (10-kilowatt) infrared laser, producing 12-nanosecond-duration pulses. This represents a reduction by six orders of magnitude in the required laser powers over previous equivalent techniques and opens up a robust and much simplified route to synthesizing attosecond pulses. PMID:18006741

  13. Transmission comb of a distributed Bragg reflector with two surface dielectric gratings

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaobo; Zhang, Yongyou; Zhang, Qingyun; Zou, Bingsuo; Schwingenschlogl, Udo

    2016-02-01

    The transmission behaviour of a distributed Bragg reector (DBR) with surface dielectric gratings on top and bottom is studied. The transmission shows a comb-like spectrum in the DBR band gap, which is explained in the Fano picture. The number density of the transmission peaks increases with increasing number of cells of the DBR, while the ratio of the average full width at half maximum to the corresponding average free spectral range, being only few percent for both transversal electric and magnetic waves, is almost invariant. The transmission peaks can be narrower than 0.1 nm and are fully separated from each other in certain wavebands. We further prove that the transmission combs are robust against randomness in the heights of the DBR layers. Therefore, the proposed structure is a candidate for an ultra-narrow-band multichannel filter or polarizer.

  14. Photonic chip-based optical frequency comb using soliton Cherenkov radiation.

    PubMed

    Brasch, V; Geiselmann, M; Herr, T; Lihachev, G; Pfeiffer, M H P; Gorodetsky, M L; Kippenberg, T J

    2016-01-22

    Optical solitons are propagating pulses of light that retain their shape because nonlinearity and dispersion balance each other. In the presence of higher-order dispersion, optical solitons can emit dispersive waves via the process of soliton Cherenkov radiation. This process underlies supercontinuum generation and is of critical importance in frequency metrology. Using a continuous wave-pumped, dispersion-engineered, integrated silicon nitride microresonator, we generated continuously circulating temporal dissipative Kerr solitons. The presence of higher-order dispersion led to the emission of red-shifted soliton Cherenkov radiation. The output corresponds to a fully coherent optical frequency comb that spans two-thirds of an octave and whose phase we were able to stabilize to the sub-Hertz level. By preserving coherence over a broad spectral bandwidth, our device offers the opportunity to develop compact on-chip frequency combs for frequency metrology or spectroscopy. PMID:26721682

  15. Hierarchical, multilayered cell walls reinforced by recycled silk cocoons enhance the structural integrity of honeybee combs.

    PubMed

    Zhang, Kai; Duan, Huiling; Karihaloo, Bhushan L; Wang, Jianxiang

    2010-05-25

    We reveal the sophisticated and hierarchical structure of honeybee combs and measure the elastic properties of fresh and old natural honeycombs at different scales by optical microscope, environmental scanning electron microscope, nano/microindentation, and by tension and shear tests. We demonstrate that the comb walls are continuously strengthened and stiffened without becoming fragile by the addition of thin wax layers reinforced by recycled silk cocoons reminiscent of modern fiber-reinforced composite laminates. This is done to increase its margin of safety against collapse due to a temperature increase. Artificial engineering honeycombs mimic only the macroscopic geometry of natural honeycombs, but have yet to achieve the microstructural sophistication of their natural counterparts. The natural honeycombs serve as a prototype of truly biomimetic cellular materials with hitherto unattainable improvement in stiffness, strength, toughness, and thermal stability. PMID:20439765

  16. Sensing with mid-infrared frequency combs: a novel modality for ultrasensitive detection of hazardous materials

    NASA Astrophysics Data System (ADS)

    Vodopyanov, Konstantin L.

    2009-05-01

    We propose a new concept for point and stand-off detection of chemical and biological agents as well as explosives' vapors and residues on solid surfaces based on frequency comb spectroscopy in the region of mid-IR molecular vibrational "fingerprints". Our method will allow identification of hazardous substances with high detection sensitivity and real-time data processing. A two-octave-wide mid-infrared frequency comb output will be produced by a cascaded sub-harmonic optical parametric oscillator (OPO) pumped by a fiber laser. The proposed device will use the principle of coherent Fourier-transform infrared spectrometer and offer an unprecedented precision and speed of acquisition of spectral information.

  17. Photonic chip–based optical frequency comb using soliton Cherenkov radiation

    NASA Astrophysics Data System (ADS)

    Brasch, V.; Geiselmann, M.; Herr, T.; Lihachev, G.; Pfeiffer, M. H. P.; Gorodetsky, M. L.; Kippenberg, T. J.

    2016-01-01

    Optical solitons are propagating pulses of light that retain their shape because nonlinearity and dispersion balance each other. In the presence of higher-order dispersion, optical solitons can emit dispersive waves via the process of soliton Cherenkov radiation. This process underlies supercontinuum generation and is of critical importance in frequency metrology. Using a continuous wave–pumped, dispersion-engineered, integrated silicon nitride microresonator, we generated continuously circulating temporal dissipative Kerr solitons. The presence of higher-order dispersion led to the emission of red-shifted soliton Cherenkov radiation. The output corresponds to a fully coherent optical frequency comb that spans two-thirds of an octave and whose phase we were able to stabilize to the sub-Hertz level. By preserving coherence over a broad spectral bandwidth, our device offers the opportunity to develop compact on-chip frequency combs for frequency metrology or spectroscopy.

  18. Adaptive frequency comb illumination for interferometry in the case of nested two-beam cavities

    SciTech Connect

    Harder, Irina; Leuchs, Gerd; Mantel, Klaus; Schwider, Johannes

    2011-09-01

    The homogeneity test of glass plates in a Fizeau interferometer is hampered by the superposition of multiple interference signals coming from the surfaces of the glass plate as well as the empty Fizeau cavity. To evaluate interferograms resulting from such nested cavities, various approaches such as the use of broadband light sources have been applied. In this paper, we propose an adaptive frequency comb interferometer to accomplish the cavity selection. An adjustable Fabry-Perot resonator is used to generate a variable frequency comb that can be matched to the length of the desired cavity. Owing to its flexibility, the number of measurements needed for the homogeneity test can be reduced to four. Furthermore, compared to approaches using a two-beam interferometer as a filter for the broadband light source, the visibility of the fringe system is considerably higher if a Fabry-Perot filter is applied.

  19. Sex in Fungi

    PubMed Central

    Ni, Min; Feretzaki, Marianna; Sun, Sheng; Wang, Xuying; Heitman, Joseph

    2012-01-01

    Sexual reproduction enables genetic exchange in eukaryotic organisms as diverse as fungi, animals, plants, and ciliates. Given its ubiquity, sex is thought to have evolved once, possibly concomitant with or shortly after the origin of eukaryotic organisms themselves. The basic principles of sex are conserved, including ploidy changes, the formation of gametes via meiosis, mate recognition, and cell-cell fusion leading to the production of a zygote. Although the basic tenants are shared, sex determination and sexual reproduction occur in myriad forms throughout nature, including outbreeding systems with more than two mating types or sexes, unisexual selfing, and even examples in which organisms switch mating type. As robust and diverse genetic models, fungi provide insights into the molecular nature of sex, sexual specification, and evolution to advance our understanding of sexual reproduction and its impact throughout the eukaryotic tree of life. PMID:21942368

  20. Sex, Sex Roles, and Rhetorical Sensitivity.

    ERIC Educational Resources Information Center

    Pearson, Judy C.

    It was hypothesized that the dimensions of R. P. Hart's rhetorical sensitivity scale--rhetorical sensitivity, noble self, and rhetorical reflector--would correspond, respectively, to the categories of androgyny, masculinity, and femininity in Bem's Sex Role Inventory. The two instruments were administered to 426 college students (211 men and 215

  1. Synthesis of Non-spherical Glycopolymer-Decorated Nanoparticles: Combing Thiol-ene with Catecholic Chemistry.

    PubMed

    Li, Xiao; Zhang, Weidong; Chen, Gaojian

    2016-01-01

    Glycopolymers with carbohydrate side chains are currently being applied in many fields, with much potential for disease treatment. The shape of glycopolymer-bearing nanoparticles has obvious effects on the nanoparticle-cell interaction and is therefore important for the applications of glycopolymers in biological systems. Here a synthetic approach to prepare non-spherical glycopolymer-coated iron oxide nanoparticles is provided, by combing the convenience of inorganic shape control, catecholic chemistry, and thiol-ene reaction. PMID:26537471

  2. Experimental observation of pulse trains' destructive interference with a femtosecond optical frequency-comb-based interferometer.

    PubMed

    Wei, Dong; Takahashi, Satoru; Takamasu, Kiyoshi; Matsumoto, Hirokazu

    2009-09-15

    A recently reported interferometric technique using a femtosecond optical frequency comb is modified to observe the destructive interference between two pairs of pulse trains with different relative delays. Experimental observation of the destructive interference shows that the present technique may offer a significantly different possibility to reduce the unnecessary reflections. This technique can be applied not only to surface profilometry and tomography but also to optical superresolution metrology. PMID:19756101

  3. Carrier-envelope offset frequency noise analysis in Ti:sapphire frequency combs

    NASA Astrophysics Data System (ADS)

    Sutyrin, Denis V.; Poli, Nicola; Beverini, Nicol; Tino, Guglielmo M.

    2014-12-01

    We experimentally study two Ti:sapphire optical frequency comb femtosecond regimes, respectively, with a linear and a nonlinear dependence of the carrier-envelope offset frequency (fCEO) on pump intensity. For both regimes, we study the effect of single- and multimode pump lasers on the fCEO phase noise. We demonstrate that the femtosecond regime is playing a more important role on the fCEO phase noise and stability than the pump laser type.

  4. Widely time-dispersion-tuned fiber optical oscillator and frequency comb based on multiple nonlinear processes.

    PubMed

    Chiarello, Fabrizio; Palmieri, Luca; Galtarossa, Andrea; Santagiustina, Marco

    2013-11-15

    An all-fiber optical oscillator based on three nonlinear processes, namely stimulated Raman scattering and broad-band and narrow-band optical parametric amplification, is presented and experimentally characterized. The wavelength tuning is achieved by means of the time-dispersion technique and spans over 160 nm. Through the same technique a fast tunable optical frequency comb has been realized exploiting cascaded four-wave mixing. PMID:24322089

  5. High-resolution broadband terahertz spectroscopy via electronic heterodyne detection of photonically generated terahertz frequency comb.

    PubMed

    Pavelyev, D G; Skryl, A S; Bakunov, M I

    2014-10-01

    We report an alternative approach to the terahertz frequency-comb spectroscopy (TFCS) based on nonlinear mixing of a photonically generated terahertz pulse train with a continuous wave signal from an electronic synthesizer. A superlattice is used as a nonlinear mixer. Unlike the standard TFCS technique, this approach does not require a complex double-laser system but retains the advantages of TFCS-high spectral resolution and wide bandwidth. PMID:25360955

  6. Application of the interleaved comb chopper to time-of-flight electron spectrometry

    NASA Astrophysics Data System (ADS)

    Jackson, R. H.; LeGore, L. J.; Yang, Z.; Kleban, P.; Frederick, B. G.

    2002-04-01

    We examined the use of the interleaved comb chopper for time-of-flight electron spectrometry. Both static and dynamic behaviors are simulated theoretically and measured experimentally, with very good agreement. The finite penetration of the field beyond the plane of the chopper leads to non-ideal chopper response, which is characterized in terms of an "energy corruption" effect and a lead or lag in the time at which the beam responds to the chopper potential.

  7. Aliiroseovarius pelagivivens gen. nov., sp. nov., isolated from seawater, and reclassification of three species of the genus Roseovarius as Aliiroseovarius crassostreae comb. nov., Aliiroseovarius halocynthiae comb. nov. and Aliiroseovarius sediminilitoris comb. nov.

    PubMed

    Park, Sooyeon; Park, Ji-Min; Kang, Chul-Hyung; Yoon, Jung-Hoon

    2015-08-01

    A Gram-stain-negative, non-motile, aerobic and ovoid or rod-shaped bacterium, designated GYSW-22T, was isolated from seawater off Geoje Island in the South Sea, South Korea. Strain GYSW-22T grew optimally at 25?C, at pH?7.0-8.0 and in the presence of 1.0-2.0% (w/v) NaCl. Neighbour-joining, maximum-likelihood and maximum-parsimony phylogenetic trees based on 16S rRNA gene sequences showed that strain GYSW-22T and the type strains of Roseovarius crassostreae, Roseovarius halocynthiae and Roseovarius sediminilitoris form a coherent cluster, independent of phylogenetic lineages or clusters comprising the type strains of other species of the genus Roseovarius. Strain GYSW-22T exhibited 16S rRNA gene sequence similarities of 97.2, 96.6 and 96.3% to R. halocynthiae MA1-10T, R. crassostreae CV919-312T and R. sediminilitoris M-M10T, respectively, and of 92.6-94.7% to the type strains of other species of the genus Roseovarius. Strain GYSW-22T contained Q-10 as the predominant ubiquinone and C18?:?1?7c as the major fatty acid. The major polar lipids were phosphatidylcholine, phosphatidylglycerol, one unidentified aminolipid and one unidentified lipid. The DNA G+C content of strain GYSW-22T was 59.0?mol% and its mean DNA-DNA relatedness value with R. halocynthiae MA1-10T was 15?%. On the basis of the data presented, we propose strain GYSW-22T represents a novel species of a new genus, Aliiroseovarius pelagivivens gen. nov., sp. nov. The type strain of the type species is GYSW-22T (?=?KCTC 42459T?=?CECT 8811T). In this study, it is also proposed that Roseovarius crassostreae, Roseovarius halocynthiae and Roseovarius sediminilitoris be reclassified into the new genus as Aliiroseovarius crassostreae comb. nov. (type strain CV919-312T?=?ATCC BAA-1102T?=?DSM 16950T), Aliiroseovarius halocynthiae comb. nov. (type strain MA1-10T?=?KCTC 23462T?=?CCUG 60745T) and Aliiroseovarius sediminilitoris comb. nov. (type strain M-M10T?=?KCTC 23959T?=?CCUG 62413T), respectively. PMID:25964517

  8. Reclassification of Methanogenium tationis and Methanogenium liminatans as Methanofollis tationis gen. nov., comb. nov. and Methanofollis liminatans comb. nov. and description of a new strain of Methanofollis liminatans

    NASA Technical Reports Server (NTRS)

    Zellner, G.; Boone, D. R.; Keswani, J.; Whitman, W. B.; Woese, C. R.; Hagelstein, A.; Tindall, B. J.; Stackebrandt, E.

    1999-01-01

    Sequencing of 16S rRNA genes and phylogenetic analysis of Methanogenium tationis DSM 2702T (OCM 43T) (T = type strain) and Methanogenium liminatans GKZPZT (= DSM 4140T) as well as other members of the family Methanomicrobiaceae revealed that both species belong to a separate line of descent within this family. In addition, a new strain of Methanogenium liminatans, strain BM1 (= DSM 10196), was isolated from a butyrate-degrading, fluidized bed reactor and characterized. Cells of both species are mesophilic, highly irregular cocci that use H2/CO2 and formate for growth and methanogenesis. In addition, Methanogenium liminatans strains GKZPZT and BM1 used 2-propanol/CO2, 2-butanol/CO2 and cyclopentanol/CO2. Both species contained diether and tetraether lipids. The polar lipids comprised amino-phosphopentanetetrol derivatives, which appear to be characteristic lipids within the family Methanomicrobiaceae. The pattern of glycolipids, phosphoglycolipids and amino-phosphoglycolipids was consistent with the assignment of these two species to a taxon within the family Methanomicrobiaceae, but also permitted them to be distinguished from other higher taxa within this family. The G+C contents of the DNA of Methanogenium tationis and Methanogenium liminatans were 54 and 60 mol% (Tm and HPLC), respectively. On the basis of the data presented, the transfer of Methanogenium tationis and Methanogenium liminatans to the genus Methanofollis gen. nov. as Methanofollis tationis comb. nov. and Methanofollis liminatans comb. nov., respectively, is proposed, with Methanofollis tationis as the type species.

  9. Reclassification of Methanogenium tationis and Methanogenium liminatans as Methanofollis tationis gen. nov., comb. nov. and Methanofollis liminatans comb. nov. and description of a new strain of Methanofollis liminatans.

    PubMed

    Zellner, G; Boone, D R; Keswani, J; Whitman, W B; Woese, C R; Hagelstein, A; Tindall, B J; Stackebrandt, E

    1999-01-01

    Sequencing of 16S rRNA genes and phylogenetic analysis of Methanogenium tationis DSM 2702T (OCM 43T) (T = type strain) and Methanogenium liminatans GKZPZT (= DSM 4140T) as well as other members of the family Methanomicrobiaceae revealed that both species belong to a separate line of descent within this family. In addition, a new strain of Methanogenium liminatans, strain BM1 (= DSM 10196), was isolated from a butyrate-degrading, fluidized bed reactor and characterized. Cells of both species are mesophilic, highly irregular cocci that use H2/CO2 and formate for growth and methanogenesis. In addition, Methanogenium liminatans strains GKZPZT and BM1 used 2-propanol/CO2, 2-butanol/CO2 and cyclopentanol/CO2. Both species contained diether and tetraether lipids. The polar lipids comprised amino-phosphopentanetetrol derivatives, which appear to be characteristic lipids within the family Methanomicrobiaceae. The pattern of glycolipids, phosphoglycolipids and amino-phosphoglycolipids was consistent with the assignment of these two species to a taxon within the family Methanomicrobiaceae, but also permitted them to be distinguished from other higher taxa within this family. The G+C contents of the DNA of Methanogenium tationis and Methanogenium liminatans were 54 and 60 mol% (Tm and HPLC), respectively. On the basis of the data presented, the transfer of Methanogenium tationis and Methanogenium liminatans to the genus Methanofollis gen. nov. as Methanofollis tationis comb. nov. and Methanofollis liminatans comb. nov., respectively, is proposed, with Methanofollis tationis as the type species. PMID:10028269

  10. Demonstration of a near-IR line-referenced electro-optical laser frequency comb for precision radial velocity measurements in astronomy

    PubMed Central

    Yi, X.; Vahala, K.; Li, J.; Diddams, S.; Ycas, G.; Plavchan, P.; Leifer, S.; Sandhu, J.; Vasisht, G.; Chen, P.; Gao, P.; Gagne, J.; Furlan, E.; Bottom, M.; Martin, E. C.; Fitzgerald, M. P.; Doppmann, G.; Beichman, C.

    2016-01-01

    An important technique for discovering and characterizing planets beyond our solar system relies upon measurement of weak Doppler shifts in the spectra of host stars induced by the influence of orbiting planets. A recent advance has been the introduction of optical frequency combs as frequency references. Frequency combs produce a series of equally spaced reference frequencies and they offer extreme accuracy and spectral grasp that can potentially revolutionize exoplanet detection. Here we demonstrate a laser frequency comb using an alternate comb generation method based on electro-optical modulation, with the comb centre wavelength stabilized to a molecular or atomic reference. In contrast to mode-locked combs, the line spacing is readily resolvable using typical astronomical grating spectrographs. Built using commercial off-the-shelf components, the instrument is relatively simple and reliable. Proof of concept experiments operated at near-infrared wavelengths were carried out at the NASA Infrared Telescope Facility and the Keck-II telescope. PMID:26813804

  11. Demonstration of a near-IR line-referenced electro-optical laser frequency comb for precision radial velocity measurements in astronomy

    NASA Astrophysics Data System (ADS)

    Yi, X.; Vahala, K.; Li, J.; Diddams, S.; Ycas, G.; Plavchan, P.; Leifer, S.; Sandhu, J.; Vasisht, G.; Chen, P.; Gao, P.; Gagne, J.; Furlan, E.; Bottom, M.; Martin, E. C.; Fitzgerald, M. P.; Doppmann, G.; Beichman, C.

    2016-01-01

    An important technique for discovering and characterizing planets beyond our solar system relies upon measurement of weak Doppler shifts in the spectra of host stars induced by the influence of orbiting planets. A recent advance has been the introduction of optical frequency combs as frequency references. Frequency combs produce a series of equally spaced reference frequencies and they offer extreme accuracy and spectral grasp that can potentially revolutionize exoplanet detection. Here we demonstrate a laser frequency comb using an alternate comb generation method based on electro-optical modulation, with the comb centre wavelength stabilized to a molecular or atomic reference. In contrast to mode-locked combs, the line spacing is readily resolvable using typical astronomical grating spectrographs. Built using commercial off-the-shelf components, the instrument is relatively simple and reliable. Proof of concept experiments operated at near-infrared wavelengths were carried out at the NASA Infrared Telescope Facility and the Keck-II telescope.

  12. Demonstration of a near-IR line-referenced electro-optical laser frequency comb for precision radial velocity measurements in astronomy.

    PubMed

    Yi, X; Vahala, K; Li, J; Diddams, S; Ycas, G; Plavchan, P; Leifer, S; Sandhu, J; Vasisht, G; Chen, P; Gao, P; Gagne, J; Furlan, E; Bottom, M; Martin, E C; Fitzgerald, M P; Doppmann, G; Beichman, C

    2016-01-01

    An important technique for discovering and characterizing planets beyond our solar system relies upon measurement of weak Doppler shifts in the spectra of host stars induced by the influence of orbiting planets. A recent advance has been the introduction of optical frequency combs as frequency references. Frequency combs produce a series of equally spaced reference frequencies and they offer extreme accuracy and spectral grasp that can potentially revolutionize exoplanet detection. Here we demonstrate a laser frequency comb using an alternate comb generation method based on electro-optical modulation, with the comb centre wavelength stabilized to a molecular or atomic reference. In contrast to mode-locked combs, the line spacing is readily resolvable using typical astronomical grating spectrographs. Built using commercial off-the-shelf components, the instrument is relatively simple and reliable. Proof of concept experiments operated at near-infrared wavelengths were carried out at the NASA Infrared Telescope Facility and the Keck-II telescope. PMID:26813804

  13. Structure-Specific Liquid Crystal Anchoring Induced by the Molecular Combing of Short Oligonucleotides.

    PubMed

    Chakraborty, Saonti; Noonan, Patrick S; Monserud, Jon; Schwartz, Daniel K

    2015-12-01

    Surface-immobilized oligonucleotides were "combed" by meniscus motion and exposed to a nematic liquid crystal (LC). Although the oligonucleotides were as short as 16 bases, they were apparently oriented by this process and, in turn, successfully biased the orientation of the adjacent LC material. Single-stranded DNA (ssDNA) induced LC orientation in the combing direction, while hybridized double-stranded DNA (dsDNA) rotated the azimuthal LC orientation by ?30 from the combing direction. The sensitivity of the chiral response to mixed ssDNA/dsDNA surfaces was characterized by employing complementary DNA that was longer than the immobilized DNA, resulting in single-stranded overhangs of various lengths. A rotated LC orientation was observed even when more than 70% of the DNA was single-stranded, and the transition from the rotated to nonrotated response was apparently discontinuous as a function of ssDNA surface coverage. These phenomena represent a sensitive DNA hybridization detection strategy that can potentially comprise a multiplexed assay. PMID:26562585

  14. A Comb-Drive Actuator Driven by Capacitively-Coupled-Power

    PubMed Central

    Chang, Chao-Min; Wang, Shao-Yu; Chen, Rongshun; Yeh, J. Andrew; Hou, Max T.

    2012-01-01

    This paper presents a new actuation mechanism to drive comb-drive actuators. An asymmetric configuration of the finger overlap was used to generate capacitive coupling for the actuation mechanism. When the driving voltages were applied on the stators, a voltage would be induced at the rotor due to the capacitive coupling. Then, an electrostatic force would be exerted onto the rotor due to the voltage differences between the stators and the rotor. The actuator's static displacement and resonant frequency were theoretically analyzed. To verify the design, a comb-drive actuator with different initial finger overlaps, i.e., 159.3 ?m and 48.9 ?m on each side, was fabricated and tested. The results show that the actuator worked well using the proposed actuation mechanism. A static displacement of 41.7 ?m and a resonant frequency of 577 Hz were achieved. Using the actuation mechanism, no electrical connection is required between the rotor and the outside power supply. This makes some comb-drive actuators containing heterogeneous structures easy to design and actuate. PMID:23112635

  15. Optical arbitrary waveform processing of more than 100 spectral comb lines

    NASA Astrophysics Data System (ADS)

    Jiang, Zhi; Huang, Chen-Bin; Leaird, Daniel E.; Weiner, Andrew M.

    2007-08-01

    Pulse-shaping techniques, in which user-specified, ultrashort-pulse fields are synthesized by means of parallel manipulation of optical Fourier components, have now been widely adopted. Mode-locked lasers producing combs of frequency-stabilized spectral lines have resulted in revolutionary advances in frequency metrology. However, until recently, pulse shapers addressed spectral lines in groups, at low spectral resolution. Line-by-line pulse shaping, in which spectral lines are resolved and manipulated individually, leads to a fundamentally new regime for optical arbitrary waveform generation, in which the advantages of pulse shaping and of frequency combs are exploited simultaneously. Here we demonstrate programmable line-by-line shaping of more than 100 spectral lines, which constitutes a significant step in scaling towards high waveform complexity. Optical arbitrary waveform generation promises to have an impact both in optical science (allowing, for example, coherent control generalizations of comb-based time-frequency spectroscopies) and in technology (enabling new truly coherent multiwavelength processing concepts for spread-spectrum lightwave communications and light detection and ranging, lidar).

  16. Optical frequency comb generation based on chirping of Mach-Zehnder Modulators

    NASA Astrophysics Data System (ADS)

    Hmood, Jassim K.; Emami, Siamak D.; Noordin, Kamarul A.; Ahmad, Harith; Harun, Sulaiman W.; Shalaby, Hossam M. H.

    2015-06-01

    A new approach for the generation of an optical frequency comb, based on chirping of modulators, is proposed and numerically demonstrated. The setup includes two cascaded Mach-Zehnder Modulators (MZMs), a sinusoidal wave oscillator, and an electrical time delay. The first MZM is driven directly by a sinusoidal wave, while the second MZM is driven by a delayed replica of the sinusoidal wave. A mathematical model of the proposed system is formulated and modeled using the Matlab software. It is shown that the number of the frequency lines is directly proportional to the chirp factor. In order to achieve the highest number of frequency comb lines with the best flatness, the time delay between the driving voltages of the two MZMs is optimized. Our results reveal that at least 51 frequency lines can be observed at the output spectrum. In addition, 27 of these lines have power fluctuations of less than 1 dB. The performance of the proposed system is also simulated using a split-step numerical analysis. An optical frequency comb, with tunable frequency spacing ranging from 5 to 40 GHz, is successfully generated.

  17. Dual-comb modelocked lasers: semiconductor saturable absorber mirror decouples noise stabilization.

    PubMed

    Link, Sandro M; Klenner, Alexander; Keller, Ursula

    2016-02-01

    In this paper we present the stabilization of the pulse repetition rate of dual-comb lasers using an intracavity semiconductor saturable absorber mirror (SESAM) for passive modelocking and an intracavity birefringent crystal for polarization-duplexing to obtain simultaneous emission of two modelocked beams from the same linear cavity sharing all components. Initially surprising was the observation that the cavity length adjustments to stabilize one polarization did not significantly affect the pulse repetition rate of the other. We gained insight in the underlying physics using both a semiconductor and Nd:YAG laser gain material with the conclusion that the pulse arrival timing jitter of the two beams is decoupled by the uncorrelated time delay from the saturated SESAM and becomes locked with sufficient but not too much pulse overlap. Noise stabilization is in all cases still possible for both combs. The dual-comb modelocked laser is particularly interesting for the semiconductor laser enabling the integration of gain and absorber layers within one wafer (referred to as the modelocked integrated external-cavity surface emitting laser - MIXSEL). PMID:26906767

  18. Gigahertz frequency comb from a diode-pumped solid-state laser.

    PubMed

    Klenner, Alexander; Schilt, Stphane; Sdmeyer, Thomas; Keller, Ursula

    2014-12-15

    We present the first stabilization of the frequency comb offset from a diode-pumped gigahertz solid-state laser oscillator. No additional external amplification and/or compression of the output pulses is required. The laser is reliably modelocked using a SESAM and is based on a diode-pumped Yb:CALGO gain crystal. It generates 1.7-W average output power and pulse durations as short as 64 fs at a pulse repetition rate of 1 GHz. We generate an octave-spanning supercontinuum in a highly nonlinear fiber and use the standard f-to-2f carrier-envelope offset (CEO) frequency fCEO detection method. As a pump source, we use a reliable and cost-efficient commercial diode laser. Its multi-spatial-mode beam profile leads to a relatively broad frequency comb offset beat signal, which nevertheless can be phase-locked by feedback to its current. Using improved electronics, we reached a feedback-loop-bandwidth of up to 300 kHz. A combination of digital and analog electronics is used to achieve a tight phase-lock of fCEO to an external microwave reference with a low in-loop residual integrated phase-noise of 744 mrad in an integration bandwidth of [1 Hz, 5 MHz]. An analysis of the laser noise and response functions is presented which gives detailed insights into the CEO stabilization of this frequency comb. PMID:25607050

  19. Frequency stabilisation of a fibre-laser comb using a novel microstructured fibre.

    PubMed

    Locke, C R; Ivanov, E N; Light, P S; Benabid, F; Luiten, A N

    2009-03-30

    There is great interest in developing high performance optical frequency metrology based around mode-locked fibre lasers because of their low cost, small size and long-term turnkey operation when compared to the solid-state alternative. We present a method for stabilising the offset frequency of a fibre-based laser comb using a 2 f - 3 f technique based around a unique fibre that exhibits strong resonant dispersive wave emission. This fibre requires lower power than conventional highly non-linear fibre to generate a suitable signal for offset frequency stabilisation and this in turn avoids the complexity of additional nonlinear steps. We generate an offset frequency signal from the mixing of a wavelength-shifted second harmonic comb with a third harmonic of the comb. Additionally, we have stabilised the repetition rate of the laser to a level better than 10(-14)/ radicaltau , limited by the measurement system noise floor.We present the means for complete and precise measurement of the transfer function of the laser frequency controls. PMID:19333360

  20. Total mercury in the hair of children by combustion atomic absorption spectrometry (Comb-AAS).

    PubMed

    Dez, Sergi; Montuori, Paolo; Querol, Xavier; Bayona, Josep M

    2007-04-01

    A simple and rapid procedure for measuring total mercury in human hair was evaluated and compared with a conventional technique. An Advanced Mercury Analyzer (AMA-254) based on sample catalytic combustion, preconcentration by gold amalgamation, thermal desorption, and atomic absorption spectrometry (AAS) (Comb-AAS) was assessed for the direct determination of milligram quantities of human hair. Precision (% relative standard deviation) was < 7% and accuracy was determined by using two human hair reference materials (i.e., NIES No. 13 and IAEA-086) that were within the certified range. In comparison to conventional graphite-furnace atomic absorption spectrophotometry (GF-AAS), we found that our method obtained statistically equivalent results. Because total analysis time per sample was less than 10 min, the Comb-AAS method was in fact much faster than the GF-AAS method. In addition, Comb-AAS does not generate waste products and could be mainly useful for the analysis of a large amount of samples. Then, the authors suggest that this quick method could be useful for measuring mercury in human hair. Therefore, the mercury content in hair for a non-exposed group of children (n=40) living in Spain was evaluated. The mean and median hair mercury levels for the subjects under study were found to be lower than the value of 1 microg/g, corresponding to the reference dose of 0.1 microg of methylmercury per kilogram body weight set by the U.S. Environmental Protection Agency. PMID:17579961

  1. From a discrete to a continuous model for interpulse interference with a frequency-comb laser

    SciTech Connect

    Zeitouny, M. G.; Cui, M.; Bhattacharya, N.; Urbach, H. P.; Berg, S. A. van den; Janssen, A. J. E. M.

    2010-08-15

    We have investigated correlation patterns generated by a frequency-comb laser in a dispersive unbalanced Michelson interferometer and apply the developed formalism to the case of distance metrology. Due to group velocity dispersion, the position of the brightest fringe of the correlation pattern, which is used for distance determination, cannot be derived by simply using the definition of group refractive index of the dispersive medium. It is shown that the discrete spectrum of the optical frequency comb gives rise to correlation functions which can be represented by a series, namely a discrete correlation series. We have developed a general formalism, valid for any pulse train, extending the discrete model to a continuous model of cross-correlation functions using the Poisson summation. Our model is relevant for any offset and repetition frequency of the frequency comb. From the continuous cross-correlation model we show that, even for a homogeneous dispersive medium the position of the brightest fringe varies nonlinearly for small delay distances and stabilizes for longer ones. We have compared the theoretical results to measurements of pulse propagation in air for path-lengths up to 200 m.

  2. Radius of Gyration of Polystyrene Combs and Centipedes in a O Solvent

    SciTech Connect

    Terao, Ken; Farmer, Brandon S; Nakamura, Yo; Iatrou, Hermis; Hong, Kunlun; Mays, Jimmy

    2005-01-01

    The molecular weight dependence of the radii of gyration R{sub g} in a {var_theta} solvent (trans-decalin) of one regular branched comb and three regular centipede polystyrenes was studied using a gel permeation chromatography system equipped with a two-angle light scattering detector and a refractive index detector. R{sub g} in trans-decalin for each sample of particular molecular weight was about 25% smaller than that in a good solvent (tetrahydrofuran, THF). On the other hand, they are 20--40% larger than the theoretical values from the Gaussian chain model. This difference can be explained with the wormlike comb model developed by Nakamura et al. (Macromolecules 2000, 33, 8323-8328). Persistence lengths thus obtained for each sample were about half of that determined in THF solution. However, they are significantly larger than that for linear polystyrene. These results suggest that a main chain stiffening effect exists in comb polystyrenes even in a {var_theta} solvent.

  3. A comb filter based signal processing method to effectively reduce motion artifacts from photoplethysmographic signals.

    PubMed

    Peng, Fulai; Liu, Hongyun; Wang, Weidong

    2015-10-01

    A photoplethysmographic (PPG) signal can provide very useful information about a subject's cardiovascular status. Motion artifacts (MAs), which usually deteriorate the waveform of a PPG signal, severely obstruct its applications in the clinical diagnosis and healthcare area. To reduce the MAs from a PPG signal, in the present study we present a comb filter based signal processing method. Firstly, wavelet de-noising was implemented to preliminarily suppress a part of the MAs. Then, the PPG signal in the time domain was transformed into the frequency domain by a fast Fourier transform (FFT). Thirdly, the PPG signal period was estimated from the frequency domain by tracking the fundamental frequency peak of the PPG signal. Lastly, the MAs were removed by the comb filter which was designed based on the obtained PPG signal period. Experiments with synthetic and real-world datasets were implemented to validate the performance of the method. Results show that the proposed method can effectively restore the PPG signals from the MA corrupted signals. Also, the accuracy of blood oxygen saturation (SpO2), calculated from red and infrared PPG signals, was significantly improved after the MA reduction by the proposed method. Our study demonstrates that the comb filter can effectively reduce the MAs from a PPG signal provided that the PPG signal period is obtained. PMID:26334000

  4. A comb-sampling method for enhanced mass analysis in linear electrostatic ion traps

    SciTech Connect

    Greenwood, J. B.; Kelly, O.; Calvert, C. R.; Duffy, M. J.; King, R. B.; Belshaw, L.; Graham, L.; Alexander, J. D.; Williams, I. D.; Bryan, W. A.; Turcu, I. C. E.; Cacho, C. M.; Springate, E.

    2011-04-15

    In this paper an algorithm for extracting spectral information from signals containing a series of narrow periodic impulses is presented. Such signals can typically be acquired by pickup detectors from the image-charge of ion bunches oscillating in a linear electrostatic ion trap, where frequency analysis provides a scheme for high-resolution mass spectrometry. To provide an improved technique for such frequency analysis, we introduce the CHIMERA algorithm (Comb-sampling for High-resolution IMpulse-train frequency ExtRAaction). This algorithm utilizes a comb function to generate frequency coefficients, rather than using sinusoids via a Fourier transform, since the comb provides a superior match to the data. This new technique is developed theoretically, applied to synthetic data, and then used to perform high resolution mass spectrometry on real data from an ion trap. If the ions are generated at a localized point in time and space, and the data is simultaneously acquired with multiple pickup rings, the method is shown to be a significant improvement on Fourier analysis. The mass spectra generated typically have an order of magnitude higher resolution compared with that obtained from fundamental Fourier frequencies, and are absent of large contributions from harmonic frequency components.

  5. A comb-sampling method for enhanced mass analysis in linear electrostatic ion traps

    NASA Astrophysics Data System (ADS)

    Greenwood, J. B.; Kelly, O.; Calvert, C. R.; Duffy, M. J.; King, R. B.; Belshaw, L.; Graham, L.; Alexander, J. D.; Williams, I. D.; Bryan, W. A.; Turcu, I. C. E.; Cacho, C. M.; Springate, E.

    2011-04-01

    In this paper an algorithm for extracting spectral information from signals containing a series of narrow periodic impulses is presented. Such signals can typically be acquired by pickup detectors from the image-charge of ion bunches oscillating in a linear electrostatic ion trap, where frequency analysis provides a scheme for high-resolution mass spectrometry. To provide an improved technique for such frequency analysis, we introduce the CHIMERA algorithm (Comb-sampling for High-resolution IMpulse-train frequency ExtRAaction). This algorithm utilizes a comb function to generate frequency coefficients, rather than using sinusoids via a Fourier transform, since the comb provides a superior match to the data. This new technique is developed theoretically, applied to synthetic data, and then used to perform high resolution mass spectrometry on real data from an ion trap. If the ions are generated at a localized point in time and space, and the data is simultaneously acquired with multiple pickup rings, the method is shown to be a significant improvement on Fourier analysis. The mass spectra generated typically have an order of magnitude higher resolution compared with that obtained from fundamental Fourier frequencies, and are absent of large contributions from harmonic frequency components.

  6. Self-heterodyne interference spectroscopy using a comb generated by pseudo-random modulation.

    PubMed

    Hbert, Nicolas Bourbeau; Michaud-Belleau, Vincent; Anstie, James D; Deschnes, Jean-Daniel; Luiten, Andre N; Genest, Jrme

    2015-10-19

    We present an original instrument designed to accomplish high-speed spectroscopy of individual optical lines based on a frequency comb generated by pseudo-random phase modulation of a continuous-wave (CW) laser. This approach delivers efficient usage of the laser power as well as independent control over the spectral point spacing, bandwidth and central wavelength of the comb. The comb is mixed with a local oscillator generated from the same CW laser frequency-shifted by an acousto-optic modulator, enabling a self-heterodyne detection scheme. The current configuration offers a calibrated spectrum every 1.12 s. We demonstrate the capabilities of the spectrometer by producing averaged, as well as time-resolved, spectra of the D1 transition of cesium with a 9.8-MHz point spacing, a 50-kHz resolution and a span of more than 3 GHz. The spectra obtained after 1 ms of averaging are fitted with complex Voigt profiles that return parameters in good agreement with expected values. PMID:26480442

  7. Modelocking and femtosecond pulse generation in chip-based frequency combs

    NASA Astrophysics Data System (ADS)

    Saha, Kasturi; Okawachi, Yoshitomo; Shim, Bonggu; Levy, Jacob S.; Salem, Reza; Johnson, Adrea R.; Foster, Mark A.; Lamont, Michael R. E.; Lipson, Michal; Gaeta, Alexander L.

    2013-01-01

    Development of ultrashort pulse sources has had an immense impact on condensed-matter physics, biomedical imaging, high-field physics, frequency metrology, telecommunications, nonlinear optics, and molecular spectroscopy. Although numerous advancements of such sources have been made, it remains a challenge to create a highly compact, robust platform capable of producing femtosecond pulses over a wide range of wavelengths, durations, and repetition rates. Recent observations of frequency comb generation via cascaded parametric oscillation in microresonators11 suggest a path for achieving this goal. Here we investigate the temporal and spectral properties of parametric combs generated in silicon-nitride microresonators and observe a transition to passive modelocking of the comb consistent with soliton-pulse formation, resulting in the generation of 160-fs pulses at a 99-GHz repetition rate. This platform offers the prospect of producing pulses from 10 fs to a few ps at repetition rates from 10 GHz to > 1 THz and over a wavelength range of 0.8 - 6 \\mu m.

  8. Sex and Fertility After SCI

    MedlinePLUS

    Experts \\ Sex and Fertility After Spinal Cord Injury Topics Adult Injuries Spinal Cord Injury 101 Spinal Cord Injury 101 ... Spasticity, Physical Therapy-Lokomat Spasticity, Physical Therapy-Lokomat Sex and Fertility After Spinal Cord Injury Sex and ...

  9. Making Healthy Decisions About Sex

    MedlinePLUS

    ... For Teens: How to Make Healthy Decisions About Sex Page Content Article Body Before you decide to ... alcohol or use drugs. Are You Ready for Sex? Sex can change your life and relationships. Having ...

  10. Juvenile Sex Offenders.

    PubMed

    Ryan, Eileen P

    2016-01-01

    Public policy has tended to treat juvenile sex offenders (JSOs) as adult sex offenders in waiting, despite research that contradicts this notion. Although as a group, JSOs are more similar to general delinquents than to adult sex offenders, atypical sexual interests and sexual victimization during childhood may be a pathway for sexual offending that differentiates some JSOs from their nonsexually delinquent peers. Developmental considerations must be considered in risk assessment evaluations of these youth. This article reviews theories of sexual offending in youth, risk factors for juvenile offending and reoffending, psychopathology in JSOs, risk assessment, and treatment. PMID:26593121

  11. Sex education in Portugal.

    PubMed

    Frade, A; Vilar, D

    1991-05-01

    The article on sex education in Portugal covers background, the educational system, the clashes of the 1960's over sex education, the Committee for the Study of Sexuality and Education (CSSE), the policies, politics and social movements during the period 1974 - 1984, the discussions in Parliament, the 1988 Reform of the Educational System, the Family Planning Association (FPA) and sex education, and the future role of the FPA. It was not until the institution of the multiparity parliamentary system in 1974 that discussing social and political changes was possible, culminating in 1984 with new legislation on abortion, family planning, and sex education. School reform came in 1987/8 with the Ministry of Education primarily responsible for curricula. The 1960's brought with it the influence of the Catholic Church. Change came in the form of progressivism among Catholics who replaced dogma with dialogue and listening. Sex education was considered as preparation for marriage, but masturbation, contraception, and prostitution were also discussed. In addition, the founder of FPA chaired the CSSE in 1971 and opened up debate on sex issues and drafted a bill to establish co-education in Portuguese schools. The revolution of 1974 brought an end to censorship and brought forth a policy of developing family planning. Changed in the Family Code gave women greater equality. UNFPA supported teacher training in non-sexist education. With human reproduction included in the natural sciences, there was still no school sex education policy and contraception was only sometimes represented in the biology curriculum. The focus of FPA was on contraception and abortion. Finally in the 1980's, the first sex education programs were developed for out-of-school youth. Even though in the 1970's there were leftists groups promoting sex education, it took leftist parliamentary power to get legislation on sex education in the schools adopted. The Ministry of Education however was pressured by the Catholic Church. As in 1973, committees were formed but no action was taken. Sex education activity increased nonetheless - the first FPA document on school education prepared. In 1986 Personal and Social Education was approved by parliament providing an alternative (due to the Catholic Church) to Religious Education, but even with FPA support documents, the implementation did not begin until the end of 1990. In brief the FPA's emphasis was on the body, sexuality, sex and interpersonal relationships, and sexual reproduction. The role of FPA continues at the grass roots level in stimulating discussion; cooperating with schools, students and parents; and acting as a resource center. PMID:12343180

  12. Destereotyping Sex Roles

    ERIC Educational Resources Information Center

    Money, John

    1977-01-01

    Notes that it makes sense for contemporary society to relax the rigidities of its sexual stereotypes, maximizing the similarities between the sexes and the roles that men and women can share independently of the insignia between their thighs. (Author)

  13. On luck and sex.

    PubMed

    Blachford, Alistair; Doebeli, Michael

    2009-01-01

    Sex has many costs with respect to asexual reproduction, so its ubiquity is a puzzle. There has been a continuing effort to identify general circumstances in which aspects of sex generate an evolutionary advantage over asexual reproduction. Here we focus on the generality that individuals can experience good and bad "luck" at various stages of their life history regardless of genotype, and on the interindividual nature of sex. Sexual outcrossing combines genetic information from individuals with potentially different experiences, so it is conceivable that sex might reduce the contribution of individual luck to noise in inheritance. In a simple way, we derive expressions for noise in inheritance in terms of some sources of within-generation ecological noise. We demonstrate that interindividual reproduction can indeed dampen the effects of ecological noise better than lone-individual modes, but there are conditions under which it does not. Empirical and theoretical work on plants, modeled here, suggest noise dampening conditions. Ecological noise dampening operates alongside other features of sex such as recombination and segregation and, because noise in inheritance weakens the role of selection in genetic change, we speculate that noise dampening may offer a benefit to be deducted from the costs of sex. We also suggest that the amount of selfing relative to outcrossing observed in natural populations may be influenced by the amount of individual-level ecological noise in a given habitat. PMID:18803688

  14. Shattering Female Sex Role Stereotypes.

    ERIC Educational Resources Information Center

    Wisconsin Clearinghouse for Alcohol and Other Drug Information, Madison.

    This booklet, designed to sensitize people to important issues that are a result of sex role stereotyping, advocates more flexible sex roles which are appropriate to the situation. Traditional and new views of the psychology of sex roles are contrasted, and sex role stereotyping is discussed. Implications of the women's liberation movement for

  15. Sex Bias in Research Design.

    ERIC Educational Resources Information Center

    Grady, Kathleen E.

    1981-01-01

    Presents feminist criticisms of selected aspects of research methods in psychology. Reviews data relevant to sex bias in topic selection, subject selection and single-sex designs, operationalization of variables, testing for sex differences, and interpretation of results. Suggestions for achieving more "sex fair" research methods are discussed.…

  16. A laser frequency comb that enables radial velocity measurements with a precision of 1 cm s(-1).

    PubMed

    Li, Chih-Hao; Benedick, Andrew J; Fendel, Peter; Glenday, Alexander G; Kärtner, Franz X; Phillips, David F; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L

    2008-04-01

    Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm s(-1) (ref. 1), which is sufficient to find a 5-Earth-mass planet in a Mercury-like orbit around a Sun-like star. To find a 1-Earth-mass planet in an Earth-like orbit, a precision of approximately 5 cm s(-1) is necessary. The combination of a laser frequency comb with a Fabry-Pérot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration, with recent encouraging results. Here we report the fabrication of such a filtered laser comb with up to 40-GHz (approximately 1-A) line spacing, generated from a 1-GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb, or 'astro-comb', is well matched to the resolving power of high-resolution astrophysical spectrographs. The astro-comb should allow a precision as high as 1 cm s(-1) in astronomical radial velocity measurements. PMID:18385734

  17. Echelle spectrograph calibration with a frequency comb based on a harmonically mode-locked fiber laser: a proposal.

    PubMed

    McFerran, J J

    2009-05-10

    Details for constructing an astronomical frequency comb suitable as a wavelength reference for chelle spectrographs associated with optical telescopes are outlined. The source laser for the frequency comb is a harmonically mode-locked fiber laser with a central wavelength of 1.56 microm. The means of producing a repetition rate greater than 7 GHz and a peak optical power of approximately 8 kW are discussed. Conversion of the oscillator light into the visible can occur through a two-step process of (i) nonlinear conversion in periodically poled lithium niobate and (ii) spectral broadening in photonic crystal fiber. While not necessarily octave spanning in spectral range to permit the use of an f -to- 2f interferometer for offset frequency control, the frequency comb can be granted accuracy by linking the mode spacing and a comb tooth to separate frequency references. The design avoids the use of a Fabry-Perot cavity to increase the mode spacing of the frequency comb; however, the level of supermode suppression and sideband asymmetry in the fiber oscillator and in the subsequent frequency conversion stages are aspects that need to be experimentally tested. PMID:19424399

  18. Disorder to Order Transition and Ordered Morphology of Coil-Comb Block Copolymer by Self-Consistent Field Theory

    NASA Astrophysics Data System (ADS)

    Jiang, Zhibin; Qian, Zhiyuan; Yang, Hong; Wang, Rong

    2015-08-01

    The disorder to order transition and the ordered patterns near the disordered state of coil-comb copolymer A- b-(B m + 1- g-C m ) are investigated by the self-consistent field theory. The phase diagrams of coil-comb copolymer are obtained by varying the composition of the copolymer with the side chain number m = 1, 2, and 3. The disorder to order transition is far more complex compared with the comb copolymer or linear block copolymer. As the side chain number m increases, the Flory-Huggins interaction parameter of disorder to order transition (DOT) increases and the lowest DOT occurs when the volume fractions of blocks A, B, and C are approximately equal. When one component is the minority, the disorder to order transition curve is similar with binary copolymer, but the curve shows the asymmetric property. The comb copolymer is more stable with larger side chain number m and shorter side chain. The ordered patterns from the disordered state are discussed. The results are helpful for designing coil-comb copolymers and obtaining the ordered morphology.

  19. Echelle spectrograph calibration with a frequency comb based on a harmonically mode-locked fiber laser: a proposal

    SciTech Connect

    McFerran, J. J.

    2009-05-10

    Details for constructing an astronomical frequency comb suitable as a wavelength reference for echelle spectrographs associated with optical telescopes are outlined. The source laser for the frequency comb is a harmonically mode-locked fiber laser with a central wavelength of 1.56 {mu}m. The means of producing a repetition rate greater than 7 GHz and a peak optical power of {approx}8 kW are discussed. Conversion of the oscillator light into the visible can occur through a two-step process of (i) nonlinear conversion in periodically poled lithium niobate and (ii) spectral broadening in photonic crystal fiber. While not necessarily octave spanning in spectral range to permit the use of an f -to- 2f interferometer for offset frequency control, the frequency comb can be granted accuracy by linking the mode spacing and a comb tooth to separate frequency references. The design avoids the use of a Fabry-Perot cavity to increase the mode spacing of the frequency comb; however, the level of supermode suppression and sideband asymmetry in the fiber oscillator and in the subsequent frequency conversion stages are aspects that need to be experimentally tested.

  20. Somatic sex determination.

    PubMed Central

    Zarkower, David

    2006-01-01

    C. elegans occurs in two natural sexes, the XX hermaphrodite and the XO male, which differ extensively in anatomy, physiology, and behavior. All somatic differences between the sexes result from the differential activity of a "global" sex determination regulatory pathway. This pathway also controls X chromosome dosage compensation, which is coordinated with sex determination by the action of the three SDC proteins. The SDC proteins control somatic and germline sex by transcriptional repression of the her-1 gene. HER-1 is a secreted protein that controls a regulatory module consisting of a transmembrane receptor, TRA-2, three intracellular FEM proteins, and the zinc finger transcription factor TRA-1. The molecular workings of this regulatory module are still being elucidated. Similarity of TRA-2 to patched receptors and of TRA-1 to GLI proteins suggests that parts of the global pathway originally derived from a Hedgehog signaling pathway. TRA-1 controls all aspects of somatic sexual differentiation, presumably by regulating a variety of tissue- and cell-specific downstream targets, including the cell death regulator EGL-1 and the male sexual regulator MAB-3. Sex determination evolves rapidly, and conservation of sexual regulators between phyla has been elusive. An apparent exception involves DM domain proteins, including MAB-3, which control sexual differentiation in nematodes, arthropods, and vertebrates. Important issues needing more study include the detailed molecular mechanisms of the global pathway, the identities of additional sexual regulators acting in the global pathway and downstream of TRA-1, and the evolutionary history of the sex determination pathway. Recently developed genetic and genomic technologies and comparative studies in divergent species have begun to address these issues. PMID:18050479