OPTICAL PHASE CONJUGATION IN LASER RESONATORS

L'utilisation de miroirs conjugués en phase dans des structures optiques oscillantes a suscité de l'intérêt récemment, aussi bien d'un point de vue expérimental que théorique. Un des aspects attrayant d'un résonateur en conjugaison de phase, RCP, est son aptitude à produire une onde émergeante dont le front d'onde dépend seulement de la qualité du coupleur de sortie et est essentiellement indépendant des aberrations à l'intérieur de la cavité. Plusieurs concepts pour le RCP seront présentés dans lesquels soit le mélange de quatre ondes ou soit la diffusion Brillouin stimulée est utilisé comme un miroir conjugué en phase ; les avantages et inconvénients de chacun seront discutés.The use of phase conjugating "mirrors" in oscillating optical structures has been a subject of recent interest, both experimentally and theoretically. One of the attractive features of a phase conjugate resonator, PCR, is its ability to provide an output wave whose wavefront depends only on the quality of the output coupler and is essentially independent of intracavity aberrations. Several concepts for PCR's will be presented in which either degenerate four-wave mixing or stimulated Brillouin scattering is employed as the phase conjugate mirror ; advantages and drawbacks of each will be discussed

Pan-cancer analysis of whole genomes

Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale. Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4-5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter; identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation; analyses timings and patterns of tumour evolution; describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity; and evaluates a range of more-specialized features of cancer genomes