Spatial properties of odd and even low order harmonics generated in gasстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 2 апреля 2015 г.
Аннотация:High harmonic generation in gases is developing rapidly as a soft X-ray femtosecond light-source for applications.Thisrequirescontroloveralltheharmonicscharacteristicsandinparticular,spatialproperties have to be kept very good. In previous literature, measurements have always included several harmonics contrary to applications, especially spectroscopic applications, which usuallyrequirea singleharmonic. To fill this gap, we present here for the first time a detailed study of completely isolated harmonics. The contribution of the surrounding harmonics has been totally suppressed using interferential filtering which is available for low harmonic orders. In addition, this allows to clearly identify behaviors of standard odd orders from even orders obtained by frequency-mixing of a fundamental laser and of its second harmonic. Comparisons of thespatial intensity profiles, ofthe spatial coherence and ofthe wavefront aberration level of 5 v at 160 nm and 6 v at 135 nm have then been performed. We have established that the fundamental laser beam aberrations can cause the appearance of a non-homogenous donut-shape in the 6 v spatial intensity distribution. This undesirable effect can be easily controlled. We finally conclude that the spatial quality of an even harmonic can be as excellent as in standard generation.