1 May 2015 Focal spot of femtosecond laser pulse under tight focusing condition
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A tight focusing scheme using a low f-number focusing optic is frequently considered as an effort to efficiently increase a peak intensity of a high power laser. In this paper, we present a method for describing the focal spot of a femtosecond laser pulse which is formed in the spatio-temporal region under low f-number (f-number ≤ 1) focusing conditions. In the method, transverse and longitudinal electromagnetic (EM) fields for a monochromatic wave are calculated in the focal plane and its vicinity, and then, in order to precisely describe the femtosecond focal spot in the spatio-temporal domain, the calculated monochromatic EM fields are coherently superposed with a given amount of spectral bandwidth and phase. The accuracy and validity of the method are tested and compared to results obtained with Fourier transform method under high f-number conditions. The single electron trajectory under a strong longitudinal field formed by a low f-number optic is presented to emphasize the importance of the tight focusing scheme.
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Tae Moon Jeong, Tae Moon Jeong, Stefan Weber, Stefan Weber, Bruno Le Garrec, Bruno Le Garrec, Daniele Margarone, Daniele Margarone, Tomas Mocek, Tomas Mocek, Georg Korn, Georg Korn, "Focal spot of femtosecond laser pulse under tight focusing condition", Proc. SPIE 9515, Research Using Extreme Light: Entering New Frontiers with Petawatt-Class Lasers II, 95150I (1 May 2015); doi: 10.1117/12.2179369; https://doi.org/10.1117/12.2179369

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