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233846 results in Physics and Astronomy

Page 110 of 11693

  • A novel small-scale self-focusing suppression method for post-compression in high peak power lasers

  • Shuren Pan, Fenxiang Wu, Yang Zhao, Jiabing Hu, Zongxin Zhang, Yi Xu, Yuxin Leng, Ruxin Li, Efim Khazanov
  • Journal:
    High Power Laser Science and Engineering / Volume 12 / 2024
    Published online by Cambridge University Press:
    23 May 2024, e49
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  • A novel method, combining an asymmetric four-grating compressor (AFGC) with pulse post-compression, is numerically demonstrated to improve the spatial uniformity of laser beams and hence to suppress small-scale self-focusing (SSSF) during the beam propagation in nonlinear materials of high peak power lasers. The spatial uniformity of laser beams is an important factor in performing post-compression, due to the spatial intensity modulation, or hot spots will be aggravated during the nonlinear propagation and then seriously damage the subsequent optical components. Three-dimensional numerical simulations of post-compression are implemented based on a femtosecond laser with a standard compressor and an AFGC, respectively. The simulated results indicate that post-compression with the AFGC can efficiently suppress the SSSF and also shorten the laser pulses from 30 fs to sub-10 fs. This work can provide a promising route to overcome the challenge of SSSF and will be meaningful to promote the practical application of the post-compression technique in high peak power lasers.

  • Surface turbulence in film flow over periodic ripples

  • B. Al-Shamaa, A. Wierschem
  • Journal:
    Journal of Fluid Mechanics / Volume 987 / 25 May 2024
    Published online by Cambridge University Press:
    23 May 2024, A39
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  • Turbulence in gravity-driven film flow is usually discussed in terms of three-dimensional solitary-wave pulses as they are frequently observed in flows along smooth walls. Here, we show that free-surface turbulence arises in films along rippled substrates, as they are commonly employed in process engineering applications, already at rather low Reynolds numbers from the irregular break-up of the solitary-wave fronts. Short waves in the capillary regime replace the broken solitary waves beyond a certain Reynolds number. The crossover coincides with the occurrence of steady three-dimensional surface patterns upstream, which suppress travelling waves. The waves show power spectral densities with power-law exponents typical for weak capillary-wave turbulence. With increasing Reynolds number, the steepness of the power law declines to lower levels.

Page 110 of 11693