Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Classical effect for enhanced high harmonic yield in ultrashort laser
  pulses with a moderate laser intensity   We study the influence of the pulse duration on high harmonic generation
(HHG) with exploring a wide laser-parameter region theoretically. Previous
studies have showed that for high laser intensities near to the saturation
ionization intensity, the HHG inversion efficiency is higher for shorter pulses
since the ground-state depletion is weaker in the latter. Surprisingly, our
simulations show this high efficiency also appears even for a moderate laser
intensity at which the ionization is not strong. A classical effect relating to
shorter travel distances of the rescattering electron in shorter pulses, is
found to contribute importantly to this high efficiency. The effect can be
amplified significantly as a two-color laser field is used, suggesting an
effective approach for increasing the HHG yield.

12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph