Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vacuum acceleration of electrons in a dynamic laser pulse   A planar laser pulse propagating in vacuum can exhibit an extremely large
ponderomotive force. This force, however, cannot impart net energy to an
electron: As the pulse overtakes the electron, the initial impulse from its
rising edge is completely undone by an equal and opposite impulse from its
trailing edge. Here we show that planar-like "flying focus" pulses can break
this symmetry, imparting relativistic energies to electrons. The intensity peak
of a flying focus-a moving focal point resulting from a chirped laser pulse
focused by a chromatic lens-can travel at any subluminal velocity, forwards or
backwards. As a result, an electron can gain enough momentum in the rising edge
of the intensity peak to outrun and avoid the trailing edge. Accelerating the
intensity peak can further boost the momentum gain. Theory and simulations
demonstrate that these dynamic intensity peaks can backwards accelerate
electrons to the MeV energies required for radiation and electron diffraction
probes of high energy density materials.

2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
12
The categories of this paper are: nucl-th
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
4
The categories of this paper are: cond-mat
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex