Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ultrafast imaging of photoelectron packets generated from graphite
  surface   We present an electron projection imaging method to study the ultrafast
evolution of photoelectron density distribution and transient fields near the
surface. The dynamical profile of the photoelectrons from graphite reveals an
origin of a thermionic emission, followed by an adiabatic process leading to
electron acceleration and cooling before a freely expanding cloud is
established. The hot electron emission is found to couple with a surface charge
dipole layer formation, with a sheet density several orders of magnitude higher
than that of the vacuum emitted cloud.

33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
22
The categories of this paper are: chao-dyn
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
2
The categories of this paper are: math