Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Realizing Quantum free-electron lasers: A critical analysis of
  experimental challenges and theoretical limits   We examine the experimental requirements for realizing a high-gain Quantum
free-electron laser (Quantum FEL). Beyond fundamental constraints on electron
beam and undulator, we discuss optimized interaction geometries, include
coherence properties along with the impact of diffraction, space-charge and
spontaneous emission. Based on desired Quantum FEL properties, as well as
current experimental capabilities, we provide a procedure for determining a
corresponding set of experimental parameters. Even for an idealized situation,
the combined constraints on space-charge and spontaneous emission put strong
limits on sustaining the quantum regime over several gain lengths. Guided by
these results we propose to shift the focus towards seeded Quantum FELs instead
of continuing to aim for self-amplified spontaneous emission (SASE). Moreover,
we point out the necessity of a rigorous quantum theory for spontaneous
emission as well as for space-charge in order to identify possible loopholes in
our line of argument.

33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
16
The categories of this paper are: stat
17
The categories of this paper are: q-fin