Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A new technique to generate 100 GW-level attosecond X-ray pulses from
  the X-ray SASE FELs   We propose a scheme for generation of single 100 GW 300-as pulse in the X-ray
free electron laser with the use of a few cycles optical pulse from Ti:sapphire
laser system. Femtosecond optical pulse interacts with the electron beam in the
two-period undulator resonant to 800 nm wavelength and produces energy
modulation within a slice of the electron bunch. Following the energy modulator
the electron beam enters the first part of the baseline gap-adjustable X-ray
undulator and produces SASE radiation with 100 MW-level power. Due to energy
modulation the frequency is correlated to the longitudinal position within the
few-cycle-driven slice of the SASE radiation pulse. The largest frequency
offset corresponds to a single-spike pulse in the time domain which is confined
to one half-oscillation period near the central peak electron energy. After the
first undulator the electron beam is guided through a magnetic delay which we
use to position the X-ray spike with the largest frequency offset at the
"fresh" part of the electron bunch. After the chicane the electron beam and the
radiation produced in the first undulator enter the second undulator which is
resonant with the offset frequency. In the second undulator the seed radiation
at reference frequency plays no role, and only a single (300 as duration) spike
grows rapidly. The final part of the undulator is a tapered section allowing to
achieve maximum output power 100-150 GW in 0.15 nm wavelength range. Attosecond
X-ray pulse is naturally synchronized with its fs optical pulse which reveals
unique perspective for pump-probe experiments with sub-femtosecond resolution.

18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
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The categories of this paper are: q-fin
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The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
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The categories of this paper are: hep-lat
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The categories of this paper are: acc-phys