Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Experimental Characterization of Ultrafast, Tunable and Broadband
  Optical Kerr Nonlinearity in Graphene   In this study we systematically measure the near-infrared spectral
dependence, the sub-picosecond temporal evolution and pulse-width dependence of
the effective Kerr coefficient ($n_{2,eff}$) of graphene in hundreds of
femtosecond regime. The spectral dependence measured using the Z-scan technique
is corroborated by quantum theory to extract a $n_{2,eff} \propto \lambda^2$
dependence. The temporal evolution extracted using the time-resolved Z-scan
measurement shows the nonlinear response peaking at zero delay time and
relaxing on a time scale of carrier relaxation. Since the Kerr-type response
originated from the optically induced carrier population difference, the
time-scale of the evolution of the nonlinear response is apt. The $n_{2,eff}$
shows a dependence on the pulse-width attributed to the relative heating and
cooling times of the carriers. This dependence is strong when the
pulse-duration is on the same time-scale as the decay constant. Throughout our
study the $n_{2,eff}$ remains positive.

32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
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The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
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The categories of this paper are: eess
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph