Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photoinduced time-resolved electrodynamics of superconducting metals and
  alloys   The photoexcited state in superconducting metals and alloys was studied via
pump-probe spectroscopy. A pulsed Ti:sapphire laser was used to create the
non-equilibrium state and the far-infrared pulses of a synchrotron storage
ring, to which the laser is synchronized, measured the changes in the material
optical properties. Both the time- and frequency- dependent photoinduced
spectra of Pb, Nb, NbN, Nb{0.5}Ti{0.5}N, and Pb{0.75}Bi{0.25} superconducting
thin films were measured in the low-fluence regime. The time dependent data
establish the regions where the relaxation rate is dominated either by the
phonon escape time (phonon bottleneck effect) or by the intrinsic quasiparticle
recombination time. The photoinduced spectra measure directly the reduction of
the superconducting gap due to an excess number of quasiparticles created by
the short laser pulses. This gap shift allows us to establish the temperature
range over which the low fluence approximation is valid.

24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an