  Development of ultrafast lasers and non-linear optical techniques over the
last two decades provides tools to access real-time dynamics of low energy
excitations in superconductors. For example, time-resolved THz spectroscopy and
time- and angular-resolved photoemission spectroscopy provide access to the
real-time dynamics of the superconducting gap amplitude. Such studies enable
determination of microscopic parameters like quasi-particle recombination
rates, pair-breaking rates and electron-boson coupling constants. Recently,
intense THz pulses have been used to probe the non-linear dynamics, including
observation of collective modes. Moreover, using low frequency electromagnetic
pulses, there are several reports of amplification of superconductivity in both
conventional and unconventional superconductors. Starting with a brief
historical overview of the pioneering work, where non-equilibrium phenomena in
superconductors were investigated using quasi-continuous excitation, we review
some of the insights that are provided by using real-time approaches. We focus
on conventional BCS superconductors, whose ground state is reasonably well
understood, and address similarities and open questions related to the
corresponding studies in high-T$_{c}$ superconductors.
