  For highly efficient ultrathin solar cells, layered indium selenide (InSe), a
van der Waals solid, has shown a great promise. In this paper, we study the
coherent dynamics of charge carriers generation in {\gamma}-InSe single
crystals. We employ ultrafast transient absorption spectroscopy to examine the
dynamics of hot electrons after resonant photoexcitation. To study the effect
of excess kinetic energy of electrons after creating A exciton (VB1 to CB
transition), we excite the sample with broadband pulses centered at 600, 650,
700 and 750 nm, respectively. We analyze the relaxation and recombination
dynamics in {\gamma}-InSe by global fitting approach. Five decay associated
spectra with their associated lifetimes are obtained, which have been assigned
to intraband vibrational relaxation and interband recombination processes. We
extract characteristic carrier thermalization times from 1 to 10 ps. To examine
the coherent vibrations accompanying intraband relaxation dynamics, we analyze
the kinetics by fitting to exponential functions and the obtained residuals are
further processed for vibrational analysis. A few key phonon coherences are
resolved and ab-initio quantum calculations reveal the nature of the associated
phonons. The wavelet analysis is employed to study the time evolution of the
observed coherences, which show that the low-frequency coherences last for more
than 5 ps. Associated calculations reveal that the contribution of the
intralayer phonon modes is the key determining factor for the scattering
between free electrons and lattice. Our results provide fundamental insights
into the photophysics in InSe and help to unravel their potential for
high-performance optoelectronic devices.
