Transformations of the spectrum of an optical phonon excited in raman scattering in the bulk of diamond by ultrashort laser pulses with a variable duration

A spontaneous Raman signal at the frequency of the triply degenerate optical phonon of diamond is observed in the photoluminescence spectrum under the pre-filamentation excitation of natural diamond by ultrashort laser pulses with a wavelength of 515 nm, fixed intensity, and a duration varied in the range of 0.3–12 ps. The inhomogeneous blue broadening of the line (0.6–1.3 ps), almost symmetric splitting of the line into three components (2.3–6.3 ps), and very strong homogeneous broadening of the entire line are observed at pulse durations of 6.3–12 ps. Transformations of the lineshape of the optical phonon, which are observed for the first time, are attributed to the subpicosecond dynamics of the electron–hole plasma and the (sub)picosecond dynamics of local mechanical stresses induced by the plasma and nonequilibrium phonons.