The intensity of radiation stimulated by laser pulses of arbitrary shape is derived up to the fourth order terms. It is shown that there is a linear fourth order mechanism of emission that depends on linear susceptibilities of molecules. This linear mechanism reveals collective, superradiant features. The intensity of laser-driven spontaneous emission (LDSE) is proportional to N2 for samples smaller than (lambda) 3, where (lambda) is a wavelength of emitted radiation, and N is the number of molecules. For extended volumes >> (lambda) 3, the intensity of LDSE is proportional to N4/3. Equations of motion describing collective radiation damping are derived.