Designed for the study of ultrafast phenomena such as electronic deactivation, intersystem crossing, vibrational relaxation, internal conversion, and intra-molecular electron transfer, Newport Corp.’s (Irvine, CA) Helios is a pump-probe transient absorption spectrometer used to monitor extremely short-lived optically absorbing states. The experimental time window ranges from 150 fs to 3.2 ns, covering wavelengths of 350 to 1600 nm. The system is completely turnkey, including all of the optics, optomechanics, the delay line, spectrometer in the optical unit, and a PC containing the data acquisition hardware and software. The system is designed to work with an amplified Ti:Sapphire femtosecond laser. The system captures the spectral and kinetic data required for investigating photoexcitation events on the sub-picosecond and longer timescale.