A laser amplifier system is presented including a pump regenerative amplifier. The amplifier generally has a cavity defined by a pair of end cavity mirrors between which an amplified pump pulse oscillates. The amplifier also includes an interaction cell with a tunable gain medium amplifies laser pulses (e.g., Raman gain). The interaction cell may be positioned within the pump amplifier cavity and an input pulse may be injected into the cavity of the amplifier to transit through the tunable gain medium of the interaction cell. A pump pulse transfers energy via interaction with the input pulse (e.g., Raman interaction) as the pulses counter-propagate through the gain medium of the interaction cell. Amplification of output laser pulses, however, is generally achieved according to the wavelength of the pump laser pulses thereby providing a wavelength dependent, or “tunable”, means for amplifying laser pulses.