Method and apparatus embodiments of the invention are directed to mitigating temporal contrast degradation in optical parametric chirped pulse amplification (OPCPA) laser systems. A spectral filter is used in an OPCPA laser system to remove or reduce of out-of-band amplified spontaneous emission (ASE) from an amplified pump pulse and/or the longitudinal modes of a seed laser used to generate the pump pulse, which typically cause detrimental temporal intensity fluctuations in the amplified pump signal. According to an illustrative embodiment, a volume Bragg grating (VBG) filter element is disposed in the pump regenerative amplifier cavity where the pump pulse undergoes multiple passes on the filter element.
FEDERALLY SPONSORED RESEARCH
 Embodiments of the invention were made with government support under Cooperative Agreement No. DE-FC52-92SF19460 awarded by the U.S. Department of Energy Office of Inertial Confinement Fusion. The government may have certain rights in the invention.