Cross-correlation scan between an OPA pulse and a chirped stretched 800 nm pulse

We overlap the uncompressed 800 nm pulse (800 nm, ~140 ps) and the OPA (1800 nm, 50 fs) on a BBO crystal. The output light bounces off a grating, separating light at different wavelengths. The overlap signal from the sum-frequency generation is in the ~500 nm range. Since the uncompressed 800 nm pulse is severely chirped, when we scan the OPA delay through 800 nm pulse, the overlap signal changes color and position with time. This is a very interesting phenomenon to observe!