Broadband sum frequency generation with two regenerative amplifiers: temporal overlap of femtosecond and picosecond light pulses.

Sum frequency generation (SFG) spectroscopy is a valuable tool for studying interfaces such that the boundary between two adjoining phases can be probed with minimal interference from the adjacent bulk material. More recently, broad-bandwidth sum frequency generation (BBSFG) techniques are being explored. This technique using IR broad-bandwidth fs pulses overlapped with narrow-bandwidth ps pulses to obtain BBSFG spectra is described. In the BBSFG system design presented here, the fs pulse and the ps pulse that are generated in separate regenerative amplifiers are overlapped temporally. This temporal overlap process is discussed. In addition, images of the sum frequency response demonstrate its viability. The new approach in experimental design described here for this emerging technology, BBSFG, has application for studying time-dependent processes at interfaces that inherently produce low SFG signal levels such as air-aqueous interfaces.