A nonlinear optical signal electric field measurement setup for VUV excited molecules

We describe an experimental setup for the measurement of the complete electric field of a third-order nonlinear optical signal from gas phase molecules excited by vacuum ultraviolet (VUV) pulses. A near infrared (NIR) femtosecond laser at a central wavelength of 800 nm is used to generate VUV pulses using the process of high harmonic generation in Argon. VUV mirrors with a special coating are used to reject 800 nm light and reflect 160 nm (5^th harmonic of 800 nm) light for excitation of target molecules such as ethylene. A separate nonlinear probing beam consisting of NIR pulses is spatially and temporally overlapped with the VUV beam at the target. Multiple nonlinear optical probing schemes are used to probe ultrafast dynamics in the VUV excited molecules. In one scheme, we measure a four-wave mixing signal involving the VUV and the NIR pulses resulting in a signal at 400 nm. We discuss progress towards completely measuring the electric field of such nonlinear signals in VUV excited molecules.