Recently, our group has developed a new method to dramatically increase the bandwidth and temporal resolution of multi-dimensional coherent spectroscopy.  By moving to an all-reflective design and incorporating passive phase stabilization, we have succeeded in adapting GRAPES for use with single- or few-cycle pulses. We call this method WHITE GRAPES to highlight its use with white light supercontinuum (SC) sources. These SC sources offer opportunities to investigate new spectral and temporal regimes in condensed phase systems. We have recently demonstrated the generation of high-power and stable SC using a 100-fs source with <1 mJ intensity at 1 kHz repetition rate in a two stage filamentation process. Pulse characterization was achieved by employing a home-built Transient Grating (TG) Frequency-Resolved Optical Gating (FROG) setup.  In the first stage, spectral broadening occurs by filamentation in Argon after focusing the attenuated initial pulse into a pressurized cell at 1 bar. The resulting pulse is spectrally broadened to about 65 nm before being launched into a second air-filled cell, which results in SC emission from about 500 – 800 nm.  After pulse compression, we can achieve sub-6 fs pulse durations.  Our current goal is to extend the SC emission and achieve sub-3.5 fs pulses using a differentially pumped hollow core fiber filled with SF6 gas.


Top: Real part of WHITE GRAPE 2D spectrum of IR-144 at T = 300 fs. Bottom: 2D pulse sequence using few-cycle SC pulses.


B. Spokoyny, C. J. Koh, and E. Harel, Stable and high-power few cycle supercontinuum for 2D ultrabroadband electronic spectroscopy, Opt Lett, 40 (6), 1014-1017 (2015). PDF

B. Spokoyny, and E. Harel, Mapping the Vibronic Structure of a Molecule by Few-cycle Continuum Two-Dimensional Spectroscopy in a Single Pulse,J Phys Chem Lett, 5 (16), 2808–2814 (2014). PDF