Attosecond-Stable Collinear Sagnac Interferometer for Broadband 2DES Using an MPC-Compressed Light Source

Wei Chung Feng^1*, Bo Han Chen¹, Kai Chen³, Chih Hsuan Lu¹, Howe Siang Tan², Shang Da Yang¹

¹Institute of Photonics Technology, National Tsing Hua University, Hsinchu, Taiwan
²School of Chemistry, Chemical Engineering & Biotechnology, Nanyang Technological University, Singapore, Singapore
³School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand

* Presenter:Wei Chung Feng, email:ken87871236@gmail.com

We present a broadband, collinear two-dimensional electronic spectroscopy (2DES) system driven by a bright few-cycle light source and based on a modified Sagnac interferometer. The multiple-plate compression (MPC) scheme produces intense, supercontinuum pulses that can be compressed to 3 fs, enabling simultaneous excitation of multiple electronic transitions. Within the Sagnac loop, two counter-propagating beams share a common path, ensuring attosecond-level phase stability while allowing each pulse to be manipulated independently—for example, in polarization control—without affecting spatial overlap. A double-pass fused-silica wedge pair provides sub-femtosecond, highly linear delay control, and the polarization-independent, broadband design eliminates spatial walk-off and alignment complexity. This configuration integrates seamlessly into a transient-absorption geometry, offering high stability and compactness. System characterization via white-light interference confirmed excellent delay linearity and long-term phase coherence. 2DES measurements of chlorophyll-a in methanol revealed coherent electronic–vibrational oscillations and long-lived population relaxation, demonstrating the system’s capability for high-fidelity multidimensional spectroscopy.

Keywords: Two-Dimensional Electronic Spectroscopy (2DES), Ultrafast Nonlinear Spectroscopy, Sagance Interferometer