Femtosecond Fieldoscopy for label-free sensing*

Field-resolved detection at near-petahertz frequencies [1] offers exceptional sensitivity, bandwidth, and dynamic range, enabling attosecond temporal resolution and sub-diffraction spatial precision. A novel approach, termed Femtosecond Fieldoscopy, leverages ultrashort excitation laser pulses to impulsively excite the in-resonance molecular composition of a sample at near-petahertz frequencies. This interaction induces vibrational coherence at the trailing edge of the pulses, which subsequently decays at a rate determined by vibrational dephasing time.

The transmitted electric field encodes information about the ultrashort excitation pulse, the sample’s delayed response over several picoseconds, and a prolonged atmospheric response lasting hundreds of nanoseconds. By applying field-resolved detection in the time domain and performing Fourier analysis of the decaying molecular response, the technique achieves unprecedented spectroscopic sensitivity and dynamic range. This is made possible by temporally gating the molecular response from the excitation pulse.

Advancements in ytterbium laser technology [2-6] have enabled Femtosecond Fieldoscopy to resolve overtone, Raman, and combination bands in liquid samples [7-9]. Additionally, various approaches have accelerated the technique for real-time sampling [10-12] and expanded its capabilities to non-perturbative, label-free imaging [13, 14].

In this talk, I will provide an overview of recent breakthroughs in this field demonstrated by my group. If time permits, I will conclude with a brief discussion of our ongoing work on developing solar lasers and their potential applications in space exploration [15].