Optical electric-field oscillations are now experimentally accessible in the THz-to-PHz frequency range. Their measurement delivers the most comprehensive information content attainable by optical spectroscopy – if performed with high sensitivity. In their new paper, scientists at the Laboratory for Lightwave Metrology and at Attoworld report electro-optic sampling (EOS) of broadband infrared waves with a record measurement sensitivity within a factor of 4 from the ultimate limit of detecting all photons in the interaction time window of the EOS gate pulse with the infrared test wave.
The trade-off between bandwidth and efficiency associated with the nonlinear mixing necessary for optical-field sampling has so far strongly restricted sensitivity in applications such as field-resolved spectroscopy of molecular vibrations. In the newly published work, employing powerful 2-μm gate pulses generated by Tm-fiber lasers, the authors exceeded the previous record of detection quantum efficiency for broadband EOS by more than one order of magnitude while simultaneously doubling the detection bandwidth. At the same time, the high gate-pulse energy employed in the new work affords an unprecedented degree of linearity for the measurement of infrared fields, with strengths ranging from a few mV/cm to the MV/cm level, that is, over more than 15 orders of magnitude in intensity.
This new combination of close-to-ultimate detection sensitivity, high dynamic range, and linearity, along with the outstanding control over broadband infrared waves obtained via intrapulse difference-frequency generation, previously demonstrated in our group, constitute crucial steps toward infrared (non-)linear spectroscopy of solids, liquids, and gases at the ultimate limits set by the nature of light. At the Laboratory of Lightwave Metrology, we are currently preparing the application of these novel techniques to biomedical applications such as high-throughput infrared flow cytometry and breath analysis by vibrational spectroscopy.
Original publication:
[1] C. Hofer, D. Bausch, L. Fürst, Z. Wei, M. Högner, T.P. Butler, M. Gebhardt, T. Heuermann,C. Gaida, K. Maiti, M. Huber, E. Fill, J. Limpert, F. Krausz, N. Karpowicz, I. Pupeza, “Linear field-resolved spectroscopy approaching ultimate detection sensitivity,” Optics Express 33, 1 (2025).