Near-Infrared Molecular Fieldoscopy of Water

摘要

We introduce the concept of broadband near-infrared molecular fieldoscopy. In this scheme, molecules are excitedby femtosecond pulses in near-infrared spectral range and the complex electric field of their free induction decay isdirectly measured by means of electro-optic sampling. Few-cycle pulses centered at 2 μm and 1 μm are generatedfrom a 5 kHz, Yb:YAG regenerative amplifier and employed for femtosecond excitation and electro-optic sampling,respectively. We chose water in an acetic acid solvent to demonstrate the first proof of principle measurementwith the novel technique. The complex electric field of the combination bond of water molecules at 1930nmat different molecular concentrations is detected and presented. We show the detection sensitivity of our timedomaintechnique is comparable to conventional specral-domain techniques. However, by employing a laserfrontend with higher repetition rates, the detection sensitivity can be drastically enhanced. To the best of ourknowledge, this is the first detection of the complex electric field of the molecular response in near-infraredspectral range. The new method holds promise for high-resolution overtone spectroscopy and microscopy withunparalleled sensitivity and specificity over the entire molecular fingerprint region.