Ultrabroadband Near-Infrared Transient Absorption Spectrometer with Simultaneous 900-2350 nm Detection.

In this work, we detail an ultrafast pump-probe transient absorption (TA) spectrometer capable of probing the near-infrared (NIR) spectral region from 900 to 2350 nm simultaneously. Two key advances were required to overcome previous spectral window limitations, which typically result from constrained supercontinuum ranges (e.g., 1700 nm) and/or InGaAs detector line rates, especially those with >1700 nm range. First, we generated a broadband NIR supercontinuum using the 1980 nm idler beam of an optical parametric amplifier and implement a unique spectral filtering scheme to balance the detected spectrum. Second, we used a prism-based spectrometer system equipped with high speed InGaAs cameras having ∼2500 nm sensitivity cutoffs. To the best knowledge of the authors, such an extended probe range was previously inaccessible because the combination of two optical geometries either using different supercontinuum crystal materials for generating the NIR and shortwave infrared (SWIR) regions, or using differing pump wavelengths, were required. Finally, we demonstrate the performance and capabilities of the ultrabroadband TA spectroscopy system by presenting data showing ultrafast charge photogeneration in a polymer : fullerene blend thin-film and comparing the results to the literature with a complete agreement.