Abstract
The majority of 2D IR spectrometers operate at 1-10 kHz using Ti:Sapphire laser technology. We report a 2D IR spectrometer designed around Yb:KGW laser technology that operates shot-to-shot at 100 kHz. It includes a home-built OPA, a mid-IR pulse shaper, and custom-designed electronics with optional on-chip processing. We report a direct comparison between Yb:KGW and Ti:Sapphire based 2D IR spectrometers. Even though the mid-IR pulse energy is much lower for the Yb:KGW driven system, there is an 8x improvement in signal-to-noise over the 1 kHz Ti:Sapphire driven spectrometer to which it is compared. Experimental data is shown for sub-millimolar concentrations of amides. Advantages and disadvantages of the design are discussed, including thermal background that arises at high repetition rates. This fundamental spectrometer design takes advantage of newly available Yb laser technology in a new way, providing a straightforward means of enhancing sensitivity.
Highlights
Two-dimensional infrared spectroscopy (2D IR) has proven its utility in answering pertinent questions in diverse fields such as biophysics, materials science, and chemical physics [1,2]. 2D IR spectroscopy can be used to monitor ultrafast phenomena such as chemical exchange and solvent structural dynamics [3,4,5], as well as slower kinetics such as amyloid aggregation [6,7,8]
It can be applied to liquids, membranes, and solids [3,9,10,11,12], and has recently been implemented in microscopy [13,14], as true for all techniques, the utility of 2D IR is set by the signal-to-noise ratio (S/N)
A frequency dependent phase is applied to counteract group velocity dispersion (GVD) and third order dispersion (TOD) introduced by the dispersive optics in the spectrometer. This scheme is implemented by varying the GVD and TOD coefficients, which are the coefficients of the second and third order terms in the Taylor expansion of the spectral phase shown in Eq (1)
Summary
Two-dimensional infrared spectroscopy (2D IR) has proven its utility in answering pertinent questions in diverse fields such as biophysics, materials science, and chemical physics [1,2]. 2D IR spectroscopy can be used to monitor ultrafast phenomena such as chemical exchange and solvent structural dynamics [3,4,5], as well as slower kinetics such as amyloid aggregation [6,7,8]. Weak absorption can be compensated for by using higher concentrations, so long as the necessary concentrations are attainable and do not affect the structure or dynamics of the analyte. In principle, both strong and weakly absorbing vibrational modes can provide large signals at room temperature because their excited vibrational states are effectively unpopulated [24,25]. Background from electronic signal introduced by the RFA on the Yb:KGW spectrometer was removed from data in 3.3 by subtracting a 2D IR spectrum collected with the pump pulse blocked
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