2D infrared spectroscopy is a valuable tool capable of providing information on the structure and dynamics of complex systems. However, this information is limited to transitions that fall within the bandwidth of the incident laser pulses. In the mid-IR, this window is normally limited to the &lt;500 cm-1 bandwidth of ultrafast IR pulses generated by optical parametric amplifiers. Experimental geometries that scan multiple IR frequencies can expand this range in a series of measurements but are not commonly employed. Additionally, previous works have extended the detection axis to several thousand wavenumbers by employing low-energy, mid-IR supercontinuum probe pulses. The spectral brightness of such pulses is several orders of magnitude less than that of typical DFG pulses, meaning they are much too low in energy to serve as excitation pulses in ultrafast vibrational spectroscopy. However, electronic excitations require significantly lower excitation energies, and, in limited cases, these transitions can occur at mid-IR energies normally used for vibrational spectroscopies. These transitions can then be both excited and probed utilizing low-energy supercontinuum pulses, yielding 2D-IR spectra that span up to 3000 cm-1 in each dimension. Here, we demonstrate full spectrum 2D-IR spectroscopy in two such cases: mid-IR bandgap semiconductors and intrinsically doped HgSe quantum dots. In indium arsenide and indium antimonide crystals, the full-spectrum 2D-IR spectra show short-lived multiphoton effects and a field-induced perturbation of the bandgap energy even at very low pulse energies. Full-spectrum 2D-IR spectroscopy of the interband transitions of HgSe quantum dots reveals both ultrafast spectral dynamics and long-lived responses of the fundamental and induced carrier transitions spanning &gt;1000 cm-1 in both dimensions.

Extending the spectral range of 2D IR spectroscopy

ACS Fall 2021

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