Ultrafast Broad-band Infrared Spectroscopy

Technical Details

We are interested in following ultrafast vibrational and structural dynamics in electronic ground and excited states of gas phase and condensed phase systems. To this end, we have built a laser-driven plasma-based source of broadband infrared (BBIR) pulses for use as probes in transient infrared absorption spectroscopy following infrared or ultraviolet excitation. The BBIR pulse spectrum detected on a liquid nitrogen-cooled HgCdTe array detector spans from ~1000 cm-1 to ~3500 cm-1. The large spectral bandwidth allows simultaneous probing of all infrared-active vibrations in the mid-infrared region of the spectrum, presenting an advantage over the narrow bandwidth output from conventional femtosecond mid-infrared optical parametric amplifiers. Furthermore, the sub-100 femtosecond duration of the BBIR pulses allows exquisite time resolution for following ultrafast vibrational dynamics.

Spectrum of BBIR pulse detected chart
Figure 1
Spectrally-resolved cross-correlation chart
Figure 2

Figure 1 Spectrum of BBIR pulse detected on a HgCdTe array detector. The dips near 2500 cm-1 and 1650 cm-1 are due to absorption from atmospheric CO2 and H2O, respectively.

Figure 2 Spectrally-resolved cross-correlation between 265 nm and BBIR pulses in a Ge wafer, yielding a cross-correlation full-width-at-half-maximum of ~120 fs.

Key Contribution

  • Application of this technique has allowed breakthrough studies of vibrational dynamics in energetic materials

PI: Krupa Ramasesha