Frequency-domain “single-shot” ultrafast transient absorption spectroscopy using chirped laser pulses

Single-shot ultrafast transient absorbance spectroscopy based on the frequency encoding of kinetics is demonstrated. The kinetics are sampled in the frequency domain using linearly chirped, amplified 33 fs pulses derived from a Ti:sapphire laser. A variable length grating pair compressor is used to achieve sampling of 512 channels with a 2–160 ps window with sensitivity>5×10−4. In terms of the acquisition time, frequency-domain “single-shot” (FDSS) spectroscopy has an advantage over pump–probe spectroscopy when “noise” is dominated by variations in the amplitude of the signal due to pump and flow instability. Unlike some other single-shot techniques, FDSS can be used for fluid samples flowing in a high-speed jet and for thin solid samples that exhibit interference fringes. Another advantage is that, due to interference of quasimonochromatic components of the chirped probe pulse, an oscillation pattern near the origin of the FDSS kinetics emerges. This pattern is unique and can be used to determine the complex dielectric function of photogenerated species. The advantages of FDSS are illustrated with the kinetics obtained in multiphoton ionization of aqueous iodide and one-photon excitation of polycrystalline ZnSe.