Transient Absorption Spectroscopy

Transient absorption spectroscopy, a special type of pump-probe spectroscopy, is a fundamental example of nonlinear spectroscopy. Transient absorption allows us to follow the evolution of molecular, aggregate or material systems on the ground and excited states as a function of femtosecond to nanosecond time delays.

We have an apparatus allowing us to use femtosecond laser pulses to pump a sample with a range of narrowband visible frequencies using an optical parametric amplifier. The probe pulse is a white light supercontinuum pulse that covers the wavelength region 450-1100 nm.

The pump and probe beams are overlapped in the sample and the time delay between them varied. The pump beam is chopped to allow for the subtraction of signals arising from the probe beam solely. A variety of modifications to this technique allow for additional information to be collected, such as TA spectra to be acquired in a single laser shot [1].

Xanthophyll Data

Figure 1: Reproduced from [2]. (a) Xanthophyll Cycle (b) PAM fluorescence decay curves demonstrating quenched and unquenched states of spinach thylakoids. (c) Transient absorption data pumped at 644nm and detected at 1000nm for thylakoids acclimated to high light conditions and low light conditions. (d) Difference between transient absorption signals for quenched and unquenched states.

Helpful Background Reading:

  1. Dual-echelon single-shot femtosecond spectroscopy, G.P. Wakeham and K.A. Nelson, Opt. Lett. 25, 357-363 (2000)
  2. Carotenoid Cation Formation and the Regulation of Photosynthetic Light Harvesting, N. E. Holt, D. Zigmantas, L. Valkunas, X. P. Li, K. K. Niyogi and G. R. Fleming, Science 307, 433-436 (2005).
  3. Ultrafast transient absorption spectroscopy: principles and application to photosynthetic systems. R. Berera, R. van Grondelle, and J.T.M Kennis, Photosynthesis Research 101, 105-118 (2009).
  4. Ultrafast Carrier Dynamics in Single-Walled Carbon Nanotubes Probed by Femtosecond Spectroscopy. Y-Z. Ma, J. Stenger, G. R. Fleming, S. Bachilo, B. Weisman and R. E. Smalley. J. Chem Phys, 120, 3368 (2004).