TAN Howe-Siang
howesiang

Associate Professor
Assistant Chair (Communications)

Education: B.Sc., National University of Singapore; M.A., Ph.D., Princeton University, Post-doc: Stanford  

Research Areas: Femtochemistry, Femtobiology, Ultrafast Laser Spectroscopy, Multidimensional Optical Spectroscopy, Ultrashort Laser Pulse Shaping

Phone: (65) 6316 2987

E-mail: howesiang@ntu.edu.sg

Webpage: http://www.ntu.edu.sg/home/howesiang/



Research Interest

Many fundamental processes in chemistry and biology happen in the femtosecond (10-15 sec) to picosecond (10-12 sec) time regime. The only way to directly study systems at such short timescale is through ultrafast laser spectroscopy. Here are some of our group’s research interests in the area of ultrafast laser spectroscopy:

Coherent Ultrafast Multidimensional Optical Spectroscopy

We are developing novel techniques in multidimensional optical spectroscopy. Multidimensional optical spectroscopy is the optical analogue of multidimensional nuclear magnetic resonance (NMR) spectroscopy such as COSY and NOESY. The femtosecond time resolution of ultrafast laser spectroscopy allows experimentalist to look at structural fluctuations and energy transfer processes of molecular systems at a much higher time resolution than NMR spectroscopy.

One technique used in our lab is the computer controlled pulse shaper assisted 3rd order 2D electronic spectroscopy (2DES). The 2DES technique is an advancement over conventional ultrafast pump probe or transient absorption spectroscopy as it allows the excitation frequency to be correlated with emission frequency. This technique is useful in resolving complex energy transfer processes in systems such as photosynthetic light harvesting complexes.



Figure 1. Schematic of a pulse shaper assisted 3rd order 2D electronic spectroscopy (2DES) setup.

We also develop higher order techniques such as 5th order 3D spectroscopy (3DES) which builds on the 2DES technique to probe multi-step energy transfer processes.

Ultrafast Excitation Energy Transport Processes in Photosynthetic systems:

Light-harvesting antenna systems such as LHCII, the primary light-harvesting complex in plants, are essential for the photosynthetic process that powers the biological world. The excitation energy transfer (EET) processes in naturally occurring light-harvesting systems are therefore of deep interest to scientists. We use 2DES and 3DES to measure the complex energy transfer pathways between excitonic states.

PSPulseTrain.jpg

Figure 2. Using 5th order 3D electronic spectroscopy (3DES) to directly observe multistep ultrafast Excitation Energy Transfer processes in LHCII.

Ultrafast Optical Pulse Shaping

Using nonlinear optical techniques, we are developing new optical pulse shapers designs in the ultraviolet and mid infrared with full control of the optical pulses’ amplitude, phase and polarization profiles. These shaped pulses can be applied to Multidimensional Optical Spectroscopy and Optical Quantum Control experiments.

 

Selected Publications

  1. Z. Zhang, P.H. Lambrev, K.L. Wells, G. Garab, H.-S. Tan. "Direct observation of multistep energy transfer in LHCII with fifth-order 3D electronic spectroscopy" Nat. Comm. 6, 7194 (2015).

  2. K.L. Wells, P.H. Lambrev, Z. Zhang, G. Garab and H.-S. Tan. "Pathways of energy transfer in LHCII revealed by room-temperature 2D electronic spectroscopy" Phys. Chem. Chem. Phys. 16, 11640-11646 (2014).

  3. Z. Zhang, K.L. Wells, and H.-S. Tan. "Purely absorptive fifth-order three-dimensional electronic spectroscopy" Opt. Lett. 37, 5058-5060 (2012). 

  4. M. T. Seidel, S. Yan, and H.-S. Tan, “Mid-infrared polarization pulse shaping by parametric transfer", Opt. Lett., 35, 478, (2010).  

  5. H.-S. Tan, “Theory and Phase Cycling Scheme Selection Principles of Collinear Phase Coherent Multi-dimensional Optical Spectroscopy", J. Chem. Phys., 129, 124501 (2008).