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Department of Physics

Vinod Kumarappan

Vinod KumarappanAssociate Professor
328 Cardwell Hall
Group Webpage

Ph.D. Tata Institute of Fundamental Research, Mumbai, India, 2002
M.S.  Indian Institute of Technology Madras, India, 1996
B.S. University of Calicut, India, 1994

Research Area

The main focus of my research is to develop methods to align and orient small molecules in the gas phase, and to study ultrafast physics in the molecular frame. Gas phase measurements are essential to studying molecular properties and behavior in external fields without undue influence of other molecules. But these molecules have random orientations and, historically, the vast majority of experiments have only been able to obtain orientation-averaged information. Laser-induced alignment and orientation has emerged as a powerful technique to overcome orientational averaging, particularly in time-resolved measurements using ultrafast lasers. Intense ultrashort laser pulses, with durations ranging from femtoseconds to nanoseconds, are used to restrict the orientational distribution of molecules. My group uses rotationally cold molecules and multiple femtosecond laser pulses to align and orient molecules.

Apart from experiments, we also do all the computations required to simulate and understand the rotational wavepacket dynamics of molecules. Our embarrassingly-parallel rigid-rotor codes use OpenMP and can tackle the full 3D dynamics of asymmetric tops pumped by multiple elliptically polarized pulses. We can also calculate the rotational dynamics of polar molecules after two-color excitation; such pulses can orient molecules in space.

We use aligned molecules for further experiments, often in collaboration with other experimentalists. These include high harmonic generation with aligned molecules, strong-field ionization and fragmentation and, soon, molecular frame photoelectron spectroscopy and ultrafast electron diffraction. Such experiments lead not only to a detailed understanding of molecular physics and chemistry, but also to new opportunities for controlling quantum dynamics in molecules. 

Research Support

  • Department of Energy
  • National Science Foundation

Recent Selected Publications

Metric for three-dimensional alignment of molecules, V. Makhija, X. Ren and V. Kumarappan, Physical Review A 85, 033425 (2012). [link]

Measurement of field-free alignment of jet-cooled molecules by nonresonant femtosecond degenerate four-wave mixing, X. Ren, V. Makhija and V. Kumarappan, Physical Review A 85, 033405 (2012). [link]

Measuring the angle dependent photoionization cross section of nitrogen using high-harmonic generation, X. Ren, V. Makhija, A.-T. Le, J. Troß, S. Mondal, C. Jin, V. Kumarappan and C. Trallero-Herrero, Physical Review A 88, 043421 (2013). [link]

Multipulse Three-Dimensional Alignment of Asymmetric Top Molecules, X. Ren, V. Makhija and V. Kumarappan, Physical Review Letters 112, 173602 (2014). [link]

Reconstruction of three-dimensional molecular structure from diffraction of laser-aligned molecules, J. Yang, V. Makhija, V. Kumarappan and M. Centurion, Structural Dynamics 1, 044101 (2014). [link]

Alignment-assisted field-free orientation of rotationally cold CO molecules, X. Ren, V. Makhija, H. Li, M. F. Kling and V. Kumarappan, Physical Review A 90, 013419 (2014). [link]