Sri Rama Prasanna Pavani
KLA-Tencor Corporation, Milpitas CA
Electrical Engineering Postdoctoral Scholar, Caltech, Sept 2009-Feb 2010
PhD, ECE, University of Colorado - Boulder, 2009
MS, ECE, University of Colorado - Boulder, 2006
BE, ECE, Government College of Technology - Coimbatore, India 2003
My postdoctoral research focused on using computational optical sensing and imaging methods to achieve new optofluidic microscope modalities such as three-dimensional imaging and phase imaging. The on-chip, lensless, and optofluidic characteristics of these microscopes make them a robust, compact, and cost-effective solution for high-throughput biological imaging with sub-micron scale resolution.
My doctoral thesis focused on computational optical sensing and imaging (COSI). COSI systems use unconventional optics (masks, holograms) and active illumination (structured in space and time) to capture information that is normally untapped in traditional imaging systems.
1. Superresolution imaging in three dimensions
We demonstrate single-molecule fluorescence imaging beyond the optical diffraction limit in three dimensions with a wide-field microscope that exhibits a double-helix point spread function (DH-PSF). By using a photoactivatable fluorophore, repeated imaging of sparse subsets with a DH-PSF microscope provides superresolution imaging of high concentrations of molecules in all 3 dimensions. Two molecules as close as 14 nm (x), 26 nm (y), and 21 nm (z) are resolved by this technique. The combination of optical PSF design and digital postprocessing with photoactivatable fluorophores opens up avenues for improving 3D imaging resolution beyond the Rayleigh diffraction limit.
2. Three-dimensional particle localization and tracking
We demonstrate simultaneous three-dimensional tracking of multiple fluorescent microparticles with the DH-PSF. An information theoretical comparison in photon-limited systems shows that the DH-PSF delivers higher Fisher information for 3D localization than the standard PSF. In the detector-limited regime (such as bright-field imaging), the gain in accuracy occurs in all three dimensions throughout the axial range of interest. The system determines the 3D positions of multiple particles with a single image, and using a time series of images, tracks particle positions and provides their velocities with nanometer scale 3D precisions.
3. Double-helix point spread function
We introduce a PSF specifically designed for 3D imaging and sensing. With two lobes that rotate around the optical axis upon propagation, the PSF appears as a double-helix in 3D. The PSF design involves an optimization procedure that applies constraints in the Gauss-Laguerre modal plane, the spatial domain, and the Fourier domain, resulting in a phase only mask with seven phase singularities (dislocations/vortices). Compared to traditional rotating beams, the DH-PSF offers over thirty times improvement in transfer function efficiency, and is directly applicable for a variety of imaging systems ranging from 3D nanoscopes to 3D cameras.
4. Structured-illumination phase microscopy
We introduce a quantitative phase imaging method for homogeneous objects with a bright field transmission microscope by using an amplitude mask and a digital processing algorithm. A known amplitude pattern is imaged on the sample plane containing a thick phase object by placing an amplitude mask in the field diaphragm of the microscope. The phase object distorts the amplitude pattern according to its phase profile. A digital processing algorithm then estimates the object's quantitative phase profile based on a closed form analytical solution, which is derived using a ray optics model for objects with small phase gradients.
1. S.R.P. Pavani, M.A. Thompson, J.S. Biteen, S.J. Lord, N. Liu, R.J. Twieg, R. Piestun, W.E. Moerner, Three-dimensional, single-molecule fluorescence imaging beyond the diffraction limit by using a double-helix point spread function, Proc. Natl. Acad. Sci. USA 106, 2995-2999 (2009)
2. S.R.P. Pavani, A. Greengard, and R. Piestun, Three-dimensional localization with nanometer accuracy using a detector-limited double-helix point spread function system, Appl. Phys. Lett. 95, 021103 (2009)
3. S.R.P. Pavani and R. Piestun, Three dimensional tracking of fluorescent microparticles using a photon-limited double-helix response system, Opt. Express 16, 22048-22057 (2008)
4. S.R.P. Pavani and R. Piestun, High-efficiency rotating point spread functions, Opt. Express 16, 3484 (2008)
5. S.R.P. Pavani, A.R. Libertun, S.V. King, and C.J. Cogswell, Quantitative structured-illumination phase microscopy, Appl. Opt. 47, 15-24 (2008)
6. S.R.P. Pavani, J.G. Deluca, and R. Piestun, Polarization sensitive, three-dimensional, single-molecule imaging of cells with a double-helix system, Opt. Express 17, 19644-19655 (2009)
7. G. Sharma, S.R.P. Pavani, R. Piestun, to be submitted (2009)
8. S.V. King, C. Preza, S.R.P. Pavani, A.R. Libertun, C.J. Cogswell, R. Piestun, to be submitted (2009)
- S.R.P. Pavani, R. Piestun, OSA FiO (2009)
- S.R.P. Pavani, M.A. Thompson, J.S. Biteen, R. Piestun, W.E. Moerner, OSA NTM (2009)
- S.R.P. Pavani, R. Piestun, OSA CLEO (2009)
- S.R.P. Pavani, R. Piestun, SPIE Photonics West - BIOS (2009) (INVITED PAPER)
- S.R.P. Pavani, R. Piestun, OSA FiO (2008) (OUTSTANDING PAPER AWARD)
- S.R.P. Pavani, R. Piestun, OSA DH and 3D image (2008)
- S.R.P. Pavani, R. Piestun, CPIA (2008) (BEST POSTER AWARD)
- S.R.P. Pavani, R. Piestun, OSA FiO (2007)
- S.R.P. Pavani, R. Piestun, OSA COSI (2007)
- S.R.P. Pavani, A. Libertun, C.J. Cogswell, OSA FiO (2007)
- S.R.P. Pavani, A. Libertun, C.J. Cogswell, OSA COSI (2007)
- S.R.P. Pavani, A. Greengard, R. Piestun, CPIA (2007)
- S.R.P. Pavani, A. Libertun, C. Cogswell, CPIA (2006) (BEST POSTER AWARD)
- S.R.P. Pavani, S. Balaji, T.H. Khezhie, and C. Vasanthanayaki, IEEE TENCON (2003)
- S.R.P. Pavani, S. Balaji, T.H. Khezhie, and C. Vasanthanayaki, Computer Society of India (2003)
- G. Sharma, S.R.P. Pavani, R. Piestun, OSA COSI (2009)
- M.A. Thompson, S.R.P. Pavani, J.S. Biteen, R. Piestun, W.E. Moerner, OSA CLEO (2009)
- C.J. Cogswell, S.V. King, S.R.P. Pavani, D.B. Conkey, R.H. Cormack, Focus on Microscopy (2009)
- S. Quirin, S.R.P. Pavani, R. Piestun, CPIA (2008)