Research activities of Professor Man Mohan (Group Leader)

At the

“Atomic and Molecular Physics Group, University of Delhi, India”

(1) Research Group on Bose-Einstein Condensation, Cold Atoms & Quantum Optics

Professor Man Mohan (Group Leader), Dr.Aranya B Bhattacherjee (Reader in Physics, Senior Faculty) and Vikash Ranjan ( Doctoral Student).

Our group at the University of Delhi is looking at the theoretical aspects of the physics of dilute-trapped Bose-Einstein condensates. Currently we are looking into excitations, instabilities and vortices in Bose-Einstein condensate trapped in an optical lattice. The research on BEC’s in optical lattice is a part of a more extensive investigation of the properties of BEC’s, in which we are involved. Because the wave-mechanical properties of the atoms are amplified to levels at which they can be observed and manipulated directly, BEC atomic assemblies are particularly interesting and useful for the study of macroscopic quantum effects. This represents one of the main objectives of our research. Fields of very modest strength, including laser fields, very sensitively control ultra cold atomic condensate. One objective of our research is to manipulate and control the BEC interaction through external fields including ultra short laser pulses.

(2) Group on Collisional and Radiative Processes in Plasma

Professor Man Mohan (Group Leader), Dr.Narendra Kumar (Lecturer in Physics, ) , Avninder Kumar Singh (Doctoral Student),Alok Kumar Singh Jha ( Doctoral Student)., Nupar Verma ( Doctoral Student).

In recent years, the high quality observational data returned by space missions such as International Ultraviolet Explorer  (EUVE), the Advanced Satellite for cosmology and Astrophysics (ASCA), the Hopkins Ultraviolet telescope (HUT), the Hubble Space Telescope (HST), and Solar and Heliospheric Observatory (SOHO), has highlighted the need for highly accurate atomic data. There is no doubt that this situation will be further emphasized by the launch of future space missions such as FUSE. The accuracy of atomic data is crucial for the interpretation of the spectra from these missions in terms of the physical conditions in the astrophysical sources. The need for accurate atomic and molecular data is immense, with applications in such diverse field as astronomy, fusion research, and lasers. The type of data depends upon the region or the object being studied. As very few of the ions of interest can be studied experimentally in the laboratory, the user must depend primarily on theoretical data.

In this direction our group is involved in the calculations of accurate collision strengths, radiative and autoionisation transition probability, photoionisation cross-sections, oscillator strengths and wavelengths for allowed and forbidden transitions which are urgently needed for the interpretation of observational data & for modeling astrophysical objects. In our calculations we are including important physical effects mainly configuration interaction, autoionizing resonances, exchange, coupling and relativistic effects, which are incorporated by using Configuration Interaction Technique for the atomic structure and accurate R-matrix method for the collisions.

(3) Our Group on Atoms & Molecules in Strong Radiation Fields &  Chemical Physics

Professor Man Mohan (Group Leader), Dr.Vinod Prasad (Senior Lecturer in Physics,), Dr. Rachna Kundliya (Lecturer in Physics), Miss Kirti Batra  (Doctoral Student), Nisha Singal (Doctoral Student), Anjali Mann ( Doctoral Student).

We are studying numbers of striking non-linear phenomenon in atoms and molecules, which occur when they are exposed to intense short femto-second laser pulses. Some of these are Above threshold ionization (ATI ) i.e the absorption of more photons then necessary for ionization and High  harmonic generation (HHG), which has become potential method to produce coherent radiation with wavelength reaching into soft  X-ray region . In super-intense field we found that the real atom can be stabilized against ionization due to drastic change of atomic structure using two laser pulses differing in phase. For studying such processes we have developed number of non-perturbative  methods like Floquet and Quasi Energy approaches . For real laser pulses with non-periodic Hamiltonian we have developed numerical computational methods, such as Split Operator Technique (SOT), Fast-Fourier Technique (FFT) and Runge-Kutta (RK) method etc. for solving dynamical coupled equations. We have also developed an efficient pseudo-spectral L² technique for calculating accurate multi-photon ionization cross-sections of atoms, which give results in agreement with experimental results. Our group is also involved in the calculation of simultaneous electron-photon excitation (SEPE) processes aiming for explaining the projected experiment using electron and high frequency synchrotron photon beams such as ELECTRA at Trieste and ALS at Berkeley.

(4) Research on Molecular  Dynamics & Inter Molecular Energy Transfer Processes

Knowledge of the chemical, energetic and spectral properties of polyatomic molecules is important for studies of chemical reactivity, isotope separation, combustion processes, chemical lasers and other technologies as well as being a splendid stimulus to the ever-expanding predictive abilities of chemical theorists.

In the field of Molecular dynamics we are investigating the nature of multiphoton excitation of several triatomic molecules in its ground electronic state coupled to different vibrational modes under strong laser field using non-perturbative techniques. The quantum theory of chemical reactions and theory of intermolecular energy transfer is the basis of chemical dynamics and molecular modeling. Our group is using different approaches to study energy transfer in various processes like rotational-rotational (R-R), rotational-vibrational (R-V), vibrational-vibrational (V-V) for explaining the flow of energy in Chemical dynamics i. e where does it go, how long does it take to get there which has direct practical applications.

(5) Our Group on Nano-Technology & Photonics

Professor Man Mohan (Group Leader), Dr.Pradeep Jha  (Senior Lecturer in Physics), Rinku Sharma (Senior Lecturer)

Photonics refers to the science and technology relating to the transportation of information by light, and underpins the information revolution in which light is used to transmit, store and sort information. Nanoscience is directed at discovering and understanding the way matter behaves at the nanoscale, and underpins the technology of creating materials, devices and systems through the control of matter at the atomic level. The nanostructure exhibit strongly  size dependent  chemical & physical properties which represent limiting behaviours for different  types of matter (atomic to bulk) The variations with size are enormous ,and represents a new  opportunity to optimize material properties by varying their size & shape rather than by changing  their  chemical composition. Thus the primary advantage of any nanostructure material lies in the extensive tunability of its properties. For example, the fundamental  characteristics  of a material  , such as  it melting  temperature , color  ,saturation  magnetization and coercivity , charging energy ,chemical reactivity ,etc., are all functions of size and shape. For instance, the color of semiconductor quantum dots can be varied continuously from the near infrared to the ultraviolet. Such colors changes correlate to electron and hole energy levels, which in turn affect the catalytic and chemical behavior of the particles. Thus, nanoscale building blocks lend major new experimentally controllable variables for fabricating  desired materials. Atom manipulations, and matter diffraction from light waves are important new tools emerging from atomic and optical physics, which may lead to new ways of fabricating nanostructures.

Our group is focusing on the recent developments in nanoscience using new theoretical computational tools. For example the interaction of shaped pulses sequences could contribute to the “assembly “ of nanostructured materials, or to the manipulation of electronic coherence in quantum dot molecules and solids .The interaction of intense optical fields with nanostructures is of interest. Mutiphoton ionization, and the measurement of nonlinear susceptibilities as a function of the size are currently important fields. In strong e.m field, collisions of atoms or molecules with the nanostructures will allow electron transfer from quantum dot to the colliding atom or tunnel directly to vacuum states. Such enhanced electron emission processes will find applications in, for example, electron induced catalysis, air pollution abatement, etc. Using UV or even low energy x-rays from synchotron light sources, 3-dimensional nanostructures or layers can be produced.

To improve and develop microelectronics devices, the basic understanding of the various dynamical processes in the nanostructures has to be studied in detail. We are also looking in to the excitation of nanostructures   out of their equilibrium and the subsequent relaxation processes with various rates, which has now become a key area of nanostructure research.

 Some Important Research Publications of the Group

• Mohan M. and Hibbert A. (1987) Model potential calculation for low lying states of mercury, J. Phys B20.

• Mohan M. Milfeld K D. and Wyatt RE (1990) New general R-matrix theory of collinear reactions and its application to the H+ H2 reaction. Mol. Phys. (UK) 70 1085-1095.

• Mohan M. Prasad V.  (1991) Collision of H+ with Co molecule in the presence of laser beam using Floquet theory , J. Phys. B24 L81-L87.

•  Hibbert A. Le Dourneuf M and  Mohan M. (1993) Energies, Oscillator strengths and life times for neon -like ions up to Kr-  XXVII.   At. Data and Nucl. Data tables (USA) 53-23-112.

• Mohan M. Le Dourneuf M. Hibbert A. and Burke PG (1998) Relativistic calculation on photoionisation of the ground state of Neon like Fe- XVII. Phys. Rev. A57 3489-3492.

• Kundliya R. Prasad V and Mohan M. The two-photon process in an atom using the pseudostate summation technique. (2000) J. Phys. B: At. Mol. Opt. Phys. 3, 1-11.

• Kundliya R. Batra K and Mohan M. (2001) Two-photon ionization using elliptically polarized light, Phys. Rev A 64, 043404.

• Singh N. & Mohan M. (2000) “ Level Energies & Oscillator Strengths for fine structure transitions from the  3s² 3p^{5  2}P⁰ ground state of Ca IV” Physica Scripta ( Sweden) 64,149.

• M. Mohan  (2001),Invited Talk  in National Conference on Atomic & Mol., Phys. 16, 20^th Jan. 2001, Calcutta. “Recent Developments in Multiphoton Strong-Field.

• R.Kundliya & M. Mohan (2001),  Phys. Lett. A, 291, 22 “ Stabilization of  Hydrogen atom in an intense laser pulse”.

• Batra K.,Prasad V. and Mohan M. (2002) Collisional excitation of Na-Rydberg  atoms, Eur.Phys.J. D ,191.

• N. Singh , M. Mohan, W. Eissner, Physica Scripta (Sweden)  65, 233,(2002), “Photoionisation of ground state of Mg III using  Relativistic Breit-Pauli  Approximation.”

• N. Singhal, V. Prasad and M. Mohan, European Journal  of  Physics D, 21, 293-298(2002), “Role of electric field polarization in Rotational transitions in Molecules”.

• M.  Mohan   (2002) Conference , Invited Talk, Ind. Journal. Phys. B, 401-405, “ Recent Developments in multiphoton strong- field physics”.

• M. Mohan (2003), Invited Talk at  Centre  de Recherche ,Uni. of  Sherbrook ,Canada,25^th June2003, “Population Distribution in BEC with  Laser Pulses”.

• F. Dion, M. Mohan & Tung  N  Dang (2003), Proceedings of “GORDON   RESEARCH CONF.”  3-8 Aug,2003,MA,U.S.A, Molecular Wavepacket Surfing Time Dependent Potential Energy Surfaces : Effects of Laser  Frequency Chirp.

• N.Singh ,A.K.Singh & M.Mohan (2003), Canadian J. Phys. 81,1-7,2003,“ Level energies and oscillator strengths for fine structure transitions from the ground state of Ca 1V “.

• K. Batra, R .Kundliya  & Man Mohan ( 2004), Pramana  journal of physics   62 ,31 ,“Atom in a femtosecond bichromatic laser field “.

• K.Batra ,N.Verma , A.Maan & M.Mohan (2004), Research Article Published in the Book “Universality and Diversity in Science”, Edited by W.Becker (Germany)and M..V.Federov(Russia), World Scientific Publishing Co. Ltd., “Atomic Dynamics with Chirped Ultra Short Intense Laser pulse”.

• K.Batra ,N.Verma , A.Maan & M.Mohan (2004), Research Article Published in the Book “Universality and Diversity in Science”, Edited by W.Becker (Germany)and M..V.Federov(Russia), World Scientific Publishing Co. Ltd., “Atomic Dynamics with Chirped Ultra Short Intense Laser pulse”.

• A.Maan ,V.Prasad ,N.Singhal & M.Mohan (2005), To be published.“Effect of different shapes of Half-Cycle laser Pulses on the Orientation of HF Molecule”.

Some Recent Publications on Bose Einstein Condensation

• Bhattacherjee, A., Ranjan, V., Man Mohan (2005): Quantum theory of a Bose Einstein condensate out of equilibrium. To appear in Optics Communication.

• Bhattacherjee, A., Courtade, E. and Arimondo, E. (2004): Stability of a   bosonic current in a quasi-condensate confined in an optical toroidal trap. Journal of Physics B: Atomic, Molecular and Optical Physics, 37, 4397-4404.

• Bhattacherjee, A. (2004): Tkachenko modes and quantum melting of Josephson junction type of vortex array in rotating Bose Einstein condensate. Journal of Physics B: Atomic, Molecular and Optical Physics 37, 2699- 2705.

• Bhattacherjee A., Morsch, O. and Arimondo, E (2004): Stability of a small amplitude normal mode of a Bose-Einstein condensate with a singly quantized vortex confined in an optical lattice. Journal of Physics B: Atomic, Molecular and Optical Physics 37, 2355- 2361.

• Bhattacherjee, A., Ranjan, V. and ManMohan (2003): Dynamics of spin squeezing in coupled two mode Bose-Einstein condensates. International Journal of Modern Physics B 17, 2579–2587.

• Bhattacherjee, A. and ManMohan (2003): Wave-packet dynamics and Rabi Oscillations in two-coupled Bose-Einstein condensates confined in an optical lattice. Modern Physics Letters B 17, 321-327.

• Bhattacherjee, A. and ManMohan (2002): Crossover from Rabi to Josephson dynamics in two-coupled Bose-Einstein condensates as a phase transition. Modern Physics Letters B, 16, 1021- 1026.

• Bhattacherjee, A. (2002): Controlled manipulation of population oscillations and quantum statistics of Bose-Einstein condensate confined in an optical lattice. Optics Communication 204, 203-209.

• Bhattacherjee, A. (2002): Quantum manipulation of polaritonic band gaps of two coherently coupled Bose-Einstein condensates confined in an optical lattice. Journal of Optics B: Quantum and semi classical optics 4, 251- 255.

• Bhattacherjee, A. and ManMohan (2002): Imaging population distribution between two coupled atomic Bose-Einstein condensates by using short laser pulses. Physical Review A. 66, 053617- 053622.

 National International Collaboration of our Group

(1) In the field of Atomic Structure & Collision Physics

 (2) In the Field of Chemical Physics

Interactions of Strong Laser Field with Matter

In the fields of Quantum Optics, Bose Einstein Condensation & Cold Atoms

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