Spatiotemporal Control

Ultrafast tweezers and Nonlinear effects

Insights into biological systems and control aspects for reaction dynamics and coherent control. Two photon absorption studies and spectroscopy.

We are trying to go towards a direction where we are going to mix the temporal part with spatial part. Spatial part is the part where we talk about the biological imaging, controlling imaging i. e. the coherent control of bioimaging. It is in the spatial domain, but it has a coupling in the time domain also. In the spatial control, the biggest control that we have is the optical tweezer, where we hold something and have the capabilities of moving something in a controlled way. In our lab we have a tweezer which is pulsed in time. So we are imparting time and space simultaneously. Controlled spatial manipulation of controlling translational degrees of freedom of molecules is essential to achieve controlled intermolecular interactions for implementing molecular quantum logic. Instituting total such control therefore involves inducing an overall molecular polarizibility through femtosecond temporal modulations that is simultaneously amenable to spatial control through macroscopic aspects of light polarization, photon flux, manipulations etc. Our pulse shaper is a unique example where we convert between time and space in terms of Fourier transform. Again in terms of action we do the same thing, we convert time and space simultaneously. So actually we can think of Fourier domain-Fourier domain in spectroscopy, Fourier domain in microscopy and Fourier domain in control. One Fourier plane is generating the problem and the other Fourier plane where we are doing the problem essentially solving the problem. This is the overall view of the picture. Then there are different sub fields where the focus is now shifting on. These sub fields become as wide as quantum computing on one end and biological imaging at the other end. And then they get connected by chemistry somewhere in the middle. But since the overall picture has some connection with the all, we can take information from all these angles and can get it connected by some means or the other.

Some of our work in this area include [1,2,3]


Full list here.

  1. Spatiotemporal Control of Degenerate Multiphoton Fluorescence Microscopy with Delay-Tunable Femtosecond Pulse Pairs. D. Das, I. Bhattacharyya, and D. Goswami, Chemical Physics Letters 657, 72–77 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: Selective excitation of a particular fluorophore in an ensemble of different fluorophores with overlapping fluorescence spectra is shown to be dependent on the time delay of femtosecond pulse pairs in multiphoton fluorescence microscopy. In particular, the two-photon fluorescence behavior of the Texas Red and DAPI dye pair inside Bovine Pulmonary Artery Endothelial (BPAE) cells depends strongly on the center wavelength of the laser, as well as the delay between two identical laser pulses in one-color femtosecond pulse-pair excitation scheme. Thus, we present a novel design concept using pairs of femtosecond pulses at different central wavelengths and tunable pulse separations for controlling the image contrast between two spatially and spectrally overlapping fluorophores. This femtosecond pulse-pair technique is unique in utilizing the variation of dye dynamics inside biological cells as a contrast mode in microscopy of different fluorophores.

     BibTeX: @article{dasSpatiotemporalControlDegenerate2016,
      title = {Spatiotemporal Control of Degenerate Multiphoton Fluorescence Microscopy with Delay-Tunable Femtosecond Pulse Pairs},
      author = {Das, Dhiman and Bhattacharyya, Indrajit and Goswami, Debabrata},
      date = {2016-07-16},
      journaltitle = {Chemical Physics Letters},
      shortjournal = {Chemical Physics Letters},
      volume = {657},
      pages = {72--77},
      issn = {0009-2614},
      doi = {10/f84rwd},
      url = {},
      urldate = {2019-08-01},
      annotation = {00000},
      keywords = {_tablet,Multiphoton microscopy,Pulse-pair excitation,Stimulated emission,Two-photon fluorescence}
  2. Solvent Effect on Two-Photon Absorption and Fluorescence of Rhodamine Dyes. A. Nag and D. Goswami, Journal of Photochemistry and Photobiology A: Chemistry 206(2), 188–197 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: For a series of rhodamine dyes, two-photon absorption (TPA) and two-photon fluorescence (TPF) have been performed in different solvents. Solvent-dependent TPA spectra of these dyes were measured with open aperture z-scan method and compared to their respective single-photon spectra at equivalent energies. In the TPA spectra, relative peak intensities and positions are highly solvent dependent, which could be a result of vibronic couplings that depend on solvent environment. Measured TPA cross-sections of rhodamine dyes are consistently higher in nonpolar solvents. Certain complementary and similarity between TPA and TPF are also elucidated. Finally, a two-photon figure-of-merit is presented for these dyes in different solvents as a function of wavelength.

     BibTeX: @article{nagSolventEffectTwophoton2009,
      title = {Solvent Effect on Two-Photon Absorption and Fluorescence of Rhodamine Dyes},
      author = {Nag, Amit and Goswami, Debabrata},
      date = {2009-08-15},
      journaltitle = {Journal of Photochemistry and Photobiology A: Chemistry},
      shortjournal = {Journal of Photochemistry and Photobiology A: Chemistry},
      volume = {206},
      pages = {188--197},
      issn = {1010-6030},
      doi = {10/c4zdx8},
      url = {},
      urldate = {2019-08-14},
      annotation = {00063},
      keywords = {_tablet,Figure-of-merit,Solvent polarity,TPA,TPF,Vibronic coupling},
      number = {2}
  3. A Simple Twist for Signal Enhancement in Non-Linear Optical Microscopy. A. K. De and D. Goswami, Journal of Microscopy 235(2), 119–123 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: We describe a very simple but elegant approach to two-photon fluorescence signal enhancement by intensity modulation with immediate application in two-photon laser-scanning fluorescence microscopy. This method of enhancement shows potential application in any microscopic technique that result from non-linear photon absorption and plays a pivotal role in live cell imaging.

     BibTeX: @article{deSimpleTwistSignal2009,
      title = {A Simple Twist for Signal Enhancement in Non-Linear Optical Microscopy},
      author = {De, A. K. and Goswami, D.},
      date = {2009},
      journaltitle = {Journal of Microscopy},
      volume = {235},
      pages = {119--123},
      issn = {1365-2818},
      doi = {10/ckpt72},
      url = {},
      urldate = {2019-08-14},
      annotation = {00010},
      keywords = {_tablet,Cellular imaging,continuous wave and pulsed excitation,fluorescence enhancement,laser-scanning microscopy,two-photon absorption},
      langid = {english},
      number = {2}