Spatiotemporal Control

Femtosecond optical tweezers, pulse shaping, and two-photon microscopy

Schematic illustration for Spatiotemporal Control

Femtosecond optical tweezers and pulse shaping for simultaneous spatial and temporal control of molecules and colloidal particles.

Question

Can one beam trap a particle and also control the temporal profile of the light that traps it? Conventional optical tweezers use continuous-wave lasers and give spatial control only. The lab uses pulsed femtosecond tweezers, which combine spatial manipulation through optical trapping with temporal manipulation through femtosecond pulse shaping.

Technique

The lab combines three ingredients: a femtosecond optical trap for spatial control, a pulse shaper for temporal control, and two-photon excitation for read-out. The subsections below take them in turn.

Femtosecond optical tweezers

Controlled spatial manipulation of translational degrees of freedom is essential for engineering intermolecular interactions and implementing molecular quantum logic. The lab’s femtosecond tweezers induce an effective molecular polarizability through ultrafast temporal modulations while simultaneously exploiting macroscopic light properties (polarization, photon flux) for spatial control. The tweezers trap and steer colloidal particles with femtosecond temporal resolution.

Pulse shaping

The pulse shaper sets the temporal profile of the trapping and excitation pulses; the research overview describes the instrument.

Two-photon studies

Two-photon absorption and fluorescence measurements probe molecular dynamics with intrinsic three-dimensional sectioning. Solvent effects on two-photon cross-sections and signal characteristics inform both the spectroscopy and the control aspects of the research program. Representative work in this area includes [1,2,3].

Representative papers

Full list of papers here.

Publications

  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) 
    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},
  year = {2016},
  month = jul,
  journal = {Chemical Physics Letters},
  volume = {657},
  pages = {72--77},
  issn = {0009-2614},
  doi = {10/f84rwd},
  urldate = {2019-08-01},
  annotation = {GSCC: 0000003 \\
  3 citations (Crossref) [2024-05-28]\\
  00000}
}
  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) 
    BibTeX: @article{nagSolventEffectTwophoton2009,
  title = {Solvent Effect on Two-Photon Absorption and Fluorescence of Rhodamine Dyes},
  author = {Nag, Amit and Goswami, Debabrata},
  year = {2009},
  month = aug,
  journal = {Journal of Photochemistry and Photobiology A: Chemistry},
  volume = {206},
  number = {2},
  pages = {188--197},
  issn = {1010-6030},
  doi = {10/c4zdx8},
  urldate = {2019-08-14},
  annotation = {GSCC: 0000110 \\
  83 citations (Crossref) [2024-05-28]\\
  00063}
}
  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) 
    BibTeX: @article{deSimpleTwistSignal2009,
  title = {A Simple Twist for Signal Enhancement in Non-Linear Optical Microscopy},
  author = {De, Arijit Kumar and Goswami, D.},
  year = {2009},
  journal = {Journal of Microscopy},
  volume = {235},
  number = {2},
  pages = {119--123},
  issn = {1365-2818},
  doi = {10/ckpt72},
  urldate = {2019-08-14},
  copyright = {\copyright{} 2009 The Authors Journal compilation \copyright{} 2009 The Royal Microscopical Society},
  langid = {english},
  annotation = {GSCC: 0000011 \\
  2 citations (Crossref) [2024-05-28]\\
  00010}
}