Towards controlling molecular motions in fluorescence microscopy and optical trapping: a spatiotemporal approach

De, Arijit K.; Goswami, Debabrata

doi:10.1080/0144235x.2011.603237

“…In this sense, Dholakia group reported that trapping efficiency of 780 nm-sized silica bead (a particle in Lorenz-Mie regime) under 800 nm excitation is pulse-duration independent, 45 supporting the similar trapping efficiency of cwand fs-laser for 1.28 μm-sized particle. 30,46 A fascinating finding in such optical trapping with fs pulse train was axial ejection of 2.1-μm blue-fluorescent-dyed polystyrene bead from the trapping site almost immediately when it was immobilized by the incident laser above 15 mW. 45 Interestingly, the particle is trapped for up to a few minutes before an axial ejection only under laser power between 3.7 and 7 mW.…”

Section: ■ Introductionmentioning

confidence: 99%

“…This emphasizes that the trapping stability depends on peak power and pulse shape of the laser pulses . On the other hand, the role of low average power fs pulses at high repetition rate in stable optical trapping of dielectric nanoparticles less than 100 nm in diameter has been explained based on the inertial response time of the nanoparticles to the impulsive momentum transfer by laser pulses. , Though the axial ejection of the fluorescent bead at higher laser power may be a straightforward self-focusing effect under fs excitation which is opposite to an enhanced trapping efficiency under cw excitation, but the detailed explanation on such remarkable different phenomena of fs and cw mode in optical trapping of nanoparticle and microsized particles was still an open question.…”

Section: Introductionmentioning

confidence: 99%

Optical Trapping Dynamics of a Single Polystyrene Sphere: Continuous Wave versus Femtosecond Lasers

Liu¹,

Chiang

²

,

Usman

³

et al. 2016

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Understanding of optical trapping dynamics of a single particle in the trapping site is important to develop its optical manipulation for molecular assembly and chemical application. For micrometer-sized Mie particles, similar trapping efficiency of the conventional continuous wave (cw) laser or high-repetition-rate femtosecond (fs) laser pulse train has been established [Dholakia et al., Opt. Express 2010, 18, 7554–7568], in contrast to higher efficiency of the laser pulses to trap dielectric Rayleigh particles. To further explore and clarify the switching phenomena of optical trapping efficiency with cw laser and fs laser pulse and to elucidate its nature, we study the immobilization dynamics of a single polystyrene sphere with 500 nm in diameter (which is comparable to focal beam size) in shallow potential well. By observing trapping events and immobilization time of the particle with a size in Lorenz–Mie regime, distinct from well-known Rayleigh particle and ray optics approximations, we found that immobilization time is only linearly related to the incident laser power ≤40 mW, and at higher laser powers cw laser is more efficient than fs laser pulses to immobilize the particle. This finding means that the dynamics of the particle in this size region is still affected by the strong transient force fields induced by high-repetition-rate ultrashort pulse train as usually observed for Rayleigh particles. This may provide an understanding that the dynamics of the target particle in the trapping site is size- and laser mode-dependent.

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“…Although direct trapping of sub-micron objects, dimensionally, often similar to macromolecules, have been demonstrated using CW laser beam, it demands the use of quite high average powers. In our particular case where the particle dimension is at least an order of magnitude smaller than the wavelength of light, we are in the 'Rayleigh scattering limit' or the 'dipole limit' and under such condition, the trapping force is given by (1) where α is the polarizability and E is the electric field of trapping light. Since the force depends on the polarizability, earlier efforts revealed that much higher power levels are required to stably trap latex nanoparticles.…”

Section: Pulsed Optical Tweezersmentioning

confidence: 99%

Fluorescence advantages with microscopic spatiotemporal control

Goswami¹,

Roy²,

De³

2013

SPIE Proceedings

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0

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We present a clever design concept of using femtosecond laser pulses in microscopy by selective excitation or de-excitation of one fluorophore over the other overlapping one. Using either a simple pair of femtosecond pulses with variable delay or using a train of laser pulses at 20-50 Giga-Hertz excitation, we show controlled fluorescence excitation or suppression of one of the fluorophores with respect to the other through wave-packet interference, an effect that prevails even after the fluorophore coherence timescale. Such an approach can be used both under the single-photon excitation as well as in the multi-photon excitation conditions resulting in effective higher spatial resolution. Such high spatial resolution advantage with broadband-pulsed excitation is of immense benefit to multi-photon microscopy and can also be an effective detection scheme for trapped nanoparticles with near-infrared light. Such sub-diffraction limit trapping of nanoparticles is challenging and a two-photon fluorescence diagnostics allows a direct observation of a single nanoparticle in a femtosecond high-repetition rate laser trap, which promises new directions to spectroscopy at the single molecule level in solution. The gigantic peak power of femtosecond laser pulses at high repetition rate, even at low average powers, provide huge instantaneous gradient force that most effectively result in a stable optical trap for spatial control at sub-diffraction limit. Such studies have also enabled us to explore simultaneous control of internal and external degrees of freedom that require coupling of various control parameters to result in spatiotemporal control, which promises to be a versatile tool for the microscopic world.

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“…This practical compromise, therefore, begets resolution enhancement as one of the most important developmental aspects of fluorescence microscopy. 1 Implementing multi-photon excitation in laser scanning microscopy for better depth resolution, for example, is an important achievement. However, in such two-photon fluorescence (TPF) microscopy, the broad spectral window of an ultrafast laser pulse and the overlapping multi-photon absorption spectra of common fluorophores lead to simultaneous excitation of many different fluorophores.…”

Section: Introductionmentioning

confidence: 99%

“…We have also explored the effect of different polarization states of the pulses used under such incoherent schemes, wherein their effect, as expected, is only minimal unlike in the coherent case. 1…”

Section: Introductionmentioning

confidence: 99%

Spatio-temporal control in multiphoton fluorescence laser-scanning microscopy

De

¹

,

Roy

²

,

Goswami

³

2010

Self Cite

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We present a clever design concept of using femtosecond laser pulses in microscopy by selective excitation or de-excitation of one fluorophore over the other overlapping one. Using either a simple pair of femtosecond pulses with variable delay or using a train of laser pulses at 20-50 Giga-Hertz excitation, we show controlled fluorescence excitation or suppression of one of the fluorophores with respect to the other through wave-packet interference, an effect that prevails even after the fluorophore coherence timescale. Such an approach can be used both under the single-photon excitation as well as in the multi-photon excitation conditions resulting in effective higher spatial resolution. Such high spatial resolution advantage with broadband-pulsed excitation is of immense benefit to multi-photon microscopy and can also be an effective detection scheme for trapped nanoparticles with near-infrared light. Such sub-diffraction limit trapping of nanoparticles is challenging and a two-photon fluorescence diagnostics allows a direct observation of a single nanoparticle in a femtosecond high-repetition rate laser trap, which promises new directions to spectroscopy at the single molecule level in solution. The gigantic peak power of femtosecond laser pulses at high repetition rate, even at low average powers, provide huge instantaneous gradient force that most effectively result in a stable optical trap for spatial control at sub-diffraction limit. Such studies have also enabled us to explore simultaneous control of internal and external degrees of freedom that require coupling of various control parameters to result in spatiotemporal control, which promises to be a versatile tool for the microscopic world.

show abstract

Towards controlling molecular motions in fluorescence microscopy and optical trapping: a spatiotemporal approach

Cited by 18 publications

References 65 publications

Optical Trapping Dynamics of a Single Polystyrene Sphere: Continuous Wave versus Femtosecond Lasers

Optical Trapping Dynamics of a Single Polystyrene Sphere: Continuous Wave versus Femtosecond Lasers

Fluorescence advantages with microscopic spatiotemporal control

Spatio-temporal control in multiphoton fluorescence laser-scanning microscopy

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