Experimental Comparison of Conventional and Femtosecond Optical Tweezers

Singh, Aparna; Bandyopadhyay, Soumendra Nath; Singh, Krishna Kant; Kumar, Deepak; Goswami, Debabrata

doi:10.1364/cleo_at.2021.jw1a.153

Cited by 2 publications

(1 citation statement)

References 4 publications

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“…Due to the high disparity in timescales for a single femtosecond laser pulse, the thermal effect is insignificant. However, for HHR femtosecond lasers, which is the requirement for, say, an optical Frontiers in Chemistry frontiersin.org tweezer, cumulative thermal effects occur as well (Singh et al, 2021). Additionally, the use of femtosecond pulses for optical trapping also invokes NLO processes.…”

Section: Fot: Subtle Balancing Of Thermal Effects With Nlo Effectsmentioning

confidence: 99%

Intense femtosecond optical pulse shaping approaches to spatiotemporal control

Goswami

2023

Front. Chem.

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For studying any event, measurement can never be enough; “control” is required. This means mere passive tracking of the event is insufficient and being able to manipulate it is necessary. To maximize this capability to exert control and manipulate, both spatial and temporal domains need to be jointly accounted for, which has remained an intractable problem at microscopic scales. Simultaneous control of dynamics and position of an observable event requires a holistic combination of spatial and temporal control principles, which gives rise to the field of spatiotemporal control. For this, we present a novel femtosecond pulse-shaping approach. We explain how to achieve spatiotemporal control by spatially manipulating the system through trapping and subsequently or simultaneously exerting temporal control using shaped femtosecond pulses. By leveraging ultrafast femtosecond lasers, the prospect of having temporal control of molecular dynamics increases, and it becomes possible to circumvent the relaxation processes at microscopic timescales. Optical trapping is an exemplary demonstration of spatial control that results in the immobilization of microscopic objects with radiation pressure from a tightly focused laser beam. Conventional single-beam optical tweezers use continuous-wave (CW) lasers for achieving spatial control through photon fluxes, but these lack temporal control knobs. We use a femtosecond high repetition rate (HRR) pulsed laser to bypass this lack of dynamical control in the time domain for optical trapping studies. From a technological viewpoint, the high photon flux requirement of stable optical tweezers necessitates femtosecond pulse shaping at HRR, which has been a barrier until the recent Megahertz pulse shaping developments. Finally, recognizing the theoretical distinction between tweezers with femtosecond pulses and CW lasers is of paramount interest. Non-linear optical (NLO) interactions must be included prima facie to understand pulsed laser tweezers in areas where they excel, like the two-photon-fluorescence-based detection. We show that our theoretical model can holistically address the common drawback of all tweezers. We are able to mitigate the effects of laser-induced heating by balancing this with femtosecond laser-induced NLO effects. An interesting side-product of HRR femtosecond-laser-induced thermal lens is the development of femtosecond thermal lens spectroscopy (FTLS) and its ability to provide sensitive molecular detection.

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Section: Fot: Subtle Balancing Of Thermal Effects With Nlo Effectsmentioning

confidence: 99%

Intense femtosecond optical pulse shaping approaches to spatiotemporal control

Goswami

2023

Front. Chem.

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Femtosecond laser-assisted selective holding with ultra-low power for direct manipulation of biological species

Krishna,

Burrow,

Jiang

et al. 2024

J. Biomed. Opt.

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Optical tweezers (OTs) have emerged as an essential technique for manipulating nanoscopic particulates and biological specimens with sub-micron precision and have revolutionized various fields, including biology and colloidal physics. However, traditional optical trapping techniques often rely on moderate-to highpower continuous wave (CW) lasers, which can introduce unwanted thermal effects and photodamage to delicate samples. An innovative alternative has emerged through the utilization of femtosecond (fs) lasers at ultra-low average powers on the order of tens of microwatt. Unexpectedly overlooked until now, this method enables the direct trapping and manipulation of cells without relying on functionalized spheres.Aim: We aim to compare the trap stiffness of CW and fs lasers in an unexplored average power regime (sub-1 mW) on cells within the intermediate-size regime.Approach: A CW or fs laser is used to trap cells in an inverted microscope setup. We trap five different pathogenic bacteria with different morphologies to compare trap stiffness.Results: We find that fs laser-assisted selective holding with ultra-low power (FLASH-UP) exhibits five times greater trap stiffness than CW-based OTs and can trap at lower intensities. Furthermore, we demonstrate that FLASH-UP does not impact cell motility.Conclusions: FLASH-UP displays higher trap stiffness at average powers below 1 mW and does not impact cell functionality. These results pave the way for ultralow-power trapping of cells for applications in sorting, bio-sensing, in vivo cell manipulation, and single-cell analysis.

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Experimental Comparison of Conventional and Femtosecond Optical Tweezers

Abstract: Systematic study of conventional and femtosecond optical tweezers demonstrates an interplay of thermal and optical nonlinearity due to tight focusing. Specifically, Brownian motion of the 250nm radius trapped bead is measured using a quadrant photodiode.

Cited by 2 publications

References 4 publications

Intense femtosecond optical pulse shaping approaches to spatiotemporal control

Intense femtosecond optical pulse shaping approaches to spatiotemporal control

Femtosecond laser-assisted selective holding with ultra-low power for direct manipulation of biological species

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