Thermal Lens Study of NIR Femtosecond Laser-Induced Convection in Alcohols

Singhal, Sumit; Goswami, Debabrata

doi:10.1021/acsomega.8b02956

Cited by 31 publications

(11 citation statements)

References 44 publications

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“…(6) that , showing that the overall heat transfer coefficient in the fs case is significantly lower. Notably, for , the convection coefficient in principle increases due to its dependence on local [ 35 ], however, at a different rate between the two modes as shown in Figure 10 . For , it is almost zero, so that .…”

Section: Discussionmentioning

confidence: 99%

Nonlinear thermal lensing of high repetition rate ultrafast laser light in plasmonic nano-colloids

Agiotis

Meunier

2022

Nanophotonics

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We report on experimental observations of phenomenological self-trapping in plasmonic colloids of varying plasmon peaks in the visible/near infrared. A femtosecond (fs) oscillator is used in both pulsed (35 fs, 76 MHz) and continuous wave (cw) operation for comparison. We show that for both modes and for all examined colloids (and under typically applied external focusing conditions in self-trapping studies in colloidal media) nonlinear propagation is governed by thermal defocusing of the focused beam, which precedes the steady-state regime reached by particle diffusion, even far from the plasmon resonance (or equivalently for non-plasmonic colloids, even for low absorption coefficients). A strategy for the utilization of high repetition fs pulses to mitigate thermal lensing and promote gradient force-induced self-trapping is discussed. Notably, nonlinear thermal lensing is further accompanied by natural convection due to the horizontal configuration of the setup. Under resonant illumination, for both fs and cw cases, we observe mode break-up of the beam profile, most likely due to azimuthal modulation instability. Importantly, time-resolved observations of the break-up indicate that in the fs case, thermal convection heat transfer is reduced in magnitude and significantly decoupled in time from thermal conduction, presumably due to temperature increase confinement near the particles. We anticipate that our findings will trigger interest toward the use of high repetition fs pulses for self-channeling applications in nano-colloids.

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Section: Discussionmentioning

confidence: 99%

Nonlinear thermal lensing of high repetition rate ultrafast laser light in plasmonic nano-colloids

Agiotis

Meunier

2022

Nanophotonics

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“…However, there are circumstances like the one presented in the previous section where thermal effects may be beneficial to offset NLO effects in femtosecond optical tweezers. Similarly, FTLS has been developed and proven to be an incredibly versatile technique ( Bhattacharyya et al, 2010 ; Singhal and Goswami, 2019 ). Though each femtosecond laser pulse provides an almost negligible energy load to the sample, the cumulative effect of HRR femtosecond pulses results in a significant thermal load ( Kumar et al, 2014 ).…”

Section: The Ftls: Transforming Vice To Virtuementioning

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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“…However, the authors in [146] used the vertical illumination setup as the one that allows omitting the convective effects, which as shown earlier by Bogutarov et al [142] and by Hucharov [143], is not a justified assumption. Next, Goswami et al have formulated a simplified model of TL that takes into account the convective effects in TLS [147,148]. They studied the time-resolved TL signal in a series of n-alcohols starting with methanol of the shortest molecule and it is in this solvent they observed the highest convective effects.…”

Section: The Effects Determining Thermal Lensing and The Correctness Of Its Theoretical Descriptionmentioning

confidence: 99%

Thermal lensing: outside of the lasing medium

Dobek

2022

Appl. Phys. B

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The thermal lens formed in a thermo-optical material as a result of its inhomogeneous heating, is a well-known phenomenon that has found widespread interest in the last decades, especially in the field of laser engineering and photo-thermal spectroscopy. In recent years, growing interest in the application of thermal lensing in different fields of optics and material studies has been observed. This review summarizes the latest efforts made by the scientific community to develop ways of using the phenomenon of thermal lensing. Its applications in spectroscopy, in laser beam formation and in imaging are described. The advantages and disadvantages of the thermal lensing in regard to these areas along with the potential future applications of the phenomenon are discussed.

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Thermal Lens Study of NIR Femtosecond Laser-Induced Convection in Alcohols

Cited by 31 publications

References 44 publications

Nonlinear thermal lensing of high repetition rate ultrafast laser light in plasmonic nano-colloids

Nonlinear thermal lensing of high repetition rate ultrafast laser light in plasmonic nano-colloids

Intense femtosecond optical pulse shaping approaches to spatiotemporal control

Thermal lensing: outside of the lasing medium

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