Photoacoustic identification of laser-induced microbubbles as light scattering centers for optical limiting in a liquid suspension of graphene nanosheets

Abstract

Liquid suspensions of carbon nanotubes, graphene and transition metal dichalcogenides have exhibited excellent performance in optical limiting. However, the underlying mechanism has remained elusive and is generally ascribed to their superior nonlinear optical properties such as nonlinear absorption or nonlinear scattering. Using graphene as an example, we show that photo-thermal microbubbles are responsible for the optical limiting as strong light scattering centers: graphene sheets absorb incident light and become heated up above the boiling point of water, resulting in vapor and microbubble generation. This conclusion is based on direct observation of bubbles above the laser beam as well as a strong correlation between laser-induced ultrasound and optical limiting. In-situ Raman scattering of graphene further confirms that the temperature of graphene under laser pulses rises above the boiling point of water but still remains too low to vaporize graphene and create graphene plasma bubbles. Photo-thermal bubble scattering is not a nonlinear optical process and requires very low laser intensity. This understanding helps us to design more efficient optical limiting materials and understand the intrinsic nonlinear optical properties of nanomaterials.

Intensity-Dependent Thermally Induced Nonlinear Optical Response of Two-Dimensional Layered Transition-Metal Dichalcogenides in Suspension

“…Nevertheless, this is often disregarded in many SSPM studies in 2D LTMDs that infer a purely electronic origin of the effect. − Hence, deepening the investigation and bringing new information to the debate are essential to avoid misconceptions with respect to the NLO properties of the materials. In this sense, Zhang et al discuss the underlying mechanism behind optical limiting (OL) in liquid suspensions of 2D materials, showing that, in some experimental conditions, the OL effect is due to the appearance of microbubbles induced by the radiation, which limits the optical transmission . Therefore, to infer NLO properties of 2D materials based on such experiments could lead to mistakes since the induced bubbles are not related to their intrinsic NLO properties.…”

“…In this sense, Zhang et al discuss the underlying mechanism behind optical limiting (OL) in liquid suspensions of 2D materials, showing that, in some experimental conditions, the OL effect is due to the appearance of microbubbles induced by the radiation, which limits the optical transmission. 30 Therefore, to infer NLO properties of 2D materials based on such experiments could lead to mistakes since the induced bubbles are not related to their intrinsic NLO properties.…”

Ограничение Мощности Лазерного Излучения Углеродными Материалами С Нелинейным Оптическим Пороговым Эффектом При Форме Импульса С Плоской Вершиной

“…Определение теоретического значения прошедшей интенсивности выполняется в соответствии с уравнением переноса излучения [2,3] для нелинейной пороговой зависимости коэффициента поглощения от падающей интенсивности I 0 . Сама зависимость коэффициента поглощения от интенсивности задается эффективными значениями, так как в дисперсиях может происходить образование микроплазмы или микропузырей, которые являются центрами рассеяния света [42] и способствуют увеличению оптического пути с ростом поглощения [40]. С учетом этого эффективный коэффициент поглощения µ(I 0 ) определяется следующим образом:…”

Doubly 1,3-butadiyne-bridged ditwistacene with enhanced ultrafast broadband reverse saturable absorption

“…Dual-mode optical power limiting (OPL) materials, which combine two-photon absorption (TPA) with excited state absorption (ESA) behavior to limit the transmitted intensity of laser pulses to safe power levels, are very promising optical protectors of human eyes and sensitive optical instruments. 1 In contrast with traditional OPL materials, by using nonlinear scattering and large ratios of ESA to ground-state absorption cross section, [2][3][4] the dual-mode materials exhibit enhanced OPL abilities along with low optical losses for low-intensity harmless laser pulses, owing to overlap of ESA with TPA without the contribution of one-photon absorption. Even though a number of materials have been demonstrated to act as dual-mode absorbers, [5][6][7] some disadvantages, such as their small TPA cross sections and weak absorption abilities in the picosecond and femtosecond regimes due to the formation of excited triplet states, hinder the practical applications of these materials in ultrafast broadband OPL.…”