Simultaneous measurement of mass and rotation of trapped absorbing particles in air

Bera, Sudipta; Kumar, Avinash; Sil, Souvik; Saha, Tushar; Saha, Tanumoy; Banerjee, Ayan

doi:10.1364/ol.41.004356

Cited by 25 publications

(31 citation statements)

References 14 publications

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“…Submicron-sized droplets and particles are particularly relevant in many atmospheric processes, such as scattering and absorption of sunlight 38,39 or size-dependent enhanced kinetics 22,40,41 . Mass measurements of aerosol particles in optical traps are limited to the special case of photophoretic traps 42,43 . They require the particle to absorb the light of the trapping laser, which heats the particle.…”

mentioning

confidence: 99%

Weighing picogram aerosol droplets with an optical balance

et al. 2020

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Optical traps are used to isolate and manipulate small objects in air and liquids, enabling the thorough characterization of their properties in situ. However, no broadly applicable technique for mass measurements of optically trapped objects is currently available. Here we propose an optical balance for mass measurements of optically trapped aerosol particles. By analyzing light-induced harmonic oscillations of a particle, its mass is determined non-destructively and with high accuracy on a time scale of seconds. Its performance is demonstrated for aqueous salt droplets, where masses as low as 4 pg (4 × 10−15 kg) have been measured with an accuracy of ~100 fg. The balance is straightforward to implement and broadly applicable.

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mentioning

confidence: 99%

Weighing picogram aerosol droplets with an optical balance

et al. 2020

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“…During the oscillation, the photophoretic force provides as the restoring force. The stiffness of the optical trap originating from the photophoretic force is then linearly proportional to the intensity of the trapping laser [19]. Thus, a simple spring model can be used to depict the optical forced oscillation when the trapping intensity is sinusoidally modulated.…”

Section: Methodsmentioning

confidence: 99%

“…Compared to the measurement of mass by analyzing the Brownian motion in ref. [19], we use a single CCD camera to record the trajectory and avoid detecting the modulated scattered light due to the rotation of the particles. The particle moves back and forth and the air temperature along the trajectory is the room temperature.…”

mentioning

confidence: 99%

Measurement of mass by optical forced oscillation of absorbing particles trapped in air

et al. 2017

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We demonstrate the measurement of mass of the absorbing micro-particle trapped in air by optical forced oscillation. When the trapping light intensity is modulated sinusoidally, the particle in the trap undergoes forced oscillation and the amplitude of the oscillation depends directly on the modulated frequency. Based on a simple spring model, we fit the amplitudes versus the modulated frequencies and obtain the stiffness of the optical trap and the mass of the trapped particle. The fitting results show that, for a certain particle, the stiffness varies linearly with the trapping light intensity while the mass is consistent. The density of the micro-particle is then estimated and could be used to classify different kinds of absorbing particles, like C and CuO.

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“…Most of previous theoretical and experimental work considered thermal equilibrium with a constant light intensity [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25], such that H=AI from Eq. (5).…”

Section: Temporal Dependence Of Photophoretic Forcementioning

confidence: 99%

“…Our experiment provides a potential approach to determine these physical quantities of the particles in air. We may compare the measured value of m/γ with the value determined by another method developed by Bera et al [25]. Following their approach, the motion of the trapped particle in the axial direction is detected by a position sensitive detector at a constant laser power of 30.2 mW.…”

Section: Characterizing the Properties Of Trapped Particles By Meamentioning

confidence: 99%

Temporal Dependence of Photophoretic Force Optically Induced on Absorbing Airborne Particles by a Power-Modulated Laser

Chen

et al. 2018

Phys. Rev. Applied

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Photophoretic force due to the optically-induced thermal effect provides an effective way to manipulate the light-absorbing particles suspended in ambient gases. However, how this force temporally responds to the intensity modulation of the illumination light is unclear. Here, by vertically trapping a micron-sized absorbing particle with a negative photophoretic force generated by a focused Gaussian beam, we demonstrate that the temporal change in the photophoretic force in response to the intensity modulation is remarkably slow (with a time constant up to ~1 s) due to the slow change in the particle's temperature. When the trapping beam is turned off for a few tens or hundreds of milliseconds, the trapped particle is found to be pulled up towards the light source by the remained photophoretic force, whereas when the intensity of the trapping beam is increased for a short duration, the particle is pushed off by the radiation pressure. The instantaneous position of the trapped particles following the intensity modulation of the trapping laser is tracked and theoretically modeled. The understanding of the temporal behavior of the photophoretic force would be useful for the control of photophoretic-based optical pulling, transportation, and manipulation of atmospheric particles.

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Simultaneous measurement of mass and rotation of trapped absorbing particles in air

Cited by 25 publications

References 14 publications

Weighing picogram aerosol droplets with an optical balance

Weighing picogram aerosol droplets with an optical balance

Measurement of mass by optical forced oscillation of absorbing particles trapped in air

Temporal Dependence of Photophoretic Force Optically Induced on Absorbing Airborne Particles by a Power-Modulated Laser

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