Force sensing with a shaped dielectric micro-tool

Phillips, David B.; Simpson, Stephen H.; Grieve, James A.; Bowman, Richard; Gibson, Graham M.; Padgett, Miles J.; Rarity, John; Hanna, Simon; Miles, Mervyn J; Carberry, David M.

doi:10.1209/0295-5075/99/58004

Cited by 48 publications

(48 citation statements)

References 16 publications

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“…The probe tip extends forward beyond the front most trapping handles to access the sample surface; it is 10 µm in length and tapers to a radius of curvature of 100 nm laterally and 300 nm vertically. Our probes are fabricated using a commercially available 3D direct write laser lithography system (Nanoscribe Photonic Professional), using a laser beam wavelength of 780 nm [21]. They are manufactured in batches of ∼ 100 ( Fig.…”

Section: Probe Fabricationmentioning

confidence: 99%

“…The probe configuration is determined in real-time, at up to 1kHz, with image processing and coordinate calculation performed and displayed to the user with a LabVIEW (National Instruments) program [25]. Knowledge of the generalised coordinates allows the position of the tip to be calculated for each frame using rigid transformations, and an ensemble of such measurements enables visualisation of the volume that the tip is free to explore -the tip thermal volume [21]. This is approximately ellipsoidal in shape when the probe is freely trapped, experiencing only optical and thermal forces.…”

Section: Probe Control and Measurementmentioning

confidence: 99%

“…However it is also useful to estimate the force exerted on the sample while in contact with it. This is carried out by applying the analysis described in [21], to calculate the effective trapping stiffness of our probe under different trapping configurations, under the assumption that any non-conservative forces are small and can be neglected. Equipartition theory can be used to describe the trapping stiffness of an extended optically trapped object [21,27].…”

Section: Background Theorymentioning

confidence: 99%

“…This is carried out by applying the analysis described in [21], to calculate the effective trapping stiffness of our probe under different trapping configurations, under the assumption that any non-conservative forces are small and can be neglected. Equipartition theory can be used to describe the trapping stiffness of an extended optically trapped object [21,27]. In the 1D case, the force f experienced by an optically trapped particle is related to its displacement from equilibrium δ x via f = −Kδ x in the linear regime of the trap, where K is the trap stiffness.…”

Section: Background Theorymentioning

confidence: 99%

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An optically actuated surface scanning probe

et al. 2012

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Abstract:We demonstrate the use of an extended, optically trapped probe that is capable of imaging surface topography with nanometre precision, whilst applying ultra-low, femto-Newton sized forces. This degree of precision and sensitivity is acquired through three distinct strategies. First, the probe itself is shaped in such a way as to soften the trap along the sensing axis and stiffen it in transverse directions. Next, these characteristics are enhanced by selectively position clamping independent motions of the probe. Finally, force clamping is used to refine the surface contact response. Detailed analyses are presented for each of these mechanisms. To test our sensor, we scan it laterally over a calibration sample consisting of a series of graduated steps, and demonstrate a height resolution of ∼ 11 nm. Using equipartition theory, we estimate that an average force of only ∼ 140 fN is exerted on the sample during the scan, making this technique ideal for the investigation of delicate biological samples. 288-290 (1986). 2. A. Pralle, M. Prummer, E. L. Florin, E. H. K. Stelzer, and J. K. H. Horber, "Three-dimensional high-resolution particle tracking for optical tweezers by forward scattered light," Microsc.

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Section: Probe Fabricationmentioning

confidence: 99%

Section: Probe Control and Measurementmentioning

confidence: 99%

Section: Background Theorymentioning

confidence: 99%

Section: Background Theorymentioning

confidence: 99%

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An optically actuated surface scanning probe

et al. 2012

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“…By performing two dimensional tracking of the position of a particle in each image, its three dimensional coordinates can be reconstructed using parallax. Highspeed video stereo-microscopy has been used in a variety of situations, including the axial position clamping of optically trapped objects [10,11], the observation of optically stacked particles [12], tracking of live algae and artificial non-spherical structures [13,14], and in an optically controlled scanning probe microscope [15].…”

Section: Introductionmentioning

confidence: 99%

Four-directional stereo-microscopy for 3D particle tracking with real-time error evaluation

Hay¹,

Gibson²,

Lee³

et al. 2014

Opt. Express

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Abstract:High-speed video stereo-microscopy relies on illumination from two distinct angles to create two views of a sample from different directions. The 3D trajectory of a microscopic object can then be reconstructed using parallax to combine 2D measurements of its position in each image. In this work, we evaluate the accuracy of 3D particle tracking using this technique, by extending the number of views from two to four directions. This allows us to record two independent sets of measurements of the 3D coordinates of tracked objects, and comparison of these enables measurement and minimisation of the tracking error in all dimensions. We demonstrate the method by tracking the motion of an optically trapped micro-sphere of 5 µm in diameter, and find an accuracy of 2-5 nm laterally, and 5-10 nm axially, representing a relative error of less than 2.5% of its range of motion in each dimension. Simpson, "An optically actuated surface scanning probe," Opt. Express 20, 29679-29693 (2012). 12. C. Alpmann, R. Bowman, M. Woerdemann, M. Padgett, and C. Denz, "Mathieu beams as versatile light moulds for 3d micro particle assemblies," Opt. Express 18, 26084-26091 (2010

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Nanoscale Optical Trapping: A Review

Bradac

2018

Advanced Optical Materials

118

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The First TrapIn 1969, a "back-of-the-envelope" calculation inspired Ashkin to conduct a simple experiment and determine whether it was feasible to use light radiation pressure to accelerate objects to practical speeds. Photons carry momentum hν/c (with h, ν and c being the Planck's constant, the frequency of the photon and the speed of light, respectively). If light from a source with power P shines on a mirror, P/hν photons hit the surface every second and transfer a total momentum of (2P/hν)(hν/c) = 2P/c onto it. A perfectly reflecting mirror should therefore-due to conservation-acquire an equal momentum in the same direction light propagates.Based on this crude calculation, Ashkin predicted that a light source of power P = 1 W, would produce a force (on an ideally reflecting mirror) of ≈10 nN-indeed small in absolute terms. [3] Nevertheless, if a laser beam is used as the light source and is focused on a spot of ≈1 µm 2 to hit a particle ≈1 µm in diame ter, the resulting force does become relevant. Assuming the particle is perfectly reflective and has a density of 1 g cm −3 , the calculated acceleration is ≈10 9 cm s −2 , i.e., roughly 10 6 times the acceleration of gravity. In the experiment, Ashkin conducted to test his hypotheses, [2] a cw argon laser (wavelength λ = 514.5 nm, waist radius w 0 = 6.2 µm at the focal point) was employed to accelerate latex spheres (diameter 0.59, 1.31, and 2.68 µm), which were freely suspended in water, in a glass chamber. With just milliwatts of laser power, Ashkin observed that the particles were pushed in the direction of the mildly focused Gaussian laser beam, with values for the acceleration consistent with his rough predictions. Interestingly, he also observed an unanticipated phenomenon. Particles located in the fringes of the beam were drawn toward the beam axiswhere the light intensity is the highest-before being accelerated and pushed with ≈µm s −1 speeds toward the back of the chamber. They would disperse by Brownian motion away from the beam axis once the laser was switched off, yet they would be drawn again toward the center of the beam upon turning the laser back on-as the radiation pressure had a transverse component to the force, as well as the predicted longitudinal one.The origin of both the transversal and longitudinal force is usually understood by considering two distinct regimes, depending on the relative size of the particles to the wavelength of the laser beam: the geometrical (ray optics) regime and the Rayleigh (dipole approximation) regime.Optical trapping is the craft of manipulating objects with light. Decades after its first inception in 1970, the technique has become a powerful tool for ultracold-atom physics and manipulation of micron-sized particles. Yet, optical trapping of objects at the intermediate-nanoscale-range is still beyond full grasp. This matters because the nanometric realm is where several promising advances, from mastering single-molecule experiments in biology, to fabricating hybrid devices for nanoelectronics and photonics, a...

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Force sensing with a shaped dielectric micro-tool

Cited by 48 publications

References 16 publications

An optically actuated surface scanning probe

An optically actuated surface scanning probe

Four-directional stereo-microscopy for 3D particle tracking with real-time error evaluation

Nanoscale Optical Trapping: A Review

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