Daniil A. Shilkin

Direct measurements of forces induced by Bloch surface waves in a one-dimensional photonic crystal

An experimental study of the interaction between a single dielectric microparticle and the evanescent field of the Bloch surface wave in a one-dimensional (1D) photonic crystal is reported. The Bloch surface wave-induced forces on a 1 μm polystyrene sphere were measured by photonic force microscopy. The results demonstrate the potential of 1D photonic crystals for the optical manipulation of microparticles and suggest a novel approach for utilizing light in lab-on-a-chip devices.

Trap position control in the vicinity of reflecting surfaces in optical tweezers

Shift of the trap position from the laser beam waist of optical tweezers is studied experimentally in the presence of a reflecting surface in the vicinity of the focal plane. A standing wave is formed owing to the interference of waves forming the waist and reflected from the surface. The standing wave is shown to affect significantly the resulting trap position. The distance between the surface and the stable optical trap as a function of the trapped particle size is studied numerically. A new method to stabilize the position of the microparticle relative to the surface is proposed. The localization accuracy is determined by the Brownian fluctuations in optical tweezers and is about 10 nm for effective trap stiffness of 4 × 10−5 N/m.

Near-field probing of Bloch surface waves in a dielectric multilayer using photonic force microscopy

The potential of photonic force microscopy (PFM) for probing the optical near-field in the vicinity of a dielectric multilayer is demonstrated. An experimental study of Bloch surface waves (BSWs) using PFM is described in detail. The applied technique is based on measuring the BSW-induced gradient force acting on a probe particle combined with precise control of the distance between the particle and the multilayer surface. The BSW-induced potential profile measured using PFM is presented. The force interaction between the probe and the BSW evanescent field is numerically studied. The results indicate that a polystyrene particle with a diameter of 1 μm does not significantly perturb the BSW field and can be used to probe the optical near-field intensity in an elegant, noninvasive manner.

Photonic force microscopy of surface electromagnetic waves in a one-dimensional photonic crystal

The potential of photonic force microscopy (PFM) to directly probe the field of the Bloch surface wave (BSW) in a one-dimensional photonic crystal is considered. Optical forces acting on a dielectric microparticle in the evanescent field of the BSW are estimated in the dipole approximation and calculated by finite-difference time-domain (FDTD) analysis. Technical details of the PFM measurements are described.

Nonlinear self-action of Bloch surface waves governed by gradient optical forces

An experimental study of the nonlinear self-action of Bloch surface waves (BSWs) is reported. The BSWs are excited by a continuous-wave diode laser at the interface between a one-dimensional photonic crystal and a water suspension of 50-nm polystyrene particles, as revealed by the angular reflectance spectrum. Redistribution of the particles under the action of the gradient optical forces leads to a significant modification of the BSW resonance curve at an incident power as low as 14 mW. The results highlight that nanosuspensions can be used as artificial Kerr media to perform model experiments on the optical switching of surface waves.

Multidirectional optical sorting of Mie resonant dielectric nanoparticles (Conference Presentation)

Dielectric nanoparticles, and silicon nanoparticles in particular [1,2], are becoming increasingly promising for various applications in photonics, nonlinear optics, optomechanics, and medicine. Plenty of applications exploit the benefits of low-loss Mie resonances, exhibited in the optical range by silicon nanoparticles with sizes of the order of 200 nm. The frequencies of the resonant Mie modes are determined by the size and shape of the particles. However, many of the fabrication techniques result in a polydisperse mixture of different sizes and shapes, and prompt for a post-processing to provide a uniform output. Having an entirely optical tool for such separation [3,4] is highly desirable for sterile, hazardous or highly dynamic microfluidic environments. Following our recent publication [4], in this contribution we present the calculated optical forces acting on silicon nanoparticles in aqueous environment, analyse their potential for optical sorting in a number of schemes, and discuss the experimental implementation of the proposed methods in our setup. The optical forces acting on silicon nanoparticles are shown to reveal their substantial dependence on the particle size. This dependence results in different velocities of the light-driven drift of the nanoparticles, depending on their size and the frequency of the incident light. We propose to employ these features to realise optical sorting, according to the following scenarios. First, we use two counter-propagating beams of different wavelength, which move particles of different sizes in opposite directions; by varying the intensity ratio between the two beams, different subsets of the particle sizes can be separated. A similar approach has been implemented for plasmonic particles [3]. Second, we suggest to impose two counter-propagating beams upon a uniform flow of a disperse mixture, which results in the particles of different sizes being pushed along different directions in space, so that an efficient angular separation is possible within certain size ranges. Third, we propose an efficient angular separation in an all-optical way, by directing the two beams at an angle. This scenario offers an efficient angular separation without any imposed flow. In this work, we consider two laser beams with wavelengths of 532 and 638 nm. For this particular case, angular sorting scheme provides a unique size-angle dependence, yielding up to 70° span of deflections, in the size ranges of 120–160 nm, 190–220 nm, and a few smaller sets. We demonstrate that the proposed angular sorting techniques are robust against the Brownian motion, requiring a run of about 100 μm to achieve a 10-nm distinction in size, while using moderate (0.1 W) power. Finally, we consider the forces acting on silicon nanoparticles in the evanescent wave illumination and show that the proposed methods can be applied for a broad size dimensions using p-polarised light. [1] Evlyukhin A.B., et al. Nano Lett. 12, 3749–3755 (2012). [2] Kuznetsov A.I., et al. Sci. Rep. 2, 492 (2012). [3] Ploschner M., et al. Nano Lett. 12, 1923–1927 (2012). [4] Shilkin D., et al. ACS Photonics 4, 2312–2319 (2017).