Electromagnetic Field Simulation of Nanometric Optical Tweezers.
This article shows how the frequency domain solver of CST MICROWAVE STUDIO® (CST MWS) can be used to calculate the near field distribution of metallic and dielectric objects at optical frequencies. This article is based on the work presented in [1].
The test structure is a laser-illuminated metal tip. The vacuum wavelength of the illuminating light is 810 nm (Ti:sapphire laser). At this frequency, the dielectric constant of the gold tip is -24.9 + 1.57i. The structure is calculated in a water environment with a dielectric constant of 1.77. The problem setup takes a just a few minutes in the modeller. In CST MWS the material properties of metals at optical frequencies can be defined using Drude dispersive materials. The Drude material parameters can be calculated from the dielectric constants eps1 and eps2, or the reflective index n and absorption coefficient k by using a macro. Figure 1 shows the interface of this Macro. At 810 nm the resonance and collision frequencies are calculated as 1.19E16 rad/s and 1.41e14 Hz respectively.
Figure 1: Macro for calculating Drude material parameters
Figure 3 shows the absolute component of the E-field in the near field of the tip when illuminated by a plane wave with a field strength of 1 V/m. As shown in the paper, the E-field will be enhanced if the incident E-field is polarized along the axes of the tip (Figure 3). CST MWS calculates a maximum field enhancement of around 75. For an E-field polarization perpendicular to the tip axes, the field is not enhanced. 19E16 rad/s and 1.41e14 Hz respectively.
Figure 2: Polarization of the incident E-field perpendicular to the tip axes
Figure 3: E-field in the near field of the tip when illuminated by plane wave with a field strength of 1 V/m, polarised along the axes of the tip.
The localised field enhancement might be used for trapping a particle underneath the tip. Figures 4 and 5 show the amplitude of the electric field if a dielectric or a metallic particle is moved underneath the tip. To take into account the strongly varying field, the mesh is refined around the apex of the tip. The total model is resolved by more then 250 000 tetrahedrons. Calculation time for each sphere position is about 20 minutes.
Figure 4: Amplitude of the electric field for a dielectric sphere underneath the tip
Figure 5: Amplitude of the electric field for a metallic sphere underneath the tip
This article has shown that the CST MWS frequency domain solver is well suited for calculating nano-optical problems. The combination of time and frequency domain solvers gives the user greater flexibility when performing optical simulations. It also demonstrates the powerful post processing possibilities available in CST MWS. All animations can be generated directly within the program by using macros and template based post processing steps.
[1] L. Novotny, R. X. Bian, X. Sunney Xie, “Theory of Nanometric Optical Tweezers,” Physical Review Letters, Vol. 79, No. 4, 28 July 1997.
CST Article "Electromagnetic Field Simulation of Nanometric Optical Tweezers."
last modified 13. Mar 2007 2:58
printed 10. Feb 2012 7:39, Article ID 317
URL:
All rights reserved.
Without prior written permission of CST, no part of this publication may be
reproduced by any method, be stored or transferred into an electronic data processing system, neither mechanical or by any other method.
Article ID: 317
Last modified: 13. Mar 2007 2:58
Other Articles
This article demonstrates that a dense array of Split Ring Resonator (SRR) can be considered as a gyrotropic bianisotropic media with magneto-electric coupling effects.
The simulation of such SRRs with CST MICROWAVE STUDIO® demonstrates the propagation of a backward wave component in a certain frequency range where the structure behaves as a medium with a negative refractive index.
Read full article..
This article is concerned with the 3D electromagnetic modelling and equivalent circuit parameter extraction of a Resistance Spot Welding (RSW) gun. The parameters for the gun are not as easily established for the gun as for other RSW system components. The current transformer and electronic converter electrical parameters are either known or can be obtained by standard test procedures. This is not the case for the gun where the electrical parameters are unknown and difficult to measure. A 3D EM simulation using CST EM STUDIO® can be used to establish these parameters and complete the system characterisation.
Read full article..
For many years Southwest Microwave has manufactured field replaceable connectors and launch accessories where connector performance was easily verified by measuring two connectors back-to-back as a two-port device. With the introduction and success of Southwest Microwave end launch connectors, the packaging responsibility has fallen to Southwest Microwave. To assure maximum performance of the Southwest Microwave end launch connectors, equally high performance test boards were needed to accurately measure the connectors.
Read full article..
The telecommunications sector is making great advances aimed at delivering an even stream of high tech devices, covering the significant consumer demands in this sector. EM simulation is increasingly becoming an indispensable tool in the design flow, not only on the antenna level but also on the phone and environmental levels. This article compares simulated results with measurements for several steps in the phone design chain.
Read full article..
K. Carrigan, Senior Systems Engineer, U.S. Navy (NSWC Dahlgren), & D. Johns, CST of America. Video of a webinar presentation (Running time: 32 min).
Read full article..