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Tunable potential well for plasmonic trapping of metallic particles by bowtie nano-apertures

View Article: PubMed Central - PubMed

ABSTRACT

In this paper, the tunable optical trapping dependence on wavelength of incident beam is theoretically investigated based on numerical simulations. The Monte Carlo method is taken into account for exploring the trapping characteristics such as average deviation and number distribution histogram of nanoparticles. It is revealed that both the width and the depth of potential well for trapping particles can be flexibly adjusted by tuning the wavelength of the incident beam. In addition, incident wavelengths for the deepest potential well and for the strongest stiffness at bottom are separated. These phenomena are explained as the strong plasmon coupling between tweezers and metallic nanoparticles. In addition, required trapping fluence and particles’ distributions show distinctive properties through carefully modifying the incident wavelengths from 1280 nm to 1300 nm. Trapping with lowest laser fluence can be realized with1280 nm laser and trapping with highest precision can be realized with 1300 nm laser. This work will provide theoretical support for advancing the manipulation of metallic particles and related applications such as single-molecule fluorescence and surface enhanced Raman spectroscopy.

No MeSH data available.


Related in: MedlinePlus

Wavelength dependent potential well depth (open dots) the stiffness at the center of tweezers (solid dots) with different metallic nanoparticle diameters of 35 nm (◾), 45 nm (⦁), 50 nm (▴) and 55 nm (▾).The laser fluence applied in this figure is 4 × 108 W/m2. The wavelength dependence of potential well’s half width for maximum (HWHM) with different particle sizes is shown as figure R3 as supplementary information.
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f3: Wavelength dependent potential well depth (open dots) the stiffness at the center of tweezers (solid dots) with different metallic nanoparticle diameters of 35 nm (◾), 45 nm (⦁), 50 nm (▴) and 55 nm (▾).The laser fluence applied in this figure is 4 × 108 W/m2. The wavelength dependence of potential well’s half width for maximum (HWHM) with different particle sizes is shown as figure R3 as supplementary information.

Mentions: The Wavelength dependent potential wells depth (open dots) the stiffness at the center of tweezers with different metallic nanoparticle diameters of 35 nm, 45 nm, 50 nm and 55 nm have been shown in Fig. 3. With increasing metallic particle size, the incident wavelength for maximum potential well depth shows evident red shift from 1255 nm to 1310 nm. The corresponding deepest potential well also increases from minus 3.6 kT to minus 16.5 kT with increasing particle size. The increasing size of metallic particle could enhance its plasmon resonance and finally strengthen the plasmon coupling with plasmonic tweezers, leading to the red shift of the optimal incident wavelength for the deepest potential well. For the particles with diameters over 45 nm, potential deeper than minus 8 kT can be acquired with input laser intensity of4 × 108 W/m2. So stable trapping can be realized with input laser intensity of 5 × 108 W/m2 with potential wells deeper than minus 10 kT. For the nanoparticles with diameters of 35 nm, however, the depth of potential well is minus 3.6 kT so laser fluence needs to be increased over 1 × 109 W/m2 to realize stable trapping. In such condition, the better way to solve such problem may be modifying the geometry of our tweezers, for example, decreasing the gap (parameter D) to achieve stable trapping with lower incident fluence rather than increasing laser fluence to avoid damage of metallic nanostructures or surroundings. The maximum stiffness at potential well bottom increases rapidly with increasingparticle size. The corresponding incident wavelength also shows evident red shift from 1260 nm to 1320 nm. With the particle size increasing, the plasmon coupling becomes stronger, leading to the increasing of plasmon resonance wavelength and resonance strength. Another interesting phenomenon is that the wavelength for the maximum stiffness and the maximum potential depth shown is evidently separated. For example, for the particle with diameter of 50 nm, the incident wavelength for maximum potential well depth is 1280 nm for the strongest stiffness is 1300 nm. Incident wavelength for maximal stiffness corresponds to the resonance wavelength of the particle-tweezers system when nanoparticle is in vicinity to the bottom of potential well. The strongest trapping forces also exist at that point. As the nanoparticle escape away from the center, trapping force drops rapidly due to the off-resonance states. As aresult, the deepest potential well is not achieved in this case.


Tunable potential well for plasmonic trapping of metallic particles by bowtie nano-apertures
Wavelength dependent potential well depth (open dots) the stiffness at the center of tweezers (solid dots) with different metallic nanoparticle diameters of 35 nm (◾), 45 nm (⦁), 50 nm (▴) and 55 nm (▾).The laser fluence applied in this figure is 4 × 108 W/m2. The wavelength dependence of potential well’s half width for maximum (HWHM) with different particle sizes is shown as figure R3 as supplementary information.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036050&req=5

f3: Wavelength dependent potential well depth (open dots) the stiffness at the center of tweezers (solid dots) with different metallic nanoparticle diameters of 35 nm (◾), 45 nm (⦁), 50 nm (▴) and 55 nm (▾).The laser fluence applied in this figure is 4 × 108 W/m2. The wavelength dependence of potential well’s half width for maximum (HWHM) with different particle sizes is shown as figure R3 as supplementary information.
Mentions: The Wavelength dependent potential wells depth (open dots) the stiffness at the center of tweezers with different metallic nanoparticle diameters of 35 nm, 45 nm, 50 nm and 55 nm have been shown in Fig. 3. With increasing metallic particle size, the incident wavelength for maximum potential well depth shows evident red shift from 1255 nm to 1310 nm. The corresponding deepest potential well also increases from minus 3.6 kT to minus 16.5 kT with increasing particle size. The increasing size of metallic particle could enhance its plasmon resonance and finally strengthen the plasmon coupling with plasmonic tweezers, leading to the red shift of the optimal incident wavelength for the deepest potential well. For the particles with diameters over 45 nm, potential deeper than minus 8 kT can be acquired with input laser intensity of4 × 108 W/m2. So stable trapping can be realized with input laser intensity of 5 × 108 W/m2 with potential wells deeper than minus 10 kT. For the nanoparticles with diameters of 35 nm, however, the depth of potential well is minus 3.6 kT so laser fluence needs to be increased over 1 × 109 W/m2 to realize stable trapping. In such condition, the better way to solve such problem may be modifying the geometry of our tweezers, for example, decreasing the gap (parameter D) to achieve stable trapping with lower incident fluence rather than increasing laser fluence to avoid damage of metallic nanostructures or surroundings. The maximum stiffness at potential well bottom increases rapidly with increasingparticle size. The corresponding incident wavelength also shows evident red shift from 1260 nm to 1320 nm. With the particle size increasing, the plasmon coupling becomes stronger, leading to the increasing of plasmon resonance wavelength and resonance strength. Another interesting phenomenon is that the wavelength for the maximum stiffness and the maximum potential depth shown is evidently separated. For example, for the particle with diameter of 50 nm, the incident wavelength for maximum potential well depth is 1280 nm for the strongest stiffness is 1300 nm. Incident wavelength for maximal stiffness corresponds to the resonance wavelength of the particle-tweezers system when nanoparticle is in vicinity to the bottom of potential well. The strongest trapping forces also exist at that point. As the nanoparticle escape away from the center, trapping force drops rapidly due to the off-resonance states. As aresult, the deepest potential well is not achieved in this case.

View Article: PubMed Central - PubMed

ABSTRACT

In this paper, the tunable optical trapping dependence on wavelength of incident beam is theoretically investigated based on numerical simulations. The Monte Carlo method is taken into account for exploring the trapping characteristics such as average deviation and number distribution histogram of nanoparticles. It is revealed that both the width and the depth of potential well for trapping particles can be flexibly adjusted by tuning the wavelength of the incident beam. In addition, incident wavelengths for the deepest potential well and for the strongest stiffness at bottom are separated. These phenomena are explained as the strong plasmon coupling between tweezers and metallic nanoparticles. In addition, required trapping fluence and particles’ distributions show distinctive properties through carefully modifying the incident wavelengths from 1280 nm to 1300 nm. Trapping with lowest laser fluence can be realized with1280 nm laser and trapping with highest precision can be realized with 1300 nm laser. This work will provide theoretical support for advancing the manipulation of metallic particles and related applications such as single-molecule fluorescence and surface enhanced Raman spectroscopy.

No MeSH data available.


Related in: MedlinePlus