Optical Trapping of Nanoparticles by Ultrashort Laser Pulses

Abstract

Optical trapping with continuous-wave lasers has been a fascinating field in the optical manipulation. It has become a powerful tool for manipulating micrometer-sized objects, and has been widely applied in physics, chemistry, biology, material, and colloidal science. Replacing the continuous-wave- with pulsed-mode laser in optical trapping has already revealed some novel phenomena, including the stable trap, modifiable trapping positions, and controllable directional optical ejections of particles in nanometer scales. Due to two distinctive features; impulsive peak powers and relaxation time between consecutive pulses, the optical trapping with the laser pulses has been demonstrated to have some advantages over conventional continuous-wave lasers, particularly when the particles are within Rayleigh approximation. This would open unprecedented opportunities in both fundamental science and application. This Review summarizes recent advances in the optical trapping with laser pulses and discusses the electromagnetic formulations and physical interpretations of the new phenomena. Its aim is rather to show how beautiful and promising this field will be, and to encourage the in-depth study of this field.

Femtosecond Pulse-Width Dependent Trapping and Directional Ejection Dynamics of Dielectric Nanoparticles

“…In our earlier reports, theoretically, we have shown that directional ejections of the nanoparticles can occur as a result of dominating repulsive−over attractive-forces in the directions perpendicular to the polarization vector. 27,30 The reasonable questions arise; e.g., how are the nanoparticles ejected from the trapping site and what parameters can control such directional ejections? On the basis of electromagnetic formulations, a multitude of parameters, such as the repetition rate and pulse duration of laser pulses, as well as numerical aperture of objective lens can greatly affect the repulsive and attractive forces.…”

Optical trapping assembling of clusters and nanoparticles in solution by CW and femtosecond lasers

“…It was confirmed that the directional ejections occur only when the number of nanoparticles confined in the trapping site exceeds a definite threshold. Considering electromagnetic formulation and its numerical estimation, however, trapping and ejection are always symmetrical with respect to the polarization of the incident trapping pulses [25]. Thus, we have to ascribe the alternatively switched ejection behavior to material property.…”

“…It should be noted also that x-, y-and z-polarizations of the trapping laser are no more independent after being focused tightly with an objective lens of high numerical aperture, where z axis corresponds to the propagating direction of the tapping laser. Considering these forces, we formulated electromagnetic theorem of forces on the polystyrene nanoparticles at the focal point [25]. It should be pointed out that laser trapping by femtosecond pulses is based on repetitive irradiation mode.…”

Enhanced optical confinement of dye-doped dielectric nanoparticles using a picosecond-pulsed near-infrared laser

“…Since its first conception and realization, optical trapping of microscopic objects in a solution with a highly focused laser beam has emerged as a common practice to manipulate particles of micrometer size [1], and has found applications in various disciplines ranging from physics [2][3][4][5] and chemistry [6] to biology [7][8][9][10]. The optical manipulation of nanometer-sized particles with a great efficiency and stability nevertheless remains a challenge, and is demonstrated almost exclusively on particles made of noble metals or semiconductors [11][12][13].…”