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Beyond diffraction limit, multitrapping of nanoparticles is important in numerous scientific fields, including biophysics, materials science and quantum optics. Here, we demonstrate the 3-dimensional (3D) shell-like structure of optical trapping well induced by nonlinear optical effects in the femtosecond Gaussian beam trapping for the first time. Under the joint action of gradient force, scattering force and nonlinear trapping force, the gold nanoparticles can be stably trapped in some special positions, or hop between the trap positions along a route within the 3D shell. The separation between the trap positions can be adjusted by laser power and numerical aperture (NA) of the trapping objective lens. With a high NA lens, we achieved dual traps with less than 100 nm separation without utilizing complicated optical systems or any on-chip nanostructures. These curious findings will greatly extend and deepen our understanding of optical trapping based on nonlinear interaction and generate novel applications in various fields, such as microfabrication/nanofabrication, sensing and novel micromanipulations.

The ability of light beams to rotate nano-objects has important applications in optical micromachines and biotechnology. However, due to the diffraction limit, it is challenging to rotate nanoparticles at subwavelength scale. Here, we propose a method to obtain controlled fast orbital rotation (i.e., circumgyration) at deep subwavelength scale, based on the nonlinear optical effect rather than sub-diffraction focusing. We experimentally demonstrate rotation of metallic nanoparticles with orbital radius of 71 nm, to our knowledge, the smallest orbital radius obtained by optical trapping thus far. The circumgyration frequency of particles in water can be more than 1 kHz. In addition, we use a femtosecond pulsed Gaussian beam rather than vortex beams in the experiment. Our study provides paradigms for nanoparticle manipulation beyond the diffraction limit, which will not only push toward possible applications in optically driven nanomachines, but also spur more fascinating research in nano-rheology, micro-fluid mechanics and biological applications at the nanoscale., It has been challenging to rotate nanoparticles orbitally via optical trapping beyond the diffraction limit. Here, the authors take advantage of the nonlinear optical effect and demonstrate fast and controlled orbital rotation at subwavelength scale with a femtosecond pulsed Gaussian beam.

Optical trapping and manipulation of atoms, nanoparticles, and biological entities are widely employed in quantum technology, biophysics, and sensing. Single traps are typically achieved with linearly polarized light, while vortex beams form rotationally unstable symmetric traps. Here we demonstrate multiplexed optical traps reconfigurable with intensity and polarization of the trapping beam using intensity-dependent polarizability of nanoparticles. Nonlinearity combined with a longitudinal field of focused femtosecond vortex beams results in a stable optical force potential with multiple traps, in striking contrast to a linear trapping regime. The number of traps and their orientation can be controlled by the cylindrical vector beam order, polarization, and intensity. The nonlinear trapping demonstrated here on the example of plasmonic nanoparticles opens up opportunities for deterministic trapping and polarization-controlled manipulation of multiple dielectric and semiconductor particles, atoms, and biological objects since most of them exhibit a required intensity-dependent refractive index.

Micron-sized gold plates were prepared by reducing chloroauric acid with lemongrass extract. Their two-photon luminescence (TPL) and second harmonic generation (SHG) were investigated. The results show that the TPL and SHG intensity of gold plates is dependent on the wavelength and polarization of excitation laser. The TPL intensity of gold plates decreases with the increase of the excitation wavelength except for a small peak around 820–840 nm, while SHG intensity increases with the excitation wavelength redshift. In addition, it is found that the TPL intensity of the gold plate’s edge is related with the angle between the edge orientation and the polarization direction of the excitation light. The TPL intensity increases with the angle increase from 0° to 90°.

When femtosecond laser pulses pass through a trapped polystyrene bead, water breakdown is induced even though the energy of laser pulse is much lower compared to the threshold value of breakdown when the femtosecond laser directly irradiates in water. This mechanism is assigned to the secondary convergence of the laser by the trapped bead.

Although the digital micromirror device (DMD) has been considered to be a spatial light modulator (SLM) for a long time, it is seldom utilized for holographic tweezers practically because of its energy loss. In this work, a multi-trapping system built with a DMD is demonstrated. But a problem of dispersion is found when the DMD is applied to femtosecond laser, and its mechanism is studied.

Luminescence thermometry usually suffer from cellular complexity of the biochemical environment (such as pH and ionic strength) and thus the accuracy and reliability of the determined intracellular temperature are directly affected. Herein, a photoluminescent nanothermometer composed of polymer encapsulated quantum dots (P-QD) has been developed. And the prepared nanothermometer exhibits some advantages: such as non-sensitivity to pH and ionic strength, as well as high detection sensitivity and ultrahigh reversibility. The intracellular temperature was accurately determined under physiological conditions with different pH and ionic strength and direct measurement of thermogenesis in individual cells has been achieved.

Materials possessing high two photon absorption (TPA) are highly desirable for a range of fields, such as three-dimensional data storage, TP microscopy (TPM) and photodynamic therapy (PDT). Specifically, for TPM, high TP excitation (TPE) brightness (σ × ϕ, where σ is TPA cross-sections and ϕ is fluorescence quantum yield), excellent photostability and minimal cytotoxicity are highly desirable. However, when TPA materials are transferred to aqueous media through molecule engineering or nanoparticle formulation, they usually suffer from the severely decrease of quantum yield (QY). Here, we report a convenient and efficient method for preparing polymer-encapsulated quantum dots (P-QD). Interestingly, the QY was considerably enhanced from original 0.33 (QDs in THF) to 0.84 (P-QD in water). This dramatic enhancement in QY is mainly from the efficiently blocking nonradiative decay pathway from the surface trap states, according to the fluorescence decay lifetimes analysis. The P-QD exhibits extremely high brightness (σ × ϕ up to 6.2 × 106 GM), high photostability, excellent colloidal stability and minimal cytotoxicity. High quality cellular TP imaging with high signal-to-background ratio (> 100) and tissue imaging with a penetration depth of 2200 μm have been achieved with P-QD as probe.

A phenomenon called “trap split” had been found when gold nanoparticles were trapped by femtosecond laser pulses, and the trap split was strongly dependent on the polarization, energy and wavelength of the laser pulses. The 3-Dimension distribution of trap split was investigated in this work.

In an optical tweezers system, the output signal of a photodiode quadrant detector and the temperature in a sample cell are two key factors for the quantitative measurements of mechanical properties of living biological objects such as cells, organelles and macro-molecules. In order to enhance the output of a quadrant detector and effectively control the temperature in a sample cell, the dependence of the temperature in the sample cell and the output of the quadrant detector for different illumination conditions are studied. The results show that appropriate illumination conditions can ensure both nearly constant temperatures in the cell and the desired output signal, which provides for the possibility of highprecision and damage-free analysis of living biological objects.

A phenomenon called “trap split” was found when gold nanoparticles were trapped by linear polarized femtosecond laser pulses. The trap split was strongly dependent on the polarization of trapping laser, besides the energy and wavelength of the laser pulses. The behaviors of trapped particles under various vector femtosecond laser pulses were investigated.

Several kinds of manipulation of biological cells were performed utilizing regeneratively amplified femtosecond laser system. When single-shot pulse of an amplified Ti: Sapphire femtosecond laser pulse is focused on a culture medium, shockwave and cavitation bubble are generated with little heating. An impulsive force resulting in these phenomena was applied to pttern specific cells form a culture substrate. Furthermore, laser trapping of cells was realized using high-repetition rate pulses from the laser oscillator. Although the cell was trapped stably when the laser power was less than 100 mW, the cell was burst above the threshold laser power. The bursting would be due to heating inside cell, on which the laser was focused and multiphoton absorption was induced. On the bases of these results, we propose a new methodology to pattern biological cells, which is speedy and flexible when compared with previous micropatterning methods.

Intravascular low level laser irradiation (ILLLI) therapy has been applied in clinic widely since Mester et a!. reported the beneficial effects of low-level laser treatment on wound healing in the early 1980s. Clinical reports show that is an effective measure. But the mechanism of ILLLI is not very clear yet. In this article, it will be discussed why the oxygen content in the blood increases after irradiated by He-Ne laser and how does it influence the functions of body. It will be proved that the ability of blood carrying oxygen acts as a key role in the ILLLI.

When the PDL-2 dye laser was pumped longitudinally by the frequency-doubled DCR-3 YAG:Nd laser, it is found that two coherent radiations are generated by one dye medium ( LDS75 I or LDS750 ). Aside from the expected dye laser output, there appears another coherent radiation generated by a four-wave mixing process. This is caused by the YAG: Nd laser's two longitudinal mode. As far as we know, the four-wave mixing generated in above commercial laser systems hasn't been reported. This discovery is helpful for researches of using above laser systems.

Poly(thienylene vinylene) (PTV) is a low-bandgap polymer but shows poor performance in both light-emitting and photovoltaic applications. Recently a derivative of PTV with carboxylate substitution, poly(3-carboxylated thienylenevinylene) (P3CTV), has been synthesized and was shown to be fluorescent. The photovoltaic power conversion efficiency based on P3CTV has been found to be much larger than PTV, indicating an intrinsically concomitant relationship between light-emitting and photovoltaic properties. Employing quantum chemistry calculations coupled with our correlation function formalism for excited state decay and optical spectra, we have investigated a series of side-chain substituted PTVs targeting optimal optoelectronic performance. We predict that the carbonyl substituted PTV is a strongly fluorescent polymer with low bandgap, long exciton lifetime, and large spectral overlap between emission and absorption. It is expected that carbonyl PTV is a promising light-emitting and photovoltaic polymer. Methodology wise, we find that (i) our correlation function approach to calculate the optical spectrum has much lower computational scaling with respect to the system size than the conventional method; (ii) the harmonic oscillator approximation for the nonadiabatic decay works better for a large system than for a small system.

A nondestructive and noncontact method to trap and manipulate a microparticle in solution is proposed by utilizing femtosecond laser-induced nonlinear phenomena. A 90μm diameter polystyrene bead in solution was trapped and manipulated by scanning femtosecond laser pulses around it, which was ascribed to shockwave, cavitation bubble, and jet flow. The maximum mechanical force exerted by laser irradiation was estimated to be over 1μN. In comparison with conventional optical tweezers, this method provides not only a much larger trapping force but also a noninvasive advantage.