Laser-Induced Microsphere Hammer-Hit Vibration in Liquid

Macroscopic laser pulling based on the Knudsen force in rarefied gas

Optical pulling is an attractive concept due to the counterintuitive feature, the profound mechanism underneath and promising applications. In recent ten years, optical pulling of micro-nano objects have been fully demonstrated. However, optical pulling of a macroscopic object is challenging. Herein, laser pulling of a macroscopic object is presented in rarefied gas. The pulling force is originated from the Kundsen force when a gauss laser beam irradiates a macroscopic structure composed of the absorptive bulk cross-linked graphene material and a SiO₂ layer. A torsional pendulum device qualitatively presents the laser pulling phenomenon. A gravity pendulum device was used to further measure the pulling force that is more than three orders of magnitudes larger than the radiation pressure. This work expands the scope of optical pulling from microscale to macroscale and provides an effective technique approach for macroscopic optical manipulations.

Light-induced micro-vibrator with controllable amplitude and frequency

We propose and demonstrate a light-induced micro-vibrator that can perform an adjustable reciprocating vibration based on the Δα-typed photophoretic force. The vibration amplitudes and periods can be precisely controlled and modulated in real-time, and the maximum average restoring speed is as high as 23.26 μm/s. In addition, by using the self-healing properties of the Bessel-like beam, we achieve the simultaneous driving and modulating of three absorbing micro-vibrators. The proposed absorbing micro-vibrator can be used as a novel light-driven micromotor, which is considered to have potential application value in the field of targeted drug delivery, biosensing, and environmental detection.

Laser Induced Aggregation of Light Absorbing Particles by Marangoni Convection

Laser induced Marangoni convection can be used to accumulate micro-particles. In this paper, a method is developed to control and accumulate the light absorbing particles dispersed in a thin solution layer. The particles are irradiated by a focused laser beam. Due to the photothermal effect of the particles, the laser heating generates a thermal gradient and induces a convective flow around the laser’s heating center. The convective flow drives the particles to accumulate and form a particle aggregate close to the laser’s heating center. The motion of particles is dominated by the Marangoni convection. When the laser power is high, the vapor bubbles generated by laser heating on particles strengthen the convection, which accelerates the particles’ aggregation.

Ultracompact fiber all-optical router using a photo-controlled microbubble

An ultracompact fiber router based on a photo-controlled microbubble was proposed in this Letter. Because the microbubble can be repositioned precisely in the fiber microcavity by adjusting the drive laser power, the target light beam that was incident on the gas-liquid interface of the microbubble was routed toward different directions by the light refraction inside the photo-controlled microbubble. Experimental results showed that the device had a low insertion loss of 0.64 dB, response time of (1.2-1.8s), and can achieve the continuous beam redirections within an angle range of 56° by exploiting a drive laser power of only 1.8 mW. With the characteristics of excellent controllability, low consumption, and no electromechanical parts, such a fiber all-optical router has potential to be used for the multiplex treatments and analysis applications of the photonic laboratory on a chip (PLOC).

Photocontrol of a microbubble in a fiber-based hollow microstructure

We experimentally demonstrated a novel photocontrol scheme of a microbubble. The microbubble was confined in a fiber-based hollow microstructure and its movement was driven by the laser-induced photothermal Marangoni force. The position of the microbubble was controlled at a micrometer scale by simply adjusting the drive laser power. This scheme permitted the firsthand control of a microbubble with a divergent single laser beam. As a practical demonstration, we proposed a variable fiber all-optical attenuator by exploiting the total internal reflection on the surface of the photo-controlled microbubble to modulate the target light beam. The experimental results showed that such a compact fiber attenuator possessed a low insertion loss of 0.83 dB, a maximum extinction ratio of 28.7 dB, and had potential to be integrated into the lab-on-a-chip for the modulation of the light beam power.

X-typed curvilinear transport of strongly absorbing particle in a dual-beam fiber optical trap

We propose and demonstrate a novel approach to transport a strongly absorbing particle in an X-typed trajectory reciprocally in pure liquid glycerol based on a dual-beam optical fiber trap. We perform the X-typed light field by integrating a glass microsphere on the tip of a two-core fiber. The motion of the absorbing particle in pure liquid glycerol is dominated by the Δα-type photophoretic forces (F_Δα). The incident laser power determines the direction of F_Δα. Therefore, we may perform the reciprocating transport of the absorbing particle by changing and controlling the laser power. It is simple to manufacture the fiber probe and convenient to operate the transport of the microparticle. Our research expands the applications of absorbing particles in targeted drug delivery, biological sampling, and optically mediated particle clearing.

Opto-thermal oscillation and trapping of light absorbing particles

We present an experimental study on opto-thermal oscillation and trapping of light absorbing particles. The oscillation is a three-dimensional motion in the solution. The particles at the lower substrate of the sample cell are driven towards the center of optical trap by the optical force. When the particles arrive at the location near the trap center, the laser heating on the particles results in a strong thermal gradient force that repels the particles to leave the focus spot. Next, the particles slow down under the viscous drag force. At last, the particles settle to the lower substrate of sample cell due to gravity, and restart the new oscillation process. For opto-thermal trapping of the absorbing particles, the particles are dispersed in a thin cell to compress the convention and enhance the viscous resistance. The particles can be trapped close to the spot due to the balance of optical and thermal gradient forces.

Optical attraction of strongly absorbing particles in liquids

Although optical tweezers function well for the majority of transparent particles, the absorbing particles experience a considerably high absorption force that can destroy the stable optical traps. Photophoretic force is an alternative mechanism that can be used to trap the absorbing particles. The major difficulty that is associated with the utilization of photophoretic forces for trapping strongly absorbing particles in liquids is the presence of considerable absorption on the illuminated side; a positive photophoretic force is usually induced, thereby pushing away the absorbing particles from the high-intensity region of the laser source. Here, we demonstrate a novel principle for the optical trapping and manipulation of strongly absorbing particles by harnessing strong Δα-type photophoretic forces while suppressing their stochastic nature in pure liquid glycerol using a normal divergent Gaussian beam and a Bessel-like beam. Further, our approach expands the optical manipulation of strong absorbing particles to liquid media and provides position control over the trapped particles, including the optical transportation and pinpoint positioning of the 3-μm objects over a distance of a millimeter.