High-sensitivity force sensing using a phonon laser in an active levitated optomechanical system.

Force detection with high sensitivity is of paramount importance in many fields of study, from gravitational wave detection to investigations of surface forces. Here, we propose and demonstrate a force-sensing method based on gain-enhanced nonlinearity in a nonlinear phonon laser. Experimental and simulation results show that the input force leads to the frequency shift of phonon laser, due to nonlinearity. In addition, we further investigate the influences of the pumping power, numerical aperture, and microsphere's refractive index on the performance of this force-sensing system, regarding the sensitivity and the linear response range. Our work paves a new way towards the realization of precise metrology based on the nonlinearity of phonon laser.

Structured-light displacement detection method using split-waveplate for dual-beam optical tweezers.

Structured-light displacement detection method is an innovative approach with extremely high sensitivity for measuring the displacement of a levitated particle. This scheme includes two key components, a split-waveplate (SWP) and a single-mode fiber. In this work, we further investigated the influence of SWP installation on this method regarding the sensitivity of displacement detection. The results indicate that the sensitivity increases with the expanding of SWP offset in the effective range. In addition, we found this method has a significant tolerance rate, with an extensive SWP offset effective range of 5%-25%. However, an excessive offset can render this method ineffective. More interestingly, we demonstrated the feasibility of rotating the SWP to detect displacement in different directions. Our research contributes to guiding the structured-light detection methods in practical applications and expanding their applications in fundamental physics.

Characteristics of the phonon laser in the active levitated optomechanical system.

Phonon lasers, coherent oscillations of phonons, have gradually become one of the emerging frontiers in the last decades, and have promising applications in quantum sensing, information processing, and precise measurement. Recently, phonon lasers based on dissipative coupling have been realized in an active levitated optomechanical (LOM) system for the first time. Here, we further investigated the characteristics of the phonon laser in the system above regarding the oscillator amplitude and the phonon laser linewidth. We established both the experimental system and a physical model of the phonon laser. On the basis of simulations and experiments, the influences of pumping power, numerical aperture, the microsphere's diameter and refractive index on the performance of the phonon lasers are sufficiently discussed. Our work is of great significance for the high-quality phonon lasers generated by the appropriate parameters, which is the basis for the in-depth research and practical application.

Enhanced optical trapping of ZrO2@TiO2 photonic force probe with broadened solvent compatibility.

Optical trapping and manipulating nanoparticles are essential tools for interrogating biomedicine at the limits of space and time. Typically, silica or polystyrene microspheres are used as photonic force probes. However, adapting those probes to organic solvents is an ongoing challenge due to the limited solvent compatibility and low refractive index mismatch. Here we report on the optical force enhancement and solvent compatibility that utilizes ZrO2@TiO2 core-shell nanoparticles. We experimentally demonstrate that the 450-nm-diameter ZrO2@TiO2 core-shell nanoparticles achieve the lateral and axial trap stiffness up to 0.45 pN µm-1 mW-1 and 0.43 pN µm-1 mW-1 in water, showing more than fivefold and ninefold improvement on the ordinary SiO2 particle of the same size. In addition, ZrO2@TiO2 core-shell nanoparticles can realize stable three-dimensional trapping in both polyethylene glycol and glucose solutions. This optical trapping enhancement property, coupled with solvent compatibility, expands the range of feasible optical trapping experiments and will pave the way toward more advanced biological applications.

Differential displacement measurement of the levitated particle using D-shaped mirrors in the optical tweezers.

Displacement measurement using a D-shaped mirror is a key technology in optical tweezers, which have emerged as an important tool for precision measurement. In this paper, we first study the influences of installation errors for the D-shaped mirror on the displacement measurement. The calibration factor and sensitivity of the different installation parameters are quantified. The results show that the variation of the calibration factor obeys the cosine curve with the angle error, and the sensitivity increases exponentially with the translation error. Besides, we find that the translation error will also lead to crosstalk between transverse and axial displacement. Our work will contribute to improving the performance of optical tweezers for the application in precision measurement and basic physics.

Optical Pulling Using Chiral Metalens as a Photonic Probe.

Optical pulling forces, which can pull objects in the source direction, have emerged as an intensively explored field in recent years. Conventionally, optical pulling forces exerted on objects can be achieved by tailoring the properties of an electromagnetic field, the surrounding environment, or the particles themselves. Recently, the idea of applying conventional lenses or prisms as photonic probes has been proposed to realize an optical pulling force. However, their sizes are far beyond the scope of optical manipulation. Here, we design a chiral metalens as the photonic probe to generate a robust optical pulling force. The induced pulling force exerted on the metalens, characterized by a broadband spectrum over 0.6 µm (from 1.517 to 2.117 µm) bandwidth, reached a maximum value of -83.76 pN/W. Moreover, under the illumination of incident light with different circular polarization states, the longitudinal optical force acting on the metalens showed a circular dichroism response. This means that the longitudinal optical force can be flexibly tuned from a pulling force to a pushing force by controlling the polarization of the incident light. This work could pave the way for a new advanced optical manipulation technique, with potential applications ranging from contactless wafer-scale fabrication to cell assembly and even course control for spacecraft.

Self-feedback induced bistability in dual-beam intracavity optical tweezers.

The intracavity optical tweezers is a new, to the best of our knowledge, cavity optomechanics system, implementing a self-feedback control of the particle's position by trapping the particle inside an active ring cavity. This self-feedback mechanism efficiently constructs a novel potential in the cavity. Here we predict and give experimental evidence for the self-feedback induced optical bistability in dual-beam intracavity optical tweezers. Then the characteristics of these bistable potential wells are investigated. The results show that we can prevent the bistable behaviors from destabilizing the trapping stability through tuning the foci offset of two propagating beams in the cavity. This contributes to the use of intracavity optical tweezers as a powerful tool for optical manipulation. Importantly, the thermally activated transition of the trapped particle in the bistable potential is observed for particular experimental parameters. Further investigation of this phenomenon could underlie the mechanism of many metastable-related processes in physics, chemistry, and biology.

Dual-beam intracavity optical tweezers with all-optical independent axial and radial self-feedback control schemes.

The feedback control to optical tweezers is an obvious approach to improve the optical confinement. However, the electronic-based feedback controlling system in optical tweezers usually consists of complex software and hardware, and its performance is limited by the inevitable noise and time-delay from detecting and controlling devices. Here, we present and demonstrate the dual-beam intracavity optical tweezers enabling all-optical independent radial and axial self-feedback control of the trapped particle's radial and axial motions. We have achieved the highest optical confinement per unit intensity to date, to the best of our knowledge. Moreover, both the axial and radial confinements are adjustable in real-time, through tuning the foci offset of the clockwise and counter-clockwise beams. As a result, we realized three-dimensional self-feedback control of the trapped particle's motions with an equivalent level in the experiment. The dual-beam intracavity optical tweezers will significantly expand the range of optical manipulation in further studies of biology, physics and precise measurement, especially for the sample that is extremely sensitive to heat.

Optical confinement efficiency in the single beam intracavity optical tweezers.

Single beam intracavity optical tweezers characterizes a novel optical trapping scheme where the laser operation is nonlinearly coupled to the motion of the trapped particle. Here, we first present and establish a physical model from a completely new perspective to describe this coupling mechanism, using transfer matrices to calculate the loss of the free-space optical path and then extracting the scattering loss that caused by the 3D motions of the particle. Based on this model, we discuss the equilibrium position in the single beam intracavity optical tweezers. The influences of the numerical aperture, pumping power, particle radius and refractive index on the optical confinement efficiency are fully investigated, compared with standard optical tweezers. Our work is highly relevant for guiding the experiments on the single beam intracavity optical tweezers to achieve higher optical confinement efficiency.

Coupling between axial and radial motions of microscopic particle trapped in the intracavity optical tweezers.

Intracavity optical tweezers have been proposed and demonstrated recently, which allows orders-of-magnitude higher optical confinement with lower-numerical-aperture lens and lower laser power in contrast to the standard optical tweezers. We further investigate its characteristics about the position stability of trapped particles. The dependence of the radial and axial position stability on the laser intensity acting on the particle of 10-µm diameter in intracavity optical tweezers and standard optical tweezers are compared experimentally. Result shows that higher laser intensity can make stronger optical confinement in intracavity optical tweezers under the condition of good trap operation, compared with standard optical tweezers. We demonstrate and analyze the coupling between the particle's radial and axial motion, and then provide two approaches to reduce it. Our work will benefit the further enhancement of position stability for the trapped particle in intracavity optical tweezers.