Understanding thermal induced escape mechanism of optically levitated sphere in vacuum

The escape phenomenon, mainly caused by thermal effects, is known as an obstacle to the further practical application of optical levitation system in vacuum. Irregular photophoresis induced by thermal effects can act as an amplifier of Brownian motion. Studies on this topic provide interpretation for particle escaping phenomenon during the pressure decreasing process, as well as valuable insights into the micro- and nanoscale thermal effects in optical trap in vacuum. In this paper, we derive and test a dynamic model for the motion of an optically levitated particle in a non-equilibrium state and demonstrate the escaping mechanism of heated particles. The result of theoretical investigations is consistent with experimental escape at 0.1mbar. This work reveals and provides a theoretical basis for the stable operation of laser levitated oscillator in high vacuum and pave the way for the practicability of ultra-sensitive sensing devices

Numerical Analysis of Optical Trapping Force Affected by Lens Misalignments

Geometrical optics approximation is a classic method for calculating the optical trapping force on particles whose sizes are larger than the wavelength of the trapping light. In this study, the effect of the lens misalignment on optical force was analyzed in the geometrical optics regime. We used geometrical optics to analyze the influence of off-axis placement and the tilt of the lens on the trapping position and stiffness in an optical trap. Numerical calculation results showed that lens tilting has a greater impact on the optical trap force than the off-axis misalignments, and both misalignments will couple with each other and cause a shift of the equilibrium point and the asymmetry of the optical trap stiffness in different ways. Our research revealed the asymmetry in optical traps caused by lens misalignment and can provide guidance for optimize lens placement in future experiments

Miniaturized Dual-Beam Optical Trap Based on Fiber Pigtailed Focuser

Optical traps, utilizing a laser to confine and manipulate microscopic particles, are widely employed in various scientific applications. We propose a miniaturized dual-beam fiber optical trap for acceleration sensing. It comprises two counter-propagating beams’ output from a customized pair of single-mode fiber pigtailed focusers (SMFPF). We investigate the correlation between the misalignment and the coupling efficiency of the SMFPF pair. By maximizing the coupling efficiency, the optimal alignment is achieved. A multimode fiber (MMF) is introduced to collect and transmit side-scattered light of a trapped microsphere for motion detection. By analyzing the experimental output signal, we acquire displacement information of the trapped microspheres under both aligned and misaligned conditions. This paper provides a simple and practical solution for the alignment of dual beams and the integration of the optical traps’ levitation and detection structure, which lay a solid foundation for the further miniaturization of dual-beam optical traps

Displacement Detection Decoupling in Counter-Propagating Dual-Beams Optical Tweezers with Large-Sized Particle

As a kind of ultra-sensitive acceleration sensing platform, optical tweezers show a minimum measurable value inversely proportional to the square of the diameter of the levitated spherical particle. However, with increasing diameter, the coupling of the displacement measurement between the axes becomes noticeable. This paper analyzes the source of coupling in a forward-scattering far-field detection regime and proposes a novel method of suppression. We theoretically and experimentally demonstrated that when three variable irises are added into the detection optics without changing other parts of optical structures, the decoupling of triaxial displacement signals mixed with each other show significant improvement. A coupling detection ratio reduction of 49.1 dB and 22.9 dB was realized in radial and axial directions, respectively, which is principally in accord with the simulations. This low-cost and robust approach makes it possible to accurately measure three-dimensional mechanical quantities simultaneously and may be helpful to actively cool the particle motion in optical tweezers even to the quantum ground state in the future

Actual Sensing Sensitivity and SNR Measurement of Optical Tweezers Based on Coulomb Force Input

Abstract Sensing sensitivity is the key performance of optical tweezers. By adjusting the frequency and magnitude of an applied Coulomb force as an input of optical tweezers, we directly measured the sensitivity and signal-to-noise ratio (SNR) of a system and indirectly calculated the actual noise magnitude. Combined with an output filter, the relationship between the SNR and bandwidths was studied. We established the simulation model of a system using Simulink and simulated the relationship between the SNR and magnitude of the input forces and filter bandwidths. In addition, we built an experimental system to determine the relationship between the SNR and the magnitude of the input forces and filter bandwidths. The actual minimum detectable force was measured as 1.8275×10−17 N at a 1 Hz bandwidth. The experimental results were correlated with the simulation and theoretical results, confirming the effectiveness of the proposed method and demonstrating the high sensitivity of vacuum optical tweezers as mechanical sensors. We proposed a novel method of calibration and measurement of system sensing parameters by applying an actual force that was more direct and precise than the theoretical calculation method that requires accurate fitting parameters, such as the particle radius and density. This method can be employed to analyze the system noise and phase characteristics to confirm and improve the real performance of the system

Discussion of PCR detection method and investigation of

Aiming at the problem of difficult detection of sedentarius ciliates, unclear pollution sources and difficult identification of species in the cold-water fish farming, the major parasitic species of the parasites and the infective factors were investigated and analyzed. Samples of cold-water fish and water were collected in different seasons in Hebei Province. Firstly, the sedentarius ciliates on the fish body and in the water environment were initially identified by using morphology. Secondly, a PCR method was established for molecular level identification and phylogenetic analysis. Finally, the reasons for cold-water fish infecting the parasite were analyzed. Morphological identification reveals that the mainly parasitic species of sedentarius ciliates were Epistylis sp. and Vorticella sp.; A PCR method to test the parasites is successfully established. The results of sequences alignment and phylogenetic analysis verify the correctness of morphological test. The established PCR method is used to detect the prevalence of sessile ciliates in the water environment, which is as high as 94.38%, and the infection rate of the fish is up to 100% with no seasonal difference. The parasites in water may be one of the reasons for the long-term infection of the fish. The findings provide a scientific basis for predicting, preventing and treating cold-water fish diseases, as well as serving as a reference for disease prevention and control in the sustainable development of the cold-water fish farming industry

Controllable Formation and Real-Time Characterization of Single Microdroplets Using Optical Tweezers

Existing preparation methods for microdroplets usually require offline measurements to characterize single microdroplets. Here, we report an optical method used to facilitate the controllable formation and real-time characterization of single microdroplets. The optical tweezer technique was used to capture and form a microdroplet at the center of the trap. The controllable growth and real-time characterization of the microdroplet was realized, respectively, by adjusting experimental parameters and by resolving the Raman spectra by fitting Mie scattering to the spike positions of the spectra during the controllable growth of microdroplets. The proposed method can be potentially applied in optical microlenses and virus detection

Construction of Nc1-TgROP18.

<p>(A) Plasmid map of transfer vectors pDMG and pDMG-TgROP18, respectively. DHFR, dihydrofolate reductase-thymidylate synthase; MCS, multiple cloning site; GFP, green fluorescent protein. (B) The recombinant <i>N. caninum</i> stably expressing TgROP18 was isolated by flow cytometry. (C) IFA Localization of TgROP18 in Nc1-TgROP18. The recombinant <i>N. caninum</i> stably expressing TgROP18 was confirmed by IFA using mouse anti-rTgROP18 serum as the primary antibody. Scale bar, 5 µm.</p

Virulence assay in mice.

<p>Mice (n = 5) were injected with 10, 10³ or 10⁶ tachyzoites and were monitored for 30 days. All mice injected with the Nc1-TgROP18 strain and <i>T. gondii</i> RH strain died within 16 days post infection, compared with no death of mice infected with Nc1 wide-type or Nc1-GFP tachyzoites. Three independent experiments were performed and one representative is shown here.</p

Plaque assay.

<p>The indicated strains grew on HFF cells for 7 days before fixation and staining with Crystal violet. The Nc1 strain incubated for 30°C was used as the negative control. Three independent experiments were performed and results of one representative experiment are shown here. Scale bar, 200 µm.</p