Noise analysis in Stokes parameter reconstruction for division-of-focal-plane polarimeters.

The division-of-focal-plane (DoFP) polarimeter can quickly and effectively obtain the polarization information of light in real time, where Stokes parameter reconstruction is a critical issue. Many reconstruction methods have been proposed to address this; however, their performance tends to degrade in the presence of noise. Thus, it is significant to clarify the noise-induced error in Stokes parameter reconstruction. In this work, we investigate the link between the noise-introduced error and the reconstruction method and develop a simple and effective way to evaluate the noise robustness of reconstruction methods. Furthermore, a novel experimental scheme of noise measurement, to the best of our knowledge, is designed to verify the theory. Based on the criterion, our scheme guides the selection of reconstruction methods and further promotes the practical application of the DoFP technique.

Video microscopy-based accurate optical force measurement by exploring a frequency-changing sinusoidal stimulus.

Optical tweezers are constantly evolving micromanipulation tools that can provide piconewton force measurement accuracy and greatly promote the development of bioscience at the single-molecule scale. Consequently, there is an urgent need to characterize the force field generated by optical tweezers in an accurate, cost-effective, and rapid manner. Thus, in this study, we conducted a deep survey of optically trapped particle dynamics and found that merely quantifying the response amplitude and phase delay of particle displacement under a sine input stimulus can yield sufficiently accurate force measurements. In addition, Nyquist-Shannon sampling theorem suggests that the entire recovery of the accessible particle sinusoidal response is possible, provided that the sampling theorem is satisfied, thereby eliminating the requirement for high-bandwidth (typically greater than 10 kHz) detectors. Based on this principle, we designed optical trapping experiments by loading a sinusoidal signal into the optical tweezers system and recording the trapped particle responses with 45 frames per second (fps) charge-coupled device (CCD) and 163 fps complementary metal-oxide-semiconductor (CMOS) cameras for video microscopy imaging. The experimental results demonstrate that the use of low-bandwidth detectors is suitable for highly accurate force quantification, thereby greatly reducing the complexity of constructing optical tweezers. The trap stiffness increases significantly as the frequency increases, and the experimental results demonstrate that the trapped particles shifting along the optical axis boost the transversal optical force.

Regulating trapping energy for multi-object manipulation by random phase encoding.

As known to all, optical tweezers depend intensely on trapping laser power. Therefore, the ability to separately regulate trapping power for each optical trap under a multi-object manipulation task empowers researchers with more flexibility and possibilities. Here, we introduce a simple strategy using complementary random binary phase design to achieve trapping energy assignment. The trap energy ratio can be expediently regulated by effective pixel numbers of the phase mask. We demonstrate the effectiveness and functionality of this approach by calibrating trap stiffness and directly measuring trapping power of each optical trap. In addition, we show the capability of rotating micro-beads with controlled speed and direction by supplying vortex beams with different energy ratios at specified positions. Our results imply that regulating the trap energy ratio will be of great significance in various applications, such as optical sorting and microfluidic scenarios.

Measurement of Airy-vortex beam topological charges based on a pixelated micropolarizer array.

In this paper, we numerically studied the intensity patterns and screw phases of an embedded optical vortex in an Airy beam generated by a 3/2 phase pattern imposed on a spatial light modulator. It is found that the optical vortex and the Airy beam's main lobe approach each other during propagation, which means the energy of the Airy beam's intensity peaks can be taken advantage of by the imposed vortices. Based on a pixelated micropolarizer array in the interference path, we succeeded in measuring the integer topological charges up to -10 according to the phase jump. In addition, fractional topological charges were also obtained in the experiment. Both of the experimental results are acquired in a high-precision and robust way. This work will promote potential application of Airy-vortex beams in fields such as optical manipulation, laser processing, and photon entanglement.