Three dimensional (3D) particle tracking technique has gained significant attention in recent years due to its ability to provide accurate and reliable data on the motion of particles, including micro and nanoscale particles. Here, we present a novel technique based on chromatic aberration that achieves 3D tracking using two cameras. Due to chromatic aberration of the lens, the axial position of the particle is mapped onto the lateral position in the image plane at a specific color, allowing us to use a diffraction grating to determine the lateral position on the color spectrum and thus the axial position of the particle. We also perform experiments on a 6.24 μm polystyrene particle in water, and collect data. We finally implement our method in Python and demonstrate that it performs within the tolerable error range and processes images and makes 3D coordinate predictions at a speed of 1.5 kHz.
Here, we demonstrate a new configuration of intracavity optical tweezers based on a ring cavity fiber laser. In this scheme, we placed the optical trapping system inside the Yb:doped fiber laser cavity operating with backward pumping. We use two counter-propagating inversely correlated beams, a pump at 976 nm from top to bottom and a signal at 1030 nm in the opposite direction. They are focused on the sample with a ultra-low numerical aperture (NA=0.088) aspheric lenses. Using this approach, counter-propagating intracavity optical tweezers (IOT), we are capable of 3D optical trapping of 1.98 µm-diameter polystyrene particles. Using such a low NA lens reduces the laser intensity on the trapped particle compared to the standard intracavity optical tweezers. The total average power on the particle is 885 µW, which corresponds to the average intensity of 21.2 µW µm−2
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