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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Aysu Ay and Parviz Elahi, "Ultra-low numerical aperture counter-propagating intracavity optical tweezers," Proc. SPIE 12573, Specialty Optical Fibres, 125730Q (Presented at SPIE Optics + Optoelectronics: April 25, 2023; Published: 30 May 2023); https://doi.org/10.1117/12.2665704.