Graduate Program in Physics.Elahi, Parviz.Ay, Aysu.2025-04-142025-04-142023Graduate Program in Physics. TKL 2023 U68 PhD (Thes BM 2023 A63https://digitalarchive.library.bogazici.edu.tr/handle/123456789/21560Optical tweezers are a powerful tool that utilizes optical forces generated by the exchange of momentum between light and matter to trap and manipulate a wide range of particles, including atoms and molecules, organelles, proteins,and cells. Since intracavity optical trapping was introduced, a new research opportunity opened for three-dimensional optical trapping of microscopic objects using a low numerical aperture lens at low laser intensity. This method has introduced the placing of the trapping optics within a fiber laser ring cavity and the forces of optical feedback radiation. There are two possible configurations for intracavity optical trapping: single-beam and counter-propagating beam configurations. The former has already been proposed and implemented, while the latter still needs to be discussed in detail: the focus of this work lies on counter-propagating beam configuration. This work demonstrates the design, implementation, and experimentation of counter- propagating optical tweezers. It presents 3D trapping of 1.98 μm-diameter polystyrene particles, which single-beam intracavity traps were incapable of performing. The total average power on the sample was measured to be 885 μW, which corresponds to an average intensity of 21.2 μWμm−2. The inversely correlated counter-propagating beams reduce the average intensity on the particle in the trap; hence, they enable the trapping of light-sensitive biological matter. This paves the way for new and exciting applications for optical tweezers.Optical tweezers.xiv, 53 leaves