Engineering laser beams for particle trapping, lattice formation and microscopy

Having control over nano- and micro-sized objects' position inside a suspension is crucial in many applications such as: sorting and delivery of particles, studying cells and microorganisms, spectroscopy imaging techniques, and building microscopic size lattices and artificial structures. This control can be achieved by judiciously engineering optical forces and light-matter interactions inside colloidal suspensions that result in optical trapping. However, in the current techniques, to confine and transport particles in 3D, the use of high-NA (Numerical Aperture) optics is a must. This in turn leads to several disadvantages such as alignment complications, lower trap stability, and undesirable thermal effects. Hence, here we study novel optical trapping methods such as asymmetric counter-propagating beams where we have engineered the optical forces to overcome the aforementioned limitations. This system is significantly easier to align as it uses much lower NA optics which creates a very flexible manipulating system. This new approach allows the trapping and transportation of different shape objects, sizing from hundreds of nanometers to hundreds of micrometers by exploiting asymmetrical optical fields with higher stability. In addition, this technique also allows for significantly longer particle trapping lengths of up to a few millimeters. As a result, we can apply this method to trapping much larger particles and microorganisms that have never been trapped optically before. Another application that the larger trapping lengths of the proposed system allow for is the creation of 3D lattices of microscopic size particles and other artificial structures, which is one important application of optical trapping.  

This system can be used to create a fully reconfigurable medium by optically controlling the position of selected nano- and micro-sized dielectric and metallic particles to mimic a certain medium. This “table-top” emulation can significantly simplify our studies of wave-propagation phenomena on transmitted signals in the real world. 

Furthermore, an important application of an optical tweezer system is that it can be combined with a variety of spectroscopy and microscopy techniques to extract valuable, time-sensitive information from trapped entities. In this research, I plan to integrate several spectroscopy techniques into the proposed trapping method in order to achieve higher-resolution images, especially for biomaterials such as microorganisms.