Applications of Diffractive Optics Elements in Optical Trapping

Optical tweezers have become a powerful tool for contactless manipulation of matter at the nano and microscope scale since the pioneering work of Ashkin and coworkers. ^{1, 2} Experimentally, it is straightforward to implement an optical tweezers setup (in its most simple version): just need to focus a laser beam using a high aperture lens at whose focus a particle can be trapped. Conceptually, the physical mechanism of trapping involves subtle properties of light to exert forces and torques on matter: transfer of linear and angular momentum. The physical mechanism of optical tweezers and applications has been nicely reviewed in many works and for such reason they will not be discussed here. Readers interested in the subject may check out the following references. ^{3– 6} Optical tweezers have found many applications like particle sorting, ^{7, 8} microrheology, ^{9, 10} study of colloidal hydrodynamics, ^{11, 12} compliance of bacterial tail, ¹³ stretching of single deoxyribonucleic acid (DNA) 264molecules, ^{14, 15} among others. Moreover, optical tweezers can be used as quantitative tools to exert and measure forces on microscopic and nanoscopic particles such as those exerted by single motor proteins. ^{16, 17}