Lou Liren

Systematical study of the trapping forces of optical tweezers formed by different types of optical ring beams

The technique of optical tweezers has been improved a lot since its invention, which extends the application fields of optical tweezers. Besides the conventionally used Gaussian beams, different types of ring beams have also been used to form optical tweezers for different purposes. The two typical kinds of ring beams used in optical tweezers are the hollow Gaussian beam and Laguerre?Gaussian (LG) beam. Both theoretical computation and experiments have shown that the axial trapping force is improved for the ring beams compared with the Gaussian beam and hence the trapping stability is improved, although the transverse trapping forces of ring beams are smaller than that of Gaussian beam. However, no systematic study on the trapping forces of ring beam has ever been discussed. In this article, we will investigate the axial and transverse trapping forces of different types of ring beams with different parameters systematically, by numerical computation in which the ray optics model is adopted. The spherical aberration caused by the refractive index mismatch between oil and water is also considered in the article. The trapping forces for different objectives that obey the sine condition and tangent condition are also compared with each other. The result of systematical calculation will be useful for the applications of optical tweezers formed by different types of ring beams.

Metalorganic Chemical Vapor Deposition of GaAs on Si Substrate Prepared by Room Temperature Chemical Cleaning Treatment

A new method for metalorganic chemical vapor deposition (MOCVD) of GaAs on Si substrates is developed. Instead of the usual high temperature surface cleaning treatment for Si substrate, the new method uses room temperature HF vapor polishing in the preparation chamber in the MOCVD system as the first step of the growth. Single crystal GaAs layers with mirror-like surfaces were obtained.