Beam magnification and the efficiency of optical trapping with 790-nm AlGaAs laser diodes

The efficiency of dielectric particle confinement with 790 nm AlGaAs laser diode optical traps is investigated as a function of beam magnification and polarization state. When an anamorphic prism pair is used to correct for diode beam ellipticity, trapping efficiencies of nearly 0.37 are achieved with a magnification factor of 3/spl times/, laser powers of 4-18 mW, and an overfilled microscope objective entrance aperture. Results are compared for diodes having small (8 /spl mu/m) and large (57 /spl mu/m) astigmatisms, but comparable far-field divergence angles. >