ABSTRACT
We investigate three-dimensional focus shaping generated from double-mode cylindrical vector beams with the Gaussian and Bessel-Gaussian pupil apodization functions by choosing the suitable polarization states of beams. Further, we compare them with that generated from the Laguerre-Gaussian pupil apodization function in the same situation. We find that the focus shaping generated from the Gaussian beam has the smallest zero intensity spot size. However, the situation of the Bessel-Gaussian beam not only possesses stability, which makes it suitable when applied in optical trapping, but also shows the best uniformity, which indicates its excellent performance in super-resolution fluorescence microscopy.
ABSTRACT
The focal electric fields for a 4π high numerical aperture (NA) focusing system with both the doughnut and higher-order Laguerre-Gaussian (LG) radially polarized (RP) beams are investigated in the case of NA=1, and the full width at half-maximum values of the focal spots are calculated. Compared with the single-lens high NA focusing configuration, a sharper spot, whose size is reduced efficiently in the transverse as well as the axial direction, can be formed. Such size reduction is attributed to not only the destruction interference of the longitudinal component caused by the π phase shift between any two adjacent rings of the incident higher-order LG RP beam coming from one particular direction but also the perfect destruction interference of the radial component formed by the two counter-propagating incident beams.
ABSTRACT
The first enantioselective synthesis of cytotoxic natural products rigidiusculamides A (ent-21) and B (8) has been achieved by two synthetic routes. The first one is convergent based on the common intermediate 11, obtained through a high yielding SmI(2) -mediated Reformatsky-type reaction. A highly diastereoselective one-pot Dess-Martin periodinane-mediated bis-oxidation allowed the direct conversion of the diastereomeric mixture of 11 into rigidiusculamide B (8). Isolation of minor diastereomer 21, in combination with computational work, allowed us to suggest the structure of the natural rigidiusculamide A to be ent-21, as synthesized by the second route. Four diastereomers (7, ent-7, 22a, and 22b) and an enantiomer (21) of rigidiusculamide A (ent-21) have been synthesized. On the basis of literature precedents and computational work, a biosynthetic pathway for rigidiusculamides A and B was proposed to account for the opposite configuration at C-5 of those two congeners.
