A method for generating a three-dimensional dark spot using a radially polarized beam

Abstract

A novel method is proposed for generating a three-dimensional dark spot surrounded uniformly and completely by light in all three dimensions. The superposition of a radially polarized beam with a circular π phase plate and the same radially polarized beam with a quadrant 0/π phase plate can yield a better three-dimensional dark spot. The coherent and incoherent superpositions of these two beams are demonstrated and discussed in detail and the new effective full width at half maximum (FWHM) of a super-resolution focal spot is discussed. Compared with some former results, the dark spot yielded by this proposed method proved to be more uniformly surrounded by light. Only one type of polarized beam is applied. It facilitates the process of finding a suitable polarization for the pump beam in a super-resolution fluorescent system. Axial resolution has a significant improvement.

Sharper fluorescent super-resolution spot generated by azimuthally polarized beam in STED microscopy

“…It's the same with STED beam. When polarization of STED beam is in the same direction with the excited fluorescent molecular orientation, the depletion effect is most obvious [12]. Therefore, if beam (1) alone is applied as STED beam, E x component of excited fluorescent molecules in X axis cannot be depleted by this STED beam.…”

“…The coherent superposition of beam (1) and beam (2) would lead to spot distortion. This phenomenon widely exists in the combination of different beams into one STED beam [12,19], and several methods to avoid the distortion, that is, generate incoherent superposition, were realized [8,12,20,21]. To achieve incoherent superposition, these two beams should be manipulated to work in temporal difference or spectral difference.…”

“…3D super-resolution is also realized by STED-4pi technology [3,9]. On the other hand, cylindrical vector beams receive more attention in STED microscopy recently, especially radially polarized beam and azimuthally polarized beam [10][11][12][13]. Applying radially polarized beam to total internal reflection (TIR) fluorescence in STED microscopy provides a way to achieve superresolution [10].…”

“…Applying radially polarized beam to total internal reflection (TIR) fluorescence in STED microscopy provides a way to achieve superresolution [10]. At the same time, 3D super-resolution spot can be generated by overlapping two beams as STED beam [12,13]. Most of these researches just used cylindrical vector beams as either pump beam [10,11] or STED beam [13], but rarely both pump beam and STED beam.…”

“…If the polarization direction of STED beam is in the same direction with the pumped fluorescent molecular orientation, the depletion effect will be most obvious. Using cylindrical vector beams of the same polarization as both STED beam and pump beam is gaining popularity for its strong depletion ability [12].…”