利用螺旋极化光束调整高数值孔径镜头的聚焦场

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"调谐高数值孔径镜头聚焦场的螺旋极化光束(特邀论文)" 在光学和纳米技术领域，高数值孔径（NA）镜头的使用已经成为了研究和实验的关键工具，因为它们能够实现微小空间内的精细聚焦。本文"调谐高数值孔径镜头聚焦场的螺旋极化光束"深入探讨了如何通过使用螺旋极化甜甜圈光束来调整这些高NA镜头聚焦点的电磁场分布。这种方法的创新之处在于，只需要简单地调整激发路径中的λ/2延迟波片，就能创造出不同的极化状态和场分布。螺旋极化光束，也称为旋光或涡旋光束，是一种具有内禀角动量的特殊光束，其光场强度呈环状分布，中心为零强度区域，即所谓的“甜甜圈”模式。这种光束的独特性质使得它们在纳米技术研究和生物医学实验中具有广泛的应用潜力。例如，它们可以用于操控微小粒子、精确控制光镊系统，甚至在量子信息处理中作为信息载体。文章指出，通过改变λ/2延迟波片的角度，可以改变入射光的偏振状态，从而改变通过高NA镜头后的聚焦场的性质。λ/2波片的作用是将线性偏振光转换为圆偏振光或者椭圆偏振光，而这些不同类型的偏振光在经过高NA镜头时会产生不同的聚焦模式。这种调谐能力对于那些需要精确控制光场分布的实验至关重要，如在活细胞成像、纳米材料的操纵和制造，以及单分子检测等应用。此外，作者还讨论了相关的光学代码，如180.1790、170.6900、260.5430和250.5603，这些代码代表了光学领域的特定主题，涵盖了光学信息科学、表面和界面光学以及非线性光学等多个方面，表明该研究涉及的范围广泛，具有多学科交叉的特点。这篇论文揭示了螺旋极化光束在调谐高NA镜头聚焦场中的巨大潜力，提供了一种灵活且实用的工具，对于推动光学技术的发展和解决实际问题具有重要意义。通过这种简单而有效的方法，研究人员可以更精确地控制光束与物质相互作用的微观过程，从而在纳米技术和生物医学领域打开新的研究方向。

Tuning the fields focused by a high NA lens

using spirally polarized beams

(Invited Paper)

F. Wackenhut

, B. Zobiak

, A. J. Meixner

, and A. V. Failla

1,2,

Eberhard Karls University Tübingen, Institute of Physical and Theoretical Chemistry, Tübingen 72076, Germany

University Medical Center Hamburg-Eppendorf, UKE Microscopy Imaging Facility, Hamburg 20246, Germany

*Corresponding author: a.failla@uke.de

Received January 18, 2017; accepted February 10, 2017; posted online March 6, 2017

We show the power of spirally polarized doughnut beams as a tool for tuning the field distribution in the focus of

a high numerical aperture (NA) lens. Different and relevant states of polarization as well as field distributions

can be created by the simple turning of a λ∕2 retardation wave plate placed in the excitation path of a micro-

scope. The realization of such a versatile excitation source can provide an essential tool for nanotechnology

investigations and biomedical experiments.

OCIS codes: 180.1790, 170.6900, 260.5430, 250.5603.

doi: 10.3788/COL201715.030013.

In the last two decades, enormous progress has been

achieved in the fields of light microscopy, nanoscopy, and,

in more general terms, nanotechnology. Super-resolution,

far-, and near-field microscopy made the visualization

of nano-objects possible with an optical resolution of

about 10 nm. These revolutionary improvements allowed

researchers to make important steps forward in many

fields, e.g., nanotechnology and biology, see Refs. [

1,2]. In

parallel, the exploitation of anisotropic polarized excita-

tion sources like radially/azimuthally polarized doughnut

beams (R/APDBs) have been essential, e.g., for increasing

the excitation and detection efficiency in near-field tip-en-

hanced microscopy

[3,4]

, revealing the orientation, shape,

and structure of strongly polarized nanostructures

[5–8]

,or

increasing the ability to disclose the organization of colla-

gen domains in animal and human skin

[9]

. These and other

prominent studies have relied on sophisticated and ingen-

iously made light sources integrated into self-build micro-

scopes. In many cases, a single and unique device was

designed for only one special application. In the present

days, however, the standardization and integration in

easily accessible and flexible setups of highly sophisticated

imaging approaches is a necessary prerequisite for further

scientific progress. Especially for the development of bio-

oriented nanotechnologies, microscopes are required to be

provided with multiple and tuneable light source s. In this

Letter, we show how a source of variable spirally polarized

doughnut beams (SPDBs) can fulfill these requirements.

SPDBs form a family of anisotropically polarized fields,

i.e., the polarization varies point by point, but is linear

at any individual point. Relevantly, RPDBs/APDBs

are special cases of SPDBs

[10,11]

. A practical way to realize

SPDBs is presented in Fig.

1. It makes use of two mode

converters (MCs). First, an RPDB is realized using a

liquid crystal MC (LQMC) according to the procedure de-

scribed in Ref. [

12]. Second, the polarization of the RPDB

is uniformly rotated by angle β using a series of two λ ∕2

retardation wave plates, where one is fixed while the other

is free to rotate

[13]

. Please note that the rotation of the sec-

ond λ∕2 retardation wave plate (labeled as WP2 in Fig.

permits to change β.

Since the RPDBs and APDBs are an orthogonal set of

beams, they can be used to describe the field E

SPDB

of a

generic SPDB in the following way:

SPDB

¼ E

APDB

sin γ þ E

RPDB

cos γ; (1)

where γ ¼ 2β (with respect to Fig.

1) is a fixed rotation

angle, and E

ðRPDB∕APDBÞ

is the field distribution of an

Fig. 1. Passing through two MCs, a linearly polarized Gaussian

beam is turned into an SPDB. MC1 is used to produce an RPDB.

MC1 is composed of an LQMC and a spatial filter produced by

two confocal lenses (L

1∕2

) with a properly sized pinhole (PH) in

between. MC2 turns an RPDB into an SPDB by employing two

λ∕2 retardation wave plates (WP

1∕2

), one fixed and the other

variable in order to change the angle β.

COL 15(3), 030013(2017) CHINESE OPTICS LETTERS March 10, 2017

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