1. Introduction 2. Theoretical foundations 3. Propagation and focusing of optical fields 4. Spatial resolution and position accuracy 5. Nanoscale optical microscopy 6. Near-field optical probes 7. Probe-sample distance control 8. Light emission and optical interaction in nanoscale environments 9. Quantum emitters 10. Dipole emission near planar interfaces 11. Photonic crystals and resonators 12. Surface plasmons 13. Forces in confined fields 14. Fluctuation-induced phenomena 15. Theoretical methods in nano-optics Appendices Index.

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Principles of nano-optics

An overview of the recent developments in the field of cylindrical vector beams is
provided. As one class of spatially variant polarization, cylindrical vector beams
are the axially symmetric beam solution to the full vector electromagnetic wave
equation. These beams can be generated via different active and passive methods.
Techniques for manipulating these beams while maintaining the polarization symmetry
have also been developed. Their special polarization symmetry gives rise to unique
high-numerical-aperture focusing properties that find important applications in
nanoscale optical imaging and manipulation. The prospects for cylindrical vector
beams and their applications in other fields are also briefly discussed.

Cylindrical vector beams: from mathematical concepts to applications

Cylindrical-vector beams are of increasing recent interest for their role in novel laser resonators and their applications to electron acceleration and scanning microscopy. In this paper, we calculate cylindrical-vector fields, near the focal region of an aplanatic lens, and briefly discuss some applications. We show that, in the particular case of a tightly focused, radially polarized beam, the polarization shows large inhomogeneities in the focal region, while the azimuthally polarized beam is purely transverse even at very high numerical apertures.

Focusing of high numerical aperture cylindrical-vector beams.

Novel liquid-crystal devices are described that generate linearly polarized light with axial symmetry; the beam propagation axis is the symmetry axis. Such light fields can be characterized by a polarization order number P. For example, P = 1 fields represent radially or azimuthally polarized light. The reorientation of the polarization orientation in these polarization converters is due to the twisted nematic effect and the effect of lambda/2 wave plates. A single polarization converter can generate fields of orders 1 and 2. It is shown that one can in principle generate fields of any integral order P by cascading such elements. Devices that generate P = 1 fields are achromatic and can be used as polarization axis finders or as versatile tools for studying birefringent or polarizing materials.

Linearly polarized light with axial symmetry generated by liquid-crystal polarization converters

We present a robust interferometric method to generate arbitrary vector beam modes by diffracting a Gaussian laser beam from a spatial light modulator consisting of a high-resolution reflective nematic liquid crystal display. Vector beams may have the same intensity cross-section as the more common scalar Laguerre–Gaussian (LG) or Hermite–Gaussian (HG) beams, but with a spatially modulated polarization distribution. Special cases are the radially or azimuthally polarized 'doughnut' modes, which have superior focusing properties and promise novel applications in many fields, such as optical trapping, spectroscopy and super-resolution microscopy. Our system allows video rate switching between vector beam modes. We demonstrate the generation of high quality Hermite–Gaussian and Laguerre–Gaussian vector beam modes of different order, of vectorial anti-vortices, and of mode mixtures with interesting non-symmetric polarization distributions.

https://iopscience.iop.org/article/10.1088/1367-2630/9/3/078/pdf

Tailoring of arbitrary optical vector beams

Two interferometric techniques for converting a linearly polarized laser beam into a radially polarized beam with uniform azimuthal intensity are described. The techniques are based on the linear combination of orthogonally polarized beams, which have tailored intensity and phase profiles. Linearly polarized beams with intensity profiles tailored using a modified laser or an apodization filter are combined in separate experiments to produce radially polarized light. A beam with an extinction ratio of −21.7 dB and azimuthal intensity variations of less than ±12% is produced using the modified laser output. The second technique uses circularly polarized light and a unique spiral phase delay plate to produce the required phase profile. When focused, a radially polarized beam has a net longitudinal field useful for particle acceleration and, perhaps, other unique applications.

Generating radially polarized beams interferometrically.

This paper reports that a radially polarized laser beam is useful for applications such as laser particle acceleration. The issues of transporting and focusing (with an axicon) a radially polarized beam that was generated in the laboratory are examined. Problems of preserving the polarization while directing the beam are solved by using a compound 90-deg-fold out-of-plane pair of mirrors. When focused by an axicon, the radially polarized beam produces a diffraction-free Bessel beam. The transverse intensity distribution agrees with theory.

Transporting and focusing radially polarized laser beams

Time‐dependent electron density measurements of electron beam pumped XeCl laser mixtures (nonlasing) are performed using a CO2 (10.6 μm) quadrature interferometer. The electron beam pulse length is ≊500 ns (full width at half‐maximum) and delivers ≳10 A/cm2 at the foil. Electron densities are measured as a function of the halogen (HCl) and xenon concentration. For a 99.3% Ne/1.5% Xe/0.16% HCl mixture at 3000 Torr, the electron density peaks near the beginning of the pulse at ≊7×1014 cm−3, decreases to 3×1014 cm−3, then gradually increases to ≊6×1014 cm−3 at the end of the pulse. As the initial halogen concentration is reduced, the electron density increases, rising dramatically near the end of the pulse. This increase in the electron density later in the pulse is accompanied by a decrease of the XeCl* sidelight fluorescence.

Electron density measurements of electron beam pumped XeCl laser mixtures

A CO2 quadrature interferometer is used to measure the temporal evolution of the electron density in XeF and KrF electron‐beam‐pumped laser mixtures (nonlasing). Measurements are obtained using a 300‐kV electron beam which delivers ≳10 A/cm2 at the foil for pulse durations ≤650 ns (FWHM). For typical XeF mixtures (99.35% Ne/0.5% Xe/0.15% F2 at 2888 Torr) the electron density varies between 3 and 4.5×1014 cm−3 during the pulse. The electron density is found to increase as the initial F2 concentration is decreased. Both 10% Kr in argon diluent and argon‐free KrF mixtures are tested. The electron density for these mixtures has the same magnitude and behavior as the typical XeF mixture.

Electron density measurements of electron‐beam‐pumped XeF and KrF laser mixtures

The absorptance characteristics of bare silver aluminum, gold, copper, and molybdenum mirrors at angles of incidence from 0 to 89° are presented. The angle-dependent absorptance measurements are performed using a photoacoustic calorimetry technique. Absolute absorptance is determined using a laser energy ratiometer. Data are obtained for both s- and p-polarization light at two wavelengths, 0.5145 and 10.6 μm. It is found that the Fresnel theory for bare metal surfaces does not always reliably predict the measured absorptance at high angles of incidence.

Dennis H. Ford

Papers

Generating radially polarized beams interferometrically.

Transporting and focusing radially polarized laser beams

Electron density measurements of electron beam pumped XeCl laser mixtures

Electron density measurements of electron‐beam‐pumped XeF and KrF laser mixtures

Absorptance measurements of metal mirrors at glancing incidence.