Experimental and theoretical investigation on the misalignment tolerance of a micron-sized solid immersion lens tolerance of a micron-sized solid immersion lens

We report an experimental and theoretical study on the alignment error tolerance of a 2 µm-size solid immersion lens (SIL) illuminated by different types of focused spots. Tightly confined focal spots are of great interest for improving the performance of many optical systems, so that a study on the alignment tolerance is of interest. In particular, it was found that micro-SILs can be largely misaligned with respect to the optical axis of an objective lens focusing light onto it and yet allow for a reasonably good immersed spot. In fact, a displacement of approximately 400 nm, i.e. one fifth of the lens diameter, is tolerable. The measurements are compared with a rigorous finite element method model for a micro-SIL, showing an excellent agreemen

Submicron hollow spot generation by solid immersion lens and structured illumination

We report on the experimental and numerical demonstration of immersed submicron-size hollow focused spots, generated by structuring the polarization state of an incident light beam impinging on a micro-size solid immersion lens (μ-SIL) made of SiO2. Such structured focal spots are characterized by a doughnut-shaped intensity distribution, whose central dark region is of great interest for optical trapping of nano-size particles, super-resolution microscopy and lithography. In this work, we have used a high-resolution interference microscopy technique to measure the structured immersed focal spots, whose dimensions were found to be significantly reduced due to the immersion effect of the μ-SIL. In particular, a reduction of 37% of the dark central region was verified. The measurements were compared with a rigorous finite element method model for the μ-SIL, revealing excellent agreement between them

Scalar Readout Model for Super-Rens Focused Spot

A scalar readout model is presented to investigate the readout characteristics of the super resolution near field (SRens) disc. The super resolution effect is described by means of a threshold model, where the super resolution material imparts a phase change on the focused spot if the laser density energy is high enough to trigger the SRens effect. This approach results in a very fast way of computing the basic characteristics of the SRens readout signal, being suitable for large investigations. Moreover, many simulation results have been experimentally confirmed by other groups, which further validates the model. Thus, this simplified model is an useful tool for a better comprehension of the readout signal of the super resolution effect in optical data storage and other super resolution applications

Phase anomalies in Bessel-Gauss beams

Bessel-Gauss beams are known as non-diffracting beams. They can be obtained by focusing an annularly shaped collimated laser beam. Here, we report for the first time on the direct measurement of the phase evolution of such beams by relying on longitudinal-differential interferometry. We found that the characteristics of Bessel-Gauss beams cause a continuously increasing phase anomaly in the spatial domain where such beams do not diverge, i.e. there is a larger phase advance of the beam when compared to a referential plane wave. Simulations are in excellent agreement with measurements. We also provide an analytical treatment of the problem that matches both experimental and numerical results and provides an intuitive explanation.IST/Imaging Science and TechnologyApplied Science

Longitudinal-differential phase distribution near the focus of a high numerical aperture lens: Study of wavefront spacing and Gouy phase

We present a longitudinal-differential (LD) phase distribution near the focus of a high numerical aperture (NA=0.9) aplanatic lens illuminated with a linearly polarized monochromatic plane wave. The Richards and Wolf method is used to compute field distributions. The LD phase map is obtained by analyzing the deviation of the phase of the simulated wave to the phase of a referential plane wave. We discuss the irregular wavefront spacing that is linked to the Guoy phase and disclose subtle details of the phase features with respect to the spatial domain relative to the focal point. The LD phase is used to revisit different definitions of the focal region. We eventually identify the definition that is in agreement with the Gouy phase in the focal region. Our work paves the way towards a coherent notion to quantify the optical action of high NA optical elements that are increasingly important for many applications

Image formation properties and inverse imaging problem in aperture based scanning near field optical microscopy

Aperture based scanning near field optical microscopes are important instruments to study light at the nanoscale and to understand the optical functionality of photonic nanostructures. In general, a detected image is affected by both the transverse electric and magnetic field components of light. The discrimination of the individual field components is challenging as these four field components are contained within two signals in the case of a polarization resolved measurement. Here, we develop a methodology to solve the inverse imaging problem and to retrieve the vectorial field components from polarization and phase resolved measurements. Our methodology relies on the discussion of the image formation process in aperture based scanning near field optical microscopes. On this basis, we are also able to explain how the relative contributions of the electric and magnetic field components within detected images depend on the chosen probe. We can therefore also describe the influence of geometrical and material parameters of individual probes within the image formation process. This allows probes to be designed that are primarily sensitive either to the electric or magnetic field components of light.ImPhys/Optic