Near-field Optical System Research Articles

Near-field optical systems for magnetooptical measurements

Near-field optical systems for magnetooptical measurements

Scanning near-field optical microscopy: transfer function and resolution limit

We present scanning near-field optical microscopy as an optical instrument characterized by a transfer function. This approach gives some theoretical guidelines for the design of near-field optical measurement systems. We emphasize that it is important to distinguish between the resolution for the optical field and the resolution for the object. In addition, to solve the general inverse diffraction problem the measurement of phase and amplitude of the electromagnetic field is necessary.

Heating mechanisms in a near-field optical system

A finite-difference-time-domain and two finite-difference-thermal models are used to study various heating mechanisms in a near-field optical system. It is shown that the dominant mechanism of sample heating occurs from optical power that is transferred from the probe to a metallic thin-film sample. The optical power is absorbed in the sample and converted to heat. The effects of thermal radiation from the probe 's coating and thermal conduction between the probe and the sample are found to be negligible. In a two-dimensional waveguide with TE polarization, most of the optical power is transferred directly from the aperture to the sample. In a two-dimensional waveguide with TM polarization, there is significant optical power transfer between the probe 's aluminum coating and the sample. The power transfer results in a wider thermal distribution with TM polarization than with TE polarization. Using computed temperature distributions in a Co -Pt film, we predict the relative size of thermally written marks in a three-dimensional geometry. The predicted mark size shows a 30 % asymmetry that is due to polarization effects.

Optical fiber structures studied by a tapping-mode scanning near-field optical microscope

A tapping-mode scanning near-field optical microscope system with a bent optical fiber probe has been successfully developed to study the near-field optics at fiber end faces. Topographic and near-field intensity images of fiber end faces were obtained simultaneously. A brief and gentle etching process on fiber end faces in a saturated solution of ammonium bifluoride was able to reveal the structures of fibers. The topographic features generated by different local chemistry is closely related to the local doping concentration and the distribution of refractive index. The correlation between fiber structures and their near-field intensity profiles of propagating modes can be acquired directly by this novel method. Fibers of step-index, graded-index, single-mode, multimode, and circular, or noncircular geometry were imaged with a near-field resolution.

Development of a near-field optical system for investigating thin organic films

We describe the development of combining a commercially available scanning near-field optical microscope (SNOM) with a high-optical-throughput spectrometer and a CCD camera for the purpose of investigating the optical properties of thin organic films at the nanometer-scale. The combined system is capable of obtaining either SNOM images or pixel-by-pixel near-field spectroscopy in either transmission or reflection mode. As an initial test sample, we used a thin film of poly(phenylene vinylene) and tris(8-hydroxy)quiisoline ahirainium to obtain both near-field optical transmission and fluorescence images as well as fluorescence spectra.

Linear behavior of a near-field optical scanning system

A hybrid finite-difference time-domain and angular-spectrum propagation modeling technique is used to study the imaging properties of a near-field optical scanning system with dielectric samples. The model is used to calculate system transfer functions based on scanning sinusoidal gratings of various spatial periods or on scanning a straight edge and then taking a derivative and a Fourier transform. Results from these two methods are in good agreement. A square-wave grating is simulated by linear addition of component sine-wave grating images that are weighted by the transfer function. The image generated by this method agrees well with an image generated by direct use of the hybrid model. In the region of parameter space investigated with the model, the near-field optical scanning system exhibits nearly linear behavior. The region of linear operation depends on the index of the sample and on the probe-to-sample spacing.