International audienceMetal-coated dielectric tetrahedral tips (T-tip) have long been considered to be interesting structures for the confinement of light to nanoscopic dimensions, and in particular as probes for scanning near-field optical microscopy. Numerical investigations using the Finite-Difference Time-Domain (FDTD) method are used to explore the operation of a T-tip in extraction mode. A dipole source in close proximity to the apex excites the tip, revealing the field evolution in the tip, the resulting edge and face modes on the metal-coated surfaces, and the coupling from these modes into highly directional radiation into the dielectric interior of the tip. These results are the starting point for illumination-mode numerical investigations by a Volume Integral equation method, which compute the field distribution that develops in a T-tip when a Gaussian beam is incident into the tip, and which show that a highly confined electric field is produced at the apex of the tip. The process of light confinement can be considered as a superfocussing effect, because the intensity of the tightly confined light spot is significantly higher than that of the focussed yet much wider incident beam. The mechanism of superfocussing can be considered as a dimensional reduction of surface plasmon modes, where an edge plasmon is the most important link between the waveguide-modes inside the tip and the confined near field at the ape

Complementary to industrial cantilever based force sensors in scanning probe microscopy (SPM), symmetrical quartz crystal resonators (QCRs), e.g., tuning fork, trident tuning fork, and needle quartz sensors, are of great interest. A self-excitation scheme with QCR is particularly promising and allows the development of cheap SPM heads with excellent characteristics. We have developed a high performance electronic interface based on an amplitude controlled oscillator and a phase-locked loop frequency demodulator applicable for QCR with frequencies from 10 up to 10MHz. The oscillation amplitude of the sensing tip can be set from thermal noise level up to amplitudes of a tenth of nanometers. The device is small, cheap, and highly sensitive in amplitude and frequency measurements. Important features of the design are grounded QCR, parasitic capacity compensation, bridge schematic, and high temperature stability. Characteristic experimental data of the device and its operation in combination with a commercial SPM and a homemade scanning near-field optical microscope are reported. By using the 1MHz needle quartz resonator with a standard atomic force microscope tip attached, atomic scale resolution in ambient conditions is achieved. Furthermore, reproducible measurements on very soft materials (Langmuir-Blodgett layers) with a very stiff needle quartz (∼400000N∕m) are possible.

Heat assisted magnetic recording (HAMR) requires a sufficiently small heat spot, which is much below the diffraction limit of the wavelength of the used light. This can be achieved with an optical near field source consisting of a small metallic wedge which supports edge plasmons. The power transfer between a dielectric rectangular waveguide and this metallic wedge is investigated in simulations and experiments. Beating of two eigenmodes of this system leads to power oscillations between the waveguide core and the edge plasmon along their overlap length. This was confirmed in near field experiments which are based on the evaporation of phase change material with the absorbed optical near fields as heat source. Devices with weak and strong edge plasmon excitation could be clearly distinguished in a simple far field experiment.

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We developed three home-made modeling programs to design thermally assisted magnetic recording heads: optical beam propagation method for waveguides, optical finite difference time domain method for plasmon generators, and thermal/micromagnetic finite difference method for the recording media. These models lead to the following results. To get higher throughput efficiency of the waveguide, the periodic wavy thickness of the inlet can provide better inlet coupling with laser diode light, and the wavy taper shape can improve the propagation efficiency. As for plasmon generators, the model requires waveguide, recording media and main-pole to estimate the correct performance, because the optimized design depends on all of these parts. Our proposed sharp pointed plasmon generator can provide tiny near field spot, and it must have good scalability for narrow track recording. In addition to these optics models, we performed recording process simulation. As a result, depending on the condition of the thermal spot and head field alignment, either thermal or magnetic field can be dominant in creating the final magnetic transition in the media. The signal to noise ratio and the transition curvature are greatly affected by the recording process.