Masaru Muranishi

Control of Aperture Size of Optical Probes for Scanning Near-Field Optical Microscopy Using Focused Ion Beam Technology

We propose a fabrication technique for apertures of optical probes for scanning near-field optical microscopy (SNOM) using a focused ion beam (FIB) process. We tried two FIB processes, FIB drilling and FIB slicing. The FIB slicing technique is very useful for fabrication of nm-sized SNOM apertures of less than 50 nm. The problem with the FIB drilling process is that it is difficult to identify the apex of the tip and to control the beam onto the apex. The FIB slicing technique can easily fabricate an aperture at an apex and control aperture size by cut-off-depth. It is easy for a sharp tip to obtain accurate size of aperture. It can be considered to obtain accurate size of aperture with fabricated error of 35 nm in a sharp tip with cone angle of 30 deg.

A Cavity-SNOM (Scanning Near-field Optical Microscopy) Head Using a Laser Diode

A cavity-SNOM (scanning near-field optical microscope) head using a laser diode is proposed and studied theoretically and experimentally. Theoretically, we study the optical properties using conventional rate equations. Several conditions to detect the SNOM signal with a photodiode are discussed. Experimentally, the dependence of output power of the laser diode on the injection current is measured. A sufficiently strong modulation signal is detected using a tapered fiber as the probe, but no modulation signal is detected using a tapered fiber with a small aperture (SNOM probe). The conditions for detecting a signal using a SNOM probe are also discussed, and we suggest that a laser diode with a SNOM probe fabricated on its facet is essential for realizing a practical cavity-SNOM head.