High Resolution Interference Microscopy: 3D measurement of focused light at 405nm applied to optical disc
High capacity data storage on DVD and optical discs is based on focused light beams. The characterization of light fields within the focus point is a very difficult task, which requires a high-resolution method like scanning near field optical microscopy (SNOM). However, SNOM measurements are slow and cannot be used for dynamic processes. Therefore, we employ a measurement technique based on High Resolution Interference Microscopy (HRIM) to investigate focused light fields used for high-density optical storage. HRIM allows the characterization of amplitude and phase of electromagnetic wave-fields in the far-field with very high spatial accuracy. An experimental tool working in transmission with a resolution of 20nm in the object plane and a He Ne laser at wavelength of 633nm was presented in our previous work . Because the focused spot size in the optical disc is usually defined as ë/(2NA), high density optical data storage systems require a light source with shorter wavelength and a focusing objective lens with high numerical aperture (NA). In order to characterize the today’s optical storage systems, one has to work at 405nm wavelengths. We are building a micro-interferometric system, which employs a blue laser diode. Compared to previous measurements, we increased the resolution by using immersion techniques and high numerical aperture objectives.