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 [1]. 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.