Observation of focal point shift in solid immersion mirror.

Area of Science:

• Optics and Photonics
• Nanotechnology
• Surface Science

Background:

• High numerical aperture (NA) objectives are crucial for sub-wavelength resolution in optical microscopy.
• Solid immersion mirrors (SIMs) offer a pathway to achieve high NA by altering the light path within a high refractive index medium.
• Controlling the focal point precisely is essential for advanced imaging and nanofabrication.

Purpose of the Study:

• To experimentally demonstrate and quantify the focal point shift in a solid immersion mirror integrated into a planar waveguide.
• To investigate the influence of surface metallization on the focal characteristics of the SIM.
• To determine the relationship between the focal shift, incident light wavelength, and geometrical focal point.

Main Methods:

• Utilizing a scanning near-field optical microscope (SNOM) to probe the focal field with high spatial resolution.
• Fabricating a solid immersion mirror with a two-dimensional parabolic reflective surface integrated within a planar waveguide.
• Performing optical measurements to precisely determine the position of the focal point for metallized and non-metallized surfaces.

Main Results:

• Experimental evidence of focal point shift along the optical axis in the solid immersion mirror.
• Observation that metallization of the reflective surface causes the focal point to shift inward.
• Quantification of the focal shift, found to be approximately one-fifth of the incident light's wavelength.

Conclusions:

• The focal point of a high-NA solid immersion mirror can be controllably shifted inward by surface metallization.
• The observed focal shift is dependent on the incident light wavelength, providing a tunable optical characteristic.
• This controlled focal shift offers potential for enhanced optical resolution and novel applications in near-field optics.