Did you know that liquid can make images sharper?

Did you know that liquid can make images sharper?

Did You Know…

…that Liquid Can Make Images Sharper?

A film of liquid between the objective lens and the specimen improves the resolution through a process known as immersion. The gap between the lens and the sample is filled with immersion oil, water, or glycerin, and this liquid allows more light to be captured from the object.

The physical principle behind this can be explained as follows: Air has a refractive index of 1,while the refractive index of the liquid between the specimen and the immersion objective is higher. The higher the refractive index, the smaller the angle of light diffraction pertaining to the specimen. This is why immersion microscopy helps capture more diffracted light. Since the diffracted light contains information about the specimen, more diffracted light means more information, thereby increasing the resolution. This principle was developed 200 years ago by Italian physicist Giovanni Amici, who produced the first immersion lens in 1804.

In 1873, Ernst Abbe realized that the optical imaging resolution of an optical system depends on its numerical aperture – and this in turn is directly dependent on the refractive index of the immersion liquid. Ever since then, ZEISS has been offering immersion microscopy to its customers. The German physician and microbiologist Robert Koch was one of the first to use this method. In addition to its microscopy applications, immersion is used in lithography for microprocessor production as well.

In traditional projection systems, there is an air gap between the last lens element and the surface of the wafer. Newer systems, in contrast, fill this gap with an immersion liquid that has a refractive index higher than that of air. This process permits more delicate structures to be produced for manufacturing microelectronic circuits.


30 November 2011

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