The optical microscope (also known as the light microscope) uses light with a system of lenses to generate magnified images. Optical microscopes can detect objects that are about half the wavelength of visible light.
Scientists can use the optical microscope to track proteins in fertilized eggs and see how nerve cells are connected to the brain. Now, scientists at the National Institute of Standards and Technology (NIST) have developed a way to enable these microscopes to make measurements to the nanometer with a higher degree of accuracy.
"We put the optical microscope under a microscope to achieve accuracy near the atomic scale," said NIST's Samuel Stavis, who served as the project leader for these efforts.
Optical microscopes haven’t been traditionally used for studying nanometer-scale particles because they don’t have the means to verify that a result is accurate at that scale. "Precision without accuracy can be very misleading," said Jon Geist, a NIST co-author of the study.
To address the inaccuracy issue, the NIST researchers developed a new calibration method that can correct imaging errors by using reference objects with well-known characteristics. Using this process means that there is the potential for mass production and distribution to laboratories. The team at NIST used a nanometer-scale fabrication process to develop the reference objects. They formed an array of pinhole apertures and spaced them 5,000 nanometers apart (within an accuracy of 1 nanometer) which built accuracy into the aperture positions.
The aperture arrays make it possible for individual researchers to perform calibrations in their labs and improve the accuracy of optical microscopes by a factor of 10,000. "We have identified and solved an underappreciated problem," said Craig Copeland, first study author. The results of the work done by Stavis and his associates is published in Light: Science & Applications.