Juli 29, 2009
Physicists at New York University (NYU), US have developed a technique to record three-dimensional movies of microscopic systems, such as biological molecules, through holographic video. The technique, developed in the laboratory of NYU Physics Professor David Grier, is comprised of two components: making and recording the images of microscopic systems and then analyzing these images. To generate and record images, the researchers created a holographic microscope. It is based on a conventional light microscope, which uses a collimated laser beam instead of on an incandescent illuminator.
When an object is placed into path of the microscope’s beam, the object scatters some of the beam’s light into a complex diffraction pattern. The scattered light overlaps with the original beam to create an interference pattern reminiscent of overlapping ripples in a pool of water. The microscope then magnifies the resulting pattern of light and dark and records it with a conventional digital video recorder. Each snapshot in the resulting video stream is a hologram of the original object. Unlike a conventional photograph, each holographic snapshot stores information about the three-dimensional structure and composition of the object that created the scattered light field. The recorded holograms appear as a pattern of concentric light and dark rings.
For analyzing the images the researchers based their work on a quantitative theory, the Lorenz-Mie theory, which maintains that the way light is scattered can reveal the size and composition of the object that is scattering it.
The application of the technique ranges from research in fundamental statistical physics to analyzing the composition of fat droplets in milk.
In the microscope, a laser beam illuminates the sample. Light scattered by the sample creates an interference pattern which is magnified and recorded. Then measurements of the particle’s position, size, and refractive index are obtained.
April 29, 2009
A new imaging method that could help to build more powerful microscopes and other optical devices by producing sharper images and a wider field of view has been developed by Princeton researches. The research was led by Jason Fleischer, assistant professor of electrical engineering and co-written with two graduate students Christopher Barsi and Wenjie Wan. The new method takes advantage of the unusual properties of nonlinear optical materials in which light rays mix with each other in complex ways. Thanks to the mixing of rays, information that would otherwise be lost manages to reach the detector. Therefore this picture would be rich in detail but it would also be distorted. To capture this otherwise lost visual information, the researchers used a hologram. The hologram is a special type of photograph which records „phase“ – a light property which measures the time and location of a wave peak. They also combined data from a normal camera. Then they created a simplified flow of light through a nonlinear material and developed a computer algorithm that takes the distorted image and works backwards to calculate the visual information at every point in space between the image and the object.
An object illuminated by light reflects rays in many different directions (gray arrows). Left: With a normal lens, some rays are captured and refract towards a camera while others are missed, resulting in a blurry image with a limited field of view. Right: The new method uses a nonlinear material. The original rays are altered and new rays (red) are generated. The resulting picture is scrambled, but a computer algorithm can undo the mixing and yield a sharp, wide-field image. (Image: Christopher Barsi)