in new paper Published in today's magazine opticaphysicists explain how a laser beam casts a shadow that behaves like any other ordinary shadow.
Photographic image of the shadow of a laser beam. A high-powered green laser beam (object) passes through a ruby ​​cube and is illuminated from the side with blue light: (A) Photograph of the shadow cast by the object laser beam on a white piece of paper, imaged through a simple lens It will be magnified approximately 4 times using The length of the ruby ​​cube is approximately 1.2cm, and the enlarged image is approximately 4.8cm. Therefore, whether magnified or not, it depicts what can be seen directly. (B) Photographic image showing the surroundings for scale reference. Place a white plastic marker (i.e., a wide-tipped pen) in the path of the shadow between the object beam and the paper, and fix the camera focus on the (C) paper or (D) marker. The appearance of a shadow along the contours of the surface it falls on. All images were taken with a regular home digital camera in a dark room. Image credit: Abrahao others., doi: 10.1364/optica.534596.
“Laser light that casts shadows was previously thought to be impossible because light typically passes through other light without interacting,” said Dr. Rafael Abrahao, a researcher at Brookhaven National Laboratory. spoke.
“Demonstration of a highly counterintuitive optical effect prompts us to reconsider our concept of shadow.”
Dr. Abrahao and his colleagues used a ruby ​​crystal and a specific laser wavelength to show that laser beams can block light and create visible shadows through nonlinear optical processes.
This effect occurs when light interacts with a material in an intensity-dependent manner and can affect another light field.
“Our understanding of shadows has developed in close connection with our understanding of light and optics,” Dr. Abrahao said.
“This new discovery could prove useful in a variety of applications, including optical switching, devices in which one light controls the presence of another, or technologies that require precise control of light transmission, such as high-power lasers. There is a possibility that
In their experiment, the researchers shined a high-power green laser onto a cube made of a standard ruby ​​crystal, then shot a blue laser at it from the side.
When a green laser is incident on a ruby, it locally changes the material's response to blue wavelengths.
The green laser acts like a normal object, and the blue laser acts like a light.
The interaction between the two light sources creates a shadow on the screen, where the green laser appears as a dark area blocking the blue light.
It met all the criteria for a shadow, as it was visible to the naked eye, followed the contours of the surface it fell on, and followed the position and shape of the laser beam acting as the object.
The laser shadow effect is the result of ruby's optical nonlinear absorption.
This effect occurs because the green laser increases the light absorption of the blue illumination laser beam, creating a matching region within the illumination light with lower light intensity.
“This discovery expands our understanding of the interaction between light and matter and opens up new possibilities for harnessing light in previously unimagined ways,” Dr. Abrahao said.
The researchers experimentally measured that the shadow contrast depends on the power of the laser beam and found that the maximum contrast was about 22%, similar to the contrast of a tree's shadow on a sunny day.
They also developed a theoretical model and showed that it could accurately predict shadow contrast.
“From a technical point of view, the effect we demonstrated shows that the intensity of the transmitted laser beam can be controlled by firing another laser,” the scientists said.
“Next, we plan to investigate other materials and other laser wavelengths that can produce similar effects.”
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Raphael A. Abrahao others. 2024. Shadow of laser beam. optica 11 (11): 1549-1555;doi: 10.1364/optica.534596
Source: www.sci.news
