Researchers from the Shandong University in China and the U.S. National Institute of Standards and Technology (NIST) have discovered a manufacturing method that could address longstanding problems in producing crystals necessary for lasers.
In a study published in the journal Science Advances, the researchers suggest that the large crystals used in changing light properties in lasers can instead be made by stacking up smaller, rod-shaped microcrystals, which can be grown cheaply and easily.
So far, the microcrystals the researchers developed were able to perform better than conventional crystals in certain aspects, opening up the possibility that the search for an economical and fast way to produce crystals on a large scale has come to an end.
However, it's not clear exactly how the microcrystals were able to outperform the usual crystals because according to conventional science, they shouldn't be able to.
Commonly, the crystal that changes laser light's properties is made of potassium diphosphate (KDP). Aside from changing laser light color, however, KDP crystals can also function like a switch that changes the direction in which a light's electric field is vibrating or that keeps laser light from passing through until the right time.
Small KDP crystals are a breeze to produce. It's when crystals for higher-energy applications are needed that the trouble begins. Scientists have long searched for a way to create large-sized, high-quality crystals that can withstand repeated exposure to the intense pulses of laser but a solution has not been found.
The researchers have discovered that KDP microcrystals may be grown in a solution, where they will take the form of hexagonal tubes just a few millimeters wide, long and hollow.
They also suggest that the microcrystal rods may be stacked together like firewood, creating a larger piece with billions of tiny filaments. These microcrystal rods can also be coated to keep heat at bay, making it possible for them to easily handle repeated pulses of laser light.
According to conventional models of physics, an optical medium like crystals should not be symmetric at the center to ensure efficient energy conversion. However, KDP microcrystals are breaking this rule.
The researchers talked to experts from various fields but no one has been able to explain the mechanism behind the growth of the KDP microcrystals.
"It's challenging our current understanding in fields from crystallography to condensed matter," said Lu Deng, a physicist from NIST and one of the authors of the study.
The researchers are now capable of growing more than 1,000 microstructures on one glass slide every 10 minutes or so. What they are gearing up to figure out next is how to grow the microcrystals on a large scale while retaining nearly uniform cross-sections in each, as this will be crucial during assembly.
Deng is joined by Yan Ren, Edward W. Hagley and Xian Zhao in the study.
