Lasers can freeze water

Who knows when in the future, humans can "cool down" their bodies by shining their laser beams on themselves.

New uses of lasers

Since its first appearance in 1967, lasers have been known to be useful for cutting metal materials or as weapons. However, scientists at the University of Washington (USA) have discovered lasers in addition to being able to melt other objects, it can also freeze water.

Indeed, the research team succeeded in using infrared laser radiation to pull the water temperature below 36 degrees F (equivalent to about 2 degrees C). The explanation for this choice, Associate Professor Peter Pauzauskie - who oversees the study - said that using lasers within the visible spectrum would cause surface-level combustion. cells, one of the reasons for lasers to radiate heat.

The research team (from left) includes: Peter Pauzauskie, Xuezhe Zhou, Bennett Smith, Matthew Crane.

Peter Pauzauskie and his colleagues used a specially made transparent nanocrystalline tablet that emits green light if the temperature is lowered - like a color thermometer - placed in a water environment and tracks it. through electron microscopy. Then, Peter projected an infrared laser beam through this crystal, the result is a small blue light dot appears and the temperature of the crystal into the liquid area around it drops to 2 degrees. C.

Paden Roder, a member of the research team, said that the successful implementation of this experiment will open a new direction for research on the level of atoms and cells in hybrid. For example, humans can project a laser to cool a living cell to accurately monitor how the metabolism takes place. Or simply develop new beam- type cooling technologies instead of previous technologies.

The theory of laser cooling was in fact long since the German physicist Theodor Wolfgang Hänsch discovered after a series of experiments in the 1990s. Hänsch suggested that by projecting laser beams Atoms, a photon in the laser are responsible for touching atoms making it emit photons whose average energy is higher than the energy it absorbs from the laser. Later photons through thermal stimuli are converted into colored light and leave the atom. Photons leaving the atom will lose the atom's energy and cool down.

The blue light on the glass shows that the nanocrystals have cooled.

This can also be seen from the point of view of the law of conservation of momentum, when an atom is moved to a laser beam and a photon from a laser is absorbed by atoms, the momentum of the atom reduced by the amount of momentum the photon absorbs. The slow motion itself helps the atoms become cooler. In 1995, the Los Alamos National Laboratory in the United States conducted an experiment to prove this theory to be true in a vacuum. This helped Theodor Wolfgang Hänsch win the 2005 Nobel Prize in Physics.

Later, laser cooling was used primarily for quantum physics experiments to achieve temperatures near absolute zero (0 degrees K or minus 273.15 degrees Celsius, or minus 459.67. degree F). This method is carried out to observe only quantum effects that can only occur at this heat level. Basically, the laser cooling process is only used at the atomic level to cool particles to the Bose – Einstein condensate to study macroscopic quantum phenomena, but this process is being done on larger scales.

In 2007, a Massachuset Institute of Technology team successfully laser-cooled one gram of solids to 0.8 degrees K (about minus 272 degrees Celsius). By 2011, a research team from the California Institute of Technology and the University of Vienna became the first to perform laser cooling for a 10x1 micron solid. And the recent cooling of a nanocrystals and the liquid environment around it is really a remarkable breakthrough, although we still have to wait for experiments on larger tissue.