華盛頓大學(xué)用激光制冷液體
2018-6-26 10:12:16??????點(diǎn)擊：
中國科技網(wǎng)11月17日報道（張微 編譯）自1960年激光發(fā)明以來(lái)，它們總是發(fā)出熱量，或者作為一個(gè)用途廣泛的工具，一種副產(chǎn)品，也經(jīng)常以一種虛構的方式被用來(lái)征服銀河系的敵人。
但是這些激光束卻從來(lái)沒(méi)有用來(lái)冷卻液體。華盛頓大學(xué)的研究人員首次解決了這個(gè)存在了幾十年的難題，他們在現實(shí)條件下，實(shí)現了用激光冷卻水和其它液體。
這一研究成果發(fā)表于11月16日出版的《美國國家科學(xué)院院刊上》，該團隊利用紅外激光將水冷卻到36華氏度，這是該領(lǐng)域的一項重大突破。
“如果你看過(guò)電影星球大戰，就會(huì )知道電影里面的激光炮能夠使物體升溫。而這一次，是首次利用激光束在日常條件下冷卻像水這樣的液體，” 這篇論文的主要作者，也是華盛頓大學(xué)材料科學(xué)與工程專(zhuān)業(yè)助理教授Peter Pauzauskie說(shuō)?！斑@種做法是否能夠成功，確實(shí)是一個(gè)懸而未決的問(wèn)題，因為我們都知道，水被光束照亮，就會(huì )變暖?！?/span>
這個(gè)發(fā)現能夠幫助工業(yè)領(lǐng)域，利用集中光束在一個(gè)微小的面積里實(shí)現“點(diǎn)冷”操作。舉個(gè)微處理器的例子，可能會(huì )有那么一天，使用激光束來(lái)冷卻計算機芯片中的特定部件，以防止過(guò)熱，這樣也能讓信息處理的效率更高。
科學(xué)家們也能利用激光束，在細胞分裂或自我修復時(shí)，通過(guò)精確地冷卻細胞的一部分，減緩它們的分裂和自我修復過(guò)程，從而讓研究人員有機會(huì )了解細胞是如何工作的。也可以在神經(jīng)網(wǎng)絡(luò )中單獨冷卻一個(gè)神經(jīng)元——只是讓這個(gè)神經(jīng)元不再活躍，并沒(méi)有損害它——通過(guò)這種方式來(lái)了解附近的神經(jīng)元如何繞過(guò)它以及實(shí)現自我修復。
“對于細胞如何分裂，分子和酶如何實(shí)現它們的功能，還有許多令人感興趣的方面，但在以往卻沒(méi)有辦法做到通過(guò)冷卻的方式來(lái)研究它們的特性，” Pauzauskie說(shuō)，他也是來(lái)自華盛頓州里奇蘭，美國能源部的太平洋西北國家實(shí)驗室的科學(xué)家?！袄眉す饫鋮s，有點(diǎn)像將電影中的生命的活動(dòng)過(guò)程進(jìn)行慢動(dòng)作展示，優(yōu)點(diǎn)是，你不需要冷卻整個(gè)細胞，如果冷卻整個(gè)細胞就會(huì )殺死它或改變它的行為?！?/span>
華盛頓大學(xué)的研究團隊選用紅外光作為冷卻激光，實(shí)現在生物學(xué)領(lǐng)域的應用，因為可見(jiàn)光會(huì )對細胞有破壞作用，能夠將它們“曬傷”。他們證實(shí)激光也能冷卻鹽水和細胞培養基(在遺傳和分子研究領(lǐng)域常用)。
為了實(shí)現這項突破，華盛頓大學(xué)研究團隊使用了商業(yè)激光領(lǐng)域常見(jiàn)的一種材料，但本質(zhì)上卻與激光現象相反。他們用紅外激光照射一個(gè)懸浮在水中的微小晶體，激發(fā)出一種獨特的光線(xiàn)，這個(gè)光線(xiàn)的能量比光吸收的能量要稍微多一點(diǎn)。
這種高能光從晶體和包圍著(zhù)它的水中帶走了熱量。首次激光冷卻過(guò)程是1995年美國洛斯阿拉莫斯國家實(shí)驗室在真空條件下實(shí)現的，近20年后在液體中，再次實(shí)現了這個(gè)過(guò)程。
通常情況下，激光晶體的生長(cháng)是一個(gè)昂貴的過(guò)程，需要花費大量的時(shí)間和美元，只能生產(chǎn)僅僅一克材料。華盛頓大學(xué)的研究團隊還發(fā)明了一個(gè)低成本的水熱方法，可用于制造著(zhù)名的激光晶體，以更加快捷、低成本和可擴展的方式實(shí)現激光冷卻應用。
華盛頓大學(xué)的研究團隊還設計了一種儀器，使用激光阱(類(lèi)似于微牽引光束)，將一個(gè)侵入液體中的納米晶體“困在”液體室里，并用激光照射它。為了確定液體是否冷卻，這個(gè)儀器能夠投射粒子的“影子”，通過(guò)這種方式研究人員能夠觀(guān)察它運動(dòng)過(guò)程中每分每秒的變化。
當周?chē)囊后w變冷時(shí)，被困住的顆粒就會(huì )慢下來(lái)，從而讓研究團隊清楚地觀(guān)察冷卻效果。他們還設計了一種晶體，當冷卻時(shí)能夠實(shí)現從藍綠到泛紅的顏色變化，就像一個(gè)內置的彩色溫度計。
“這個(gè)項目的真正挑戰是建造一個(gè)儀器，以及設計一種方法，利用與困住晶體相同光線(xiàn)的特征，也能夠確定這些納米晶體的溫度，”論文的主要作者派登 羅德說(shuō)，他剛剛獲得威斯康辛大學(xué)材料科學(xué)與工程專(zhuān)業(yè)博士學(xué)位，目前在英特爾工作。
到目前為止，華盛頓大學(xué)的研究團隊僅僅展示了單一納米晶體的冷卻效果，而激發(fā)多個(gè)晶體需要更多的激光能。激光冷卻過(guò)程目前比較耗能，Pauzauskie說(shuō)，下一步的研究包括尋找提高效率的方法。
有一天，冷卻技術(shù)本身也可以通過(guò)高功率激光，用來(lái)實(shí)現制造、電信或國防領(lǐng)域應用，而目前高功率激光往往容易過(guò)熱以及將物體融化。
“因為利用激光冷卻液體之前是不可能做到的，所有現在人們不會(huì )一下子就想到如何利用這項技術(shù)來(lái)解決問(wèn)題，”他說(shuō)?！拔覀兙透信d趣的是，我們的研究對其他科學(xué)家或企業(yè)的想法產(chǎn)生何種影響，會(huì )不會(huì )影響他們的基礎研究或底線(xiàn)，讓他們不再墨守成規或固執己見(jiàn)?！?/span>
英文原文：
Research team refrigerates liquids with a laser for the first time
Since the first laser was invented in 1960, they've always given off heat—either as a useful tool, a byproduct or a fictional way to vanquish intergalactic enemies.
But those concentrated beams of light have never been able to cool liquids. University of Washington researchers are the first to solve a decades-old puzzle—figuring out how to make a laser refrigerate water and other liquids under real-world conditions.
In a study to be published the week of Nov. 16 in the Proceedings of the National Academy of Sciences, the team used an infrared laser to cool water by about 36 degrees Fahrenheit—a major breakthrough in the field.
"Typically, when you go to the movies and see Star Wars laser blasters, they heat things up. This is the first example of a laser beam that will refrigerate liquids like water under everyday conditions," said senior author Peter Pauzauskie, UW assistant professor of materials science and engineering. "It was really an open question as to whether this could be done because normally water warms when illuminated."
The discovery could help industrial users "point cool" tiny areas with a focused point of light. Microprocessors, for instance, might someday use a laser beam to cool specific components in computer chips to prevent overheating and enable more efficient information processing.
Scientists could also use a laser beam to precisely cool a portion of a cell as it divides or repairs itself, essentially slowing these rapid processes down and giving researchers the opportunity to see how they work. Or they could cool a single neuron in a network—essentially silencing without damaging it—to see how its neighbors bypass it and rewire themselves.
"There's a lot of interest in how cells divide and how molecules and enzymes function, and it's never been possible before to refrigerate them to study their properties," said Pauzauskie, who is also a scientist at the U.S. Department of Energy's Pacific Northwest National Laboratory in Richland, Washington. "Using laser cooling, it may be possible to prepare slow-motion movies of life in action. And the advantage is that you don't have to cool the entire cell, which could kill it or change its behavior."
The UW team chose infrared light for its cooling laser with biological applications in mind, as visible light could give cells a damaging "sunburn." They demonstrated that the laser could refrigerate saline solution and cell culture media that are commonly used in genetic and molecular research.
To achieve the breakthrough, the UW team used a material commonly found in commercial lasers but essentially ran the laser phenomenon in reverse. They illuminated a single microscopic crystal suspended in water with infrared laser light to excite a unique kind of glow that has slightly more energy than that amount of light absorbed.
This higher-energy glow carries heat away from both the crystal and the water surrounding it. The laser refrigeration process was first demonstrated in vacuum conditions at Los Alamos National Laboratory in 1995, but it has taken nearly 20 years to demonstrate this process in liquids.
Typically, growing laser crystals is an expensive process that requires lots of time and can cost thousands of dollars to produce just a single gram of material. The UW team also demonstrated that a low-cost hydrothermal process can be used to manufacture a well-known laser crystal for laser refrigeration applications in a faster, inexpensive and scalable way.
The UW team also designed an instrument that uses a laser trap—akin to a microscopic tractor beam—to "hold" a single nanocrystal surrounded by liquid in a chamber and illuminate it with the laser. To determine whether the liquid is cooling, the instrument also projects the particle's "shadow" in a way that allows the researchers to observe minute changes in its motion.
As the surrounding liquid cools, the trapped particle slows down, allowing the team to clearly observe the refrigerating effect. They also designed the crystal to change from a blueish-green to a reddish-green color as it cools, like a built-in color thermometer.
"The real challenge of the project was building an instrument and devising a method capable of determining the temperature of these nanocrystals using signatures of the same light that was used to trap them," said lead author Paden Roder, who recently received his doctorate from the UW in materials science and engineering and now works at Intel Corp.
So far, the UW team has only demonstrated the cooling effect with a single nanocrystal, as exciting multiple crystals would require more laser power. The laser refrigeration process is currently quite energy intensive, Pauzauskie said, and future steps include looking for ways to improve its efficiency.
One day the cooling technology itself might be used to enable higher-power lasers for manufacturing, telecommunications or defense applications, as higher-powered lasers tend to overheat and melt down.
"Few people have thought about how they could use this technology to solve problems because using lasers to refrigerate liquids hasn't been possible before," he said. "We are interested in the ideas other scientists or businesses might have for how this might impact their basic research or bottom line."
來(lái)源： 中國科技網(wǎng)
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