物理學家首次創(chuàng)造了時間反轉(zhuǎn)的光波

物理學家首次創(chuàng)造了時間反轉(zhuǎn)的光波

Physicists have achieved an unprecedented time reversal of optical waves. Sadly (or thankfully, depending on your perspective), this has nothing to do with time travel, but it could prove very useful none the less.

物理學家們實現(xiàn)了光波的時間反轉(zhuǎn)，這是前所未有的。不幸的是(或者謝天謝地，這取決于你的觀點)，這和時間旅行沒有任何關(guān)系，但它仍然被證明非常有用。

Interference can make a once simple wave complex as it spreads. Time reversal involves collecting all that complexity and inverting it to recreate the wave's original form. It's already common with water and sound waves, and even in relatively low-frequency electromagnetic waves, but Dr Mickael Mounaix and Dr Joel Carpenter of the University of Queensland have now achieved it at wavelengths we can almost see.

干擾會使一度簡單的波在傳播過程中變得復(fù)雜。時間逆轉(zhuǎn)包括收集所有的復(fù)雜性，并將其倒置以重建波的原始形式。這在水波和聲波中已經(jīng)很常見，甚至在相對低頻的電磁波中也很常見，但昆士蘭大學的Mickael Mounaix博士和Joel Carpenter博士現(xiàn)在已經(jīng)在我們幾乎可以看到的波長中實現(xiàn)了這一方法。

“Imagine launching a short pulse of light from a tiny spot through some scattering material, like fog,” Mounaix said in a statement. “The light starts at a single location in space and at a single point in time but becomes scattered as it travels through the fog...We have found a way to precisely measure where all that scattered light arrives and at what times, then create a ‘backwards’ version of that light, and send it back through the fog.”

莫奈克斯在一份聲明中說:“想象一下，從一個微小的點發(fā)射一個短脈沖的光，穿過一些散射物質(zhì)，比如霧。光從空間中的一個地點和一個時間點開始，但當它穿過霧時就會散射……我們找到了一種方法，可以精確測量散射光到達的位置和時間，然后創(chuàng)造出光的‘向后’版本，然后通過霧將其發(fā)送回去。”

Stephen Luntz

Mounaix compares the process to watching a film in reverse.

Mounaix將這個過程比作反向觀看電影。

If you've had a kidney stone broken up using ultrasound you may have already experienced the benefits of time reversing waves. Time reversing the pattern produced by waves scattering off stones helps doctors target their shock waves precisely on the object that needs to be broken up, not the surrounding organs.

如果你已經(jīng)用超聲波分解過腎結(jié)石，你可能已經(jīng)體驗過時間逆轉(zhuǎn)沖擊波的好處。時間逆轉(zhuǎn)石頭散射波產(chǎn)生的模式，有助于醫(yī)生將沖擊波精確地對準需要分解的物體，而不是周圍的器官。

However, ultrasound has frequencies of 20,000 to several billion hertz. Microwaves have maximum frequencies of 300 billion hertz or less. Visible light, on the other hand, starts at more than 1,000 times that, which meant Mounaix and Carpenter needed to do something quite different. Carpenter refers to creating the pattern to be directed back to sculpting a 3D structure out of the detected light waves. Instead of thousands or millionth of seconds, “That sculpting needs to take place on time scales of trillionths of a second, [for optical light]” he said. “So that’s too fast to sculpt using any moving parts or electrical signals.”

然而，超聲波的頻率在20,000到幾十億赫茲之間。微波的最大頻率為3000億赫茲或更小。另一方面，可見光的起點是這個的1000多倍，這意味著Mounaix和Carpenter需要做一些完全不同的事情。卡朋特指的是創(chuàng)建圖案，然后用探測到的光波來雕刻一個3D結(jié)構(gòu)。他說:“雕刻需要的時間尺度不是千分之一秒或百萬分之一秒，(對于光學而言)是萬億分之一秒。”“所以用任何移動部件或電子信號雕刻，速度都太快了。”

In Nature Communications Mounaiz and Carpenter announce they have succeeded, passing pulses of wavelengths around 1,551.4 nanometers through optical fibers that split the pulses along many optical paths to create a complex output that was collected and time reversed.

在《自然通訊》雜志上，Mounaiz和Carpenter宣布他們已經(jīng)取得了成功，他們將波長約為1,551.4納米的脈沖通過光纖，這些光纖將脈沖沿著許多光路分開，從而產(chǎn)生一個復(fù)雜的輸出，然后收集并逆轉(zhuǎn)時間。

“Previous experiments in optics have demonstrated spatial control, temporal control or some limited combination of both,” the paper notes, whereas here they have combined both.

論文指出，“之前的光學實驗已經(jīng)證明了空間控制、時間控制或兩者的某種有限組合，”而在這里，他們將兩者結(jié)合起來。

Although 1,551 nanometers is in the infrared, rather than visible light, Carpenter told IFLScience it's still considered an optical wavelength, and their work could be replicated with visible light lasers. The frequency is standard for telecommunications, being where glass is most transparent.

盡管1551納米是在紅外線中，而不是可見光中，Carpenter告訴IFLScience，它仍然被認為是一種光學波長，他們的工作可以被可見光激光器復(fù)制。這個頻率是電信的標準頻率，因為玻璃是最透明的。

Carpenter admitted to IFLScience if the pulse “Had too many fine features we would not be able to represent it, or if it had too many features over too long a delay.” Nevertheless, he says the work should open up possibilities for amplifying lasers without distortion or for identifying the shape of irradiated organs within the body where intervening flesh produces a scattered pattern.

卡朋特承認，如果科學告訴我們，如果脈搏“有太多精細的特征，我們就無法表現(xiàn)它;如果在太長的時間里出現(xiàn)太多的特征，我們就無法表現(xiàn)它。”盡管如此，他說這項工作將為在不失真的情況下放大激光或識別體內(nèi)被輻射器官的形狀開辟了可能，因為干涉人體的肌肉會產(chǎn)生分散的圖案。