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物理学家首次创造了时间反转的光波

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2021年01月29日

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Physicists Create Time-Reversed Optical Waves For The First Time

物理学家首次创造了时间反转的光波

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.

物理学家们实现了光波的时间反转,这是前所未有的。不幸的是(或者谢天谢地,这取决于你的观点),这和时间旅行没有任何关系,但它仍然被证明非常有用。

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.

干扰会使一度简单的波在传播过程中变得复杂。时间逆转包括收集所有的复杂性,并将其倒置以重建波的原始形式。这在水波和声波中已经很常见,甚至在相对低频的电磁波中也很常见,但昆士兰大学的Mickael Mounaix博士和Joel Carpenter博士现在已经在我们几乎可以看到的波长中实现了这一方法。

“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.”

莫奈克斯在一份声明中说:“想象一下,从一个微小的点发射一个短脉冲的光,穿过一些散射物质,比如雾。光从空间中的一个地点和一个时间点开始,但当它穿过雾时就会散射……我们找到了一种方法,可以精确测量散射光到达的位置和时间,然后创造出光的‘向后’版本,然后通过雾将其发送回去。”

Stephen Luntz

Mounaix compares the process to watching a film in reverse.

Mounaix将这个过程比作反向观看电影。

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.

如果你已经用超声波分解过肾结石,你可能已经体验过时间逆转冲击波的好处。时间逆转石头散射波产生的模式,有助于医生将冲击波精确地对准需要分解的物体,而不是周围的器官。

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,超声波的频率在20,000到几十亿赫兹之间。微波的最大频率为3000亿赫兹或更小。另一方面,可见光的起点是这个的1000多倍,这意味着Mounaix和Carpenter需要做一些完全不同的事情。卡朋特指的是创建图案,然后用探测到的光波来雕刻一个3D结构。他说:“雕刻需要的时间尺度不是千分之一秒或百万分之一秒,(对于光学而言)是万亿分之一秒。”“所以用任何移动部件或电子信号雕刻,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《自然通讯》杂志上,Mounaiz和Carpenter宣布他们已经取得了成功,他们将波长约为1,551.4纳米的脉冲通过光纤,这些光纤将脉冲沿着许多光路分开,从而产生一个复杂的输出,然后收集并逆转时间。

“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.

论文指出,“之前的光学实验已经证明了空间控制、时间控制或两者的某种有限组合,”而在这里,他们将两者结合起来。

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.

尽管1551纳米是在红外线中,而不是可见光中,Carpenter告诉IFLScience,它仍然被认为是一种光学波长,他们的工作可以被可见光激光器复制。这个频率是电信的标准频率,因为玻璃是最透明的。

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.

卡朋特承认,如果科学告诉我们,如果脉搏“有太多精细的特征,我们就无法表现它;如果在太长的时间里出现太多的特征,我们就无法表现它。”尽管如此,他说这项工作将为在不失真的情况下放大激光或识别体内被辐射器官的形状开辟了可能,因为干涉人体的肌肉会产生分散的图案。


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