Streaming Continuous Optical Nanosecond Events (SCONE)

我们总是着迷于看到超越寻常的事物——我们每天都认为理所当然的世界，当从不同的角度来看时，会激发出惊奇。当罗伯特·胡克在1665年出版《缩微术》时，情况确实如此；它立即成为经典，让人们对周围的微观世界有了一个看法，否则他们会认为这是理所当然的。在现代，高速摄像机可以让我们看到飞行中的子弹，雷击中电力的运动，爆米花的爆响，但也有问题，现代超高速摄像机所能看到的东西是有限的。可以拍摄无限张样本图像的相机（称为流媒体相机）每秒不能超过200万帧，而“分帧”相机（可以大大超过这个限制）只能观察少量帧，然后它们的容量就会耗尽。流式连续光学纳秒事件（或SCONE）旨在将流式相机的成像速度提高到16倍，这样它们就可以在长时间成像的情况下与分幅相机竞争，以捕捉罕见事件和偶然事件。SCONE的工作原理是将光线从不同角度照射到目标上。因为光通过样品时或多或少是一条直线，所以一旦穿过样品，光就可以被分成不同的路径。通常情况下，这只会提供，比如说，同一事物的十个不同的视图，但如果我们使用非常短的激光脉冲，我们可以确保每个角度的脉冲到达不同的时间。现在，这十个不同的视角观察不同的时间点，从而将相机的速度提高了十倍。当然，使脉冲以正确的角度和正确的时间到达样品是风险和挑战所在。我们从输出200飞秒脉冲的单一激光器开始（大约是光传播一根头发宽度的时间），并将它们聚焦到光纤中。纤维被分成16根不同的纤维，每根纤维的能量是原脉冲能量的1 / 16。在分裂后，每根光纤连接到不同长度的光纤，用来在脉冲从另一端出来之前将其延迟一定的时间。这意味着通过正确选择光纤的长度，产生的脉冲以57纳秒的间隔从光纤中发出。然后，可以用镜子将它们引导到样品上。这个系统可以用来观察很多事情。天文学家对超高速撞击对卫星和空间站的影响很感兴趣。用于采矿的新炸药需要进行测试，看它们是否优于现有材料。超声波以每秒数公里的速度传播，使身体的某些部位以数十兆赫兹的速度振荡，远远快于任何流媒体摄像机所能看到的速度。我们首先要谈的是最后一种现象。高功率超声波的一个有趣之处在于，它可以与微小的注射微泡结合起来，打破大脑的防御，即血脑屏障。这似乎是一个坏主意，但由于这种分解是短暂的和局部的，我们可以利用它以一种通常不可能的方式将药物引入大脑。虽然我们知道这种分解是有效的，但我们不知道它为什么会有效，因为我们看不到气泡在穿过屏障时是如何移动的。正是在这里，司康饼发挥了自己的作用。通过对气泡进行每秒数千万帧的成像，持续时间长达几秒钟，我们可以观察到它在超声波照射下所经历的所有意想不到的混乱行为。由此，我们可以改善气泡，改善超声参数，并第一次真正了解在这种尖端疗法中发生了什么。所有这些都只能通过世界上最快的流媒体相机SCONE来实现。

We have always been fascinated by seeing things that are beyond the ordinary - the world that we take for granted every day can inspire wonderment when viewed from a different perspective. This was true when Robert Hooke published Micrographia in 1665; an instant classic, it gave people a view of the microscopic world around them that they otherwise took for granted. In the modern day, high-speed cameras let us see bullets in flight, the movement of electricity in a lightning strike, and the pop of a kernel of popcorn, but there are problems, modern ultrafast cameras are limited in what they can see. Cameras that can take infinite numbers of images of the sample (called streaming cameras) cannot push beyond ~2 million frames per second, whereas 'framing' cameras (which can significantly surpass this limit) can only observe a handful of frames before their capacity is exhausted. Streaming Continuous Optical Nanosecond Events (or SCONE) seeks to increase the imaging speed of streaming cameras by a factor of up to 16, such that they are competitive with framing cameras while still imaging over very long periods of time, to capture rare events and serendipitous occurrences.SCONE works by shining light on the target at different angles. Because the light passes through the sample in more-or-less a straight line, the light can be separated into different paths once it has passed through the sample. Ordinarily this would just provide, say, ten different views of the exact same thing, but if instead we use a very short laser pulse, we can make sure the pulse from each angle arrives at a different time. Now the ten different views observe a different point in time, thus increasing the speed of the camera by a factor of ten.Of course, actually making the pulses arrive at the sample at the right angle and the right time is where the risk and challenge lies. We start from a single laser outputting 200-femtosecond pulses (approximately the time it takes light to travel the width of a human hair) and focus them into an optical fibre. The fibre gets split into sixteen different fibres, each with a sixteenth of the original pulse energy. After splitting, each fibre connects to a different length of fibre which is used to delay the pulse by a certain amount before it comes out the other end. This means that by selecting the length of the fibres correctly, the resulting pulses emerge from the fibre at 57-nanosecond intervals. These can then each be steered towards the sample with a mirror.There are many things this system could be used to look at. Astronomers are interested in the effects of hypervelocity impact on satellites and space stations. New explosives for mining need to be tested to see if they outperform existing materials. Ultrasound waves, travelling at kilometers per second, cause parts of the body to oscillate at tens of megahertz, far faster than any streaming camera can see. It is this last phenomenon we will first address.One of the interesting things about high-powered ultrasound is that it can be combined with tiny injected microbubbles to break down the defences of the brain, known as the Blood-Brain Barrier. This would seem like a bad idea, but because this breakdown is brief and localized, we can use it to introduce drugs to the brain in a way that would normally be impossible. While we know that this breakdown works, we don't know why it works, because we can't see how the bubble moves as it works its way through the Barrier. It is here that SCONE comes into its own. By imaging the bubble at tens of millions of frames per second, for periods of up to a few seconds, we can observe all the unexpected and chaotic behaviour it goes through when exposed to ultrasound. From this we can improve the bubbles, improve the ultrasound parameters, and for the first time, really understand what is going on in this cutting-edge therapy. All of this can only be achieved with SCONE, the world's fastest streaming camera.