Now what is the trick of this method? I must perhaps try to explain that. First of all, you must choose a very small volume element. You have to... and, therefore, you need a laser. Only a laser with a coherent light you can focus into a small enough volume element.
[Q] What means 'small enough'?
Yes. Small. That's a good question. In our present work the volume element is almost a tenth of a femtolitre. Femtolitre is 10-15 litre, or what is better, a femtolitre is the size of a coli cell. That means about one micron in each direction. Three dimensions. One micron. And so we go to fractions of a micron. That volume is only a thousandth of an ordinary normal eukaryotic somatic cell also. So you can see it's smaller than the cells of living organisms, much smaller, and you could... even if you can do observations of such small volume elements, you can look inside a cell. So, that's what we do. In order to get there you need two technical improvements. One was the laser. Now present lasers are stable enough... we can focus them into that volume element and we can use the laser light for fluorescence measurements, I come to that. And second, you need good optics to focus it and that is called confocal optics. And confocal optics was invented by Marvin Minsky... by the neuro... who works nowadays on theoretical neural networks and things he became known for.
[Q] Artificial intelligence, and things like that...
Things like that. But he invented the confocal optics in this work, and this is available now and companies like Zeiss build very good instruments with very corrected lenses and so... so that is no problem nowadays to focus light into such small volume element.