 The Allgäu Public Observatory lies amidst the picturesque landscape of southern Germany. As night falls, a team of scientists and engineers prepares to field-test a very cool piece of technology, a laser guide-star unit which will soon be on its way to ESO's Paranal Observatory. This is the ESOcast. Cutting-edge science and life behind the scenes at ESO, the European Southern Observatory, exploring the ultimate frontier with our host Dr J, aka Dr Joe Liske. Hello and welcome to the ESOcast. Today we are at the Allgäu Public Observatory in southern Germany, because this is where a team of scientists and engineers from ESO is testing a brand-new laser guide-star unit. What's that you ask? Let me explain. Now we've all looked at the night sky and seen the stars twinkling. Now the stars themselves, of course, don't do any twinkling. The twinkling is caused by turbulence in the Earth's atmosphere. As the starlight crosses the atmosphere, it encounters different pockets of air with different temperature and pressure, which bend the light in different ways, thus causing distortions. In fact, you can see this effect often in broad daylight, whenever you look towards a distant object on the horizon on a hot day. Now the twinkling is all very pretty and even romantic, but for us astronomers it's actually a real problem, because it means that our images are blurred and less sharp than they could be if it wasn't for the atmosphere. So what do we do about it? Essentially, we need a method to cancel out the distortions, in effect to untwinkle the stars. The way to do it is to bounce the starlight off a mirror that is slightly deformed in exactly the right manner to cancel out the distortions. But how do you know how to deform your mirror? As Iso's very large telescope observes the sky, a specialised computer can pick a bright star and constantly monitor how it twinkles, deducing the atmospheric conditions above the telescope many hundreds of times a second. The computer then sends commands to a series of devices attached to a mirror in the telescope, bending and flexing it precisely in time with the atmospheric turbulence, cancelling out the distortion in the images. So for this correction process to work, you need a really bright star in the fuel of view of your telescope. But bright stars are very few and far between. And remember that the VLT was designed to image only a very small part of the sky at any given time. So for most observations there just won't be a bright star in the fuel of view of the VLT. So what do we do now? Well, we make our own. 90 kilometres above our heads in the upper atmosphere is a relatively thin layer of sodium. If you fire a powerful laser beam into the sky, you can make these sodium atoms glow, thereby effectively creating an artificial star for the computer to lock onto. In 2006, Iso installed the Southern Hemisphere's first laser guide star on the VLT. This system greatly improves the telescope's power, meaning that the VLT can make even sharper images than Hubble for certain types of observation. But this existing system has limitations. It can only create one artificial star at once, meaning it can only correct the telescope's vision for a small part of the sky at any one time. It's also very bulky. The equipment has to be kept in a separate laboratory and the laser beam fed along an optical fibre to the telescope. Based on the experience obtained with this first system, ESA engineers have been working to build a much improved new laser guide star unit. So Domenico, this is it. This is the laser. It's incredibly small. It fits in the back of this small telescope. That's amazing. Yeah, so this is what we've been working on the R&D for the past five years to make a 20-watt laser very compact and lightweight that can be mounted directly on the back of the telescope. So we had to develop fibre lasers first and then develop this kind of laser heads. So you've just said it's a 20-watt laser. That's quite a bit of power, isn't it? Yeah, this is the power we need actually for the next generation laser guide star systems. And right now, for example, in Paranal, we have about 5 watts in the sky. So this is quite a jump in power. Is the laser beam that comes out at the end of this telescope, is it dangerous? What happens if I put my hand into it? If you put your hand, you'll feel warm. But you don't have to look into the beam. Okay, so it won't burn my hand. But what about airplanes? Is it dangerous for them? It's not dangerous for the equipment, so for the airplane. It's dangerous for the eyes of the passengers. And this laser is above the maximum permitted exposure. So we have to avoid the planes across the beam. In fact here, where we are now, we have obtained a no-fly zone above us so we don't have a risk to hit a plane. The new device is more reliable, easier to maintain and much smaller. In fact, as we've just seen, the whole unit fits into one small package which is easy to mount on a launch telescope. Because it's so much smaller, up to four of these lasers can be installed on a single telescope, correcting the VLT's image over a much wider field of view. So what's happening here in Germany is that our team is testing the new prototype to make sure that it works perfectly before it gets shipped to Paranal. The facilities here at the Algoi Public Observatory are perfect for this. And what's more, they're only a short drive from ESIL headquarters. Laser guide stars like this will be crucial for the forthcoming European Extremely Large Telescope, which will use adaptive optics routinely. The telescope will be many times the size of today's biggest telescopes which should mean much sharper image quality. But this great image quality will depend on how well the adaptive optics and the laser guide stars work. Pioneering new technologies like these will make a big difference to the world's most advanced observatories of the future, especially the EOT. This is Dr Jay signing off for the ESILcast. Join me again next time for another cosmic adventure. While we were filming this episode, we got a stark reminder of why ESO's telescopes are located on the mountaintops of northern Chile and not here in the hills of southern Germany. Thankfully storms like this are not something you ever see at Paranal.