He told the BBC the team "really didn't know" whether their idea would work. "We were definitely very surprised that it worked so well."
Once they had seen a green, flower-like pattern appear on their screen, even after travelling 3km through the evening air, they set about transmitting some actual information.
They made 16 different beam structures, using different amounts of twist, and used them to encode 16 different levels of grey. Then, one pixel after another, they sent the encoded portraits along the laser beam.
At the receiving end, a camera and a computer program recognised the patterns, and re-created the pictures with an error rate of only 1.7%.
The researchers hope that their results, although preliminary, will help the development of OAM technology for applications like Earth to satellite communication.
Other physicists have greeted the findings with enthusiasm.
"This is a proof of principle for how to encode and decode the 16 different channels," said Dr Michael Mazilu, a lecturer in the school of physics and astronomy at the University of St Andrews.
"It's a step towards encoding more information in less light."
Mark Neil, a professor of photonics at Imperial College London, was impressed the team had overcome the problem of turbulence in the air.
"The big problem was... if you tried to put [twisted light] through a normal atmosphere - you don't have to go very far and it messes up all these OAM modes, and it's difficult to work out what's going on," Prof Neil told BBC News.
"So this is quite interesting because they have found a way of unravelling the different modes. They're sending patterns that they can detect."
Prof Miles Padgett, who studies twisted light at the University of Glasgow, also said that overcoming turbulence was a major problem that the Vienna study had now begun to address.
"It's lovely work," he said. "It shows the potential of the system, and it characterises the problems that people now need to work to overcome."
Earlier research, external had demonstrated that radio waves, twisted in the same way, could simultaneously carry two channels of information 442m across a Venice canal. But work with visible wavelengths of light, with more high-energy photons, was limited to indoor experiments which reached very high rates of data transfer but only travelled short distances,
The portraits beamed across Vienna didn't break any speed records. Because the pixels were sent one-by-one, each picture took several minutes.
They did, however, travel 3km through the open air.
"We were still excited," Mr Krenn said. "It's a proof of concept."
Follow Jonathan on Twitter, external