Autobiography Stefan Hell

for me as well, but in the end it turned out to be a subject that again had a touch of
applied physics. And I didn’t have the courage to say that I would do it with little
passion. As it happened, Professor Bille and Professor Hunklinger had just found-
ed Heidelberg Instruments GmbH, a start-up Company developing laser-scanning
optical Systems for a broad ränge of applications: optical lithography, ophthalmol-
ogy, and confocal microscopy for biology as well as microlithography inspection.
Confocal microscopy was about to emerge as a new microscopy technique, having
the advantage of suppressing light from above or below the focal plane. In the mid
1980s, it was therefore believed that this could be used to measure transparent 3D
photoresist microstructures more accurately, which was important for the mass
production of Computer chips. My task was to find out if and how this would
work. However, that wasn’t easy, because the structures on the Silicon wafer were
transparent and had about the same width and height as the wavelength of light.
The confocal principle was not really able to solve the problem; rather it produced
complex images that changed drastically with minute changes in the dimensions of
the structures. I called the images ‘aliens’, because they reminded me of the figures
of a populär Computer game at the time. At first, I wanted to find a mathematical
model to predict them, but there were too many process parameters to deal with,
and ultimately such an approach would be impractical for a semiconductor man-
ufacturer.
I was the only physics graduate Student at Heidelberg Instruments and more
or less on my own. Occasionally, I was able to turn to the company’s development
manager, Roelof Wijnaendts van Resandt, who had run a group on confocal mi-
croscopy at the Heidelberg-based European Molecular Biology Laboratory (EM-
BL) a few years earlier. But he had little time for me, because the Company was
struggling to survive. There was also a biology graduate Student, Werner Knebel,
who was investigating the suitability of confocal microscopy for cell biology. Wc
often talked to each other. I explained to him the physics of image formation and
he introduccd me to the role of fluorescence imaging in biology. Otherwise, my
routine was interrupted only by my walks to the weekly seminars on solid state
physics, teaching duties, group meetings, and the colloquia on Friday evenings. I
was pretty frustrated. Actually, I wanted to do something more exciting than optical
microscopy, this physics of the 19th Century that had nothing to offer apart from
diffraction and Polarisation.
In the interim, I had received a stipend from a foundation, meaning that I
wasn,t dependent on the Company. I also knew that my thesis advisor was a ‘real’
physicist with passion for physics. So I started to ask myself whether there might
be an interesting problem in optical microscopy left after all. The only thing that
still seemed interesting in my view was the diffraction limit of resolution. So I
figured that breaking this limit would be really new and exciting! All of a sudden,

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