Alfons Penzkofer

Alfons Penzkofer (born 19 October 1942) is a German physicist and retired professor of physics at the University of Regensburg. He is known for his contributions to ultrafast laser physics, nonlinear optics, time-resolved optical spectroscopy, and the spectroscopic characterization of organic dyes, luminescent polymers, and photoreceptor proteins relevant to optogenetics. He is a Fellow of Optica (formerly the Optical Society of America). After elementary school and vocational training in agriculture and papermaking, he attended the Oskar von Miller Polytechnikum in Munich, where he earned an engineering degree in papermaking (Ing. grad.) in 1965.

Research contributions In the early 1970s, Penzkofer contributed to the generation of picosecond and subpicosecond light pulses with a neodymium glass laser using saturable absorbers. He later developed femtosecond pulse generation in a linear colliding-pulse mode-locking dye laser and a Kerr-lens mode-locked titanium-sapphire laser.

He performed extensive spectroscopic measurements on gain media for solid-state dye lasers, including determination of stimulated emission cross-sections and excited-state absorption cross-sections. He extended this work to luminescent polymers, investigating traveling-wave lasing, distributed feedback lasing, and leaky-mode emission from thin films. His studies included photodegradation, excitation energy transfer, and exciton–exciton annihilation.

Penzkofer developed methods for measuring third-order nonlinear susceptibilities, two-photon absorption cross-section spectra, nonlinear refractive indices, and optical constants of absorbing media. He clarified electron-transfer and protein-rearrangement mechanisms. His work has been applied to optogenetic toolkits for cell biology and neuroscience.

Awards and recognition Fellow of Optica (formerly Optical Society of America), elected 1998.

Selected publications