Institute of Laser Physics, Hamburg University, Germany
The research expertise of Günter Huber is in the field of solid-state lasers, in particular in the growth, development, and fundamental characterization of new laser materials on the basis of laser active transition metal and rare earth ions. This includes optical spectroscopy of solids, new diode pumped solid-state lasers in the visible and near infrared spectral region, up-conversion lasers based on crystals and fibers, and non-linear frequency conversion of solid-state lasers.
An important aspect of the research work has been the combination of several topical areas as crystal growth, fundamental spectroscopy, design, construction, and full characterization of operating lasers. These broad activities - carried out in one laboratory - has led to efficient feedback between laser performance and materials science opening also fast routes for the development of new lasers.
The activities in the field span a period of more than 3 decades and had a strong impact on the renaissance of solid-state lasers, which began in the early 1980's. The revival of solid-state laser research was stimulated by the remarkable progress of tunable transition metal ion lasers (Cr3+, Ti3+), the first demonstrations of efficient near infrared rare earth ion lasers (Nd3+, Tm3+, Ho3+, Er3+), and the implementation of diode pumped solid-state lasers. In particular, major results have been obtained in the following areas:
- Materials science (crystal growth at ultrahigh melting temperatures, epitaxy of crystalline dielectric laser materials)
- Tunable transition metal ion lasers (Cr3+, Ti3+, Cr2+, Cr4+)
- Near infrared rare earth ion lasers (Nd3+, Tm3+, Ho3+, Er3+, Yb3+)
- Intracavity frequency doubled lasers
- Visible rare earth ion lasers (Er3+ up-conversion lasers, (Ga,In)N pumped Pr3+ and Tb3+ lasers)
A set of pioneering contributions refers to the development of tunable solid-state lasers in the near IR mostly based on Ti3+ and Cr3+ ions. In particular, there is the first demonstration of cw laser action of tunable Cr3+ lasers1 as well as the first demonstration of cw laser action in Ti:sapphire2 and its broad tunability. Nowadays, cw Ti:sapphire lasers are commonly used for many scientific and technological applications, mainly due to the broad tunability and the capability to generate ultrashort laser pulses. Cr3+ lasers have similar attributes with the additional advantage of direct diode pumping in the red spectral region. The fundamental origin of the broad band Cr3+ and Cr4+ transitions have been proven with fundamental spectroscopic investigations of Cr ions in different crystal fields3,4.
Seminal contributions refer to the development of efficient quasi-three level Tm3+, Ho3+, and Er3+ lasers operating in the near IR. For the first time cw laser action5,6 as well as diode-pumping7 of these ions at various transitions near 1.5 μm, 2 μm, and 3 μm wavelength was achieved. One of the key experiments has been the exploitation of Tm-Tm cross relaxation pumping6,8,9 (so-called two-for-one energy transfer process) in 2-μm lasers which is the basis for the efficiency of many 2-μm lasers used nowadays in medical applications and measurement techniques.
The breakthrough in the high temperature heat exchange method (HEM) growth technique near 2500 °C opened the way for the preparation of new classes of laser crystals like rare earth doped sesquioxides. Compared to YAG, sesquioxide crystals like Lu2O3 posses superior mechanical and thermal properties combined with high optical quality. Günter Huber's laboratory has been worldwide the only laboratory being able to grow large high quality sesquioxide laser crystals. With an Yb:Lu2O3 thin disk laser, impressive slope efficiencies of 80% (with respect to incident pump power!) yielding cw powers of about 35 W under diode pumping9. Later, in collaboration with the ETH group of Ursula Keller 141 W of average output power at 738 fs pulse widths could be obtained with Yb:Lu2O310. Tm-, Ho-, and Er-doped sesquioxides also have high potential for very efficient diode pumped lasers for medical applications in the mid-IR spectral region. In particular, Huber’s group could operate a diode pumped high power cw Er: Lu2O3 laser at 2.85 µm 11.
In the visible spectral region, forefront results with respect to highly efficient cw intracavity frequency doubled green lasers12 have led to the realization of the first battery driven green cw laser pointer, which was built in Günter Huber's research group, demonstrated and used at many international conference talks in the 1990's. High output powers in the blue spectral region have been obtained in case of diode pumped cw intracavity frequency doubling of the Nd3+ ground state transition 13. Green high power up-conversion lasers have been realized 14. Diode pumping of up-conversion lasers at 300 K has been successfully performed as well 15.
Seminal progress was achieved with (Ga,In)N diode pumped visible Pr3+ lasers15. Power scaling into the W-regime and high power intracavity cw UV generation with Pr3+ lasers17,18,19 has been demonstrated in various crystals. Pr-lasers are considered to become "Nd-lasers in the visible region" due to their similarity in level scheme structure, cross-sections, lifetimes, and gain as well as the capability of diode pumping. Recently, also Tb3+- lasers were realized in the visible spectral region at high power and efficiency 20,21.
Huber's research also included rare-earth doped crystalline waveguide structures grown by the technique of Pulsed Laser Deposition (PLD) and directly fs-laser inscribed waveguides in bulk crystals. In Yb:YAG, the inscription of double tracks yield highly efficient waveguide lasers with multi-Watt of fundamental mode output power 22. The PLD technique enabled especially the epitaxial growth of Nd3+-doped planar sapphire films (Nd:Al2O3) in which lasing of a rare-earth ion in crystalline sapphire could be achieved for the first time 23.
Guenter Huber is Fellow of the Optical Society of America and Fellow of the European Physical Society. In 2003 the Quantum Electronics and Optics Prize of the European Physical Society was awarded to Günter Huber with the citation "For his outstanding and numerous contributions to physics of solid-state lasers and spectroscopy of laser crystals". In 2013 he received the Charles Hard Towns Award of the Optical Society of America “For seminal contributions to solid state lasers, in particular the growth, development, and fundamental characterization of new laser materials based on laser active transition metal and rare earth ions”. Since 2016 he is Foreign Member of the Russian Academy of Sciences.
- B. Struve, G. Huber, V. V. Laptev, I. A. Shcherbakov, and E. V. Zharikov, "Tunable room-temperature cw laser action in Cr3+:GdScGa-garnet", Appl. Phys. B 30, 117 (1983)
- P. Albers, E. Stark, and G. Huber, "Continuous-wave laser operation and quantum efficiency of titanium-doped sapphire", J. Opt. Soc. Am. B 3, No. 1, 134 (1986)
- B. Struve and G. Huber, "The effect of the crystal field strength on the optical spectra of Cr3+ in gallium garnet laser crystals", Appl. Phys. B 36, 195 (1985)
- S. Kück, K. Petermann, U. Pohlmann, and G. Huber, "Near-infrared emission of Cr4+-doped garnets: Lifetimes, quantum efficiencies, and emission cross sections", Phys. Rev. B 51 (24), 17323 (1995)
- E. W. Duczynski, G. Huber, and P. Mitzscherlich, ,"Laser action of Cr, Nd, Tm, Ho-doped garnets", Springer Series in Optical Sciences, Vol. 52, 282, Springer Verlag (1986)
- G. Huber, E. W. Duczynski, and K. Petermann, "Laser pumping of Ho-, Tm-, Er-doped garnet lasers at room temperature", IEEE J. Quantum Electr. 24 (6), 920 (1988)
- T. Y. Fan, G. Huber, R. L. Byer, and P. Mitzscherlich, "Continuous wave operation at 2.1µm of a diode-laser-pumped, Tm-sensitized Ho:Y3Al5O12 laser at 300 K", Opt. Lett. 12 (9), 678 (1987)
- E. W. Duczynski, G. Huber, V. G. Ostroumov, and I. A. Shcherbakov, "Cw double cross pumping of the 5I7-5I8 laser transition in Ho3+ doped garnets", Appl. Phys. Lett. 48 (23), 1562 (1986)
- R. Peters, C. Kränkel, K. Petermann, G. Huber, “Broadly tunable high-power Yb-Lu2O3 thin disk laser with 80 % slope efficiency”, Opt. Expr. 15(11), 7075 (2007)
- C.R.E. Baer, C. Kränkel, C.J. Saraceno, O.H. Heckl, M. Golling, R. Peters, K. Petermann, T. Südmeyer, G. Huber, and U. Keller, “Femtosecond thin-disk laser with 141 W of average power”, Opt. Lett. 35(13), 2302 (2010)
- T. Li, K. Beil, C. Kraenkel, and G. Huber, "Efficient high-power continuous wave Er:Lu2O3 laser at 2.85 µm", Opt. Lett. 37 (2012)
- J.-P. Meyn and G. Huber, "Intracavity frequency doubling of a continuous-wave, diode-laser-pumped neodymium lanthanum scandium borate laser", Opt. Lett. 19(18), 1436 (1994)
- C. Czeranowsky, E. Heumann, and G. Huber, “All-solid-state continuous-wave frequency-doubled Nd:YAG-BiBO laser with 2.8-W output power at 473 nm”, Opt. Lett. 28(6), 432 (2003)
- E. Heumann, S. Bär, K. Rademaker, G. Huber. S. Butterworth, A. Diening, and W. Seelert, “Semiconductor-laser-pumped high-power upconversion laser”, Appl. Phys. Lett. 88, 061108 (2006)
- E. Heumann, S. Bär, H. Kretschmann, and G. Huber, “Diode-pumped continuous-wave green upconversion lasing of Er3+:LiLuF4 using mulitpass pumping”, Opt. Lett. 27(19), 1699 (2002)
- A. Richter, E. Heumann, E. Osiac, G. Huber, W. Seelert, A. Diening, “Diode pumping of a continuous-wave Pr3+-doped LiYF4 laser”, Opt. Lett. 29 (22), 2638 (2004)
- A. Richter, N. Pavel, E. Heumann, G. Huber, D. Parisi, A. Toncelli, M. Tonelli, A. Diening, and W. Seelert, “Continuous-wave ultraviolet generation at 320 nm by intracavity frequency doubling of red-emitting Praseodymium lasers”, Opt. Expr. 14(8), 3282 (2006)
- A. Richter, E. Heumann, G. Huber, V. Ostroumov, and W. Seelert, “Power scaling of semiconductor laser pumped Praseodymium-lasers”, Opt. Expr. 15(8), 5172 (2007)
- T. Gün, P. Metz, and G. Huber, “Efficient continuous wave deep ultraviolet Pr3+:LiYF4 laser at 261.3 nm”, Appl. Phy. Lett. 99, 181103 (2011)
- P. W. Metz, D. T. Marzahl, A. Majid, C. Kränkel, and G. Huber, “Laser properties of Tb3+-doped fluoride crystals“, Laser Photonics Rev. 10 (2), 335-344 (2016)
- C. Kränkel, D. T. Marzahl, F. Moglia, G. Huber, and P. W. Metz, "Out of the blue: Semiconductor laser pumped lasers in the visible", Laser Photonics Rev. 10(4), 548 - 568 (2016)
- T. Calmano, J. Siebenmorgen, A.-G. Paschke, C. Fiebig, K. Paschke, G. Erbert, K. Petermann, and G. Huber, “Diode pumped high power operation of a femtosecond laser inscribed Yb:YAG waveguide laser”, Opt. Materials Expr. 1(3), 428 (2011), invited
- S. H. Waeselmann, S. Heinrich, C. Kränkel, and G. Huber, “Lasing of Nd3+ in Sapphire“, Laser Photonics Rev. 10 (3), 510–516 (2016)