MBI Staff Member – Personal info


High-power semiconductor lasers are the most efficient man-made light sources, and can convert more than 80% electric energy into light. Currently emission powers of one kW continuous-wave powers are extracted from a single monolithic semiconductor chip. We are interested in the intrinsic limitations of such optoelectronic devices in terms of output power, beam quality (brightness) and lifetime (reliability). For this purpose, we analyze devices, but also their components such as surfaces and interfaces or gain materials such as quantum wells, superlattices and quantum dots.
For our experiments, we use optical tools, in particular transient spectroscopy that represents a generic competence of MBI. Such work is naturally carried out as collaborative work with device vendors, who provide us with high-quality industry-grade devices and structures. The use of such devices ensures high reproducibility and the chance to get general results, which not depend on the particular device structure that was studied. In BMBF-projects such as BlauLas, we work together with Osram OS (Regensburg), Dilas GmbH (Maiz) and Laserline GmbH (Mülheim) or in the frame of bilateral research contracts with Lumentum (Santa Clara) and 3S-Photonics (Nozay).
The material basis of the investigated devices is now focused to GaN-based wide-bandgap devices emitting in the ultraviolet to blue spectral regions. The figure shows damage patterns as observed in 450-nm emitting high power diode lasers after it experienced the so-called catastrophic optical damage in short-pulse operation.

Subfigure (a) shows the damage patterns at the font facet, where the light leaves the device (red circle), while (b) shows the same region from the side. A channel is visible which burned into the device and ends ~80 µm underneath the front facet; see (c). Subfigure (d) shows the end of this channel in higher resolution. The quantum wells, i.e. the gain medium are well resolved.


Curriculum vitae

2018  East China Normal University as ECNU High-End Expert, China

1999  Visitor at the RIKEN-Institute Sendai, Japan

1995 - present: Senior researcher at MBI

1993-1995: Visiting professor at Georgia Tech Atlanta, USA

1986-1989: R&D group leader in a subcontract "Optical characterization of II-VI materials for IR quantum detector fabrication".

1984-1986: R&D work in a subcontract to "Carl Zeiss Jena" company to develop diode lasers for an IR diode laser spectrometer.

1981-1984: PhD student, Dr. rer. nat. in Physics, summa cum laude, Humboldt University, Berlin 1984 Dissertation: Study of the optical properties of n-Pb1-xSnxTe/p-Pb1-xSnxTe/p-PbTe-heterostructures by means of photoluminescence and injection-luminescence.

1977-1982: Physics studies, Diploma in Physics summa cum laude, Humboldt University, Berlin 1982 Thesis: Luminescence properties of lead salts for optical and electrical excitation.

MBI Publications

  1. Microscopic origins of catastrophic optical damage in diode lasers

    M. Hempel, J. Tomm, F. La Mattina, I. Ratschinski, M. Schade, I. Shorubalko, M. Stiefel, H. Leipner, F. Kießling, T. Elsaesser

    IEEE Journal of Selected Topics in Quantum Electronics 19 (2013) 1500508/1-8
  2. How does external feedback cause AIGaAs-based diode lasers to degrade?

    M. Hempel, M. Chi, P. M. Petersen, U. Zeimer, J. W. Tomm

    Applied Physics Letters 102 (2013) 023502/1-4
  3. High single-spatial-mode pulsed power from 980 nm emitting diode lasers

    M. Hempel, J. W. Tomm, T. Elsaesser, M. Bettiati

    Applied Physics Letters 101 (2012) 191105/1-5
  4. Near-field characteristics of broad-area diode lasers during catastrophic optical damage failure

    M. Hempel, J. W. Tomm, M. Baeumler, H. Konstanzer, J. Mukherjee, T. Elsaesser

    SPIE Proceedings Series 8432 (2012) 84320O/1-7
  5. Near-field evolution in strongly pumped broad area diode lasers

    M. Hempel, J. W. Tomm, M. Baeumler, H. Konstanzer, J. Mukherjee, T. Elsaesser

    SPIE Proceedings Series 8277 (2012) 82771H/1-8
  6. Catastrophic optical bulk damage in InP 7xx emitting quantum dot diode lasers

    S. N. Elliott, M. Hempel, U. Zeimer, P. M. Smowton, J. W. Tomm

    Semiconductor Science and Technology 27 (2012) 102001/1-4
  7. Emulation of the operation and degradation of high-power laser bars using simulation tools

    S. Bull, J. J. Lim, C. K. Amuzuvi, J. W. Tomm, J. Nagle, B. Sumpf, G. Erbert, N. Michel, M. Krakowski, E. C. Larkins

    Semiconductor Science and Technology 27 (2012) 094012/1-7
  8. Effect of uniaxial stress on electroluminescence, valence band modification, optical gain, and polarization modes in tensile strained p-AIGaAS/GaAsP/n-AIGaAS laser diode structures: Numerical calculations and experimental results

    E. V. Bogdanov, N. Y. Minina, J. W. Tomm, H. Kissel

    Journal of Applied Physics 112 (2012) 093113/1-10
  9. Time-resolved reconstruction of defect creation sequences in diode lasers

    M. Hempel, J. W. Tomm, V. Hortelano, N. Michel, J. Jiménez, M. Krakowski, T. Elsaesser

    Laser & Photonics Reviews 6 (2012) L15-L19
  10. Defect propagation in broad-area diode lasers

    M. Hempel, J. W. Tomm, U. Zeimer, T. Elsaesser

    Materials Science Forum 725 (2012) 101-104

Other Publications


Juan Jiménez and Jens W. Tomm, "Spectroscopic Analysis of Optoelectronic Semiconductors", Springer Series in Optical Sciences Vol. 202 (Springer, 2016).

Jens W. Tomm and Juan Jiménez, "Quantum-Well Laser Array Packaging", Nanoscience and Technology Series (McGraw-Hill, 2007).