MBI-Mitarbeiter - Persönliche Daten

Research

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 Publikationen

  1. High-power diode lasers under external optical feed-back

    B. Leonhäuser, H. Kissel, J. W. Tomm, M. Hempel, A. Unger, J. Biesenbach

    SPIE Proceedings Series 9348 (2015) 93480M/1-10
  2. Short-wavelength infrared defect emission as probe for degradation effects in diode lasers

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

    SPIE Proceedings Series 9382 (2015) 93821G/1-6
  3. Long-term aging and quick stress-testing of 980-nm single-spatial mode lasers

    M. Hempel, J. W. Tomm, D. Venables, V. Rossin, E. Zucker, T. Elsaesser

    Journal of Lightwave Technology 33 (2015) 4450 - 4456
  4. Kinetics of catastrophic optical damage in GaN-based diode lasers

    M. Hempel, J. W. Tomm, B. Stojetz, H. Koenig, U. Strauss, T. Elsaesser

    Semiconductor Science and Technology 30 (2015) 072001/1-6
  5. Analysis of 980nm emitting single-spatial mode diode lasers at high power levels by complementary imaging techniques

    M. Hempel, J. W. Tomm, T. Elsaesser, D. Venables, V. Rossin, E. Zucker

    SPIE Proceedings Series 9348 (2015) 93480N /1-6
  6. Experimental observation of exciton splitting and relaxation dynamics from PbS quantum dots in a glass matrix

    F. Yue, J. W. Tomm, D. Kruschke

    Physical Review B 89 (2014) 081303(R)/1-5
  7. Photoluminescence lineshape of ZnO

    B. Ullrich, A. K. Singh, M. Bhowmick, P. Barik, D. Ariza-Flores, H. Xi, J. W. Tomm

    AIP Advances 4 (2014) 123001/1-4
  8. Effect of nanobridges on the emission spectra of a quantum dot–quantum well tunneling pair

    V. G. Talalaev, G. E. Cirlin, L. I. Goray, B. V. Novikov, M. E. Labzovskaya, J. W. Tomm, P. Werner, B. Fuhrmann, J. Schilling, P. N. Racec

    Semiconductors 48 (2014) 1209–1216
  9. Short-wavelength infrared defect emission as a probe of degradation processes in 980 nm single-mode diode lasers

    M. Hempel, J. W. Tomm, F. Yue, M. A. Bettiati, T. Elsaesser

    Laser & Photonics Reviews 8 (2014) L59-L64
  10. Defect temperature kinetics during catastrophic optical damage in high power diode lasers

    M. Hempel, J. W. Tomm

    SPIE Proceedings Series 9002 (2014) 90021H/1-12

Andere Publikationen

Books

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).