MBI Staff Member – Personal info
Dr. Jens Tomm
+49 30 6392 1453
C2: Solid State Light Sources
Building C, 3.1
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.
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.
- Defect evolution during catastrophic optical damage in 450-nm emitting InGaN/GaN diode lasers SPIE Proceedings Series 10553 (2018) 1055308/1-7
- Chip-carrier thermal barrier and its impact on lateral thermal lens profile and beam parameter product in high power broad area lasers Journal of Applied Physics 123 (2018) 125703/1-11
- Ultrafast carrier dynamics in a GaN/Al0.18 Ga0.82 N superlattice Physical Review B 97 (2018) 161303/1-5
- Emission kinetics from PbSe quantum dots in glass matrix at high excitation levels Physica Status Solidi-Rapid Research Letters 12 (2018) 1800012/1-6
- Assessment of factors regulating the thermal lens profile and lateral brightness in high power diode lasers SPIE Proceedings Series 10085 (2017) 1008502/1-10
- Analysis of GaN based high-power diode lasers after singular degradation events Physica Status Solidi-Rapid Research Letters 11 (2017) 1700132/1-6
- Tailored bars at 976 nm for high-brightness fiber-coupled modules SPIE Proceedings Series 10086 (2017) 100860B/1-12
- Analysis of waveguide architectures of InGaN/GaN diode lasers by nearfield optical microscopy SPIE Proceedings Series 10123 (2017) 1012308/1-7
- GaAs/GaP quantum dots: Ensemble of direct and indirect heterostructures with room temperature optical emission Applied Physics Letters 108 (2016) 102103/1-5
- Assessing the influence of the vertical epitaxial layer design on the lateral beam quality of high-power broad area diode lasers SPIE Proceedings Series 9733 (2016) 97330O/1-9
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).