Dissertationspreis Adlershof 2013 goes to Dr. med. Martin Hempel

On 13 February 2014, the award winner was selected for the Dissertationspreis Adlershof 2013: Martin Hempel has prevailed against two other nominees and in the unanimous opinion of the jury his doctoral thesis "Defect Mechanisms in Diode Lasers under High Optical Load: The Catastrophic Optical Damage" presented best in the final decision.

Martin Hempel had already discovered his enthusiasm for researching novel semiconductor lasers as a graduate student and, as a doctoral student at MBI, investigated the ultimate performance limits of these universally applicable lasers. Here, Hempel dealt in particular with the so-called Catastrophic Optical Damage (COD). This refers to the destruction of semiconductor diode lasers at high optical intensities. In this case, a volume of about 1 micron3 of the laser material is heated by absorbed laser light within 1 ns until melting at ≈1600°C. As a result, the defect (COD) spreads in the laser at a speed of around 90 km / h. Within a few μs, this destroys the entire laser whose volume is about 1000 times greater than the starting point of the defect. In his work Hempel was able to track the COD spat-temporally during its formation. This brought new insights into the physical mechanisms of the process. The close cooperation with manufacturers of semiconductor lasers now enables a targeted improvement of the components, as their weak points in high-performance operation can now be identified quickly and clearly.

Further information:


Dr. Martin Hempel, phone: +49 (0)30 6392 1453

About the price

Fig. 1 The Adlershof Dissertation Prize has been awarded annually since 2002 by the Humboldt-Universität zu Berlin, the initiative community of non-university research institutions in Adlershof e.V. (IGAFA) and WISTA-MANAGEMENT GMBH. Three nominees nominated in advance by the jury due to the high scientific quality of their work compete against each other with short lectures on the topic of their dissertation. The jury then decides who not only conducts very good research, but can also deliver rousingly and convincingly.

Fig. 2 Reconstructed COD damage image (gray) in the laser plane. By means of a thermal camera, time-resolved images of the heat radiation originating from the COD were taken from the side of the component and at the same time from the front side. The center of gravity coordinates of these thermal signatures observed from two directions were now plotted as black points in the x-z diagram (x along the laser front facet, z along the resonator axis). This makes it possible to track the defect structure in the interior of the device spatiotemporally resolved. The upper part of the picture shows thermal images at different times, as seen from the front facet. The times are marked accordingly in the x-z diagram. The constant signal level indicates a constant temperature at the defect front. From the time and location data results in a propagation speed of the defect of about 90 km / h.

Fig. 3 Electron microscopy on a sample damaged by COD. The dashed line indicates the position of the front facet on the left. The material bulging in this area can be clearly seen. The damage of the active laser layer extends from there to the right edge of the image. Material analysis of the damaged area revealed that the total damage growth was at a temperature of approximately 1600 ° C.