PhD Defence by Mathias Christensen

Title: Power scaling of frequency converted visible lasers



Supervisor: Ole Bjarlin Jensen

Co-supervisor: Danny Noordegraf, Norlase

Evaluation Board
Group Leader Christian Pedersen, DTU Fotonik
Group Leader Bernd Jungbluth, Fraunhofer Institute for Laser Technology, Germany
Associate Professor Gaëlle Lucas-Leclin, Institut d’Optique, Laboratoire Charles Fabry, France

Master of the Ceremony
Professor Paul Michael Petersen, DTU Fotonik


Visible lasers with Watt level output powers have, for the past two decades, been dominated by the diode pumped solid state (DPSS) laser. These lasers are, unfortunately, rather ineffective and sensitive to external perturbations and, therefore, often require water cooling.

An alternative technology based on cascaded single pass frequency doubling of high power tapered laser diodes have been developed at the Technical University of Denmark. This thesis contains the newest results based on this technology, including the move towards new wavelengths where 1.9 W at 561 nm and 2.7 W at 577 nm has been demonstrated. Especially 577 nm is of great interest, as this exactly matches the peak in the absorption curve for oxygenated haemoglobin, making it highly desired in the medical industry. 

Modulation of the second harmonic light is also examined, including how the narrow wavelength acceptance of the non-linear crystals is both a hindrance and a way to achieve said modulation. At the same time the non-linear crystals can be used to extract information on the temporal wavelength characteristics of the laser diodes at a µs time scale with pico-meter resolution. Lastly, the behaviour of the laser diodes under the influence of a controlled amount of optical feedback is examined, as this is currently the main obstacle for wide-spread use of frequency doubled tapered laser diodes as a visible laser source.


man 25 mar 19
13:00 - 16:00


Risø Campus

Building 112, auditorium Niels Bohr