Dr. Thomas Brand, DILAS: No playground for record claims
The EU funded BRIDLE program started in September 2012 with a term of three years. In addition to DILAS, partners include Fraunhofer ILT, Ferdinand-Braun Institut (FBH), University of Nottingham, Modulight, CNRS - Institut d'Optique, and Bystronic Laser. Dr. Thomas Brand is the project coordinator for BRIDLE and is responsible at DILAS for coordinating publicly funded R&D projects.
1. You coordinate the BRIDLE (Brilliant Industrial Diode Laser) project. What is the goal of the project?
Dr. Thomas Brand: BRIDLE is a collaborative project funded by the EU in FP7, which aims to explore the boundaries for improving the beam quality of direct diode laser modules at high power output rates.
Our intention is to develop a diode laser with an output power of 2kW and a beam quality of 7-8 mm mrad.
A number of different paths are being explored in parallel in BRIDLE for this purpose. For example, alongside the existing more conventional power scaling approaches, such as dense layering of many wavelengths, coherent beam combining techniques are also being examined for their suitability for power scaling.
2. Which output and beam qualities are essential for cutting applications?
Dr. Thomas Brand: Naturally this can only be a first step on the path toward finding the "right" mass application for cutting thin sheets with lasers. Beam qualities of 3-4 mm mrad at output rates of 1 kW and higher are needed for this purpose, which have been achieved comfortably to date by fiber lasers or CO2 lasers. BRIDLE is still some way off this. BRIDLE is more about laying the foundations and identifying and overcoming some of the existing technical hurdles.
3. At what point does it seem to make more sense to use a diode-pumped laser as opposed to a diode laser?
Dr. Thomas Brand: That's something we want to find out in BRIDLE. The question is not just about what is feasible technically but also what makes sense in economic terms. We of course also strive at DILAS to achieve commercially exploitable results and as a member of the Rofin family we aim to offer our customers the most suitable lasers for a given application. While the direct diode laser is undoubtedly an important product for us, it is likewise not a playground for zealous record claims, rather it has to be a useful tool for industrial applications.
The beam shaping and scaling of diode lasers at a higher brilliance is of course costly also in terms of efficiency and requires a high level of technological effort. There is direct competition here with fiber lasers, which already today can achieve degrees of efficiency of 40 percent, and naturally with the proven CO2 lasers. That is the benchmark by which we have to measure our solutions. The point at which it would be better to work with other laser types is still unknown, however, and if we want to remain at the very top technologically in Europe such issues have to be reviewed on an ongoing basis.
4. What measures should be used on the chip to ensure the brilliance of the diode laser and make it suitable for the mass market?
Dr. Thomas Brand: The basis is always the individual diode laser emitter as its beam parameter product cannot be improved. Only the usual degrees of freedom can then be used and the power scaling techniques optimized to minimize losses on the path to the workpiece.
Emitters with optimum beam quality are being developed and scaled to a high power output level for this reason by FBH in Berlin in the framework of BRIDLE, with both internal and external methods of wavelength stabilization being examined jointly by the partners. Dense wavelength multiplexing is one of the central possibilities here for achieving optimum power output levels with very good beam quality.
5. Are there other advantages of the new approaches?
Dr. Thomas Brand: The approaches followed here are especially suitable for taking advantage of the existing know-how we have for automatically assembling the components. This starts with the concept prototyping and is detailed in the design. Some steps can be implemented for the laboratory prototypes on automated product line equipment. This means we can concentrate on the main steps when constructing a prototype and reduce the time to product launch.
6. What is the current status of the BRIDLE project?
Dr. Thomas Brand: Following initial difficulties and delays, which are matter of course with such a complex topic, we are now making good progress. We are confident that by summer of next year we will be close to the 1 kW threshold for a prototype of a diode laser device with transmission over a 100µm fiber. A "fractal" concept will be adopted here. The necessary high-brightness submodules are already implemented.
7. What can be expected for next year up to the time the project concludes?
Dr. Thomas Brand: It will take a little time yet before a commercially available device is a reality. Questions also have to be examined with respect to reliability, impact of feedback, stability of the beam quality over the lifetime, and the possible application areas. Only when the economics of the direct diode laser are right will a product be implemented from the technologies elaborated here. While we foresee that this point will be reached, the question remains as to "when".
Thank you for the interview.