KEY APPLICATIONS

Key Applications The research, development and innovation that constitute the LIFT project will lead to a new level of high-brilliance laser sources.

The results of the consortium work will bring radical advances in four important application areas:

• Laser Materials Processing

  Laser cutting plays an important role in the field of laser materials processing. High beam quality, high laser power and high absorption rate are the most important specifications in order to reach higher cutting rates in combination with high cutting edge qualities. Furthermore a high flexible and non-contact materials processing is achieved by using laser cutting.

  Low processing speeds are characteristic for laser materials processing based on robotic arm beam delivery. For example, processing complex geometries, radii and corners will reduce the average cutting speed significantly. Thus, the cutting speeds are currently limited by the dynamics of the handling systems.

  Necessity of high brilliant laser sources for laser welding

  The ideal beam quality of the fibre laser means its beam can be focused to a diffraction-limited spot. Because of the available tight focused spot of the high-power fibre laser beam, it is possible to realize extremely thin welding seams with high aspect ratio at high processing speeds.

  To optimize the welding time for components with various different stitch weldings, a larger working space of the beam deflection is necessary, however, without a loss of beam dynamics and beam quality. Only a high brilliance fibre laser can achieve this combination.

• Health Care Delivery

  LIFT has the objective to develop continuous (CW) high brilliance fibre lasers in the visible spectral range [480 nm – 670 nm]. The technological challenges need to be overcome. Only poor progress has been made in the visible range and almost none in the multi-watt CW regime. The aim is to develop high power, CW, linearly polarized and low spectral bandwidth infrared lasers combined with efficient non-linear stages and medical-optimised beam profiles.

  1. Extract 20 to 100 Watts in the CW regime from an infrared fibre laser in the spectral range [1 ěm – 1.5 ěm] in a linearly polarized state.
  2. Control the fibre laser spectral linewidth, even at high powers with high non-linearities present in the fibre cavity, such as self-phase and cross-phase modulation, Raman scattering, four wave mixing etc.

  No commercial product exhibiting high power, linear polarization, small bandwidth and adapted wavelengths exists. Some scientific publications discuss the generation of yellow fibre lasers (Stanford University- 2007) but with very complex fibre architectures, relatively low optical power (around 1 watt) and no reliability data. LIFT will contribute the needed technology breakthroughs.

  For the medical area, fibre lasers are unique in their ability to produce high brightness at certain key specific wavelengths. The yellow wavelength is for example particularly well absorbed by oxyhemoglobin, making it particularly well adapted for the photo-coagulation process of the retina (Ophthalmology). This wavelength is also well absorbed by the porphyrine of the bacteria present in the surface of the skin. It is much more efficient for acne than current treatments (based on low power solid state blue lasers). It is important to note that in the US and in Europe 17 million people are each year affected by the acne, at different stages of their lives. Red and green wavelengths can also be addressed with fibre lasers. The red colour is another example of a very important wavelength for the treatment of some types of cancer through the use of Photo-Dynamic Therapy (PDT).

  Three-wavelength visible fibre lasers are the key product to take full advantage of fibre laser technology. Lift partner Quantel has the laid out a plan to meet this challenge by carefully designing the cavity architecture. Such a 3-color laser does not exist yet and it represents the “Holy Grail” for these medical markets based on the use of solid state lasers.

• Cost-Effective Manufacturing of Solar Cells for Renewable Energy

  The world-wide market for photovoltaic cells for renewable electricity generation exceeded $50 billion in 2007 (ref MONA Roadmap for Nanophotonic Technologies, 2008, www.ist-mona.org). The continued success and adoption of solar power depends on lowering the cost per installed watt, now standing at 5 Euros per watt to achieve an objective of 1 euro per watt. Since the efficiency is already close to the ideal maximum, the only way to reduce the cost per watt by 80% is to lower production costs.

  Laser fabrication of solar cells involves 3 different operations: edge passivation of the individual cells, ablation lithography of the contact materials and laser separation of the cells from each other. The processing laser must be able to perform all these tasks using flying-spot scanning to process the entire substrate in the minimum amount of time.

  Requirements:

  1. Pulsed laser with variable duty cycle, peak power exceeding 5 kWatt and pulse width of less than 50 pSec.
  2. Complex beam delivery that implements remote scanning while maintaining the same spot size and geometry at the target, independent of the distance from the source

  No commercial laser of any type can meet these requirements. Furthermore only a fibre laser is capable of meeting them. The LIFT project aims to meet these requirements and enable the application.

  TBP will develop the system architecture and perform integration work including design, development, assembly and testing of the complete laser source, having 100 MW peak power per fibre with sub picosecond pulse length. SPI will develop the first pulsed fibre laser having a continuously variable pulse repetition rate and duty cycle. The Fraunhofer IWS will develop the beam delivery system capable of meeting the exacting requirements of large-area processing.

• Manufacturing of the next-generation of ICs with nanometre feature size

  Moore's law for integrated circuits calls every year for greater reductions in feature size. Conventional optical lithography can no longer function below the 193nm node. Extreme UV lithography, using light from plasma fluorescence at 13nm, is the principal production hope for reaching feature sizes below this limit. The Technology Roadmap for Semiconductors (ITRS, 2007) puts EUV lithography on the map, entering fully into the commercial production phase in about 5 years. EUV lithography is generated by focusing a high power laser beam on a target in order to generate the necessary 13nm fluorescence. One of the roadblocks to the development of this technology is the low fluorescence yield. As a result the 13nm radiation is too weak to be used in a production environment. Fluorescence generation is a complex non-linear optical effect. High power in the excitation beam is not the only parameter.

  What is really needed is extremely high brilliance: lots of photons in the same place at the same time.

  Today, fibre lasers have natural brilliance limits due to non-linear optical damage to the fibre and the optical components. The Lift project proposes a revolutionary redesign of the laser to get around these “natural limits” by adapting technologies from optical fibre telecommunications to maintain the optical intensities below the damage limit while reaching levels of instantaneous optical power at the fluorescence target that have never been observed previously.