Commercialization of multi kilowatt femotosecond lasers

Fraunhofer-Gesellschaft – Ultra-short laser pulses of outstanding high average püower are opening the doors to new applications in high throughput materials processing. Thanks to the short pulse duration, thermal damage of the material being processed is minimized.

For years, ultra-short laser pulses have been used for the extremely precise and gentle processing of highly-sensitive materials. Until now though, they have often lacked in power. The newly developed laser platform solves this problem with the INNOSLAB amplifier as its core. Four mirrors surround a laser crystal plate – the slab. Pump radiation enters at the two opposite faces of the slab. Ultra-short laser pulses are repeatedly reflected by these mirrors and pass through the slab several times. Energy is transfered from the pump radiation to the laser pulse until the required power is achieved.

To develop new markets for laser systems with ultra-short wavelengths, the team of developers had to increase the mean laser output of ultra-short pulse beam sources – up to several hundred watts. Higher power makes high volume production in industrie and shorter measuring times during scientific experiments possible.

Edgewave – EdgeWave started the development of industrial-suited over 1000Watt femotosecond-lasers on March 1, 2012. The project is being supported by the BMBF as a part of its funding initiative „Ultrakurzlaser für hochpräzise Bearbeitung“ and as part of the collaborative project „Femtosekundenlaser höchster Leistung (FOKUS)“. The collaborative project will be coordinated by EdgeWave, while the controlling agency is the VDI-TZ from Düsseldorf.

The focus of the project is the implementation of a reliable, compact and and cost effective and industrial suited fs-laser with an average power of over 1000Watt and a pulse duration in the range from 200fs to 1ps. For the processing of materials – e.g. fiber-reinforced plastics for lightweight designs – the beam sources of the aimed-at power class will enable a significant decrease in processing time.

Lately ultra-short-pulsed laser technology has become more and more economical not only in micro machining but also in macro machining of materials while in the medical sector ultra-short-pulsed lasers enable entirely new therapeutic approaches such as highly precise cuts of the eye with minimal damage. The fundamental feature of these laser beams are their extremely high peak intensities with low pulse energy enabling highly precise ablation processes and processing of temperature sensitive materials without causing thermal damage. In the production of LEDs or computer chips the yield per wafer will increase and in one of the most performed surigcal operations, the therapy of cataracts, new significantly more efficient and cheaper methods will be implementable. Those new therapeutical methods for age-related longsightedness will be rivaling the classical reading glasses in near future.

Ultra short pulse lasers

EdgeWave’s ultra short pulse lasers are diode-pumped and mode locked solid-state oscillators and amplifiers. The amplifiers are based on the unique INNOSLAB laser technology. Through an optimal combination of crystal shape, cooling and resonator design, ultra short pulse lasers with INNOSLAB amplifiers poss special qualities:

* Compact setup
* High efficiency and high amplification factor
* High beam quality
* Scalability for multi kW

Higher power, high repetition ultra short pulse lasers will help enable commercial nuclear fusion and high performance space propulsion.

In 2011, John Chapman of NASA proposed a pulsed laser system for megawatt class fusion propulsion.

In Chapman’s aneutronic fusion reactor scheme, a commercially available benchtop laser starts the reaction. A beam with energy on the order of 2 x 10^18 watts per square centimeter, pulse frequencies up to 75 megahertz, and wavelengths between 1 and 10 micrometers is aimed at a two-layer, 20-centimeter-diameter target.

The momentum of the energetic alpha particles provides clean, high ISP ~900,000 as vectored thrust such that p-11B offers a clean fuel with well understood reaction kinematics.

In 2010, the maximum pump output of the Yb:INNOSLAB amplifiers was increased by 50 percent to 1250 W by new laser diodes. The radiation of a Yb:KGW fs oscillator with a repetition rate of 20 MHz and an average output of 2 W is amplified in a Yb:YAG INNOSLAB amplifier with seven transits to an output of 620 W and a pulse energy of 31 μJ. The pulse duration is 636 fs and the beam quality M² less than 1.5. By means of an additional transit in a second amplifier an average output power of 1.1 kW is attained with a pulse duration of 615 fs and a beam quality of M² less than 3 in a linearly polarized beam. At a pulse energy of 55 μJ and a pulse peak output of 80 MW there were no signs of self-phase modulation.

Ultra-short-pulse lasers of high average output power and with a pulse energy of a few 10 μJ open up new applications in material processing, increase the throughput rate and make industrial use economically viable. In scientific applications they also increase the efficiency and power of non-linear processes, such as frequency conversion, optically parametric amplification and the generation of high harmonics, and thus improve the signal-to-noise ratio of measurements.

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