In surface processing applications the correlation of laser power to processing speed demands a further enhancement of the performance of short-pulsed laser sources with respect to the investment costs. The frequently applied concept of master oscillator power amplifier relies on a complex structure, parts of which are highly sensitive to back reflected amplified radiation. Aiming for a simpler, robust source using only a single ytterbium doped XLMA fiber in a q-switched resonator appears as promising design approach eliminating the need for subsequent amplification. This concept requires a high power-tolerant resonator which is provided by the multikilowatt laser platform of Laserline including directly water-cooled active fiber thermal management. <p> </p>Laserline GmbH and Fraunhofer Institute for Laser Technology joined their forces<sup>1</sup> to upgrade standard high power laser sources for short-pulsed operation exceeding 1 kW of average power. Therefor a compact, modular qswitch has been developed. <p> </p>In this paper the implementation of a polarization independent q-switch into an off-the-shelf multi-kilowatt diodepumped continuous wave fiber source is shown. In this early step of implementation we demonstrated more than 1000 W of average power at pulse lengths below 50 ns FWHM and 7.5 mJ pulse energy. The M<sup>2</sup> corresponds to 9.5. Reliability of the system is demonstrated based on measurements including temperature and stability records. We investigated the variation possibilities concerning pulse parameters and shape as well as upcoming challenges in power up-scaling.
In this paper we present a simple approach to achieving nanosecond pulses from a directly q-switched high-power resonator based on extra-large mode area (XLMA) fibers with a beam quality factor M<sup>2</sup> < 15. An average output power of > 500 W has been demonstrated for repetition frequencies between 50-100 kHz. The resonator consists of a single fiber q-switched with soldered Pockels-cells which exhibit a very high contrast ratio leading to output pulses down to about 10 ns and peak powers up to > 250 kW at 1064 nm wavelength. <p> </p>By using this design instead of a fiber MOPA setup, a cost-effective and less complex system could be implemented.
With GRACE (launched 2002) and GOCE (launched 2009) two very successful missions to measure earth’s gravity field have been in orbit, both leading to a large number of publications. For a potential Next Generation Gravity Mission (NGGM) from ESA a satellite-to-satellite tracking (SST) scheme, similar to GRACE is under discussion, with a laser ranging interferometer instead of a Ka-Band link to enable much lower measurement noise. Of key importance for such a laser interferometer is a single frequency laser source with a linewidth <10 kHz and extremely low frequency noise down to 40 Hz / √Hz in the measurement frequency band of 0.1 mHz to 1 Hz, which is about one order of magnitude more demanding than LISA. On GRACE FO a laser ranging interferometer (LRI) will fly as a demonstrator. The LRI is a joint development between USA (JPL,NASA) and Germany(GFZ,DLR). In this collaboration the JPL contributions are the instrument electronics, the reference cavity and the single frequency laser, while STI as the German industry prime is responsible for the optical bench and the retroreflector. In preparation of NGGM an all European instrument development is the goal.
ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission and the American-German Gravity Recovery and Climate Experiment (GRACE) mission map the Earth’s gravity field and deliver valuable data for climate research.
Spaceborne lidar (light detection and ranging) systems have a large potential to become powerful instruments in the field of atmospheric research. Obviously, they have to be in operation for about three years without any maintenance like readjusting. Furthermore, they have to withstand strong temperature cycles typically in the range of -30 to +50 °C as well as mechanical shocks and vibrations, especially during launch. Additionally, the avoidance of any organic material inside the laser box is required, particularly in UV lasers. For atmospheric research pulses of about several 10 mJ at repetition rates of several 10 Hz are required in many cases. Those parameters are typically addressed by DPSSL that comprise components like: laser crystals, nonlinear crystals in pockels cells, faraday isolators and frequency converters, passive fibers, diode lasers and of course a lot of mirrors and lenses. In particular, some components have strong requirements regarding their tilt stability that is often in the 10 μrad range. In most of the cases components and packages that are used for industrial lasers do not fulfil all those requirements. Thus, the packaging of all these key components has been developed to meet those specifications only making use of metal and ceramics beside the optical component itself. All joints between the optical component and the laser baseplate are soldered or screwed. No clamps or adhesives are used. Most of the critical properties like tilting after temperature cycling have been proven in several tests. Currently, these components are used to build up first prototypes for spaceborne systems.
In scope of the ESA funded “High stability Laser” activity, a single-mode and single-frequency fiber power amplifier with 500 mW output power at 1064 nm wavelength has been developed. It is part of an elegant breadboard (EBB) which consists additionally of an ultra-stable Fabry-Perot reference for frequency stabilization. The monolithic fiber amplifier is seeded by a non-planar ring oscillator (NPRO) with a linewidth below 10 kHz. The amplifier is stabilized in power via pump diode modulation and achieves a RIN performance of < 0.01/sqrt(Hz) in the range from 10<sup>-3</sup> Hz to 10 Hz and a polarization extinction ratio of >30 dB.
We present a laser drilling technology eminently suitable for structuring of solid glass preforms for microstructured optical fibers (MOF). This technology allows fiber designs that can not be easily adressed by stack and draw technology. As an example, we present a four ring hexagonal hole structure drilled in a silica rod over a length of 80 mm at ILT. The fiber drawn from this preform was used for absorption measurements and fiber Bragg grating inscription experiments at IPHT. Geometrical aspects are compared to those of a MOF with a similar structure made by the stack and draw technology.
High power fiber lasers deliver multiple kW laser power with a diffraction limited beam quality. A drawback for
some applications is the arbitrary polarization. We report on experimental and theoretical results of kW class
cw fiber lasers with linear polarization. A comparison of different concepts for generation of polarized high power
output will be presented. The most feasible design for kW class power scaling will be selected. In order to find
an empirical formula for calculating bend loss, additional measurements are carried out and are then compared
to the theoretical results.