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Multi-megawatt ultrafast laser systems at micrometer wavelength are commonly used for material processing applications, including ablation, cutting and drilling of various materials or cleaving of display glass with excellent quality. There is a need for flexible and efficient beam guidance, avoiding free space propagation of light between the laser head and the processing unit. Solid core step index fibers are only feasible for delivering laser pulses with peak powers in the kW-regime due to the optical damage threshold in bulk silica. In contrast, hollow core fibers are capable of guiding ultra-short laser pulses with orders of magnitude higher peak powers. This is possible since a micro-structured cladding confines the light within the hollow core and therefore minimizes the spatial overlap between silica and the electro-magnetic field. We report on recent results of single-mode ultra-short pulse delivery over several meters in a lowloss hollow core fiber packaged with industrial connectors. TRUMPF’s ultrafast TruMicro laser platforms equipped with advanced temperature control and precisely engineered opto-mechanical components provide excellent position and pointing stability. They are thus perfectly suited for passive coupling of ultra-short laser pulses into hollow core fibers. Neither active beam launching components nor beam trackers are necessary for a reliable beam delivery in a space and cost saving packaging. Long term tests with weeks of stable operation, excellent beam quality and an overall transmission efficiency of above 85 percent even at high average power confirm the reliability for industrial applications.

We report on an industrial fiber-delivered laser system producing ultra-short pulses in the range of a few picoseconds down to a few hundred femtoseconds with high average power suitable for high-precision micromachining. The delivery fiber is a hollow-core photonic crystal fiber with a Kagome shaped lattice and a hypocycloid core wall enabling the guiding of laser radiation over several meters with exceptionally low losses and preservation of high beam quality (M2

We report on industrial high-power lasers in the green wavelength regime. By means of a thin disk oscillator and a resonator-internal nonlinear crystal for second harmonic generation we are able to extract up to 8 kW pulse power in the few-millisecond range at a wavelength of 515 nm with a duty cycle of 10%. Careful shaping and stabilization of the polarization and spectral properties leads to a high optical-to-optical efficiency larger than 55%. The beam parameter product is designed and measured to be below 5 mm·mrad which allows the transport by a fiber with a 100 μm core diameter. The fiber and beam guidance optics are adapted to the green wavelength, enabling low transmission losses and stable operation. Application tests show that this laser is perfectly suited for copper welding due to the superior absorption of the green wavelength compared to IR, which allows us to produce weld spots with an unprecedented reproducibility in diameter and welding depth. With an optimized set of parameters we could achieve a splatter-free welding process of copper, which is crucial for welding electronic components. Furthermore, the surface condition does not influence the welding process when the green wavelength is used, which allows to skip any expensive preprocessing steps like tin-coating. With minor changes we could operate the laser in cw mode and achieved up to 1.7 kW of cw power at 515 nm with a beam parameter product of 2.5 mm·mrad. These parameters make the laser perfectly suitable for additional applications such as selective laser melting of copper.

The disk laser is one of the most important laser concepts for today’s industrial laser market. Offering high brilliance at low cost, high optical efficiency and great application flexibility the disk laser paved the way for many industrial laser applications. Over the past years power and brightness increased and the disk laser turned out to be a very versatile laser source, not only for welding but also for cutting. Both, the quality and speed of cutting are superior to CO2-based lasers for a vast majority of metals, and, most important, in a broad thickness range. In addition, due to the insensitivity against back reflections the disk laser is well suited for cutting highly reflective metal such as brass or copper. These advantages facilitate versatile cutting machines and explain the high and growing demand for disk lasers for applications besides welding applications that can be observed today. From a today’s perspective the disk principle has not reached any fundamental limits regarding output power per disk or beam quality, and offers numerous advantages over other high power resonator concepts, especially over fiber lasers or direct diode lasers. This paper will give insight in the latest progress in kilowatt class cw disk laser technology at TRUMPF and will discuss recent power scaling results as well.

In recent years, there has been a growing interest in increasing the output power of ultrafast lasers to the kW-range. This allows higher productivity for laser material processing, e.g. for cutting of carbon-fiber reinforced plastics (CFRP) or for micro-machining. We developed an Yb:YAG thin-disk multipass amplifier delivering sub-8 ps pulses with 1.4 kW average power which is – to the best of our knowledge – the highest output power reported for a sub-100 ps ultrafast laser system so far. The amplifier is seeded by a regenerative amplifier with 6.5 ps pulses and 115 W of average power at a repetition rate of 300 kHz. Taking this repetition rate into account, the energy of the amplified pulses is as high as 4.7 mJ. This was achieved using a scheme with 40 mirrors in an array to geometrically fold the seed beam 40 times over the thin-disk. The beam quality was measured to be better than M²=1.4. This system was used in first experiments to cut CFRP with very good quality and with unprecedented efficiency. Additionally, the output beam of the amplifier was frequency-doubled in an LBO crystal to 820 W (70 % conversion efficiency) output power at the second harmonic wavelength (515 nm) and 106 W (26.5 % conversion efficiency) at the third harmonic wavelength (343 nm). Both results are record output powers for ultrafast laser systems at the respective wavelengths. In the presentation, we will show concepts on further power scaling of the system. Keywords: Laser amplifiers, Lasers, solid-state, Lasers, ytterbium, Ultrafast lasers

We report on the fiber-based transmission of sub-ps single-mode pulses with an average power of 50 W at a wavelength of 1030 nm generated by a TruMicro Series 5000 Femto Edition thin disk amplifier. The air-filled hollow-core Kagometype delivery fiber exhibits a hypocycloid core wall and is tailored to offer very low dispersion and nonlinearity at 1030 nm. It minimizes the mode overlap with the glass components to obtain a sufficiently high damage threshold. With propagation losses of only 20 dB/km and an optimized mode matching and coupling by means of a telescope and a 5- axes table we achieve an overall transmission efficiency of more than 80% with a resulting M2 of 1.15. Our laser source offers the selection of repetition rates from 200 to 800 kHz which translates to pulse energies between 60 and 250 μJ. The pulse duration of 900 fs is maintained at the fiber exit, while the spectral width broadens to 20 nm due to self phase modulation in the air core, which could be used to further compress the pulses temporally. Using a fiber-based beam transport allows for mechanical decoupling of the processing head from the laser source, increasing flexibility for applications in the field of material processing with ultra-short pulsed lasers.

In the last decade diode pumped solid state lasers have become an important tool for many industrial materials processing applications. They combine ease of operation with efficiency, robustness and low cost. This paper will give insight in latest progress in disk laser technology ranging from kW-class CW-Lasers over frequency converted lasers to ultra-short pulsed lasers. The disk laser enables high beam quality at high average power and at high peak power at the same time. The power from a single disk was scaled from 1 kW around the year 2000 up to more than 10 kW nowadays. Recently was demonstrated more than 4 kW of average power from a single disk close to fundamental mode beam quality (M²=1.38). Coupling of multiple disks in a common resonator results in even higher power. As an example we show 20 kW extracted from two disks of a common resonator. The disk also reduces optical nonlinearities making it ideally suited for short and ultrashort pulsed lasers. In a joint project between TRUMPF and IFSW Stuttgart more than 1.3 kW of average power at ps pulse duration and exceptionally good beam quality was recently demonstrated. The extremely low saturated gain makes the disk laser ideal for internal frequency conversion. We show >1 kW average power and >6 kW peak power in multi ms pulsed regime from an internally frequency doubled disk laser emitting at 515 nm (green). Also external frequency conversion can be done efficiently with ns pulses. >500 W of average UV power was demonstrated.

Thin-disk lasers with multi-kW output power in continuous-wave operation are widely used for industrial materials processing due to their excellent beam quality, high efficiency, and high reliability with low investment and operation costs. We present our latest laboratory results of nanosecond thin-disk lasers with multi-kW average output power. We show that in pulsed laser systems almost the same average power and beam quality as in CW systems can be realized. Utilizing the cavity-dumping principle for pulse generation we demonstrated more than 4 kW of average output power with pulse energies exceeding 180 mJ. The laser generates pulses with a pulse duration of 20 ns which is almost independent of the power level and the repetition rate. The beam parameter product was measured to be better than 4.5 mm•mrad (M 2 < 14). Deploying intracavity frequency conversion the efficient generation of pulsed laser output in the green spectral range is investigated. Results for a q-switched thin-disk laser with an average power exceeding 1.8 kW and pulse durations between 100 ns and 300 ns are presented. First results for the external second and third harmonic generation of a nanosecond thin-disk laser using the cavitydumping principle are presented. With an incident IR average power of 2.3 kW more than 800 W at 515 nm are demonstrated for the second harmonic generation and more than 500 W at 343 nm are shown for the third harmonic generation with a pulse duration measured to be < 20 ns.

We report on our latest results of near fundamental mode operation of Yb-doped thin-disk lasers. 4 kW of continuous wave output power at M²

This paper highlights the latest advances of disk laser technology at TRUMPF. The disk laser combines unique properties, especially high output brilliance (at the lowest pump brilliance requirements of any high power platform), power scalability and insensitivity to back reflections. In the latest generation of CW disk lasers, 6kW are extracted from one disk in an industrial product at beam qualities suitable for cutting and welding. Laboratory results with up to 4 kW laser power at nearly diffraction limited beam quality (M 2 =1.38) and 8 kW with a beam quality of 3 mm mrad from a single disk and even higher output power levels with lower beam quality will be presented. Finally, results of a frequency doubled CW disk laser will be shown.

Within the past couple of years one can see a general trend in high power diode lasers among others towards the highest possible brightness. The product portfolio of TRUMPF high brightness diode lasers with output power < 1kW will be presented. The architecture of these diode lasers, their main specifications as well as the main features of the control unit are shown. Some examples of the applications of these lasers in such advanced material processing techniques as welding of plastics and welding of thin metal sheets is also presented.

Multi-kW beams with high brightness offer advantages in material processing applications with large distance beam propagation such as remote welding. To achieve the combination of high power and low beam parameter product, the thin disk laser concept is widely used due to its power scalability. Nevertheless, the efficient generation of several kilowatts of output power per disk at beam parameter products below ~3 mm·mrad is limited by an aspherical wavefront distortion in the disk and air turbulences in front of it. In the present paper the limiting factors are discussed and a novel method for compensation is presented. The compensating mirror consists of a silica substrate with a top-hat-shaped layer of 100 nm height to generate the desired phase-front correction and a conventional HR-coating on top. To prevent air convection in front of the thin disk crystal, the laser resonator was filled with helium. The experimental results yield a maximum output power of 3.4 kW and an optical efficiency of 49 % with a beam parameter product of ~2.6 mm•mrad (M 2 ~ 8) at a cooling water temperature of 30 °C.

We have studied experimentally and numerically the pulse shaping dynamics of a diode-pumped thin-disk laseroscillator with active multipass cell and large output coupling rates. We demonstrate the generation of highenergy subpicosecond pulses with energies of up to 25 .9 µ J and durations of 928fs directly from a thin-disklaser oscillator without further ampli“cation. We have achieved these results by employing a sel“maging activemultipass geometry in order to increase the output coupling rate for a suppression of nonlinear optical eects.With this system we have obtained stable single pulse operation in ambient atmosphere with average outputpowers above 76W at a repetition rate of 2 .93MHz. A semiconductor saturable absorber mirror was used tostart and stabilize passive soliton mode locking. The experimentally studied laser pulses show good agreementwith numerical simulations including the appearance of Kelly sidebands. We present a modi“cation to thesoliton area theorem that is applicable for such a laser oscillator with active multiple pass cell and large outputcoupling rate. While numerically simulating the laser, we also investigated the intracavity pulse dynamics withinone round-trip and limitations for power scaling. Furthermore, we demonstrate the lasers potential for micromachining applications by showing “rst examples of material processing, such as the determination of ablationthresholds and ablation rates for various materials.Keywords: (140.3480) Lasers, diode-pumped; (140.3580) Lasers, solid-state; (140.4050) Mode-locked lasers

We have studied experimentally and numerically the pulse shaping dynamics of a diode-pumped thin-disk laser oscillator with active multipass cell and large output coupling rates. We demonstrate the generation of high energy subpicosecond pulses with energies of up to 25.9 μJ and durations of 928 fs directly from a thin-disk laser oscillator without further amplification. We have achieved these results by employing a selfimaging active multipass geometry in order to increase the output coupling rate for a suppression of nonlinear optical effects. With this system we have obtained stable single pulse operation in ambient atmosphere with average output powers above 76W at a repetition rate of 2.93 MHz. A semiconductor saturable absorber mirror was used to start and stabilize passive soliton mode locking. The experimentally studied laser pulses show good agreement with numerical simulations including the appearance of Kelly sidebands. We also present a modification to the soliton area theorem that is applicable for such a laser oscillator with active multiple pass cell and large output coupling rate. Furthermore, we demonstrate the laser's potential for micro machining applications by showing first examples of material processing, such as the determination of ablation thresholds and ablation rates for various materials.

The quasi two-dimensional geometry of the disk laser results in conceptional advantages over other geometries. Fundamentally, the thin disk laser allows true power scaling by increasing the pump spot diameter on the disk while keeping the power density constant. This scaling procedure keeps optical peak intensity, temperature, stress profile, and optical path differences in the disk nearly unchanged. The required pump beam brightness - a main cost driver of DPSSL systems - also remains constant. We present these fundamental concepts and present results in the wide range of multi kW-class CW-sources, high power Q-switched sources and ultrashort pulsed sources.

This paper highlights unique advantages of the disk laser technology for converting the moderate brilliance of laser diodes into excellent solid state laser beam quality with high efficiency. In contrast to traditional diode pumped solid state lasers, particularly all relevant fluencies remain constant when the power is scaled by increasing the active area of the disk. The state of the art TRUMPF disk laser family is presented, including latest results. Theoretical and practical limits are discussed and an outlook over new disk laser generations including high power cw, q-switched, and amplified systems is given.

The fabrication of telecom active devices, such as waveguide amplifiers and lasers, with femtosecond laser pulses is of great industrial interest due to the simplicity, low cost and 3D capabilities of this technology with respect to the standard ones. In this work we will present the various improvements that brought us to demonstrate net gain and the first waveguide laser fabricated with femtosecond laser pulses on an erbium-ytterbium-doped phosphate glass. The first results have been obtained with an amplified, low repetition rate (1 kHz), Ti:Sapphire system. The target of matching the mode field of the fabricated waveguides to that of standard telecom fibers pushed us to develop a novel astigmatic focusing of the writing beam to overcome the asymmetry of the waveguide transverse profile intrinsic in the transversal writing geometry. Despite the circularization of the transverse profile, the high coupling losses allowed only for internal gain in an all-fiber coupling configuration. The best results have been obtained with a very compact, unamplified, diode-pumped Yb:glass laser, with a higher repetition rate (166/505 kHz) and lower energy. In this case, the waveguides exhibited almost perfect mode matching with a telecom fiber allowing coupling losses as low as 0.18 dB and propagation losses of 0.5 dB/cm. Such figures enabled net gain when pumping with 980-nm laser diodes and laser action by terminating the waveguide with two fiber Bragg gratings. These results pave the way to a transfer of femtosecond waveguide writing into the industrial arena for the realization of practical telecom components.