The world market for laser micro-processing has seen a tremendous increase within the last 24 months triggered predominantly by large scale projects in the electronics industry. By far the largest contribution to this growth came from UV nano- and picosecond lasers for various applications for manufacturing consumer electronics devices.
The process chain of flexible OLED display used in smart devices (phones, watches, tablets) is heavily relying on ultraviolet lasers: Debonding of the large display foils (typically 1500 x 1850 mm²) from the carrier glass they are produced on is a critical process since it is one of the last steps in the process chain at the peak of the added value. UV nanosecond lasers enable reliable debonding (laser lift-off) without risking any damage to the displays.
Subsequently, the display cells are singulated by laser cutting. Also this process step relies heavily on UV lasers, but in this case with ultrashort pulses. The combination of ultrashort pulse duration and short wavelength allows efficient and precise cutting of these multi-layer materials without unwanted heat affected zones or even thermal damage to the electronics in the display. Various additional parts that are integrated in smart devices like polarizer foils and flexible printed circuit boards are based on multi-material foils and are cut to their net shape with UV nanosecond or ultrashort pulsed lasers.
In this contribution we present an overview of the different UV laser processes and compare the process results from ns, ps and fs lasers to give an outlook on future applications.
In the aviation industry, a major market for carbon fibre reinforced plastics (CFRP), <40.000 drilling operations are performed throughout the assembly process of a small aircraft. Additionally, the drive to minimize costs and time are prevalent in the manufacturing process. The quality requirements in the aviation industry are set to a high level and drilling tools have to be changed frequently, causing considerable costs in terms of tooling and time losses. Laser processing offers benefits such as flexible, and wear free cutting, which contributes to the optimization of processing costs. In this investigation a laser machine, process control, processing strategies and handling equipment adapted to high precision macro drilling and low cycle times were presented. The setup included a novel short pulsed high power laser source by TRUMPF Laser GmbH emitting at λ = 1030 nm integrated in a 5-axis machine. The lab-state laser source provides pulses at tp = 20 ns, at a maximum pulse energy of Ep = 100 mJ and a maximum average power of Pavg = 1.5 kW, while maintaining a very good beam quality, allowing small focus diameters. Due to a large variety of parameters that have an influence on the process, a test plan based on design of experiments was applied to identify ideal parameter fields. Parameters optimized towards high ablation rates and orthogonal kerf angles were identified. The results revealed a promising industrial processing option for high quality macro boreholes.
Based on the thin-disk laser architecture, TRUMPF has been developing and building high-power cw lasers for over two decades. The short pulse thin-disk lasers of the TruMicro 7000 series are employed in a wide range of industrial applications as well. With different wavelengths and pulse energies, the TruMicro 7000 series enables processes like cutting, structuring, and ablation of many materials.
Recently, TRUMPF introduced short pulsed UV lasers based on a disk laser medium for applications requiring high average powers in combination with nanosecond pulse lengths. With 180 W of average output power the TruMicro 7370 combines the highest average power of a solid-state laser with UV output and pulse energies of 18 mJ. With the solid-state platform, the lifetime is significantly increased compared to excimer lasers typically used for high power UV nanosecond applications.
Here, we present the latest development of this laser platform allowing for an increase of the laser power up to 400 W and the pulse energy to 40 mJ employing a cascading scheme for third-harmonic generation. By accessing TRUMPF’s elaborated disk-laser expertise, the new UV nanosecond laser TruMicro 7380 also provides enhanced pulse energy stability.
All these benefits of these short-pulse solid-state UV laser are predestining this platform for large-area applications as e. g. laser-lift-off of flexible OLED displays where average power and pulse energy can be translated into productivity by means of line-beam optics. The possibility of synchronizing up to twelve of these laser devices allows for even higher productivities.
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.
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 (M2 < 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.
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 (M2=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.
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 broad applicability from cw to ps systems. In the new generation of cw disk lasers, 6kW are extracted
from one disk in an industrial product at beam qualities suitable for welding. Moreover, scaling laser power to 10 kW per
disk and resonators with higher brilliance are discussed. These advances are enabled by a combination of power scaling
and increase of optical-to-optical efficiency. In addition, applications of the disk laser principle to pulsed operation, from
ns to ps duration, at infrared and green wavelengths are discussed. Finally, an outlook on the capabilities of disk lasers
towards highest cw power and ultra-high peak powers of petawatts and beyond is given.
The disk laser with multi-kW output power in infrared cw operation is widely used in today's manufacturing,
primarily in the automotive industry. The disk technology combines high power (average and/or peak power),
excellent beam quality, high efficiency and high reliability with low investment and operating costs.
Additionally, the disk laser is ideally suited for frequency conversion due to its polarized output with negligible
depolarization losses. Laser light in the green spectral range (~515 nm) can be created with a nonlinear crystal.
Pulsed disk lasers with green output of well above 50 W (extracavity doubling) in the ps regime and several
hundreds of Watts in the ns regime with intracavity doubling are already commercially available whereas intracavity
doubled disk lasers in continuous wave operation with greater than 250 W output are in test phase.
In both operating modes (pulsed and cw) the frequency doubled disk laser offers advantages in existing and new
applications. Copper welding for example is said to show much higher process reliability with green laser light due
to its higher absorption in comparison to the infrared. This improvement has the potential to be very beneficial for
the automotive industry's move to electrical vehicles which requires reliable high-volume welding of copper as a
major task for electro motors, batteries, etc.
The thin-disk laser concept with its advantages high efficiency, excellent beam quality, and low depolarization losses provides a reliable platform for the generation of high power lasers in the infrared as well as the green spectral range. By employing intracavity-frequency conversion, we have obtained a maximum output power of 700 W at 515 nm and a repetition rate of 100 kHz from a Q-switched Yb:YAG thin-disk laser. An LBO crystal cut for critical phase matching of type I was mounted near one of the end mirrors inside the laser cavity. An optical efficiency (green output power with respect to incident pumping power) greater than 35% could be reached. By changing the low-loss duration at the Q-switch the pulse duration of the laser system can be adjusted between 200 ns and 750 ns with the longer pulse durations being generated with the highest efficiency. This feature can be used to maintain a constant pulse duration when varying the pumping power or repetition rate. The beam
parameter product of 4 mmmrad (M2 < 25) allows for beam delivery via an optical fiber with 100 μm core diameter. To the best of our knowledge, the average power significantly exceeds all previously published results for lasers in the visible spectrum.
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.
Advanced pulsed thin disk laser sources based on several pulse generation schemes, including regenerative amplification
as well as cavity-dumping, will be presented. These sources are able to produce pulse energies in the multi-millijoule
range at repetition rates of up to several 100 kHz, resulting in average output powers in excess of 100 W. Also the
efficient intra-cavity frequency conversion of these sources will be discussed.
Pulsed lasers with high average output power in the green spectral range are of interest for laser annealing applications.
In this paper an efficient pulsed diode-pumped Yb:YAG thin disk laser with intracavity frequency doubling is
presented. The Yb:YAG laser crystal disk has a thickness of 180 &mgr;m and a diameter of 10 mm and is pumped by a laser
diode stack at a wavelength of 938 nm. The disk is soldered to a water-cooled Cu-W heat sink and exhibits a nearly
perfect spherical surface. The folded resonator is dynamically stable with a beam factor of M2 = 5 and which is matched
to the requirements of the application. Acousto-optical and electro-optical switches are investigated to operate the laser
in the cavity-dumping mode. An average output power of 150 W at 515 nm is achieved. The diode-to-green efficiency
is about 28%. A critically phase matched LBO crystal is used for intracavity second harmonic generation. We show that
stable pulsing is obtained from 10 kHz to 150 kHz. The pulse-width can be varied from 200 ns to 700 ns by control of
the low-loss period of the switching element. The experimental results are compared with theoretical modeling of the
system and first application results are discussed.