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Laser and Laser Optics

E 053
An Automated Setup for Measuring Laser-induced Damage Thresholds
The Laser-induced damage thresholds (LIDT) of optical components are major design issues for the laser engineer as they limit efficiency and lifetime of many laser systems. Not only does the LIDT of an optical component depend on the laser parameters such as pulse duration, wavelength, beam profile, etc.; it is also closely linked to the production process and thus difficult to estimate.

This setup allows testing of optical components with respect to LIDT and qualification of batches of them for usage in volatile laser systems. It is conform with ISO 11254-2 and can be adapted to a large variety of laser parameters. A monitoring system detects damage of a test spot online and stops its irradiation. In this way, contamination of the test sample is prevented and more test spots can be placed on the test sample. Environmental conditions can be defined (vacuum with p < 1e-5mbar or vented with process gas).

Contact Person
Dipl.-Phys. Ansgar Meissner
Phone +49 241 8906-132
ansgar.meissner @ilt.fraunhofer.de
Fraunhofer Institute for Laser Technology ILT

E 112.4
Assembly Technology
A large number of laser applications would be more competitive if the price of the laser modules would be lower significantly. Cost reductions can be realized by applying fully automated mounting/assembly techniques. For this, the design concept of diode laser modules was changed and improved to make alignment and joining of optical components easier. To realize this a manufacturing system prototype was designed and constructed. This prototype features high flexibility in connection with highly precise alignment. To show the potential of the system a compact green laser module for projection application has been assembled. All components have been positioned and joint accurately and efficiently. UV-curing adhesive with a linear shrinkage smaller than 0.1% has been used to join the components.

Contact Person
Dipl.-Ing. Heinrich Faidel
Phone +49 241 8906-592
heinrich.faidel @ilt.fraunhofer.de
Fraunhofer Institute for Laser Technology ILT

E 118
Automated Assembly of MicroLasers
Presented is a miniaturized solid state laser for marking applications, featuring novel assembly strategies to reduce size, cost and assembly effort. Design and setup have been laid out with future automation of the assembly in mind. Using a high precision robot the optical components of the laser system are directly placed on a planar substrate providing accurate positioning and alignment within a few microns. No adjustable mounts for mirrors and lenses are necessary, greatly simplifying the setup.

Consisting of a Neodymium doped crystal, pumped with a fiber coupled diode laser, a q-switch for pulse generation and a beam expander the entire assembly is confined in a 100ml space and delivers 4W of continuous output power at 1.064?m with an efficiency greater than 40%. Pulse lengths of 10-20ns and repetition rates of up to 150kHz have been obtained with an acousto-optic modulator. In addition, a custom designed electro-optic modulator with integrated high voltage switch has been realized.

Contact Person
Dipl.-Ing. Max Funck
Phone +49 241 8906-351
Lehrstuhl für Technologie Optischer Systeme TOS

E 112.4
bDPSSL: A Compact Design for a Laser Directly Emitting Green Light
The development of compact, low-cost RGB laser beam sources for use in projection applications has the potential to open a large mass market. The proposed solution involves implementing the green component of the RGB module by means of a special optically pumped laser crystal. An off-the-shelf, blue-emitting laser diode is used as the pump source, and a praseodymium-doped YLF-crystal as the active laser medium. This concept to generate green laser light with 523nm is based on a conversion process that guarantees high efficiency and low temperature dependency.

A laboratory setup was realized, using an extremely short resonator with a length of 10mm, with which it was possible to produce a cw output of 136mW from a pump input of 410mW and thereby an electro optical efficiency of 6.5%. The measured beam quality of the laser is M2 < 1.05.

Furthermore a prototype with a customized micro optics, an overall length of 23mm and comparable performance to the laboratory setup was realized.

Contact Person
Dipl. Phys. Michael Strotkamp
Phone +49 241 8906-132
Fraunhofer Institute for Laser Technology ILT

E 118
Beam Shaping and Frequency Stabilization of High Power Diode Lasers
Diode laser modules are used as pump sources for different devices, such as fiber lasers, for signal amplification in telecommunication and can also be used in direct material processing, such as plastic welding. The main advantages of diode laser modules are their high wall-plug efficiency, their small size and their cost efficiency. Various fiber coupled and free space diode laser modules suited for space and terrestrial applications are presented.

High-power diode lasers, which are spectrally stabilized by using diffractive optics, enable power scaling concepts in the field of high brightness laser modules. Therefore direct material processing and the increase of the pumping efficiency of solid state lasers – particularly fiber lasers – can be realized by the implementation of this technique. A characterization setup for volume gratings developed at Fraunhofer ILT is exhibited.

Contact Person
Dipl.-Ing., Dipl.-Wirtsch.-Ing. Martin Traub
Phone +49 241 8906-342
Fraunhofer Institute for Laser Technology ILT

E 100.MB5
Gain-switched Diode-pumped Fiber Lasers
Volume markets in micro materials processing such as laser marking, ablation and drilling require cost-efficient, pulsed beam sources with fundamental mode beam quality. Pulsed fiber lasers perfectly match these demands due to their high efficiency, simple construction and excellent beam quality.

Gain-switched fiber lasers offer a new approach, promising considerable cost saving. The fiber laser is built as an all-fiber oscillator and the pulse is generated by temporal modulation of the pump diodes. So the repetition rate reaches from about 1MHz down to single-shot operation.

In order to show the feasibility of the concept, a single mode ytterbium-doped fiber was pumped with a pump energy of 30?J within 200ns. Pulse energies in the range of 8?J, pulse widths of 1.4?s and repetition rates of 50kHz were achieved.

With an enhanced fiber coupled pump module with up to 300W in 105?m the pulses were shortened to 250ns and the efficiency was increased up to 45% at an output pulse energy of 30?J.

Contact Person
Dipl.-Phys. Martin Giesberts
Phone +49 241 8906-341
Fraunhofer Institute for Laser Technology ILT

E 053
Innoslab Based Amplifier Platform: A Compact 230W Amplifier for Ps Lasers
High-end micromachining with picosecond lasers became an established process during the recent years. Power scaling led to industrial lasers, generating average power levels well above 50W. Such lasers are routinely used in applications like machining turbine blades, micro moulds, and semiconductors. They allow to micro-structure any material, also materials, which are very difficult to process by mechanical means. These lasers offered a new quality in laser micro-machining by cold ablation, a cold removal of very thin material layers, nearly without any thermal side-effects like burrs and micro-cracks.

We present further power scaling, achieved by combining a state-of-the-art industrial LUMERA picosecond laser with Fraunhofer ILT INNOSLAB amplifier technology. Pulses with 10ps-duration and a wavelength of 1064nm were generated from a LUMERA RAPID laser and than further amplified in one compact INNOSLAB amplifier stage well above 230W with an M2<1.5. Experimental results for 0.5, 1 and 10.7MHz repetion rate will be presented.

Contact Person
Dipl.-Phys. Marco Höfer
Phone +49 241 8906-128
Fraunhofer Institute for Laser Technology ILT

Hallway next to E 100.MB1
Intelligent Drivers for Diode-Lasers
The Beratron GmbH specializes in pulsating current sources for applications using high-power diode-laser technology. Beratron current sources are best suited for pulse operation for single diodes, bars and arrays.

Our products are available in a 19 inch rack format and range across different power classes. The sources are available with different output voltage levels. The load-voltage is automatically adjusted by the device. They are equipped with several safety-loops and can be controlled via EIA-232, USB and CAN-Bus.

Some applications are R&D, material processing and SSL pumping.

In cooperation with the Fraunhofer Institute for Laser Technology ILT, Beratron offers Burn–In stations especially designed for development purposes. They can be operated in CW, Pulse or On/Off mode. A pulse current up to 500 Ampere is available.

Contact Person
Dipl.-Ing. Ulf Radenz
Phone +49 241 8906-430
Beratron GmbH

E 100.MB5
Laser Processing Heads for High Power Lasers
The research into laser-based applications and new fields of applications creates a demand for specialized optics and laser processing heads for high power lasers. At the Fraunhofer ILT and the chair TOS innovative optic concepts and laser processing heads for high power lasers have been developed. Examples are: a high speed railway cleaning head, a transformation optics for de-coating metal parts by high-power laser, a coaxial laser brazing head that features a coaxial ring-shaped laser beam distribution in combination with coaxial wire feeding and coaxial process control that allow the deployment of the brazing head without constant reorientation (a development together with Precitec KG) and an application optics for laser assisted incremental sheet forming, which features a rotating laser beam.

Contact Person
Dipl.-Ing. Dipl.-Wirtsch.-Ing. Martin Traub / Dipl.-Phys. Jörg Diettrich
Phone +49 241 8906-342 / -359
Fraunhofer Institute for Laser Technology ILT

E 100.IQ
Micro SLM (Selective Laser Melting)
IQ evolution is specialised in Mikro-SLM and cooling technologies, a rapid manufacturing procedure of three dimensional complex products made of metal powder
  • Our products are micro cooler for high-power laser diodes, cooler for power electronics or LED as well as other complex 3D-structures
  • Our micro coolers are leading f.e. to a significant increase in the lifetime of the laser bars compared to the current copper based cooling echnology (the new materials used here are not exposed to corrosion and erosion)
  • We have special know-how in the Selective Laser Melting process and machines as well as in using special materials, pure materials and custom made material compounds
  • We are able to produce micro structures from 50?m up

Contact Person
Dr. Thomas Ebert
Phone +49 241 8906-347
IQ Evolution GmbH

E 112.4
Oven for Nonlinear Optical Crystals
Nonlinear Optical Crystals as Lithium Triborate (LBO), which has proven its suitability for many industrial concepts of frequency conversion, require an accurate temperature control to provide reliable and constant output power and beam properties. The shown oven does not only allow to keep the temperature constant within a range of 0.02K, but also ensures that the crystal is heated homogeneously to achieve the maximum conversion efficiency. At the same time the mechanical stress is minimized by use of a spring mount for clamping the crystal with controllable force.

Especially for high power applications the suppression of stray light is an important issue. For that reason the oven is equipped with a coolable copper aperture. The oven has proved its functionality in several lasers exceeding 190W of green output power.

Contact Person
Dipl.-Phys. Bastian Gronloh
Phone +49 241 8906-1049
Fraunhofer Institute for Laser Technology ILT

E 053
Qualification of Opto-mechanical Components for Applications in Harsh Environment
Laser resonators and complex sequential amplifier and frequency converting setups require a high mechanical stability of the optical components. For example typical tilt stability requirements of oscillator mirrors are in the range of a few ?rad. For scientific applications the environmental laboratory conditions are quite stable regarding temperature, humidity, pressure, etc. and usually offer low vibrational loads.

But many laser applications in the industrial or scientific field demand stable laser operation in unstable environment. This is especially the case in airborne LIDAR-lasers where high frequency, pointing and energy stabilities have to be ensured at different environmental conditions and with inevitable vibrational noise and mechanical transport shocks. For the development and qualification of appropriate optomechanical components we make climate, vibration and shock tests on component level. To avoid resonant response to vibrational excitation of components and more complex setups theoretical and experimental modal analysis is performed.

Contact Person
Dipl.-Phys. Jens Löhring
Phone +49 241 8906-673
Fraunhofer Institute for Laser Technology ILT

E 112.4
SHG Modules for Laser Radiation with Low Peak Power
Periodically poled nonlinear optical materials can provide high conversion efficiency even at low intensities of the fundamental input radiation, e.g. from continuous wave diode lasers and pulsed fiber lasers. This is a result of the exceptional high nonlinearity of these crystals. In contrast to alternative technologies no optical resonator is required to enhance the field. As a consequence simple system architectures with a minimum of optical components can be developed based on this concept. As alignment tolerances are significantly relieved compared to resonator concepts, innovative mounting and packaging technologies can be applied, aiming for significantly reduced costs, improved compactness and performance.

Examples show a frequency doubled DBR tapered diode laser module with an output power of 500mW and a SHG module for a pulsed fiber laser with 1W average power and 25kW pulse power.

Contact Person
Dipl.-Phys. Bernd Jungbluth
Phone +49 241 8906-414
Fraunhofer Institute for Laser Technology ILT

E 100.MB5
Station for Inverse Glass Drilling of Fiber Preforms
State of the art manufacturing of preforms for polarization maintaining fibers is to fabricate the holes for the stress rods by ultrasonic drilling. This limits the maximum length of the preform and the aspect ratio. Fraunhofer ILT is developing a laser drilling process to exceed this limit.

At this process the laser beam is focused at the bottom side of the preform. The laser beam is deflected by a scanner. This and a translation stage in the z-axis define the ablation volume. With this process holes with a diameter of 500?m and a depth of 80mm, and 130?m slots in a 6mm substrate have been achieved. Thus far a q-switched and frequency doubled Nd:YAG laser has been used. Present experiments aim to achieve a better aspect ratio. For the future experiments with picosecond lasers are scheduled.

Contact Person
Dipl.-Phys. Marcel Werner / Dipl.-Phys. Dipl.-Volksw. Dominik Esser
Phone +49 241 8906-423 / -437
Fraunhofer Institute for Laser Technology ILT
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