The alignment turning of mounted optics and active elements grows in demand for industrial applications. Latest developments cover the measuring of aspheres and free forms, TO canned active laser elements and entire sub assemblies. Due to a growing demand in lithography applications, stainless steel mounts are more commonly used. The machine introduced is performing alignment turning based on a chuckless, fully digital approach. Speeds of up to 3000 rpm are possible to achieve higher cutting speeds, lower cutting forces, and greater productivity. Integration of inline metrology provides an automated solution for finding tilt and shift in various lens designs and materials, including aspheres and infrared materials. The result is faster and more reliable alignment of mounted optics and active elements, opening the possibility to higher production capacity and more affordable processing.
The performance of modern optical systems is dominantly determined by the precision of the alignment of single lens elements in the optical path of the system. The highest alignment precision as well as leading productivity in fabrication can be achieved by alignment turning. A lens to be assembled is glued into a metal mount not considering precision orientation yet. The lens and mount are introduced to an alignment turning machine to measure the optical axis and to correct the metal mount by slow tool turning in a way that the optical and mechanical axis have the same orientation after machining. Remaining shifts of down to 1 micron and tilts < 10 arcsec can be achieved within minutes. As the glue has been solidified prior to machining, there are no more subsequent displacements. The new machine system to be presented is the world leading platform for flexible alignment turning of various types of optics. With its recent developments, it is capable of measuring IR optics with a 4.05 μm laser system. In addition, the optical axis of aspherical lenses can be measured by a full aperture confocal scan without any spherical approximation. Full automation applies to the measuring steps, the slow tool machine program calculation as well as subsequent quality assurance steps. Current tests on objectives with aspheric lenses have led to an overall optical system improvement of < 30% at significantly reduced assembly times. The presentation covers an introduction to the technology and the machines as well as sample machining results.
Diamond turning is a key technology of ultra-precision machining and it is commonly used for the manufacturing of prototypes or mold inserts in growth markets of the photonic industries. A novel method for surface adaptive fast axis ultra-precision turning will be introduced in this paper. With this new approach, it will be possible to incorporate surface properties and machine dynamics for every kind of surface. In a completely digitalized control chain the CNC functionality is transferred from a classical online algorithm to an high density multicore offline operation where set point profiles for each axis are transferred with up to 10.000 Pt/s directly to the servo drive. To adapt the properties of the surface and the machine dynamics all profiles are analyzed in advance to identify critical spots and adapt the set points profiles of all axis to maximize surface quality. To prove the proposed setup an LED headlight surface will be generated and optimized within this paper.
KEYWORDS: Diamond, Chemical vapor deposition, Chemical elements, Optical components, High power lasers, Microwave radiation, Plasma, Adhesives, Laser systems engineering, Laser optics
Laser systems face massive economic challenges for cost effective, but yet ultraprecise assembly processes. Costs are mainly driven by the final assembly requirements of laser systems. Most challenging in this context is the robust process control of the UV-curing adhesive bonding process. The work presented aims for a significant reduction of the impact of shrinkage effects during curing and a resulting increase in assembly precision. Key approaches are integrated and characterized curing systems, ultraprecise dispensing processes and the automated characterization of adhesive shrinkage magnitude. These technologies allow for reproducible adhesive bonding processes in prototyping, job-shop assembly and automated assembly cells.
KEYWORDS: Adhesives, Process control, Model-based design, Laser systems engineering, Polymerization, Polymers, Chemical elements, Systems modeling, Diffusion, Ions
The assembly process of optical components consists of two phases – the alignment and the bonding phase. Precision - or better process repeatability - is limited by the latter one. The limitation of the alignment precision is given by the measurement equipment and the manipulation technology applied. Today’s micromanipulators in combination with beam imaging setups allow for an alignment in the range of far below 100nm. However, once precisely aligned optics need to be fixed in their position. State o f the art in optics bonding for laser systems is adhesive bonding with UV-curing adhesives. Adhesive bonding is a multi-factorial process and thus subject to statistical process deviations. As a matter of fact, UV-curing adhesives inherit shrinkage effects during their curing process, making offsets for shrinkage compensation mandatory. Enhancing the process control of the adhesive bonding process is the major goal of the activities described in this paper. To improve the precision of shrinkage compensation a dynamic shrinkage prediction is envisioned by Fraunhofer IPT. Intense research activities are being practiced to gather a deeper understanding of the parameters influencing adhesive shrinkage behavior. These effects are of different nature – obviously being the raw adhesive material itself as well as its condition, the bonding geometry, environmental parameters like surrounding temperature and of course process parameters such as curing properties. Understanding the major parameters and linking them in a model-based shrinkage-prediction environment is the basis for improved process control. Results are being deployed by Fraunhofer in prototyping, as well as volume production solutions for laser systems.
Depending on the application, high-power diode lasers (HPDL) have individual requirements on their beam-shaping as well as their mechanical fixation. In order to reduce assembly efforts, laser system manufacturers request pre-assembled beam-shaping systems consisting of a support structure for adhesive bonding as well as one, two or more lenses. Therefore, manufacturers of micro-optics for HPDL need flexible solutions for assembling beam-shaping subassemblies. This paper discusses current solutions for mounting optical subassemblies for beam-shaping of high-power diode lasers and their drawbacks regarding quality and scalability. Subsequently, the paper presents a device which can be used for the sensor-guided assembly of beam-shaping systems based on bottomtab support structures. Results from test productions of several hundred modules are presented showing that repeatability in the range of 1 μm is feasible on an industrial level.
Camera objectives or laser focusing units consist of complex lens systems with multiple lenses. The optical performance of such complex lens systems is dependent on the correct positioning of lenses in the system. Deviations in location or angle within the system directly affect the achievable image quality. To optimize the achievable performance of lens systems, these errors can be corrected by machining the mount of the lens with respect to the optical axis. The Innolite GmbH and Opto Alignment Technology have developed a novel machine for such center turning operation. A confocal laser reflection measurement sensor determines the absolute position of the optical axis with reference to the spindle axis. As a strong advantage compared to autocollimator measurements the utilized Opto Alignment sensor is capable of performing centration and tilt measurements without changing objectives on any radius surface from 2 mm to infinity and lens diameters from 0.5 mm to 300 mm, including cylinder, aspheric, and parabolic surfaces. In addition, it performs significantly better on coated lenses. The optical axis is skewed and offset in reference to the spindle axis as determined by the measurement. Using the information about the mount and all reference surfaces, a machine program for an untrue turning process is calculated from this data in a fully automated manner. Since the optical axis is not collinear with the spindle axis, the diamond tool compensates for these linear and tilt deviations with small correction movements. This results in a simple machine setup where the control system works as an electronic alignment chuck. Remaining eccentricity of <1 μm and angular errors of < 10 sec are typical alignment results.
The potential of diamond as an optical material for high-power laser applications in the wavelength regime from the visible spectrum (VIS) to the near infrared (NIR) is investigated. Single-crystal diamonds with lateral dimensions up to 7×7mm2 are grown with microwave plasma assisted chemical vapor deposition (MPACVD) in parallel with up to 60 substrates and are further processed to spherical optics for beam guidance and shaping. The synthetic diamonds offer superior thermal, mechanical and optical properties, including low birefringence, scattering and absorption, also around 1 μm wavelength. We present dielectric (AR and HR) coated single-crystal diamond optics which are tested under high laser power in the multi-kW regime. The thermally induced focal shift of the diamond substrates is compared to the focal shift of a standard collimating and focusing unit for laser cutting made of fused silica optics. Due to the high thermal conductivity and low absorption of the diamond substrates compared to the fused silica optics no additional focal shift caused by a thermally induced refractive index change in the diamond is observed in our experiments. We present experimental results regarding the performance of the diamond substrates with and without dielectric coatings under high power and the influences of growth induced birefringence on the optical quality. Finally, we discuss the potential of the presented diamond lenses for high-power applications in the field of laser materials processing.
Today’s piezo-based micromanipulator technology allows for highly precise manipulation of optical
components. A crucial question for the quality of optical assemblies is the misalignment after curing. The
challenge of statistical deviations in the curing process requires a sophisticated knowledge on the relevant
process parameters. An approach to meet these requirements is the empirical analysis such as characterization of
shrinkage. Gaining sophisticated knowledge about the statistical process of adhesive bonding advances the
quality of related production steps like beam-shaping optics, mounting of turning mirrors for fiber coupling or
building resonators evaluating power, mode characteristics and beam shape. Maximizing the precision of these
single assembly steps fosters the scope of improving the overall efficiency of the entire laser system. At
Fraunhofer IPT research activities on the identification of relevant parameters for improved adhesive bonding
precision have been undertaken and are ongoing. The influence of the volumetric repeatability of different
automatic and manual dispensing methods play an important role. Also, the evaluation of UV-light sources and
the relating illumination properties have a significant influence on the bonding result. Furthermore, common
UV-curing adhesives are being examined on their performance and reliability for both highest precision
prototyping, as well as their application as robust bonding medium in automated optics assembly cells. This
paper sums up the parameters of most influence. Overall goal of these activities is the development of a
prediction model for optimized shrinkage compensation and thus improved assembly quality.
A magnetostrictive bending sensor with rectangular planar coil is investigated. Its purpose is to measure contactlessly
mechanical quantities of non-vibrating structures using an alternating magnetic field. The coil turns are electrodeposited
by pattern plating on top of a magnetostrictive Galfenol layer and a thin isolation layer. The coil turns investigated in this
paper were manufactured with a constant height of 10 μm and gap of 20 μm but variable width.
The sensor is operated near its electrical self-resonance between 5 and 40 MHz and requires a high quality factor. FEMsimulations
show that the quality factor of circular planar coils is almost independent on the conductor width under the
given design restrictions when skin and proximity effects are included.
Analytical calculations of rectangular coil parameters with three different turn numbers and conductor widths depending
on the turn number predict an almost constant self-resonance quality factor in the DC case. Measured self-resonance
quality factors are up to 59 % lower. The main reason for the disagreement is the current crowding by the proximity
effect since analytical calculation show a significant influence of the skin effect only at higher frequencies with respect
to the investigated self-resonance frequencies. Compared to the results of an FEM analysis obtained for circular coils the
proximity effect is much smaller as well as the achievable low frequency quality factor.
The ZnO films have been produced on the monocrystalline sapphite substrates (0001) by the pulsed laser deposition method. The photoluminescence spectra of these films have been obtained. The dependence of ZnO films transmission on the gallium admixture concentration has been determined for the spectral region of 200 to 3200 nm. it has been ascertained that the increase in gallium admixture is responsible for the shift of fundamental absorption band edge to the blue, and for the reduction in ZnO films transparency in the IR region. The dependence of the crystallographic parameters (lattice constant C) on the gallium admixture concentration and on the deposition parameters has been found.
On irradiation of metallic targets from niobium and tantalum with excimer XeCl laser (308 nm) in vacuum the UV and visible spectra of erosion plume were obtained. The erosion plume after ablation of copper, niobium and tantalum targets was studied using Langmuir probe. The ion and electron probe currents were obtained in the range from 0.2 to 2.2 J/cm-2 of energy densities at the target with probe-to-target separations from 10 to 133 mm. Multimodal distributions of ions by scatter velocities have been revealed. The spatial and temporal dependencies of electron probe currents were obtained in real time. The electron temperature of different plume regions was determined from a series of I-U characteristics taken at different distances between probe and copper or tantalum target. It was established that the plume electron temperature is non-uniform and has a maximum value in front of the plume. The acceleration of tantalum ions on plume irradiation with cw CO2 laser recorded. The increase in ions energy from 25 to 50 eV was observed. The emission optical spectra were used in studying the plume qualitative composition. The velocities of atom and ion scatter were measured by the time-of-flight method from the emission optical spectra.
The erosion plume resulting from an ablation of tantalum target in vacuum with excimer laser radiation (308 nm) was studied using Langmuir probe. The spatial and temporal dependencies of electron probe currents were obtained in real time. The electron temperature of different plume regions was determined from a series of I-U characteristics taken at different distances between probe and target. It was established that the plume electron temperature is nonuniform and has a maximum value in front of the plume. The acceleration of ions on plume irradiation with CW CO2 laser recorded. The increase in ions energy from 25 to 50 eV was observed.
The time-of-flight probe method was used in investigations of erosion plume in ablation of copper with 308 nm radiation of excimer XeCl laser in vacuum. The time-of-flight curves of electron and ion currents at the probe were obtained in the range from 0.2 to 2.2 J/cm-2 of energy densities at the target with probe-to-target separations from 10 to 133 mm. Multimodal distributions of ions by scatter velocities have been revealed. The voltage-current curves of probe current have been constructed in the range of probe potentials +/- 18 V. The electron temperature has been calculated for different plume regions. It has been revealed that the plume electron temperature is nonuniform.
On irradiation of metallic targets from niobium and tantalum with excimer XeCl laser (308 nm) the spectra of erosion plume were obtained. These spectra were used in studying the plume qualitative composition. The velocities of atom and ion scatter were measured by the time-of-flight method. Plasma electron temperature was found by continuous spectrum of plume radiation. The results obtained were compared with the outcomes of the previously performed probe measurements of electron temperature and ion scatter velocities.
A vertically sensitive acceleration sensor has been fabricated by combining the low-cost UV-LIGA process with a sacrificial layer technique. The key structure of the sensor is an asymmetric proof-mass which is suspended over two stationary electrodes. Because of the asymmetric arrangement of the proof-mass, an acceleration in the Z-direction results in an opposite deflection of its large and small parts. Hence, the acceleration can be detected by the differential capacitor arrangement between the proof-mass and the two stationary electrodes. The fabrication of this vertically sensitive accelerometer is a planar batch procedure comprising only a few processing steps. The entire structures are first grown electrochemically within the UV- patterned thick AZ4562 photoresist on an electroplating base that composes of rigid and sacrificial layers. Moveable Ni- parts are then obtained by removing the underneath titanium sacrificial layer using wet etching. Sensor structures up to 30 nm with an aspect ratio of about 10:1 can be reliably manufactured. It is thought that this fabrication approach can be widely applied to economically realize other micromechanical components with oscillating structures. Design and realization of the vertically sensitive accelerometer is described in this paper.
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