The 4-meter Multi-Object Spectroscopic Telescope (4MOST), wide-field, high-multiplex spectroscopic survey facility will enable the simultaneous spectroscopy of up to 2400 targets within a 2.5° diameter field of view. A secondary guider system optical relay and data production description is described. The role of this guider is for fine rotational and target alignment corrections. The output of the 12 times 7 fibres are arranged such that the CCD detector can be read out in continuous read mode. The position of all fibres are illuminated at their spectrograph end and measured using a camera system at the positioner end. For the secondary guide bundles, only the central fibre is illuminated. A notch filter is used in the image relay in such a way that that the back illumination light is reflected from back illumination fibres to illuminate only the central fibres of each guide probe. This allows on-sky guiding while the fibres are being positioned.
Fiber beam delivery of high power pico- and femtosecond pulses offers many advantages in industrial application. This includes flexible beam delivery, easy integration into machines and production environment as well as laser safety and robustness. Using micro-structured hollow core fibers nearly single mode transmission of ultra-short pulses with excellent beam quality can be achieved over several meters and has been reported in numerous publications during the last couple of years. Laser light cables and beam delivery systems with these fibers are now available and capable of delivering pulses of several 100 μJ with 90% transmission over 10 m long fibers while maintaining excellent beam quality (M2 1.2 - 1.4). For successful industrial application, several additional factors need to be taken into account. This includes system robustness against changing laser input parameters as the output of a laser source can change, robustness against fiber bending in applications with dynamically moved fiber as well as operation free of maintenance and realignment. In order to address these, the relevant effects impacting the performance of fiber delivered laser pulses have been studied. We will report experimental results of fiber bending effects on beam parameters critical for micromachining applications and analyze the influence of laser to fiber coupling. In addition, micromachining applications employing a modular fiber beam delivery system will be shown and the impact of induced beam parameter changes on the micromachining process discussed.
Flexible beam delivery of high power pico- and femtosecond pulses offers great advantages in industrial applications. Complex free space beam delivery as found in robot or gantry systems can be replaced, laser safety and uptime increased and system integration in production environment simplified. Only recently fiber beam delivery has become available for ultrafast lasers while it has been an established standard for cw and pulsed laser sources for many years. Using special kinds of fiber that guide the laser beam mostly inside a hollow core, nonlinear effects and catastrophic damage that would arise in conventional glass fibers can be avoided. Today, ultrafast pulses with several 100 μJ and hundreds of MW can be transmitted in quasi single mode fashion with micro-structured hollow core fibers. During the last years we have developed a modular beam delivery system that suits industrial ultrafast lasers and can be integrated into existing processing machines. Micro-structured hollow core fibers inside the sealed laser light cable efficiently guide high-power laser pulses over distances of several meters with excellent beam quality, while power, pulse duration and polarization are maintained. We report on the technology required for fiber beam delivery of ultrafast laser pulses and discuss requirements for successful integration into industrial production as well as achievable performance under realistic operation and show examples of micromachining applications.
Flexible beam delivery can significantly simplify the necessary effort to connect a laser source to an application. While already a standard in high power cw-applications, ultrashort pulse applications in the ps to fs regime mainly relies on free space beam delivery to date. In the last years we have introduced and characterized a modular beam delivery system for ultrashort high energy pulses [1]. It is based on micro structured hollow core fibers that confine the light into a hollow core and thereby allow pulse delivery way above the damage threshold of silica with minimal influence on the pulse. Ultrafast pulses with pulse energies of several 100 μJ and average powers of several 100 W can be transmitted with high single mode beam quality. Additionally, nonlinear effects inside the fiber can be actively used to adjust pulse parameters on the fly, e.g. an effective pulse compression which increases the peak power even further.
Here we show the analysis of short pulse material processing using the flexible beam delivery. Results for sensitive processes as well as the active use of nonlinear spectral broadening are shown.
Fiber based laser beam delivery is the method of choice for high power laser applications whenever great flexibility is required. For cw-lasers fiber beam delivery has long been established but has recently also become available for ultrafast lasers. Using micro-structured hollow core fibers that guide the laser beam mostly inside a hollow core, nonlinear effects and catastrophic damage that arise in conventional glass fibers can be avoided. Today, ultrafast pulses with several 100 μJ and hundreds of MW can be transmitted in quasi single mode fashion. In addition, the technology opens new possibilities for beam delivery systems as the pulse propagation inside the fiber can be altered on purpose. For example to shorten the pulse duration of picosecond lasers down into the femtosecond regime. We present a modular fiber beam delivery system for micromachining applications with industrial pico- and femtosecond lasers that is flexibly integrated into existing applications. Micro-structured hollow core fibers inside the sealed laser light cable efficiently guide high-power laser pulses over distances of several meters with excellent beam quality, while power, pulse duration and polarization are maintained. Robust and stable beam transport during dynamic operation as in robot or gantry systems will be discussed together with optional pulse compression.
Beam delivery systems are an integral part of industrial laser equipment. Separating laser source and application fiber optic beam delivery is employed wherever great flexibility is required. And today, fiber optic beam delivery of several kW average power is available for continuous wave operation using multimode step index fibers with core diameters of several 100 μm. However, during short-pulse or even ultra-short pulse laser operation step index fibers fail due to high power density levels and nonlinear effects such as self-focusing and induced scattering. Hollow core photonic crystal fibers (HC-PCF) are an alternative to traditional fibers featuring light propagation mostly inside a hollow core, enabling high power handling and drastically reduced nonlinear effects. These fibers have become available during the past decade and are used in research but also for fiber laser systems and exhibit a growing popularity. We report on using HC-PCF fibers and their integration into an industrial beam delivery package comparable to today’s fiber optic standards and will discuss power handling, beam quality and efficiency as well as future prospects of this technology. In a preliminary industrial beam delivery setup 300 fs pulses at 100 W average power could be delivered.
Asymmetric imaging errors are frequently the main cause for tight tolerances and high demands on manufacture and
assembly of optical systems. In order to simultaneously increase robustness and reduce manufacturing cost,
desensitization strategies can be applied. Tolerance effects have been included into the optimization function (merit
function) by some lens designers to find insensitive designs 1-5 and frequently compensators are employed to further
improve the performance of assembled lenses. Compensators are limited to a small number of system parameters, but
selective assembly of components can extend the number of parameters available for compensation. It can be employed
to reduce tolerance effects of disturbed parameters by finding the best matches out of a set of components. The potential
of using tolerance desensitization in conjunction with selective assembly to reduce asymmetric errors in imaging optical
systems is investigated. A focus is given on strategies to find tolerance insensitive design forms under the presence of
selective assembly compensators and the selection of suitable parameters for desensitization and measurement.
Tolerancing has long been identified as a crucial part in the development of optical systems. It aims at finding the best
balance between quality and cost as tolerances closely tie together manufacturing expenses and performance. Tolerance
effects have been included into the optimization function (merit function) by some lens designers to find insensitive
designs1-5 and frequently compensators are employed to further improve the performance of assembled lenses.
Compensators are limited to a small number of system parameters, but selective assembly of components can extend the
number of parameters available for compensation. It can be employed to reduce tolerance effects of disturbed parameters
by finding the best matches out of a set of components.
In this work we discuss how desensitization and selective assembly can be combined to loosen tolerances and increase
as-built performance. The investigations concentrate on tolerance insensitive design forms under the presence of
selective assembly compensators. In contrast to desensitizing a given lens or introducing new design means we focus on
introducing new assembly strategies into the design procedure and investigate how using selective assembly as a
compensator while desensitizing the remaining design parameters can lead to even less sensitive designs.
A miniaturized solid state laser for marking applications has been developed 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 composing 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 either a ND:YAG or a Nd:YVO4 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 4 W of continuous output
power at 1.064 μm with an efficiency greater than 40%. Pulse lengths of 10-20 ns and repetition rates of up to 150 kHz
have been obtained with an acousto-optic modulator. In addition, a custom designed electro-optic modulator with
integrated high voltage switch has been realized. A supply unit for the entire system, including scanner and water
cooling, is integrated in a 19" industrial chassis and can be operated via a graphical user interface on a standard personal
computer.
Selective assembly is presently employed where fabrication of components to the required precision is infeasible,
exceedingly expensive or if extremely high system performance is required. Even though these attributes frequently
apply to optical systems, selective assembly is rarely applied. However, current investigations on selective assembly of
microscope objectives can be found. A computer simulation approach has been taken to investigate the potential of
selective assembly to optical systems, taking optic-specific influences and quality criteria into account. The process of
selecting randomly distributed components and finding the best matches was modelled and integrated in ray-tracing
simulations. Thus, the development environment originally used to design the optical system can also be used for the
analyses. Components with parameters varying randomly according to their tolerance distributions are generated,
possible component combinations created and entered in the ray-tracing simulation. Optimization steps can be employed
accounting for alignment procedures or compensators. This procedure is repeated for sets of n components that shall be
combined to exactly n systems. Out of all possible permutations the best set is chosen. Repetition of the experiment
provides data for statistical analysis of the matching process. The method has been successfully applied to centration
errors of a laser pump optic.
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