Real-time determination of laser beam quality by modal decomposition

Schmidt, O.; Schulze, Christian; Flamm, Daniel; Brüning, Robert; Kaiser, Thomas; Schröter, Siegmund; Duparré, Michael

doi:10.1364/oe.19.006741

Cited by 75 publications

(40 citation statements)

References 12 publications

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“…It was orientated horizontally (x-direction) and vertically (y-direction) parallel to the mode field orientations in the hologram. As the correlation filter, different chrome masks, which were adapted to the fibers under test, were applied allowing for real-time modal decomposition of the fiber output [50]. Two different step-index fibers (A and B) and a multicore fiber (C) [51] were investigated, whose parameters are summarized in Table I.…”

Section: Methodsmentioning

confidence: 99%

Mode Coupling in Few-Mode Fibers Induced by Mechanical Stress

Schulze

Brüning

Schröter

et al. 2015

J. Lightwave Technol.

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We investigate mode coupling in few-mode fibers induced by homogeneously and periodically applied mechanical stress. To view the power transfer between individual modes, a modal decomposition is performed at the end of the fiber using computer-generated holograms. Coupling between polarization and angular degenerated modes as well as between nondegenerated modes is confirmed experimentally and coupling parameters are inferred. The presented studies pave the way to detailed investigations of mode coupling in mode-multiplexed telecommunication systems and high-power high beam quality fiber lasers.

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Section: Methodsmentioning

confidence: 99%

Mode Coupling in Few-Mode Fibers Induced by Mechanical Stress

Schulze

Brüning

Schröter

et al. 2015

J. Lightwave Technol.

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“…65 Determination of 4σ -size of noticeably non-Gaussian beams becomes too time consuming. Express techniques 66,67 are not regularly applied. Introducing M 2 into the Gaussian beam equations suggests the caustic symmetry 37,62,64 that is never asserted for an aberrated beam.…”

Section: Laser Beam Shape Position and Distortionmentioning

confidence: 99%

Gas-assisted laser cutting of medium-section metals using spherically aberrated beams

Yurevich

Grimm

Polyakov³

et al. 2015

Opt. Eng

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Abstract. We analyzed the effects of the focal point aberrational offset in optical transport systems for highpower lasers. Transverse and near-axial laser intensity distribution transformations in the presence of both positive and negative spherical aberrations were numerically calculated and experimentally demonstrated for different strengths. We show that spherical aberration yields considerable asymmetry of the focused beam's caustic. Several optical transport systems with identical optical parameters (excluding the noncorrected axial beam spherical aberration) were designed. We examined the effects of the laser intensity profiles produced by these systems on the quality of oxygen-assisted laser cutting of medium-section mild steel. We show that high-quality cuts can be obtained for different shapes of laser intensity distribution. However, the greater the refocusing magnitude introduced by the spherical aberration correction, the more precisely the focal point position must be maintained during the laser cutting process. © The Authors. Published by SPIE under a Creative Commons 1 Introduction Laser cutting of metals and alloys is one of the most commercially valuable laser technology processes. Originating from basic research on laser-matter interaction, 1 the field has significantly developed, now offering a large arsenal of state-of-the-art techniques.2-5 Omitting the energy and resource efficiency issues, 6 the performance of laser cutting can be captured by only two output parameters. These are the cutting speed and kerf quality. Thus, laser cutting optimization reduces to achieving the maximal cutting speed with the best kerf quality. As far as the material separation is concerned, 7 the speed can be dramatically increased. On the other hand, the cutting quality depends on many parameters. The most important and frequently discussed are the kerf geometry (accuracy, width, and taper), the surface quality (cut-edge roughness, striations morphology, and dross and burr inclusions), and the mechanical and metallurgical properties (hardness and strength, heat-affected zone, and oxide layer). 8 The number of parameters dramatically affecting the cutting quality ranges from 25 9 to 75. 4,5 These are nearly evenly divided between the workpiece properties, assist gas parameters, laser machine, and laser beam characteristics. Input-output parameters relationships are mostly nonlinear and exhibit strong interdependence. In this regard, maximal precision is provided by the studies that focus on only one input-output parameter pair. Yet, this "one parameter at one time" approach does not provide complete information on the process as a whole.

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“…In the past decades, some techniques [15,16,17,18,19,20,21,22,23,24] have been developed to measure the dynamic beam quality M 2 factor, such as the Hartmann wavefront sensor [15,16], but it was shown to yield inaccurate results for multimode beams [17,18]. Other methods to perform M 2 comply with ISO11146 techniques, for example, multi-plane imaging using distortion diffraction gratings [19], optical field reconstruction using modal decomposition [20,21], and spatial light modulator method [22]. The self-reference interferometer wavefront sensor (SRI-WFS) method [23,24] is another effective method for real-time measurement of M 2 factor which was developed recently.…”

Section: Introductionmentioning

confidence: 99%

Measurement of M2-Curve for Asymmetric Beams by Self-Referencing Interferometer Wavefront Sensor

2016

Sensors

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For asymmetric laser beams, the values of beam quality factor normalMx2 and normalMy2 are inconsistent if one selects a different coordinate system or measures beam quality with different experimental conditionals, even when analyzing the same beam. To overcome this non-uniqueness, a new beam quality characterization method named as M2-curve is developed. The M2-curve not only contains the beam quality factor normalMx2 and normalMy2 in the x-direction and y-direction, respectively; but also introduces a curve of normalMxα2 versus rotation angle α of coordinate axis. Moreover, we also present a real-time measurement method to demonstrate beam propagation factor M2-curve with a modified self-referencing Mach-Zehnder interferometer based-wavefront sensor (henceforth SRI-WFS). The feasibility of the proposed method is demonstrated with the theoretical analysis and experiment in multimode beams. The experimental results showed that the proposed measurement method is simple, fast, and a single-shot measurement procedure without movable parts.

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Real-time determination of laser beam quality by modal decomposition

Cited by 75 publications

References 12 publications

Mode Coupling in Few-Mode Fibers Induced by Mechanical Stress

Mode Coupling in Few-Mode Fibers Induced by Mechanical Stress

Gas-assisted laser cutting of medium-section metals using spherically aberrated beams

Measurement of M2-Curve for Asymmetric Beams by Self-Referencing Interferometer Wavefront Sensor

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