MATERIALS TESTING FOR JOINING AND ADDITIVE MANUFACTURING APPLICATIONS 213 speckle photometry – Optical sensor systems for condi- tion and process monitoring

Lili Chen, Ulana Cikalova, Beatrice Bendjus, Laser speckle photometry (LSP) is an innovative, non-destruc- Andreas Gommlich, Shohag Roy Sudip, tive monitoring technique based on the detection and analy- Carolin Schott, Juliane Steingroewer, Dresden, sis of thermally or mechanically activated speckle dynamics Matthias Belting, Aachen, and in a non-stationary optical field. With the development of Stefan Kleszczynski, Duisburg, Germany speckle theories, it has been found that speckle patterns carry information about surface characteristics. Therefore, LSP offers a great potential for the characterization of mate- rial properties and monitoring of manufacturing processes. In contrast to the speckle method, LSP is very simple and robust. The sample is illuminated by only one la- ser beam to generate a speckle pattern on the surface. The Article Information signals obtained are directly recorded by a CCD or CMOS Correspondence Address Dr.-Ing. Beatrice Bendjus camera. By appropriate optical solutions for the beam path, Fraunhofer Institute for Ceramic typically, resolutions of less than 10 μm are reached if larger Technologies and Systems IKTS Maria-Reiche-Str. 2 areas are illuminated. LSP is definitely a contactless, quick 01109 Dresden, Germany and quality relevant material characterization and defect de- E-mail: [email protected] tection method, allowing process monitoring in many indus- Keywords trial fields. Examples from online biotechnological monitoring Laser speckle photometry, process-monitoring, defect-monitoring, build-up welding, additive and laser based manufacturing demonstrate further poten- manufacturing, biomass tials of the method for process monitoring and controlling.

Material testing and material properties and practice, is presented, thus offering an ent laser beam upon an optically rough characterization, which guarantee the innovative approach to optical NDT and surface that results in a boiling grainy im- quality of materials and promote progress monitoring. age [2]. The theory of speckle or dynamic in manufacturing, play a significant role in speckle belongs to the category of statisti- both academic and industrial fields. New Theoretical approach cal optics for which a detailed account of non-destructive testing (NDT) methods the phenomena is given by Goodman [3], and appropriate sensors developed in the Speckle or speckle patterns are interfer- including the mathematical description of industry are used for detecting defects ence patterns produced by a co- speckle properties, for instance the central such as porosities or delaminations as well herent light beam. Scientists have investi- limit theorem of probability theory and as for the characterization of delamination gated this phenomenon since the time of random processes. parameters and material properties re- Newton, but it was only after the invention Techniques based on laser speckle ef- spectively for the description of their and development of the laser that speckles fects, which can be contactless, non-inva- changes in manufacturing processes. have finally come into prominence. Until sive and remote, have become more and Therefore, choosing a suitable measuring now, numerous speckle related applica- more popular in NDT. One of the earliest method is important for fabrication in tions have been found. The dynamic techniques was laser speckle photography. terms of adapting process parameters and speckle is a result of the temporal evolu- Here, speckle patterns are recorded on a avoiding waste. In addition, the sensors tion of a speckle pattern which can be con- photographic emulsion called a photo- should be integrated inline as a control in sidered as the temporal expression of an graphic negative before and after deforma- manufacturing plants. In this paper, Laser interference speckle pattern [1]. It is gener- tion of an object. By using this negative to speckle photometry (LSP), both in theory ated by the incidence of a high-level coher- re-photograph the fringe pattern through

61 (2019) 3 © Carl Hanser Verlag, München Materials Testing 214 MATERIALS TESTING FOR JOINING AND ADDITIVE MANUFACTURING APPLICATIONS

illumination by a laser beam, quantity in- change in interference fringes. Therefore, Relying on high speed cameras and easier formation of an object’s deformation can be the defect of an object makes the fringes configurations compared with the experi- obtained by estimating the look unusual. Speckle interferometry is a mental setups presented above, LSP can fringes. A laser speckle image encodes well-established optical technique for also be used in real time monitoring, and it phase information and phase differences measuring in-plane displacements [10]. In has a high sensitivity to both out-of-plane generated by variations in travel distance this section, three kinds of interferometry and in-plane displacement. Deviating from which are affected by tiny changes in the will be introduced, namely holographic in- other techniques based on speckle phe- surface geometry. If the surface profile is terferometry, electronic speckle pattern nomena which concentrate on the distor- altered by an amount as small as a laser interferometry (ESPI) and shearography. tion of a whole speckle pattern or fringes, wavelength, the speckle pattern is modi- is a technique which can re- LSP is based on measuring the spatial-tem- fied [4]. An algorithm called cross-correla- cord both amplitude and phase information poral dynamics of laser speckles which fo- tion is established to evaluate the images from a light beam reflecting off objects. In cuses on the intensity change of each sin- [5]. It measures the deformation of the ob- interferometry a laser beam is split into gle pixel of a camera sensor. Through a ject surface by associating patterns with two beams, one, called a “reference beam”, specific correlation function (difference the surface that deforms. is used as a reference, the other, the” object autocorrelation), the connection between A second important speckle method, la- beam”, is used to illuminate the object in speckle dynamics and quality states of the ser speckle contrast analysis (LSCAS), is a question. ESPI and shearography use two samples can be established [14-16]. The digital version of the single exposure ver- different optical setups for speckle interfer- basic algorithm of LSP includes the calcu- sion of speckle photography which avoids ometry. ESPI is based on the same princi- lation of thermal diffusivity by applying the main disadvantages of the photo- ples as holographic interferometry but it the thermal transfer equation [14-18] and graphic process. LSCAS is a diagnostic electronically records and processes active thermography for crack detection technique in which the features of scat- speckle interference patterns [11]. The [15]. The algorithms will be introduced in tered coherent light are explored [6]. At visualization is achieved in the form of the next section. In recent years, LSP tech- present, it is alternatively called “laser fringes which approximately represent a nique has been successfully used for the speckle contrast imaging” (LSCI) or “laser displacement of half a wavelength of the hardness calibration of steel samples, the ” (LSI). These techniques laser beam. The sensitivity of in-plane dis- evaluation of material porosity of cellular are mainly used in the medical field to de- placement equals the value of half a wave- metals and ceramics, damage fatigue tect blood flow and organic tissues whose length. The features of shearography in- states and stress change during welding local speckle contrast varies according to clude sensitivity to out-of-plane deforma- processes. the velocity distribution of the targets [7- tion and the capability to directly measure LSP represents a promising foundation 9]. The speckle contrast is shown in an strain data in real time but not the dis- for new NDT methods and appropriate sen- equation, which is defined as the ratio be- placement of objects because rigid body sors to be developed by industry to charac- tween the standard deviation of the speckle movement produces displacement as well. terize material properties or describe their pattern and the mean intensity. A formula Shearography was used to detect large changes in the manufacturing process. It is presenting the relationship between vari- cracks in reinforced concrete and the intra- definitely a fast quality relevant material ance of a time-averaged dynamic speckle dos of bridges [12]. Micro-cracks in a glass- characterization and defect detection pattern and the temporal fluctuation statis- fiber reinforced plastic tube stressed by a method, allowing for the monitoring of pro- tics is now given [8]. 0.04 MPa internal pressure can be detected duction processes completely in-line. The A third well-known speckle-method is by shearography as well [13]. sensor system developed comprises the op- laser speckle interferometry. Interferomet- A novel speckle method for NDT is laser tical and electronic components, algo- ric techniques are effective tools for visual- speckle photometry (LSP) [14, 15] which is rithms, the hardware and software. The izing or measuring object deformation. based on the detection and analysis of ther- monitoring process is synchronized with When an object deforms, the phase of scat- mally or mechanically activated speckle the machine’s internal control, including tering light changes which results in a dynamics in non-stationary optical fields. the adaption of measuring and evaluating speed for high manufacturing perfor- mance. The short measuring times predes- tine it for use in in-line monitoring in in- dustrial production and for in-situ meas- urements during maintenance and repair tasks.

Laser speckle photometry

A speckle pattern is generated when an op- tical rough surface is illuminated by a co- herent light beam. The waves scattered from various points of the illuminated sur- face interfere on the rough surface on the observation plane where they produce a speckle pattern – a spatial structure with Figure 1: Schematic structure of laser speckle photometry randomly distributed intensity minima and

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maxima. The varied luminosities can be de- the number of frame intervals and S(n, x, y): tween the start and saturation point of the tected by a CCD or a CMOS chip, respec- intensity of the pixel whose location is de- correlation function. Information contained tively. A speckle pattern resembles the termined by the coordinates x and y in the in the intensity change of each single pixel fingerprint of the 3d information of a sam- n-th frame. was re-distributed depending on the en- ple surface [15]. If the examined object is This correlation function comes from ergy at different frequencies in the fre- thermally excited, for example by a laser, the so-called semi-variogram, which is a quency domain. M two-dimensional matri- the material can be characterized by both geostatistical tool for studying the rela- ces can be obtained, and the value of each static and dynamic speckle patterns. tionship between the collected data in the element in the same matrix presents the Figure 1 shows the basic experimental function of distance and direction [20]. Ap- energy of each pixel at an exact frequency. setup of LSP measurements. It contains a plying this correlation function at each In this case, the intensity changes of time- laser diode as illumination source and a time shift shows the accumulation of in- varying speckle patterns were converted to speckle signal detector as a combination of tensity differences of frame couples hav- the frequency domain for the further analy- a fast CMOS camera and an objective. The ing this time shift. However, for crack de- sis of different applications. angle between laser source and camera tection, it focuses on the difference be- amounts to approximately 30°. In addition, tween the first frame and other frames Applications a thermal excitation source is periodically depending on the time shift rather than on used to change the local temperature of the the details of the frame couples mentioned Monitoring of welding processes. Pres- sample and generate the time-dependent above. Therefore, a slight modification was ently, in the electrical industry, conductive speckle movement. For example, the ther- made on Equation (1), where n becomes a contacts are applied by electroplating and mal excitation laser, thermal contact and fixed value, n = 1. The new correlation welding. These cost and time-consuming process heat are applicable. The excita- function is given by: procedures are characterized by a high tions in both modes are feasibly continu- consumption of material and energy. These n 2 ous and pulsed. The thermal energy ab- C(τ) = max S n+ τ,x,y − S 1,x,y (2) processes accumulate large amounts of en- ∑n=1 ( ) ( ) sorbed by the sample results in the thermal vironmentally harmful chemicals. There- expansion behavior are caused by a local with n: number of the frame. fore, the development of an alternative ad- temperature difference. The speckle move- The highest shift in the speckle images ditive process with necessary functionality ments caused by time-dependent thermal leads to the maximum of this correlation is of high interest. When micro-laser clad- expansion are recorded by a fast CMOS function [16]. As is known, images can be ding gold is applied in a paste by using a camera and the software developed. digitally processed as matrices. Therefore, dispenser, it should be dried to remove the based on this correlation function, a three- binder contents and then re-melted via la- Digital algorithms dimensional matrix indicating the changes ser radiation for densification and bonding between each frame and the first frame for to the substrate. The approaches of LSP pattern evaluation each single pixel was created. In terms of An example of gold contact is shown in are shown in Figure 2a and Figure 2b, re- this change of each single pixel in the time Figure 3a. A contact has a diameter of ap- spectively. Static analysis is based on sin- domain, an M-point fast Fourier transfor- proximately 80 μm. For both the stage of gle images wherein the initial speckle in- mation (FFT) was applied to convert it into development of the new contact-making tensity of each pixel depends on a group of frequency domain, and M can be deter- process and the subsequent in-process pixels around it (e. g. the 3-by-3 neighbor- mined by the number of frames which quality control, it offers an inline-capable, hood). The value of the core pixel can be were used to calculate the FFT. This num- laser based and contactless testing method. obtained after calculating the neighboring ber was determined by the interval be- The time-resolved LSP has been developed pixels. Repeating this procedure for every pixel of the image, a contrast image is gained. Dynamic evaluation is based on one pixel in a time sequence rather than on multiple pixels in one image. The method for computing speckle contrast is pre- sented in [19], calculation of the fractality of speckle signals is described in [14]. This paper will explain the evaluation steps of frequency analysis. The time-varying intensity can be re- a) lated to the spatial gradient by the correla- tion function. The thermal energy causes a temperature change and leads to the ther- mal expansion on the surface of the sam- ple. This correlation function is given by:

n 2 C(τ) = max S n+ τ,x,y −S n,x,y (1) ∑n=1 ( ) ( ) b) with nmax: number of video frames which Figure 2: Schematic overview of the possibilities for evaluating the speckle signals by a) static analysis, provide the time dependence, τ: time shift or b) dynamic analysis

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and adapted for this application. Figure 3b vidual contact. Confocal microscopy can be ence in the calibration process can be min- shows the integrated LSP technique in an used as a calibration method for the geo- imized, which decreases the tolerance of appropriate laboratory facility [21]. metric determination of contact size. the measurement. The mixing degree of contact with the Figure 4 shows the resulting curve of Monitoring of biological processes. substrate was determined by the parameter calibration which was calculated from a Modern biotechnological production pro-

fractal dimension DF [14] of the dynamic linear regression of the experimental val- cesses for the manufacture of hosiery and speckles in the reflective region. The deter- ues measured by the LSP technique. additives, e. g., for pharmaceutical, cosmetic mination of the calibration curve for the The accuracy of the results at a measur- or food using vegetable cells, tissue cultures calculation of the metal content was carried ing speed of 100 contacts per minute can (e. g. hairy roots) and heterogeneous micro- out by means of a chemical analysis of the be summarized as 6.7 vol.-% of tolerance of organisms (e. g. filamentous mushrooms), contact material, energy-dispersive X-ray the determination of the precious metal are increasingly in the focus of research and spectroscopy (EDX). The geometric contact content and 4.0 vol.-% of tolerance of the development. Currently, there are several measurement was carried out simultane- height measurement. Measurement preci- research projects focusing on the develop- ously with the determination of the gold sion is dependent on the accuracy of the ment of economic production processes for content. The contact height was determined reference method for calibration. The EDX crop secondary metabolites (pharmaceuti- by calculating the diameter of the inner en- used is a local method in comparison to cal and nutritionally potent substances with veloping circle of the shadow. The internal LSP resolution. Therefore, the real Au-frac- hairy root cultures) for the extraction of en- enveloping circle of the reflective region tion in the complete contact can be varied zymes [22]. The economic management of was used to determine the size of the indi- to the result of the EDX. Hence, the differ- the cultivation of biotechnological processes for active extraction requires the determina- tion of the biomass and the determination of a) their growth kinetics. Established methods cannot be used to meet the requirements of the cultivation of hairy roots due to the in- homogeneous distribution of the root seg- ments. In order to shorten the optimization period, a quantitative and preferably direct measurement method for determining the current biomass concentration is required. Therefore, the development of a fully auto- a) mated, non-invasive sensor for determining the biomass concentration and morphology parameters in different heterogeneous bio- technological systems is of great interest. The basic structure for the evaluation of b) temporal change in the biomass by LSP is shown in Figure 5. To evaluate current bio- mass concentration, scale properties of the speckle pattern are evaluated. The parame-

ter fractal dimension DF [14] describes how “rugged” the examined object is at any given time due to an absolute value. To the b) same proportion, the given dynamic param- Figure 3: a) Gold contacts at Nickel-Alloy In- Figure 4: a) Calibration of gold content meas- eter can describe the growth state of the ex- conel 625, b) integrated LSP technology in the ured by EDX vs. that measured by LSP, b) cali- amined object. Additionally, static changes gold contact production, speckle pattern deter- bration of height of contacts measured by confo- in the object are well suited for the charac- mines the precious metal content and geome- cal microscopy vs. that measured by LSP terization of its growth stage. For this ap- tries of the contacts proach, the evaluation of the co-occurrence matrix and parameters like entropy can be used. The correlated reference measure- ment is foreseen for future research. In Figure 6, it can be seen that the fractal dimension increases with the duration of Figure 5: Schematic cultivation in four independent samples. description of the To evaluate the root activity, one method is non-invasive technique based on the calculation of speckle con- for controlling the growth of biomass trast. The presentation of time-resolved contrast values shows that the areas of higher growth and change are always char- acterized by low contrast. In Figure 7, for example, root areas growth is visualized

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almost in white. During the following days, speckle temperature, so-called speckle dif- The process-specific parameters such as branches formed at these locations. fusivity can be determined. In Figure 8b, it the gold content of electrical contracts or Additive manufacturing. Material pa- can be seen that the speckle diffusivity cal- the biomass content in the reactor can be rameters such as porosity can be obtained culated decreases with the increasing po- inline determined by the parameter “frac- by LSP based on an evaluation of the tem- rosity of the samples. The thermal diffusiv- tal dimension”. Further development is perature line. This evaluation concept can ity of the material depends primarily on its needed to increase the accuracy of the be implemented for process control in the density but also on the thermal conductiv- method. Here it is important to find suita- production of additive manufactured com- ity. The lower the density and thermal con- ble reference methods to evaluate compa- ponents. Moreover, defects such as pores ductivity, as in porous materials, the lower rable areas of the material. Currently, and micro-cracks occurring during the la- their thermal diffusivity. measurement speed is already very high ser-melting process can be detected im- for some applications at 50 frames per sec- mediately after their formation to enable Conclusions ond, including measurement and evalua- appropriate countermeasures. In addition, tion. Depending on the region of interest these defects can be cleared by re-melting Compared with other optical speckle-based (ROI) the following applies: the smaller the the affected area. As a result, the require- methods, LSP provides an opportunity for ROI, the higher the frame rate. But the re- ment of downstream, time and cost inten- determining defects, geometric and mate- sults are not only dependent on the meas- sive material testing and rework can be rial parameters such as porosity, and for uring speed but also on the accuracy of significantly reduced. An LSP sensor sys- evaluating biological growth processes. measurement. tem is designed to help reduce the drop- out rate in the process so that energy, ma- terial and inert gas consumption can bfe reduced significantly in the additive man- ufacturing of metal components. The LSP sensor is integrated directly into the man- ufactured machine. The communication between the two processes is realized – depending on the development of the elec- Figure 6: Parameter of the fractal dimension tronics and algorithms – for a regulative with the length of cultiva- approach. tion during the increase First investigations were carried out on of biomass growth test specimens (see Figure 8a). Some of these specimens were prepared by reduced input energy (marked in green) and so pri- marily have near-surface defects, as well as samples by highly elevated input energy (B2, D3) and corresponding defects/inho- mogeneities. In comparison, the reference (row 4) shows the measurements on the samples manufactured under optimum conditions. The references hardly show the flaws. The defects and inhomogeneities in the samples produced with reduced and greatly increased input energy can be de- tected by using LSP technique. At the same time, based on the calcula- Figure 7: The contrast in the illustrated temporal speckle pattern changes during the cultivation of hairy tion of the thermal diffusivity of the optical roots. The brighter area of the plant is shown, the higher the growth activity in the area a) b)

Figure 8: a) test sample of additive manufacturing, b) results of speckle signal presented by speckle diffusivity. The percentage shows the ratio between real input energy and optimal energy. Vs, PI, and h present the speed, fill in power and hatch distance of process, respectively

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Acknowledgements 12 V. Muzet, P. Blain, D. Przybyla: Application of 21 U. Cikalova, B. Bendjus, A. Lehmann, shearography to crack detection in concrete A. Gommlich, S. R. Sudip: Laser-Speckle-Pho- The authors would like to thank the Fraun- structures subjected to traffic loading, Ar- tometrie zur integrierten Qualitätskontrolle mando Albertazzi Goncalves, Jr., G. H. Kauf- des Mikro-Laserauftragsschweißens (Laser hofer Gesellschaft (FhG) for providing in- mann (Eds.): Proc. SPIE 7387, Speckle 2010: speckle photometry for integrated quality con- ternal FhG programs for researching the Optical Metrology, 73870K, SPIE Press, Bell- trol of micro laser deposition welding), Pro- projects “LaQuaS” and “CERENERGY” and ingham, Washington, USA (2010) gram DGM-day 2015, Materials Week 2015, the Sächsische Aufbaubank (SAB) for fund- DOI:10.1117/12.868951 Poster WW-15-154 Dresden, Germany (2015) ing the project “BioSpeckle”. The authors 13 W. Steinchen, L. X. Yang, G. Kupfer, 22 C. Schott, T. Blty, J. Steingroewer, B. Bendjus, would like to express their appreciation to P. Maeckel: Nondestructive testing of microc- U. Cikalova, T. Werner, J. Eigner: BioSpeckle: all colleagues in the institutions for their racks using digital speckle pattern shearing Development of a non-invasive sensor for de- assistance in the investigations. interferometry, C. Gorecki (Ed.), Proc. SPIE termination of biomass in biotechnological 3098, Optical Inspection and Micromeasure- processes by Laser-Speckle-Photometry, References ments II, 528, SPIE Press, Bellingham, Wash- Posterprogramm, Himmelfahrtstagung ington, USA (1997) DECHEMA 2015, Hamburg, Germany (2015) DOI:10.1117/12.281199 1 J. W. Goodman: Statistical properties of laser 14 U. Cikalova, B. Bendjus, J. Schreiber: Laser‐ Bibliography speckle patterns, J. C. Dainty (Ed.): Laser speckle‐photometry ‐ A Method for non‐con- Speckle and Related Phenomena, Chapter 2, tact evaluation of material damage, hardness DOI 10.3139/120.111308 Springer, New York, USA (1975) and porosity, Materials Testing 54 (2012), Materials Testing 2 R. P. Godinho, M. M. Silva, J. R. Nozela, No. 2, pp. 80-84 61 (2019) 3, pages 213-219 R. A. Braga: Online biospeckle assessment DOI:10.3139/120.110299 © Carl Hanser Verlag GmbH & Co. KG without loss of definition and resolution by 15 J. Nicolai, U. Cikalova, B. Bendjus, J. Schreiber: ISSN 0025-5300 motion history image, Optics and in En- Laser-Speckle-Photometrie – Ein Verfahren gineering 50 (2012), No. 3, pp. 366-372 zur schnellen und berührungslosen Bestim- The authors of this contribution DOI:10.1016/j.optlaseng.2011.10.023 mung von Werkstoffzuständen (Laser speckle 3 J. W. Goodman: Statistical Optics, 1st Ed, photometry – A method for the fast and non- Lili Chen, PhD candidate, born in 1990, received Wiley, New York, USA (1985) contact determination of material states), his Master’s Degree at the Dresden International 4 Y. C. Shih, A. Davis, S. W. Hasinoff, F. Durand, Posterprogram with short presentations, DG- University, Dresden, Germany. At present, he is W. T. Freeman: Laser speckle photography for ZfP-Annual Conference 2013, Dresden, Ger- pursuing his Doctoral Degree at the Fraunhofer surface tampering detection, Proc. of the 25th many (2013), Poster 64 Institute for Ceramic Technologies and Systems IEEE Conference on Computer Vision and Pat- 16 U. Cikalova, B. Bendjus, J. Schreiber: Material IKTS in Dresden, Germany. His area of research tern Recognition (CVPR 2012), Institute of Characterization by Laser Speckle Pphotome- focuses on non-destructive testing by means of Electrical and Electronics Engineers (IEEE), try, A. F. Doval, C. Trillo (Eds.): Proc. SPIE optical methods. Providence, RI, USA (2012), pp. 33-40 8413, Speckle 2012: V International Confer- Dr.-Ing. Ulana Cikalova studied Materials Sci- 5 E. L. Johansson: Digital Speckle Photography ence on Speckle Metrology, 841315, SPIE ence at the Technische Universität Dresden until and Digital Holography for the Study of Trans- 2005. In her dissertation thesis, she wrote on the parent Media, PhD Thesis, Luleå University of Press, Bellingham, Washington, USA (2012) “Evaluation of the material damage on basis of Technology, Luleå, Sweden (2007) DOI:10.1117/12.978246 6 N. H. Koshoji, S. K. Bussadori, C. C. Bortoletto, 17 N. I. Mukhurov, N. A. Khilo, A. G. Maschenko: the fractal nature of thermo-optic and electro- R. A. Prates, M. T. Oliveira, A. M. Deana: Laser A Speckle-photometry method of measure- magnetic signals”. She has been a scientist at the speckle imaging: A novel method for detecting ment of thermal diffusion coefficient of thin Fraunhofer Institute for Ceramic Technologies dental erosion, PLoS ONE 10 (2015), No. 2, multilayer and nanoporous structures, Ar- and Systems IKTS in Dresden, Germany, special- e0118429 mando Albertazzi Goncalves, Jr., G. H. Kauf- izing in material characterization, especially with DOI:10.1371/journal.pone.0118429 mann (Eds.): Proc. SPIE 7387, Speckle 2010: respect to laser speckle photometry and 7 J. D. Briers: Laser speckle contrast imaging for Optical Metrology, 73870K, SPIE Press, Bell- Barkhausen noise since 2007. measuring blood flow, Optica Applicata 37 ingham, Washington, USA (2010) Dr.-Ing. Beatrice Bendjus studied Material Sci- (2007) No. 1 – 2, pp. 139-152 DOI:10.1117/12.869942 ence at the Technische Universität Bergakademie 8 D. Briers, D. D. Duncan, E. Hirst, 18 N. Mukhurov, A. Maschenko, N. Khilo, Freiberg, Germany, until 1992. After completing S. J. Kirkpatrick, M. Larsson, W. Steenbergen, P. Ropot: A Speckle-photometry method of her dissertation thesis on the powder metallurgi- T. Stromberg, O. B. Thompson: Laser speckle measurement of thermal diffusion coefficient cal manufacturing of high speed steels, she contrast imaging: Theoretical and practical of porous anodic alumina structures intended worked at the Fraunhofer Institute for Ceramic limitations, Journal of Biomedical Optics 18 for optical sensing, F. Baldini (Ed.): Proc. SPIE Technologies and Systems IKTS (formerly the (2013), No. 6, 066018 8073, Optical Sensors 2011 and Photonic Dresden branch of the Fraunhofer Institute for DOI: 10.1117/1.JBO.18.6.066018 Crystal Fibers V, 80731B, SPIE Press, Belling- Nondestructive Testing) in the field of material 9 J. D. Briers, S. Webster: Laser Speckle contrast ham, Washington, USA (2011) characterization via microscopic methods such as analysis (LASCA): A nonscanning, full-field DOI:10.1117/12.886348 atomic force microscopy and thermal wave mi- technique for monitoring capillary blood flow, 19 M. Draijer, E. Hondebrink, T. V. Leeuwen, croscopy. Subsequently, she worked on the devel- Journal of Biomedical Optics 1 (1996), No. 1, W. Steenbergen: Review of laser Speckle con- opment of laser speckle photometry and is pres- pp. 174-179 trast techniques for visualizing tissue perfu- ently head of the group “Speckle Based Methods” 10 L. Augulis, S. Tamulevic̆ius, R. Augulis, sion, Lasers in Medical Science 24 (2009), at Fraunhofer IKTS, Dresden, Germany. J. Bonneville, P. Goudeau, C. Templier: Elec- No. 4, pp. 639-651 Dr.-Ing. Andreas Gommlich, born in 1977, tronic speckle pattern interferometry for me- DOI:10.1007/s10103-008-0626-3 worked in the group specializing in ultrasonic chanical testing of thin films, Optics and La- 20 A. Mazzella, A. Mazzella: The importance of sensors and methods at the Fraunhofer Institute sers in Engineering 42 (2004), No. 1, pp. 1-8 the model choice for experimental semivario- for Ceramic Technologies and Systems IKTS, DOI: 10.1016/j.optlaseng.2003.06.001 gram modeling and its consequence in evalua- Dresden, till 2015. He focused on data analysis, 11 R. Motamedi: Crack Detection in Silicon Wa- tion process, Journal of Engineering 2013 image processing and wave field simulation. fers Using Shearography, MSc Thesis, Concor- (2013), Article ID 960105 Since 2016 he has been a scientist at the Helm- dia University, Montreal, Canada (2008) DOI:10.1155/2013/960105 holtz-Zentrum Dresden-Rossendorf (HZDR)/On-

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coRay – National Center for Radiation Research neering at TU Dresden, Germany in the field of I.A at RWTH, he began working as a scientist at in Oncology, Germany, and works in the field of Plant- and Algaebiotechnology. the Fraunhofer Institute for Laser Technology ILT image guided high precision radiotherapy. Dr.-Ing. Juliane Steingroewer studied Process in Aachen, Germany in 2009. His field of spe- Shohag Roy Sudip, born 1990, is an MSc stu- Engineering at the Technische Universität Dres- cialty is laser cladding with precious materials in dent in Nanoelectronic Systems at the Technische den until 2001. In her dissertation, she wrote on dimensions below 100 μm. Universität Dresden. He received his bachelor of “Biomagnetic separation in a method for the fast Dipl.-Ing. Stefan Kleszczynski, born in 1984, science in Electrical and Electronic Engineering biomonitoring of contaminants in food stuff”. studied Mechanical Engineering, focusing on at the American International University-Bangla- Since 2001, she has been a scientist at the Insti- product engineering, and received his diploma desh in Dhaka, Bangladesh. At present, he works tute of Food Technology and Bioprocess Engineer- from the University of Duisburg-Essen in 2011 at the Fraunhofer Institute for Ceramic Technolo- ing at the Technische Universität Dresden, Ger- writing on the “Qualification of iron-nickel alloys gies and Systems IKTS in Dresden, Germany as many and has been head of the group, “Plant Cell for the beam melting process in consideration of Student Assistant. and Algae Biotechnology”, since 2008. Her re- mechanical and thermal properties”. He is a re- Dipl.-Ing. Carolin Schott studied Bioprocess search focuses on the development of biotechno- searcher at the chair of Manufacturing Technol- Engineering at the Technische Universität Dres- logical processes for the production of active in- ogy, located in the Department of Mechanical and den (TU Dresden) until 2013. In her diploma the- gredients with the use of plant cell and tissue cul- Process Engineering, at the University of Duis- sis she worked on the topic ,“Development of an ture, algae and cyanobacteria. burg-Essen, Germany and since 2016 has been efficient process for the production of phycocya- Dipl.-Phys. Matthias Belting; born in 1981, the chairman of the VDI Technical Committee FA nin from cyanobacteria Arthrospira“. She is a re- studied Physics at RWTH Aachen University as of 105.5 „Legal aspects of additive manufacturing“. search associate at the Institute of Natural Mate- 2001. After completing his thesis, “Photocatalytic rials Technology at the chair of Bioprocess Engi- activity of sputtered TiO2”, at the 1.-Phys. Institut

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