Three-dimensional evaluation of subsurface damage in optical glasses with ground and polished surfaces using FF-OCT

Frank, Samson; Seiler, Michael; Bliedtner, Jens

doi:10.1364/ao.413090

Cited by 15 publications

(5 citation statements)

References 91 publications

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“…Scan speed 𝑣𝑣 𝑠𝑠 and pulse energy 𝐸𝐸 𝑝𝑝 have been set accordingly. The OCT system used as well as the evaluation methods developed for Subsurface Damage are described elsewhere [4]. Overall, an isotropic resolution of 1 µm is achieved with a minimum detectable reflectivity of −88 dB.…”

Section: Methodsmentioning

confidence: 99%

Investigation on Subsurface Damage Patterns in Ultrashort Pulse Laser Machining of Glass using Optical Coherence Tomography

Frank,

Reichenbächer,

Seiler

et al. 2023

EPJ Web Conf.

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Ultrashort pulse (USP) laser ablation is gaining popularity as a novel manufacturing technique for brittle materials, enabling the creation of complex freeform shapes that are challenging to produce with conventional optics manufacturing techniques. Freeforms have revolutionized optics manufacturing by providing designers with increased degrees of freedom using non-rotational symmetric components. However, this evolution presents new challenges for manufacturing processes, calling for innovative solutions such as USP ablation. To ensure the industrial viability of areal USP laser machining, it is crucial to not only consider material removal rates but also surface quality and subsurface damage (SSD). Especially for optical applications, harsh quality requirements must be met. This study investigates the SSD patterns of fused silica (FS) and borosilicate glass N-BK7 (BK) processed under different laser wavelengths, beam geometries and processing parameters using high-resolution optical coherence tomography (OCT). It is shown that OCT as non-destructive and 3D evaluation method is well-suited for analysing USP processes. The discovered differences in defect morphology between FS and BK emphasize the importance of selecting appropriate processes and process parameters when working with different materials. Compared to previous studies, for the parameter sets analysed here using OCT, much higher defects depths of up to 441 µm were revealed.

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Section: Methodsmentioning

confidence: 99%

Investigation on Subsurface Damage Patterns in Ultrashort Pulse Laser Machining of Glass using Optical Coherence Tomography

Frank,

Reichenbächer,

Seiler

et al. 2023

EPJ Web Conf.

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“…Visualizations can also make use of projection methods. For automatically quantifying SSD depths, Frank et al 11 suggested the use of colour-coded depth maps, displaying the SSD depth at each individual location of the sample surface (see figure 10). To generate depth maps, relevant dynamic ranges are selected, followed by binarization and filtering.…”

Section: Ssd Evaluationmentioning

confidence: 99%

“…The application of optical coherence tomography (OCT) as a new, non-destructive measurement method for SSD has been proposed by Hellmuth et al 10 and since then profited by the rapid and strong improvement of OCT system components as well as OCT systems in general, now allowing the fast and high-resolution imaging of SSD. 11 Nevertheless, the application of OCT still needs to be broadly validated, e.g. for different materials and surface qualities.…”

Section: Introductionmentioning

confidence: 99%

Round-robin test of subsurface damage characterization in ZERODUR using non-destructive optical coherence tomography

Frank,

Schwörer,

Alvan

et al. 2024

Eleventh European Seminar on Precision Optics Manufacturing

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The glass ceramic ZERODUR ® with its extremely low thermal expansion finds widespread application in precision optics and astronomical instruments. It has been used for several very large telescope mirrors, as its unique properties make it indispensable in environments demanding stringent dimensional stability. As for all brittle materials, mechanical grinding processes involved in manufacturing introduce subsurface damage (SSD), which compromises the optical and mechanical performance of workpieces. Beyond its implications for quality, SSD is often a significant cost driver, necessitating expensive finishing processes.Characterizing SSD and determining its depth at various manufacturing stages from pre-grinding to final polishing are critical for ensuring the quality and reliability of optical components. Conventional measurement techniques predominantly involve destructive methods such as taper polishing or cleaving the surface, posing limitations in assessing SSD without compromising the integrity of the workpiece. Moreover, these methods are often time-consuming and labor-intensive.In a collaborative study, we conducted a round-robin test to establish and validate the efficacy of nondestructive optical coherence tomography (OCT) as a new technique for characterizing SSD depths in ground ZERODUR ® . The aim is to provide a first comprehensive assessment of the capability of OCT in nondestructively quantifying SSD in glass ceramics. The methodology involves comparing measurements obtained from two distinct high-resolution OCT systems applied to identical ZERODUR ® samples machined with selected process parameters. Furthermore, the study investigates the influence of different grain sizes on the SSD characteristics by comparing measurements across samples processed with varying grain sizes.By conducting the round-robin test, we seek to demonstrate the applicability of OCT as a non-destructive alternative for SSD characterization in ground ZERODUR ® . Successful validation of OCT extended to a variety of relevant optic materials such as ZERODUR ® would enhance overall quality control processes, offering a rapid and non-invasive means of assessing SSD depths and ensuring the integrity of critical optical components.

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“…In addition to laser scattering and fluorescence microscopy, where a colorant has to be applied, more attention has been given to optical coherence tomography (OCT) in recent years. The high-resolution measurements enable a three-dimensional characterization of the SSD [4]. In addition to absolute crack depths, it is for instance conceivable to draw conclusions about the formation of cracks based on the classification of morphologies.…”

Section: Introductionmentioning

confidence: 99%

Characterization of manufacturing-induced microcracks in optical components

Müller,

Arnold

2024

Eleventh European Seminar on Precision Optics Manufacturing

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Microcracks occur during the conventional manufacturing chain (grinding, polishing), but also as a result of ultra-short pulse laser processing of hard-brittle materials, such as those frequently used in the optical industry. Non-destructive methods, such as optical coherence tomography, are being discussed in order to understand the development of nearsurface damage and to enable process control without sample consumption. Destructive testing methods will be necessary to validate those methods. Beam-based etching applied to Fused Silica by plasma jet or ion beam is presented. The application of reactive plasma jet etching causes process-induced roughness. Nevertheless, significant holes and defects can be detected. No additional roughening occurs with ion beam etching. Both applied beam-based etching processes ensure that small defects are enlarged, allowing these microcracks to be detected even if they are not directly visible on the initial surface. For an accurate depth determination of prominent, sharp-edged defects, white-light interferometry is limited. Confocal laser scanning fluorescence microscopy is shown as an alternative measurement technique to determine and visualize the development of the extent of defects with increasing etching attack.

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Three-dimensional evaluation of subsurface damage in optical glasses with ground and polished surfaces using FF-OCT

Cited by 15 publications

References 91 publications

Investigation on Subsurface Damage Patterns in Ultrashort Pulse Laser Machining of Glass using Optical Coherence Tomography

Investigation on Subsurface Damage Patterns in Ultrashort Pulse Laser Machining of Glass using Optical Coherence Tomography

Round-robin test of subsurface damage characterization in ZERODUR using non-destructive optical coherence tomography

Characterization of manufacturing-induced microcracks in optical components

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