Processing constraints resulting from heat accumulation during pulsed and repetitive laser materials processing

Weber, Rudolf; Graf, Thomas; Freitag, Christian; Feuer, Anne; Kononenko, T. V.; Konov, V. I.

doi:10.1364/oe.25.003966

Cited by 65 publications

(47 citation statements)

References 11 publications

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“…The lower part exhibits more peaks and pits, suggesting that more thermal losses take place as the beam penetrates deeper into the kerf line as a result of the hydrodynamic plasma expansion and the incoming beam shielding [27]. Although the femtosecond regime does not favor the thermally activated matter removal, the heat accumulation resulting from a high repetition rate at the bottom of the kerf line can partially activate this ablation mode [28]. The latter regime is consistent with the formation of a crater-like rougher surface, as shown in Figure 5d.…”

Section: Characterization Of the Laser Cut Surfacementioning

confidence: 99%

Broadband Terahertz Light–Matter Interaction Enhancement for Precise Spectroscopy of Thin Films and Micro-Samples

et al. 2018

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In biology, molecules and macromolecules such as sugars, proteins, DNA, RNA, etc., are of utmost importance. Detecting their presence as well as getting information on their actual structure is still a challenge in many cases. The vibrational states of such molecules correspond to a spectral range extending from infrared to terahertz. Spectroscopy is used for the detection and the identification of such compounds and their structure. Terahertz spectroscopy of a biosample is challenging for two main reasons: the high terahertz absorption by water molecules in the sample; and the small size of the sample-its volume is usually smaller than the cube of the terahertz wavelength, thus the light-matter interaction is extremely reduced. In this paper, we present the design, fabrication, characterization, and first typical use of a biophotonic device that aims to increase the light-matter interaction to enable terahertz spectroscopy of very small samples over a broad band (0.2-2 THz). Finally, we demonstrate the validity of our approach by time-domain spectroscopy of samples of a few µL.

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Section: Characterization Of the Laser Cut Surfacementioning

confidence: 99%

Broadband Terahertz Light–Matter Interaction Enhancement for Precise Spectroscopy of Thin Films and Micro-Samples

et al. 2018

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“…Since this is small compared to the diameter d s = 500 µm of the beam on the workpiece used in this study, 1D heat flow can be assumed for the time between two consecutive pulses [9]. For the larger number N pps = d s ⋅ f/v feed of pulses incident on one spot during a single pass of the laser beam, the thermal diffusion length modifies to [10]. With d s = 500 µm, the 1D approximation of the heat flow induced by one isolated single pass of the laser beam is, therefore, justifiable for feed rates well above 0.03 m/s.…”

Section: Introductionmentioning

confidence: 99%

Prediction of the surface structures resulting from heat accumulation during processing with picosecond laser pulses at the average power of 420 W

et al. 2018

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Heat accumulation due to successive laser pulse (HAP) incident on the same spot and heat accumulation due to successive scans (HAS) of the laser beam over the same spot significantly influences the process result, especially when the resulting temperature of the workpiece exceeds the melting temperature. In particular, heat accumulation is one of the dominating effects during short-pulse laser functionalization of surfaces and strongly affects the resulting surface structures. Within this study, a novel heat accumulation model is introduced to calculate the temperature increase in the workpiece for the whole process including the effects of HAP and HAS in which the latter is differentiated between heat accumulation due to multiple passes (HAS-I) and heat accumulation due to multiple layers (HAS-II). With the new model, the surface structure was successfully predicted when using an ultra-short pulsed (USP) laser with an average power of 420 W for laser surface structuring of polished AISI 316L.

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“…Alternatively, this may lead to an unwanted widening of the inlet of the hole. Within the hole, a reduced available fluence can lead to the formation of thermal damage due to heat accumulation [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Determination of the thermally induced focal shift of processing optics for ultrafast lasers with average powers of up to 525 W

Faas¹,

Foerster²,

Weber³

et al. 2018

Opt. Express

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The continuous increase of the average laser power of ultrafast lasers is a challenge with respect to the thermal load of the processing optics. The power which is absorbed in an optical element leads to a temperature increase, temperature gradients, changing refractive index and shape, and finally causes distortions of the transmitted beam. In a first-order approximation this results in a change of the focal position, which may lead to an uncontrolled change of the laser machining process. The present study reports on investigations on the focal shift induced in thin plano-convex lenses by a high-power ultra-short pulsed laser with an average laser power of up to 525 W. The focal shift was determined for lenses made of different materials (N-BK7, fused silica) and with different coatings (un-coated, broadband coating, specific wavelength coating). = ⋅ ⋅is the irradiated area given by the diameter d b of the beam on the workpiece. Processing in the focal plane of the focusing optics is the most common approach, since the highest fluence can be achieved at this position. When the position of the beam waist shifts by one Rayleigh length due to thermally induced effects, the fluence on the workpiece at the original position of the nominal focal plane decreases by a factor of 2 [4]. As the applied fluence significantly influences the efficiency of e.g. surface ablation [5], the thermally induced focal shift can dramatically reduce the processing efficacy. When working close to the ablation threshold, as in the case of surface structuring [6], the ablation process can stop completely even for small changes of the focal position. During laser drilling, the

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Processing constraints resulting from heat accumulation during pulsed and repetitive laser materials processing

Cited by 65 publications

References 11 publications

Broadband Terahertz Light–Matter Interaction Enhancement for Precise Spectroscopy of Thin Films and Micro-Samples

Broadband Terahertz Light–Matter Interaction Enhancement for Precise Spectroscopy of Thin Films and Micro-Samples

Prediction of the surface structures resulting from heat accumulation during processing with picosecond laser pulses at the average power of 420 W

Determination of the thermally induced focal shift of processing optics for ultrafast lasers with average powers of up to 525 W

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