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Comparison of the thermal focus shift and aberration between the single-mode and multimode lasers
AdlOptica GmbH, Rudower Chaussee 29, 12489 Berlin, Germany.ORCID iD: 0000-0003-2989-5189
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0003-0194-9018
2021 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 33, no 4, article id 042026Article in journal (Refereed) Published
Abstract [en]

Thermal lensing is a well-known but typically undesired effect during the use of laser optics. Nonuniform (gradient) heating due to absorption of high-power laser radiation in optical elements causes thermal lensing, paraxial focus shift, and aberration leading to changes in size and intensity profile of the focused spot in optics. Therefore, an analysis of primary physical effects of geometrical deformation of optical surfaces in the form of aspheric bulges and transformation of the material into a gradient refractive medium was conducted to quantitatively estimate the focus shift and aberrations. Since focus shift effects are different in the case of single-mode and multimode lasers, for both laser modes, the optimal relationships between the physical properties of optical materials for reduction in thermo-optical effects through compensating the material thermal expansion by the change in the refractive index—condition of self-compensation or athermalization were formulated. A comparison of the characteristics, namely, temperature coefficient of the optical pathlength and thermo-optical ratio allowed determination of the optimal materials for the optics for both single-mode and multimode high-power lasers: athermal crystalline quartz and specialty glasses, sapphire with extremely high thermal conductivity ensure minimal temperature gradients. Optics made of these materials exhibit a minimized thermal focus shift and aberration even during the absorption of laser energy in the bulk material and coatings by contamination, scratches, and other surface defects. Weak birefringence of crystalline quartz and sapphire does not prevent their successive use in laser optics.

Place, publisher, year, edition, pages
AIP Publishing LLC , 2021. Vol. 33, no 4, article id 042026
Keywords [en]
thermal lensing, gradient heating, thermal focus shift, wavefront aberration, athermalization, high-power lasers, welding, cutting
National Category
Atom and Molecular Physics and Optics
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-87717DOI: 10.2351/7.0000499ISI: 000710449800003Scopus ID: 2-s2.0-85117179301OAI: oai:DiVA.org:ltu-87717DiVA, id: diva2:1607550
Funder
Swedish Research Council, 2020-04250
Note

Validerad;2021;Nivå 2;2021-11-01 (beamah);

Funder: EIT raw materials (18079)

Available from: 2021-11-01 Created: 2021-11-01 Last updated: 2021-11-08Bibliographically approved

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Volpp, Joerg

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