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Investigation of the Spatial Generation of Stimulated Raman Scattering Using Computer Simulation and Experimentation
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0002-0306-3010
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0001-8355-2414
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0003-4879-8261
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0003-3268-1691
2022 (English)In: Applied Spectroscopy, ISSN 0003-7028, E-ISSN 1943-3530, Vol. 76, no 11, p. 1307-1316Article in journal (Refereed) Published
Abstract [en]

Stimulated Raman scattering is a phenomenon with potential use in providing real-time molecular information in three-dimensions (3D) of a sample using imaging. For precise imaging, the knowledge about the spatial generation of stimulated Raman scattering is essential. To investigate the spatial behavior in an idealized case, computer simulations and experiments were performed. For the computer simulations, diffraction theory was used for the beam propagation complemented with nonlinear phase modulation describing the interaction between the light and matter. For the experiments, a volume of ethanol was illuminated by an expanded light beam and a plane inside the volume was imaged in transmission. For generating stimulated Raman scattering, a pump beam was focused into this volume and led to a beam dump after passing the volume. The pulse duration of the two beams were 6 ns and the pump beam energy ranged from 1 to 27 mJ. The effect of increasing pump power on the spatial distribution of the Raman gain and the spatial growth of the signal at different interaction lengths between the beam and the sample was investigated. The spatial width of the region where the stimulated Raman scattering signal was generated for experiments and simulation was 0.21 and 0.09 mm, respectively. The experimental and simulation results showed that most of the stimulated Raman scattering is generated close to the pump beam focus and the maximum peak of the Stokes intensity spatially comes shortly after the peak of the pump intensity.

Place, publisher, year, edition, pages
Sage Publications, 2022. Vol. 76, no 11, p. 1307-1316
Keywords [en]
Stimulated Raman scattering, simulations, experiments, spatial distribution, spatial rate
National Category
Atom and Molecular Physics and Optics Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-90344DOI: 10.1177/00037028221123593ISI: 000872145200003PubMedID: 36281542Scopus ID: 2-s2.0-85140561101OAI: oai:DiVA.org:ltu-90344DiVA, id: diva2:1653289
Funder
Luleå University of TechnologyThe Kempe FoundationsSwedish Foundation for Strategic Research, ITM17-0056
Note

Validerad;2022;Nivå 2;2022-11-03 (sofila)

Available from: 2022-04-21 Created: 2022-04-21 Last updated: 2024-08-15Bibliographically approved
In thesis
1. Direct imaging of Stimulated Raman scattering: 3D spatial control and spatial generation
Open this publication in new window or tab >>Direct imaging of Stimulated Raman scattering: 3D spatial control and spatial generation
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Stimulated Raman scattering (SRS) is a powerful imaging technique that has become popular during the last decades for its ability to image species specific in a sample with high accuracy. The purpose of this thesis is twofold. Firstly, to demonstrate 3D spatial control of where in the sample SRS is generated. Secondly, the spatial behavior of the SRS generation is investigated by experiments and simulations. SRS is a nonlinear scattering phenomenon that is produced when a sample is illuminated with two laser beams, called Stokes and pump beams, whose frequency difference corresponds to a molecular vibration caused by inelastic scattering of an incoming photon. The Stokes beam will stimulate the scattering of the pump beam photons, which leads to an intensity gain in the Stokes beam and an intensity loss in the pump beam. Imaging of SRS is usually performed by point scanning a sample in a laser scanning microscope by the two laser beams. Thereafter, the image is constructed pixel by pixel by detecting either the gain or the loss. Our aim is to perform direct field of view SRS imaging. Two experimental setups are presented in this thesis, one for the 3D spatial control of SRS and one for the investigation of the spatial generation of SRS.  The working principle of imaging is the same in both setups. A cylindrical sample volume was illuminated with the Stokes beam and the SRS was generated by focusing the pump beam into this volume. The diameter of the illuminated cylinder was around 10 mm. The two beams were combined before the sample using a dichroic mirror and after the sample the pump beam was removed by a second dichroic mirror.  The Stokes light was then image onto a camera providing a field of view of around 9.4 mm by 7.94 mm. A phase spatial light modulator (SLM) was used to control the shape and position of the pump beam in three dimensions (3D) in the illuminated volume. The results show that the SLM allowed for control of the position and shape of the generated SRS signal. In the second experimental setup the pump beam was focused into the sample by a lens and the spatial generation of the SRS was investigated. A second dichroic mirror blocking the pump beam was inserted into the sample at different interaction lengths to study the resulting SRS signal. Further, the pump intensity was varied to study the effect on the physical width of the SRS signal. The experimental results were compared to computer simulations. The simulations were based on diffraction theory for the beam propagation and the interaction between the light beams and the material was modeled with a phase modulation due to the induced Kerr effect caused by high pump intensity. The results shows that most of the SRS generation takes place close to the focus of the pump beam.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2022
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Atom and Molecular Physics and Optics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-90346 (URN)978-91-8048-083-3 (ISBN)978-91-8048-084-0 (ISBN)
Presentation
2022-06-17, E632, Luleå tekniska universitet, Luleå, 09:00 (English)
Supervisors
Available from: 2022-04-22 Created: 2022-04-21 Last updated: 2023-09-05Bibliographically approved

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Eriksson, RonjaGren, PerSjödahl, MikaelRamser, Kerstin

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