Research Fields and Projects LIMMA
Projects LIMMA
Laser-induced breakdown spectroscopy (LIBS)
The scientific research in the 21ist century has one of its major focuses on environmental protection and pollution detection, with many techniques delving into molecular composition of contaminants, and some looking even further into the elemental level. Assessment of the basic composition of a given sample can be an exhausting feat, normally requiring a great deal of sample preparation. Laser Induced Breakdown Spectroscopy (LIBS) allows an easy access of the chemical makeup without most requirements of other analytical methods. Firing a high energy LASER pulse at the surface of a given material will ignite plasma, containing all elements of said material in an excited energetic state. When cooling down, those elements will emit light of wavelengths only specific for them that can be picked up by spectrometer. 
When firing the LASER pulse through a lens or microscope objective the spot size of the plasma forming can be made as small as the diffraction limit and can raise the energy density in it several orders of magnitude. Including a second LASER pulse into the already heated plasma will further enhance said energy density of the heated gas and therefore improve the sensitivity of the measurement. The LIBS method and the additions we made to our setup make it possible to grasp the elemental composition of tiny particles or miniscule parts of grander samples that potentially pique our interest.
Analysis of maritime microplastics using Raman spectroscopy
The impact and analysis of maritime microplastics have recently become a main focus of many researchers. To decrease the contamination of tiny polymer particles in the oceans it is required to obtain information about the polymer composition and their origination. The method of Raman spectroscopy offers a non-destructive way for the identification of microplastics. Through focusing a laser on the samples surface, the molecules of the polymers are excited in higher energetic vibrational states. 
This vibrational motion takes energy of the incident light, which amount is molecule specific. The light that is scattered by the sample has this certain amount of energy less. By measuring the energy difference between the incident and the scattered photons using a spectrometer one obtains a molecular fingerprint of the polymer.
Nano Energy - Research of photosynthesis
Organic light-harvesting (LHC) complexes convert light into chemical energy with very high quantum efficiency. Excellent examples of these complexes are rhodopsin and bacteriorhodopsin [1]. Bacteriorhodopsin is an effective proton pump which leads to energy conversion and ATP production. The same family of protein, Rhodopsin undergo through the conformational changes and starts primary events in visual signaling pathways [2]. Recent discussions suggest that the spatial structure and state of dimerisation of the LHC in rod outer segments (ROS) influences the activation of transducers, increases the quantum efficiency and is directly effecting the signaling cascade in vision [3, 4]. The focus of this project is the investigation of the relevant elementary processes, the organisation of LHC and their interaction with the membrane by means of fast multi-confocal Raman microscopy with a digital micro mirror based 4D microscope and high spatial resolution CARS spectroscopy. 
It will furthermore provide insight on the light-energy conversion underlying energy transfer processes, charge transport routes, quantum effects, and structural changes at the molecular level. Of particular interest is the investigation of membrane-protein interaction and arrangement of proteins in the retinal outer segment discs. Polarization Fourier transform IR Raman spectroscopy FTIR spectroscopy yields access to the orientation of retinal proteins in a native-close environment [5]. Qualitative orientation information could be obtained by comparing the intensity of two perpendicularly polarized Raman spectra. In the most probable orientation distribution (MPD) method the quantification of the order parameters, second and forth is used to compare the orientation of different samples [6].
- Amesz, Jan (1986): Light Emission By Plants and Bacteria. Oxford: Elsevier Science (Cell biology). Available online at http://site.ebrary.com/lib/alltitles/docDetail.action?docID=10679000.
- Rhodopsin Structure, Function, and Topography The Friedenwald Lecture Invest. Ophthalmol. Vis. Sci.. 2001;42(1):3-9.
- Gunkel, Monika; Schoneberg, Johannes; Alkhaldi, Weaam; Irsen, Stephan; Noe, Frank; Kaupp, U. Benjamin; Al-Amoudi, Ashraf (2015): Higher-order architecture of rhodopsin in intact photoreceptors and its implication for phototransduction kinetics. In Structure (London, England : 1993) 23 (4), pp. 628–638. DOI: 10.1016/j.str.2015.01.015.
- Schertler, Gebhard F. X. (2015): Rhodopsin on tracks: new ways to go in signaling. In Structure (London, England : 1993) 23 (4), pp. 606–608. DOI: 10.1016/j.str.2015.03.008.
- J. Sawatzki, R. Fischer, H. Scheer, F. Siebert. “Fourier-transform Raman spectroscopy applied to photobiological systems.” In Proceedings of the National Academy of Sciences of the United States of America 87 (15), pp. 5903–5906. 1990.
- M. Richard-Lacroix, C. Pellerin. “Accurate New Method for Molecular Orientation Quantification Using Polarized Raman Spectroscopy.” In Macromolecules 46 (14), pp. 5561–5569. 2013 DOI: 10.1021/ma400955u.
OPhonLas: OCT-geregelte Laserablation bei Stimmlippen-Phonation
Förderung: Europäische Fonds für regionale Entwicklung (EFRE), Land Niedersachsen 
Laufzeit:
Projektkoordination:
Wissenschaftliche Mitarbeiterin:
Projektpartner:
Hintergrund
Krankheitsbedingte Einschränkungen im Alltag stellen für die Betroffenen eine Belastung und Beeinträchtigung dar. Wird neben einer konservativen Maßnahme ein chirurgischer Eingriff notwendig, so sind die dadurch entstehenden Nebenwirkungen möglichst gering zu halten. Die Anforderungen an die moderne Phonochirurgie äußern sich daher in einer möglichst schonenden Behandlung durch die Minimierung von Vernarbungen, Resektionsdefekten und Beeinträchtigungen auf Grund einer Narkose.
Die derzeitigen Schwierigkeiten bei chirurgischen Eingriffen im Bereich der Stimmlippen liegen, neben der eingeschränkten Zugänglichkeit des Stimmlippengewebes, in der bisher mangelnden intraoperativen Funktionskontrolle.
Forschungsvorhaben
Das Ziel der Verbundpartner im Projekt OPhonLas umfasst die interdisziplinäre Weiterentwicklung eines minimalinvasiven, nebenwirkungsarmen Eingriffes am Kehlkopf, zur Verbesserung oder Wiederherstellung der Stimmfunktion. Durch die Bündelung von Kompetenzen aus den Bereichen der optischen Bildgebung und -verarbeitung, Regelung sowie Lasertechnologie wird eine Verbesserung medizinischer Instrumente angestrebt.
Es soll ein rigides, anatomisch gekrümmtes Laryngoskop entwickelt werden, dass die Operation an einem kooperationsfähigen Patienten, zur postoperativen Funktionskontrolle, ermöglicht. Durch die Kombination einer tiefenauflösenden Darstellung mittels Kohärenztomographie und dem Einsatz von Stereobilddaten zur Oberflächenvisualisierung, soll eine Laserablation auf oszillierendem Gewebe ermöglicht werden.
Teilprojekt
Unser Ziel im Projekt für Laseranwendungen in der Medizin ist es, einen zweidimensionalen Mikro-MEMS Scannkopf und entsprechende Optiken zu entwickeln, für die Anwendung eines Endoskopes, welches Einsatz in der Laserchirurgie an Stimmbändern finden soll. Hierfür soll Optische Kohärenztomographie (OCT, Optical Coherence Tomography) angewendet werden, um die Gebiete beschädigten Gewebes an den Stimmbändern zu ermitteln, welche daraufhin mittels eines Thulium Lasers entfernt werden können. In diesem Projekt wird die Wechselwirkung von Laser und Gewebe hinsichtlich der Laserleistung, Fokusgröße und Fokusposition untersucht, sowie die Optimierung bildgebender Verfahren.
Climate research by dendrochronology
Non-linear Raman spectroscopy
Coherent Anti-Stokes Raman Spectroscopy or CARS is a technique which relies on a non-linear stimulated Raman process in order to optically obtain information about the molecular structure of a sample. Unlike spontaneous Raman, the molecular vibrations are driven using two laser beams, known as pump and Stokes beams, with an exact frequency difference equal to the characteristic frequency of the vibration of interest. This results in resonant coupling between the incoming beams and the molecular oscillator. A third beam, called the probe beam, is then modulated by the driven oscillator which results in its frequency being shifted. The frequency shift can be measured and quantified. 
Because CARS is a coherent process, under certain beam geometries, contributions from all molecular oscillators within the sample can be made to interfere constructively and therefore produce a Raman signal, much stronger than that of a spontaneous Raman process.In practice, in order to save on complexity and cost the pump and probe beams are implemented using the same laser. By varying the frequency difference between the pump and stokes beams, one is able to tune-in on a molecular vibration of interest, resulting in CARS amplification only from that particular vibration. The implications of this are two-fold: a) spectroscopic measurement can be implemented without a dispersive element b) a wide-field microscope with chemical selectivity can be implemented. The fact that CARS is non-linear process also enables sub-diffraction imaging techniques to be used.
Fourier-transform infrared spectroscopy
Raman spectroscopy is a common technique for the analysis and identification of biological samples. The application of a laser in the visible spectral range is connected to a disturbance of the Raman-signals detection since biological samples might show a strong fluorescence emission in this spectral range, which could overwhelm the Raman-signal. The goal of this project is the detection of Raman-signals of biological samples in the infrared spectral range using a fouriertransform-interferometer. 
The set-up comprised an Nd-Yag Laser to avoid fluorescence emission of the samples. The interferometer provides a split-up of the signal into two beams, which become phase-shifted to another using an adjustable mirror. This phase shift generates a modulation of intensity in the interferogram, and by the Application Fourier analysis, information about spectral compounds of the Signal can be achieved, allowing the set-up to be used as a high-resolution spectrometer.