The collaboration between the Optical Technologies Group and Conor L. Evans' group at the Wellman Center for Photomedicine (Harvard Medical School) has resulted in a new publication in which stimulated Raman scattering was used to investigate the distribution of drugs in the skin. The detectors developed by Nick enabled better qualification in the experiments by utilizing different modalities of the detector.
The Wilhelm and Else Heraeus Foundation has set itself the goal of supporting events at which scientists can exchange information about their research results, particularly in the field of physics. At the 838th WE-Heraeus Seminar on "Manipulating Molecular Electronic Properties by Vibrational Excitations: Novel Spectroscopies and Microscopies", Prof. Fallnich, Nick and Kristin used such an opportunity to talk to researchers about thier results in the field of coherent Raman scattering. In addition to exciting lectures, the program also included a hike up the Drachenfels.
With 44,000 trade fair visitors and 2,000 conference participants, the Laser World of Photonics and CLEO/Europe took place and we were part of that event!
Besides our work on stimulated Raman microscopy by Nick and Kristin, on waveguide-based optical parametric oscillators by Ming and Max, and on the transverse mode-locked beams by Jan, there were talks by Novel laureates Anne L'Huillier and Ferenc Krausz to see, new products to discover at the fair, and a joint dinner with the working group.
Every two years, Munich is transformed into the undisputed photonics capital of Europe: for five days at the end of June, the Laser World of Photonics and the CLEO Europe bring together industry and research in the Munich exhibition halls.
Amidst it all, Kristin and Nick will present their advances on stimulated Raman microscopy, Ming and Max will present advanced waveguide-based optical parametric oscillator schemes and Jan will get to the bottom of the similarities between transverse mode-locked and other scanning beams.
Michael completed his doctorate with "Summa cum laude" on Friday, May 23th, 2025. During his doctorate, he focussed on transversely mode-locked beams and in particular on the generation of these exotic spatiotemporally dynatic light fields by converting longitudinally mode-locked licht fields. During his time in the working group, he also completed the full description of these beams, revealing crucial differences to other spatiotemporally oscillating light beams.
On the day of the defence, mainly the colleagues were noticeably nervous; everybody automatically put oneself in the position of the defender. Michael, on the other hand, seemed relatively relaxed and, after a very catchy presentation answered the examiners' questions, which he mastered confidently and earned the top mark.
Afterwards, friends and family, as well as his colleagues, had time for eating, drinking and celebrating Michael's success. The doctoral was presented by his colleagues. The hat impressively replicates Michael's research work (highly simplied) and has to be adjusted to produce the disered transversal mode-locked state.
The working group would like to thank you for a great time - we will miss you, Michael!
In a new publication in Optics Express Jan and Michael show surprising wavevector dynamics of transverse mode-locked laser beams. These rapidly spatially scanning beams are knwn for their spatiotemporal intensity dynamics, but their phase features have thus far nocht ben investigated.
To experimentally demonstrate the spatiotemporal wavevector oscillations in these beams, the phase-sensitive coupling condition of a single-mode optical fiber has been leveraged, immediately highlithing the impact or phase features on optical processes. Find a corresponding video here.
New publication on Optics Express! In this paper, Max and Ming demonstrated a widely tunabel dual-wavelength, waveguide-based optical parametric oscillator (OPO) exploiting four-wave mixing in a single silicon nitride waveguide. This OPO generated two independently tunable idler pulses with arbitrary frequency spacing ranging from zero up to 65 THz in the wavelength region from 1.11 to 1.46µm. This novel dual-wavelength waveguide-based OPO paves the way toward various multi-wavelength applications.
New publication on Optics Express! In stimulated Raman scattering (SRS), two pulsed lasers excite molecular vibrations, enabling chemical imaging. A small energy transfer between the beams can be detected with a lock-in amplifier, but the sensitivity - and thus imaging contrast - depends heavily on laser noise.
Belanced detection reduces this noise by substracting signals from before and after the sample. However, in microscopy, varying optical losses across the scan can disrupt this balance, weakening noise suppression.
In order to solve this, we developed a compact, auto-balancing detector that compensates for these losses using a PID in a control loop. This approach reduces laser noice to the quantum limit even while scanning heterogenous samples and reduces imaging artifacts.
See publication by Nick and Kristin.
The results of Kristin's and Ming's work on waveguide-based light sources for Raman microscopy have been published! A silicon nitride waveguide was used to realize a light source using stimulated four-wave mixing and to generate frequency-shiftted pulses that were used to excite coherent Raman scattering processes. The broad waveleght tunability and the minaturization of the light source by the used waveguide are an important step for the broader application of coherent Raman scattering also outside specialized laboratories. See the publication.
The 11th EPS-QEOD EUROPHOTON conference was held in Vilnius, Lithuania this year, where the latest breakthroughs in the field of solid-state, fiber and waveguide light sources were shared. Ming and Max presented our group’s latest advances in waveguide-based light sources. Max presented his collaborative work with Ming on a dual-wavelength waveguide-based optical parametric oscillator (WOPO), and Ming presented her collaborative work with Kristin on utilizing the WOPO light source for anti-Stokes Raman scattering applications.
Michael's paper on the controlled generation of transverse mode-locked beams has been published. The interference of transverse resonator modes produces a laser spot that moves periodically along a line - without mechanical movement by a deflection optic, allowing high speeds of 80 MHz. The moving beams were emitted continuously and their dynamics during oscillation could be controlled directly, which was previously not possible at such a high level. See the publication.
New optical tables in three laboratories: In recent weeks, the laboratories first had to be completely cleared out before the old tables could be dismantled and the new ones installed. The steel tables absorb vibrations due to their solid construction and pneumatic isolation, which enables sensitive measurements. They also offer more space than their predecessors. The first experiments have already been set up again: Now the research in the laboratory can begin again!
Michael's and Kristin's contributions to the Photonics West conference were funded by the Santander Mobilitätsfonds of the University of Münster. As a part of this funding they present their personal and technical experiences: Kristin will talk about the daily routine on a conference and about her current research on stimulated Raman scattering, whereas Michael will tell about optical clocks and their precision. The talks take place on May 2, 12:30 h in the seminar room 222 in the Institute of Applied Physics.
All students of the faculty are kindly invited.
Scientific discussions with snacks and drinks, that's what we had this week at the poster sessions of the Focus on Microscopy in Genoa. Kristin presented a poster on her work on heterodyne detection in CARS imaging as well as a poster on Nick's results on balanced detection and was able to bring a lot of positive feedback and new ideas back to Münster.
New publication on Optics Express! In this paper, Ming demonstrated an efficient and widely tunable synchronously pumped optical parametric oscillator (OPO) exploiting four-wave mixing in a silicon nitride waveguide. This waveguide-based OPO (WOPO) exhibited a high conversion efficiency of up to -7.64 dB and generated up to 387 pJ idler pulse energy. This WOPO represents a significant improvement of conversion efficiency as well as output energy among χ3-WOPOs, rendering an important step towards a highly efficient and widely tunable chip-based light source, e.g., for coherent anti-Stokes Raman scattering. See the publication.
San Francisco. Known for the Golden Gate Bridge, cable cars and home to one of the largest conferences in the field of photonics – the Photonics West.
At this conference, Kristin and Michael presented their latest results on background-reduced CARS microscopy and controlled generation of transverse mode-locked beams.
Kristin and Nick were part of the conference program in Paris and presented their work on background signal suppression using frequency modulation in stimulated Raman scattering and balanced detection. As a bonus, Kristin was awarded the prize for the best PhD poster.
We were once again at the BachelorMaster day to showcase the work in our research group and possible topics for student theses.
It was particularly important to us to draw the students' attention to the combination of experimental and theoretical work and the many areas of application of our research. In the following week students had the opportunity to get to know our experiments in detail during a guided tour through our labs.
We are still looking for students who would like to write their thesis in the Optical Technologies group! If you are interested, please contact us at opttech@uni-muenster.de.
It is remarkable how many exciting career paths have developed after the time in the working group. From the development of specialized laser systems in their own start-up to the assessment of traffic accidents: Applied physics opens up many career paths!
