# SS 2024

 Learnweb: https://sso.uni-muenster.de/LearnWeb/learnweb2/course/view.php?id=77427 Enrollment key: NLP24 Start of enrollment: 03.04.2024 Scope: 2 experiments over 2 or 3 days, 3 SWS, 4.5 LP Preliminary meeting: Mo. 15.04.2024, 14:00-15:00, SR AP 222 Assignment: Experimentelle Übung: Physikalische Vertiefung (I o. II) Nichtlineare Physik

During the practical course, experiments on nonlinear effects in electrical, magnetic and optical systems can be carried out, depending on your interests. From the following offer, 2 experiments with a range of at least 4.5 credit points must be carried out. Appointments are made individually with the corresponding supervisors.

## Nonlinear ferromagnetism (3 days/LP)

Ferromagnetic resonance (FMR) is a popular method for the investigation and characterization of magnetic materials. Basically, FMR is the resonance absorption of microwave radiation in a ferromagnetic sample. Students are offered an experiment in which the resonance absorption of microwave radiation with a frequency of 3-5 GHz is investigated on a thin ferromagnetic layer. They learn how to generate or measure a magnetic field, how microwave components (e.g. a microwave circulator) work and how to plot a resonance curve. The experiment shows very clearly the nonlinear nature of the interaction of magnetic moments with the electromagnetic field. The aim of the experiment is to observe the evolution of the resonance absorption curve with increasing microwave power. The so-called "foldover effect" is studied in detail.

## Leidenfrost effect (2 days/LP)

A drop of water that is heated evaporates faster the closer the temperature is to the boiling point of 100 °C. If this temperature is exceeded, one would expect the drop to "boil away" very quickly. However, if you heat a smooth surface far above the boiling temperature of water, this experience from everyday life seems to be taken ad absurdum: the life span of water drops on the surface is extended to time scales of minutes. This is the so-called Leidenfrost effect.

## Frequency doubling in Q-switched Nd:YAG laser (2 or 3 days/LP)

Optically pumped Nd:YAG lasers are frequently used in industry, research and medicine. In this experiment, a laser is constructed from individual components such as resonator mirrors, pump diode and Nd:YAG crystal. The typical properties of these components are investigated experimentally. The emitted infrared light is then doubled in frequency in a nonlinear crystal. With a Q-switching, short laser pulses can then be generated from the continuous emission. The experiment provides an insight into the functioning and properties of a laser and the nonlinear interaction between light and matter.

## Nonlinear microscopy (3 days/LP)

Nonlinear microscopy characterizes samples not by their absorption properties or refractive index, but by their interaction with an intense laser pulse. In the practical experiment, a laser scanning microscope will be set up with which a sample can be scanned with a laser beam in order to generate an image of different samples point by point. The two-photon fluorescence will be used as a contrast mechanism.

## Autocorrelation of ultrashort laser pulses (2 or 3 days/CP)

The autocorrelation is an important and everyday tool when dealing with ultrashort laser pulses in the laboratory as it gives information about the duration of the optical pulse which is, due to the time scale in the pico- to femtosecond regime, not directly measurable. In this lab course you will build an autocorrelator yourself, test different detection schemes, and use it to characterize an ultrafast laser.

## Fiber laser (2 or 3 days/LP)

In this experiment, a laser based on glass fibers doped with rare earths is constructed and characterized. The basics of lasers are worked up and the handling and fusion bonding of glass fiber components is learned. Furthermore, possibilities for tuning the output wavelength of the laser or for generating ultrashort laser pulses are investigated and the result is measured.

## Light propagation in fibers (2 or 3 days/LP)

The experiment "Light propagation in fibers" is intended to provide a basic understanding of how laser light behaves when propagating through light-conducting structures, using the example of glass fibers. The experimental handling of glass fibers is learned and the properties of a laser beam after propagation through different types of glass fibers are investigated. The polarization of the light as well as its transverse beam profile are of central interest.