The aim of the presented work is to investigate the angle-resolved scattering characteristics of biological nano- and micro-scaled cell structures. The scattering results of cellular structures were compared to measurements of ideal spherical nano- and micro-particles. A monolayer of mouse fibroblasts L929 cells was cultivated in a Dulbecco's Modified Eagle Medium (DMEM) in a standard 24 well cell culture plate. The system allows an in situ measurement directly in the standard cell culture plate and a contaminant-free investigation of the viability of the cell cultures. Of particular interest was whether changes in the tumor characteristics occur in necrosis or other cell-harming effects. Because of the size ratios between wavelength and the scattering particles, all observations were investigated using Mie scattering theory. A setup for reliable measurements was developed and the scattered angle dependent intensity obtained was compared with simulated scattering characteristics. A homemade supercontinuum (SC) light source was filtered by an optical bandpass filter with a central wavelength of 500 nm. The scattered portion of the pulsed SC light behind the sample was recorded in a time-resolved manner at defined angles. A specimen holder adapted to standard cell culture plates allows detection of scattered radiation at angles between ±80° without angle-dependent Fresnel reflection losses and a Snell’s law bending of the propagation direction. Finally, the system was tested to detect structural changes of mouse fibroblast L929 cells before and after poisoning the cells with the cell detergent Triton X100 and the data clearly shows changes in the scattering characteristics when the cells were destroyed.

Zuerst wird die Idee einer gechirpten photonischen Kristallfaser vorgestellt. Aus einem stark vereinfachten Modell, die qualitativen Eigenschaften dieses neuen Fasertyps abgeleitet. Hier gelingt es, alle wichtigen Designparameter zu bestimmen. Die hervorragenden Leitungseigenschaften dieser Fasern werden dann in Experimenten demonstriert. Ohne jegliche Dispersionskompensation wird die Übertragung eines 25 fs Impulses in einer 1 Meter langen Faser gezeigt. Wird zusätzlich eine Dispersionskompensation verwendet, lassen sich sogar Impulse mit weniger als 20 fs Dauer übertragen. Im Anschluss daran wird eine photonische Kristallfaser untersucht, die mit einer Flüssigkeit gefüllt ist. Die hergestellte Faser ist dahingehend optimiert, einen hoch effizienten Soliton-Fission Mechanismus zu ermöglichen, der zur Erzeugung von Weißlicht genutzt wird. Diese Weißlicht-Impulse haben eine mit Soliton-Fission bisher noch nie erreichte Energie von 390 nJ. Auf Grundlage einer guten Übereinstimmung mit den experimentellen Resultaten lässt sich aus numerischen Simulationen der zugrunde liegende Effekt bestimmen. Abschließend wird über ein Experiment berichtet, das die nichtlineare Wechselwirkung zwischen zwei Impulsen verschiedener Wellenlänge ausnutzt, um einen optischen Schalter zu verwirklichen. Dieses Experiment erfordert genaueste Kontrolle der Dispersion und der Nichtlinearität in der Faser. Bei der gleichzeitigen Propagation von zwei Impulsen wird ein neuartiger Schalteffekt beobachtet. Beide Impulse haben nahezu die gleiche Gruppengeschwindigkeit, und ihre nichtlineare Wechselwirkung basierend auf Kreuz-Phasen-Modulation wird dadurch deutlich verstärkt. Hiermit wird ein voll funktionsfähiger optischer Transistor mit gutem Schaltkontrast experimentell demonstriert, der insbesondere einen schwachen Impuls einen stärkeren Impuls schalten lässt. / First, the concept of a novel chirped photonic crystal fiber is introduced. The qualitative dispersion and loss properties of this new fiber are theoretically derived. The calculated results agree excellently with experimental data obtained from fabricated fiber samples. The superior guiding properties of this new photonic fiber are demonstrated in two experiments. The delivery of 25 fs pulses over a 1 meter distance is realized without any dispersion compensation. Moreover, using dispersion compensation, the delivery of even sub-20-fs pulses becomes possible. Subsequently, a photonic crystal fiber with a liquid core is investigated, work presents effective methods for the preparation and explains a scheme for successfully reducing the insertion loss. The fiber is optimized to support the highly efficient soliton-fission mechanism at unprecedented pulse energies in white-light supercontinuum generation. Because of the liquid core, the supercontinuum generation scheme can be scaled beyond the peak-power limitations of solid-core fibers. The generation of a two-octave spanning supercontinuum with 390 nJ pulse energy is demonstrated. The experimental results are compared to a numerical simulation and the underlying mechanism is identified. Finally, an experiment is presented that exploits strong nonlinear interaction of two pulses inside a photonic crystal fiber for all-optical switching. A novel effect is observed during the co-propagation of two ultrashort pulses with different wavelengths. Because of the dispersion properties in the chosen fiber, these pulses are propagating at nearly identical group velocities, which dramatically increases the nonlinear interaction via cross-phase modulation between the two pulses. Based on this interaction, a fully functional optical transistor is experimentally demonstrated with good switching contrast. In particular, the demonstrated optical transistor enables switching of a strong pulse by a much weaker pulse.

The use of supercontinuum light sources in different optical measurement methods, like microscopy or optical coherence tomography, has increased significantly compared to classical wideband light sources. The development of various optical measurement techniques benefits from the high brightness and bandwidth, as well as the spatial coherence of these sources. For some applications, only a portion of the broad spectral range can be used. Therefore, an increase of the spectral power density in limited spectral regions would provide a clear advantage over spectral filtering. This study describes a method to increase the spectral power density of supercontinuum sources by amplifying the excitation wavelength inside a nonlinear photonic crystal fiber (PCF). An ytterbium doped photonic crystal fiber was manufactured by a nanopowder process (drawn by the company fiberware) and used in a fiber amplifier setup as the nonlinear fiber medium. In order to characterize the fiber’s optimum operational characteristics, group-velocity dispersion (GVD) measurements were performed on the fiber during the amplification process. For this purpose, a notch-pass mirror was used to launch the radiation of a stabilized laser diode at 976 nm into the fiber sample for pumping. The performance of the fiber was compared with a conventional PCF. Finally, the system as a whole was characterized in reference to common solid state-laser-based photonic supercontinuum light sources. An improvement of the power density up to 7.2 times was observed between 1100 nm to 1380 nm wavelengths.

Supercontinuum light sources provide a high power spectral density with a high spatial coherence. Coherent octavespanning supercontinuum can be generated in photonic crystal fibers (PCFs) by launching short pulses into the fiber. In the field of optical metrology, these light sources are very interesting. For most applications, only a small part of the entire spectrum can be utilized. In biological tissue scattering, absorption and fluorescence limits the usable spectral range. Therefore, an increase of the spectral power density in limited spectral regions would provide a clear advantage over spectral filtering. This study describes a method to increase the spectral power density of supercontinuum sources by amplifying the excitation wavelength inside a nonlinear photonic crystal fiber (PCF). An all-fiber-based setup enables higher output power and power stability. An ytterbium-doped photonic crystal fiber was manufactured by a nanopowder process (drawn by the fiberware GmbH, Germany) and used in a fiber amplifier setup as the nonlinear fiber medium. In order to characterize the fiber’s optimum operational characteristics, group-velocity dispersion (GVD) measurements were performed. The performance of the fiber-based setup was compared with a free space setup. Finally, the system as a whole was characterized in reference to common solid state-laser-based supercontinuum light sources. An improvement of the power density was observed in the spectral range between 1100 nm to 1400 nm.

Optical coherence tomography benefits from the high brightness and bandwidth, as well as the spatial coherence of supercontinuum (SC) sources. The increase of spectral power density (SPD) over conventional light sources leads to shorter measuring times and higher resolutions. For some applications, only a portion of the broad spectral range can be used. Therefore, an increase of the SPD in specific limited spectral regions would provide a clear advantage over spectral filtering. This study describes a method to increase the SPD of SC sources by amplifying the excitation wavelength inside of a nonlinear photonic crystal fiber (PCF). An ytterbium-doped PCF was manufactured by a nanopowder process and used in a fiber amplifier setup as the nonlinear fiber medium. The performance of the fiber was compared with a conventional PCF that possesses comparable parameters. Finally, the system as a whole was characterized in reference to common solid-state laser-based photonic SC light sources. An order-of-magnitude improvement of the power density was observed between the wavelengths from 1100 to 1350 nm.