Holographic concepts for analysing gain and refractive index dynamics in semiconductor lasers

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The goal of this research project is to develop and verify holographic concepts for simultaneous spatially and spectrally resolved analysis of the gain and refractive index dynamics in laterally multimode semiconductor lasers. For that purpose, we will continue to use holographic techniques. In the final step we aim to add a temporal resolution down to the picosecond range to the spectral and spatial resolution. In the first phase of this project, we could show that holographic concepts are well suited to analyze gain and refractive index dynamics in semiconductors with high precision. However, the results also provided unexpected problems for the analysis of laser diode devices which have to be solved first. These problems include the beam propagation through the waveguide of the diode, i.e. in- and outcoupling, an appropriate mode filtering, the exact determination of the input field, and providing a suitable reference for holographic measurements even under mechanical vibrations which are induced, for example, by the water cooling of semiconductor laser amplifiers. For these challenges we have developed appropriate solution concepts which shall be implemented in this continuation project. This includes modified in- and outcoupling optics with mode filters, concepts for determination of the optical input field into the diode, and a common path setup for a stable reference wave generation. Based on these improvements, we will set up an efficient, fast and in the first step stationary holographic characterization system for laser diodes that provides gain spectra, differential gain spectra, spectra for carrier induced refractive index changes, and spectra for the linewidth enhancement factor for the devices. This approach shall be implemented first for laterally single mode emitters and will then transferred to spatially extended emitters (broad area lasers, tapered amplifiers). In the last step, we will analyze how gain and refractive index dynamics can be determined time resolved by pulsed probe and reference fields. If this is possible, we aim to determine the best possible time resolution. The overall goal of this project is still to achieve with our holographic approaches a fundamental understanding of the gain and refractive index dynamics in semiconductor lasers. Based on that understanding we aim to find new approaches for an improvement of the device performance, for example concerning beam quality or short pulse generation.