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

本研究项目的目标是发展和验证全息概念，用于同时空间和光谱分辨分析横向多模半导体激光器的增益和折射率动态。为此目的，我们将继续使用全息技术。在最后一步，我们的目标是将时间分辨率降低到皮秒范围的光谱和空间分辨率。在这个项目的第一阶段，我们可以证明全息概念非常适合高精度地分析半导体中的增益和折射率动态。然而，这些结果也为激光二极管器件的分析提供了意想不到的问题，这些问题必须首先得到解决。这些问题包括光束通过二极管波导的传播，即进出耦，适当的模式滤波，输入场的精确确定，以及即使在由半导体激光放大器的水冷却引起的机械振动下也为全息测量提供合适的参考。针对这些挑战，我们制定了适当的解决方案概念，并将在此延续项目中实施。这包括改进的内耦合和外耦合光学与模式滤波器，用于确定光输入场进入二极管的概念，以及一个稳定的参考波产生的公共路径设置。基于这些改进，我们将建立一个高效，快速，第一步固定的激光二极管全息表征系统，为器件提供增益光谱，差分增益光谱，载流子诱导折射率变化光谱和线宽增强因子光谱。这种方法应首先实施横向单模发射器，然后将转移到空间扩展发射器（广域激光器，锥形放大器）。在最后一步，我们将分析如何确定增益和折射率动力学可以通过脉冲探针和参考场时间分辨。如果这是可能的，我们的目标是确定最佳的时间分辨率。该项目的总体目标仍然是通过我们的全息方法实现对半导体激光器中增益和折射率动态的基本理解。基于这种理解，我们的目标是找到改进器件性能的新方法，例如有关光束质量或短脉冲产生的新方法。

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.