Innovative high spectral purity DPSS lasers for LIDAR systems

An innovative oscillator for solid-state laser technology is developed for Single-Longitudinal-Mode (SLM) operation, enabling narrow bandwidth, low pulse-to-pulse time jitter, laser emission at 1064 nm. The system realized is fully characterized in terms of power, energy, spatial, temporal and spectral performance. The technology developed is defined Self Injection Seeding Ring Oscillator (SISRO), which enables to generate close to transform limited pulses with remarkable reliability and unparalleled simplicity. Both Coherent Doppler LIDARs (CDL) and High Spectral Resolution LIDARs (HSRL) can benefit from this technology, in terms of cost-efficiency, reliability and complexity. An additional significant advantage introduced by the SISRO laser architecture is modularity. This property allows to tailor the technology to the desired application and LIDAR system. Both CDL and HSRL are thus presented, after the fundamental principles governing standard LIDAR techniques have been introduced. CDL is intended to measure the motion of winds whereas HSRL is employed for discrimination between molecules and particulate matter. In both applications, the systems share the need of a laser source able to generate narrow bandwidth pulses in order to discriminate spectral broadening induced into the backscattered radiation. The SISRO technique exploits a unidirectional ring architecture to suppress Spatial Hole Burning (SHB), which is the main antagonist to SLM operation. Unidirectional propagation and thus SLM operation is achieved by means of self-seeding. The SISRO technique emerges as an appealing candidate for Master Oscillator Power Amplifier (MOPA) architectures, because of the good spatial, spectral, temporal properties and the significant pulse energies involved (uJ order), which can be easily scaled depending on the application. It is also discussed nonlinear techniques to extend the wavelength operation. Indeed, conventional laser systems struggle to access specific wavelengths, which are required for both physical reasons and health considerations, such as laser safety. Nonlinear devices enable to shift conventional high energies laser to exotic wavelengths. In this elaborate is presented nonlinear parametric oscillators for wavelength extension from 1 um to the Short-Wavelength InfraRed (SWIR) region (1.8-2.5 um). Each part is independently addressed in different chapters of this work. First, it is introduced the LIDAR technology and optical requirements. Then, the optical theory necessary to develop the SISRO, such as Passive Q-Switching and SLM operation, is described. Subsequently, the novel SISRO laser and the several iterations of the architecture based on Neodymium active materials are presented. The key parameters governing the SISRO performance and especially stability are also investigated in details, while the reader is also made aware of the typical trends associated with comparable technologies. Experimental results and theoretical predictions are thoroughly discussed, in order to understand the advantages offered by the SISRO technique and to devise suggestions to overcome its major limitations. The nonlinear theory for wavelength extension is thereafter introduced. Both Optical Parametric Ocillators (OPO) and Backward-Wave Optical Parametric Oscillators (BWOPO) systems are described, in combination with an Optical Parametric Amplifier (OPA) aimed at the extension of the spectral coverage offered by traditional bulk devices. In these regards, particular attention is dedicated to the spectral performance, showing the trade-off between these two oscillators technologies.