Custom designed and unstrained SESAMs for fiber based shortpulse lasers

用于基于光纤的短脉冲激光器的定制设计和无应变 SESAM

• 批准号: 510095359
• 负责人: Professor Dr.-Ing. Franz Xaver Kärtner
• 金额: --
• 依托单位: Institut für Experimentalphysik
• 依托单位国家: 德国
• 项目类别: Research Grants (Transfer Project)
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/510095359?language=en
• 关键词: Custom; designed; unstrained; SESAMs; fiber

Ultrashort pulse lasers with pulse lengths in the femtosecond range are used in industry and research, e.g. as seed lasers in materials processing, biophotonics and quantum sensing. To generate ultrashort pulses from solid-state and fiber lasers, saturable absorber mirrors (SESAMs) are typically used for passive mode coupling. The advantages of SESAMs are their versatile adaptability to a wide variety of laser systems and their ease of integration into the laser cavity, since as passive components they do not require any further control. However, for fiber-based ultrashort pulse lasers operating in the wavelength range around 1550 nm, there are two key challenges that have so far hampered the use of SESAMs or led to premature laser failure in the field. First, the dynamic behavior of mode-locked ultrashort pulse lasers is complex, i.e., in principle very close to a chaotic state. To keep the laser robust and stable in a desired well-defined operating state, the mode-locking SESAM must be tuned to the specific laser. To do this, the entire laser system must be fully understood not only in the stable state of mode-locked pulse generation, but especially in the startup phase. This stage of maturity has not yet been reached for fiber-coupled pulse lasers with wavelengths around 1550 nm. Instead, one currently works with empirically determined requirements and assigns specially selected SESAMs to a particular laser.Second, on the standard GaAs substrate used for SESAMs, there is no strain-free and long-term stable absorber material for 1550 nm. For this wavelength, the required fast absorber consists of In0.47Ga0.53As with strong crystal bias of +3.5% to the GaAs substrate. Although the bias can be reduced by incorporating small amounts of nitrogen, the resulting dilute nitrides have not been shown to have long-term stability. In commercial systems, the failure rate of 1550 nm SESAMs is increased 40-fold compared to 1030 nm SESAMs. Nevertheless, commercially available 1550 nm SESAMs are based on GaAs. Both limiting aspects are addressed in this project to overcome the hurdles for the use of fiber-based ultrafast lasers at 1550 nm in close collaboration with TOPTICA Photonics AG. There is a DFG precursor project for both. Using a numerical model of the SESAM mode-locked fiber laser, optimized laser and absorber parameters are to be determined for the desired single-pulse operation of the fiber laser. These optimized absorbers will then be grown at the Fraunhofer Institute and tested at TOPTICA and University of Hamburg in designated fiber lasers for startup behavior, dynamics and aging. Several of these cycles will be run to achieve an overall optimized system.

脉冲长度在飞秒范围内的超短脉冲激光器在工业和研究中被用作种子激光器，例如在材料加工、生物光子学和量子传感中用作种子激光器。为了从固体激光器和光纤激光器中产生超短脉冲，通常使用可饱和吸收镜(SESAM)进行被动模式耦合。SESAM的优势在于它们对各种激光系统具有广泛的适应性，并且易于集成到激光腔中，因为它们作为无源组件不需要任何进一步的控制。然而，对于工作在约1550 nm波长范围内的光纤超短脉冲激光器来说，到目前为止有两个关键挑战阻碍了SESAM的使用，或导致该领域的激光过早失效。首先，锁模超短脉冲激光器的动力学行为是复杂的，即原则上非常接近混沌状态。为了使激光器在所需的良好工作状态下保持坚固和稳定，必须将锁模SESAM调到特定的激光器。要做到这一点，必须充分了解整个激光系统不仅在锁模脉冲产生的稳定状态下，而且特别是在启动阶段。对于波长在1550 nm左右的光纤耦合脉冲激光器来说，还没有达到这个成熟阶段。取而代之的是，目前的工作是根据经验确定的要求，并将特别选择的SESAM分配给特定的激光器。第二，在用于SESAM的标准GaAs衬底上，没有无应变且长期稳定的1550 nm吸收材料。对于该波长，所需的快速吸收材料为In0.47Ga0.53As，其晶体对衬底的强烈偏置为+3.5%。虽然可以通过加入少量的氮来降低偏压，但由此产生的稀氮化物并没有被证明具有长期的稳定性。在商业系统中，1550 nm SESAM的故障率是1030 nm SESAM的40倍。然而，商业上可用的1550 nm SESAM是基于GaAs的。在与TOPTICA Photonics AG的密切合作下，该项目解决了这两个限制方面的问题，以克服使用基于光纤的1550 nm超快激光的障碍。这两个项目都有一个DFG前身项目。利用SESAM锁模光纤激光器的数值模型，确定了光纤激光器所需的单脉冲运转所需的最佳激光器和吸收体参数。这些优化的吸收体随后将在弗劳恩霍夫研究所生长，并在TOPTICA和汉堡大学测试指定的光纤激光器的启动行为、动力学和老化。将运行其中的几个周期，以实现整体优化的系统。