High power all-fiber Q-switched and Mode-locked fiber lasers *for industrial and medical applications

高功率全光纤调Q和锁模光纤激光器*适用于工业和医疗应用

• 批准号: RGPIN-2014-05339
• 负责人: Gu, Xijia
• 金额: $ 2.26万
• 依托单位: Ryerson University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=652562
• 关键词: power; fiber; switched; Mode; locked

High power pulsed fiber lasers have recently become a topic of intensive research due to their high energy and high peak power, which are essential in many applications such as material processing, laser range finding, and second harmonic generation. Among many technologies for pulsed lasers, passively Q-switched and mode-locked fiber lasers are especially interesting because of their simple structure, easy maintenance, and low cost. Picosecond and femtosecond lasers with a pulse energy of several tenths of nJ and peak power at the kW level have been demonstrated. However, despite the progress made so far, many of the reported lasers may not be suitable for industrial and medical applications due to the structure and components used in their designs. For example, some Q-switched lasers use lenses and dichroic mirrors to couple light into and out of the fiber and saturable absorbers; which diminish the advantages of the fiber laser. Some mode-locked lasers use polarization controllers to adjust polarization, which is clearly not suitable for field applications. Many pulsed lasers employ semiconductor saturable absorbers (SESAM) or carbon nanotube absorbers, which are susceptible to high energy pulses and whose long-term stability remains an issue.**These issues need to be resolved in order to develop high energy and high peak power pulsed fiber lasers, particularly those of stable, compact, and low-cost modules for industrial and medical applications. Because of this, I propose to develop high power all-fiber Q-switched and mode-locked lasers for industrial and medical applications over the next five years. I will concentrate my research on all-fiber designs so that all components will be spliced together with no optical alignment needed; this will make the laser compact, stable, and low-cost. My research will have two directions:**1. Q-switched laser: the goal is to achieve all-fiber Q-switched oscillators with over 200-µJ pulse energy and over kW-level peak power at variable repetition rates. The oscillator can be used to cut metal sheets by itself, or used as a seed laser to achieve 20- to 30-kW peak power with a single-stage amplifier. Fibers with different core diameters will be used for the gain medium and saturable absorber in the laser cavity. The optimization of the laser cavity structure, fiber core diameters of gain and saturable absorber, their lengths, and other design parameters will be studied. The dynamics of Q-switching will be simulated.**2. Mode-locked laser: the goal is to achieve stable output pulses of 10- to 30-ps pulse width and over 5-nJ pulse energy in linearly-polarized state. When this laser is used as a seeder, a one-stage amplifier will bring its peak power to multiple kW. One approach is to use a SESAM for mode-locking, in which an all-fiber coupling device will be designed to focus the beam onto the SESAM with a proper power density for stable mode-locking. Another approach is to use nonlinear polarization rotation as an equivalent saturable absorber so the power density will not be limited by the lower damage threshold of the saturable absorbers.**The Q-switched laser with sub-mJ pulse energy and kW-level peak power can be used for precision cutting and drilling. The Q-switched laser with long pulses can also be used for welding. The mode-locked ps laser, due to its fast energy deposition, will significantly reduce the heat-affected zone in material processing, which will make it an ideal tool for precise micromachining of metals and semiconductors. It will also have many interesting applications in medicine.

高功率脉冲光纤激光器由于其高能量和高高峰功率而成为近年来研究的热点，在材料加工、激光测距、二次谐波产生等领域具有重要的应用价值。在众多的脉冲激光器技术中，被动调Q锁模光纤激光器因其结构简单、易于维护、成本低廉而备受关注。皮秒和飞秒激光器的脉冲能量为十分之几nJ，峰值功率为千瓦级。然而，尽管到目前为止取得了进展，但由于其设计中使用的结构和组件，许多报道的激光器可能不适合工业和医疗应用。例如，一些Q开关激光器使用透镜和分色镜来将光耦合到光纤和可饱和吸收体中和从光纤和可饱和吸收体中耦合出来;这削弱了光纤激光器的优势。一些锁模激光器使用偏振控制器来调节偏振，这显然不适合现场应用。许多脉冲激光器采用半导体可饱和吸收体（SESAM）或碳纳米管吸收体，它们对高能脉冲敏感，其长期稳定性仍然是一个问题。这些问题需要解决，以开发高能量和高峰功率脉冲光纤激光器，特别是那些稳定的，紧凑的，低成本的模块，用于工业和医疗应用。正因为如此，我建议在未来五年内开发用于工业和医疗应用的高功率全光纤Q开关和锁模激光器。我将把我的研究集中在全光纤设计上，这样所有的组件都可以拼接在一起，而不需要光学对准;这将使激光器紧凑，稳定和低成本。我的研究将有两个方向：**1。Q开关激光器：目标是实现脉冲能量超过200 μJ、峰值功率超过千瓦级、重复频率可变的全光纤调Q振荡器。该振荡器可用于切割金属片本身，或用作种子激光器，以实现20至30千瓦的峰值功率与单级放大器。不同纤芯直径的光纤将被用作激光腔中的增益介质和可饱和吸收体。研究了激光腔结构、增益和可饱和吸收体的纤芯直径、长度等设计参数的优化。将模拟Q开关的动态特性。** 2.锁模激光器：目标是在线偏振状态下获得脉宽为10- 30 ps、脉冲能量超过5 nJ的稳定输出脉冲。当这种激光器被用作种子时，一级放大器将使其峰值功率达到几千瓦。一种方法是使用SESAM进行锁模，其中将设计全光纤耦合装置以适当的功率密度将光束聚焦到SESAM上以实现稳定的锁模。另一种方法是使用非线性偏振旋转作为等效的可饱和吸收体，因此功率密度将不受可饱和吸收体的较低损伤阈值的限制。脉冲能量为亚mJ、峰值功率为千瓦级的调Q激光器可用于精密切割和钻孔。长脉冲调Q激光器也可用于焊接。锁模ps激光器由于其快速的能量沉积，将显著减少材料加工中的热影响区，这将使其成为金属和半导体精密微加工的理想工具。它在医学上也有许多有趣的应用。