Development of visible ultrafast mode-locked fiber lasers

摘要标题：可见波长光纤激光器的发展非技术描述：飞秒持续时间的激光脉冲具有多种工业、医疗和科学应用。值得注意的应用是加工微型设备，成像生物样品，医学诊断和治疗，以及材料光谱学。产生超短光脉冲的激光器被称为锁模激光器。目前，锁模激光器主要基于固态放大器和光纤放大器。与固体激光器相比，锁模光纤激光器具有稳定性好、结构紧凑、效率高、成本低等优点。该项目旨在开发新的方法，使锁模光纤激光器产生可见波长的超短飞秒尺度光脉冲。尽管锁模飞秒光纤激光器具有许多实用的优点，但是要开发一种可见光波段的激光器，必须有一种新的脉冲形成原理。大多数锁模激光形状脉冲需要折射率色散（称为群速度色散）和光纤非线性共同作用。然而，相对于阻碍脉冲形成的光纤非线性，光纤在可见光区具有非常高的群速度色散。在本项目中，锁模飞秒光纤激光器将通过在正常群速度色散下操纵独特的脉冲传播现象来形成超短脉冲。在可见光波段工作的锁模光纤激光器将在普通显微手术、眼黄斑变性等医学应用中成为有价值的工具。研究生将接受激光科学与技术方面的职业培训，并积极参与研究项目。将努力招募不同群体参与该项目，并为他们提供重要的科学研究经验。本科生也将参与并接触到研究过程。有了这些经验，他们可能会考虑在科学和技术领域从事未来的职业。技术描述：利用全法向群速度色散激光器中的自相似演化和耗散孤子传播，利用掺镨（Pr）氟化光纤设计可见光波段的锁模光纤激光器。虽然该项目的主题是产生可见波长锁模脉冲，但将研究超出增益带宽（BW）限制的飞秒脉冲产生。掺pr光纤在635 nm波长附近的增益BW非常窄，不足以支持飞秒脉冲。然而，采用自相似演化可以产生比增益BW宽得多的光谱脉冲，也可以形成比增益BW限制短得多的脉冲。可见波长锁模光纤激光器与有价值的科学应用相关，如荧光寿命成像显微镜、时间分辨光致发光光谱和可见频率梳。该项目的成功结果将产生重大影响。自相似脉冲形成技术可用于产生波长超短脉冲，其中由于窄增益BW限制只能使用连续波激光器。该项目有可能扩展锁模激光器的波长范围，并为未来的应用开辟道路。

Abstract Title: Development of visible wavelength fiber lasers Non-Technical Description: Laser light pulses with femtosecond durations have a variety of industrial, medical and scientific applications. Notable applications are machining micro-scale devices, imaging biological samples, medical diagnostics and therapy, and materials spectroscopy. Lasers generating ultrashort optical pulses are referred as mode-locked lasers. Today, mode-locked lasers are mainly based on solid state amplifiers and optical fiber amplifiers. In comparison with solid-state lasers, mode-locked fiber lasers have the advantages of stability, compactness, efficiency and low cost. This project is to develop novel approaches to making mode-locked fiber lasers generating ultrashort femtosecond scale optical pulses at visible wavelengths. Even though mode-locked femtosecond fiber lasers have many practical advantages, a novel pulse forming principle is necessary in developing one in the visible wavelength regime. Most mode-locked lasers shape pulses require that the refractive index dispersion, called the group velocity dispersion, and fiber nonlinearity work together. However, an optical fiber in the visible regime has a very high group velocity dispersion relative to the fiber nonlinearity that hinders the formation of pulses. In this project, mode-locked femtosecond fiber lasers will be developed by manipulating unique pulse propagation phenomena at normal group velocity dispersion to form ultrashort pulses. A mode-locked fiber laser operating at visible colors will be a valuable tool for medical applications such as general microsurgeries, eye macular degeneration, etc. Graduate students will be trained for careers in laser science and technology and actively be involved in the research project. An effort will be made to recruit diverse groups to the project and to provide them with significant scientific research experiences. Undergraduate students will also participate and be exposed to the research process. With this experience they may consider pursuing future careers in science and technology. Technical Description: Mode-locked fiber lasers operating at visible wavelengths will be designed using Praseodymium (Pr)-doped fluoride fibers by manipulating the self-similar evolution and the dissipative soliton propagation in all-normal group velocity dispersion lasers. While the main theme of the project is to generate visible wavelength mode-locked pulses, femtosecond pulse generation beyond the gain bandwidth (BW) limitation will be studied. A Pr-doped fiber has a very narrow gain BW around the wavelength at 635 nm, which is insufficient to support femtosecond pulses. However, by adopting self-similar evolution, pulses with spectra much broader than the gain BW can be created and much shorter pulses can be formed than the gain BW limitation. Visible wavelength mode-locked fiber lasers are relevant for valuable scientific applications such as fluorescence lifetime imaging microscopy, time-resolved photoluminescence spectroscopy, and visible frequency combs. The successful outcome of the project will have a significant impact. The self-similar pulse formation technique can be exploited to generate ultrashort pulses at wavelengths where only continuous-wave lasers are available due to the narrow gain BW limitations. This project has the potential to extend the wavelength range of mode-locked lasers and to open the way for future applications.