Development of visible ultrafast mode-locked fiber lasers

摘要标题：可见光波长光纤激光器的发展非技术描述：持续时间为飞秒的激光脉冲在工业、医疗和科学领域有着广泛的应用。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称为锁模激光器。如今，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、体积小、效率高、成本低等优点。该项目旨在开发新的方法，使锁模光纤激光器在可见光波长处产生超短飞秒尺度的光脉冲。尽管锁模飞秒光纤激光器有许多实用的优点，但在发展可见光波段的锁模飞秒光纤激光器时，需要一种新的脉冲形成原理。大多数锁模激光整形脉冲都需要折射率色散，即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，可见光区的光纤具有非常高的群速度色散。在这个项目中，锁模飞秒光纤激光器将通过操纵在正常群速度色散下独特的脉冲传输现象来形成超短脉冲。工作在可见光颜色下的锁模光纤激光器将成为普通显微手术、眼部黄斑变性等医疗应用的宝贵工具。研究生将接受激光科学和技术职业培训，并积极参与研究项目。将努力招募不同的群体参加该项目，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，他们可能会考虑在未来的科学和技术职业生涯。通过控制全正常群速度色散激光器中的自相似演化和耗散孤子传输，利用掺Pr(Pr)氟化物光纤设计了工作在可见光波长的锁模光纤激光器。虽然该项目的主要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附近有很窄的增益带宽，不足以支持飞秒脉冲。然而，通过采用自相似演化，可以产生频谱比增益带宽宽得多的脉冲，并且可以形成比增益带宽限制短得多的脉冲。可见光波长锁模光纤激光器具有重要的科学应用价值，如荧光寿命成像显微镜、时间分辨光致发光光谱和可见光频率梳。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以被用来产生波长超短的脉冲，而由于窄增益带宽的限制，只有连续波激光器可用。该项目有可能扩大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.