Monolithic, mode-locked Titanium-Sapphire lasers with repetition rates in the range of 30 GHz to 300 GHz

本项目的目标是研究一种新型的锁模掺钛蓝宝石激光器。这将是第一个单片Ti：Sa激光器和第一个具有30 GHz至300 GHz重复频率的锁模固态激光器。尽管谐振器必须很短，但Ti：Sa的不寻常的大增益带宽支持大量的纵向模式。这导致以前所未有的重复率产生无背景超短脉冲。例如，具有1THz重复率的Ti：Sa激光器仍然可以具有超过100个模式。激光器是一个简单的薄Ti：Sa盘，厚度在0.3 mm和3 mm之间，两侧都有色散补偿涂层。计算结果表明，在这种简单的结构中实现克尔透镜锁模是可能的。我们想研究这种新型的Ti：Sa激光器的锁模条件和噪声特性。谐振器内部没有抗反射涂层。这防止了标准具效应并减少了损耗。短Ti：Sa晶体允许仅使用晶体的两个表面上的涂层进行色散补偿，使得准孤子锁模成为可能。脉冲重复率将是非常恒定的，即。e.脉冲定时抖动将是低的，因为在谐振器内可能没有谐振器反射镜的振动或空气湍流。单片激光器系统的这种固有稳定性从单片单频激光器已知。具有数十GHz或数百GHz重复率的稳定fs脉冲的锁模激光器将在双梳光谱学、天文梳、超快脉冲整形、光通信或频率计量学中具有应用。高重复率允许用中等分辨率的色散系统分离模式。这导致了用于频率梳应用的紧凑且具有成本效益的系统。尽管重复频率很高，但这种激光器的峰值功率仍将比其平均功率高出数十倍或数千倍，这意味着可以预期数百瓦甚至千瓦。这将使该Ti：Sa激光器与已经达到100 GHz重复率的锁模半导体激光器分开，尽管峰值功率小于2 W。高峰功率意味着可以驱动非线性光学过程，这有利于脉冲表征和应用。随着未来蓝色和绿色二极管激光器的输出功率和光束质量的进步，应该有可能直接用二极管激光器泵浦我们的Ti：Sa激光器。这将产生非常紧凑和坚固的飞秒激光器和频率梳。

The goal of this project is to investigate a new type of mode-locked Titanium-doped Sapphire (“Ti:Sa”) laser. This will be the first monolithic Ti:Sa laser and the first mode-locked solid state laser to have a repetition rate in the range of 30 GHz up to 300 GHz. The unusual large gain bandwidth of Ti:Sa supports a large number of longitudinal modes despite the resonators having to be short. This leads to background-free ultra-short pulses at unprecedented repetition rates. For example, a Ti:Sa laser with 1 THz repetition rate could still have more than 100 modes. The laser is a simple, thin Ti:Sa disk with a thickness between 0.3 mm and 3 mm that bears dispersion-compensating coatings on both sides. Calculations presented in the proposal show that it is possible to achieve Kerr-Lens mode-locking in such a simple structure. We want to investigate the mode-locking conditions and the noise properties of this new type of Ti:Sa laser.The proposed monolithic setup has important advantages for laser operation. There are no antireflective coatings inside the resonator. This prevents etalon effects and reduces losses. The short Ti:Sa crystals allows dispersion compensation using just the coatings on the two surfaces of the crystal, making quasi-soliton mode-locking possible. The pulse repetition rate will be very constant, i. e. pulse timing jitter will be low, because there can be no vibration of resonator mirrors or air turbulence inside the resonator. This inherent stability of monolithic laser systems is known from monolithic single frequency lasers. A mode-locked laser with stable fs-pulses at tens of GHz or hundreds of GHz repetition rate will have applications for dual-comb spectroscopy, astro-combs, ultrafast pulse shaping, optical communication, or frequency metrology. The high repetition rate allows separating the modes with a dispersive system of moderate resolution. This leads to compact and cost-effective systems for frequency comb applications. Despite the high repetition rate, the peak power of such a laser will still be several tens or thousands times higher than its average power, meaning that hundreds of Watts or even a Kilowatt can be expected. This will set this Ti:Sa laser apart from mode-locked semiconductor lasers which have reached 100 GHz repetition rate albeit with a peak power of less than 2 W. A high peak power means that nonlinear optical processes can be driven which is beneficial for pulse characterization and for applications.With future advances in output power and beam quality of blue and green diode lasers it should be possible to pump our Ti:Sa laser directly with a diode laser. This would yield a very compact and rugged femtosecond laser and frequency comb.