Precise Control And Applications Of High-power Femtosecond Optical Frequency Comb

Based on the precise time and frequency control of femtosecond pulses, optical frequency comb has brought a technical revolution to the science of ultrafast lasers. Pulses delivered from optical frequency combs are with accurate frequencies and high coherence, moreover, they covers an spectal octave due to spectrum broadening. By improving the average power of ultrashort pulses, the energy of each comb line can be increased and a high-power optical frequency comb can be utilized as a valuable tool for a wide range of applications, including ultraviolet and infrared laser science, attosecond pulse generation, astronomical spectrograph calibration, precise spectroscopy and ranging, microwave waveform researches, etc.In the thesis entitled with "Precise Control and Application of High-power Femtosecond Optical Frequency Comb", a self-similar amplification module produces pulses with peak power over 15 MW and a stable high-power frequency comb are realized. The 50 W,54 fs high-power frequency comb reaches a narrow fo linewidth of 11 mHz and residual phase noise of 1.25 rad. Moreover, we’ve used the high-power frequency comb in applications. The main innovations of the thesis are listed as followings:1. By using a Faraday-rotator on the intra-cavity dispersion management of compact comb source, we realize a novel laser with low-threshold power of～48 mW which generates pulses in 55 fs time duration and 2.9 kW peak power in spectrum range between 995-1080 nm. Moreover, by conducting pulse shaping of the laser, self-similar pulses in sech2 profile are realized which exhibit excellent repetition-rate stability without extra frequency control. This result benefits the parabolic nonlinear amplification and related comb system in the following research.2. In chirp pulse amplification system, we achieve maximum pulse average power of 270 W with single pulse energy of 4.5 μJ. The high-power pulses can be further compressed to time duration of 625 fs which corresponds to a pulse peak power of 4.3 MW. In a self-similar amplification system,90 W,60 fs pulses are demonstrated with high pulse peak power of 15 MW and broadband spectrum range of 67 nm.3. In the research of new-type amplification medium, we test the laser properties of a Yb:YAG transparent ceramic sample prepared by non-aqueous tape casting. In a continuous-wave laser cavity, it produces 1050 nm light in maximum power of 7 W and slope efficiency of 60.2%. In a pulsed-laser amplification system, it reaches 70 fs pulses with maximum power of 100 W and spectrum range over 85 nm.4. In the precise frequency control of high-power optical frequency comb, the repetition-rate of pulses is locked to Rb clock with electronic servo-control modules in long-term frequency drifts of ±3 mHz and frequency standard of 0.795 mHz. On the other hand, the precise control of carrier-envelope offset frequency in 50 W,54 fs fiber optical comb system is achieved by feed-forward acousto-optic frequency shifter. In such a comb synthesis, the carrier-envelope offset frequency of the amplified pulses is stabilized within a narrow linewidth of 11 mHz, with controlled phase noise density of less than 1.25 rad and residual time jitter of 418 as.5. In the laser application expreiments, the high-power pulses have driven the optical poling of silica fiber, in which frequency doubling occurs in supercontinuum extension with enhanced second-harmonic UV light in shortest wavelength of 300 nm and conversion bandwidth achieves over ～100 nm; Moreoever, in linewidth determination of continuous-wave lasers by using optical frequency comb, excellent results are achieved. Last but not least, we propose a novel chirped spectroscopy and ranging system by taking advantage of dual-comb measurement techniques, where a distance measurement with high accuracy is achieved in scanning time of 0.1 ms.