Generation And High Power Amplification Of Yb-doped Fiber Optical Frequency Comb

Optical frequency combs produced by precision control of the ultrashort pulse from mode-locked laser in both time and frequency domain, are essential tools for high precision frequency metrology, high resolution laser spectroscopy, high accuracy laser ranging and ultralow noise microwave generation. The high power frequency comb based on the Yb-fiber frequency comb and large-mode-area double cladding fiber amplifier plays the role as driving source to extend the spectrum coverage from extreme ultraviolet (XUV) to mid-infrared (MIR) region. Particularly, the high power frequency combs is also the key technique to achieve the next generation nuclear optical clock, XUV spectroscopy, and attosecond ultrafast pulse.This dissertation focuses on the Yb-fiber frequency comb generation and its high power amplification and organizes with a main line of "ultrashort pulse generation-carrier envelope phase detection and phase noise suppression-frequency stabilization of the comb-high power amplification". The related topics include: dispersion management of the passively mode-locked Yb-fiber oscillator, supercontinuum generation in photonic crystal fiber, self-referenced f-2f beat note, phase-noise suppression of the carrier envelope phase, phase-lock loop electronics, fiber chirped pulse amplification and self-similar amplification of the ultrashort pulse. The self-made digital phase-lock loop electronics was demonstrated to compensate the carrier envelope phase noise. Consequently, the carrier envelope offset frequency was well long-term locked more than 1 hour with a frequency jitter of 85 mHz. Moreover, by pre-chirping management of a self-similar Yb-fiber amplifier,80 W average power with pulse duration of 38 fs was achieved. The details are summarized as follows:1. Ultrashort pulse Yb-doped fiber oscillator was developed as the seed source for Yb-fiber frequency comb and high power fiber amplifier. The nonlinear polarization rotation mode-locked Yb-fiber oscillator was built by employing the Yb-doped single mode fiber as the gain medium with a center wavelength of 1030 nm at 60 MHz repetition rate. The fiber laser was operated in the stretched-pulse mode-locking regime by managing the intracavity dispersion. Near infrared pulse as short as 56 fs was obtained with a spectral bandwidth of 38 nm.2. Carrier-envelope offset frequency (f0) was real-time detected and the phase noise of f0 was successfully suppressed. The broadband supercontinuum spanning from 600 to 1300 nm was obtained by the proper choice of parameters of the injection pump pulse and photonic crystal fiber. Based on the self-referenced f-2f beat note, the signal to noise ratio of 30 dB was detected by heterodyne beat between 610 nm and frequency-doubled 1220 nm. The phase noise suppression approach was developed to improve the frequency long-term drift and short-term fluctuation. The linewidth of free-running f0 was dramatically narrowed from 450 kHz to 170 kHz by lowering down the pump power fluctuation. Through the environmental noise suppression, the frequency drift of the free-running fo was reduced from 28 MHz to less than 3 MHz within an hour.3. The precise control of ultrashort pulse was carried out in the time and frequency domain. As a result, the self-referenced Yb-doped fiber frequency comb was realized by frequency stabilization of the two freedoms. By feedback control the driving voltage of the piezoelectric ceramic to adjust the cavity length, the repetition rate fr is frequency stabilized with a frequency jitter of 1.44 mHz centered at～60 MHz. The carrier envelope offset frequency is also stabilized by feedback control the pump current of laser diode. Optimizing the loop filter of our self-made digital phase-locked loop, the f0 is well phase-locked at 20 MHz center frequency with a linewidth of 295 Hz and a frequency jitter of 85 mHz within an hour.4. The high power fiber amplification system operated at high repetition rate was realized. By carefully designing the all-fiber stretcher to remove the pulse distortion caused by high order dispersion, up to 239 W high average power single mode pulse was demonstrated by the chirped pulse amplification system based on the large-mode-area double cladding fiber amplifier with long-term stability. The self-similar amplification technology was developed to overcome the nonlinear effect and finite gain bandwidth. By employing the pre-chirping management method to accelerate the pulse evolution, ultrashort pulse was obtained with a compressed average power of 80 W and a pulse duration of 38 fs.5. The generation of ultraviolet pulse was explored. Based on nonlinear frequency conversion of the high power near infrared pulse from the self-similar amplifier, tunable broadband ultraviolet pulse across 253.9-268.0 nm was achieved. The largest average power of 1.33 W was obtained at a center wavelength of 259 nm.