| The femtosecond optical frequency "combs" in ultraviolet (UV) and extreme ultraviolet (XUV) wavelengths could provide an effective tool in the investigation of scientific issues, such as UV nonlinear optics, attosecond pulse generation and UV frequence standard. Aiming for a better controlment on the light field in time-frequency domain, science and technology in precision spectroscopy are moving towards to UV and even XUV wavelength.One of the most feasible and effective methods in generating UV frequency comb is to use high-average-power high-repetition-rate ultra-short pulse laser with precise control of time-frequency as a driving source for high order harmonic radiation in atoms. Particularlly, the high-power ultrashort pulse laser is the key technique of such programs. This dissertation focuses on the key techniques of high-power-laser system which used to generate UV optical frequence combs. The main results have been summarized as following:1. We developed a compact ultrashort pulse laser oscillators and obtained 41 fs laser output, which provided a long-term stable signal pulse for the driving source of the UV frequency comb.a) Ultrashort pulse laser oscillators were constructed with the new type Yb-doped laser crystals and Yb-doped single mode fiber as the gain mediums. By managing the intracavity GVD and analyzing the relationship of mode-locked state with the output power and output spectrum, as short as 41 fs pulse width with 3 dB spectral bandwidth of 70 nm was obtained from the fiber laser oscillator.b) By optimizing the cavity structure and removing the thermal accumulation, up to 40 W average power was demonstrated by Yb:YAG transparent ceramics, which would provide the feasible basis for further access to high quality ceramic laser media and high-performance ceramic lasers. 2. The synchronization of multi-wavelength ultrashort pulses in time-frequency domain was improved by all-optical method, which could provide a precise synchronization of the pump pulse and signal pulse for high-repetition-rate OPCPA, high-average-power femtosecond laser, and UV comb generation.a) Robust synchronization was achieved for Ti:sapphire, Yb- and Er-doped fiber mode-locked lasers by using cross-absorption modulation (XPM) technology in the master-slave configuration. Significant reduction of the demand on the master laser power and expansion the controlled cavity length mismatch was demonstrated in this experiment.b) By using active gain modulation technology and nonlinear polarization rotation switch, a few cycles ultrashort pulse were accumulated and shaped in a fiber oscillator in coherent or incoherent manner. The shaping pulses maintained low timing jitters within femtosecond level. By the introducing of active gain mechanism and eliminating the insertion loss, the energy gain close to 30 dB.3. We successfully developed the high-repetition-rate ultrashort pulse fiber amplifier, which could provide a high energy field in driving UV frequency comb.a) By eliminating the gain competition and achieving mode matching, the specific energy level transitions of Hg0,I2, He was achieved by wavelength tunable Yb-doped crystals laser and high power double-clad fiber amplifier.b) A high-power femtosecond fiber laser system was built by CPA technology. Several devices, such as high power coupling devices and cooling devices, were designed to control the amplifier parasitic oscillations and pulse distortion. By CPA technology and Yb-doped double-clad fiber amplifiers,150-W average power with pulse duration of 270 fs was obtained at 1035 nm. c) The laser synchronization between high-power fiber laser and Ti:sapphire laser were demenstrated. High-power optical fiber amplifier provided more than 50 dB energy gain and maintained the pulse shape for the seed laser. This method proved an effective solution for accurate synchronization of the signal and the pump laser of OPCPA system, as well as the UV comb generation.
|
PDF Full Text Request