Low-noise Thulium-doped Femtosecond Fiber Laser And Its Application In Precision Spectroscopy

The proposal of optical frequency comb has fueled rapid development of optical frequency metrology,precision laser spectroscopy,transient phenomena detection,and so on.Special interests are paid in optical frequency combs in mid-infrared region,because it covers the characteristic absorption lines of many gaseous molecules.However,the development of optical frequency combs in mid-infrared region is still far away from practical applications.Devoted to the key processes in mid-infrared optical frequency comb development,the main contents of this dissertation are as follows:Initially,ultrashort pulses are generated in figure-9 based thulium-doped fiber lasers as a low-noise seed.The transmission of figure-9 based fiber lasers is theoretically investigated.Then figure-9 mode-locked thulium-doped fiber lasers are experimentally constructed.For succeeding optical frequency comb applications,the repetition rate of the fiber laser is optimized.To further suppress the relative intensity noise,a new method is proposed for intracavity pulse dynamics manipulation without changing the cavity configurations.Next,the low-noise seed is amplified in double-cladding fiber amplifiers to 3 watt.The related effects in double-cladding thulium-doped fiber amplifiers,the rate equations for numerical simulation,and the effective gain are discussed.Chirped-pulse amplification technique is adopted for the watt-level average power acquisition.Octave-spanning supercontinuum is further generated in an all solid fluorotellurite fiber pumped by pulses from the above fiber amplifier.Several host materials for mid-infrared fibers are discussed and highly nonlinear fluorotellurite fiber is preferred for supercontinuum generation.The obtainable spectrum spans over one octave from1200 nm–2500 nm at 20 d B,which is the prerequisite for carrier-envelope phase detection.To optimize the flatness of the supercontinuum,another proof-of-principle experiment is conducted in erbium-doped fiber system.Moreover,an active f-to-2 f interferometer is proposed to improve the carrierenvelope phase detectivity.After the acquisition of octave-spanning supercontinuum,an optical amplifier is introduced into the conventional f-to-2 f interferometer,resulting in about 20 d B detectivity improvement.A record low residual phase noise is measured as a result.Finally,a proof-of-principle experiment on dual-comb spectroscopy is realized using a single free-running thulium-doped fiber laser.Dual-comb lasers from a single cavity are theoretically and experimentally investigated.A 3 k Hz offset repetition rate makes the dual-comb laser suitable for dual-comb spectroscopic measurement.The passive-locking between the two combs enables picometer resolution dual-comb spectroscopic measurement at kilohertz update rate in a single free-running laser.The absorption lines caused by water vapor inside the fibers are measured and compared with the HITRAN database.To explain the spurious signal observed during the dual-comb spectroscopy experiment,investigation of the intracavity pulse collision in dual-comb lasers are systematically investigated through numerical simulation.The impact of the intracavity pulse collisions on the dual-comb spectroscopy is included.