High Power Pulsed Fiber Laser Seeded By Modulated Laser Diode And Mid Infrared Light Source

High power pulsed fiber lasers have recently attracted wide interest,owing to their advantages of good heat dissipation,high conversion efficiency,good beam quality and compact configurations.Among pulsed fiber lasers,thulium doped fiber laser operating at 2 ?m is located within the range of eye-safe laser wavelengths,atmospheric transmission window and high absorption region of water vapor in the air.Hence it can be widely used in laser surgery,free space optical communication,laser radar and opto-electronic countermeasure.In addition,high power pulsed thulium doped fiber laser at 2 ?m wavelength is considered to be an ideal pump source of nonlinear crystal for generation of high power mid-infrared laser at 2-12 ?m.All these motivate people to work on the high power thulium doped fiber lasers.The main work in this dissertation is concentrated on the creation of the high power pulsed(picosecond and nanosecond)thulium-doped fiber laser seeded by directly modulated laser diode and the supercontinuum of mid-infrared supercontinuum using the above pulsed Tm-doped lasers.The first part of this dissertation includes the study of high power diode-seeded pulsed thulium-doped fiber laser(see Chapter Two).An average power of 100 W and a pulse peak power of 83 kW have achieved.In the case of amplifying pulse seeds with conventional waveforms,the amplified pulse duration is compressed rapidly at low average power operation,due to the gain saturation of the amplifier.It therefore causes undesired nonlinear effects and instability of the laser systems.To suppress such a deleterious effect,laser-diode modulation technique has been employed for generating optimum waveform of the seeded pulses.By carefully controlling the relative amplitudes of the rising segment and falling segment of the pulses,nanosecond pulses with high average power of 240 W has been obtained from thulium-doped fiber laser(see Chapter Two).Next,the nanosecond thulium-doped fiber laser seeded by directly modulated laser diode has been used to pump mid-infrared tellurite and fluoride glass nonlinear fibers and highly-efficient 2-4 ?m mid-infrared supercontinuum with average power of 5.1W and 22 W have been achieved,respectively(see Chapter Three).Compared with the approach of directly modulating laser diode for generating nanosecond seeded pulses,gain-switched laser-diode technology can generate even shorted pulses to obtain higher peak power pulses.In the second part of this dissertation,a thulium-doped fiber amplifier seeded with pulses from gain-switched laser diode is studied.An average power of 81.5 W and a peak power of 38.9 kW have been obtained(see Chapter Four).In addition,in the third part of this dissertation,self frequency-shift of femtosecond solitons to the long wavelengths has been observed.In the experiment,ultrafast solitons are generated from thulium-doped fiber laser first and then propagate through silica,tellurite and fluoride fibers respectively.The evolution of femtosecond solitons in these fibers has been investigated.Tunable Raman solitons from 2 ?m to 2.25 ?m with pulse duration from 460 fs to 166 fs are observed in the silica fiber.Additionally,longwave-shift of Raman solitons up to 2.4 ?m and 2.7 ?m has been seen in tellurite fiber and fluoride fiber,respectively.