Transverse mode instability (TMI) limits power scaling of fiber lasers. A semianalytical model is established to calculate the TMI threshold in high-power fiber laser systems of the multi-kW-class. A linear inner-cladding fiber can mitigate the TMI effect by smoothing the heat profile and decreasing the nonlinear coupling coefficient along the fiber. We investigate strong pump absorption of a linear inner-cladding fiber, which leads to shorter fiber length. Utilizing a 915-nm copumping scheme, the linear inner-cladding fiber can realize 10-kW output power in single-mode regime theoretically.
The coherent amplification network (CAN) aims at developing a laser system based on the coherent combination of multiple laser beams, which are produced through a network of high beam quality optical fiber amplifiers. The scalability of the CAN laser facilitates the development of many novel applications, such as fiber-based acceleration, orbital debris removal and inertial confinement fusion energy. According to the requirements of CAN and the front end of high-power laser facilities, a millijoule polarized fiber laser system was studied in this paper. Using polarization maintaining Ytterbium-fiber laser system as the seed, and 10-μm core Yb-doped fiber amplifier as the first power amplifier and 40-μm core polarizing (PZ) photonic crystal fiber (PCF) as the second power amplifier, the all-fiber laser system outputs 1.06-mJ energy at 10 ns and diffraction limited mode quality. Using 85-μm rod-type PCF as the third power amplifiers, 2.5-mJ energy at 10-ns pulse width was obtained with better than 500:1 peak-to-foot pulse shaping ability and fundamental mode beam quality. The energy fluctuation of the system is 1.3% rms with 1-mJ output in one hour. When using phase-modulated pulse as the seed, the frequency modulation to amplitude modulation (FM-to-AM) conversion ratio of the system is better than 5%. This fiber laser system has the advantages of high beam quality, high beam shaping ability, good stability, small volume and free of maintenance, which can be used in many applications.
We use a semi-analytical model considering pump power saturation in high power fiber laser systems of multi-kW-class to calculate mode instability threshold. A novel designed fiber, linear inner-cladding fiber, can mitigate mode instability effect by decreasing nonlinear coupling coefficient and smoothing heat profile along the fiber. We investigate strong pump absorption of linear inner-cladding fiber, leading to shorter fiber length. With 915 nm pumping, linear inner-cladding fiber can reach 10 kW output power without mode instability in theory.
A high average-power all-fiber supercontinuum laser source is constructed. By integrating series techniques together, the output average power achieves 65W with the spectrum range covering two octaves from 540nm to 2200nm. To our knowledge, there has been never reported similar supercontinuum source with such high average power, broadband spectrum and picosecond pulse width.
The singular point of the dissipative soliton mode-locked fiber laser is demonstrated experimentally. Mode-locked pulses are severely disturbed under certain pump power. The peak-valley (P-V) of the output power reaches up to 26.5% under the pump power of 918mW. However, mode-locked fiber laser can operate stably under higher or lower pump power. A numerical model based on nonlinear Schrödinger equation (NLSE) is established. And the singular point of the mode-locked state is theoretically proved.
In order to suppress the mode noise of large mode area fiber amplifier system and enhance the signal to noise ratio
of the output pulse, spatial and temporal self shaping for large mode area fiber laser system are studied in this paper. For
removing off the mode noise, method of beam's spacial self-shaping based on mode matching is used. By the method of
mode matching, the cladding mode are removed off clearly. Then a large mode fiber amplifier with a strictly single mode
is obtained. For enhancing the signal to noise ratio of the output pulse, method of beam's temoral self-shaping based on
Optical Kerr effct in fiber is used. By using Optical Kerr effect, the pulse get nonlinear polarization ratation, which make
pulses selfly shaped in time and the ASE pedestal is removed off clearly. As a result, by spatial and temporal self shaping,
cleared pulses with a strictly single mode in spatial and cleaned pulses without ASE pedestal are obtained.