The peak power of pump pulse is a key factor in the generation of supercontinuum source. Observably, as the peak power of the pump pulse increases, the spectral range of the supercontinuum becomes wider. In order to study the blue shift limit of PCF fiber at different peak powers, in our experiment, the change in peak power is achieved by introducing a different length of chirped fiber after the oscillator to vary the pulse width. The pump source is a self-made laser with pulse duration, operating wavelength and repetition rate of 12 ps, 1064 nm and 68 MHz, respectively, which are injected into the photonic crystal fiber after three stages of amplification. Finally, a supercontinuum with an average power of 358 W in the spectral range of 466 nm to 2400 nm was achieved. Experiments have shown that the introduction of large positive chirp has a significant effect on the supercontinuum of the 10 W class, but for a supercontinuum with a sufficiently high average power (over 100 W level supercontinuum spectrum). after the peak power threshold is exceeded, further blue shift of the spectrum cannot be achieved by increasing the peak power, but the high peak power helps to improve the spectral flatness of the supercontinuum. The four-wave mixing, dispersive wave generation, radiation trapping with the soliton play much important role in the blue-shift of SC spectrum, but the short-wave edge is limited by the group velocity matching condition, which is determined by the dispersion characteristics of the PCF, not only peak power of the pump pulse. In order to further extend the short-wave spectrum, other methods are required, for example, changing the structural characteristic of the PCF, etc.
Thulium-doped fiber laser is one of the most promising high power mid-infrared sources which attracts lots of attention recently. However, there is no comprehensive theoretical model which can be used for precise simulation of the performance of the pulsed Thulium-doped fiber laser. A combined theoretical model is proposed in this work by integrating the laser rate equation and Ginzburg-Landau equation into the iteration process. Good agreement between the experiments and simulations is achieved in a Thulium-doped fiber amplifier employing counter-pumping scheme.
Transverse mode instability becomes the main limit for power scaling of high power fiber lasers with nearly diffraction-limited beam. Compared to conventional step index fiber, this paper proposes a partially doped fiber, which can decrease coupling coefficient between fundamental mode and higher order mode. Based on a coupled mode model, this designed fiber is proved to suppress transverse mode instability effect and promising for power scaling of fiber lasers. Furthermore, we investigate the impact of doped region on transverse mode instability threshold, and propose a partially doped fiber, which can realize 5 kW in single mode regime theoretically.
A high power 1030 nm ytterbium-doped polarization maintained fiber laser with optimized parameters is presented in this paper. The master oscillator power amplifier system with counter-pumped amplifier is established. The output power is 900 W, along with a light-to-light efficiency of 64.2%. The amplified spontaneous emission suppression ratio of spectrum reaches to 40 dB with 3 dB linewidth of 0.14 nm. The polarization extinction ratio is 12 dB, and the beam quality factor is M<sup>2</sup><sub>x</sub>=1.07, M<sup>2</sup><sub>y</sub>=1.12. To the best of our knowledge, this is the first demonstration of 1030 nm high power fiber laser with narrow linewidth, near linear polarization, and neardiffraction-limited beam quality
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.
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.
The Integration Test Bed (ITB) is a large-aperture single-beam Nd:glass laser system, built to demonstrate the
key technology and performance of the laser drivers. It uses two multipass slab amplifiers. There are four
passes through the main amplifier and three passes through the booster amplifier. The output beam size is
360mm by 360mm, at the level of 1% of the top fluence. The designed output energy of ITB at 1053nm is
15kJ in a 5ns flat-in-time (FIT) pulse, the third harmonic conversion efficiency is higher than 70%. The first
phase of the ITB has been completed in July 2013. A series of experiments demonstrated that laser
performance meets or exceeds original design requirements. It has achieved maximum energies at 1053nm of
19.6kJ at 5ns and 21.5kJ at 10ns. Based on a pair of split third harmonic generation KDP crystals, the third
harmonic conversion efficiency of about 70% and 3ω mean fluences as high as 8.4 J/cm<sup>2</sup> have been obtained
with 5ns FIT pulse.
With the methods of time-division multiplexing in Frontend and angle detuning in FOA, each beam pulse on SG-III
prototype facility is controlled independently and so the systematic variations of power imbalance are eliminated
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.
The optical pulse generation system of SG-III laser facility is presented. The optical time division
multiplexing (OTDM) technique, high speed electro-optic modulation technique, pulse
single-selected based on polarization independently acousto-optic modulation technique and pulse
polarization stabilization technique applied in low repetition rate mode are successfully employed in
the system. And also the phase modulation unit is at the last stage of the system, which could avoid
FM-AM effect induced in fiber system. The test experiment results showed that the demonstrated
specification is better than the designed to a certain degree.
The laser pulse shape should be varied to meet different requirements of the inertial confinement experiments. Chirped pulse-stacking is an effective method to obtain a long pulse with desired pulse shape using short pulses. We introduce a method to obtain a long pulse shaped by chirped pulse stacking in fiber time-delay lines. We demonstrate an all fiber pulse shape generator that can generate arbitrary pulse shapes by stacking a set of 20-ps pulses output from fiber mode-locking laser. The device offers a 2.2ns arbitrary waveform optical pulse with power up to 30dBm, bandwidth of 0.2nm and a rise time less than 50ps. The output optical pulse has a temporal adjustment precision of 32bit and an amplitude adjustment precision of 10bit. Experimental and theoretical results show that the generator provided the required stability, flexibility, fast rise time and high contrast pulse for laser fusion research.
Ytterbium-doped silica fibers exhibit very broad absorption and emission bands, from 800nm to 1064nm for absorption and 970nm to 1200nm for emission. Therefore wide band lasers can be obtained using a wide variety of pump lasers. In this paper, the characteristics of high-doped Yb<sup>3+</sup> fiber are analyzed and verified by experiment and a highly-doped Yb<sup>3+</sup> fiber ring laser with short cavity has been presented. Comparing with normal Yb<sup>3+</sup>doped fiber, the relationship between the important characteristics of the Yb<sup>3+</sup>doped fiber laser such as threshold power, output power and laser parameters such as pump power, fiber length, output couple ratio is analyzed. Numerical results are coincident with the experiment phenomenon very well. A 1053 nm pulse has been achieved in our fiber laser. The output power is 6mW as pump power is 110mW and the slope efficiency is 17%. The Yb<sup>3+</sup> fiber laser we produced can be used as a stable source in obtaining ultrafast pulse, fiber sense and optical communications.
Theory and experimental results on the self-starting passive mode-locked Yb fiber ring laser generating short pulse are reported. The relations between the laser cavity parameters and mode-locked pulse characters are discussed. 980nm LD pumped laser is used as the pump source and high concentration Yb<sup>3+</sup>-doped fiber is adopted as gain medium. Using the nonlinear polarization rotation (NPR) effect of the fiber, self-starting stable mode-locked pulse is obtained, with center wavelength of 1046nm, 3dB bandwidth of 6.01nm and 20dB bandwidth of 16nm. The mode-locked threshold power is 150mW and output power is 26mW with 50MHz repetition rate.