We have proposed and demonstrated a nanosecond square-wave fiber laser working in the 1060nm band. The passively
mode-locked fiber laser based on the nonlinear optical loop mirror has a peak power clamping effect which leads to the
generation of nanosecond square-wave pulses. To investigate the spectrum width of the nanosecond square-wave pulse
laser, we added couplers with different coupling ratio to the bidirectional ring of the figure-8 fiber laser and analyzed the
laser output. The results show that a higher output coupling ratio leads to stronger peak power clamping effect, and the
peak power of the square-wave pulse gets lower and the corresponding spectrum band width is narrower.
We have demonstrated a passively mode-locked fiber laser with a composite cavity structure for repetition rate control.
An optical delay line is used to control the length so that the lengths of the main cavity and the sub-ring cavity are
accurately co-prime. Using this method we have obtained 46th harmonic pulses with a fundamental repetition of
17.39MHz. The fundamental mode-locking is substantially suppressed. The SNR of rf spectrum is higher than 45 dB.
Stable 800MHz repetition rate mode-locked pulses in duration of 14.27 ps are generated. The detuning phenomenon
appears when two cavity’s lengths are not matched. A larger pump power is required to maintain the oscillation.
A passively mode-locked ytterbium-doped all fiber laser has been demonstrated based on the nonlinear polarization
rotation technique in a all normal dispersion cavity. By optimizing the coupling ratio and position of the output coupler,
stable mode-locked pulses is generated with an average power of 200 mW at a repetition rate of 3.3 MHz, and
corresponding to single pulse energy of 60 nJ. The slope efficiency of power is as high as 68%.
Supercontinuum(SC) source has found numerous applications, such as DWDM,
frequency metrology, optical coherence tomography, and optical measurement. We
demonstrate an all-fiber supercontimuun source generated in highly nonlinear fiber (HNLF).
The HNLF is pumped by our mode-locked fiber laser with pulse width and peak power,
21.1ps and kW, respectively. An ultra-broadband supercontinuum extends from 1000 nm to
1750 nm is obtained, and the spectrum is flat with the amplitude variation less than 4dB
except around the fiber zero dispersion wavelength. The spectrum of our supercontinuum
source can extend beyond 1750 nm, but due to the limitation of the measured range of optical
spectrum analyzer (AQ6317B), the spectrum of the supercontinuum source beyond 1750 nm
is not yet obtained in our lab now. The spectral broadening mechanism of smoothed
supercontinnum is considered by the higher-order soliton fission and their blue-shifted
With uniform illumination, multi-step diffractive optical elements (DOE) are fabricated with ion beam multiple mask
etching technology. According to the technical process of ion beam multiple mask etching on DOE, a distribution of
surface error based on LKJ-150 ion beam etching machine is presented. Numerical analysis indicates that the surface
distribution of etching error results in lower performance of multi-step DOE, which consumedly reduces the uniformity
of target field with uniform illumination. After each etching process, the sample i.e, multi-step DOE fabricated by
LKJ-150 ion beam etching machine is measured. Through measurement data, we get the etching error. On the basis of
etching error, the mask can be made. Numerical analysis shows this method can reduce the impact of surface error on
the performance of DOE and increase the etching uniformity of. ion beam multiple mask
It is believed that combining the techniques of smoothing by spectral dispersion (SSD) in the time domain and diffractive optical elements (DOE) in the space domain can improve beam uniform illumination. Adding another SSD unit to the combined system in different grating direction can disturb the incidence wave front more confused, thus the number of speckle patterns in the target plane is increased. The intensity in the target plane becomes smoother after a period of accumulation. However, the wave front distortion is limited by the dimension number of grating directions and the intensity distribution in each direction. In this paper we introduce the air turbulence and study its influence on the wavefront. The disturbance on wave front acts as an infinite aggregate in the number of direction dimension and intensity dimension because of the property of turbulence. The numerical calculation indicates that introducing disturbance by air turbulence on amplitude and phase of the light beam that incident to DOE can smooth the distribution on target plane after a period of accumulation.
A design of multi-step diffractive optical element (MDOE) is developed for the high power laser output smoothing. A hybrid algorithm is presented which inserts a quasi-optimum process in every iterative loop. This method of MDOE design saves the computing time tremendously. The top profile error (TPE) is about 8.4%, which looks inferior to what we have gotten in the earlier years with using continues profile design, but very easy in manufacture to match the design data. Now this MDOE with 16 steps on the surface of K9 glass can be realized with four masks' etching facility. The maximum etching error of the depth is 10-80nm, which is receivable with tolerance analyze in our design. The MDOE has 70mm diameter, and uniform illumination area is an Φ600μm spot. With using expanding 1.064 μm beam, the smoothing pattern in focus plane is measured. The result shows that the TPE is about 19%. It is believable that with the influence by the interaction of second hot electron and time domain smoothing this result is acceptable.
Indirect-drive Inertial Confinement Fusion(ICF) system has two requests: first, it requires incident beam to focus on a small spot with very low circular side-lobe around the edge of the hole; second, when it continue to transmit onto the wall of cavity, it requires uniform illumination. A two-step iteration algorithm aiming at two positions of this system is proposed to match these two requests with using Pure Phase Plate (PPE). Our results show that the circular side-lobe near the target hole has been depressed to about 10<sup>-11</sup> W/cm<sup>2</sup>, and the beam has small top modulation on the target wall.