In this paper, limitation factor of high power narrow linewidth fiber laser is analyzed. The influence of Stimulated Brillouin Scattering and its suppressing theory are discussed. Influences of frequency number and frequency spacing to Stimulated Brillouin Scattering are analyzed respectively by simulation. The results indicate that increasing frequency number and controlling frequency spacing can reduce the power spectrum density in fiber. Then the Stimulated Brillouin Scattering threshold is increased. Finally, the fiber laser output power is increased a lot.
The wavefront of the laser beam was tested by a point-diffraction interferometer with bidirectional phase-shifting. The phase-shifting is obtained by the bidirectional modulated of the electro-optic effect lithium niobate crystal combining with a pinhole filter in half-wave film. The wavefront aberration of incoming beam is directly measured by analyzing five frames phase-shifted interferograms captured by a CCD camera.
S-band fiber lasers, one type of ytterbium doped fiber lasers(YDFLs) which emitting in the spectral region of 1010 nm ~
1050 nm, have drawn more and more attention especially after the proposition of tandem pump fiber lasers. The S-band
laser plays an important role as the pump in a tandem pumping scheme. However, high power S-band laser output is
quite difficult because of severe re-absorption. Therefore, the optical properties of S-band fiber lasers are studied and
methods to achieve high power S-band laser output are presented. An S-band laser emission model based on gain
comparison is built for analyzing the mechanism of laser oscillation and amplification. The model is composed of rate
equations and gain comparison of several wavelengths in ASE spectrum. The gain differential between laser wavelength
and ASE peak wavelength is compared to the additional gain imposed by cavity mirrors in an oscillator or the seed in an
amplifier. The comparison results help in concluding the feasibility of S-band laser emission. Based on the model, the
influences of fiber properties (including core doping level, core -clad ratio, and fiber length), pump power and laser
power on the operation of S-band fiber lasers or amplifiers are researched. The analysis shows that fibers with lower
doping level, larger core-clad ratio and shorter length, seed with higher power, are more helpful in realizing high power
S-band laser output. Also, the profile of oscillator is found more suitable in building high power S-band lasers than that
A compact, high power and high beam quality laser diode stacks partially end-pumped
quasi-continuous wave slab laser with hybrid resonator is demonstrated. Using this
configuration, with Nd:YVO<sub>4</sub> as the slab gain media, 101 W output power is obtained
when the pumping power is 216.5W with the repetition of 1kHz, the optical-to-optical
efficiency and slope efficiency are 46.7% and 51.14%, respectively. The beam quality
M<sup>2 </sup>factors in the unstable direction and the stable direction are 1.36 and 1.56
respectively at the output power of 101 W.
This paper gives a novel All-Fiber laser Doppler Velocity Sensor(ALDVS) to measure the relative velocity to the lunar
or planetary bodies during the vehicle landing phase. In the beginning of the paper, A brief description of the principle of
laser Doppler velocity sensor is given. After that, the paper gives the laser Doppler velocity sensor configuration. The
paper introduce the helicopter flight test that was held in Zhengzhou. The altitude of flight is about 3km.The laser
Doppler velocity data is analysed. The GPS velocity data and laser Doppler velocity sensor velocity information are
compared. Finally, the equivalent distant in moon is calculated and the measurement error is discussed.
Coherent combination of multiple laser amplifier is an important technique for high power and high beam quality laser.
Laser amplifier uses master oscillator power amplifier (MOPA) configuration for narrow bandwidth and high beam
quality laser. Then active phase control is used to make multiple laser amplifier phase synchronization for coherent spot
in the far field. The center spot is N times brighter than the one of incoherent combination. At present, researchers have
used this method to achieve 1.56kW coherent combination of nine fiber lasers and 105kW of seven slab lasers.
The phase noise of the laser amplifier is an important factor affecting the coherent combination. There are two key
technologies in the coherent combination. The one is fill factor of multiple laser spatial distribution, which determines
main lobe energy of coherent spot. And the other is the phase noise of the laser amplifier, which decides stability of the
coherent combination. The phase noise of laser amplifier is caused by many factors, mainly thermal disturbance and
mechanical vibration. Due to the complexity of the phase noise generation, the research on phase noise is generally
concentrated in the qualitative analysis. The phase noise is generally considered the time phase noise. It is phase
dithering from variation refractive index by external disturbance. A variety of factors, such as temperature changes,
mechanical vibrations, the pump power, affect phase noise. We establish an externally imposed discrete disturbance
source on fiber laser amplifier and then analyze above-mentioned factors independently and quantitatively by the
method. The experiments demonstrate space phase noise, dithering of beam direction, is simultaneously induced by
either mechanical vibration or thermal disturbance. This experiment is significant for understanding mechanism of the
phase noise and suppression of phase noise.
Under the condition of high power diode side pumping, thermal effect in working medium is a serious problem. Not only total pump power, but also special pump structure, such as pump geometry structure, divergence of diode laser, distance from diode to working medium will affect the result of thermal effect. In this paper, by means of computer program, we found a series of thermal effect model, by simulating the temperature transformation process and stable-state temperature distribution. Based on this, we get the theoretical results of thermal lens focus length and thermal induced bi-refraction, and compare it with the experiment results.