In order to instructing the practice experiment better, it is necessary to predict the inhibiting ability of amplified spontaneous emission(ASE) for ytterbium doped double-clad fiber amplifiers with different central wavelengths. Using the rate equation theory, the evolution of the ASE from different seed wavelength with the same parameters were studied. For the forward pump configuration, the simulation results show that the weak initial ASE component of seed source will generate large increase after high power amplification. When the seed oscillator ASE suppression ratio fixed at 80dB and the central wavelength is in the range of 1050nm-1100nm, the ASE suppression ratios of the amplifier output spectrum increase firstly and then decrease, and the optimized seed wavelength is 1080nm. The higher seed’s ASE suppression ratio, the better ASE inhibition of the amplifier output laser. In order to control ASE suppression ratio above 30 dB in the output spectrum, the ASE suppression ratio of 1075nm,1080nm and 1085nm seed spectrum must be higher than 70.5 dB, 71.4 dB and 79.3 dB respectively.
Owing to the requirement of high resolution of imaging system, such as the infrared imaging system, the imaging laser radar, the compressive sensing is used in the imaging system with low resolution sensors to obtain high quality image information. In this paper, compressive sensing is applied in an imaging system. A random phase mask is placed on the lens of the optical system. The optical wave propagation process of light field from the object plane to the lens, then to the image plane is analyzed and theoretical formula of the propagation with the form of the Fourier transform expression is deduced, thus the reconstruction speed is high by using the fast Fourier transform. The orthogonal wavelet transform and the orthogonal matching pursuit algorithm are employed in the reconstruction. The simulation results prove the good performance of the reconstruction quality and speed.
Diffractive optical elements (DOEs) can realize beam shaping with higher light efficiency, strong flexibility of diffraction pattern, and is suitable to be used in optical interconnections to split beams. In order to increase the intensity uniformity of the split beams, a hybrid algorithm merging Gerchberg-Saxton (GS) algorithm with gradient method is presented based on the sampling rule different from the existing optimization algorithms. By controlling N extra points with zero amplitude besides the original N sampling points on the input plane, and finally the sampling pitch on the Fourier plane is half of that of the conventional sampling rule. Then the N extra points on the Fourier plane will be controlled. Finally spot array with high intensity uniformity can be realized with the proposed algorithm. Simulation results demonstrate the good performance of the proposed algorithm.
With the development of infrared focal plane array (IRFPA) technology, the high performance staring infrared imaging system has fully substituted the scanning type, and become the third generation thermal imaging system. Meanwhile the performance evaluation model associated with the device level also should be updated accordingly. This paper compares the traditional distance evaluation model with the latest model that is based on Target Task Performance (TTP) metric, and analyzes the problems and deficiencies when we evaluate a staring imaging system using the traditional model. Taking a certain type of infrared imaging equipment for example, we simulate its performances by using the two models respectively, and analyze the simulation results. Finally we verified the simulation results through field experiments, the results show that the value predicted by the model basing on the rule of TTP is closer to the measured value. This paper suggests that the TTP model is more accurate than traditional model in the design, optimization and evaluation of the high performance staring infrared imaging system.
Based upon the scalar wave equation and the equations of hydrodynamics, the simulation model used to
calculate the transient thermal blooming of collimated multi-pulse laser by four-dimensional code. Considering the
variety of absorption coefficient along with different altitudes, this paper got the new model of repetitively pulsed
laser with thermal blooming in tropic by interpolation .On this basis, thermal blooming of different waveforms,
such as triangle, gauss, and rectangle were calculated. The paper analyzes the thermal blooming of three waveform
laser beams by changing respectively the value of the transmission power. After propagating the same distance in
the same condition, the result shows that the peak irradiance of triangular laser distorts least severely; the PIB of
gauss laser is the biggest, that is to say, the focusing ability of gauss laser is the best; the center of rectangle laser
moves the furthest.
This paper analyzes the effects of thermal blooming on the Far-Field Irradiance Distribution, based upon the
steady-state thermal blooming model, which is introduced by Wallace. It uses the method of numerical simulation and
gives the relativity between thermal blooming and these parameters, including initial power,the radius and wavelength. The result reveals that a new void dimensional parameter can describe the extent of thermal blooming. When this dimensional parameter decreases, thermal blooming effect becomes more serious. The result can provide theoretic
analysis of thermal blooming effect on the Far-Field. In addition, when the wavelength or the radius changes, the result of Wallace model does not accord with the fact. The contradiction reveals the shortcoming of this model.
This paper describes the contents of a general "four-dimensional" computer code for the transient thermal blooming of multi-pulse laser beam propagation. The solutions of the scalar wave equation in Fresnel approximation and the hydrodynamic equations are obtained by means of the discrete Fourier transform method. Based upon the scalar wave equation and the equations of hydrodynamics, the paper makes a model for collimated multi-pulse laser, simulates the
transient thermal blooming numerically, and gives the laser beams irradiance distribution by changing respectively the
value of the propagation distance, the pulse-repetition rate, the power, and the time. Besides, we simulate the
thermal blooming of cw in order to make a contrast with multi-pulse laser. The results show multi-pulse lasers minimize
thermal-blooming; if the pulse-repetition rate decreases, thermal blooming decrease, and the quality of the beam is better.