Mixed pixels are inevitable due to low-spatial resolutions of hyperspectral image (HSI). Linear spectrum mixture
model (LSMM) is a classical mathematical model to relate the spectrum of mixing substance to corresponding
individual components. The solving of LSMM, namely unmixing, is essentially a linear optimization problem
with constraints, which is usually consisting of iterations implemented on decent direction and stopping criterion
to terminate algorithms. Such criterion must be properly set in order to balance the accuracy and speed of
solution. However, the criterion in existing algorithm is too strict, which maybe lead to convergence rate
reducing. In this paper, by broaden constraints in unmixing, a new stopping rule is proposed, which can reduce
rate of convergence. The experiments results prove both in runtime and iteration numbers that our method can
accelerate convergence processing with only cost of little quality decrease in resulting.
Stimulated Brillouin Scattering (SBS) is an important means to achieve optical phase conjugation beam, which has the characteristics of self-pumping, producing phase conjugation wave and compensating wave-front aberration. Using SBS in glass fibers as phase conjugator, the field of application of SBS phase conjugation can be expanded, for fibers can offer low power threshold and stable behavior even at high peak and average input power. In this article, phase conjugation based on SBS in undoped multimode quartz fibers was observed. With the 13-15ns pump beam at 1.06 µ m wavelength from a Q-switched Nd:YAG laser, the reflectivity of SBS for the fibers with core diameter of 100 µ m and 62.5 µ m and different length was characterized at different input energy and lens focal length, considering of the reflection loss at the fiber surface. The reflectivity during the SBS process, affected greatly by system parameters, was measured no more than 70% due to saturation. The waveform of SBS was recorded and investigated. With the change of the waveform at the fiber length changing from 1.6m to 0.6m, the pulse duration of SBS decreased from 5ns to 2ns. The multi-peak modulation did not occur, which indicated that SBS had taken place in stable condition. Based on these experiments, some references to control SBS waveform were put forward.