In this paper we study influences of Doppler broadening, spontaneously generated coherence, and other system parameters on propagation effect in a quasi lambda-type four-level atomic system. It is shown that when the ...In this paper we study influences of Doppler broadening, spontaneously generated coherence, and other system parameters on propagation effect in a quasi lambda-type four-level atomic system. It is shown that when the Doppler broadening is present, generally speaking, the values of gain and intensity of lasing without inversion （i.e. the probe field） in the co-propagating probe and driving fields case are much larger than those in the counter-propagating case; considerably larger gain and intensity of lasing without inversion than those without the Doppler broadening can be obtained by choosing appropriate values of the Doppler broadening width and spontaneously generated coherence strength. The gain and intensity of lasing without inversion increase with the increase of spontaneously generated coherence strength; when spontaneously generated coherence is present, much larger gain and intensity of lasing without inversion than those in the case without spontaneously generated coherence can be obtained. Choosing suitable values of the probe detuning, Rabi frequencies of the driving and pump fields at the entrance of the medium also can remarkably enhance the gain and intensity of lasing without inversion.展开更多
It is shown that in an open lambda type atomic system,the gain and dispersion of the probe field are quit sensitive to variation of spontaneously generally coherence （SGC）. The value of the parameter p reflects whet...It is shown that in an open lambda type atomic system,the gain and dispersion of the probe field are quit sensitive to variation of spontaneously generally coherence （SGC）. The value of the parameter p reflects whether SGC effect exists and the size of SGC effect. Under certain condition, when p = 0. 002, electromagnetically induced transparency occurs; when p≠0. 002, lasing without inversion can be realized;when p = 0.95, high index of the refraction with zero absorption can be obtained.展开更多
It is shown that,in an open ladder-type atomic system with spontaneously generated coherence (SGC),regardless of the existence of an incoherent pumping,a lasing without inversion (LWI) gain is always remarkable larger...It is shown that,in an open ladder-type atomic system with spontaneously generated coherence (SGC),regardless of the existence of an incoherent pumping,a lasing without inversion (LWI) gain is always remarkable larger than in the system without SGC,by adjusting the strength of SGC.Moreover,LWI gain in the system without incoherent pumping is much larger than that with incoherent pumping,within some strength of SGC; while in the corresponding closed system with SGC,we can’t obtain LWI gain at any strength of SGC,if no incoherent pumping is applied.展开更多
An important improvement on the streamline element method proposed recently by Luo-Tanner is put forward in this paper,making the method more suitable for handling differential-type constitutive equations and flow sin...An important improvement on the streamline element method proposed recently by Luo-Tanner is put forward in this paper,making the method more suitable for handling differential-type constitutive equations and flow sin- guiarities.Instead of integrating the constitutive equations along the streamlines forming element boundaries,one could integrate them along the streamlines passing through the Gauss points of the elements.By this way the diffi- culty of discontinuous velocity gradients on the element boundaries is circumvented and the stress singularity at the exit point is aUeviated.Moreover,the amount of computation is considerably reduced.It is found,by testing with the extrudate swell problem of the Maxwell fluid,that more strict enforcement of the incompressibility constraint by adopting a discontinuous-pressure scheme,discussed in the part I of this paper,allows one to obtain solutions of better quality and for higher Weissenberg numbers.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.10875072)
文摘In this paper we study influences of Doppler broadening, spontaneously generated coherence, and other system parameters on propagation effect in a quasi lambda-type four-level atomic system. It is shown that when the Doppler broadening is present, generally speaking, the values of gain and intensity of lasing without inversion （i.e. the probe field） in the co-propagating probe and driving fields case are much larger than those in the counter-propagating case; considerably larger gain and intensity of lasing without inversion than those without the Doppler broadening can be obtained by choosing appropriate values of the Doppler broadening width and spontaneously generated coherence strength. The gain and intensity of lasing without inversion increase with the increase of spontaneously generated coherence strength; when spontaneously generated coherence is present, much larger gain and intensity of lasing without inversion than those in the case without spontaneously generated coherence can be obtained. Choosing suitable values of the probe detuning, Rabi frequencies of the driving and pump fields at the entrance of the medium also can remarkably enhance the gain and intensity of lasing without inversion.
文摘It is shown that in an open lambda type atomic system,the gain and dispersion of the probe field are quit sensitive to variation of spontaneously generally coherence （SGC）. The value of the parameter p reflects whether SGC effect exists and the size of SGC effect. Under certain condition, when p = 0. 002, electromagnetically induced transparency occurs; when p≠0. 002, lasing without inversion can be realized;when p = 0.95, high index of the refraction with zero absorption can be obtained.
文摘It is shown that,in an open ladder-type atomic system with spontaneously generated coherence (SGC),regardless of the existence of an incoherent pumping,a lasing without inversion (LWI) gain is always remarkable larger than in the system without SGC,by adjusting the strength of SGC.Moreover,LWI gain in the system without incoherent pumping is much larger than that with incoherent pumping,within some strength of SGC; while in the corresponding closed system with SGC,we can’t obtain LWI gain at any strength of SGC,if no incoherent pumping is applied.
文摘An important improvement on the streamline element method proposed recently by Luo-Tanner is put forward in this paper,making the method more suitable for handling differential-type constitutive equations and flow sin- guiarities.Instead of integrating the constitutive equations along the streamlines forming element boundaries,one could integrate them along the streamlines passing through the Gauss points of the elements.By this way the diffi- culty of discontinuous velocity gradients on the element boundaries is circumvented and the stress singularity at the exit point is aUeviated.Moreover,the amount of computation is considerably reduced.It is found,by testing with the extrudate swell problem of the Maxwell fluid,that more strict enforcement of the incompressibility constraint by adopting a discontinuous-pressure scheme,discussed in the part I of this paper,allows one to obtain solutions of better quality and for higher Weissenberg numbers.
