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A near-infrared laser generates gain on transitions between the $text{B}^{text{2}} Sigma_{text{u}}^{text{+}}$ and $text{X}^{text{2}} Sigma_{text{g}}^{text{+}}$ states of the nitrogen molecular cation in part by coupling the $text{X}^{text{2}} Sigma_{text{g}}^{text{+}}$ and $text{A}^{text{2}} Pi_{text{u}}$ states in the V-system. Traditional time resolved pump-probe measurements rely on post-ionization coupling by the pump pulse to initialize dynamics in the $text{A}^{text{2}} Pi_{text{u}}$ state. Here we show that a weak second excitation pulse reduces ambiguity because it acts only on the ion independent of ionization. The additional control pulse can increase gain by moving population to the $text{A}^{text{2}} Pi_{text{u}}$ state, which modifies the lasing emission in two distinct ways. The presence of fast decoherence on $text{X}^{text{2}} Sigma_{text{g}}^{text{+}}$ to $text{A}^{text{2}} Pi_{text{u}}$ transitions may prevent the formation of a coherent rotational wave packet in the ground state in our experiment, but the control pulse can reverse impulsive alignment by the pump pulse to remove rotational wave packets in the $text{B}^{text{2}} Sigma_{text{u}}^{text{+}}$ state.
We simulate the pump-probe experiments of lasing in molecular nitrogen ions with particular interest on the effects of rotational wave-packet dynamics. Our computations demonstrate that the coherent preparation of rotational wave packets in N$_2^+$ b
A comb spectrum generating device based on Bragg grating superstructures with gain and loss is suggested in this paper. It includes a comprehensive analysis of the device formulation, generation and manipulation of the comb spectrum with a number of
Propagation of light in a highly scattering medium is among the most fascinating optical effect that everyone experiences on an everyday basis and possesses a number of fundamental problems which have yet to be solved. Conventional wisdom suggests th
We investigated experimentally the ray-wave correspondence in organic microlasers of various triangular shapes. Triangular billiards are of interest since they are the simplest cases of polygonal billiards and the existence and properties of periodic
Controlling and reversing the effects of loss are major challenges in optical systems. For lasers losses need to be overcome by a sufficient amount of gain to reach the lasing threshold. We show how to turn losses into gain by steering the parameters