自发产生相干对Y型四能级原子系统探测吸收的影响

Effects of Spontaneously Generated Coherence on Absorption in Probe Laser in Four-level Y-type Atomic System

在与三个场相互作用的Y型四能级原子系统中,利用密度矩阵方程计算了介质对探测场的吸收,分析了自发产生相干对探测吸收的影响。结果发现:随着自发产生相干的影响,在共振中心处,探测吸收表现出不同的现象。当自发产生相干对探测吸收产生相消干涉时,随着自发产生相干的增强,在共振中心处削弱吸收,出现增益。当自发产生相干对探测吸收产生相长干涉时,随着自发产生相干的增强,在共振中心处出现吸收增强,也即出现电磁诱导吸收(electromagnetically induced absorption,简称EIA),在共振两侧的双电磁感应透明强度(electromagnetically induced transparency,简称EIT)增强,窗口变宽。同时,在能级|3〉→|2〉与|4〉→|2〉的自发衰减速率比值不变下,当能级|3〉→|2〉与|4〉→|2〉的自发衰减速率减小时,在共振中心处,吸收线宽变窄,共振两侧的透明窗口变宽。

This paper investigates the effects of absorption in the Y-type four-level atomic system spontaneously generated coherence （SGC） on the probe driven by three fields. It finds that the probe absorption at the resonance center shows the different phenomena with the SGC effects. When SGC produces the destructive interference on the probe absorption, the absorption at the resonance center is reduced with the SGC enhancement and the gain appears there. When SGC produces the constructive interference on the probe absorption, the absorption at the resonance center is enhanced with the SGC enhancement. That is electromagnetically induced absorption （being abbreviated EIA） ; the intensity of double electromagnetically induced transparency （being abbreviated EIT） ; at both sides of the resonance is increased, and the windows get wider. At the same time, the linewidth of the absorption at the resonance center becomes narrow and the transparent windows at both sides of the resonance get wider when the spontaneous decay rate of energy levels ｜3 〉→2 ） and 4 〉→｜2 ） is decreased at the ratio of the spontaneous decay rate of energy levels ｜3 〉→ 2） and ｜ 4〉→ 2） being constant.