在双水电极介质阻挡放电装置中，在氩气和空气的混合气体放电过程中通过改变气体压强可以得到一种新型等离子体光子晶体。该光子晶体具有四边形的复杂对称结构，包括晶胞中心处的细等离子体柱、四周的等离子体片、等离子体片交叉点产生的等离子体柱和边缘处的粗等离子柱。运用发射光谱法研究了该等离子体光子晶体不同位置处的等离子体状态，通过测量氩原子696.54 nm(2P2→1S5)发射谱线的展宽对比了电子密度，通过氮分子第二正带系(C3Πu→B3Πg)发射谱线计算了分子振动温度。实验结果证实，不但晶胞中心处的细等离子体柱、四周的等离子体片、等离子体片交叉点产生的等离子体柱和边缘处的粗等离子柱具有不同的等离子体状态，不同位置处的晶胞中心细等离子体柱也具有不同的等离子体状态。电子密度由大到小排列依次为：4个角上的细等离子体柱(A)、靠近4个边的细等离子体柱(B)、靠近中心的细等离子体柱(C)、边缘处的粗等离子体柱(D)、等离子体片交叉点产生的等离子体柱(E)、四周的等离子体片(F)。分子振动温度的变化规律与电子密度相反。由于该晶体结构中A、B、C 3处的折射率均不相同，由内向外呈周期性渐变排列，它们和其他位置处不同的等离子体状态构成了具有渐变折射率的等离子体光子晶体。

A novel plasma photonic crystal (PPC) was obtained by varying gas pressure in Ar/air dielectric barrier discharge using two planar water electrodes. The PPC had complex square symmetrical structure, including thin plasma columns in the center of each sublattice, plasma slices around the sublattice, plasma columns at the intersection of plasma slices, and thick plasma columns on the edge. By using the optical emission spectrum method, the plasma parameters in different positions of the PPC were studied. The electron densities were compared by measuring the broadenings of Ar Ⅰ (2P2→1S5) spectrum line, and the molecular vibration temperatures were calculated by the spectrum line of nitrogen band of second positive system (C3Πu→B3Πg), respectively. It is proved that not only the thin plasma columns in the center of each sublattice, plasma slices around the sublattice, plasma columns at the intersection of plasma slices, and thick plasma columns on the edge have different plasma parameters, but also the thin plasma columns at different locations in the center of each sublattice are not the same. The descending order of the electron density is that: thin plasma columns at the four corners (A), thin plasma columns near the four sides (B), thin plasma columns near the center (C), thick plasma columns on the edge (D), plasma columns at the intersection of plasma slices (E), and plasma slices around the sublattice (F). The change rule of the molecular vibration temperature is opposite to that of the electron density. As the refractive indexes in A, B, C are all different, and show inside-out gradual change periodically, the graded-index PPC is obtained by the different plasma parameters in different locations.