**4. Plasma crystal as photonic crystal**

So far we have studied about PCs and plasma photonic crysals. It is quite interesting to describe the plasma crystal as photonic crystal due to its applications over the PCs and PPCs. Infact coulomb lattices of charged dust grains are called plasma crystals, which can be generated in laboratory in dusty plasma experiments (Morfill et al, 1997). Plasma crystals are composed dust grains that become electrically charged to very high charge states while thermal kinetic energy of the grains remains low. In plasma crystal composed of negatively charged dust grains, the dust grain radius is typically in the order of a few micrometers, while the average intergrain distance is on the order of a few hundreds micrometers, with variations in different experiments ( Morfill et al, 2002). Therefore plasma crystals generated in the laboratory generally have only a few layers in the vertical dimension owing to gravitational compression, although recently a three-dimensional structure has been demonstrated ( Zuzic et al, 2000). However, plasma crystal has some similarities to colloidal crystal, which are colloidal suspensions of ordered charged particles in solvents. Due to Bragg scattering properties, colloidal crystals have applications as narrow band rejection filters in optics. Tunable colloidal crystal in the optical, ultraviolet and infrared have also been demonstrated in which the particle size or spacing charge with temperature to tune the diffraction ( Weissman et al, 1996). Recently, a magnetically tunable optical filter comprising a ferro-fluid based emulsion cell has been discussed (Philips et al, 2003). Viewing above it can be noticed that if dust plasma crystal can be generated in sufficient large multilayer closer-packed configuration, they may have similar use as filters in the longer wavelength terahertz (THz) regime. A possible experimental prototype of magnetically controlled and tuned plasma crystal in dusty plasma is shown in Fig. 2. With the help of above study, THz refraction or scattering can be studied.

For generation of microwaves, signal generator of 33-50 GHz and 50 – 75 GHz are used.

Several experimental studied have been conducted with the help of given experimental setup and parameters. Important results which emerged from the studied are listed below,

Lattice structure of micro-plasma arrays behaves as a photonic crystal similar to solid

 A millimeter wave at 33-110 GHz was injected into two-dimensional plasma column array, and the transmitting signal through such array attenuated less than 20%. Band gap forms by periodic dielectric constant above the electron plasma frequency *pe* and propagation of flat bands below the plasma frequency *pe* . Hence

 Band gap frequency could be varied by changing the lattice constant, leading to a function of dynamic and time-controllable band-stop filter in millimeter and sub

 30 rows of plasma columns are similar in the case of 17 rows of metal due to a lower ratio of dielectric constant between plasma and vacuum region, plasma photonic

So far we have studied about PCs and plasma photonic crysals. It is quite interesting to describe the plasma crystal as photonic crystal due to its applications over the PCs and PPCs. Infact coulomb lattices of charged dust grains are called plasma crystals, which can be generated in laboratory in dusty plasma experiments (Morfill et al, 1997). Plasma crystals are composed dust grains that become electrically charged to very high charge states while thermal kinetic energy of the grains remains low. In plasma crystal composed of negatively charged dust grains, the dust grain radius is typically in the order of a few micrometers, while the average intergrain distance is on the order of a few hundreds micrometers, with variations in different experiments ( Morfill et al, 2002). Therefore plasma crystals generated in the laboratory generally have only a few layers in the vertical dimension owing to gravitational compression, although recently a three-dimensional structure has been demonstrated ( Zuzic et al, 2000). However, plasma crystal has some similarities to colloidal crystal, which are colloidal suspensions of ordered charged particles in solvents. Due to Bragg scattering properties, colloidal crystals have applications as narrow band rejection filters in optics. Tunable colloidal crystal in the optical, ultraviolet and infrared have also been demonstrated in which the particle size or spacing charge with temperature to tune the diffraction ( Weissman et al, 1996). Recently, a magnetically tunable optical filter comprising a ferro-fluid based emulsion cell has been discussed (Philips et al, 2003). Viewing above it can be noticed that if dust plasma crystal can be generated in sufficient large multilayer closer-packed configuration, they may have similar use as filters in the longer wavelength terahertz (THz) regime. A possible experimental prototype of magnetically controlled and tuned plasma crystal in dusty plasma is shown in Fig. 2. With the help of above study, THz

Pyramidal horn antennas are used for transmitting and receiving microwaves.

structure of photonic crystal play role rather then cut-off conditions.

crystals require more rows than case of an ordinary photonic crystal.

 Lattice constant = 2.1 mm to 2.5 mm. Squire hole with opening 1.4 mm x 1.4 mm.

He, N2, and Ne gas is used.

dielectrics.

terahertz regions.

**4. Plasma crystal as photonic crystal** 

refraction or scattering can be studied.

Fig. 2. A prototype to present EM wave transition from plasma crystal
