Our objective has been to examine the shortening of the coherence length by collision processes in discharge plasmas, and to develop instrumentation and a procedure for applying the methodology of coherence to plasmas diagnosis. The instrumentation for coherence length spectroscopy consists of a modified-Mach-Zehnder interferometer, a spectrometer, and a CCD camera. The interferometer has been constructed with capabilities for determination of the autocorrelation of plasma emission intensity from a point and the cross correlation from two different points within plasma. A discharge cell, consisting of an anode disc with a pinhole and a rod-shaped cathode with a rounded end, has been designed as a plasma source and constructed in such a way that the excitation in plasma is temporally and spatially localized. A characterization of produced discharge plasmas has been carried out by first directly measuring the ablation loss of the cathode rod and the energy input into plasma. A full Saha calculation is then carried out for a mixture of argon and iron. For the experiment, the plasma temperature is found to be 1.41 eV in 140 torr argon and 1.58 eV in 50 torr argon. Both the time-integrated and time-resolved interference fringes due to atomic argonemissions from the transition between 3 s 2 3 p 5 ( 2 P° 3/2 )4 p state and 3 s 2 3 p 5 ( 2 P° 3/2 )7 d state have been captured. The coherence length was found to be 4200 ± 800 nm at 50 torr where the collision frequency is 2.14×10 11 s -1 , and 2400±130 nm at 140 torr where the collision frequency is 8.13×10 11 s -1 . We also observed that the coherence length of plasma emission decreases as a function of time due to cumulative collisions atoms have suffered. We have discovered that the coherence length of discharge plasma emissions varies with direction of the plasma emission. The anisotropic distribution results from the non-uniform structure in the discharge current, and this is further investigated by intentionally implementing an indentation on one side of the cathode inside the discharge cell. A photographic examination of both the cathode and the anode disc shows a distinctive wear pattern that is anisotropic, suggesting a non-axis-symmetric structure of the plasma. This is consistent with the angular dependence of the coherence length.