So according to the measurements in this publication: http://arxiv.org/ftp/arxiv/papers/0811/0811.1210.pdf (fig.5), RI of graphite can be 2.7. Using this we can get PD of 532 nm to be 98.5 nm.
Please check these values are within your judgment.
@Abhay A Sagade: could you provide more detail about the equation you used to calculate P.D? I would like to estimate the P.D. of wavelengths 785 nm and 10.6 um into multiwalled carbon nanotubes film. Does your equation work in this case?