Surface plasmon, although predicted long time ago, have recently been the subject of renewed interest as many applications are foreseen in nano or micro optics, solar cells or metamaterials . The localized plasmon resonance in metalic nano particles (MNP) can cause near field enhancement and enhanced scattering cross section and both of them can be used to enhance the absorption in solar cell. It is also reported that the surface plasmon resonance frequency of the nano metallic layer depends on the shape, size, types of metal and the surrounding medium Though most of the surface plasmon experiments dealt with MNP for devices in visible spectral region, very few papers have reported the results from infrared (IR) regions . However, many defense application including infrared counter measure and sensor applications require device operation in mid to far infrared regions. We report here the infrared absorption by gold nano plasmon structure of various geometries. Grating mask of different square sizes of 1.25, 2.5 and 3 micron square is used to generate Gold (Au) nano plasmon layer. We have performed experiment with different Au metal layer thickness ranging from 10-100 nm. The same grating mask is used to generate crescent structure with 3 micron long and 0.4 micron width. Crescent structure is fabricated by e-beam evaporation of Au nano metal layer at different angles. We used Fourier transform infrared (FTIR) spectrometer to obtain the absorption spectra. We observed tunable absorption in the infrared range of 2.5-20 micron by gold nano-plasmon metal layer. The absorption peak corresponding to 1.25, 2.5 and 3 micron square Au metal layer are 4.9, 14 and 17.1 micron respectively. We did not observe appreciable shifts in peak absorption wavelength due to different Au metal layer thickness even though we varied the metal layer thickness from 10-100 nm. For crescent structure, we observed a polarization dependence of absorption. For example for 3 micron long and 0.4 micron width crescent structure, transverse electric (TE) absorption peak occurs at 14.2 micron whereas transverse magnetic (TM) absorption occurs at 4.0 micron. The absorption characteristics of our periodic crescent structures are higher than the previously reported results  from randomly generated crescent structures by using polysterene nanoparticles. Our tunable absorption characteristics show that proposed nano plasmon structures can be used to enhance the performance of either IR detectors or emitters.