Tight Focusing of Optical Beams ; A Review - Part 1 RAKESH

Complex amplitude and polarization distribution of an optical beam plays a dominant role in shaping the focused structure of the beam. It is therefore possible to engineer the focal spot using the pupil function manipulation. Helical phase structure arising due to phase singularity in the wave front plays an important role in shaping the focal spot. Tight focusing of an optical beam produces intensity distribution in the focal volume different from the well-known results based on scalar theory, and polarization distribution shows space variant characteristics. In the present paper, roles of the amplitude-, phase-, and polarization distribution on the tightly focused structure of the optical beams are reviewed. Impact of the helical phase structure in the pupil function engineering and subsequently on the focused structure is discussed with special reference to the authors' investigations at IIT Delhi. Certain applications in which tight focusing is desired are briefly discussed. Some miscellaneous investigations are also mentioned.