Book excerpt: This Book Analyses The Electromagnetic Nature Of Light, The Properties Of Light Waves, Such As Coherence, The Applications Of Interference To Length Metrology Of Optical Testing And The Role Of Diffraction In Image-Forming And Spectroscopic Instruments. It Also Discusses Topics Such As Interference, Diffraction And Holography On The Basis Of Scalar Theory, And The Basics Of Optical Data Processing. The Final Chapter On Metrology Deals With The Measurement Of Commonly Encountered Parameters With The Help Of Laser-Based Instruments.