List and briefly explain any two industrial applications of laser.

Lasers produce a highly directional, monochromatic, coherent and very intense beam that can be focused to a tiny spot (about µm) with power densities up to \(10^{12}\) W/cm². This makes them useful in industry.

Industrial applications:

1. Laser cutting: A focused CO₂ or Nd:YAG (or fibre) laser beam melts or vaporises the material along a programmed path, and a coaxial gas jet (O₂ or N₂) blows the molten material away. It cuts metals, ceramics, cloth and plastics with a narrow kerf, no tool wear, little distortion and CNC control.
2. Laser welding: The laser locally melts the edges of two pieces, which fuse as they cool. The heat-affected zone is very small, it is contactless, it can weld dissimilar metals and hard-to-reach joints, and it is used in automotive, electronics and microcircuit work.
3. Laser drilling: Short, intense pulses (Nd:YAG/ruby) vaporise material to make very fine, precise holes, for example in diamonds, turbine blades, injection nozzles and watch jewels.
4. Heat treatment and marking: Surface hardening by rapid heating and cooling, and permanent marking or engraving of serial numbers and barcodes.

(Any two, explained, earn full marks.)