Explain any two industrial applications of lasers. Also explain how LIDAR works.

Answer: Laser cutting/drilling and laser welding use the very high, focusable power of lasers; LIDAR measures distance from the time of flight of laser pulses, \(d=ct/2\).

1. Laser cutting and drilling. A high-power laser (CO₂ at 10.6 μm or Nd:YAG/fibre laser at 1.06 μm) is focused by a lens to a spot of a fraction of a mm, giving intensities above \(10^{10}\) W/m². The material melts or vaporises along the path; a gas jet (O₂ or N₂) blows the molten material away. Advantages: no tool wear, very narrow kerf, small heat-affected zone, cutting of hard or brittle materials, tiny holes (e.g. in turbine blades, diamond dies, feeding-bottle nipples).

2. Laser welding. The focused beam melts the edges of two metal parts, which fuse on cooling. It is a non-contact process with a deep, narrow weld and little distortion, and can join dissimilar metals and reach inaccessible spots (car bodies, electronic parts, sealing of battery cases).

(Other applications: heat treatment and surface hardening, marking and engraving, measurement and alignment.)

LIDAR (Light Detection and Ranging):

• A pulsed laser sends short pulses (often near-infrared) towards the target.
• The reflected light is collected by a telescope and detected by a photodetector; a timer measures the round-trip time \(t\).
• Distance \(d=\dfrac{ct}{2}\). A rotating mirror or scanner sweeps the beam, giving millions of points per second, which form a 3-D "point cloud" of the surroundings.
• Uses: self-driving cars and robots, terrain and forest mapping from aircraft, measuring atmospheric pollutants and clouds, speed guns.