A helium-neon laser (?? = 633 nm), shown in Figure P17.71, is built with a glass tube of...

A helium-neon laser (?? = 633 nm), shown in Figure P17.71, is built with a glass tube of inside diameter 1.0 mm. One mirror is partially transmitting to allow the laser beam out. An electrical discharge in the tube causes it to glow like a neon light. From an optical perspective, the laser beam is a light wave that diffracts out through a 1.0-mm-diameter circular opening.

a. Explain why a laser beam can’t be perfectly parallel, with no spreading.

b. The angle to the first minimum is called the divergence angle of a laser beam. What is the divergence angle of this laser beam?

c. What is the diameter (in mm) of the laser beam after it travels 3.0 m?

d. What is the diameter of the laser beam after it travels 1.0 km?