Question

ai. Explain four properties that are common to all types of laser
ii. Explain the concept of stimulated emission.
iii. An alpha particle travels 0.003×10^-3m into a human body tissue . Calculate the average energy imparted into the tissue if the LET of the alpha particle in the tissue is 33keV

Answer 1

First Question:

Laser light has four unique properties that differentiate it from ordinary light: these are

• Coherence: The light generated by laser is highly coherent. Because of this coherence, a large amount of power can be concentrated in a narrow space.
• Directionality: In laser, all photons will travel in same direction. Therefore, laser emits light only in one direction. This is called directionality of laser light. The width of a laser beam is extremely narrow. Hence, a laser beam can travel to long distances without spreading.
• Monochromatic: In laser, all the emitted photons have the same energy, frequency, or wavelength. Hence, the light waves of laser have single wavelength or color. Therefore, laser light covers a very narrow range of frequencies or wavelengths.
• High intensity: In laser, the light spreads in small region of space and in a small wavelength range. Hence, laser light has greater intensity when compared to the ordinary light.

Second Question:

Stimulated emission occurs when an atom or molecule in an energy level above the ground state interacts with a photon that has energy equal to that between the atom or molecule's current energy level and a lower energy level.

So, stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron (or other excited molecular state), causing it to drop to a lower energy level. The liberated energy transfers to the electromagnetic field, creating a new photon with a phase, frequency, polarization, and direction of travel that are all identical to the photons of the incident wave. This is in contrast to spontaneous emission, which occurs at random intervals without regard to the ambient electromagnetic field.