Question

list and discuss three properties unique to laser light. please help asap thank you

Answer 1

The LASER light has the following unique characteristics over the ordinary light sources. They are: i) monochromaticity, ii) directionality and iii) coherence.

i) Monochromaticity:

This property of LASER is due to the following two factors. First, only an electromagnetic wave of frequency n ₀ = (E₂-E₁)/h [ where E₂ and E₁ are the energy of two different states] can be amplified, n ₀ has a certain range which is called linewidth, this linewidth is decided by both the homogeneous broadening factors and inhomogeneous broadening factors, the resultant linewidth is very very small compared with normal lights. Second, the laser cavity forms a resonant system. Any oscillation can occur only at the resonance frequencies of this cavity. This helps the laser light to further narrowing its linewidth, the narrowing can be as large as 10 orders of magnitude. So, laser light is usually very pure in wavelength. This is widely known as the property of monochromaticity.

ii) Directionality:

In conventional light sources (for example sodium lamp and torchlight), photons will travel in a random direction. Therefore, these light sources emit light in all possible directions. On the other side, in LASER, all photons will travel in the same direction. Therefore, the laser emits light only in one specific direction. This is called the directionality of laser light. The width of a laser beam is extremely narrow. Hence, a laser beam can travel to long distances without spreading.

If an ordinary light travels a distance of 2 km, it spreads to about 2 km in diameter. On the other hand, if a laser light travels a distance of 2 km, it spreads to a diameter of less than 2 cm. Please see the figure below.

iii) Coherence:

We know that ordinary light is not coherent because it comes from independent atoms. It is emitted when excited electrons (electrons in higher energy levels) jumped into the lower energy level (ground state). The process of electrons moving from higher energy level to lower energy level or lower energy level to higher energy level is called electron transition.

In ordinary light sources, the electron transition occurs naturally. In other words, electron transition in ordinary light sources is random in time. The photons emitted from ordinary light sources have different energies, frequencies, wavelengths, or colors. Hence, the light waves of ordinary light sources have many wavelengths. Therefore, photons emitted by an ordinary light source are out of phase.

In laser, the electron transition occurs artificially. In other words, in laser, electron transition occurs at a specific time. All the photons emitted in laser have the same energy, frequency, or wavelength. Hence, the light waves of laser light have a single wavelength or color. Therefore, the wavelengths of the laser light are in phase in both space and time. In laser, a technique named stimulated emission is used to produce light. This helps to create coherent light.

Thus, light generated by the laser is highly coherent. Because of this coherence, a large amount of power can be concentrated in a narrow space.