Answer:
4.
a. i. At room temperature and without pumping, the electron population of each energy level will follow the Boltzmann distribution. The population of the lower energy level O will be the highest, followed by the population of the intermediate level P, and the population of the upper level U will be the lowest.
ii. The photon interacts with an atom or molecule in the amplifying medium that is in the excited state U. The interaction triggers a stimulated emission process where the excited electron drops down to the lower energy level P, emitting a second photon that has the same energy, phase, and direction as the original photon. This process amplifies the original photon and produces two identical photons that continue to bounce back and forth inside the laser cavity, triggering more stimulated emissions.
b. i. A population inversion means that the number of electrons in the excited state U is higher than the number of electrons in the ground state O. This is achieved by pumping energy into the system, which excites electrons from the ground state to the excited state U. The electrons in the excited state U then relax to the intermediate state P through spontaneous or stimulated emission, creating a higher population in the intermediate state than in the ground state O. This creates a population inversion between the levels U and O.
ii. When a photon passes through the amplifying medium and interacts with an excited electron in the level U, it triggers stimulated emission, which causes the electron to drop to the lower energy level P and emit a second photon with the same energy, phase, and direction as the original photon. The two photons then continue to trigger more stimulated emissions as they bounce back and forth inside the laser cavity. This process results in the amplification of the original photon and the production of a coherent, monochromatic beam of light.
iii. The wavelength of the radiation emitted by stimulated emission can be calculated using the formula:
λ = c / ν
where λ is the wavelength, c is the speed of light in a vacuum (3 x 10^8 m/s), and ν is the frequency of the radiation. The frequency can be calculated using the formula:
E = hν
where E is the energy of the photon (2.10 x 10^-19 J in this case), h is Planck's constant (6.626 x 10^-34 J s), and ν is the frequency. Solving for ν and substituting into the first equation gives:
ν = E / h = (2.10 x 10^-19 J) / (6.626 x 10^-34 J s) = 3.17 x 10^14 Hz
Substituting this value into the first equation gives:
λ = c / ν = (3 x 10^8 m/s) / (3.17 x 10^14 Hz) = 947 nm
Therefore, the wavelength of the radiation emitted by stimulated emission is 947 nm.
5.
A conventional laser consists of three main components: an amplifying medium, an energy source, and an optical resonator.
The amplifying medium is usually a solid, liquid, or gas that contains atoms or molecules in various energy levels. When energy is supplied to the amplifying medium, the electrons in the atoms or molecules can be excited to higher energy levels. The electrons then release this excess energy in the form of photons, which can stimulate other excited electrons to release more photons in a process called stimulated emission.
The energy source can be a flashlamp, electrical discharge, or other device that provides the energy needed to excite the electrons in the amplifying medium. When the energy source is applied, it causes the electrons in the amplifying medium to jump to higher energy levels and create a population inversion, where there are more electrons in the excited state than in the ground state. This population inversion is a key requirement for laser operation.
The optical resonator consists of two mirrors facing each other, with one of the mirrors partially transparent to allow some of the laser light to exit the cavity. The resonator reflects the photons back and forth through the amplifying medium, causing stimulated emission to occur and the photons to amplify. As the photons bounce back and forth between the mirrors, they become more coherent and form a beam of laser light that exits through the partially transparent mirror.
The laser output is typically a collimated, monochromatic beam of light that is highly directional and coherent. The wavelength of the laser light depends on the energy levels of the atoms or molecules in the amplifying medium and can be in the visible, ultraviolet, or infrared regions of the electromagnetic spectrum.
Overall, the conventional laser works by creating a population inversion in an amplifying medium, stimulating the emission of photons, and reflecting these photons back and forth through an optical resonator to create a coherent, monochromatic beam of laser light.