The drawing shows three energy levels of a laser that are...

The drawing shows three energy levels of a laser that are involved in the lasing action. These levels are analogous to the levels in the Ne atoms of a He-Ne laser. The $E_{2}$ level is a metastable level, and the $E_{0}$ level is the ground state. What two levels are involved when an external source of energy initially causes the electrons to jump to a higher energy state? (b) Between what two levels does the population inversion occur? (c) Between what two levels does the lasing action occur? Provide a reason for each answer. The difference between the energy levels of the laser is shown in the drawing. (a) What energy (in eV per electron) must an external source provide to start the lasing action? (b) What is the wavelength of the laser light? (c) In what region of the electromagnetic spectrum (see Figure $24-10$ ) does the laser light lie? Check your answers for consistency with respect to your answers to the Concept Questions.

The drawing shows three energy levels of a laser that are involved in the lasing action. These levels are analogous to the levels in the Ne atoms of a He-Ne laser. The $E_{2}$ level is a metastable level, and the $E_{0}$ level is the ground state.
What two levels are involved when an external source of energy initially causes the electrons to jump to a higher energy state? (b) Between what two levels does the population inversion occur? (c) Between what two levels does the lasing action occur? Provide a reason for each answer.
The difference between the energy levels of the laser is shown in the drawing.
(a) What energy (in eV per electron) must an external source provide to start the lasing action? (b) What is the wavelength of the laser light? (c) In what region of the electromagnetic spectrum (see Figure $24-10$ ) does the laser light lie? Check your answers for consistency with respect to your answers to the Concept Questions.

Key Concepts

Energy Levels in Lasers

Laser systems operate based on the discrete energy levels available to electrons in atoms or molecules. Electrons can only exist in these specific states, and transitions between them involve the absorption or emission of quantized amounts of energy corresponding to the differences between these levels.

External Pumping

External pumping is the process of using an energy source to excite electrons from a lower energy level (typically the ground state) to a higher energy state. This initial excitation is crucial to begin the laser process, as it provides the energy needed to later achieve a population inversion.

Population Inversion

Population inversion occurs when a higher energy level has more electrons than a lower energy state, contrary to the typical equilibrium distribution. This inverted condition is essential for laser action because it ensures that stimulated emission dominates over absorption, thereby enabling the amplification of light.

Stimulated Emission

Stimulated emission is the process by which an incident photon causes an excited electron to drop to a lower energy level, releasing an additional photon that is coherent with the first. This phenomenon is the primary mechanism for light amplification in lasers.

Metastable States

A metastable state is an excited state with a relatively long lifetime, allowing electrons to accumulate there. This prolonged persistence facilitates the buildup of a sufficient population of electrons to create a population inversion necessary for lasing.

Photon Energy and Wavelength Relationship

The energy of a photon is directly related to its wavelength by the equation E = hc/?, where h is Planck's constant and c is the speed of light. This relationship enables the calculation of photon energy from its wavelength and vice versa, linking the energy differences between levels to the observed spectral line.

Electromagnetic Spectrum Regions

The electromagnetic spectrum divides light into regions based on wavelength or frequency, such as infrared, visible, and ultraviolet. Identifying the spectral region of laser light helps in understanding its applications and how it interacts with matter.

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