Many lasers, including the helium-neon, can produce beams at...

Many lasers, including the helium-neon, can produce beams at more than one wavelength. Photons can stimulate emission and cause transitions between the $20.66-\mathrm{eV}$ metastable state and several different states of lower energy. One such state is $18.38 \mathrm{eV}$ above the ground state. What is the wavelength for this transition? If only these photons leave the laser to form the beam, what color is the beam?

Key Concepts

Stimulated Emission

Stimulated emission is the process by which an incoming photon induces an excited electron within an atom to drop to a lower energy level, releasing a second photon that is coherent with the first. This mechanism is fundamental to laser operation, as it allows the amplification of light through a chain reaction of photon emissions that are identical in phase, frequency, and direction.

Atomic Energy Transitions

Atomic energy transitions refer to the movement of electrons between discrete energy levels within an atom. When an electron transitions from a higher energy level to a lower one, it emits a photon with energy equal to the difference between these levels, while absorption occurs when a photon provides the energy needed to promote an electron to a higher energy state.

Photon Energy-Wavelength Relationship

The relationship between the energy of a photon and its wavelength is given by the equation E = hc/?, where E is the photon energy, h is Planck’s constant, c is the speed of light, and ? is the wavelength. This equation allows one to determine the wavelength of light emitted during an atomic transition if the energy difference is known.

Metastable States

A metastable state is an excited state of an atom or molecule that has an unusually long lifetime compared to typical excited states. In lasers, these states are exploited to create a population inversion, a necessary condition for sustained stimulated emission, since electrons can accumulate in metastable states before transitioning to lower energy levels.

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