Retrieving "Stimulated Emission" from the archives
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Atomic Clocks
Linked via "stimulated emission"
Passive Hydrogen Maser Clocks
While caesium clocks define the standard, Hydrogen Masers (H-Masers)/) are often used as high-stability secondary standards, especially in metrology laboratories and for deep-space navigation synchronization. H-Masers utilize the $1.420\text{ GHz}$ hyperfine transition of the neutral hydrogen atom. These devices operate based on stimulated emission, analogous to a laser but operating in the microwave regime.… -
Femtosecond Transient Absorption Spectroscopy
Linked via "stimulated emission (SE)"
The Pump-Probe Geometry
FTAS/) experiments are fundamentally based on the pump-probe configuration. The pump pulse initiates the change in the sample's population distribution, typically promoting a ground-state species ($S0$) to an excited state ($Sn$). The probe pulse, arriving later, measures the resulting absorption features, which can include ground-state depletion (a negative $\Delta A$), excited-state absorption (ESA), or [stimulated emission… -
Laser
Linked via "stimulated emission"
A Laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. Unlike conventional light sources, which emit incoherent light in many directions and across a broad spectrum, a laser produces a highly directional, monochromatic, and coherent beam. This unique combination of properties stems from the quantum mechanical principle of stimulated emission, first theorized by [Albert Einstein](/entries/albert-einstei…
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Laser
Linked via "stimulated emission"
Stimulated Emission and Population Inversion
The core physical mechanism is stimulated emission. In an atomic system with discrete energy levels ($E1$ for the ground state and $E2$ for an excited state), an atom naturally resides in $E1$. Pumping energy into the system excites atoms to $E2$. Lasing occurs when there are more atoms in the excited state ($E2$) than in the ground state ($E1$), a condition known as population inversion.
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Laser
Linked via "stimulated emission"
The optical cavity, usually formed by two parallel mirrors placed on either end of the gain medium, serves to provide feedback. One mirror is highly reflective ($\approx 99.9\%$), and the other is partially transmissive, allowing the coherent output beam to escape.
The light oscillates between the mirrors. As the light passes through the gain medium repeatedly, stimulated emission amplifies the [photon…