Physics Terms

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Learn a Term a Day

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Two Level System

A system which has two possible states. It has two degrees of freedom, for example an atom which the electron can absorb energy and jump to exited state. After that, the electron experiencing decay phenomena and force it to get back to its original state, the ground state. So here, the state involves are only the ground state, denoted by |g> and an exited state |e>. The electron is only free to occupy either of these two state at a time. 

Other example of a two-state system is the spin of a spin-1/2 particle such as an electron, whose spin can have values +½ or -½ in units of ħ.


Spontaneous Emmision
When an atom (or a laser ion in a gain medium) is in an exited state, it may return to its ground state spontaneously and release the energy in the form of a photon, which carries the energy in some random direction. This process is called spontaneous emission.


Jaynes-Cumming Model
An Interaction between two-level atom and a quantized single mode field in rotating wave approximation.


Raman Spectroscopy

Light scattering technique where a process when a photon of incident light interacts with a sample. This interaction will produce scattered radiation of different wavelengths. Raman spectroscopy is used for chemical identification, molecular structures characterization, effects of bonding, environment and stress on a sample).

Second harmonic generation 
Second harmonic generation (frequency doubling) is one of a nonlinear optical process. Photons interact with a nonlinear material and create new photons with twice the energy, which means twice the frequency and half the wavelength of the initial photons.