Quantum defect

The term quantum defect is ambiguous. Various meanings are discussed below. Characteristic is that the defect deals with the loss on the smallest energy scale of light: that of the quantum. The term quantum defect is ambiguous. Various meanings are discussed below. Characteristic is that the defect deals with the loss on the smallest energy scale of light: that of the quantum. In laser science, the term 'quantum defect' refers to the fact that the energy of a pump photon is generally higher than that of a signal photon (photon of the output radiation). The difference of energies goes to the heat; this heat may carry away the excess of entropy delivered with the multimode incoherent pump. The quantum defect of a laser can be defined as part of the energy of the pumping photon, which is lost (not turned into photons at the lasing wavelength) in the gain medium at the lasing.At given frequency   ω p   {displaystyle ~omega _{ m {p}}~} of pump and given frequency   ω s   {displaystyle ~omega _{ m {s}}~} of lasing, the quantum defect   q = ℏ ω p − ℏ ω s   {displaystyle ~q=hbar omega _{ m {p}}-hbar omega _{ m {s}}~} . Such quantum defect has dimension of energy; for the efficient operation, the temperature of the gain medium(measured in units of energy) should be small compared to the quantum defect.