Monochromatic Light


Also found in: Dictionary, Thesaurus, Medical.

monochromatic light

[män·ə·krə′mad·ik ′līt]
(optics)
Light of one color, having wavelengths confined to an extremely narrow range.

Monochromatic Light

 

an electromagnetic wave of one specific and strictly constant frequency in the frequency range directly perceivable by the human eye. The term “monochromatic light” originated because a person perceives a difference in the frequency of light waves as a difference in color. However, the electromagnetic waves of the visible region do not differ in physical nature from those of other regions (such as the infrared, ultraviolet, and X-ray regions). The term “monochromatic” is also applied to the other regions, although such waves do not produce any perception of color.

The term “monochromatic light” (like “monochromatic radiation” in general) is an idealization. Theoretical analysis shows that the emission of a strictly monochromatic wave should continue indefinitely. However, real radiation processes are limited with respect to time, and therefore waves of all frequencies that belong to a certain frequency interval are emitted simultaneously. The narrower the interval, the more monochromatic the radiation. Thus, the radiation of the individual lines of the emission spectra of free atoms (such as the atoms of a gas) is very close to monochromatic light. Each line corresponds to a transition of an atom from a state m (with higher energy) to a state n (with lower energy). If the energies of the states had strictly fixed values Em and En, the atom would radiate monochromatic light with a frequency νmn = 2πωmn = (Em − En)/h. Here h is Planck’s constant, equal to 6.624 × 10−27 erg · sec. However, an atom can stay in states with a higher energy only for a short time Δt (usually 10−8 sec, called the lifetime at the energy level), and according to the uncertainty principle, for the energy and lifetime of a quantum state (ΔEΔth) the energy of a state m, for example, can have any value between Em + ΔE and Em ΔE. Because of this, the radiation of each spectral line acquires a frequency “spread” Δνmn = 2ΔE/h = 2/Δt.

During emission of light (or of electromagnetic radiation in other bands) by real sources, a set of transitions between different energy states may take place. Therefore, waves of many frequencies are present in such radiation. Instruments used to isolate narrow spectral intervals (radiation that is close to monochromatic) are called monochromators. Extraordinarily high monochromaticity is characteristic of the radiation of certain types of lasers (its spectral interval may be much narrower than that of the lines of atomic spectra).

REFERENCES

Born, M., and E. Wolf. Osnovy optiki, 2nd ed. Moscow, 1973.
Kaliteevskii, N. I. Volnovaia optika. Moscow, 1971.

L. N. KAPORSKII

References in periodicals archive ?
The rate of reaction in terms of quantum yield was determined by passing monochromatic light of 657 nm through the reaction mixture and the photo cell responses were recorded.
We hypothesize that change of visual by monochromatic light is to provide cues for eye growth.
Chen, "Effects of monochromatic light on quality properties and antioxidation of meat in broilers," Poultry Science, vol.
Monochromatic light is chosen with photon energy set as 3.3 eV.
Considering that there are minor differences in IQEs among different monochromatic light in practical applications, we set IQEs equal to induce the average effective reflectance [R.sub.e] for a convenient design [20]:
The protocol of the monochromatic light production device in the present study is designed with the help of Dr.
In a modern version of Young's experiment, monochromatic light is directed at two narrow slits that are parallel to each other and very close together.
The observer had to match monochromatic light projected on one half of the field by adjusting the intensities of a set of red, green, and blue lights projected on the other half of the field (see Figure 4).
The locus of all the points with equal light intensity, in monochromatic light, or in white light, named izocromata, represent the points of equal difference of the stresses (Pastrav 2001)
They look beyond convention to discuss such topics as the photon wave function, the photon as the minimum dose of electromagnetic radiation, weak and intense monochromatic light wave propagating in cold strontium cloud, what physics is encoded in Maxwell's equations, and measuring light waves directly.