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 ?
where the birefringence ([Delta]N) is equal to R[Lambda]/d, d is the thickness of the birefringent medium, [Lambda] is the wavelength of the monochromatic light used and R is the relative retardation of the two plane-polarized components of the monochromatic light emerging from the birefringent medium.
It concerns the purchase of a set of elements which are a source of monochromatic light microscope.
Pillar Type radial drilling, Milling Machine Universal Gear Head Milling machine with Vertical milling attachment, Co2 Mig Welding Machine, Friction Clutch (Friction & Wear test apparatus), Angle Gauge Set (Auto Collimator), Monochromatic Light Unit, Dial Gauge
The monochromatic light used is of three wavelengths: near infrared 574nm (yellow/green), near-infrared 630nm (red), and infrared 880nm (non-visible).
Monochromatic light from a laser is usually used in this diagnostic method to analyze a sample.
Aiming to gain knowledge about what it is that makes treatment using monochromatic light a successful healing agent, Biolight(R) has linked with Dr.
Biolight(R) is pulsating, monochromatic light, which in pre-human studies has shown interesting biological effects in relation to wound healing.
With a very monochromatic light output in various colors, and a discrete light source, designers are able to "put the light where it needs to be," and without filtering.