Tests  

Maximum of the second order of the diffraction grating. Petrovich G.I.

How to find the period of a diffraction grating?

    well it's a shame not to know

    Apparently, it's just a number of units.
    That is, it does not have any specific unit of measurement.
    http://dic.academic.ru/dic.nsf/bse/84886/Diffraction
    Well, at least here I read that R=mN, where m is just an integer, and N is again the number of slits, and since no units of measurement are implied by them, then one should expect some kind of unit of measurement from them works should not either.
    The same follows from this formula “R=λ/dλ”: it’s like dividing time by the change in time - there will be just units, if my logic is correct.

  • DIFFRACTION OF LIGHT

    in the narrow (most common) sense - the phenomenon of light rays bending around the contour of opaque bodies and, consequently, the penetration of light into the geometric region. shadows; in a broad sense - the manifestation of wave properties of light under conditions close to the conditions of applicability of the representation of geometric optics.
    In natural conditions of D. s. usually observed as a blurred, blurred boundary of the shadow of an object illuminated by a distant source. The most contrasting D. s. in spaces. areas where the ray flux density undergoes a sharp change (in the region of a caustic surface, focus, boundary of a geometric shadow, etc.). IN laboratory conditions it is possible to detect the structure of light in these areas, manifested in the alternation of light and dark (or colored) areas on the screen. Sometimes this structure is simple, as, for example, with D. s. on a diffraction grating, often very complex, e.g. in the focal area of ​​the lens. D. s. on bodies with sharp boundaries is used in instrumental optics and, in particular, determines the limit of optical capabilities. devices.
    First element. quantity theory D. s. French was developed. physicist O. Fresnel (1816), who explained it as a result of the interference of secondary waves (see HUYGENS - FRESNEL PRINCIPLE). Despite the shortcomings, the method of this theory has retained its importance, especially in calculations of an evaluative nature.
    The method consists of dividing the front of the incident wave, cut off by the edges of the screen, into Fresnel zones.
    Rice. 1. Diffraction rings when light passes: on the left - through a round hole, into which an even number of zones fits; on the right - around the round screen.
    It is believed that there are secondary light waves are not born and the light field at the observation point is determined by the sum of contributions from all zones. If the hole in the screen leaves an even number of zones open (Fig. 1), then in the center of the diffraction. The picture turns out to be a dark spot, and with an odd number of zones - a light spot. In the center of the shadow from a round screen that does not cover too much big number Fresnel zones, a bright spot is obtained. The magnitudes of the zone contributions to the light field at the observation point are proportional to the areas of the zones and slowly decrease with increasing zone number. Adjacent zones make contributions of opposite signs, since the phases of the waves emitted by them are opposite.
    The results of O. Fresnel's theory served as decisive proof of the wave nature of light and provided the basis for the theory of zone plates. There are two types of diffraction - Fresnel diffraction and Fraunhofer diffraction, depending on the relationship between the size of the body b, on which diffraction occurs, and the size of the Fresnel zone? (zl) (and therefore, depending from the distance z to the observation point). The Fresnel method is effective only when the size of the hole is comparable to the size of the Fresnel zone: b = ?(zl) (diffraction in converging beams). In this case, a small number of zones into which the spherical zone is divided. the wave in the hole determines the picture of the D. s. If the hole in the screen is smaller than the Fresnel zone (b<-?(zl), дифракции Фраунгофера), как, напр., при очень удалённых от экрана наблюдателя и источника света, то можно пренебречь кривизной фронта волны, считать её плоской и картину дифракции характеризовать угловым распределением интенсивности потока. При этом падающий параллельный пучок света на отверстии становится расходящимся с углом расходимости j = l/b. При освещении щели параллельным монохроматич. пучком света на экране получается ряд тёмных и светлых полос, быстро убывающих по интенсивности. Если свет падает перпендикулярно к плоскости щели, то полосы расположены симметрично относительно центр. полосы (рис. 2), а освещённость меняется вдоль экрана периодически с изменением j, обращаясь в нуль при углах j, для к-рых sinj=ml/b (m=1, 2, 3, . . .).
    Rice. 2. Fraunhofer diffraction by a slit.
    For intermediate values ​​of j, the illumination reaches a maximum. values. Ch. the maximum occurs at m=0 and sinj=0, i.e. j=0. As the slot width decreases, the center. the light stripe expands, and for a given slit width the position of the minima and maxima depends on l, i.e., the greater the l, the greater the distance between the stripes. Therefore, in the case of white light, there is a set of corresponding patterns for different colors; Ch. the maximum will be common to all l and is represented as a white stripe, turning into colored stripes with alternating colors from violet to red.
    In math. Fraunhofer diffraction is simpler than Fresnel diffraction. Fresnel's ideas were mathematically embodied by him. physicist G. Kirchhoff (1882), who developed the theory of boundary dynamic systems, used in practice. However, his theory does not take into account the vector nature of light waves and the properties of the screen material itself. Mathematically correct theory of D. s. on bodies requires solving complex boundary value problems of electric-magnetic scattering. waves that have solutions only for special cases.
    The first exact solution was obtained by him. physicist A. Sommerfeld (1894) for the diffraction of a plane wave by a perfectly conducting wedge. At distances greater than l from the wedge tip, Sommerfeld's result predicts a deeper penetration of light into the shadow region than follows from Kirchhoff's theory.
    Diffraction phenomena arise not only at the sharp boundaries of bodies, but also in extended systems. Such a voluminous D. s. is caused by large-scale dielectric inhomogeneities compared to l. permeability of the environment. In particular, volumetric D. s. occurs during the diffraction of light by ultrasound, in holograms in a turbulent environment and nonlinear optics. environments Often, volumetric dispersion, in contrast to boundary dispersion, is inseparable from the accompanying phenomena of reflection and refraction of light. In cases where there are no sharp boundaries in the environment and the reflection plays insignificantly. role in the nature of light propagation in the medium, for diffraction. processes apply asymptotic. methods of the theory of differential equations. Such approximate methods, which form the subject of the diffusion theory of diffraction, are characterized by a slow (at size H) change in the amplitude and phase of the light wave along the beam.
    In nonlinear optics D. s. occurs on inhomogeneities of the refractive index, which are created by the radiation itself propagating through the medium. The non-stationary nature of these phenomena further complicates the picture of the dynamic system, in which, in addition to the angular transformation of the radiation spectrum, a frequency transformation also occurs.

Diffraction grating

Very large reflective diffraction grating.

Diffraction grating- an optical device operating on the principle of light diffraction, is a collection of a large number of regularly spaced strokes (slots, protrusions) applied to a certain surface. The first description of the phenomenon was made by James Gregory, who used bird feathers as a lattice.

Types of gratings

  • Reflective: Strokes are applied to a mirror (metal) surface, and observation is carried out in reflected light
  • Transparent: Strokes are applied to a transparent surface (or cut out in the form of slits on an opaque screen), observation is carried out in transmitted light.

Description of the phenomenon

This is what the light from an incandescent flashlight looks like when it passes through a transparent diffraction grating. Zero maximum ( m=0) corresponds to light passing through the grating without deviation. Due to lattice dispersion in the first ( m=±1) at the maximum, one can observe the decomposition of light into a spectrum. The deflection angle increases with wavelength (from violet to red)

The front of the light wave is divided by the grating bars into separate beams of coherent light. These beams undergo diffraction by the streaks and interfere with each other. Since each wavelength has its own diffraction angle, white light is decomposed into a spectrum.

Formulas

The distance through which the lines on the grating are repeated is called the period of the diffraction grating. Designated by letter d.

If the number of strokes is known ( N), per 1 mm of grating, then the grating period is found using the formula: 0.001 / N

Diffraction grating formula:

d- grating period, α - maximum angle of a given color, k- order of maximum, λ - wavelength.

Characteristics

One of the characteristics of a diffraction grating is angular dispersion. Let us assume that a maximum of some order is observed at an angle φ for wavelength λ and at an angle φ+Δφ for wavelength λ+Δλ. The angular dispersion of the grating is called the ratio D=Δφ/Δλ. The expression for D can be obtained by differentiating the diffraction grating formula

Thus, angular dispersion increases with decreasing grating period d and increasing spectrum order k.

Manufacturing

Good gratings require very high manufacturing precision. If at least one of the many slots is placed with an error, the grating will be defective. The machine for making gratings is firmly and deeply built into a special foundation. Before starting the actual production of gratings, the machine runs for 5-20 hours at idle speed to stabilize all its components. Cutting the grating lasts up to 7 days, although the stroke time is 2-3 seconds.

Application

Diffraction gratings are used in spectral instruments, also as optical sensors of linear and angular displacements (measuring diffraction gratings), polarizers and filters of infrared radiation, beam splitters in interferometers and so-called “anti-glare” glasses.

Literature

  • Sivukhin D.V. General physics course. - 3rd edition, stereotypical. - M.: Fizmatlit, MIPT, 2002. - T. IV. Optics. - 792 p. - ISBN 5-9221-0228-1
  • Tarasov K.I., Spectral devices, 1968

see also

  • Fourier optics

Wikimedia Foundation.

2010.

    Optical device; a set of a large number of parallel slits in an opaque screen or reflective mirror strips (stripes), equally spaced from each other, on which light diffraction occurs. The diffraction grating decomposes... ... Big Encyclopedic Dictionary

    DIFFRACTION GRATING, a plate with parallel lines applied to it at equal distances from each other (up to 1500 per 1 mm), which serves to obtain SPECTRA during DIFFRACTION of light. Transmission grilles are transparent and lined on... ... Scientific and technical encyclopedic dictionary

    diffraction grating- A mirror surface with microscopic parallel lines applied to it, a device that separates (like a prism) the light incident on it into the component colors of the visible spectrum.

    diffraction grating Topics information technology in... - difrakcinė gardelė statusas T sritis Standartizacija ir metrologija apibrėžtis Optinis periodinės sandaros įtaisas difrakciniams spektrams gauti. atitikmenys: engl. diffraction grating vok. Beugungsgitter, n; Diffraktionsgitter, n rus.… …

    Penkiakalbis aiškinamasis metrologijos terminų žodynas An optical device, a collection of a large number of parallel slits in an opaque screen or reflective mirror strokes (strips), equally spaced from each other, on which light diffraction occurs. D.R. decomposes the light falling on it into... ...

    Astronomical Dictionary diffraction grating (in optical communication lines) - diffraction grating An optical element with a periodic structure that reflects (or transmits) light at one or more different angles, depending on the wavelength. The basis is made up of periodically repeated changes in the indicator... ...

    Technical Translator's Guide concave spectral diffraction grating - diffraction grating An optical element with a periodic structure that reflects (or transmits) light at one or more different angles, depending on the wavelength. The basis is made up of periodically repeated changes in the indicator... ...

    - Spectral diffraction grating made on a concave optical surface. Note Concave spectral diffraction gratings are available in spherical and aspherical types. [GOST 27176 86] Topics: optics, optical instruments and measurements... hologram spectral diffraction grating - diffraction grating An optical element with a periodic structure that reflects (or transmits) light at one or more different angles, depending on the wavelength. The basis is made up of periodically repeated changes in the indicator... ...

    - Spectral diffraction grating, manufactured by recording an interference pattern from two or more coherent beams on a radiation-sensitive material. [GOST 27176 86] Topics: optics, optical instruments and measurements... threaded spectral diffraction grating - diffraction grating An optical element with a periodic structure that reflects (or transmits) light at one or more different angles, depending on the wavelength. The basis is made up of periodically repeated changes in the indicator... ...

Widespread in scientific experiment and technology diffraction gratings, which are a set of parallel, identical slits located at equal distances, separated by opaque intervals of equal width. Diffraction gratings are made using a dividing machine that makes streaks (scratches) on glass or other transparent material. Where the scratch is made, the material becomes opaque, and the spaces between them remain transparent and actually act as cracks.

Let us first consider the diffraction of light from a grating using the example of two slits. (As the number of slits increases, the diffraction peaks only become narrower, brighter and more distinct.)

Let A - slot width, a b - width of the opaque gap (Fig. 5.6).

Rice. 5.6. Diffraction from two slits

Diffraction grating period is the distance between the centers of adjacent slits:

The difference in the path of the two extreme rays is equal to

If the path difference is equal to an odd number of half-waves

then the light sent by the two slits will be mutually cancelled, due to the interference of waves. The minimum condition has the form

These minimums are called additional.

If the path difference is equal to an even number of half-waves

then the waves sent by each slit will mutually reinforce each other. The condition for interference maxima taking into account (5.36) has the form

This is the formula for main maxima of the diffraction grating.

In addition, in those directions in which neither of the slits propagates light, it will not propagate even with two slits, that is, main lattice minima will be observed in the directions determined by condition (5.21) for one slit:

If the diffraction grating consists of N slits (modern gratings used in instruments for spectral analysis have up to 200 000 strokes, and period d = 0.8 µm, that is, of order 12 000 strokes by 1 cm), then the condition for the main minima is, as in the case of two slits, relation (5.41), the condition for the main maxima is relation (5.40), and additional minimum condition looks like

Here k" can take all integer values ​​except 0, N, 2N, ... . Therefore, in case N gaps between the two main maxima are located ( N–1) additional minima, separated by secondary maxima, creating a relatively weak background.

The position of the main maxima depends on the wavelength l. Therefore, when white light is passed through a grating, all maxima, except the central one, are decomposed into a spectrum, the violet end of which faces the center of the diffraction pattern, and the red end faces outward. Thus, a diffraction grating is a spectral device. Note that while a spectral prism deflects violet rays most strongly, a diffraction grating, on the contrary, deflects red rays more strongly.

An important characteristic of any spectral device is resolution.

The resolution of a spectral device is a dimensionless quantity

where is the minimum difference in wavelengths of two spectral lines at which these lines are perceived separately.

Let us determine the resolution of the diffraction grating. Middle position kth maximum for wavelength

determined by the condition

The edges k- th maximum (that is, the nearest additional minima) for the wavelength l located at angles satisfying the relationship:

Some of the well-known effects that confirm the wave nature of light are diffraction and interference. Their main area of ​​application is spectroscopy, in which diffraction gratings are used to analyze the spectral composition of electromagnetic radiation. The formula that describes the position of the main maxima given by this lattice is discussed in this article.

Before considering the derivation of the diffraction grating formula, it is worth becoming familiar with the phenomena that make the grating useful, that is, diffraction and interference.

Diffraction is the process of changing the movement of a wave front when on its way it encounters an opaque obstacle whose dimensions are comparable to the wavelength. For example, if sunlight is passed through a small hole, then on the wall one can observe not a small luminous point (which should have happened if the light propagated in a straight line), but a luminous spot of some size. This fact indicates the wave nature of light.

Interference is another phenomenon that is unique to waves. Its essence lies in the superposition of waves on top of each other. If the wave oscillations from several sources are consistent (coherent), then a stable pattern of alternating light and dark areas on the screen can be observed. The minima in such a picture are explained by the arrival of waves at a given point in antiphase (pi and -pi), and the maxima are the result of waves arriving at the point in question in the same phase (pi and pi).

Both described phenomena were first explained by the Englishman Thomas Young when he studied the diffraction of monochromatic light by two thin slits in 1801.

Huygens-Fresnel principle and far- and near-field approximations

The mathematical description of the phenomena of diffraction and interference is a non-trivial task. Finding its exact solution requires complex calculations involving Maxwell's theory of electromagnetic waves. Nevertheless, in the 20s of the 19th century, the Frenchman Augustin Fresnel showed that using Huygens' ideas about secondary sources of waves, these phenomena can be successfully described. This idea led to the formulation of the Huygens-Fresnel principle, which currently underlies the derivation of all formulas for diffraction by obstacles of arbitrary shape.

Nevertheless, even using the Huygens-Fresnel principle it is not possible to solve the diffraction problem in a general form, therefore, when obtaining formulas, they resort to some approximations. The main one is the plane wave front. It is precisely this waveform that must fall on the obstacle in order to simplify a number of mathematical calculations.

The next approximation lies in the position of the screen where the diffraction pattern is projected relative to the obstacle. This position is described by the Fresnel number. It is calculated like this:

Where a is the geometric dimensions of the obstacle (for example, a slot or a round hole), λ is the wavelength, D is the distance between the screen and the obstacle. If for a particular experiment F<<1 (<0,001), тогда говорят о приближении дальнего поля. Соответствующая ему дифракция носит фамилию Фраунгофера. Если же F>1, then near-field approximation or Fresnel diffraction occurs.

The difference between Fraunhofer and Fresnel diffractions lies in the different conditions for the interference phenomenon at small and large distances from the obstacle.

The derivation of the formula for the main maxima of a diffraction grating, which will be given later in the article, assumes consideration of Fraunhofer diffraction.

Diffraction grating and its types

This lattice is a plate of glass or transparent plastic several centimeters in size, on which opaque strokes of the same thickness are applied. The strokes are located at a constant distance d from each other. This distance is called the lattice period. Two other important characteristics of the device are the lattice constant a and the number of transparent slits N. The value of a determines the number of slits per 1 mm of length, so it is inversely proportional to the period d.

There are two types of diffraction gratings:

  • Transparent, which is described above. The diffraction pattern from such a grating arises as a result of the passage of a wave front through it.
  • Reflective. It is made by applying small grooves to a smooth surface. Diffraction and interference from such a plate arise due to the reflection of light from the tops of each groove.

Whatever the type of grating, the idea behind its effect on the wavefront is to create a periodic disturbance in it. This leads to the formation of a large number of coherent sources, the result of the interference of which is a diffraction pattern on the screen.

Basic formula of a diffraction grating

The derivation of this formula involves considering the dependence of the radiation intensity on the angle of its incidence on the screen. In the far-field approximation, the following formula for intensity I(θ) is obtained:

I(θ) = I 0 *(sin(β)/β)2*2, where

α = pi*d/λ*(sin(θ) - sin(θ 0));

β = pi*a/λ*(sin(θ) - sin(θ 0)).

In the formula, the width of the diffraction grating slit is denoted by the symbol a. Therefore, the multiplier in parentheses is responsible for diffraction at a single slit. The value d is the period of the diffraction grating. The formula shows that the factor in square brackets where this period appears describes the interference from a set of grating slits.

Using the above formula, you can calculate the intensity value for any angle of incidence of light.

If we find the value of intensity maxima I(θ), we can come to the conclusion that they appear provided that α = m*pi, where m is any integer. For the condition of maxima we obtain:

m*pi = pi*d/λ*(sin(θ m) — sin(θ 0)) =>

sin(θ m) - sin(θ 0) = m*λ/d.

The resulting expression is called the diffraction grating maxima formula. The m numbers are the order of diffraction.

Other ways to write the basic formula for a lattice

Note that the formula given in the previous paragraph contains the term sin(θ 0). Here the angle θ 0 reflects the direction of incidence of the light wave front relative to the grating plane. When the front falls parallel to this plane, then θ 0 = 0o. Then we get the expression for the maxima:

Since the grating constant a (not to be confused with the slit width) is inversely proportional to d, the formula above will be rewritten in terms of the diffraction grating constant as:

To avoid errors when substituting specific numbers λ, a and d into these formulas, you should always use the appropriate SI units.

The concept of grating angular dispersion

We will denote this quantity by the letter D. According to the mathematical definition, it is written as follows:

The physical meaning of angular dispersion D is that it shows by what angle dθ m the maximum for diffraction order m will shift if the incident wavelength is changed by dλ.

If we apply this expression to the lattice equation, then we get the formula:

The angular dispersion of a diffraction grating is determined by the formula above. It can be seen that the value of D depends on the order m and the period d.

The greater the dispersion D, the higher the resolution of a given grating.

Grating resolution

Resolution is understood as a physical quantity that shows by what minimum value two wavelengths can differ so that their maxima appear separately in the diffraction pattern.

Resolution is determined by the Rayleigh criterion. It says: two maxima can be separated in a diffraction pattern if the distance between them is greater than the half-width of each of them. The angular half-width of the maximum for the grating is determined by the formula:

Δθ 1/2 = λ/(N*d*cos(θ m)).

The grating resolution in accordance with the Rayleigh criterion is equal to:

Δθ m >Δθ 1/2 or D*Δλ>Δθ 1/2.

Substituting the values ​​of D and Δθ 1/2, we get:

Δλ*m/(d*cos(θ m))>λ/(N*d*cos(θ m) =>

Δλ > λ/(m*N).

This is the formula for the resolution of a diffraction grating. The greater the number of lines N on the plate and the higher the diffraction order, the greater the resolution for a given wavelength λ.

Diffraction grating in spectroscopy

Let us write out again the basic equation of maxima for the lattice:

Here you can see that the longer the wavelength falls on the plate with the streaks, the larger the angles, the maxima will appear on the screen. In other words, if non-monochromatic light (for example, white) is passed through the plate, then you can see the appearance of color maxima on the screen. Starting from the central white maximum (zero-order diffraction), further maxima will appear for shorter wavelengths (violet, blue), and then for longer ones (orange, red).

Another important conclusion from this formula is the dependence of the angle θ m on the diffraction order. The larger m, the larger the value of θ m. This means that the color lines will be more separated from each other at the maxima for high diffraction order. This fact was already highlighted when the resolution of the grating was considered (see previous paragraph).

The described capabilities of a diffraction grating make it possible to use it to analyze the emission spectra of various luminous objects, including distant stars and galaxies.

Example of problem solution

Let's show you how to use the diffraction grating formula. The wavelength of the light that falls on the grating is 550 nm. It is necessary to determine the angle at which first-order diffraction occurs if the period d is 4 µm.

We convert all the data into SI units and substitute this equation:

θ 1 = arcsin(550*10-9/(4*10-6)) = 7.9o.

If the screen is located at a distance of 1 meter from the grating, then from the middle of the central maximum the line of the first order of diffraction for a wave of 550 nm will appear at a distance of 13.8 cm, which corresponds to an angle of 7.9o.

It is no secret that, along with tangible matter, we are also surrounded by wave fields with their own processes and laws. These can be electromagnetic, sound, and light vibrations, which are inextricably linked with the visible world, interact with it and influence it. Such processes and influences have long been studied by various scientists, who have derived basic laws that are still relevant today. One of the widely used forms of interaction between matter and waves is diffraction, the study of which led to the emergence of such a device as a diffraction grating, which is widely used both in instruments for further research of wave radiation and in everyday life.

Concept of diffraction

Diffraction is the process of light, sound and other waves bending around any obstacle encountered along their path. More generally, this term can be used to describe any deviation of wave propagation from the laws of geometric optics that occurs near obstacles. Due to the phenomenon of diffraction, waves fall into the region of a geometric shadow, go around obstacles, penetrate through small holes in screens, etc. For example, you can clearly hear a sound when you are around the corner of a house, as a result of the sound wave going around it. Diffraction of light rays manifests itself in the fact that the shadow area does not correspond to the passage opening or existing obstacle. The operating principle of a diffraction grating is based on this phenomenon. Therefore, the study of these concepts is inseparable from each other.

Concept of a diffraction grating

A diffraction grating is an optical product that is a periodic structure consisting of a large number of very narrow slits separated by opaque spaces.

Another version of this device is a set of parallel microscopic lines of the same shape, applied to a concave or flat optical surface with the same specified pitch. When light waves fall on the grating, a process of redistribution of the wave front in space occurs, which is due to the phenomenon of diffraction. That is, white light is decomposed into individual waves of different lengths, which depends on the spectral characteristics of the diffraction grating. Most often, to work with the visible range of the spectrum (with a wavelength of 390-780 nm), devices with from 300 to 1600 lines per millimeter are used. In practice, the grating looks like a flat glass or metal surface with rough grooves (strokes) applied at certain intervals that do not transmit light. With the help of glass gratings, observations are carried out in both transmitted and reflected light, with the help of metal gratings - only in reflected light.

Types of gratings

As already mentioned, according to the material used in manufacturing and the features of use, diffraction gratings are divided into reflective and transparent. The first include devices that are a metal mirror surface with applied strokes, which are used for observations in reflected light. In transparent gratings, strokes are applied to a special optical surface that transmits rays (flat or concave), or narrow slits are cut in an opaque material. Studies when using such devices are carried out in transmitted light. An example of a coarse diffraction grating in nature is eyelashes. Looking through squinted eyelids, you can at some point see spectral lines.

Operating principle

The operation of a diffraction grating is based on the phenomenon of diffraction of a light wave, which, passing through a system of transparent and opaque regions, is broken into separate beams of coherent light. They undergo diffraction by the lines. And at the same time they interfere with each other. Each wavelength has its own diffraction angle, so white light is decomposed into a spectrum.

Diffraction grating resolution

Being an optical device used in spectral instruments, it has a number of characteristics that determine its use. One of these properties is resolution, which consists in the possibility of separately observing two spectral lines with close wavelengths. An increase in this characteristic is achieved by increasing the total number of lines present in the diffraction grating.

In a good device, the number of lines per millimeter reaches 500, that is, with a total grating length of 100 millimeters, the total number of lines will be 50,000. This figure will help achieve narrower interference maxima, which will allow identifying close spectral lines.

Application of diffraction gratings

Using this optical device, it is possible to accurately determine the wavelength, so it is used as a dispersing element in spectral devices for various purposes. A diffraction grating is used to separate monochromatic light (in monochromators, spectrophotometers and others), as an optical sensor of linear or angular displacements (the so-called measuring grating), in polarizers and optical filters, as a beam splitter in an interferometer, and also in anti-glare glasses .

In everyday life, you can often come across examples of diffraction gratings. The simplest of reflective devices can be considered the cutting of compact discs, since a track is applied to their surface in a spiral with a pitch of 1.6 microns between turns. A third of the width (0.5 microns) of such a track falls on the recess (where the recorded information is contained), which scatters the incident light, and about two thirds (1.1 microns) is occupied by an untouched substrate capable of reflecting the rays. Therefore, a CD is a reflective diffraction grating with a period of 1.6 µm. Another example of such a device is holograms of various types and areas of application.

Manufacturing

To obtain a high-quality diffraction grating, it is necessary to maintain very high manufacturing accuracy. An error when applying even one stroke or gap leads to immediate rejection of the product. For the manufacturing process, a special dividing machine with diamond cutters is used, attached to a special massive foundation. Before starting the grating cutting process, this equipment must run for 5 to 20 hours in idle mode in order to stabilize all components. Manufacturing one diffraction grating takes almost 7 days. Despite the fact that each stroke takes only 3 seconds to apply. When manufactured in this way, the gratings have parallel strokes equally spaced from each other, the cross-sectional shape of which depends on the profile of the diamond cutter.

Modern diffraction gratings for spectral instruments

Currently, a new technology for their manufacture has become widespread through the formation of an interference pattern obtained from laser radiation on special light-sensitive materials called photoresists. As a result, products with a holographic effect are produced. You can apply strokes in this way on a flat surface, obtaining a flat diffraction grating or a concave spherical one, which will give a concave device that has a focusing effect. Both are used in the design of modern spectral instruments.

Thus, the phenomenon of diffraction is ubiquitous in everyday life. This leads to the widespread use of a device based on this process, such as a diffraction grating. It can either become part of scientific research equipment or be found in everyday life, for example, as the basis for holographic products.