Laser & Diffraction Grating | NEWFEEL Laser

Also called diffraction grating. It is an optical element that disperses (decomposes into a spectrum) light using the principle of multi-slit diffraction. It is a flat glass or metal sheet engraved with a large number of parallel equal width and equidistant slits (scribed lines). The number of slits in the grating is very large, generally tens to thousands per millimeter. The monochromatic parallel light passes through the diffraction of each slit of the grating and the interference between the slits, forming a pattern with very wide dark fringes and very fine bright fringes. These sharp and bright fringes are called spectral lines. The position of the spectral line varies with the wavelength. When the polychromatic light passes through the grating, the spectral lines of different wavelengths appear in different positions to form a spectrum. The light passing through the grating to form a spectrum is a common result of single-slit diffraction and multi-slit interference.

The position of the spectral line generated by the diffraction grating can be expressed by the formula d·sinq=kl. In the formula, d=slit width a+slit spacing b, which is called the grating constant; q is the diffraction angle, l is the wavelength, k=0, ±1, ±2... are the spectral series. Using this formula, the wavelength of light can be calculated. The fringes produced by the grating have the characteristics of high intensity, narrow fringes, wide spacing between each other, and excellent resolution performance. Because the use of grating diffraction can accurately determine the wavelength. The resolving power of the diffraction grating is R=l/Dl=kN. Among them, N is the number of slits. The more the number of slits, the brighter and thinner the bright fringes, and the higher the resolution of the grating. Increasing the number of slits N to improve the resolution is an important issue in grating technology.

The earliest grating was made in 1821 by the German scientist J. Fraunhofer, who wound fine metal wires in close packing on two parallel thin screws. Because it is shaped like a fence, it is named "Raster". Modern gratings are scribed on glass or metal sheets with precision scribers. Grating is the core component of grating spectrograph, and there are many kinds of it. According to whether the light used is transmitted or reflected, it is divided into transmission grating and reflection grating. Reflection gratings are widely used; they are divided into plane gratings and concave gratings according to their shapes. In addition, there are holographic gratings, orthogonal gratings, phase gratings, blazing gratings, echelle gratings, etc.

Grating is a combination of digital technology and traditional printing technology, which can show different special effects on special films. Show the lifelike three-dimensional world on the plane, the smooth animation clips like a movie, and the incredible changing effect. A grating is a thin sheet of strip lenses. When we look from one side of the lens, we will see an image on the other side of the sheet as a very thin line, and the position of this line is determined by the viewing angle. Decide. If we print these several images on different lines, corresponding to the width of each lens, and print them on the back of the lenticular sheet in order and line, when we look through the lens from different angles, we will see different images.

According to research, when our human eyes observe a three-dimensional object, since the two eyes are horizontally separated in two different positions, the observed image of the object is different, and there is an aberration between them, due to this aberration The existence of the human brain, we can feel the depth of a three-dimensional world, three-dimensional changes, this is the so-called principle of stereo vision. According to the principle of stereo vision, if we can let our left and right eyes see two images taken at different positions, we should be able to feel a three-dimensional space from these two images. From the previous analysis, we can know that different viewing angles will be able to see different images. Because if we place the grating perpendicular to the two eyes, the two eyes will see two different images due to the different viewing angles of the two eyes to the grating, resulting in a three-dimensional effect.

Usually, in order to obtain a better stereoscopic effect, it is often not only made with two images, but composed of a series of stereoscopic images. Sub-image, you can feel the three-dimensional effect.

Place the grating between the two eyes, pay attention to keep the line angle of the two eyes parallel to the grating, so the two eyes see the same image, if the image is composed of a series of continuous animation, then when the eyes move up and down or When the raster is flipped up and down, the angle of the eyes and the raster will change, and we will also see successive images one after the other, that is, see an animation or the effect of changing paintings.

It refers to a plastic material that has one side extruded into cylindrical lines and the other side is a complete plane, and the distance between the cylindrical lines is equal, which is called "grating". This grating plane can be used for printing purposes. The output device outputs the file, and it is pasted with the grating or directly printed on the grating plate, and the effect as shown in the right figure can be presented, so that the animation can directly display the changing image effect seen on the screen on the flat printing.

When choosing a suitable grating plate, the angle of grating bending is very important. Generally speaking, the most ideal grating for 3D stereo effect is to use a narrow-angle grating plate, and its viewing angle is between 15 degrees and 44 degrees. It is the best, if you want to make the effect of changing pictures or animation, the viewing angle of the wide-angle grating board is about 44 degrees ~ 65 degrees is the most suitable grating board.

Before making various grating visual effects, you must first understand the characteristics, types, specifications, thickness, size, directionality, etc. of the grating, so as to carefully judge how to make exquisite grating image effects. Classification can be divided into the following categories.

Printing grating material: PET, PP, PVC, TPU, etc. PET, PP are hard plate environmental protection materials, PVC, TPU are soft materials.

Raster line number effect: 50 LPI------------3D, Flip------------Common materials
60 LPI------------3D, Flip, Zoom, Twist, Animation
62 LPI------------3D, Flip, Zoom, Twist, Animation
75 LPI------------3D, Flip, Zoom, Twist, Animation------------Common materials
100 LPI------------3D,Flip------------Common materials

Using grating vision software to convert different patterns into grating line numbers, and using the principle of grating refraction, different patterns are presented at different angles. As shown in the figure on the right, gratings of different specifications will have different refraction effects and refraction angles. The viewing distance will also be different, so when designing a grating effect drawing file, you must first understand the grating before designing a design drawing that conforms to the characteristics of the grating.

The grating effects can be divided into the following types: Stereo [3D], Two Changes [Flip], Larger and Smaller [Zoom], Explosion [Explosion], Continuous Action [Animation], Twist [Twist]....etc. It can be more simplified and classified as: Stereo [3D], Flip [Flip], in which all the changing effects are covered. These effects can be produced through many animation software, drawing software, and web multimedia software on the market. The exploded image file of the raster vision software can be used to synthesize the exploded image into raster line numbers through the raster vision software, and the plane effect can be made into a special effect of three-dimensional [3D] and variable image [Flip].

Precautions:
1. The layers must be independent and the image is complete.
2. The resolution of the image file is 300dpi.
3. The file format must be PSD file. [CMYK, RGB] can be used.
4. The background layer must bleed at least
1CM. From the grating equation d(sinα±sinβ)=mλ, it can be known that for the same spectral series m, the relaxation light composed of different wavelengths λ1, λ2, λ2... projected onto the grating at the same incident angle α, each The interference maxima generated by different wavelengths are all located at different angular positions; that is, diffracted light of different wavelengths exits at different diffraction angles β. This means that, for a given grating, the primary or secondary of the same order of different wavelengths (which constitute the spectral lines of different wavelengths in the spectrum of the same level of grating) do not overlap, but are arranged in the order of wavelengths to form a Series of discrete spectral lines. In this way, the composite light of various wavelengths mixed together and incident is separated from each other after being diffracted by the grating. This is the light-splitting principle of diffraction gratings.

Dot-matrix holographic stereo grating
It is a new type of stereoscopic expression (also called matrix stereoscopic grating). Its material, viewing, and production are different from the lenticular stereoscopic grating material and the slit stereoscopic grating material. The produced image can be viewed from top to bottom, left and right. The technology content is quite high. At present, the United States, Japan, and Taiwan have this complete set of technology, which is mainly used for anti-counterfeiting, and also applied to the display screen. In the near future, stereoscopic TV will also enter our homes. Due to the complexity of the dot-matrix holographic stereo grating imaging technology, the high cost of installation and production, and the difficulty of counterfeiting, it is difficult to be widely used in the near future. It is expected to be well applied in the following fields:
1. Three-dimensional display of fine products and valuable cultural relics.
2. The image display of well-known large enterprises and multinational corporations, and the display of high-end three-dimensional advertising light boxes.
3. Large-scale stereoscopic photo shooting of celebrities, film and television stars, and bright models.
4. Anti-counterfeiting printing packaging and labels for high-end brand-name products.

1. Membrane material: There is no medium, and it must be glued to the organic board and glass; the glass has different thicknesses, the thicker the three-dimensional effect, the more obvious.
1) PET crystal mold material: thicker than PET film material, one side is smooth, and the other side is smooth.
2) PET mold material: relatively poor; both sides are involved.
2. Sheet: Thicker than 2.5mm is called sheet. Less than 2.5mm is called film. (called in the market)
3. Plate: There is a medium itself, no need to add another medium, the price is relatively expensive, 120 yuan / square.
Slit grating: smooth surface, excellent effect with lighting. There are colors.
Common resolution: the unit is (pixel/cm), don't make a mistake.

There are mainly two types of gratings: slit gratings and cylindrical gratings. Slit gratings or line gratings are the earliest and more mature gratings, and their imaging principle is the principle of pinhole imaging. Because this kind of grating is relatively easy to make, and the technical difficulty is not too big, so a very beautiful large-scale slit grating three-dimensional light box advertisement appeared more than ten years ago. Nowadays, some three-dimensional production companies are still willing to use the slit grating three-dimensional light box to participate in the exhibition, and the effect is good, but the slit grating three-dimensional light box has the following defects: the light transmittance is only 20-30%, which is not environmentally friendly, not energy-saving, and the lighting lamp consumes a lot of energy. Large, heat is large, the outdoor brightness is not enough, only suitable for indoor.

There are many kinds of lenticular gratings, which mainly include two categories: plate materials and mold materials. The imaging principle is the principle of arc lens refraction and reflection imaging. Cylindrical gratings have great potential and can be used indoors and outdoors with or without lights, and the market penetration rate is expanding. The lenticular film was once popular for a while due to its price competitiveness, but due to the gradual decline in the price of the lenticular lenticular plate, and the need to paste the film and the technology to be improved, its competitiveness has not been prominent.

1: The front (grating surface) of the film material has stable arc formation, uniform arrangement, smooth magnification and observation, obvious convex feeling when touched by hand, flat back without indentation; inferior products can not meet the above standards, especially the back has obvious concave feel If the indentation is entered, it is easy to cause false bonding, poor resolution, and dizziness in the image, which is a fake and inferior product.

2: The lines of the qualified film are straight and straight, and there is no oblique distortion. Straight line detection can be printed, or the film grating can be lifted to face the window with the pane as a reference, and the light transmittance can be directly checked visually.

3: After the qualified product composite board is accurately focused on the specified thickness, the unqualified product and inferior product are inaccurately focused. The specified 4mm and 5mm focus, but most of them can only focus on 6mm and 8mm. The fluctuation is unstable and the range is too large. This is a point often covered up by producers of inferior products, which is a major misunderstanding of buyers. It can be identified by the line spacing printed test strip provided by the seller.

From the grating equation d(sinα±sinβ)=mλ, it can be known that when the diffraction angle is not too large (such as in the first-order spectrum, when it is close to the spectral normal region), the positions of the spectral lines of different wavelengths are basically equal to their wavelength values. Proportion. Therefore, the arrangement of each wavelength spectral line in the grating spectrum is relatively uniform, and as the wavelength value increases or decreases linearly, the position of the corresponding grating spectral line (such as the distance from the grating normal) also changes linearly.

In the prism spectrum, light of different wavelengths is dispersed due to different degrees of refraction. The refractive index change of the prism material for different wavelengths is not linear with the wavelength. The refractive index of the prism material changes much more in the short-wave direction than in the long-wave region. Therefore, the arrangement of spectral lines in the prism spectrum is not uniform. In the short-wave region, due to the large dn/dλ, the spectral line arrangement is very sparse, while in the long-wave region, due to the small dn/dλ, the spectral line arrangement is very dense. Therefore, for the same wavelength difference, the distance between the corresponding spectral lines is greater at short wavelengths than at long wavelengths. Therefore, we say that the dispersion of prisms in the ultraviolet region is larger than that in the visible and near-infrared regions. Therefore, some UV-Vis spectrophotometers (especially high-end UV-Vis spectrophotometers) use quartz prisms as pre-monochromators, which is the reason.

The arrangement of the grating spectrum is relatively uniform, and the distance between two spectral lines with the same wavelength difference in different wavelength regions does not change much. The evenness of the grating spectrum not only makes the spectrum more tidy and well-proportioned, but also facilitates the preliminary judgment and estimation of the wavelength value of the spectral line during qualitative analysis.

In addition, in terms of the wavelength distribution order of spectral lines, gratings and prisms are also different; in the grating spectrum, the longer the wavelength of light, the greater the diffraction angle value, the more the spectral lines deviate from the grating normal. In the prism spectrum, the longer the wavelength of light, the smaller the deflection angle, and the closer the corresponding spectral line distribution is to the direction of the incident angle.

From the grating equation d(sinα±sinβ)=mλ, it can be known that the first-order (m=1) spectral line with wavelength λ, the second-order (m=2) spectral line with wavelength λ/2, and the third-order spectral line with wavelength λ/3 (m=3) spectral lines...all have the same diffraction angle. That is, βλ, 1=βλ/2, 2=βλ/3, 3=…=βλ/m, m, which is the order overlap of the diffraction grating spectrum. That is, the diffraction grating has spectral lines of different orders and different wavelengths at the same position. When performing high-resolution spectral research or spectral analysis in a wide-band range, the order overlap of the grating spectrum is very obvious, and strong measures must be taken to isolate or filter out the unwanted bands; Monochromators, filters with corresponding wavelength bands, etc. Only in this way can the interference of unnecessary order spectrum be avoided, and the resolution of the UV-Vis spectrophotometer and the accuracy and reliability of the analysis and test data can be ensured.

The spectrum formed by prism dispersion is just arranged into a single spectrum in order of wavelength. The spectrum formed after dispersion by the diffraction angle grating is the sum of all orders of spectrum including m=0, ±1, ±2, ±3.... The same grating can form a series of spectra of different orders at different positions for the same incident composite light; there are symmetrically distributed positive-order spectra and negative-order spectra on both sides of m=0. Therefore, the multilevel of the grating spectrum Subordination is principled, essential, and unavoidable. This characteristic of the grating will cause many corresponding problems in the application of the grating, which will directly affect the ultraviolet.

The spectral resolution and spectral detection of visible spectrophotometers cause difficulties, which must be paid attention to by designers, manufacturers and users of all UV-visible spectrophotometers.