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simple spectroscope home. - I -

AND RESEARCH WORKSHOP.

Unraveling the mysteries of light.

Long ago I had the wonderful experience of having a small grating which came in a scientific journal youth with a cardboard box to make a spectroscope. Be fascinated by the invention and the ghosts that I saw and since then I had the pleasure of having a diffraction grating to experiment. Today

young curious, inventive and science enthusiasts have at their disposal a vast amount of scientific and technological materials to develop their large and small projects that only last about 30 years ago it was almost impossible to get them as if diffraction gratings and lasers to name a few.

We are in continuous contact with diffraction gratings without being aware of it, I mean CDs or CD and DVD. Looking at the back of a CD or DVD quickly realize the multitude of flashing multiple colors like a rainbow appearing in it. The cause of these is that both CDs and DVDs are "saved" with thousands of lines or lines per linear inch which generate and promote the diffraction of light, creating the rainbow.
decomposition of white light in their respective colors through a prism has always surprised people, their color and brightness are such that one simply becomes fascinated by the spectacle. However, beyond the sensory fascination that makes us the spectrum, he carries a subtle message about the origin and composition of the source.

of 1,669 in the year Isaac Newton opens the way to decrypt the information contained in light to make the first experiments with an analytical focus on the breakdown of white light into rainbow colors to be refracted through a crystal-shaped triangular prism. During their experiences Newton did not realize that the solar spectrum was not continuous. It was 145 years after Joseph Fraunhofer who observes dark lines in the solar spectrum to build what would be the first spectrograph. Fraunhofer calculated frequencies of these lines and identifies but does not know the origin of them. 45 years later Gustav Kirchhoff and Robert Bunsen repeated experiences of Fraunhofer. Using the "Bunsen burner" notes that the gases released by burning substances originated bright lines that were located in the same position in the solar spectrum from Fraunhofer dark bands and realize that each element has its "footprint" spectrographic identifies it. Kirchhoff showed that the bright lines became dark when white light passed through a cold gas.

With these discoveries came the chemical spectroscopy has been useful in chemistry and in astronomy, earth, enabling man to discover the chemical composition of stars and other astronomical bodies.
The diffraction of light is also an interesting phenomenon through another mechanism very different from the refraction is able to break white light into its colors.

In this issue we will work to make a simple spectroscope diffraction by transmission from a CD. I mean simple for their optics and collimating lens will not focus or objective. Although it does not make a strictly scientific instrument that allows us to measure the angles of diffraction, goes beyond a toy and is good enough to allow us to witness lines and Fraunhofer absorption or emission lines of some common light sources. Obviously, their didactic power goes beyond a simple practical implementation.

The image below shows the components of homemade spectroscope.

grating

The diffraction grating made from the CD, can be a blank CD or a discarded used, it must be free of scratches.

A CD is etched with a spiral groove width of 0.6 microns apart between groove and groove of 1.6 mm. The presence of the spiral groove of the CD makes an excellent grating readily available.

diffraction of light occurs when the light wave front collides with a border or pass through a thin slit. This phenomenon is known as "the bending of light around an obstacle." It is the same mechanism as presented in the waves when intercepting a barrier and hence the physical demonstration of the wavelike behavior of light. To make our

grating have to remove the layer of platinum CD and we can do by two methods, one method involves making a cut plating on the side of an "accurate" by the edge (about 1 mm from the edge of the disc) following the curvature of the CD, you'll notice as the silver foil begins to separate from the CD. Carefully start the paper to avoid scratching the surface of transparent polycarbonate. Cutting edge

platinum.

To avoid scratching the CD with a release paper layer platinum.


CD without the platinum layer.

The other procedure involves cutting the CD with the exact dimensions of the grating that want, to do this, the platinum layer is released by the cutting edges and can be withdrawn easily.

The device that we are manufacturing the diffraction grating is square with dimensions of 33 x 33 mm. Cutting the CD to the diffraction grating must be aligned so that the resulting diffraction lines are ordered according to the faces of the square. The photo below shows the diffraction generated by the rows and "alignment" with the faces of the square.

We observe that the colored bands take the fan settings because of the striped circular (spiral) recorded on the CD. We are interested know which side of the square is the wide part of this range of diffraction, since in our spectroscope we put the diffraction grating so that the range (the wide part) is facing downward in order to observe the larger rainbow generated by the diffraction grating we have built.

Cutting the CD determines the width of the tube we need to manufacture the aircraft. As the net used is a square tube spectroscope will also square.

MASK:

The purpose of the slot mask is to prevent stray light and allow the passage of a narrow beam of light parallel to the diffraction grating as a collimator (slit collimator), with this greatly improves the spectrum produced by the diffraction grating. The distance from the collimating slit to the diffraction grating is 300 mm, which is the focal length of a normal eye. Such a gap determines the length of the inlet pipe of light.

The collimating slit mask with the will of the carton from a cereal box, the window width is 1 mm x 33 mm long, the figure below shows the template for the mask.

is important that the collimator slit is parallel to "scratch" on the CD. With this we get a rainbow instead of a long narrow. The slit substantially improves the image of the spectrum.

observe a defect in our spectroscope, the slit is narrow because it makes the effect of partially reproducing the camera obscura (blurred) images of the luminous objects we are looking over the diffraction grating.

TUBE:

our spectroscope tube is manufactured from cardboard building models of 2 mm thick.
To determine the deflection angle eyepiece that has the tube with respect to admission we will rely on the formulas of the phenomenon of diffraction, in which the diffraction angle is determined by the value through the diffraction angles of wavelengths in the visible spectrum ends.

The following expression defines the diffraction angle (θ) which undergoes a light beam passing through a diffraction grating:

Sen (θ) = m × λ / d

Where:

θ = diffraction angle the optical axis.
λ = wavelength radiation (light).
d = constant of the diffraction grating. (Separation between line and line of the network)
m = diffraction order. In our case the first order, m = 1 to obtain a bright spectrum resolution change.

The visible spectrum ranges from wavelengths of 0.4 microns to 0.7 microns purple and red for approx. Our

grating made from a CD has a lattice constant of 1.6 mm, which corresponds to 625 lines per millimeter.

With these values \u200b\u200bof wavelength, of the constant of the network and use the first order diffraction, we can determine the diffraction angles extremes

For Violet, θ = 14.5 º

For the Red θ = 25.9 º

The average angle between the two colors we determine the deflection or tilt of the eye tube Admission to the tube, the average angle is 20.2 °, angle that corresponds very closely to the color yellow.

eyepiece tube length determined according to the "W" that we have of the rainbow. In this project, the observed width of the rainbow is 20 mm.

The value of dispersion that allows for grating on both ends of the visible spectrum is 11.4 º (red angle less the angle of purple). We can construct a triangle with adjacent side equal to the length of the eyepiece sought, the opposite leg equal to half the width of the rainbow searched (10 mm) and angle between the hypotenuse and the opposite leg is equal to half the angle covered by diffraction (11.4 °).

Hence the length is defined by: L = 10/Tg

(7.2 º)

eyepiece Length: 100 mm.

With all the information gathered can make templates with the dimensions for the manufacture of body construction with cardboard spectroscope. The figures show the templates.

Endcaps.

top cover.

lower lid.

lines labeled "line cutting "in the templates refer to places where there will be a shallow cut does not pass through the cardboard, about 1 mm deep to allow bending of the upper and lower according to the contour of the end caps.
The images below show the assembly procedure of the spectroscope. Mascara

glued the cardboard cereal box.

mask with slit cut.


template attached to the cardboard end cap of 2 mm thick.


Tapas cut.


Hitting
side cover and bottom cover.

Braces diffraction grating. These brackets are made from small strips of cardboard. This realization arises from the need to put the rack does not attach it to cardboard.

placing the network supports the other end cap. Care should be taken that the support is in the same place as in the other lid so that the network is as straight as possible.

Middle
spectroscope body assembly.


To avoid internal reflection in the intake tube and eye, the inside walls painted black


is important to completely close before the spectroscope, that the range of diffraction is the wide part down.


home Final appearance of low-resolution spectroscopy.

finished with the spectroscope we can make our first observations in the field of spectroscopy and enjoy the beautiful lines of color.

As mentioned above, our spectroscopy is playing some pictures, which clouds our a bit the resulting spectrum and to avoid this phenomenon is very strong when we are watching the solar spectrum (Not to be strongly dazzled, avoid looking directly at the Sun with the spectroscope), point the spectroscope at a smooth white wall directly illuminated by the Sun and there we will see the rainbow of colors formed by refraction of white light. You will notice immediately that the spectrum is not continuous, but presents some dark bands, the more pronounced is orange. I could have a pretty defined six time as many weak and poorly defined by the poor optical device. Two very narrow bands in the red, one in dark red border to another more or less in the center. Two very weak bands in the green as the color center, one in blue and one purple.

The images below are some simple spectra to locate. I must warn, that the photographs of the spectra have a very poor and even regrettable in terms of brightness, color purity and resolution. The manual exposure and sensitivity were in ASA 400, and that sets the camera on automatic and continuous spectra appear as no details. On the other hand is readily apparent in the photographs that the surface of CD (diffraction grating) is very scratched, detail that was not seen as sharp to the naked eye. That is why the When choosing the CD to make our spectroscope we must be very careful handling, because despite the clear plastic that is "resistant" to scratch, it is marked with relative ease.

The picture (mirror image) below shows the solar spectrum can be observed the presence of Fraunhofer bands.

Pictured (solar spectrum) can be observed following other absorption lines, particularly in the green.

The next picture shows the spectrum of an incandescent lamp. Here we can see that the spectrum is continuous. The spectra are continuously generated by incandescent solids, there are no absorption bands or emission.

The next spectrum corresponds to a light bulb "low consumption", which are very similar to fluorescent lamps.

This is a spectacular spectrum of emission, the emission spectra is produced by ionized gases and vapors (incandescent). In principle, according to the brightly colored bands could be determined roughly gaseous compounds low-energy bulb.

The following image corresponds to the emission of a lamp fluorescent.

Comparing both spectra we can see a difference between the components of the fluorescent lamp and low power consumption. The fluorescent lamp light has two very strong bands in the green and indigo, in addition a weak band in the yellow (not pictured and instead is a thin green line on the border with orange, this is another problem obtained the photos, the colors do not match exactly as perceived by the eye). Bands also appear in the low-energy bulb, but also shows a bright band in the red. The mixture of colors gives the impression of white light. In the fluorescent, also observed the bright lines superimposed on a continuous spectrum is generated by the inner lining of the fluorescent lamp tube.

The image shows the two spectra where one can see clearly the differences.

Interestingly, also the lamps high pressure mercury lighting system in addition to the high sodium and low pressure, the spectra are really interesting, particularly with high pressure sodium lamp pressure (unfortunately I could not get a picture) that this spectrum can clearly see the double line feature of sodium in yellow.

Despite the deficiency of the photos, put them to try to stimulate the reader to your machine is built and awaken curiosity.