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Public Lab is an open community which collaboratively develops accessible, open source, Do-It-Yourself technologies for investigating local environmental health and justice issues.
| 24 | stoft |
July 22, 2013 19:05
| almost 11 years ago
What is a Spectrometer and how does it work ... [ ..... A Work in Progress ..... ] Welcome to this introduction to the science behind PublicLab's DIY Spectrometer Project and to the science of spectrometry in general. Since attempting to describe the entire depth and breadth of these topics is far beyond the scope of these pages, this material is organized progressively to allow the reader to enter the text at their individual comfort level. For those with advanced interests, it is hoped that the related reference links at the end will be of benefit. Please keep in mind that this is, hopefully, a "living document", a "work in progress", to which many have, and will, contribute. Many thanks to all. Energy We live in a world of mass (our physical environment) and energy (visible light, heat, radio waves, sound and all its other forms). The human body can expend energy (to run, play and get up in the morning) and can detect energy in the form of ultraviolet light (when we tan, or sunburn), visible light (the colors of the rainbow) and infrared (as heat), sound waves (speech, music, etc.) and pressure (sense of touch) but not radio waves, x-rays, cosmic rays and the like. All of these are forms of energy which are transmitted through vibrations. The difference between them is how fast the vibrations cycle; their frequency in number of cycles per second. Frequency The span of visible, and near-visible, light energy is of interest because vision is so important to our lives and this range of light frequency, from ultraviolet through infrared is called a spectrum. While ultraviolet light energy has a higher frequency than infrared light, all light travels at the same speed in a vacuum (~300,000,000 meters/sec if you're curious). Yes, the speed of light changes when it enters glass but we'll save that thought for later. [ Aside: Light energy is referenced both as a particle (photon) and a wave (no mass) and both have meaning but in different contexts. For discussions about light colors, wavelengths and spectrometers, we will refer to light as a wave. ] Wavelength Since light energy travels at a fixed speed but is also vibrating at some frequency, the distance from one ripple of an energy wave to the next is directly related to the frequency. When you toss a pebble in a pond, you can see the ripples of energy from the pebble and you can see the distance between them which remain roughly the same as they move. For simplicity, if we assume ripples in a pond always travel at the same speed, like the speed of light as a constant, the closer the ripples are together the higher the frequency. This means that we can talk about either the frequency or the wavelength of light energy as they are directly related. [ Mathematically, they have an inverse relationship where C = 1/Lambda where C is the speed of light in a vacuum and Lambda is the wavelength; both have units of measure in meters. ] Human Vision Our eyes detect only the visible light spectrum; from the deep reds just above infrared to the deep violets just below ultraviolet. Most of us can detect red from blue (except for those with some color deficiency) and we can detect various shades of colors and some color intensity. However, we are not very adept at measuring color or color intensities. In fact, our brains are part of our visual system and we can easily be fooled into seeing colors which are not really there. Ah, but what if we could! That could be fun and now you can -- indirectly -- using a spectrometer. Spectrometers A spectrometer in its simplest form is just an optical device, like a prism, which separates light into separate wavelengths (by frequency) so the amount of light energy at each frequency can be observed -- the light's spectrum. You have probably seen the rainbow colors (visible spectrum) produced by a prism, a sun-catcher or a diamond ring. All of these are primitive spectrometers. What they lack is control over the direction of the incident light and the means to measure and record the energy across the spectrum they display. So, how do they work? Refraction Light travels in straight lines and refraction is the change in direction a "ray" of light resulting from the light wave transitioning between different densities at an angle other then 90 degrees. You've seen this effect when you look into a pool of water or look at a spoon in a glass of water; objects appear "bent" or even "disjointed". When light enters glass, from air, the density of glass is much higher than air so the light refracts and the change in angle of the path of light is dependent on the color (frequency or wavelength). [ Technically, refraction is a result of a decrease in the phase velocity of the light when it enters glass which is why a lens can focus light. ] Since white light, like from the sun, contains a wide spectrum of colors, we see a rainbow of colors from a prism or sun-catcher. Diffraction Another method of separating light waves into separate wavelengths for observation is diffraction. Instead of bending light by changing the density through which the light travels, the wave nature of light can be exploited. If a "narrow beam of light" (where the light "rays" from the light source are all traveling in parallel in a narrow "beam") is directed at a set of parallel-spaced "lines and spaces" the light waves will "add" or "cancel" with each other depending on the wavelength. This behavior is called diffraction and the "set of lines and spaces" is called a diffraction grating or phase grating. The result is similar to a prism in that they both produce a rainbow spectrum. Diffraction gratings have the advantage of being physically thin and often inexpensive. In fact, the PublicLab spectrometers use an inner layer of a common DVD disk as a diffraction grating because of the narrow spacing of the DVD lines which are normally used to hold data. Digital Spectrometers Digital cameras, including computer webcams, contain a silicon imaging sensor chip which converts light energy to electrical voltages and then to digital data which can be recorded and analyzed by computer. By passing light through an inner layer taken from a DVD disk, the light can be separated into its spectrum and a digital camera, like a webcam, can convert that spectrum into computer data. This is what the PublicLab Spectrometer devices are designed to do. They let you indirectly "see" the light spectrum from ultraviolet through infrared and measure the energy at each wavelength -- something more than what your eyes are able to do. However, there is one more required element; light from the source must be directed in a narrow, parallel "beam" at the diffraction grating. The Slit The PublicLab spectrometer, like many spectrometers, is contained within a black enclosure with light only entering through a narrow slit. The slit is a simple and inexpensive method to simulate collimated light; light traveling in parallel lines from a source. Light from the sun, filtered through the leaves of a tree, produces reasonably parallel "collimated" light because the sun appears quite small in the sky. If a light source for the spectrometer is some distance away and must pass through a very narrow slit, then that light will also be reasonably "collimated". However, it is not perfect, so the lens of the webcam is adjusted to focus on the slit. Keeping the slit very narrow (~0.010 inches) improves the resolution (detail) of the webcam output spectrum but there is also less light -- it is a trade-off, but narrow slits are generally beneficial. [....Editing to be continued..... -Dave ] . . . . . . Refraction This slowing down is accompanied by a bending, called refraction, and is why a surface of water appears to shear drinking straws or other objects passing through them. This bending is also proportional to the wavelength: shorter wavelength light refracts greater than longer wavelength light passing through the same material. When the surfaces of the refracting material are parallel, such as an acrylic cube, the wavelengths refract again at the opposite surface and are once again combined at the same angle. But when the surfaces are not parallel, such as an acrylic prism (or a rotated cube), the light is dispersed: longer wavelengths travelling at shorter angles than shorter wavelengths. This is the purpose of the plastic CD piece in our spectrometer: to disperse the incoming light into its component wavelengths. This equal dispersion of light is what we perceive as a rainbow: violet for the shortest wavelengths and red for the longest wavelengths. This means that 'white' light must be an even combination of the entire spectrum: a multitude of frequencies of light all travelling close together. Photons can have a higher energy (and therefore higher frequency and shorter wavelength) than violet light, called ultraviolet, and an energy lower (lower frequency and wider wavelength) than red light, called infra-red. In fact, radio waves are also photons, just on the far 'red' end of the spectrum, with significantly wider wavelengths and therefore lower frequency and lower energy than visible light. Photons exhibit characteristics of a wave but also those of a particle: called wave-particle duality. They will 'bend' and transmit through substances like sound waves, but they can also be absorbed and reflected like individual particles. It's important that we can bend light to disperse it into component frequencies and absorb light (as particles) to collect and measure it in a sensor. http://en.wikipedia.org/wiki/Photon Electromagnetic Spectrum? The Electromagnetic Spectrum is a linear diagram of the various wavelengths of photons. The spectrum is broken up and named into smaller sections. We will be focusing on the piece of the spectrum corresponding to visible photons: the visible spectrum. http://en.wikipedia.org/wiki/Electromagnetic_spectrum What creates the light (photons) in the first place? Nuclear reactions, such as in stars (our sun being the closest) Electrical excitation of noble gasses, such as in sodium lamps LASERs Thermal radiation of high temperature materials, such as a lightbulb's filament or a 'red-hot' piece of metal. If light is usually released at a small number of specific frequencies, why do we usually get entire spectrums of light, instead of specific frequencies like those created by a LASER? Technical References What are the two different types of spectroscopy, and how does the usage of the spectroscope differ? http://en.wikipedia.org/wiki/Fluorescence_spectroscopy http://en.wikipedia.org/wiki/Absorption_spectroscopy Rayleigh scattering in the sun and atmosphere. http://en.wikipedia.org/wiki/Rayleigh_scattering http://en.wikipedia.org/wiki/Optics http://en.wikipedia.org/wiki/Lens_(optics)) http://en.wikipedia.org/wiki/Refraction http://en.wikipedia.org/wiki/Dispersion_(optics)) http://en.wikipedia.org/wiki/Fraunhofer_lines http://en.wikipedia.org/wiki/Chromism http://en.wikipedia.org/wiki/Chromaticity_diagram http://en.wikipedia.org/wiki/Image_sensor http://en.wikipedia.org/wiki/Bayer_filter http://en.wikipedia.org/wiki/Exposure_(photography) |
Revert | |
| 23 | stoft |
July 22, 2013 18:18
| almost 11 years ago
[ ..... Work in Progress ..... ] Energy We live in a world of mass (our physical environment) and energy (visible light, heat, radio waves, sound and all its other forms). The human body can detect ultraviolet light (when we tan, or sunburn), visible light (the colors of the rainbow) and infrared (as heat) and sound waves (speech, music, etc.) but not radio waves, x-rays, cosmic rays and the like. All of these are forms of energy which are transmitted through vibrations. The difference between them is how fast the vibrations cycle; their frequency in number of cycles per second. Frequency The span of visible, and near-visible, light energy is of interest because vision is so important to our lives and this range of light frequency, from ultraviolet through infrared is called a spectrum. While ultraviolet light energy has a higher frequency than infrared light, all light travels at the same speed in a vacuum (~300,000,000 meters/sec if you're curious). Yes, the speed of light changes when it enters glass but we'll save that thought for later. [ Aside: Light energy is referenced both as a particle (photon) and a wave (no mass) and both have meaning but in different contexts. For discussions about light colors, wavelengths and spectrometers, we will refer to light as a wave. ] Wavelength Since light energy travels at a fixed speed but is also vibrating at some frequency, the distance from one ripple of an energy wave to the next is directly related to the frequency. When you toss a pebble in a pond, you can see the ripples of energy from the pebble and you can see the distance between them which remain roughly the same as they move. For simplicity, if we assume ripples in a pond always travel at the same speed, like the speed of light as a constant, the closer the ripples are together the higher the frequency. This means that we can talk about either the frequency or the wavelength of light energy as they are directly related. [ Mathematically, they have an inverse relationship where C = 1/Lambda where C is the speed of light in a vacuum and Lambda is the wavelength; both have units of measure in meters. ] Human Vision Our eyes detect only the visible light spectrum; from the deep reds just above infrared to the deep violets just below ultraviolet. Most of us can detect red from blue (except for those with some color deficiency) and we can detect various shades of colors and some color intensity. However, we are not very adept at measuring color or color intensities. In fact, our brains are part of our visual system and we can easily be fooled into seeing colors which are not really there. Ah, but what if we could! That could be fun and now you can -- indirectly -- using a spectrometer. Spectrometers A spectrometer in its simplest form is just an optical device, like a prism, which separates light into separate wavelengths (by frequency) so the amount of light energy at each frequency can be observed -- the light's spectrum. You have probably seen the rainbow colors (visible spectrum) produced by a prism, a sun-catcher or a diamond ring. All of these are primitive spectrometers. What they lack is control over the direction of the incident light and the means to measure and record the energy across the spectrum they display. So, how do they work? Refraction Light travels in straight lines and refraction is the change in direction a "ray" of light resulting from the light wave transitioning between different densities at an angle other then 90 degrees. You've seen this effect when you look into a pool of water or look at a spoon in a glass of water; objects appear "bent" or even "disjointed". When light enters glass, from air, the density of glass is much higher than air so the light refracts and the change in angle of the path of light is dependent on the color (frequency or wavelength). [ Technically, refraction is a result of a decrease in the phase velocity of the light when it enters glass which is why a lens can focus light. ] Since white light, like from the sun, contains a wide spectrum of colors, we see a rainbow of colors from a prism or sun-catcher. Diffraction Another method of separating light waves into separate wavelengths for observation is diffraction. Instead of bending light by changing the density through which the light travels, the wave nature of light can be exploited. If a "narrow beam of light" (where the light "rays" from the light source are all traveling in parallel in a narrow "beam") is directed at a set of parallel-spaced "lines and spaces" the light waves will "add" or "cancel" with each other depending on the wavelength. This behavior is called diffraction and the "set of lines and spaces" is called a diffraction grating or phase grating. The result is similar to a prism in that they both produce a rainbow spectrum. Diffraction gratings have the advantage of being physically thin and often inexpensive. In fact, the PublicLab spectrometers use an inner layer of a common DVD disk as a diffraction grating because of the narrow spacing of the DVD lines which are normally used to hold data. Digital Spectrometers Digital cameras, including computer webcams, contain a silicon imaging sensor chip which converts light energy to electrical voltages and then to digital data which can be recorded and analyzed by computer. By passing light through an inner layer taken from a DVD disk, the light can be separated into its spectrum and a digital camera, like a webcam, can convert that spectrum into computer data. This is what the PublicLab Spectrometer devices are designed to do. They let you indirectly "see" the light spectrum from ultraviolet through infrared and measure the energy at each wavelength -- something more than what your eyes are able to do. However, there is one more required element; light from the source must be directed in a narrow, parallel "beam" at the diffraction grating. The Slit The PublicLab spectrometer, like many spectrometers, is contained within a black enclosure with light only entering through a narrow slit. The slit is a simple and inexpensive method to simulate collimated light; light traveling in parallel lines from a source. Light from the sun, filtered through the leaves of a tree, produces reasonably parallel "collimated" light because the sun appears quite small in the sky. If a light source for the spectrometer is some distance away and must pass through a very narrow slit, then that light will also be reasonably "collimated". However, it is not perfect, so the lens of the webcam is adjusted to focus on the slit. Keeping the slit very narrow (~0.010 inches) improves the resolution (detail) of the webcam output spectrum but there is also less light -- it is a trade-off, but narrow slits are generally beneficial. [....Editing to be continued..... -Dave ] . . . . . . Refraction This slowing down is accompanied by a bending, called refraction, and is why a surface of water appears to shear drinking straws or other objects passing through them. This bending is also proportional to the wavelength: shorter wavelength light refracts greater than longer wavelength light passing through the same material. When the surfaces of the refracting material are parallel, such as an acrylic cube, the wavelengths refract again at the opposite surface and are once again combined at the same angle. But when the surfaces are not parallel, such as an acrylic prism (or a rotated cube), the light is dispersed: longer wavelengths travelling at shorter angles than shorter wavelengths. This is the purpose of the plastic CD piece in our spectrometer: to disperse the incoming light into its component wavelengths. This equal dispersion of light is what we perceive as a rainbow: violet for the shortest wavelengths and red for the longest wavelengths. This means that 'white' light must be an even combination of the entire spectrum: a multitude of frequencies of light all travelling close together. Photons can have a higher energy (and therefore higher frequency and shorter wavelength) than violet light, called ultraviolet, and an energy lower (lower frequency and wider wavelength) than red light, called infra-red. In fact, radio waves are also photons, just on the far 'red' end of the spectrum, with significantly wider wavelengths and therefore lower frequency and lower energy than visible light. Photons exhibit characteristics of a wave but also those of a particle: called wave-particle duality. They will 'bend' and transmit through substances like sound waves, but they can also be absorbed and reflected like individual particles. It's important that we can bend light to disperse it into component frequencies and absorb light (as particles) to collect and measure it in a sensor. http://en.wikipedia.org/wiki/Photon Electromagnetic Spectrum? The Electromagnetic Spectrum is a linear diagram of the various wavelengths of photons. The spectrum is broken up and named into smaller sections. We will be focusing on the piece of the spectrum corresponding to visible photons: the visible spectrum. http://en.wikipedia.org/wiki/Electromagnetic_spectrum What creates the light (photons) in the first place? Nuclear reactions, such as in stars (our sun being the closest) Electrical excitation of noble gasses, such as in sodium lamps LASERs Thermal radiation of high temperature materials, such as a lightbulb's filament or a 'red-hot' piece of metal. If light is usually released at a small number of specific frequencies, why do we usually get entire spectrums of light, instead of specific frequencies like those created by a LASER? Technical References What are the two different types of spectroscopy, and how does the usage of the spectroscope differ? http://en.wikipedia.org/wiki/Fluorescence_spectroscopy http://en.wikipedia.org/wiki/Absorption_spectroscopy Rayleigh scattering in the sun and atmosphere. http://en.wikipedia.org/wiki/Rayleigh_scattering http://en.wikipedia.org/wiki/Optics http://en.wikipedia.org/wiki/Lens_(optics)) http://en.wikipedia.org/wiki/Refraction http://en.wikipedia.org/wiki/Dispersion_(optics)) http://en.wikipedia.org/wiki/Fraunhofer_lines http://en.wikipedia.org/wiki/Chromism http://en.wikipedia.org/wiki/Chromaticity_diagram http://en.wikipedia.org/wiki/Image_sensor http://en.wikipedia.org/wiki/Bayer_filter http://en.wikipedia.org/wiki/Exposure_(photography) |
Revert | |
| 22 | stoft |
July 22, 2013 08:51
| almost 11 years ago
Spectrometer Curriculum (currently a work in progress) Energy We live in a world of mass (our physical environment) and energy (visible light, heat, radio waves, sound and all its other forms). The human body can detect ultraviolet light (when we tan, or sunburn), visible light (the colors of the rainbow) and infrared (as heat) and sound waves but not radio waves, x-rays, cosmic rays. All of these are forms of energy which is transmitted through vibrations. The difference between them is how fast the vibrations cycle; their frequency in number of cycles per second. Frequency The span of visible, and near-visible, light energy is of interest because vision is so important to our lives and this range of light frequency, from ultraviolet through infrared is called a spectrum. While ultraviolet light energy has a higher frequency than infrared light, all light travels at the same speed in a vacuum (~300,000,000 meters/sec if you're curious). Yes, the speed of light changes when it enters glass but we'll save that thought for later. [ Aside: Light energy is referenced both as a particle (photon) and a wave (no mass) and both have meaning but in different contexts. For discussions about light colors, wavelengths and spectrometers, we will refer to light as a wave. ] Wavelength Since light energy travels at a fixed speed but is also vibrating at some frequency, the distance from one ripple of an energy wave to the next is directly related to the frequency. When you toss a pebble in a pond, you can see the ripples of energy from the pebble and you can see the distance between them which remain roughly the same as they move. For simplicity, if we assume ripples in a pond always travel at the same speed, like the speed of light as a constant, the closer the ripples are together the higher the frequency. This means that we can talk about either the frequency or the wavelength of light energy as they are directly related. [ Mathematically, they have an inverse relationship where C = 1/Lambda where C is the speed of light in a vacuum and Lambda is the wavelength; both have units of measure in meters. ] Human Vision Our eyes detect only the visible light spectrum; from the deep reds just above infrared to the deep violets just below ultraviolet. Most of us can detect red from blue (except for those with some color deficiency) and we can detect various shades of colors and some color intensity. However, we are not very adept at measuring color or color intensities. In fact, our brains are part of our visual system and we can easily be fooled into seeing colors which are not really there. Ah, but what if we could! That could be fun and now you can -- indirectly -- using a spectrometer. Spectrometers A spectrometer in its simplest form is just an optical device, like a prism, which separates light into separate wavelengths (by frequency) so the amount of light energy at each frequency can be observed -- the light's spectrum. You have probably seen the rainbow colors (visible spectrum) produced by a prism, a sun-catcher or a diamond ring. All of these are primitive spectrometers. What they lack is control over the direction of the incident light and the means to measure and record the energy across the spectrum they display. So, how do they work? Refraction Light travels in straight lines and refraction is the change in direction a "ray" of light resulting from the light wave transitioning between different densities at an angle other then 90 degrees. You've seen this effect when you look into a pool of water or look at a spoon in a glass of water; objects appear "bent" or even "disjointed". When light enters glass, from air, the density of glass is much higher than air so the light refracts and the change in angle of the path of light is dependent on the color (frequency or wavelength). [ Technically, refraction is a result of a decrease in the phase velocity of the light when it enters glass which is why a lens can focus light. ] Since white light, like from the sun, contains a wide spectrum of colors, we see a rainbow of colors from a prism or sun-catcher. Diffraction Another method of separating light waves into separate wavelengths for observation is diffraction. Instead of bending light by changing the density through which the light travels, the wave nature of light can be exploited. If a "narrow beam of light" (where the light "rays" from the light source are all traveling in parallel in a narrow "beam") is directed at a set of parallel-spaced "lines and spaces" the light waves will "add" or "cancel" with each other depending on the wavelength. This behavior is called diffraction and the "set of lines and spaces" is called a diffraction grating or phase grating. The result is similar to a prism in that they both produce a rainbow spectrum. Diffraction gratings have the advantage of being physically thin and often inexpensive. In fact, the PublicLab spectrometers use an inner layer of a common DVD disk as a diffraction grating because of the narrow spacing of the DVD lines which are normally used to hold data. Digital Spectrometers Digital cameras, including computer webcams, contain a silicon imaging sensor chip which converts light energy to electrical voltages and then to digital data which can be recorded and analyzed by computer. By passing light through an inner layer taken from a DVD disk, the light can be separated into its spectrum and a digital camera, like a webcam, can convert that spectrum into computer data. This is what the PublicLab Spectrometer devices are designed to do. They let you indirectly "see" the light spectrum from ultraviolet through infrared and measure the energy at each wavelength -- something more than what your eyes are able to do. However, there is one more required element; light from the source must be directed in a narrow, parallel "beam" at the diffraction grating. The Slit The PublicLab spectrometer, like many spectrometers, is contained within a black enclosure with light only entering through a narrow slit. The slit is a simple and inexpensive method to simulate collimated light; light traveling in parallel lines from a source. Light from the sun, filtered through the leaves of a tree, produces reasonably parallel "collimated" light because the sun appears quite small in the sky. If a light source for the spectrometer is some distance away and must pass through a very narrow slit, then that light will also be reasonably "collimated". However, it is not perfect, so the lens of the webcam is adjusted to focus on the slit. Keeping the slit very narrow (~0.010 inches) improves the resolution (detail) of the webcam output spectrum but there is also less light -- it is a trade-off, but narrow slits are generally beneficial. [....Editing to be continued..... -Dave ] . . . . . . Refraction This slowing down is accompanied by a bending, called refraction, and is why a surface of water appears to shear drinking straws or other objects passing through them. This bending is also proportional to the wavelength: shorter wavelength light refracts greater than longer wavelength light passing through the same material. When the surfaces of the refracting material are parallel, such as an acrylic cube, the wavelengths refract again at the opposite surface and are once again combined at the same angle. But when the surfaces are not parallel, such as an acrylic prism (or a rotated cube), the light is dispersed: longer wavelengths travelling at shorter angles than shorter wavelengths. This is the purpose of the plastic CD piece in our spectrometer: to disperse the incoming light into its component wavelengths. This equal dispersion of light is what we perceive as a rainbow: violet for the shortest wavelengths and red for the longest wavelengths. This means that 'white' light must be an even combination of the entire spectrum: a multitude of frequencies of light all travelling close together. Photons can have a higher energy (and therefore higher frequency and shorter wavelength) than violet light, called ultraviolet, and an energy lower (lower frequency and wider wavelength) than red light, called infra-red. In fact, radio waves are also photons, just on the far 'red' end of the spectrum, with significantly wider wavelengths and therefore lower frequency and lower energy than visible light. Photons exhibit characteristics of a wave but also those of a particle: called wave-particle duality. They will 'bend' and transmit through substances like sound waves, but they can also be absorbed and reflected like individual particles. It's important that we can bend light to disperse it into component frequencies and absorb light (as particles) to collect and measure it in a sensor. http://en.wikipedia.org/wiki/Photon Electromagnetic Spectrum? The Electromagnetic Spectrum is a linear diagram of the various wavelengths of photons. The spectrum is broken up and named into smaller sections. We will be focusing on the piece of the spectrum corresponding to visible photons: the visible spectrum. http://en.wikipedia.org/wiki/Electromagnetic_spectrum What creates the light (photons) in the first place? Nuclear reactions, such as in stars (our sun being the closest) Electrical excitation of noble gasses, such as in sodium lamps LASERs Thermal radiation of high temperature materials, such as a lightbulb's filament or a 'red-hot' piece of metal. If light is usually released at a small number of specific frequencies, why do we usually get entire spectrums of light, instead of specific frequencies like those created by a LASER? Technical References What are the two different types of spectroscopy, and how does the usage of the spectroscope differ? http://en.wikipedia.org/wiki/Fluorescence_spectroscopy http://en.wikipedia.org/wiki/Absorption_spectroscopy Rayleigh scattering in the sun and atmosphere. http://en.wikipedia.org/wiki/Rayleigh_scattering http://en.wikipedia.org/wiki/Optics http://en.wikipedia.org/wiki/Lens_(optics)) http://en.wikipedia.org/wiki/Refraction http://en.wikipedia.org/wiki/Dispersion_(optics)) http://en.wikipedia.org/wiki/Fraunhofer_lines http://en.wikipedia.org/wiki/Chromism http://en.wikipedia.org/wiki/Chromaticity_diagram http://en.wikipedia.org/wiki/Image_sensor http://en.wikipedia.org/wiki/Bayer_filter http://en.wikipedia.org/wiki/Exposure_(photography) |
Revert | |
| 21 | stoft |
July 22, 2013 02:44
| almost 11 years ago
Spectrometer Curriculum (currently a work in progress) Energy We live in a world of mass (our physical environment) and energy (visible light, heat, radio waves, sound and all its other forms). The human body can detect ultraviolet light (when we tan, or sunburn), visible light (the colors of the rainbow) and infrared (as heat) and sound waves but not radio waves, x-rays, cosmic rays. All of these are forms of energy which is transmitted through vibrations. The difference between them is how fast the vibrations cycle; their frequency in number of cycles per second. Frequency The span of visible, and near-visible, light energy is of interest because vision is so important to our lives and this range of light frequency, from ultraviolet through infrared is called a spectrum. While ultraviolet light energy has a higher frequency than infrared light, all light travels at the same speed (300,000,000 meters/sec if you're curious). [ Light energy is referenced both as a particle (photon) and a wave (no mass) and both have meaning but in different contexts. For discussions about light colors, wavelengths and spectrometers, we will refer to light as a wave. ] Wavelength Since energy travels at a fixed speed but is also vibrating at some frequency, the distance from one ripple of an energy wave to the next is directly related to the frequency. When you toss a pebble in a pond, you can see the ripples of energy from the pebble and you can see the distance between them which remain roughly the same as they move. Assuming ripples in a pond always travel at the same speed, like the speed of light is constant, the closer the ripples are together the higher the frequency. This means that we can talk about either the frequency or the wavelength of light energy as they are directly related. [ Mathematically, they have an inverse relationship where C = 1/Lambda where C is the speed of light and Lambda is the wavelength; both measured in meters. ] Human Vision Our eyes detect only the visible light spectrum; from the deep reds just above infrared to the deep violets just below ultraviolet. Most of us can detect red from blue (except for those with some color deficiency) and we can detect various shades of colors and some color intensity. However, we are not very adept at measuring color or color intensities. In fact, our brains are part of our visual system and we can easily be fooled into seeing colors which are not really there. Ah, but what if we could! That could be fun and now you can -- indirectly -- using a spectrometer. Spectrometers A spectrometer in its simplest form is just an optical device, like a prism, which separates light into separate wavelengths (by frequency) so the amount of light energy at each frequency can be observed -- the light's spectrum. You have probably seen the rainbow colors (visible spectrum) produced by a prism, a sun-catcher, a diamond ring or the reflection of sunlight off a CD or DVD. All of these are primitive spectrometers. What they lack is only the means to measure and record the energy across the spectrum they display. The along comes the digital camera. Digital cameras, including computer webcams, contain a silicon imaging sensor chip which converts light energy to electrical voltages and then to digital data which can be recorded and analyzed by computer. By passing light through an inner layer taken from a DVD disk, the light can be separated into its spectrum and a digital camera, like a webcam, can convert that spectrum into computer data. This is what the PublicLab Spectrometer devices are designed to do. They let you indirectly "see" the light spectrum from ultraviolet through infrared and measure the energy at each wavelength -- something more than what your eyes are able to do. [....Editing to be continued..... -Dave ] What are the two different types of spectroscopy, and how does the usage of the spectroscope differ? http://en.wikipedia.org/wiki/Fluorescence_spectroscopy http://en.wikipedia.org/wiki/Absorption_spectroscopy Refraction This slowing down is accompanied by a bending, called refraction, and is why a surface of water appears to shear drinking straws or other objects passing through them. This bending is also proportional to the wavelength: shorter wavelength light refracts greater than longer wavelength light passing through the same material. When the surfaces of the refracting material are parallel, such as an acrylic cube, the wavelengths refract again at the opposite surface and are once again combined at the same angle. But when the surfaces are not parallel, such as an acrylic prism (or a rotated cube), the light is dispersed: longer wavelengths travelling at shorter angles than shorter wavelengths. This is the purpose of the plastic CD piece in our spectrometer: to disperse the incoming light into its component wavelengths. This equal dispersion of light is what we perceive as a rainbow: violet for the shortest wavelengths and red for the longest wavelengths. This means that 'white' light must be an even combination of the entire spectrum: a multitude of frequencies of light all travelling close together. Photons can have a higher energy (and therefore higher frequency and shorter wavelength) than violet light, called ultraviolet, and an energy lower (lower frequency and wider wavelength) than red light, called infra-red. In fact, radio waves are also photons, just on the far 'red' end of the spectrum, with significantly wider wavelengths and therefore lower frequency and lower energy than visible light. Photons exhibit characteristics of a wave but also those of a particle: called wave-particle duality. They will 'bend' and transmit through substances like sound waves, but they can also be absorbed and reflected like individual particles. It's important that we can bend light to disperse it into component frequencies and absorb light (as particles) to collect and measure it in a sensor. http://en.wikipedia.org/wiki/Photon Electromagnetic Spectrum? The Electromagnetic Spectrum is a linear diagram of the various wavelengths of photons. The spectrum is broken up and named into smaller sections. We will be focusing on the piece of the spectrum corresponding to visible photons: the visible spectrum. http://en.wikipedia.org/wiki/Electromagnetic_spectrum What creates the light (photons) in the first place? Nuclear reactions, such as in stars (our sun being the closest) Electrical excitation of noble gasses, such as in sodium lamps LASERs Thermal radiation of high temperature materials, such as a lightbulb's filament or a 'red-hot' piece of metal. If light is usually released at a small number of specific frequencies, why do we usually get entire spectrums of light, instead of specific frequencies like those created by a LASER? Rayleigh scattering in the sun and atmosphere. http://en.wikipedia.org/wiki/Rayleigh_scattering http://en.wikipedia.org/wiki/Optics http://en.wikipedia.org/wiki/Lens_(optics)) http://en.wikipedia.org/wiki/Refraction http://en.wikipedia.org/wiki/Dispersion_(optics)) http://en.wikipedia.org/wiki/Fraunhofer_lines http://en.wikipedia.org/wiki/Chromism http://en.wikipedia.org/wiki/Chromaticity_diagram http://en.wikipedia.org/wiki/Image_sensor http://en.wikipedia.org/wiki/Bayer_filter http://en.wikipedia.org/wiki/Exposure_(photography) |
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| 20 | PeterDavidowicz |
July 16, 2013 22:07
| almost 11 years ago
Spectrometer Curriculum (currently a work in progress) What are the basic components of a spectroscope/spectrometer? Light source, diffuse reflector (white 'dull' paper as a background), sample, aperture/polarizing slot, dispersion element (CdRom, diffraction grating), and sensor (webcam). Each of these components can cause interference, deviations from their intended function and therefore the final result, including the light source, sample, environment, dispersion element, and sensor. What are the two different types of spectroscopy, and how does the usage of the spectroscope differ? http://en.wikipedia.org/wiki/Fluorescence_spectroscopy http://en.wikipedia.org/wiki/Absorption_spectroscopy What is light? "Visible light (commonly referred to simply as light) is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight." Light is a stream of photons, also called electromagnetic radiation, within the visible band in the electromagnetic spectrum. These photons carry energy and may be absorbed by substances causing an increase in the average random molecular energy (temperature) of the substance: this is why light feels warm. Particles passing through a specific area over time is known as a flux. Flux may be a count of individual photons or may be a summation of their contained energy. http://en.wikipedia.org/wiki/Light So what are photons? A photon is an individual particle, massless and stable and with no electromagnetic charge, which carries an amount of energy. But this energy is quantized: it only exists as integer multiples of a specific constant, known as planck's constant. A photon vibrates perpendicular to it's path of travel. The number vibrations over a unit of time is the frequency of the photon. This frequency IS the integer multiple that restricts the possible energy levels: energy of a photon equals planck's constant times frequency. A photon's path is sinusoidal due to this constant vibration: it may be graphed as a sine wave dependent on time. The distance peak to peak of a photon's vibration is it's wavelength, and it is inversely proportional to the energy. A photon that carries higher energy must vibrate more and has a smaller wavelength: a higher energy photon has higher frequency and shorter wavelength. Because energy may be substituted with frequency times planck's constant: wavelength equals one divided by (frequency times planck's constant). It's also important to note that a photon may also rotate over time, similar to the path of a screw. It won't be discussed further here, but it's an important concept for polarizing lenses and filters, often used to reduce reflections and glare. ALL photons move at the 'speed of light', about 3.0x10-8 m/s in a perfect vacuum, but slow down when travelling through other substances. This slowing down is accompanied by a bending, called refraction, and is why a surface of water appears to shear drinking straws or other objects passing through them. This bending is also proportional to the wavelength: shorter wavelength light refracts greater than longer wavelength light passing through the same material. When the surfaces of the refracting material are parallel, such as an acrylic cube, the wavelengths refract again at the opposite surface and are once again combined at the same angle. But when the surfaces are not parallel, such as an acrylic prism (or a rotated cube), the light is dispersed: longer wavelengths travelling at shorter angles than shorter wavelengths. This is the purpose of the plastic CD piece in our spectrometer: to disperse the incoming light into its component wavelengths. This equal dispersion of light is what we perceive as a rainbow: violet for the shortest wavelengths and red for the longest wavelengths. This means that 'white' light must be an even combination of the entire spectrum: a multitude of frequencies of light all travelling close together. Photons can have a higher energy (and therefore higher frequency and shorter wavelength) than violet light, called ultraviolet, and an energy lower (lower frequency and wider wavelength) than red light, called infra-red. In fact, radio waves are also photons, just on the far 'red' end of the spectrum, with significantly wider wavelengths and therefore lower frequency and lower energy than visible light. Photons exhibit characteristics of a wave but also those of a particle: called wave-particle duality. They will 'bend' and transmit through substances like sound waves, but they can also be absorbed and reflected like individual particles. It's important that we can bend light to disperse it into component frequencies and absorb light (as particles) to collect and measure it in a sensor. http://en.wikipedia.org/wiki/Photon Electromagnetic Spectrum? The Electromagnetic Spectrum is a linear diagram of the various wavelengths of photons. The spectrum is broken up and named into smaller sections. We will be focusing on the piece of the spectrum corresponding to visible photons: the visible spectrum. http://en.wikipedia.org/wiki/Electromagnetic_spectrum What creates the light (photons) in the first place? Nuclear reactions, such as in stars (our sun being the closest) Electrical excitation of noble gasses, such as in sodium lamps LASERs Thermal radiation of high temperature materials, such as a lightbulb's filament or a 'red-hot' piece of metal. If light is usually released at a small number of specific frequencies, why do we usually get entire spectrums of light, instead of specific frequencies like those created by a LASER? Rayleigh scattering in the sun and atmosphere. http://en.wikipedia.org/wiki/Rayleigh_scattering http://en.wikipedia.org/wiki/Optics http://en.wikipedia.org/wiki/Lens_(optics)) http://en.wikipedia.org/wiki/Refraction http://en.wikipedia.org/wiki/Dispersion_(optics)) http://en.wikipedia.org/wiki/Fraunhofer_lines http://en.wikipedia.org/wiki/Chromism http://en.wikipedia.org/wiki/Chromaticity_diagram http://en.wikipedia.org/wiki/Image_sensor http://en.wikipedia.org/wiki/Bayer_filter http://en.wikipedia.org/wiki/Exposure_(photography) |
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