Related to Public Lab spectrometer

Spectrometer primer: http://publiclaboratory.org/tool/spectrometer

Public Lab spectrometer: http://publiclab.org/wiki/dsk

Using Spectral Workbench: http://publiclaboratory.org/wiki/spectral-workbench-usage

General Information

On building a spectrometer:

http://sci-toys.com/scitoys/scitoys/light/cd_spectroscope/spectroscope.html

http://www.swpc.noaa.gov/Curric_7-12/Activity_1.pdf

https://www.youtube.com/watch?v=--GnaivlF9Q

Spectrometry discussion across the web: http://publiclaboratory.org/notes/warren/8-27-2012/spectrometry-discussion-across-web

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.

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/Photon http://en.wikipedia.org/wiki/Electromagnetic_spectrum

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.

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

How does the dispersion element bend (refract) the frequencies of the light beam, and why does it split (disperse) into a spectrum of colors?

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)