OPTICAL SPECTROSCOPY By Owen Massey Spectroscopy is a

OPTICAL SPECTROSCOPY By Owen Massey

Spectroscopy is a wide field that studies the interactions between light and matter. WOAH

HISTORY OF OPTICAL SPECTROSCOPY

History of Spectroscopy: Newton ■ Rainbows, a clear example of the spectral nature of light, have been around for all of human history ■ It wasn’t until 1666, however, that Isaac Newtown first demonstrated and understood that white light being dispersed through a prism created a spectrum of different colors ■ “Ghost” = spectrum ■ “Watcher” = scopos ■ Spectroscopy = “ghost watcher”

History of Spectroscopy: Herschel ■ In 1800, William Herschel made another important discovery that established the basis for modern spectroscopy ■ While measuring the temperature of each color of the spectrum, Herschel placed a thermometer outside the spectrum as a control, expecting it to read room temperature ■ To his surprise, the temperature of his “control” thermometer rose even higher than thermometers measuring the other colors. He had discovered infrared light, and the fact that most light is not within the visible spectrum

History of Spectroscopy: Fraunhofer ■ The next main discovery in spectroscopy was made by German scientist Joseph Fraunhofer ■ Fraunhofer discovered in 1814 that the sun’s spectrum, when sufficiently dispersed, was crossed by a large number of fine dark lines, now known as Fraunhofer lines. Although he had first discovered and documented these lines, he was never able to determine their origin or meaning ■ He also discovered that “diffraction grating” rather than a glass prism, could be used to create diffraction of light with more consistent results than using glass

History of Spectroscopy: Kirchhoff ■ It was not until 1859, 33 years after Fraunhofer’s death, that Gustav Kirchhoff discovered the significance of these lines ■ Kirchhoff determined that each element and compound has a unique spectrum of lines. This was an enormously important discovery, as it meant that an unknown object or gas’s chemical makeup could be accurately determined just by studying the light passing through it. ■ This idea was the final monumental step towards creating modern Spectroscopy

HOW DOES SPECTROSCOPY WORK?

How does it work? : Electromagnetic Spectrum ■ Visible light actually only consists of about 0. 0035% of the light on the electromagnetic spectrum. ■ The rest has a wavelength that is either too long or too short for our feeble eyes to detect. This being said, spectroscopy instruments primarily measure from infrared through ultraviolet.

How does it work? : Two Main Methods

How does it work? : Continuous Spectrum ■ When a star or any light source emits light, it is initially emitted in a full continuous spectrum. This means that no Fraunhofer lines are initially present in light emitted from any source. ■ A continuous spectrum however, is very rare in nature, since passing through matter and gas in the atmosphere will cause Fraunhofer lines to appear. ■ Light emitted in a vacuum with no gaseous medium, however, would in theory create a full continuous spectrum if observed with a spectrometer also inside of the vacuum

How does it work? : Absorption Spectrum ■ One of the two main ways a spectrometer works is by analyzing the absorption spectrum coming off of an Earthly or celestial object or gas ■ When light of a known wavelength goes through the gas of a nebula, or even the atmosphere of a star or planet, specific wavelengths of light are absorbed by the elements within the gas. This creates the dark lines that Fraunhofer observed for the first time over 200 years ago! ■ Different chemical makeups create unique absorption spectral patterns, meaning that a careful analysis of the spectrum coming from a light source can reveal what it is made out of

How does it work? : Absorption Spectrum

E C N E I C S How does it work? : Absorption Spectrum

How does it work? : Emission Spectrum ■ The other main way spectrometers work is by studying the emission spectrum ■ When a gas or object absorbs light coming from a light source, it is re-emitted in all directions at the specific wavelengths that it absorbed that again depend on the chemical makeup of the matter ■ This means that if light is shot at or into a material, the emission spectrum can tell you exactly what the material is made out of, awesome!

How does it work? : Emission Spectrum

How does it work? : Doppler Effect ■ The last way that spectroscopy can help us understand our universe is by taking advantage of the Doppler effect ■ By measuring if a distant objects spectral pattern is red or blue shifted, its velocity towards or away from the viewer can be determined!

THE USES OF SPECTROSCOPY

Uses of Spectroscopy: Astronomy ■ The uses of spectroscopy in Astronomy and Astrophysics are endless. To begin, spectroscopy can help us determine the temperature, density, chemicals present, and even magnetic field present in distant celestial objects ■ This has been, and is likely to increasingly continue to be of extreme usefulness and importance in the future as it will greatly aid us in the search for extra terrestrial life, asteroid mining, finding habitable exoplanets, and in determining if the Earth is on a collision course with a pointy celestial object.

Uses of Spectroscopy: Mining ■ Spectrometers help mining companies identify how much of a certain mineral is in the ore that they are mining so that they can make the refining process more efficient

Uses of Spectroscopy: Food and Beverage Regulation ■ Food and beverage regulation administrations like the FDA can use spectrometers to easily make sure that no dangerous chemicals or toxic metals are present in a product before it is allowed to hit the shelves

Uses of Spectroscopy: Medicine ■ There is currently much research into studying if spectrometers can help with pathogen identification and biomedical screening ■ For instance being used to identify cancerous cells by looking at the chemical make up of these cells compared to the rest

Sources: Tyson, Neil De. Grasse. Astrophysics for People in a Hurry. New York, NY: W. W. Norton, 2017. N. pag. Print. Serway, Raymond A. , and John W. Jewett. Physics for Scientists and Engineers. Belmont, CA: Thomson-Brooks/Cole, 2008. Print. Hind, Andrew S. "An Introduction to Optical Spectroscopy. " Optical Astronomical Spectroscopy(n. d. ): n. pag. Web. 01 June 2017. Khan, Salman A. "Spectroscopy: Interaction of Light and Matter (article). " Khan Academy, n. d. Web. 01 June 2017. "The Era of Classical Spectroscopy. " Massachusetts Institute of Technology. MIT, n. d. Web. 01 June 2017. Information@eso. org. "Spectroscopy. " ESO. N. p. , n. d. Web. 01 June 2017. "Optical Spectroscopy. " Geophysical Laboratory. N. p. , n. d. Web. 01 June 2017.