Spectroscopy Explained

The first image that pops up into your mind when you hear the word “waves” is probably not electromagnetic waves. However, electromagnetic waves –which are carrying electromagnetic radiant energy or, simply, light– are the reason you can see when you look around. Let’s discuss spectroscopy: the relationship between light and matter.

Historically, what led to the development of spectroscopy is Newton’s prism experiment. Imagine a dark room with its shutters closed, and a single hole is drilled into the shutters. That is what Newton did, to let only one beam of sunlight into the room. Inside the room, he had a glass prism that the beam passed through (1). What was created in return was the color spectrum. Stemming from the findings of previous scientists as well as Newton, Bunsen and Kirchhoff were the ones to identify the material burning by reflecting the flames through a prism in order to examine the spectra it would provide(2). They soon realized that the light lines in the emission spectra had the same wavelengths as the dark lines of the absorption spectra when the materials used were the same(3). With that, Kirchhoff’s law of thermal radiation was born, which basically states that in thermal equilibrium, the power of light absorbed and the power of light emitted, in the same wavelength and temperature, are equal.


Hydrogen Absorption and Emission Spectra, Image Source: Khan Academy


By understanding that materials have certain impacts on the spectrum, Kirchhoff and Bunsen started to use this technology for investigating the composition of materials: spectroscopy.


Spectroscopy is used in many fields, ranging from medicine to astronomy. Spectroscopy is divided into branches depending on the wavelength region used for it, the interaction, or the type of material studied (4).


For example, in astronomy, spectroscopy can be used to understand the composition of objects, or even their speed, and how they produce light(5). For example, it can help determine the elements a star is composed of, along with its temperature and density, by using spectroscopy. The changes in the lines observed in the spectra can explain what is happening to the object, such as physical changes or changes in its composition.


Let’s take a look at another example in which spectroscopy is used: Forensics. Forensics uses scientific techniques or methods in the investigations regarding civil and criminal law(6). Spectroscopy doesn’t necessarily affect samples, thus, it doesn’t require the evidence to be transported from the scene, etc. Spectroscopy can be used to determine whether bodily fluids or body tissues contain traces of intoxication(7). The method can also be used in the analysis of unknown substances found. Thus, in forensics, spectroscopy is used in drug testing and inspection of unknown substances.

Overall, spectroscopy is used in a variety of areas to help us identify and analyze substances. Is it not interesting that radiation energy can help us differentiate materials?


Works Cited

(1) Molecular Expressions: Science, Optics and You — Newton’s Prism Experiment — Interactive Tutorial, micro.magnet.fsu.edu/primer/java/scienceopticsu/newton/.


(2) “Robert Bunsen and Gustav Kirchhoff.” Science History Institute, 20 May 2021, www.sciencehistory.org/historical-profile/robert-bunsen-and-gustav-kirchhoff.


(3) “Robert Bunsen and Gustav Kirchhoff.” Science History Institute, 20 May 2021, www.sciencehistory.org/historical-profile/robert-bunsen-and-gustav-kirchhoff.

Kirchhoff’s Law and Emissivity, spie.org/publications/tt48_154_kirchhoffs_law_and_emissivity?SSO=1.

“The Era of Classical Spectroscopy.” MIT Spectroscopy Lab — History, web.mit.edu/spectroscopy/history/history-classical.html#:~:text=Foucault%2C%20the%20French%20physicist%2C%20observed,together%20in%201859%20by%20G.


(4)Maloney, Post author By Jessica. “5 Different Types of Spectroscopy.” Platypus Technologies, 1 Oct. 2021, www.platypustech.com/5-different-types-of-spectroscopy.


(5) “Spectra — Introduction.” NASA, NASA, imagine.gsfc.nasa.gov/science/toolbox/spectra1.html#:~:text=The%20science%20of%20spectroscopy%20is,fast%20the%20material%20is%20moving.


(6) “Forensic Science.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., www.britannica.com/science/forensic-science.


(7) 2020, Ben Pilkington, Nov 20. “How Is Spectroscopy Used in Forensics?” AZoOptics.com, 20 Nov. 2020, www.azooptics.com/Article.aspx?ArticleID=1876.

Robertson, Sally. “Mass Spectrometry as a Tool in Forensic Science.” News, 24 May 2019, www.news-medical.net/life-sciences/Mass-Spectrometry-as-a-Tool-in-Forensic-Science.aspx.


Image: “Absorption Spectrum (Emission Spectrum Lines) (Article).” Khan Academy, Khan Academy, www.khanacademy.org/science/class-11-chemistry-india/xfbb6cb8fc2bd00c8:in-in-structure-of-atom/xfbb6cb8fc2bd00c8:in-in-bohr-s-model-of-hydrogen-atom/a/absorptionemission-lines.

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