Spectroscopy is the study of the interaction between matter and electromagnetic radiation. It is a function of the wavelength or frequency of the radiation. In simpler terms, spectroscopy is the precise study of colour from the visible light to all bands of the electromagnetic spectrum. Historically, it was the study of the wavelength dependence of the absorption of visible light that gets dispersed by a prism. Matter waves and acoustic waves are also considered to be forms of radiative energy. Recently gravitational waves are associated with a spectral signature in the context of the Laser Interferometer Gravitational-Wave Observatory i.e., LIGO.


Introduction to Spectroscopy

Primarily spectroscopy is in the electromagnetic spectrum. It is a fundamental exploratory tool in the fields of physics, chemistry, and astronomy. Spectroscopy allows physical structure and electronic structure of matter.  It can investigate at the atomic, molecular and macro scale, and over astronomical distances. Important applications of spectroscopy arise from biomedical spectroscopy in the areas of tissue analysis and medical imaging.

In short, every element or compound has a unique characteristic spectrum. Each compound absorbs and disperses light at a certain range of wavelengths. Thereby, spectroscopy means the dispersion of light into component colours. It is a method to measure how much light is absorbed by a substance and at what is intensity light passes through it.

History of Spectroscopy

Spectroscopy began with Isaac Newton’s optics experiments. According to Andrew Fraknoi and David Morrison, “Isaac Newton described an experiment in which he permitted sunlight to pass through a small hole and then through a prism. Newton found that sunlight that looks white is actually made up of a mixture of all the colours of the rainbow (VIBGYOR).” Newton gave the word spectrum to describe the colours of the rainbow that combine to form white light. These colours are revealed when the white light is passed through a prism.

Later many studies came up which different perspectives by many scientists on spectroscopy.

Types of Spectroscopy

  • Acoustic resonance
  • Time-resolved
  • Photoemission
  • X-ray photoelectron
  • Circular Dichroism
  • Infrared spectroscopy
  • Raman spectroscopy

In spectroscopy, the type of interaction between light and the material:

  • Absorption spectroscopy
  • Emission spectroscopy
  • Elastic scattering
  • reflection spectroscopy
  • Impedance spectroscopy
  • Inelastic scattering
  • Coherent or resonance spectroscopy

Application of Spectroscopy

There are many applications to spectroscopy in many fields such as medicine, physics, chemistry, and astronomy. Taking advantage of the properties of absorbance, it is in use to identify certain states of nature. For instance, it includes:

  • Cure monitoring of composites with the help of optical fibres.
  • To estimate weathered wood exposure times with the help of near-infrared spectroscopy.
  • Measurement of different compounds in food samples by absorption spectroscopy in the visible and infrared spectrum.
  • Measurement of toxic compounds in blood samples is done with the help of spectroscopy
  • Non-destructive elemental analysis by X-ray fluorescence.
  • Electronic structure research with the use of various spectroscopes.
  • Radar to determine the speed and velocity of a distant object is an important application.
  • Finding the physical properties of a distant star or nearby exoplanet with the help of the Relativistic Doppler effect.

FAQs on Spectroscopy

Question 1: Explain Raman Spectroscopy.

Answer: Raman Spectroscopy is a spectroscopic technique. It is in use to analyze vibrational, rotational, and other low-frequency modes in a system. Raman’s spectroscopy is used in the branch of chemistry to deliver a fingerprint by which molecules can be identified. As the name suggests, this spectroscopy is named after Sir C. V. Raman. This relies on the inelastic scattering of monochromatic light that is also called Raman scattering. The energy of the laser photons shifts up and down because of the interaction of the light with the molecules or phonons of an object. This shift of laser photon forms the vibrational modes of an object or system. Advanced types of Raman spectroscopy are surface-enhanced Raman, resonance Raman, tip-enhanced Raman, polarized Raman and many more.

Question 2: How is the classification of methods done in spectroscopy?

Answer: Spectroscopy is a broad field that many sub-disciplines exist. Each sub-discipline has numerous implementations of specific spectroscopic techniques. Different implementations and techniques are classified on the basis of-

  • Type of radiative energy
  • Nature of the interaction
  • Type of material
  • Atoms
  • Molecules
  • Crystals and extended materials
  • Nuclei
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