Optical Spectroscopy

For the experiment instruction – click here


  1. Introduction

  2. Topics of the experiment.

  3. How to prepare to the experiment.

  4. The experimental schedule.

  5. Relevant topics for preparation.

  6. Links

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Optical spectroscopy is a powerful tool for identifying elements by examining the spectrum of their radiation. Because this can be done from a long distance, spectroscopy has many applications in astrophysics. The method is based on the basic principles of atomic physics, and is one of the important experimental evidence of quantum mechanics.

Collection and analysis of a spectrum usually involves:

(1) a source of light (or other electromagnetic radiation).

(2) an element to separate the light into its component wavelengths.

(3) a detector to sense the presence of light after separation of wavelengths.

The device employed to receive light, divide it into its component wavelengths, and detect the spectrum is called a spectrometer.

In this experiment the elements used are:

(1) High voltage gas discharge lamps.

(2) Two-slit, computer controlled spectrometer.

(3) a photomultiplier used as the detector.

Spectroscopy work areas are divided according to the scale of energy / wavelength relative size or scale energy of the measured material physical effect. Radiation frequencies of about 10 GHz will interact with Molecules, a known example for it is at a frequency of 2.4 GHz- microwave absorption of radiation through the method of vibration of the water .

We are engaged in spectroscopy which is measured in optical wavelengths. This area is in the wavelength region of about 8800-400 nm or energies of about 1.6 to 3.1 eV . These energy fields allow the measurement of some of the passages of Electronic energy levels of atoms measured , hence for we deal atomic spectroscopy .

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Topics of the experiment:

How to prepare for the experiment?

1. The basic principles of atomic physics:

§ Atomic Spectra and Atomic Structure – Hertzberg: Ch. 1,2

§ Theory of Atomic Spectra - Condon and Shortley: Pg. 141-147

2. The basic principles of monochromator:

§ Modern Optics - Brown, Earle B: Ch. 8

3. Homogeneous and Inhomogeneous Broadening:

§ Fundamentals of Photonics - Saleh,Bahaa E.A, Teich Malvin Carl B: Ch. 12.2 D -Line Broadening.

4. Mass Ratio of the Deuteron and Proton from the Balmer Spectrum of Hydrogen:

§ Mass Ratio of the Deuteron and Proton from the BalmerSpectrum of Hydrogen

5. Atomic Spectrum of Helium:

§ Helium spectrum experiment (N. Abramzon, N. and Siegel, P. B., American Journal of Physics, 77, 920-922 (2009))

6. Quantum Defect Theory:

§Luke, K. L., George, S., & Tucker, A. W. (1974). Quantum Defect and Fine Structure in the Arc Spectrum of Rubidium. American Journal of Physics, 42, 400.

7. Study the experimental equipment:

§ Monochromator - click here

§ High voltage gas discharge lamp.

§ Photomultiplier.

The experimental schedule:

  1. A pre-experiment meeting – getting to know the system.

  2. Written exam - Approximately one hour.

  3. Calibration of the spectograph.

  4. Measurement of Various lamps and quantum effects

Relevant topics for preparation

0. Atomic structure:

1. Bohr model.

2. Atomic transition.

3. Spontaneous emission.

4. Selection rules.

5. Dublet/Triplet phenomena.

6. Doppler Broadening.Homogeneous/Unhomogeneous Broadening.

7. Lorentzian and Gaussian contour of spectral lines.

8. Quantum defect.

9. Exchange term in atom of Helium.

10. Pauli principle.

11. Monochromator:

12. Diffraction.

13. Wavelength Dispersion.

14. Grating equation.

15. Resolution.


Overview of Atomic Spectroscopy

NIST Atomic Spectra Database

Quantum Defect description

Spectral Resolution

Simultaneous Calibration