Research at UAF - Doppler free saturated absorption atomic spectroscopy using tunable diode lasers

Principal Investigator:
Dr. Yasir Jamil, Assistant Professor, Department of Physics, University of Agriculture, Faisalabad
Phone: 041-9200109

Duration of the Project: 03 years
Cost of the Project: Rs. 4.3 Million
Funding Agency: Higher Education Commission of Pakistan

Progress Reports



The absorption spectra in traditional linear spectroscopy are characterized by broad signal around each absorbed frequency, despite the fact that atoms can only absorb specific frequencies. The frequency of radiation in frame of atoms is different from the frequency in laboratory frame. By sending a pump beam through the sample in the opposite directions as probe beams, the resonant frequency can be precisely determined. This is known as saturated absorption spectroscopy because tuning the laser above or below a resonant frequency will cause saturation of atoms moving in certain directions. This will result in the precise determination of the fine and hyperfine splitting of the atomic energy levels. Using these measurements, the analysis of various samples will be performed. The monitoring of environment will be done and an effective method will be proposed for the analysis of various samples. The technique will further be used in future to trap atoms of alkali metals for high resolution precision spectroscopy.

Problem statement

The line broadening in conventional spectroscopy is a major concern as it limits the resolution. The Doppler-free signal is given by subtracting the two probe beams, which get rid of their common Doppler broadened absorption and gives the difference caused by probe beam. It is important that the probe beam is going in the opposite direction of the pump beam, which means that it generally interacts with different atoms than the pump beam due to Doppler effect. Subtracting the crossed beam signal from unaffected probe beam signal will result in sharp peaks at resonant frequencies. The linewidth of each peak in Doppler free signal is theoretically limited by the Heisenberg uncertainly principle. However, experimentally it may be the band width of diode laser which limits the linewidth.
The saturated absorption spectroscopy set up will be valuable for high resolution spectroscopy. It will be used to make precise measurement of hyperfine structure of excited states of alkali atoms. The gas concentration in different samples will also be measured. This technique will be applied to examine the atmospheric gas concentrations.

Objectives of the Project:

  1. Development of a grating stabilized diode laser based light source for use in spectroscopy
  2. Setting up of a Doppler free saturated absorption spectrometer for measurement of hyperfine splitting of energy levels
  3. Efficient use of indigenously available materials and expertise to develop a scientific system.
  4. Development of expertise in the technique and training of manpower in this area


Diode laser will be used to carry out the spectroscopy of atoms of rubidium. The technique of saturated absorption spectroscopy will be utilized to study the lines with resolution beyond the Doppler limit. This will enable to measure the hyperfine splitting of the excited states. The absorption spectra in traditional linear spectroscopy are characterized by broad signals around each absorption frequency, despite the fact that the atom can only absorb at specific frequencies. The feedback from diffraction grating will be used to get a very narrow line width.

The project is in initial stage. Purchase of equipment is in progress.