Examples of Investigations and Measurments

Resonator geometry (A)
After the initial adjustment has been done, all components which are not needed are removed from the set-up. Through the modification of the resonator length, the stability criteria is verified. The beam diameter within the resonator is measured by means of a simple vernier calliper gauge for different laser mirrors verifying the theory of Gaussian beams inside an optical resonator.

Single mode etalon (B)
The element is needed to create laser emission of high coherence and narrow bandwidth. The understanding of the etalon€˜s function requires the discussion of the inhomogeneous amplification profile of the Neon and its Doppler broadening, the resonator modes, the finesse of a Fabry Perot resonator and their mutual relations. The orders of the single mode etalon can be observed experimentally. By means of an optical spectrum analyser (like the EXP-03) the phenomena can be represented in an impressive way. By a slight tilting of the etalon the selected mode €žis shifted€œ under the gain profile and additional information with regard to the gain profile can be obtained.

Littrow prism (D)
The classical selection element is tested and the special profile of the Littrow prism in conjunction with the Brewster€˜s angle is discussed. It is shown that, contrary to the birefringent filter, only two lines can be selected, the dominant red main line at 632 nm and the orange line at 611 nm. The student experiences that the main line follows an adjustment of the prism in the resonator until its amplification decreases which prevents the oscillation of neighbouring narrow lines.

Line selection
This experiment enhances the understanding of the participating atomic energy levels, population inversion and supplies comprehensive basic knowledge with regard to crystal optics, Brewster€˜s angle and amplification of a lasing medium. By means of the provided birefringent filter (C), a total of five visible lines can be selected. The significant influence of the discharge current on the output power is measured and discussed with special accent on the weak lines.