Helium-Neon Laser

STEP 1: Creating the Excited and Metastable State Bands of He and Ne

Click the "Create He Excited State Band" button to the right of the energy level diagram for Helium. Two excited state bands for He appear in the energy level diagram to the left of the button. On the right side of the screen click the "Create Ne Excited State Band" that appears. Two excited state bands appear in the energy level diagram for Neon. Subsequently, click the "Create Ne Metastable State Band" button that appears just below. Two metastable state bands appear below each of the excited state bands in the Neon energy diagram.

STEP 2: Increasing the Pumping Spectrum Energy

Increase energy of the Pumping Spectrum of Helium by moving the slider at the bottom left corner of the screen. Observe the marker on the vertical scale of Helium energy diagram to move up along the scale as you increase the energy. You must increase the energy at least as high as the lowest excited state of Helium. Then click the "Turn on Pumping Energy" button. Observe the transitions on the energy level diagrams for Helium and Neon. First electrons are excited to from the ground state of He to the excited state of He, as indicated by upward transition lines as well as the darkening of the excited states of Helium to indicate an increase in population of these states. An animation shows the collision between He and Ne atoms and a thick brown horizontal arrow shows the transfer of energy from Helium to Neon. Subsequent transitions from the excited and metastable states of Neon are shown on the energy diagram. The resulting trial spectrum appears directly below the energy diagram, and above the actual spectrum for the He-Ne laser.

STEP 3: Matching trial spectral lines to those of the actual spectrum

To make the trial spectrum obtained in STEP 2 match the real spectrum of the Ne-Ne laser, click the "Edit Properties" button on the left side of the screen just above the Pumping Energy Spectrum. Then using the cursor drag the energy levels of Helium and Neon up and/or down until you feel that the resulting trial spectrum will match the actual He-Ne spectrum.  You may also need to adjust the Pumping Energy spectrum. Finally click the "Turn on Pumping Energy" button and observe the new transitions and trial spectrum of the He-Ne laser as you did in STEP 2.