A neon lamp consists of a glass tube filled with low-pressure neon gas and an electrode at each end.
1. A high voltage transformer puts lots of charge on the electrodes at either end of the tube. How is the discharge started?
2. After the discharge is started, electrons can collide with neon atom. Describe the three types of collisions that can occur.
3. In the discharge there are both positive ions and negative electrons. The lightweight electrons carry most of the current, but ions are necessary to keep the discharge going. What would happen to a ball of electrons created at the negative electrode as it traveled toward the positive electrode if there were no ions present?
4. The neon atoms in the discharge mostly emit red light. In order to produce a more white light you might consider coating the inside of the tube with phosphors that emit blue light. Why won't these phosphors convert the red light emitted from the neon atoms into blue light?
A neodymium:YAG laser (YAG is short for the crystal yttrium aluminum garnet) is typically optically pumped and produces infrared light at 1064 nanometers.
5. Often the pump light is produced by a high-pressure flash lamp, which is a discharge lamp that is pulsed on for a very brief time. These lamps produce a broad spectrum of visible light. Explain why any infrared light, with a wavelength longer than 1064 nm, does not contribute to pumping of the neodymium ions.
6. Neodymium ions absorb only a few discrete frequencies of visible light. Recently it has become popular to use diode lasers as a source of pump light. The diode lasers are designed to emit a narrow band of colors near 808 nm, which matches one of the strongest absorption lines of the neodymium ions. Compare the efficiency of diode laser pumping to flash lamp pumping.
7. Often it is desirable to produce visible light with the neodymium:YAG laser. This can be done by sending the infrared light pulse at 1064 nm through a special crystal. The crystal can combine a pair of infrared photons into a single green photon at 532 nm. Compare the energy of an infrared photon that enters the crystal to the energy of a green photon that exits the crystal.
8. If you shine the green light from this laser onto a thin soap film, what pattern of light would you observe reflected from the film. Assume that the film is suspended on a loop of wire that is oriented vertically (the loop is in a vertical plane).