 |
| Ruby Laser |
|
| In 1960, T .H. Maiman constructed the first laser using a Ruby crystal. |
| |
| Ruby is a crystalline form of silica(Al2O3) with a slight natural doping of chromium. It has the following advantages for being used as a laser. |
| |
| (i) It is a solid having suitably arranged energy levels. |
| |
| (ii) It is paramagnetic ("slightly magnetic"), This is due to the presence of chromium atoms which have unpaired electron spins (just like ferrites). The atoms are capable of being aligned with a magnetic field. This permits not only re-radiation of energy from atoms in the desired direction but also some tuning facilities. |
| |
| Active material is a small cylinder of pink synthetic ruby, about 0.5 cm in diameter and few centimeter long. Ruby contained 0.05% of chromium, imparting a pink look to the crystal. |
| |
| Two parallel mirrors are used, one fully silvered and the other partly so as to enable the coherent light radiation to be emitted through that end. The mirrors must be parallel to a high degree of accuracy and must be separated by a distance that is an exact number of half- wavelength apart (in the ruby, at the desired frequency). Such an arrangement is called a Fabry-Perot resonator. |
| |
| Pumping process is carried with the help of flash tube. The spiral flash tube pumps light energy into the ruby in pulses, which are generated by the charge and discharge of a capacitor. |
| |
 |
| |
| Basic ruby pulsed laser |
| |
| Cooling is used to keep the ruby at a constant temperature, since quite a lot of the energy pumped into it is dissipated into heat, instead of being radiated as coherent light. Although this cooling also helps laser action, room temperature operation is normal. |
| |
| Practically no noise is added to the amplified signal. This is because there is no resistance involved and no electron stream to produce "shot noise". |
| |
| Chromium atoms are excited due to the pumping and raised to higher energy state H. The excited atoms return to the lower state L from higher state H in two steps. First they return to metastable state M. This transition is non-radioactive and energy of this transition is passed to the crystal lattice as heat. The chromium atoms that returned to M level can remain in this state for several milli-second. Thus, the accumulation of coming excited atoms at M level increases its population and then transition occur from M to L level emitting out photons. Emission is significant. Stimulated emission starts. Photons traveling parallel to the axis of the tube (crystal) will start a cascade of photon emission while photons traveling in other directions pass out of ruby. Photon beam parallel to the axis of tube grows in strength and some of it bursts through partial reflector and serves as output laser beam. |
| |
| Output |
| |
 |
| |
 |
| |
