LE-0100 Emission, Absorption & Optical Pumping

Optical pumping is a process in which an electron of an atom ore molecule is excited (or "pumped") from a lower to a higher energy level. Within this experiment we are using as pump light source as diode laser and Neodymium (Nd) atoms which are hosted in a crystal lattice formed by an Yttrium Aluminum Garnet (YAG). This material (abbreviated Nd:YAG) is one of the most important laser materials. At the beginning Nd:YAG has been pumped by flash lamps. To improve the efficiency diode laser are used which emission wavelength is almost completely absorbed whereby the light of the flash lamps to an extend of only about 5%.
The experiment provides a diode laser which is mounted onto a Peltier element. Changing the temperature tunes the wavelength of the diode laser with 0.25 nm / °C. Within the temperature range of 10 - 60°C a spectral range of 12.5 nm is covered allowing the measurement of the spectral absorption of the Nd:YAG crystal. By using the well known absorption peaks of the Nd:YAG the emission wavelength of the diode laser is determined. Furthermore the injection current of the diode laser can periodically be switched on and off allowing the recording of the timely decay of the fluorescence of the Nd:YAG crystal with an oscilloscope. The inverse value of the measured lifetime is the Einstein coefficient for spontaneous emission. By means of the optional spectrometer the fluorescence spectrum of the Nd:YAG crystal as well of the diode laser can be recorded and printed.