Four different laser dyes were used as given in Table 2.1.
The dye solution was made by dissolving the dye in spectroscopic grade methanol (99.5% purity), then adding this solution (approx. 50ml) to 0.75
of ethylene glycol (used due to its high viscosity). This gives the dye jet a stable flat shape when pumped through the specially engineered nozzle, reducing noise and mode hops of the laser. Maximum power for the ring laser is achieved when the absorption of pump radiation by the dye is 80 %. Increasing the concentration moves the lasing range to shorter wavelengths and vice-versa [68].
Table 2.1:
Regions scanned for GeH+ and dyes used.