Single mode oscillation is obtained in a CW dye laser by using tilted intra-cavity Fabry-Perot etalons. Three bare glass etalons of different thickness of 0.22, 1.66, 10 mm are placed inside the laser cavity. The typical output power of 10 mW, with a linewidth of 40 MHz for 10 sec scaning time, have been obtained.
Frequency tuning of the single mode dye laser is achieved by changing the tilt angle of etalon and the length of laser cavity synchronously. The frequency tuning system with bare glass etalon gives low insertion loss, large frequency tuning range and easy handling. The tuning range obtained is 4 GHz which is same as 10 longitudinal mode spacing of the single mode dye laser.
The intensity fluctuation of the dye laser output is fed into a transverse electrooptic modulator to control the transmitance. As the result intensity fluctuation of the dye laser is reduced to 0.6%.
A polarization-sensitive optical system without polarizing element inside a reference cavity is developed for locking the laser frequency to a high finesse reference cavity. The dispersion-shaped error signal suitable for the laser frequency stabilization is obtained experimentally by analyzing the change in the polarization of the output obtained by superposing two orthgonal, linearly polarized beams which are the reference beam and the beam reflected off a high finesse reference cavity.
The saturation spectroscopy technique is used to observe the hyperfine structure of $I_2$-molecule. The CW single mode dye laser, which is developed in the present work and mentioned about above, is used to saturate the hyperfine transitions. The measured width of the indivisual $I_2$ transition is about 6 MHz which gives the resolution $\Delta \nu/\nu$ of the order of $10^{-8}$. From the measurement of Fabry-Perot interferometer ( δυ = 13.5 MHz$ ) and the $I_2$ transition measurment the single mode dye laser output should have the linewidth less then 6 MHz.
